GD4.2 | Initiation and evolution of subduction: dynamics, volatiles and melts from the surface to the deep mantle
EDI
Initiation and evolution of subduction: dynamics, volatiles and melts from the surface to the deep mantle
Co-organized by GMPV2/SM6/TS6
Convener: Ágnes Király | Co-conveners: Patricia Cadenas Martínez, Jeroen van Hunen, Oğuz H Göğüş, Taras Gerya, Brandon Shuck, César R. Ranero
Orals
| Thu, 27 Apr, 08:30–12:30 (CEST), 14:00–15:45 (CEST)
 
Room D1
Posters on site
| Attendance Fri, 28 Apr, 08:30–10:15 (CEST)
 
Hall X2
Posters virtual
| Attendance Fri, 28 Apr, 08:30–10:15 (CEST)
 
vHall GMPV/G/GD/SM
Orals |
Thu, 08:30
Fri, 08:30
Fri, 08:30
Subduction drives plate tectonics, generating the major proportion of subaerial volcanism, releasing >90% seismic moment magnitude, forming continents, and recycling lithosphere. Numerical and laboratory modeling studies have successfully built our understanding of many aspects of the geodynamics of subduction zones. Detailed geochemical studies, investigating compositional variation within and between volcanic arcs, provide further insights into systematic chemical processes at the slab surface and within the mantle wedge, providing constraints on thermal structures and material transport within subduction zones. However, with different technical and methodological approaches, model set-ups, inputs, and material properties, and in some cases conflicting conclusions between chemical and physical models, a consistent picture of the controlling parameters of subduction-zone processes has so far not emerged.

This session aims to follow subducting lithosphere on its journey from the surface down into the Earth's mantle and to understand the driving processes for deformation and magmatism in the over-riding plate. We aim to address topics such as: subduction initiation and dynamics; changes in mineral breakdown processes at the slab surface; the formation and migration of fluids and melts at the slab surface; primary melt generation in the wedge; subduction-related magmatism; controls on the position and width of the volcanic arc; subduction-induced seismicity; mantle wedge processes; the fate of subducted crust, sediments and volatiles; the importance of subducting seamounts, LIPs, and ridges; links between near-surface processes and slab dynamics and with regional tectonic evolution; slab delamination and break-off; the effect of subduction on mantle flow; and imaging subduction zone processes.

With this session, we aim to form an integrated picture of the subduction process, and invite contributions from a wide range of disciplines, such as geodynamics, modeling, geochemistry, petrology, volcanology, and seismology, to discuss subduction zone dynamics at all scales from the surface to the lower mantle, or in applications to natural laboratories.

Orals: Thu, 27 Apr | Room D1

Chairpersons: Ágnes Király, César R. Ranero, Jeroen van Hunen
08:30–08:35
08:35–08:45
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EGU23-15571
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solicited
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Highlight
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On-site presentation
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Fabio Crameri

Current research on how, when, and where subduction zones initiate (one of the key, long-lasting open questions in the Earth Sciences) spans a multitude of (if not all) Earth and Planetary Science disciplines, engages most geoscientists at least once during their career, occupies research vessels and supercomputers, remains a steady appearance in overarching science journals, and often is considered the holy grail of our field.

It is maybe not surprising that the study of subduction zone initiation (SZI) has therefore created a multitude of different research approaches and divided sub-disciplines applying specific methodologies and field-specific jargons and terms, of which neither is understood across sub-discipline boundaries any longer. To make it worse, a few leading SZI researchers have stopped acknowledging each other’s work, even scientifically.

Within all sub-disciplines that exploit the rock record, plate reconstructions, geophysical measurements like seismic tomography, and theoretical and numerical modelling, we have never learned more about the formation of subduction zones than in the past couple of years. As a community, however, we failed to bring the dispersed knowledge (and sources of information) to a common ground and progress: Numerous numerical models on passive margin SZI made some geoscientists believe that it is the most likely place for SZI to occur. Misleading terminology made others believe that SZI can occur "spontaneously" or that "fore-arc basalts" (FABs) are formed in fore-arcs.

With the community-based, community-driven, community-accessible Subduction-Zone Initiation (SZI) Database (www.SZIdatabase.org), we turn the helm towards a more unified, collaborative approach again. We provide the most extensive and detailed collection of current, trans-disciplinary SZI data (and from just this, a wealth of new insights), suggest a commonly-accessible SZI-related terminology, and offer a platform for community-wide, always-on discussion (see Crameri et al., 2020).

Everything is put in place to reunite, and not loose track of, all our individual efforts and advances, so we, as a community, can learn and understand more about this enigmatic, truly cross-disciplinary hallmark of our fascinating planet.

 

Crameri, F., V. Magni, M. Domeier, G.E. Shephard, K. Chotalia, G. Cooper, C. Eakin, A.G. Grima, D. Gürer, A. Király, E. Mulyukova, K. Peters, B. Robert, and M. Thielmann (2020), A transdisciplinary and community-driven database to unravel subduction zone initiation, Nature Communications, 11, 3750. doi:10.1038/s41467-020-17522-9

How to cite: Crameri, F.: Sharpening our community research on the initiation of subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15571, https://doi.org/10.5194/egusphere-egu23-15571, 2023.

08:45–08:55
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EGU23-2071
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ECS
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On-site presentation
Sandrine Ritter, Attila Balázs, Julia Ribeiro, and Taras Gerya

Subduction of oceanic lithosphere has been proposed as the main driving mechanism for plate tectonics for decades and it represents a key process for the geochemical cycles on Earth. However, the physical processes and melting that occur as the subduction zone began foundering and evolved to reach a mature stage is still debated. The Izu-Bonin-Mariana (IBM) intra-oceanic subduction zone, that represents the boundary between the Pacific Plate and the Philippine Sea, is an ideal natural laboratory to study subduction zone processes from their inception to their stabilization. The rock record produced in IBM reveals a rapid compositional variability in slab-fluid tracers as well as in mantle depletion-enrichment over a short timescale (within 1 to 5 Ma of subduction inception). Despite this geochemical evolution, it is still highly debated whether IBM initiated as a forced or spontaneous subduction zone, i.e. induced by or in the absence of horizontal forcing, respectively.

Here, we conducted 2D high-resolution petrological-thermomechanical subduction models that include spontaneous deformation, erosion, sedimentation and slab dehydration processes, as well as melting, assuming a visco-plastic rheology using the i2VIS code. We aimed to model the initiation and the early stage of IBM with ultra-low horizontal forcing and inception triggered by transform collapse. Our new numerical model proposes a viable scenario for the transition from juvenile to mature subduction zone. This evolution includes initiation by gravitational collapse of the slab and the development of a near-trench spreading, the gradual build-up of a return flow of asthenospheric mantle and the progressive maturation of the volcanic arc. Our numerical results of mantle depletion within the mantle wedge and the overall subduction history of IBM are compared further with seismological and geochemical evidences.

How to cite: Ritter, S., Balázs, A., Ribeiro, J., and Gerya, T.: Magmatic Fingerprints of Subduction Initiation and Mature Subduction of the Izu-Bonin-Mariana Subduction Zone: Numerical Modelling and Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2071, https://doi.org/10.5194/egusphere-egu23-2071, 2023.

08:55–09:05
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EGU23-2981
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On-site presentation
Takeshi Imayama, Akinori Sato, Dripta Dutta, Yasuaki Kaneda, Shota Watanabe, Takeshi Hasegawa, Masayo Minami, Yuki Wakasugi, Shigeyuki Wakaki, and Yi Keewook

Early Cretaceous Nidar Ophiolite Complex (NOC, eastern Ladakh) is associated with the north-dipping supra-subduction of the Neo-Tethyan Ocean along the Indus suture zone. The supra-subduction zone ophiolite formed in the forearc setting records the magmatic response to the subduction initiation, but the magmatic evolution in the NOC is poorly constrained. The low-Ti gabbros have low SiO2 in whole-rock composition and high Mg# in clinopyroxene. They also record highly depleted magma In contrast, dolerites and basalts have relatively higher SiO2 in whole-rock composition and lower Mg# in clinopyroxene, with flat REE patterns accompanied by fractional crystallization. Significant variation in Yb content relative to Tb/Yb ratio also supports fractional crystallization from gabbros to basalts. In Th/Yb-Nb/Yb diagram, all samples plot in the region from the MORB type to the island arc tholeiite. The Nd-Sr isotopes and high Ba/La ratio suggest that the NOC was originally derived from a single depleted mantle source similar to the MORB and was subsequently affected by hydrothermal alteration, resulting in greenschist- to lower amphibolite-facies overprint to form albite, actinolite, epidote and chlorite. Detrital zircon U-Pb ages from volcanic sediments associated with the NOC concentrated at ca. 136 Ma, representing the timing of the main magmatic phase in the NOC. Our data, combined with the geochronological and geochemical data in previous studies, suggest that the low-Ti, highly depleted magma in the NOC was firstly generated at extensional spreading in the upper plate during subduction initiation, and then changed to island arc tholeiite composition with the development of the subduction zone during Early Cretaceous.

How to cite: Imayama, T., Sato, A., Dutta, D., Kaneda, Y., Watanabe, S., Hasegawa, T., Minami, M., Wakasugi, Y., Wakaki, S., and Keewook, Y.: Magmatic response to the subduction initiation of Early Cretaceous Nidar Ophiolite Complex, eastern Ladakh, NW Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2981, https://doi.org/10.5194/egusphere-egu23-2981, 2023.

09:05–09:15
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EGU23-7211
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Highlight
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On-site presentation
João C. Duarte, Nicolas Riel, Patricia Cadenas, Filipe M. Rosas, J. Kim Welford, and Boris Kaus

There is a long-standing mystery regarding how subduction zones enter internal Atlantic-type oceans to complete their Wilson cycle. While the process of subduction initiation is challenging to tackle, the Atlantic is a natural laboratory that allows understanding of some of the different stages of the process of invasion of new subduction zones. Three different subduction zones seem to be entering the Atlantic from different edges: the Caribbean Arc, the Scotia Arc and around the Iberia Peninsula. While the first two examples constitute fully developed subduction zones, it is unknown how they will propagate in the future. Will they spread intra-oceanically or will the subduction migrate along the Atlantic passive margins? Iberia is a good place to investigate the processes involved in the formation of new subduction zones. There have been places of aborted subduction (along the Cantabrian margin), places of incipient subduction (North, West and Southwest Iberia) and there is a subduction arc currently propagating into the Atlantic Ocean (the Gibraltar Arc). We will focus on this last case. Last year, we presented a numerical model that showed that the Gibraltar Arc may indeed further propagate into the Atlantic. This year, we present new models that investigate the factors controlling such propagation. We test different parameters such as the presence of weak zones in the adjacent margins and in the oceanic lithosphere (fracture zones) to obtain insights into the main factors controlling the first stages of propagation of new subduction zones in Atlantic-type oceans.

 

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL

How to cite: Duarte, J. C., Riel, N., Cadenas, P., Rosas, F. M., Welford, J. K., and Kaus, B.: How do subduction zones spread over Atlantic-type oceans?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7211, https://doi.org/10.5194/egusphere-egu23-7211, 2023.

09:15–09:25
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EGU23-5747
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On-site presentation
Wouter P. Schellart, Vincent Strak, Anouk Beniest, Joao C. Duarte, and Filipe M. Rosas

The initiation of subduction remains an enigmatic process and a variety of conceptual models has been proposed to explain such initiation. Conceptual models have been tested with geodynamic models and have been applied to various subduction settings around the globe. None of these tested models, however, are applicable to the Scotia subduction zone in the Southern Atlantic (also referred to as South Sandwich subduction zone), where subduction started in the Late Cretaceous/Early Cenozoic in a pristine ocean basin setting devoid of other subduction/collision zones. How this subduction zone initiated remains intensely debated, as exemplified by the variability of published plate tectonic reconstructions. We present new tectonic reconstructions of the Scotia region involving a relatively simple middle-Late Cretaceous plate boundary configuration that involves a new mechanism of subduction initiation, Subduction Invasion Polarity Switch (SIPS). SIPS involves a long-lived, wide and deep subduction zone (South American-Antarctic subduction zone) that imposes major horizontal trench-normal compressive deviatoric stresses on the overriding plate. The overriding plate consists of a narrow continental lithospheric (land) bridge at the trench (Cretaceous-Early Cenozoic Antarctica-South America land bridge) with oceanic lithosphere behind it (Weddell Sea-Atlantic Ocean). The stresses cause shortening and thrusting at the continent-ocean boundary in the backarc region of the overriding plate, forcing oceanic lithosphere under continental lithosphere, starting the subduction initiation process, and eventually leading to a new, self-sustaining, subduction zone (Scotia subduction zone) with an opposite polarity (dipping westward) compared to the long-lived subduction zone (dipping eastward). The model thus involves invasion of a new subduction zone into a pristine ocean basin (Atlantic Ocean), with the primary driver being a long-lived subduction zone in another ocean basin (Pacific Ocean). To test the physical viability of the SIPS model, we have conducted numerical geodynamic simulations of buoyancy-driven subduction. Numerical results demonstrate that the SIPS model is viable, with compressive stresses in the overriding plate resulting from strong trenchward basal drag induced by subduction-driven whole-mantle poloidal return flow and compression at the subduction zone plate boundary due to the high resistance of the subduction zone hinge of the long-lived subduction zone to retreat westward. Subduction initiation starts in the overriding plate after ~100 Myr of long-lived subduction, eventually resulting in the formation of a new, opposite-dipping, subduction zone. Notably, this new subduction zone develops at the continent-ocean boundary for models without and with a pre-imposed weak zone. Apart from the Scotia Sea region, the SIPS model might also be applicable to subduction initiation that has occurred elsewhere in the geological past (e.g. the New Caledonia, Lesser Antilles-Puerto Rico, Rocas Verdes and Arperos subduction zones), and that is presently in a very early stage of development in the Japan Sea.

How to cite: Schellart, W. P., Strak, V., Beniest, A., Duarte, J. C., and Rosas, F. M.: Subduction invasion polarity switch (SIPS):  A new mechanism of subduction initiation, with an application to the Scotia Sea region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5747, https://doi.org/10.5194/egusphere-egu23-5747, 2023.

09:25–09:35
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EGU23-5162
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ECS
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On-site presentation
Leif Tokle, Whitney Behr, Zoe Braden, and Miguel Cisneros

The subduction zone interface is a shear zone of varying thickness that defines the boundary between the subducting slab and overriding plate. The rheology of this shear zone controls several important aspects of subduction dynamics, but accurately estimating its rheology can be complex due to the wide range of subduction materials and their varying rheological properties. Of particular importance is the relative strengths of metasedimentary and metabasic rocks at various temperature and pressure conditions. To better understand these rheological contrasts in naturally deformed rocks, we are conducting field and microstructural work in the Eclogite Zone in the Tauern Window, Austria. The eclogite zone preserves intercalated metamafic (metabasalt and metagabbro) and metasedimentary (quartzite, garnet mica schist, marble and calc-schist) rocks that were subducted and exhumed to the surface as a single structural unit. Using high resolution drone imaging, 2D structural mapping, and 3D structural modeling, we have documented map-scale relationships between metamafic and metasedimentary rocks in the Eissee region near Matrei. Our mapping demonstrates that the mafic eclogites consistently define slabs, lenses and boudins of up to 2 km in along-strike length and 0.2 km in thickness, embedded within the metasedimentary units, all of which are relatively uniformly deformed to very high strain. This suggests that eclogitized metamafic rocks persisted as rheological heterogeneities within the subduction channel through both the subduction and exhumation paths. Additionally, we are using microstructural observations to document the deformation mechanisms of individual rock units and to understand the weakening mechanisms that allowed some of the eclogites to break down from boudins to strongly foliated layers intercalated with the metasediments. At the interface between select metasedimentary and eclogite units there is a marked rheological change in eclogite rheology, likely due to fluids leached from the metasedimentary rocks, resulting in strain localization and increased foliation development within eclogite layers from meter to micron length scales. Integration of our mapping, outcrop, and microstructural observations will provide insights into the length scales of rheological heterogeneity on the deep interface and large-scale geodynamics of subduction through influencing the bulk viscosity of the interface.

How to cite: Tokle, L., Behr, W., Braden, Z., and Cisneros, M.: Persistence of initial lithological heterogeneity to deep subduction conditions: Implications for the rheology of the subduction zone interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5162, https://doi.org/10.5194/egusphere-egu23-5162, 2023.

09:35–09:45
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EGU23-3130
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ECS
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On-site presentation
Austin Arias, Andreas Beinlich, Lisa Eberhard, Marco Scambelluri, Timm John, Alissa Kotowski, and Oliver Plümper

On Earth, subduction zones facilitate the cycling of volatiles between the Earth’s surface and interior. Volatile cycling has significant effects on the long-term state of the Earth’s climate and tectono-magmatic events, including volcanism and earthquakes. A key stage in the volatile cycle is the devolatilization of the subducting oceanic lithosphere, in which volatiles can escape the previously hydrated rocks. However, it is not well known how efficiently volatiles are transported at this stage. To better understand how volatiles escape at these conditions, we have analyzed the dehydration-related vein networks of the Erro-Tobbio meta-serpentinites (ET-MS), Italy. The ET-MS display well preserved networks of metamorphic olivine veins. These veins are the result of the dehydration reaction of antigorite and brucite to produce H2O and olivine. However, due to the low permeability of serpentinite at depth, the dehydration reaction requires the formation of self-organizing vein networks to allow the produced fluid to escape [1]. Thus, the metamorphic olivine veins in ET-MS may be used as a proxy for fluid flow pathways. We took a multiscale approach to analyzing the network architectures. For microscale (~16 µm voxel size) and mesoscale (~200 µm voxel size) resolutions, X-ray tomography methods are sufficient to visualize the three-dimensional structure of the networks. However, for large scale observations these methods are inapplicable. To solve this, we apply a novel workflow to analyze outcrop scale (~10 m) network systems in three dimensions using only two-dimensional data. By training a generative adversarial network (GAN) with two-dimensional data conditioned by spatial orientation, we can generate statistically representative three-dimensional networks that mimic those of the ET-MS. These representations also display similar characteristics in their respective pore-network-models. With this method, it is possible to produce reasonable three-dimensional approximations of the ET-MS vein networks using only photogrammetry data of the outcrops. In turn, this allows us to extract metrics, such as permeability, that describe the volatile transport efficiency of the ET-MS, and further, how these characteristics change at a broad range of scales.  

[1] Plümper et al. (2017) Nature Geoscience 10(2), 150-156. 

How to cite: Arias, A., Beinlich, A., Eberhard, L., Scambelluri, M., John, T., Kotowski, A., and Plümper, O.: Micro to Macroscale: the three-dimensional network characteristics of serpentinite dehydration veins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3130, https://doi.org/10.5194/egusphere-egu23-3130, 2023.

09:45–09:55
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EGU23-9814
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On-site presentation
Matthias Willbold and Gerhard Wörner

Molybdenum (Mo) isotopes in magmatic rocks are a promising tool in high-temperature isotope geochemistry. In particular, basalts from subduction zones that are geochemically controlled by mass transfer through slab-fluid addition have systematically higher δ98Mo values (i.e. measured 98Mo/95Mo ratio in a sample relative to that in a standard) than the depleted mantle (δ98Mo = –0.21‰). In these rocks, the elevated δ98Mo values are linked to high Pb/Ce and high (238U/230Th) ratios and can be reconciled by the addition of isotopically heavy Mo via a slab fluid component1,2. So far, these systematics are best expressed in subduction zone basalts from the Mariana and Izu arc systems that also form coherent mixing trends between fluid-enriched mantle domains in δ98Mo versus 143Nd/144Nd and 176Hf/177Hf space1,2.

The Kamchatka arc system represents the northernmost expression of the W-Pacific convergent margin. Volcanic front lavas are dominated by slab-to-mantle mass transfer through fluid transport, whereas subduction of the Emperor seamount ridge gives rise to back-arc basalts with a geochemical and isotopic affinity to within-plate basaltic rocks3.

Here, we report δ98Mo data for 47 basalts from an E-W transect across the Kamchatka peninsula that have previously been analysed for their major, trace element, radiogenic and stable isotope data. The δ98Mo data extent the trend defined by samples from the Marianas and Izu arcs starting from moderately high δ98Mo and Pb/Ce values towards sub-depleted mantle δ98Mo and mantle-like Pb/Ce ratios that indicate the presence of a source component formed by partial melts of a rutile-bearing mafic crust4.

The common geochemical and isotopic trends formed by the combined Mariana – Izu – Kamchatka datasets suggest a surprisingly uniform Mo isotope composition of a subduction zone fluid endmember for more than 5000 km along-strike of the Circum-Pacific subduction zone system. Our data also confirm the presence of an enriched source component in the Kamchatka mantle wedge, possibly originating from the subducted Emperor seamount chain5.

1Freymuth, H., et al., EPSL 432, 176-186 (2015). 2Villalobos-Orchard, J., et al., GCA 288, 68-82 (2020). 3Churikova, T., et al. JPet 42, 1567-1593 (2001). 4Chen, S., et al., Nat. Comm. 10, 4773 (2019). 5Shu,Y., et al.,Nat. Comm. 13, 4467 (2022).

How to cite: Willbold, M. and Wörner, G.: Molybdenum Isotope Systematics of the Kamchatka Subduction Zone System, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9814, https://doi.org/10.5194/egusphere-egu23-9814, 2023.

09:55–10:05
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EGU23-11540
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ECS
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On-site presentation
Stephen Hicks, Lidong Bie, Catherine Rychert, Nicholas Harmon, Saskia Goes, Andreas Rietbrock, Songqiao Wei, Jenny Collier, Timothy Henstock, Lloyd Lynch, Julie Prytulak, Colin Macpherson, David Schlaphorst, Jamie Wilkinson, Jonathan Blundy, George Cooper, Richard Davy, and John-Michael Kendall

Volatiles expelled from subducted plates promote melting of the overlying warm mantle, feeding arc volcanism. However, debates continue over the factors controlling melt generation and transport and how these determine the placement of volcanoes. To broaden our synoptic view of these fundamental mantle wedge processes, we image seismic attenuation beneath the Lesser Antilles arc, an end-member system that slowly subducts old, tectonised lithosphere. Punctuated anomalies with high ratios of bulk-to-shear attenuation (Qκ-1/Qµ-1 > 0.6) and VP/VS (>1.83) lie 40 km above the slab, representing expelled fluids that are retained in a cold boundary layer, transporting fluids towards the back-arc. The strongest attenuation (1000/QS~20), characterising melt in warm mantle, lies beneath the back-arc, revealing how back-arc mantle feeds arc volcanoes. Melt ponds under the upper plate and percolates toward the arc along structures from earlier back-arc spreading, demonstrating how slab dehydration, upper plate properties, past tectonics, and resulting melt pathways collectively condition volcanism.

How to cite: Hicks, S., Bie, L., Rychert, C., Harmon, N., Goes, S., Rietbrock, A., Wei, S., Collier, J., Henstock, T., Lynch, L., Prytulak, J., Macpherson, C., Schlaphorst, D., Wilkinson, J., Blundy, J., Cooper, G., Davy, R., and Kendall, J.-M.: Slab to back-arc to arc: fluid and melt pathways through the mantle wedge beneath the Lesser Antilles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11540, https://doi.org/10.5194/egusphere-egu23-11540, 2023.

10:05–10:15
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EGU23-9669
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ECS
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Virtual presentation
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Mingqi Liu and Taras Gerya

Although positive buoyancy of young lithosphere near spreading centers does not favor spontaneous subduction, subduction initiation occurs easily near ridges due to their intrinsic rheological weakness when plate motion reverses from extension to compression. It has also been repeatedly proposed that inherited detachment faults may directly control the nucleation of new subduction zones near ridges subjected to forced compression. However, recent 3D numerical experiments suggested that direct inversion of a single detachment fault does not occur. Here we further investigate this controversy numerically by focusing on the influence of brittle-ductile damage on the dynamics of near-ridge subduction initiation. We self-consistently model the inversion of tectonic patterns formed during oceanic spreading using 3D high-resolution thermomechanical numerical models with strain weakening of faults and grain size evolution. Numerical results show that forced compression predominantly reactivates and rotates inherited extensional faults, shortening and thickening the weakest near-ridge region of the oceanic lithosphere, thereby producing ridge swellings. As a result, a new megathrust zone is developed, which accommodates further shortening and subduction initiation. Furthermore, brittle/plastic strain weakening has a key impact on the collapse of the thickened ridge and the onset of near-ridge subduction initiation. In contrast, grain size evolution of the mantle only slightly enhances the localization of shear zones at the brittle-ductile transition and thus plays a subordinate role. Compared to the geological record, our numerical results provide new helpful insights into possible physical controls and dynamics of natural near-ridge subduction initiation processes recorded by the Mirdita ophiolite of Albania.

How to cite: Liu, M. and Gerya, T.: Forced subduction initiation near spreading centers: effects of brittle-ductile damage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9669, https://doi.org/10.5194/egusphere-egu23-9669, 2023.

Coffee break
Chairpersons: Ágnes Király, Taras Gerya, Jeroen van Hunen
10:45–10:50
10:50–11:00
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EGU23-10756
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solicited
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On-site presentation
Adam Holt, Cailey Condit, Valeria Turino, Gabe Epstein, Ryan Stoner, and Victor Guevara

The thermal structure of subduction zones enacts a first-order control on many geological processes and properties, including the locus and degree of slab devolatilization, and the associated densities and strengths of subducting material. Modeling studies with fixed subduction geometries and plate velocities have been used to map out how various subduction parameters affect the pressure-temperature conditions of slabs and, in turn, the depths of major dehydration reactions. However, there is abundant geological evidence that slab properties, and the associated temperatures, evolve over few-Myr timescales. In this study, we use numerical subduction models to target this time dependence. Specifically, we focus on the styles and drivers of thermal transience and the imprint of this on subducting slab dehydration and slab strength.

Specifically, we have developed 2-D and 3-D subduction models that enable slab properties to evolve through time in a dynamically consistent fashion using the ASPECT finite element code1-3. We use these models to investigate: i) the extent to which slab thermal conditions – and the associated metamorphic reactions and slab strength – evolve throughout the lifetime of a subduction zone, ii) the effects of first-order subduction zone properties on this evolution, and iii) the degree to which three-dimensionality (i.e., the presence of a slab edge) impacts this evolution. Regardless of imposed basic subduction parameters (e.g., plate ages, crustal strengths), our model subduction zones exhibit highly time-dependent thermal evolutions. The slab top, for example, exhibits rapid cooling during initiation and slower cooling subsequently, with along-strike temperature variations of up to ~40°C in the 3-D models. This thermal transience has fundamental implications for the geophysical and geochemical evolution of subduction zones; it manifests in a strong time dependence of dehydration depths and magnitudes and, in turn, substantial variability in slab strength. 

 

1: Bangerth, W., Dannberg, J., Gassmoeller, R., & Heister, T. (2020). ASPECT v2.1.0, Zenodo. https://doi.org/10.5281/ZENODO.3924604

2: Heister, T., Dannberg, J., Gassmöller, R., & Bangerth, W. (2017). High accuracy mantle convection simulation through modern numerical methods - II: Realistic models and problems. Geophys. J. Int., 210(2), https://doi.org/10.1093/gji/ggx195

3: Holt, A. F., & Condit, C. B. (2021). Slab temperature evolution over the lifetime of a subduction zone. Geochem., Geophys., Geosys., 22, doi:10.1029/2020GC009476.

How to cite: Holt, A., Condit, C., Turino, V., Epstein, G., Stoner, R., and Guevara, V.: Time dependent slab temperatures, metamorphism, and mechanical properties: Insights from dynamic subduction models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10756, https://doi.org/10.5194/egusphere-egu23-10756, 2023.

11:00–11:10
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EGU23-5221
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ECS
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On-site presentation
Silvia Brizzi, Thorsten Becker, Claudio Faccenna, Whitney Behr, Iris van Zelst, Luca Dal Zilio, and Ylona van Dinther

It is widely recognized that sediments play a key role for subduction. For example, sediments subducted along the shallow seismogenic plate interface are thought to influence seismic coupling and the occurrence of megathrust earthquakes, as well as the morphologies of accretionary prisms. Due to their weakening and/or lubricating effect, subducted sediments are also thought to promote faster plate speeds. However, global observations are not clear-cut on the relationship between the amount of sediments and plate motion. Here, we use 2D thermomecanical models to investigate how incoming plate sediments can influence subduction dynamics and geometry. We find that thick sediments can promote slower subduction due to an increase of the shear stress along the plate interface as the accretionary wedge gets wider, and a decrease of slab pull as more buoyant material is subducted. Our results also show that the larger interface shear stress and slab buoyancy due to thick sediments increase the slab bending radius. This study offers a new perspective on the role of sediments on large-scale subduction dynamics, suggesting that sediment buoyancy and wedge geometry might also affect plate motion and geometry.

How to cite: Brizzi, S., Becker, T., Faccenna, C., Behr, W., van Zelst, I., Dal Zilio, L., and van Dinther, Y.: The role of sediments on subduction dynamics and geometry: insights from numerical modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5221, https://doi.org/10.5194/egusphere-egu23-5221, 2023.

11:10–11:20
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EGU23-7314
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ECS
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Virtual presentation
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Pedro J. Gea, Flor de Lis Mancilla, Ana M. Negredo, and Jeroen van Hunen

Subducting slabs are the main drivers of plate motion and flow in Earth’s mantle. Thus, much effort has been put into understanding the main factors controlling slab dynamics and subduction-induced mantle flow. Slab width (W) has been shown to have a major role in controlling the subduction dynamics and more specifically, the trench motion (e.g., Stegman et al., 2006; Schellart et al., 2007). Both numerical modelling experiments and retreat velocities observed in wide subduction zones show that the trench retreat velocity (VT) decreases as the slab is wider. However, observations on natural narrow subduction zones (W ≤ 1000 km, e.g. Calabria, Gibraltar, Scotia) do not show a direct relation between W and VT, thus indicating that other factors, still poorly understood, may play a more relevant role on trench retreat velocities. The aim of this work is to identify which are these factors that exert a dominant control. To accomplish this, we use self-consistent 3D numerical subduction models to systematically evaluate the effect of slab width, strength of coupling with the lateral plate and overriding plate thickness on trench motion. In contrast to what happens in moderate to wide subduction zones, our simulations show that slab width has little influence on trench retreat velocity for narrow subduction zones, which is a robust result for different viscous couplings at the lateral slab edge.  On the contrary, our results indicate that the major influence is exerted by the thickness of the overriding plate, with the trench retreat velocities decreasing noticeably as the plate thickness increases. These results are in agreement with retreat velocities observed in narrow subduction zones showing no direct relation with slab width, but an inverse dependence on overriding plate thickness.

 

References

Schellart, W. P., Freeman, J., Stegman, D. R., Moresi, L., and May, D. (2007). Evolution and diversity of subduction zones controlled by slab width, Nature, 446(7133), 308–311. doi:10.1038/nature05615

Stegman, D. R.; Freeman, J.; Schellart, W. P.; Moresi, L.; May, D. (2006). Influence of trench width on subduction hinge retreat rates in 3-D models of slab rollback, Geochemistry Geophysics Geosystems, 7(3), Q03012–. doi:10.1029/2005gc001056

How to cite: Gea, P. J., Mancilla, F. D. L., Negredo, A. M., and van Hunen, J.: Trench retreat rates in narrow subduction zones controlled by overriding plate thickness, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7314, https://doi.org/10.5194/egusphere-egu23-7314, 2023.

11:20–11:30
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EGU23-6155
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On-site presentation
Zoltán Erdős, Susanne Buiter, and Joya Tetreault

Microcontinent accretion during oceanic subduction is one of the main contributors to continental crustal growth. Many of the continental mountain belts we find today were built from accretionary orogenesis, for example, the Cordillera of the west coast of the Americas, the European Alps, and the Australian Lachlan orogen. Continental growth can also be observed in modern accretionary orogens such as the Pacific accretionary belt, with the collision of the Philippine microplate, and the Taiwan-Luzon-Minduro Belt. In many of these systems, multiple bathymetric highs, such as microcontinental terranes, island arcs, or oceanic plateaus, are accreted before full oceanic closure, thus significantly altering the subduction zone before continental collision occurs.
The process of accretion implies a complex balance of multiple geodynamic forces that can result in either microcontinent subduction, microcontinent accretion, or subduction stalling (which could lead to the initiation of an altogether new subduction zone). The most important driving forces in this system are the slab-pull force arising from the negative buoyancy of the down-going slab and the far-field force which is the result of large-scale plate-motions external to the subduction zone. These forces are counteracted (among others) by friction along the subduction interface and the buoyancy of the downgoing microcontinent. The resulting net forces control the overall stress-field of the overriding plate as well as the state of stress and potential deformation of any further microcontinents embedded within the oceanic lithosphere that are not yet in the subduction zone. 
When multiple microcontinents are embedded in the subducting oceanic plate, the friction along the subduction interface and its temporal variations can take a crucial role. The accreting microcontinents have a first order effect on the length and the rheology of the subduction channel, thereby controlling the interface friction. The fate of the microcontinents (e.g. full or partial accretion, or subduction) also affects the overall buoyancy of the slab, altering the balance of forces through the slab-pull.
Using 2D thermo-mechanical experiments with the finite-element software SULEC-2D, we explore the roles of the structure and rheology of multiple accreting microcontinents (controlling their integrated strength) as well as the velocity of the subducting plate (controlling the far-field and the slab-pull force) to better understand how accretion of crustal units can modify the subduction zone and affect later continental collision. Our setup is comprised of a subducting oceanic basin surrounded by two continents. In this setup the oceanic plate is either “empty” or one or two microcontinents are embedded within it.
Our first results show that microcontinent accretion is promoted by the presence of a weak rheological detachment layer within the microcontinent. In turn, strong coupling of the microcontinental crust to its host-lithosphere promotes terrane subduction and may ultimately lead to the stalling of subduction. Moreover, the behavior of the microcontinents during accretion and subsequent continental collision has a first order effect on the structural style of the resulting orogen as the rheology of the microcontinents controls the degree of localization of deformation in the subduction channel.

How to cite: Erdős, Z., Buiter, S., and Tetreault, J.: Dynamics of multiple microcontinent accretion during oceanic subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6155, https://doi.org/10.5194/egusphere-egu23-6155, 2023.

11:30–11:40
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EGU23-2103
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On-site presentation
Neil Ribe, Alexander Chamolly, Gianluca Gerardi, Stephanie Chaillat, and Zhong-hai Li

Because Earth's tectonic plates are doubly curved shells, their mechanical behavior during subduction can differ significantly from that of flat plates. We use the boundary-element method (BEM) to study free (gravity-driven) subduction in axisymmetric and 3-D geometry, with a focus on determining the dimensionless parameters that control the dynamics. The axisymmetric model comprises a shell with thickness h and viscosity η1 subducting in an isoviscous planet with radius R0 and viscosity η2. The angular radius of the trench is θt. Scaling analysis based on thin-shell theory reveals two key dimensionless parameters: a `flexural stiffness' St = (η12)(h/lb)3 that is also relevant for flat plates, and a new `dynamical sphericity number' ΣD = (lb/R0)cotθt that is unique to spherical geometry. Here lb is the `bending length', or the sum of the lengths of the slab and of the seaward flexural bulge. The definition of ΣD implies that the dynamical effect of sphericity is greater for small plates than for large ones; we call this the `sphericity paradox'. By contrast, the purely geometric effect of sphericity is opposite, i.e. greater for large plates than for small ones. The dynamical and geometrical effects together imply that sphericity significantly influences subduction at all length scales. We confirm the scaling analysis using BEM numerical solutions, which show that the influence of sphericity on the slab sinking speed (up to a few tens of percent) and on the hoop stress (up to a factor of 2-3) is largest for small plates such as the Juan de Fuca, Cocos and Philippine Sea plates. We next study a 3-D model comprising a plate bounded by a ridge and a semicircular trench subducting in a three-layer earth consisting of an upper mantle, a lower mantle and an inviscid core. We examine the linear stability of the shell to longitudinal perturbations corresponding to buckling, and determine a scaling law for the most unstable wavelength that we compare with the observed shapes of northern/western Pacific trenches. 

How to cite: Ribe, N., Chamolly, A., Gerardi, G., Chaillat, S., and Li, Z.: Scaling of Free Subduction on a Sphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2103, https://doi.org/10.5194/egusphere-egu23-2103, 2023.

11:40–11:50
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EGU23-4710
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On-site presentation
Rhodri Davies, Fangqin Chen, Saskia Goes, and Lior Suchoy

It has long been recognised that the shape of subduction zones is influenced by Earth’s sphericity, but the effects of sphericity are regularly neglected in numerical and laboratory studies that examine the factors controlling subduction dynamics: most existing studies have been executed in a Cartesian domain, with the small number of simulations undertaken in a spherical shell incorporating plates with an oversimplified rheology, limiting their applicability. There are therefore many outstanding questions relating to the key controls on the dynamics of subduction. For example, do predictions from Cartesian subduction models hold true in a spherical geometry? When combined, how do subducting plate age and width influence the dynamics of subducting slabs, and associated trench shape? How do relic slabs in the mantle feedback on the dynamics of subduction? These questions are of great importance to understanding the evolution of Earth's subduction systems but remain under explored.

In this presentation, we will target these questions through a systematic geodynamic modelling effort, by examining simulations of multi-material free-subduction of a visco-plastic slab in a 3-D spherical shell domain. We will first highlight the limitation(s) of Cartesian models, due to two irreconcilable differences with the spherical domain: (i) the presence of sidewall boundaries in Cartesian models, which modify the flow regime; and (ii) the reduction of space with depth in spherical shells, alongside the radial gravity direction, the impact of which cannot be captured in Cartesian domains, especially for subduction zones exceeding 2400 km in width. We will then demonstrate how slab age (approximated by co-varying thickness and density) and slab width affect the evolution of subducting slabs, using spherical subduction simulations, showing that: (i) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased bending resistance and sinking rates; (ii) wider slabs can develop along-strike variations in trench curvature due to toroidal flow at slab edges, trending toward a `W'-shaped trench with increasing slab width, and (iii) the width effect is strongly modulated by slab age, as age controls the slab's tendency to retreat. Finally, we will show the diverse range of ways in which remnant slabs in the mantle impact on subduction dynamics and the evolution of subduction systems.

How to cite: Davies, R., Chen, F., Goes, S., and Suchoy, L.: Controls on the Dynamics of Subducting Slabs in a 3-D Spherical Shell Domain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4710, https://doi.org/10.5194/egusphere-egu23-4710, 2023.

11:50–12:00
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EGU23-7188
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ECS
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On-site presentation
Yang Liu, Nicolas Coltice, Laetitia Le Pourhiet, and Ziyin Wu

Plateau subduction is a common process at different plate convergent margins, and they often modify subduction and affect slab behaviour. However, fewer studies have been conducted in the intraoceanic subduction context, and the physical and rheological parameters involved imply a strong hypothesis on the initial conditions (thermal state, no flow in the mantle, no interaction with the tectonic network). Here, we use global three-dimensional spherical mantle convection models to investigate the potential impacts of a subducting plateau on subduction zones and plate reorganization from regional to global scales in a fully self-consistent plate-like tectonics system. Our models show that plateaus with different sizes (length, width and thickness) can locally slow down the trench retreat rate. A larger plateau prevents trench migration, eventually terminating the subduction. The buoyancy of plateaus is found to influence the shape of the trench. Low buoyancy plateaus do not deform the trench as they subduct while in models with buoyant plateaus, the trench advances landward in front of a plateau forming an arcuate shape in the map. This arcuate shape of the trench is further enhanced with decreasing buoyancy and increasing viscosity. If the oceanic plateau has a higher yield stress, it will always drive the formation of the arcuate trench before fully subducted, regardless of the buoyancy. The simulations suggest that any single plateau rheology variable (buoyancy, or yield stress) except the viscosity can influence trench migration behaviour on a regional scale. We will also explore how plateau subduction modifies the global tectonic evolution over 100 My.

How to cite: Liu, Y., Coltice, N., Le Pourhiet, L., and Wu, Z.: How a subducting plateau impacts regional and global tectonics?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7188, https://doi.org/10.5194/egusphere-egu23-7188, 2023.

12:00–12:10
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EGU23-8910
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ECS
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On-site presentation
Erkan Gün, Russell Pysklywec, Philip Heron, Gültekin Topuz, and Oğuz Göğüş

The theory of plate tectonics acknowledges that drifting lithospheric plates are rigid and do not undergo substantial deformation except near or at plate boundaries. However, studies have shown that intra-plate deformation is a feature for continental lithosphere and can originate from different mechanisms such as lithospheric drips, delamination, and in-plane stresses. On the other hand, there is not well-known understanding of tectonic deformation within the interior of ocean plates. We compile data to show there is geological and geophysical evidence documenting that the drifting Pacific plate has been undergoing appreciable extensional deformation at the locations of its oceanic plateaux. Namely, the Ontong Java, Shatsky Rise, Hess Rise, and Manihiki plateaux show extensive evidence for normal faults, horst-graben structures, and extension related magmatic activity at a significant distance from plate boundaries. Furthermore, this deformation occurred after the initial emplacement of their associated large igneous provinces (LIPs) and before their arrival to subduction zones.

We present numerical geodynamic experiment results demonstrating that terranes embedded in ocean plates can undergo extensional deformation prior their accretion to the overriding plate due to slab-pull (e.g., a “subduction pulley”).  Our numerical models show that the subduction pulley is also a valid mechanism for the extensional deformation of the Pacific oceanic plateaux even at remote locations from the plate boundaries. For instance, tensional stress originated from down-going slabs can be transmitted through strong oceanic lithosphere over long distances (>1000 km) and deform the plate at its weak oceanic plateaux regions. The numerical experiments further demonstrate that high crustal thickness reduces the bulk strength of ocean lithosphere at the location of oceanic plateaux and makes them susceptible to slab-pull related extension—manifesting on the surface as intra-ocean plate deformation.

How to cite: Gün, E., Pysklywec, R., Heron, P., Topuz, G., and Göğüş, O.: Intra-Plate Deformation of the Pacific: Evidence from Oceanic Plateaux and Geodynamic Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8910, https://doi.org/10.5194/egusphere-egu23-8910, 2023.

12:10–12:20
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EGU23-14049
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On-site presentation
Lior Suchoy, Saskia Goes, Fangqin Chen, and D. Rhodri Davies

The subduction of positively buoyant features has been suggested to cause flat or shallow dipping slabs, the formation of cusps in trench geometry and periods of reduction or full cessation of arc magmatism. Additionally, recent earthquake data indicates that the subduction of the Hikurangi plateau near New Zealand causes a rotation of intraplate stresses. In this study, we present a series of multi-material 3-D simulations of free subduction to investigate how subduction of buoyant elongated features, or ridges, impact downgoing plate velocities, trench motions, slab morphology and intraplate stress regime. We examine how these parameters are affected by the age of the subducting plate and the relative buoyancy and position of the buoyant ridge. We find that buoyant ridges change slab sinking and trench retreat rates and locally rotate intraplate stresses. These, in turn, modify the evolution of slab morphology at depth and trench shape at the surface, as trench retreat is reduced, or switches to trench advance, where the ridge subducts. These effects depend strongly on downgoing plate age: on young and weak plates, the change in trench shape is more localised than on old and strong plates. We observe slab shallowing around the ridge only in young plates, while the stronger pull by the more negatively buoyant old plates causes slab steepening near the buoyant ridge. Buoyant ridges on old plates which are located near stagnating or advancing regions, typical in wide slabs, modify trench behaviour more strongly than ridges in other regions of the trench. Bending-related intraplate earthquakes are more likely in older plates where higher stress is accumulated and the rotation due to the buoyant ridge is more widespread than for younger plates. The combined effects of buoyant feature location, subducting plate age and overriding plate properties can result in a range of responses: from mainly trench deformation, through local slab shallowing, to the formation of a flat slab, a variation in expressions also observed on Earth.

How to cite: Suchoy, L., Goes, S., Chen, F., and Davies, D. R.: A 3-D numerical investigation of the impact of buoyant features on subduction dynamics and stress, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14049, https://doi.org/10.5194/egusphere-egu23-14049, 2023.

12:20–12:30
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EGU23-1322
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On-site presentation
Antoniette Greta Grima and Thorsten Becker

Shallowing of slabs during their descend into the upper ~200 km of the mantle, i.e. flat subduction, can be associated with extensive geochemical, structural, and dynamic modification of the continental lithosphere. Anomalously buoyant oceanic lithosphere, overthrusting, and interactions with cratonic keels have been suggested to explain flat slabs, but the dynamics of flat slab subduction remain to be fully understood. Here, we explore self-consistent flat-slab subduction using the finite element code ASPECT with adaptive mesh refinement and a free surface boundary condition. We focus on the role of the structure of the overriding continental plate including the role of keels. Results show that flat slabs arise when the subduction interface is weak and the overriding continental lithosphere is positively buoyant, leading to trench rollback. Substantiating previous work, we also observe that a strong continental keel further enhances flat slab formation. Our results also indicate that as the slab flattens, regions of pronounced subsidence and extension develop within the foreland region, on top of more typical, larges-scale subsidence recorded within the continental interior. Regional uplift and subsidence of the overriding plate are not only linked to flat slab emplacement and removal, but also affected by slab dynamics of the shallow upper mantle. Our work can contribute to a better understanding of continental deformation including sediment transport on continent-wide scales.

How to cite: Grima, A. G. and Becker, T.: Modeling the interactions between slab dynamics and continental overriding plate deformation during flat subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1322, https://doi.org/10.5194/egusphere-egu23-1322, 2023.

Lunch break
Chairpersons: Ágnes Király, Taras Gerya, César R. Ranero
14:00–14:01
14:01–14:11
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EGU23-8492
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On-site presentation
Michael Pons, Constanza Rodriguez Piceda, Stephan V. Sobolev, Magdalena Scheck-Wenderoth, and Manfred R. Strecker

The Sierras Pampeanas (29 - 35°S) located south of the Altiplano-Puna plateau above the Chilean subduction zone, consist of uplifted foreland basement blocks that are an expression of the eastward propagation of compresive deformation. Their presence is one of the most enigmatic features of the Andes. The formation of these ranges is considered an end member of the thick-skinned foreland deformation style, which involves the deformation of the sedimentary cover and the crystalline basement. At 33°S, the onset of compression occurs at 22Ma, and the change between thin and thick skinned deformation style at 16Ma. However, the mechanism responsible for this evolution remains controversial. Two main hypotheses have been proposed to explain this evolution. The first one atributes the change in foreland deformation style to the setting of the Pampean flat slab at 12 Ma, which is contemporanous to the southward migration and subduction of the Juan Fernandez hotspot ridge at 33S. Alternatively, it has been proposed that the reactivation of pre-existing structures inherited from pre-Neogen tectonic events could better explain the onset of deformation about 10 Ma before the arrival of the flat-slab. To resolve this controversial debate, we have developed a data-driven 3D geodynamic model using the FEM geodynamic code ASPECT. We incorporated the present-day geometrical and thermal configuration of the southern central Andes and the flat-slab from previous models. This approach allowed us to study the structural and thermomechanical factors responsible for the location of deformation in the Sierras Pampeanas (e.g., topography, temperature and composition, strength of the lithosphere and velocity of the plates).  Moreover,  we investigated the role of the geometry of the Nazca plate on the foreland deformation, and proposed a new mechanism ("flat slab conveyor)" that reconciles the timing of the main geological events (onset of shortening, change in tectonics style of deformation of the foreland, growth of the topography, cessation of volcanic activity, uplift of the basement, and propagation of the deformation). This work expands our understanding of how plates interact at convergent boundaries, in particular at the subduction zones, and how and where deformation is expressed at the surface of the the upper continental plate.

How to cite: Pons, M., Rodriguez Piceda, C., Sobolev, S. V., Scheck-Wenderoth, M., and Strecker, M. R.: Understanding the role of structural inheritance and flat slab geometry in Central Andes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8492, https://doi.org/10.5194/egusphere-egu23-8492, 2023.

14:11–14:21
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EGU23-7182
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On-site presentation
Robin Lacassin, Tania Habel, Anne Replumaz, Benjamin Guillaume, Martine Simoes, Thomas Geffroy, and Jean-Jacques Kermarrec

To explore the conditions that lead to mountain-building in the case of an oceanic subduction, we conduct analog experiments (with silicon putty upper and lower plates, glucose syrup upper mantle) where subduction is driven by slab pull but also by an underlying mantle flow. Here, plate displacement is not imposed as in most models, but is controlled by the overall balance of forces in the system. We simulate three scenarios: no mantle flow (slab-pull driven subduction), mantle flow directed toward the subducting plate, and mantle flow directed toward the overriding plate. In the case of this latter scenario, we also test the influence of pre-existing rheological contrasts in the upper plate to best reproduce natural cases where inheritance is common. Our experiments show that when plate convergence is also driven by a background mantle flow, the continental plate deforms with significant trench-orthogonal shortening (up to 30% after 60 Myr), generally associated with thickening. We further identify that upper plate shortening and thickening is best promoted when the mantle flow is directed toward the fixed overriding continental plate. The strength of the upper plate is also a key factor controlling the amount and rates of accommodated shortening. Deformation rates increase linearly with decreasing bulk strength of the upper plate, and deformation is mostly localized where viscosity and strength are lower. When compared to the particular natural case of the Andes, our experiments provide key insights into the geodynamic conditions that lead to the building of this Cordilleran orogen since the Late Cretaceous - Early Cenozoic.

 

How to cite: Lacassin, R., Habel, T., Replumaz, A., Guillaume, B., Simoes, M., Geffroy, T., and Kermarrec, J.-J.: Upper-plate shortening and Andean-type mountain-building in the context of mantle-driven oceanic subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7182, https://doi.org/10.5194/egusphere-egu23-7182, 2023.

14:21–14:31
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EGU23-4644
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ECS
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On-site presentation
Marie Genge, César Witt, Massimiliano Zattin, Delphine Bosch, Olivier Bruguier, and Stefano Mazzoli

Shifts in isotopic and trace element composition in magmatic zircon are commonly related to internal forcing independent of plate parameters (e.g., crustal thickness, delamination), or external factors that are governed by parameters of the down-going plate, particularly the slab dip. U-Pb geochronology, trace elements and Hf-O isotope analyses on detrital zircon from central Patagonia (45 °S – 48 °S) were used in this study as fingerprint for monitoring slab dip variations and related processes (e.g., arc migration, slab rollback) as well as upper-plate stress regime evolution. According to literature, main geodynamic events include: (i) two shallow slab episodes during late Triassic and late Early Cretaceous – early Paleogene times, the latter characterized by significant contraction; (ii) two phases of slab rollback during Jurassic – Early Cretaceous and late Paleogene, associated to a steep slab configuration, extensional processes and crustal thinning; (iii) a slab window episode during the Paleogene; and (iv) a Miocene contractional phase following an increase of plate convergence rates. Although slab dynamics seems structurally related with upper-plate architecture, it appears to exert little to null control on the magmatic arc reservoirs. Indeed, our results, integrated with published data from a larger area (40 °S – 52 °S), show long-lasting trends ( > 70 Ma) in the isotopic and trace elements record, that are mostly independent of these events. We thus consider that other processes, eventually coeval, controlled the enrichment of magmas and may overtake the influence of slab dip and upper-plate architecture on the isotopic and trace elements signature. These other processes include subduction erosion, ridge subduction, subduction of a younger slab, potential slab tearing, and/or change in convergence rates that affects mantle flow. 

How to cite: Genge, M., Witt, C., Zattin, M., Bosch, D., Bruguier, O., and Mazzoli, S.: Are the long-lasting isotope trends in central Patagonia independent from slab dynamics and upper-plate architecture?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4644, https://doi.org/10.5194/egusphere-egu23-4644, 2023.

14:31–14:41
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EGU23-9902
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ECS
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On-site presentation
Xiang Ren, Yunpeng Dong, Dengfeng He, and Christoph Hauzenberger

A forearc environment is usually characterised by a relatively low geothermal gradient and hence little magmatic activity occurs. However, S-type granites were discovered within the forearc accretionary complex of the East Kunlun Orogenic Belt. The S-type granites intruded into an upper amphiolite facies partially migmatitic crystalline basement in form of dikes and sills at ca. 440 Ma which corresponds to the transition of the Proto-Tethyan to the Paleo-Tethyan realm in the northern Tibetan Plateau. The observed granites contain either garnet + biotite + muscovite or garnet + muscovite: (1) muscovite granite is strongly peraluminous with an aluminous saturation index (ASI) of more than 1.1 (ASI = molar [Al2O3/(Na2O+K2O+CaO]) and has high-K calc-alkaline characteristics, low Sr/Y (1.9–16.1) and LaN/YbN (1.85–13.2) ratios. (2) Two-mica granite is moderately peraluminous (ASI = 1.02–1.09), has high Ca and low K contents as well as high Sr/Y (16.8–67.7) and LaN/YbN(10.9–33.3) ratios. Other trace element contents and their ratios also show striking differences with high Sr (207–324 ppm) content and CaO/Na2O (0.47–0.96) ratio, and a low Rb/Sr (0.04–0.32) ratio for two-mica granite, but low Sr (63–126 ppm) content and CaO/Na2O (0.08–0.20) ratio, and a high Rb/Sr (0.56–2.53) ratio for muscovite granite. The observed differences are due to different protolith chemistries and melting mechanisms. Based on melting experiments of metasedimentary rocks (Patiño Douce and Harris, 1998), muscovite granite was most likely produced by dehydration melting of a metapelitic source and the two-mica granite by H2O-fluxed melting of a metagreywacke. Zircon Hf isotopes of the two S-type granites have εHf(440 Ma) values of -6.85 to +12.02 indicating the involvement of a mantle-derived magma which probably triggered the anatexis of supracrustal rocks deposited in a forarc regime. Coveal adakites with a younging westward trend as well as mafic rocks have been reported in this accretionary complex, which together with anatexis and metamorphism of accreted material support the occurrence of a slab window beneath the forearc accretionary complex of the East Kunlun Orogenic Belt during subduction of the Tethyan oceanic slab.

 

References

Patiño Douce, A.E., Harris, N., 1998. Experimental constraints on Himalayan anatexis. Journal of Petrology 39, 689–710.

How to cite: Ren, X., Dong, Y., He, D., and Hauzenberger, C.: Origin of S-type granites in the forearc accretionary complex of the East Kunlun Orogenic Belt, northern Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9902, https://doi.org/10.5194/egusphere-egu23-9902, 2023.

14:41–14:51
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EGU23-13615
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ECS
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On-site presentation
Simon Stephenson, Mark Hoggard, Marcus Haynes, Karol Czarnota, and Krystian Czado

Lithospheric structure in subduction settings controls the distribution of thermal, compositional and rheological interfaces.  It therefore plays a key role in the generation, fractionation and transport of subduction-related melts that are a vital ingredient of the formation of porphyry copper deposits.  Renewed efforts to understand the linkage between lithospheric structure and the location, grade and endowment of porphyry copper deposits has raised the possibility of using crustal and lithospheric mantle structure as an exploration tool.  One example is a suggested relationship between the genesis of porphyry copper deposits – known to be associated with evolved, silica-rich magmas – and the thickness of the crust.  Here, using a new compilation of spot measurements, we explore the utility of crustal thickness as an exploration tool for porphyry copper deposits.

How to cite: Stephenson, S., Hoggard, M., Haynes, M., Czarnota, K., and Czado, K.: Lithospheric Controls on the Distribution of Porphyry Copper Deposits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13615, https://doi.org/10.5194/egusphere-egu23-13615, 2023.

14:51–15:01
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EGU23-13467
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On-site presentation
Frédéric Mouthereau, Marine Larrey, Louise Boschetti, Nicolas Beaudoin, Stéphanie Brichau, Nick Roberts, Damien Huyghe, Matthieu Daëron, Véronique Miegebielle, and Sylvain Calassou

The Alboran margin in the Betics formed as a result of backarc crustal thinning oblique to the direction of the slab retreat. The history of sediment infill, subsidence and faulting reveals extension at upper crustal levels operated from the Serravallian-early Tortonian to the late Tortonian (14-8 Ma) synchronously with Ca-K magmatism. Only recently, around 8 Ma, the retreating slab detached resulting in the onset of the tectonic inversion of the margin. Here we report new apatite (U-Th)/He thermochronological analyses from Cabo de Gata magmatic province, and new U-Pb dating, Oxygen (O) and carbon (C) stable isotopic analyses of calcite-filled veins from the Tabernas basin combined with fluid temperatures determined by clumped isotope D47 analyses. U-Pb ages from 8.56 ± 0.21 to 4.88 ± 0.45 Ma are remarkably synchronous with late alkaline Tortonian-Messinian magmatic events and post-Messinian uplift. Low-temperature thermochronology confirms that magmatic edifices cooled below sea-level at around 8-7 Ma, and then slowly exhumed onshore during shortening along the Carboneras fault and regional kinematic reorganisation associated with slab detachment. C and O isotopic compositions (-17.23‰ to -9.08‰ for O and -15.77‰ to -1.60‰ for C, in V-PDB) of calcite veins are close to carbonates endmember of the Alpujárride basement. The O and C isotopes trend highlights a burial where all δ18O and δ13C calcite have depleted values compared with host rocks indicating a higher temperature of calcite precipitation (estimated at 83.7°C) and an increasing organic matter degradation with depth. The concordance on ages suggests that deep processes including mantle delamination and hot mantle triggered CaCO3 fluid precipitation and uplift during the transition from extension to onset of tectonic inversion. The deep mantle processes related to the 8 Ma event impacted not only the uplift of the Alboran basin that caused the Messinian Salinity Crisis that is well recorded in the Betics, but also the recent uplift of Iberia and Western Europe.

How to cite: Mouthereau, F., Larrey, M., Boschetti, L., Beaudoin, N., Brichau, S., Roberts, N., Huyghe, D., Daëron, M., Miegebielle, V., and Calassou, S.: Processes related to the rift-to-collision transition in the eastern Betics as revealed by low-temperature thermochronology on magmatic, U-Pb dating and clumped isotopes on calcite-filled veins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13467, https://doi.org/10.5194/egusphere-egu23-13467, 2023.

15:01–15:11
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EGU23-10944
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ECS
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On-site presentation
Jung-Hun Song, Seongryong Kim, and Junkee Rhie

The geometry of subducting slabs is largely controlled by mantle rheology and time evolving processes of surface plate boundaries. Imaging of a detailed slab distribution and its surrounding can provide information of physical, chemical, and dynamical properties of the upper mantle. Based on new high-resolution 3-D tomography of subducting Pacific slab in northeast Asia, we revealed a prominent gap within the stagnant portions of the slab showing an abrupt change in its lateral trends that follow the trace of plate junctions associated with plate reorganization at the western Pacific margin during the Cenozoic. Focused partial melting above the slab gap was inferred based on the spatial coincidence between the high Vp/Vs anomaly and the negative reflectivities above the 410-km discontinuity from local receiver function studies. The slab gap is possibly filled with low-velocity anomalies within the MTZ as evidenced by wavefield focusing of teleseismic body waves and absolute velocity imaging from previous studies. We explain the spatial coincidence between the low-velocity anomaly within the MTZ and the focused melt layer above the MTZ by the process of mantle dynamics related with secular variation of slab geometries by tearing. Isolated low-velocity anomalies within the MTZ imaged by seismic tomography without previous thermal disturbances (e.g., hot plume) are suggested to be the products of distinct MTZ compositions disturbed by former nearby slab subductions. Our results suggest a close dynamical relationship between the subducting slab and the MTZ, which promotes the formation of multi-scale chemically distinct domains in the deeper upper mantle.

How to cite: Song, J.-H., Kim, S., and Rhie, J.: Seismic Evidence of Slab Segmentation and Melt Focusing Atop the 410-km Discontinuity in NE Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10944, https://doi.org/10.5194/egusphere-egu23-10944, 2023.

15:11–15:21
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EGU23-1559
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On-site presentation
Alexander Koptev, Nevena Andrić-Tomašević, Giridas Maiti, Taras Gerya, and Todd Ehlers

Slab break-off is usually referred to as an early collisional process driven primarily by the slowing of the subduction rate as negatively buoyant oceanic lithosphere detaches from positively buoyant continental lithosphere that is attempting to subduct. In this context, slab tearing (or slab break-off propagation) is traditionally attributed to continental corner dynamics, when the subducting plate first detaches in the area of continental collision and then the slab window opens toward the adjacent segment of the convergence boundary, where ocean-continent subduction continues. Another important process, previously thought to be independent of slab break-off and horizontal slab tearing, is a fragmentation of the subducting slab along vertical planes perpendicular to the convergence direction. Previous numerical studies have linked this vertical slab tearing to pre-existing weakness within the subducting plate and/or abruptly changing convergence rates along the trench.

In our study, we use a 3D thermo-mechanical numerical approach to study slab tearing in a non-collisional geodynamic context. The effects of subduction obliquity angle, age of oceanic slab, and partitioning of boundary velocities have been investigated. We show, for the first time, that horizontal and vertical slab tearing are different stages of the same process, which can develop in a self-sustained manner in a non-collisional environment of oblique ocean-continent subduction. Even with an initially absolutely homogeneous oceanic plate and laterally unchanging and temporally constant boundary velocities, the obliquity of the active margin appears to be a sufficient factor to trigger complex system evolution, which includes the transition from horizontal to vertical slab tearing along with additional processes such as retreat and rotation of the trench, decoupling of the overriding and downgoing plates by upwelling asthenosphere in the mantle wedge (also termed “delamination”), initiation of new subduction, and formation of a transform fault.

Our results show striking similarities with several features – such as trench curvature, subduction zone segmentation, magmatic production, lithospheric stress/deformation fields, and associated topographic changes – observed in many subduction zones (e.g., Marianas, New Hebrides, Mexico, Calabrian).

How to cite: Koptev, A., Andrić-Tomašević, N., Maiti, G., Gerya, T., and Ehlers, T.: Horizontal and vertical slab tearing as different stages of a self-sustaining process developing in a non-collisional setting with oblique subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1559, https://doi.org/10.5194/egusphere-egu23-1559, 2023.

15:21–15:31
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EGU23-14144
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ECS
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On-site presentation
Andrea Piccolo, Marcel Thielmann, and Arne Spang

Slab detachment is a process that has been invoked to explain rapid uplift, deep seismicity and magmatic activity in several active orogens (e.g., Alps, Himalaya). The negative buoyancy force associated with a slab at depth and its progressive removal during detachment results in a reorganization of forces within the lithosphere and the detaching slab. However, it is not yet clear to which extent slab detachment is the primary cause of the different observations. Deciphering the impact of slab detachment on the observations mentioned above therefore requires a thorough understanding of the physical processes controlling deformation within and around the detaching slab. 

Here, we employ numerical models to investigate the nonlinear coupling between mantle flow and slab detachment. Due to the three-dimensional nature of slab detachment and the variety of involved processes, it is difficult to pinpoint the first order controls on the time scale of this process. As a first step, we therefore develop a simplified 0D necking model that describes the temporal evolution of the thickness of a detaching slab, additionally taking into account the effects of the nonlinear coupling between upper mantle and detaching slab. This allows us to derive a set of nondimensional numbers which ultimately control the slab detachment process.  

Based on these findings, we then use 2D and 3D numerical models to further determine higher dimensional geometrical effects on slab detachment. Results show that the predictions from the 0D experiments predict the 2D and 3D experiments sufficiently well if simple slab geometries are used. For more complex slab geometries, higher dimensional results deviate from the 0D predictions. Nevertheless, the combination of 0D and 2D/3D numerical models allows to efficiently determine first order controls on slab detachment and thus also on specific geological observations such as seismicity and surface response. 

How to cite: Piccolo, A., Thielmann, M., and Spang, A.: Insights into slab detachment dynamics from 0D to 3D numerical experiments  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14144, https://doi.org/10.5194/egusphere-egu23-14144, 2023.

15:31–15:41
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EGU23-14232
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On-site presentation
Arijit Laik, Wouter Schellart, and Vincent Strak

Continental collision zones form at convergent plate boundaries after negatively buoyant oceanic lithosphere subducts entirely into the Earth's mantle, whereafter collision ensues, and colliding continents are sutured together. In models of free subduction, the volume of the preceding and adjacent negatively buoyant oceanic lithosphere controls the system's driving force and dynamics. To investigate the dynamics of long-term continental subduction, indentation and collisional boundary migration and associated slab dynamics we designed large-scale numerical models of subduction-and-collision including two sets of modelled depths: whole mantle (2880 km) and upper mantle + partial lower mantle (960 km) and varying the trench parallel length ratio (1.5 - 2) of the indenting continental lithosphere (~2300 km) and adjacent oceanic lithosphere. In this contribution, we present the contrasting evolution of continental subduction and indentation coupled with adjacent oceanic slab rollback focusing on the different slab dynamics observed by varying the depth of the mantle in the models. Intriguingly, the whole mantle models show sustained continental indentation and concurrent deep continental subduction to mid-low upper mantle depths resulting in deep slab tearing at the subducted continental margin and shallow slab tearing at the trench parallel boundaries of the continental plate. In addition, the models also show continental underthrusting beneath the overriding plate and underplating of the continent, coeval with indentation and adjacent oceanic slab rollback. Together, these results provide insights into the India-Eurasia collision zone where the prolonged northward indentation of India during the last 50 Myrs and the rollback of the Sunda slab appear linked.

How to cite: Laik, A., Schellart, W., and Strak, V.: Protracted continental subduction, indentation and collisional boundary migration coupled with adjacent oceanic slab-rollback and slab detachment in large-scale buoyancy-driven 3D whole-mantle scale numerical models of subduction-and-collision., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14232, https://doi.org/10.5194/egusphere-egu23-14232, 2023.

15:41–15:45

Posters on site: Fri, 28 Apr, 08:30–10:15 | Hall X2

Chairpersons: Ágnes Király, Patricia Cadenas Martínez
X2.105
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EGU23-2573
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ECS
Frank Zwaan, Sascha Brune, Anne Glerum, John Naliboff, and Dylan Vasey

The tectonic exhumation of mantle material is a well-known phenomenon and may occur during both rifting and subsequent (large-scale) basin inversion. However, the processes leading to the exhumation of dense and therefore negatively buoyant (sub-)lithospheric mantle material remain poorly understood. We therefore conducted a series of thermomechanical simulations using the geodynamics code ASPECT (coupled with FastScape for the inclusion of surface processes) testing the impact of various parameters on mantle exhumation in inverted rift systems.

We find that rift duration strongly impacts mantle exhumation, both during the rift phase, as well as during subsequent inversion. When only limited rifting is applied, the dense mantle material cannot reach the surface as the overlying crustal layers remain connected. Basin inversion then tends to create a symmetric pop-up structure by reactivating rift boundary faults, and the dense mantle material is forced down by the thickening of low-density crustal layers on top of it. Only after certain amount of extension, the crust is sufficiently thinned so that mantle material can be exhumed. This mantle material may then remain near the surface or be further exhumed during basin inversion. Such further mantle exhumation is favoured if asymmetric reactivation of the rift basin occurs, so that mantle material is thrust on top of the downgoing plate.

The establishment of such asymmetric orogenic systems allowing for efficient mantle exhumation is further promoted by having only short-lived tectonic quiescence between rifting and inversion, so that no thermal equilibration of the exhumed mantle domain can occur. As a result, the rift basin remains a weakness that is readily exploited during inversion. Longer periods of tectonic quiescence restore the strength of the lithosphere, so that delayed inversion generates more symmetric structures, with limited opportunities for mantle exhumation.

Within this tectonic context, erosion efficiency is another key factor. First, more efficient erosion during inversion removes crustal material so that the mantle can be exhumed (even in symmetric orogenic systems). Second, efficient erosion also leads to the development of asymmetric orogenic systems, thus doubly contributing to mantle exhumation. Somewhat similarly, high plate velocities during inversion introduce larger amounts of crustal material into the system, which erosion cannot remove in a timely manner, whereas slow plate velocities allow erosion more time to remove material. Hence, mantle exhumation is positively correlated to erosion efficiency, and is negatively correlated to plate velocities during inversion

Finally, serpentinization of mantle material can occur close to the Earth’s surface (i.e. in the uppermost kilometres) and strongly reduces the material’s density and brittle strength. Although our models so far only show a limited effect of serpentinization, the overall weakness of serpentinized mantle material at the rift basin floor seems to reduce localization of inversion-related deformation, thus generating more symmetric inversion systems with limited mantle exhumation.

How to cite: Zwaan, F., Brune, S., Glerum, A., Naliboff, J., and Vasey, D.: Numerical modelling of mantle exhumation in inverted rift systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2573, https://doi.org/10.5194/egusphere-egu23-2573, 2023.

X2.106
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EGU23-4422
Rashmi Battan, Truong Tai Nguyen, Sun-Lin Chung, Tsuyoshi Komiya, Shigenori Maruyama, Andrew Tien-Shun Lin, Hao-Yang Lee, and Yoshiyuki Izuka

Intra-oceanic arc’s collision with an oceanic plateau plays a crucial role in the development of complex tectonic setting and induce subduction polarity reversal. Despite several studies and investigations, the origin and timing of subduction initiation in Solomon Island Arc (SIA) is still ambiguous. This study presents first robust zircon U-Pb ages and in-situ Hf isotope data from Choiseul, Santa Isabel (SI) and New Georgia Group (NGG), three major islands of SIA. Magmatic zircons and Hf isotope data from one gabbro sample, geochemically identical to N-MORB with Nb, Ta depletion in spidergram yielded 46 ± 1 Ma, which we decipher as the timing of Stage I magmatism by subduction of Pacific plate and subduction initiation in Choiseul. Six Choiseul andesites gave a mean age 206Pb/238U of 0.7 Ma, with εHf(t) values from +9 to +15 which represents the youngest crystallization age of Stage II magmatism with typical island arc-like signatures and a depleted mantle source. Detrital zircons from two sand sample yielded a population of mean age ranging from 0.3-0.7 Ma, 10 Ma and 48-46 Ma with εHf(t) values +9 to 15, +11 to +12 and +11 to +14 respectively and third sample has yielded a mean age 207Pb/206Pb 2.6 Ga and 500-1600 Ma with εHf(t) values -8 to +9, probably associated with Australian-type source indicating presence of a continental fragment beneath SIA. 

Similar ages of ca. 2.6 Ma have been obtained from inherited zircons from three gabbroic dyke sample from Santa Isabel with εHf(t) values +1 to +9 whereas one gabbroic dyke sample yields 110 ± 1 Ma, with εHf(t) values +14 to + 16 which we interpret as the basement age of SI.

U-Pb dating of zircons from mafic to felsic rocks along NGG, covered mostly by Quaternary eruptive lavas. The youngest age population indicate Late Pliocene-Pleistocene 206Pb/238U ages, 2.5-1.5 Ma, interpreted as  zircon crystallization ages of Stage II arc magmatism resulting from subduction of the Solomon Sea plate, as those of Choiseul Andesite. The first U-Pb age from ca. 36.8±0.5 Ma granite on Ghizo Island in New Georgia Group, revealing Late Eocene-aged magmatic zircon. This age represents the magmatic emplacement as the basement of plutonic rock from NGG that has not been reported before.

We conclude that, (i) The Solomon Islands has a Cretaceous basement preserved in SI. (ii) The timing of subduction initiation and Stage I N-MORB type tholeiitic magmatism in SIA is 46 Ma followed by episodic eruptions from the early Eocene to late Eocene. (iii) Oligocene (30-20 Ma) magmatic hiatus, probably the time of subduction polarity reversal from subduction of Pacific plate to subduction of Solomon Sea plate. (iv) Stage II island arc magmatism initiated at 20-18 Ma in NGG to youngest emplacement age of Pliocene to Pleistocene in Choiseul as well as in NGG. (v)Abundant Archean zircons are present in samples from all three islands, indicate presence of micro-continent beneath Islands of Solomon. We are still working on the whole rock isotopic analysis to better constrain the tectonic and magmatic evolution of SIA.

How to cite: Battan, R., Nguyen, T. T., Chung, S.-L., Komiya, T., Maruyama, S., Lin, A. T.-S., Lee, H.-Y., and Izuka, Y.: From Subduction Initiation to Polarity Reversal: Zircon Age and Geochemical Constraints from Solomon Islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4422, https://doi.org/10.5194/egusphere-egu23-4422, 2023.

X2.107
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EGU23-2657
Walter Kurz, Irena Miladinova, Kurt Krenn, and Thomas Hilmbauer-Hofmacher

The Mariana convergent margin provides the environment where a natural process brings materials from great depths directly to the surface. The Mariana forearc contains the only current active serpentine mud volcanism in a convergent margin setting. Here, serpentinite mud volcanoes are numerous, large (averaging 30 km diameter and 2 km high) and active. They are composed principally of unconsolidated flows of serpentine muds containing clasts of serpentinized mantle peridotite and several other lithologies, such as blueschist materials derived from the subducting slab.

IODP Expedition 366 recovered cores from three serpentinite mud volcanoes at increasing distances from the Mariana trench subduction zone along a south-to-north transect: Yinazao (Blue Moon), Fantangisña (Celestial), and Asùt Tesoru (Big Blue). These cores consist of serpentinite mud containing lithic clasts and minerals derived from the underlying forearc crust and mantle, as well as from the subducting Pacific Plate. Fluids upwell within these mud volcanoes at a rate that is in excess of the mud matrix. Such fluids originate from the downgoing plate but are highly altered, are reducing and have pH values in the range of 9 to 12.5.

For the purposes of this study ultramafic and mafic rock clasts from the flanks and summits of both Asùt Tesoru and Fantangisña Seamounts were analyzed in order to reconstruct processes of fore-arc mantle alteration, fluid activity and fluid-rock interaction. Additionally, several samples from Asùt Tesoru Seamount consisting of cryptocrystalline serpentine mud with commonly occurring lithic clasts (>2 mm) in different amounts and size were investigated.

In general the mineral paragenesis of the serpentinized peridotite clasts, including mainly lizardite and chrysotile serpentine group minerals, along with brucite as well as andradite, and the apparent absence of high-temperature phases such as antigorite and anthophyllite, tentatively constrains an upper temperature limit of 200 – 300 °C. However, the presence of fine-grained matrix antigorite associated with lizardite suggests metamorphic temperature of at least 340 °C.

Hydrogarnet is a common secondary, hydrothermal mineral phase in the studied samples and it defines a serpentinization temperature of c. 230 °C. Garnet crystals with subhedral habitus and almost pure andraditic composition are found within a carbonate matrix. However, also Cr-rich garnets are common within the serpentinite clasts. They are subhedral to anhedral and contain chromite inclusions with similar composition to the unaltered chromites in the same sample. These textural observations suggest a secondary origin for the Cr-rich garnets as well, most probably related to hydrothermal fluids that infiltrated the ultramafic protolith. The formation of Cr-rich garnet after Cr-rich spinel is usually associated with hydrothermal or metasomatic reactions, although the precise mechanism of formation remains unclear. Generaly Cr-rich hydrogarnets in serpentinites crystallize below 400 °C, which is in line with the obtained metamorphic conditions and indicate an overall evolution of a hydrothermal fluid from c. 350 °C (antigorite in serpentinites) to c. 100 °C and below.

How to cite: Kurz, W., Miladinova, I., Krenn, K., and Hilmbauer-Hofmacher, T.: Fore-arc mantle alteration, fluid activity and fluid-rock interaction revealed from Serpentinite Mud Seamounts at the Mariana Convergent Margin System (IODP Expedition 366), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2657, https://doi.org/10.5194/egusphere-egu23-2657, 2023.

X2.108
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EGU23-6363
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ECS
Alex Bisch, Antoine Triantafyllou, Gweltaz Mahéo, Jamal El Kabouri, Olivier Bruguier, Delphine Bosch, Julien Berger, Jérôme Ganne, and Frédéric Christophoul

Convergence zones are marked by a variety of settings that may follow each other in modern-day tectonics, including compressive phases such as subduction, obduction, collision but also extensive ones such as back-arc opening or stress-relaxation during orogenesis. Hence, the protracted evolution leading to a super-continent block amalgamation may be difficult to decipher and so may be the forcings on external enveloppes such as volcanism or erosion caused by the different phases.

This question arises critically at the time of the Pan-African Orogenesis (1-0.5 Ga) assembling Gondwana, a time of supposedly dramatic and diachronical changes for external envelopes: glaciations of debated scales, deposition of various Banded Iron Formations, first (Ediacarian) fauna, replacement by Cambrian faunas. Our goal is to explore in detail the geodynamical succession leading to the amalgamation of blocks along the northern margin of the West African Craton (WAC), outcropping in the Central Anti-Atlas region, Morocco. This region is characterized by the occurrence of extended convergence-related magmatism, ophiolite emplacement and basins fillings (including BIF) during Cryogenian and Ediacaran periods.

Data obtained from compilation of cartographic work, whole-rock geochemistry and datation reveals a polyphased but still poorly constrained evolution through proxies of continentality (εNd) and of crustal thickness (Sr/Y ratio). We present new data spanning metamorphic petrology, basin stratigraphy, coupled datation and trace element analysis in detrital zircons in order to better understand the evolution of the geodynamic, magmatic and drainage systems. We propose a geodynamic scenario based on these data:

  • Development of an early oceanic arc (760-720 Ma) with juvenile magmatic signature (3<εNd(t)<7), its accretion on the WAC is followed by an episode of calc-alkaline magmatism (710-700 Ma).

  • Second arc development (700-670 Ma) only seen in detrital and inherited zircons, its accretion at 670 Ma is followed by late-orogenic magmatism (660-650 Ma) associated with decreasing crustal thickness (from 70 to 25 km).

  • Third arc development on the newly formed continent margin (640-600 Ma) until oceanic closure and collision. Intense late orogenic magmatism occurs (590-570 Ma), coeval with the decreasing crustal thickness (from 100 to 30 km).

  • A late phase of calc-alkaline is recorded (570-550 Ma) at constant and regular crustal thickness (25 km). A 550 Ma compressive event is recorded, very few calc-alkaline follows.

  • The onset of Cambrian with the development of a large passive margin capping the whole region. This change coincides with disappearance of ice-house climate evidence from the global sedimentological record.

How to cite: Bisch, A., Triantafyllou, A., Mahéo, G., El Kabouri, J., Bruguier, O., Bosch, D., Berger, J., Ganne, J., and Christophoul, F.: 200 Ma of magmatism along the northern border of the West African Craton during Pan-African convergence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6363, https://doi.org/10.5194/egusphere-egu23-6363, 2023.

X2.109
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EGU23-10847
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Highlight
Ben Mather, Dietmar Müller, Christopher Alfonso, Maria Seton, and Nicky Wright

The recycling of oceanic lithosphere at subduction zones constitutes the largest driving force of plate tectonic motion. The angle at which subducting plates enter the mantle influences the magnitude of this force, the distribution of subduction-related earthquakes, intensity of volcanism, and mountain building. However, the factors that control subduction angle remain unresolved. We develop a novel formulation for calculating the subduction angle based on trench migration, convergence rate, slab thickness, and plate density which reproduces the present-day dynamics of global subduction zones. Applying this formulation to reconstructed subduction boundaries from the Jurassic to present day, we relate subduction angle combined with slab flux to pulses in kimberlite eruptions. High rates of subducting slab material trigger mantle return flow that stimulates fertile reservoirs in the mantle. These convective instabilities transport slab-influenced melt to the surface at a distance inbound from the trench corresponding to the subduction angle. Our deep-time slab dip formulation has numerous potential applications including modelling the deep carbon and water cycles, and an improved understanding of subduction-related mineral deposits.

How to cite: Mather, B., Müller, D., Alfonso, C., Seton, M., and Wright, N.: Reconstructing slab dip through deep time to explain pulses in kimberlite eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10847, https://doi.org/10.5194/egusphere-egu23-10847, 2023.

X2.110
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EGU23-5229
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ECS
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Betti Hegyi, Luca Dal Zilio, Whitney Behr, and Taras Gerya

Various geological and geophysical observations from different subduction zones attest to the importance of pore pressure fluctuations and fluid flow in triggering regular earthquakes, slow slip events and tectonic tremors. We use the Hydro-Mechanical Earthquake Cycle (H-MEC) code to model fluid-driven earthquake cycles in a subduction megathrust environment. The code uses  a finite differences-marker in cell method, and couples solid rock deformation with fluid flow. The code solves the mass and momentum conservation equations for both solid and fluid phases, with the addition of gravity and temperature-dependent viscosity. The brittle/plastic deformation is resolved through a rate-dependent strength formulation and the development of slip instabilities is governed by compaction-induced pore fluid pressurization. With such code we can demonstrate how the fluid pressurization can lead to localisation of deformation with slip rates up to m/s in a fully compressible poro-visco-elasto-plastic media. The models can reproduce all slip modes observed in nature from regular earthquakes to transient slow slip phenomena to aseismic creep. Here we investigate various controls on dominant slip mode and their expected distributions and interactions along a subduction interface model setup. Our initial results show that the dominant slip mode depends on porosity, permeability, plastic dilatation and viscosity of the matrix. An increase in the porosity will lead to aseismic deformation in the form of slow slip events and creep. We also investigate the effects of inclusions (clasts) along the subduction channel, acting as stress heterogeneities, with physical properties different from the subduction channel. We attempt to understand the role of inclusions with different viscosities and permeabilities embedded in the matrix. With this numerical framework, we can better understand fluid-driven seismicity, and the effects of fluids on long-term geodynamic processes. Our study also contributes to better understand the role of fluid pressure cycling in seismic and aseismic deformation in subduction zone environments, as well as provides new insights in the role of stress heterogeneities within the frictional-viscous shear zone. 

How to cite: Hegyi, B., Dal Zilio, L., Behr, W., and Gerya, T.: Modeling fluid-driven seismic cycles in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5229, https://doi.org/10.5194/egusphere-egu23-5229, 2023.

X2.111
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EGU23-7467
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ECS
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Ana Lorena Abila, Whitney Behr, and Jonas Ruh

The integrated stress magnitude or bulk effective viscosity of subduction interface shear zones is a key component of both long- and short-term subduction dynamics. Current constraints on average subduction interface viscosity come from laboratory flow laws for subduction-related rock types and range from 1018 Pa.s (quartz-rich lithologies) to 1023 Pa.s (metabasaltic lithologies) for typical subduction strain rates and viscous subduction interface conditions (e.g. T between 400-900 °C). However, this viscosity range is based on end-member flow laws, which means it likely overestimates the true range in viscosity that is possible along the subduction interface. In nature, subduction shear zones are commonly a mixture of multiple rock types in various distributions (e.g. clast-matrix melanges); and furthermore, natural shear zones show a range in width from place to place, suggesting varying strain rates. Our goal in this study is to place more precise bounds on the global range of shear zone viscosity (or integrated shear stress) for natural subduction shear zones at deep subduction conditions. To do so, we curated a set of 9 geologic maps of eclogite facies shear zones from existing literature, focusing on those that a) show minimal retrogressive overprint, b) have defined shear zone widths, and c) have well-constrained PT conditions. These maps were digitized and implemented in a simple shear visco-elasto-plastic numerical model with constant strain rate (10-12 s-1) boundary conditions and experimentally constrained flow laws assigned to each rock type, including eclogite (eclogite mafic blocks), wet quartz (quartz-rich blocks, schists, gneisses), blueschist (blueschist mafic blocks), wet olivine (peridotites), antigorite (serpentinites), and aragonite (calcareous blocks). Numerical experiments  ran for a restricted amount of time steps to assure  steady-state stress/viscosity (<10 ky). Resulting integrated shear stresses and viscosities were then compared for the different example shear zones. Initial results indicate that natural shear zones should exhibit effective viscosities that vary by at least 1-2 orders of magnitude at a specific temperature, depending on the distribution of weak vs. strong blocks and the matrix rheology. Additional results and statistical analysis of all of the shear zones will be presented at the meeting. 

How to cite: Abila, A. L., Behr, W., and Ruh, J.: Combined natural and numerical-modeling constraints on subduction interface strength at deep metamorphic conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7467, https://doi.org/10.5194/egusphere-egu23-7467, 2023.

X2.112
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EGU23-11688
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ECS
Derek Neuharth, Whitney Behr, and Adam Holt

Because subduction zones can extend thousands of kilometers along-strike, many previous studies have used 2D subduction models which inherently assume homogeneity along-strike. However, in nature we see that subduction zones are often heterogeneous along-strike and can exhibit significant variations in the subducting plate age, thickness, and viscosity, trench location, as well as in the geometry of the overriding plate. While 2D models can test large system-wide changes to these parameters by assuming homogeneity along-strike, how variabilities in the geometry and rheology interact with each other in a three-dimensional setting is poorly understood.

To understand how along-strike variations affect an evolving subduction zone, we developed self-consistent 3D subduction models using the finite element code ASPECT. The models include a thermally-defined subducting plate and overriding plate, and a constant-viscosity crust/interface. We vary two primary parameters along-strike: 1) the viscosity of the interface shear zone and 2) the thickness of the overriding plate, which affects the interface shear zone length. We explore how varying each of these parameters affects the subduction, convergence, and trench rollback velocities, slab morphology, and the stress distribution and topography formation within the overriding plate.

We find that along-strike variations to the interface viscosity or overriding plate thickness has only minor effects on the slab morphology and convergence velocities, but largely affects the surface stress distribution. While variations in the overriding plate thickness or interface viscosity do not affect the convergence velocity along-strike, having a thicker overriding plate or stronger interface leads to a reduction in the system-wide convergence velocity. Despite the similar velocities along-strike, slab morphology changes along-strike, with lower dips seen in regions with a greater overriding plate thickness or weaker interface viscosity. Most importantly, along-strike changes to either parameter results in significant differences in the surface stress distribution. Higher stresses build within the side that has a thicker overriding plate or stronger interface. This increase in stresses results in greater topography, with a maximum variation along-strike of up to ~1.2 km.

How to cite: Neuharth, D., Behr, W., and Holt, A.: Numerically modelling along-strike rheologic variations in 3D subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11688, https://doi.org/10.5194/egusphere-egu23-11688, 2023.

X2.113
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EGU23-13902
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ECS
Paraskevi Io Ioannidi and Wouter Pieter Schellart

The physical nature and the rheology of the subduction interface play an important role in the deformation of the overriding plate, the degree of locking of the subduction zone plate boundary, and the rate of subduction. Here, we employ the Finite Element Method (FEM) to determine the effect of matrix rheology on the bulk interface deformation. We use the open-source particle-in-cell FEM code Underworld (Moresi et al., 2007) to create synthetic 2D visco-plastic models of the subduction interface that deform by simple shear. The models comprise meter-scale blocks of continental affinity encompassed within a metasedimentary matrix. We investigate the effect of constant, Newtonian, and non-Newtonian matrix viscosities on the deformation and stress distribution in the models for large finite shear strains. We vary the percentage of block concentration from 10% to 65%, as well as the shear velocity while making sure the strain rates produced remain within the interseismic range, and we calculate strain localization and stresses within the models. Finally, we use the same viscosity formulations in large-scale 2D models of a subduction zone to investigate their influence on upper plate deformation and subduction rate during the interseismic stage. With this multi-scale analysis, we gain insight into how the same rheological law can affect deformation at different scales.

How to cite: Ioannidi, P. I. and Schellart, W. P.: Multi-scale numerical modelling of subduction interface rheology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13902, https://doi.org/10.5194/egusphere-egu23-13902, 2023.

X2.114
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EGU23-6505
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ECS
Umedzhon Kakhkhorov, Børge Arntsen, Wiktor Waldemar Weibull, and Espen Birger Raknes

Traveltime tomography is applied to investigate seismic structures of the Earth's subsurface. An accurate tomographic velocity model is important for a high-resolution waveform velocity building and its availability is one of the main components to mitigate the nonlinear inverse problem. We present a new methodology of obtaining velocity models for traveltime tomography studies. We found a way to get a highly accurate first-arrival traveltime tomography in combination with global optimization. The role of global optimization is twofold: to find initial solutions that are close to ‘truth’, and to guide tomographic inversion towards a geologically consistent model that explains the data. The main advantage of our workflow is a data-driven approach avoiding the use of a conventional layer-based parameterization and incorporation of manual interpretations into the velocity model. 

To date, a few geophysical studies have been focused on developing data-driven and a labour non-intensive regional tomographic velocity model building workflow. In our study, we present the tomographic velocity model building workflow as a combination of first-arrival traveltime tomography and global optimization. Global optimization allows to search for velocity parameters and depth to interfaces in the larger search area with a higher chance of convergence. After defining the geometry of main layers and general velocity trends, traveltime tomography with a bi-cubic B-spline model parameterization can be fitted to further update the velocity model. Our approach allows obtaining a highly accurate velocity model which can be used for seismic depth migration and as a starting model for a FWI seismic imaging. The workflow is developed and applied to synthetic and field regional seismic datasets. 

The developed methodology is applied for a shallow seismic engineering data and regional Ocean Bottom Seismic data. We identify four key components that lead to building an accurate tomographic velocity model: (i) understanding prominent horizons and possible velocity distribution of a layer within the study area. (ii) Performing ray penetration test to define offset ranges which carry the velocity information for the defined layers. (iii) Determining inversion schema to a perform global search for the velocity trends and major boundaries, and a local search to update lateral velocity variation. (iv) Iteratively update a set of defined layers (i.e., sediment, igneous crust and basement) in a top-down manner. 

How to cite: Kakhkhorov, U., Arntsen, B., Weibull, W. W., and Raknes, E. B.: Global inversion and parametrization for building tomographic velocity models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6505, https://doi.org/10.5194/egusphere-egu23-6505, 2023.

X2.115
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EGU23-6845
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ECS
Nazia Hassan and Christian Sippl

Intermediate-depth earthquakes in many subduction zones occur in two distinct layers, forming an upper and a lower seismic zone separated vertically by an aseismic or weakly seismic region. This setting is widely known as Double Seismic Zone (DSZ). Notably, intermediate-depth seismicity in Northern Chile shows a pattern of intraslab seismicity which is distinct from the aforementioned conventional DSZ. Here, two parallel seismicity planes are present in the updip part of the slab, but at a depth of ∼80–90 km, there is a sharp transition to a highly seismogenic volume of 25–30 km thickness, which closes the gap between the two seismicity planes.

While such an observation is unique to Northern Chile, understanding the processes behind the formation of this feature should provide important constraints on the mineral processes that govern seismicity in DSZs as well as the role and involvement of fluids. As seismic velocities contain important information about mineralogy and fluid content, we aim at a high-resolution characterization of the seismic wavespeeds of the Northern Chile subduction zone, mainly focusing on the subducting Nazca slab. Data from the seismic stations of the permanent IPOC (Integrated Plate boundary Observatory Chile) deployment in the Northern Chile forearc form the backbone of the dataset, but are complemented by several temporary deployments that span shorter time sequences as well. We use the seismicity catalog of Sippl et al. (2018) that contains >100,000 earthquakes and 1,200,404 P- and 688,904 S-phase picks for the years 2007 to 2014, and limit our analysis to events that have more than 14 P-arrivals as well as more than 7 S-arrivals. Constraining the hypocentral depth range to 40-155 km and the longitude range to 68° W- 72°W, we perform local earthquake tomography using the FMTOMO algorithm (Rawlinson et. al., 2006) with a dataset of 10102 events comprising 163,359 P- and 113,036 S- phase picks.

We present first 3D models of P- and S-wavespeeds from the Northern Chile forearc between about 18.5° S and 24.5° S, as well as images of ray coverage, relocated seismicity and synthetic resolution tests. Tomography models for different choices of grid spacing and damping-smoothing parameters are compiled and compared in order to derive the optimal settings for the inversion.

 

The presented seismic velocity distribution will eventually be compared with theoretical wavespeeds that are forward calculated assuming different mineralogical compositions in order to narrow the range of possible reactions that may be occurring at depth.

 

How to cite: Hassan, N. and Sippl, C.: Looking deep into the subducting Nazca plate under the Northern Chile forearc with local earthquake tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6845, https://doi.org/10.5194/egusphere-egu23-6845, 2023.

X2.116
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EGU23-8670
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Highlight
Philip Heron, Erkan Gün, Grace Shephard, Juliane Dannberg, Rene Gassmöller, Erin Martin, Aisha Sharif, Russell Pysklywec, R. Damian Nance, and J. Brendan Murphy

Large igneous provinces (LIPs) have been linked to both surface and deep mantle processes related to supercontinent formation. During the formation, tenure, and breakup of Pangea, the most recent supercontinent, there is a noted contemporaneous increase in the number of emplacement events of both continental and oceanic LIPs. There is currently no clear consensus on the origin of LIPs, but the most widely recognized hypothesis relates their formation to crustal emplacement of hot plume material originating in the deep mantle. The interaction of subducted slabs with the lowermost mantle thermal boundary and subsequent return-flow is a key control on plume generation. This mechanism has been explored for LIPs below the interior of a supercontinent (e.g., continental LIPs). However, a number of LIPs related to Pangea formed at the supercontinent’s exterior (e.g., Ontong Java Plateau in the Pacific Ocean), with no consensus on their formation mechanism. In this research, we consider the dynamics of global-scale supercontinent processes resultant from numerical models of mantle convection, and analyse whether circum-supercontinent subduction could generate both interior (continental) and exterior (oceanic) deep-mantle plumes. Our 2-D and 3-D numerical models show that subduction related to the supercontinent cycle can reproduce the location and timing of the Ontong Java Plateau, Caribbean LIP, and potentially the Shatsky Rise, when relating these LIPs to a deep mantle exterior plume. The findings here highlight the importance of taking into consideration mantle dynamics in every stage of the supercontinent cycle.

How to cite: Heron, P., Gün, E., Shephard, G., Dannberg, J., Gassmöller, R., Martin, E., Sharif, A., Pysklywec, R., Nance, R. D., and Murphy, J. B.: The role of subduction in the formation of Pangean oceanic large igneous provinces, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8670, https://doi.org/10.5194/egusphere-egu23-8670, 2023.

X2.117
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EGU23-11018
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ECS
Carlos Errázuriz-Henao, Arturo Gómez-Tuena, Mattia Parolari, and Marion Weber

Magmatic arcs modulate global climate over geological timescales through outgassing and rock weathering, but recognizing the fingerprints of climate change in arc magmas remains challenging. Based on a detailed reconstruction of oceanographic, atmospheric, and climatic processes since the middle Miocene, as well as an extensive geochemical database of Miocene and active arc-front magmas from the Trans-Mexican Volcanic Belt, Central American Volcanic Arc, and the North Andean Colombian Arc we developed a conceptual framework by which biogeochemical proxies in oceanic sediments can be tracked down to the composition of arc magmas. Using this framework, we show that the well-documented increases in biologically mediated authigenic Ba and U contents of seafloor sediments from the Eastern Equatorial Pacific (EEP) at the onset of the so-called “carbonate crash” (12–9 Ma) were triggered by an escalation in biological productivity and an augmented efficiency of respiratory carbon storage. We suggest that the temporal modification of the oceanic carbon cycle was regulated by the synchronous formation of three wind-powered seasonal upwellings systems —Tehuantepec, Papagayo, and Panama— that developed in the context of steepening meridional temperature gradients, intensified atmospheric circulation and global climate cooling since the Middle Miocene. Sediments deposited in the context of these newly established upwelling systems became anomalously enriched in authigenic U and Ba not only in comparison to older sediments, but also with respect to geographically adjacent areas of the EEP where vigorous upwellings are absent. These peculiar environmental conditions thus produce a heterogeneous ocean floor that upon subduction and eventual interaction with the mantle wedge creates arc volcanoes with compositional fluctuations that mimic those of the ocean sediments. These findings indicate that the oceanographic and biogeochemical effects of climate change can be engraved on the continental crust and mantle.

How to cite: Errázuriz-Henao, C., Gómez-Tuena, A., Parolari, M., and Weber, M.: Magmatic arc compositions governed by climate change: A biogeodynamic perspective from the Eastern Equatorial Pacific, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11018, https://doi.org/10.5194/egusphere-egu23-11018, 2023.

X2.118
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EGU23-14047
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ECS
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Uğurcan Çetiner, Jeroen van Hunen, Oguz H. Gogus, Mark B. Allen, and Andrew P. Valentine

The Arabia-Eurasia collision, which started during Late Eocene (~35 Ma) or afterward across the Bitlis-Zagros suture, resulted in the formation of the Turkish – Iranian Plateau. Even though the average elevation throughout the plateau is around 2 km, the lithospheric structures between East Anatolian and the Iranian parts may be different. For instance, seismological studies suggest that East Anatolia is underlain by anomalously low-speed anomalies/hot asthenosphere whereas the Iranian part is associated with a rather thick (>200 km in some places) and strong lithosphere. Therefore, the area may be regarded as two distinct regions, namely, the East Anatolian Plateau and the Iranian Plateau. The growth of the plateau is mostly attributed to slab break-off combined with crustal shortening. Other processes often associated with the collision are lithospheric delamination and tectonic escape of microplates. These hypotheses suggested for the growth of the plateau are yet to fully explain the dualistic nature of the lithosphere in a region where elevations are roughly similar. In this work, by using 2D numerical experiments we aim to investigate the physical, geometric, and rheological parameters affecting the deformation of the plate during pre-, syn-, and post-collision. Our preliminary model results show an extension (up to ~70 km) on the terrane that is dragged behind the subducting plate, while the overriding plate undergoes shortening during the collision. The collision results in ~100 km of underthrusting in 50 Myrs which is in the range for the measured amounts of underthrusting across the plateau. We aim to expand the study by creating comparative model sets (i.e., models representing East Anatolia vs. models representing Iran) with a parameterization of varying lithospheric structures (e.g., different crust and mantle thicknesses), and strength profiles, which will help us to understand the kinematics and dynamics of such orogenic growth.

How to cite: Çetiner, U., van Hunen, J., Gogus, O. H., Allen, M. B., and Valentine, A. P.: The growth of Turkish – Iranian Plateau and comparative models for understanding the deformation on the overriding plate during plateau formation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14047, https://doi.org/10.5194/egusphere-egu23-14047, 2023.

Posters virtual: Fri, 28 Apr, 08:30–10:15 | vHall GMPV/G/GD/SM

Chairpersons: Ágnes Király, Jeroen van Hunen
vGGGS.14
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EGU23-5078
Vlad Constantin Manea, Marina Manea, and Lucian Petrescu

Oceanic plates are far from homogeneous, and a large number of bathymetric discontinuities such as seamounts of different sizes are transported along by plate motion towards the mid ocean trenches and beyond. Seamounts currently colliding with plate margins show a major role in shaping the forearc morphology, and several studies even suggest that they might be related with seismicity. However, it is not clear what happens after seamounts are subducted, they can be accreted to the forearc, carried down into the subduction zone and recycled into the deep mantle, or a mix of the two scenarios. Using high-resolution two-dimensional thermomechanical numerical simulations, we investigate subduction processes of oceanic plates with a heterogeneous structure marked by a series of basaltic seamounts arranged in a chain like structure. We solve the 2D momentum, continuity and energy equations with the finite differences coupled with PIC (particle-in-cell) method. Our models also incorporate a depth-dependent, realistic non-Newtonian visco-elasto-plastic rheology, and plasticity is implemented using a yield criterion which limits the creep viscosity. Preliminary results show that initially seamounts preserve they structure when impacting with the trench. Their integrity is partially conserved until they subduct to a depth of about 25-30 km when they finally start to succumb to the great deformations and stresses along the slab interface. We observed that the lower part of the seamount continuously deforms and amalgamates along the slab interface. The upper part is detached and incorporated into the forearc structure. The subsequent seamounts that trail the first seamount, follow the same deformation pattern, and the top of them are maintained in the highly deformed forearc region. Our preliminary modeling results confirm that seamount subduction represent a key tectonic process that influences on a long-term time scale the structure and evolution of subduction zones.

How to cite: Manea, V. C., Manea, M., and Petrescu, L.: Subduction of bathymetric irregularities along active margins: insights from numerical modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5078, https://doi.org/10.5194/egusphere-egu23-5078, 2023.