GD4.3

Geodynamics of plate convergences

Many new high quality and high resolution geophysical and geological data had been acquired in the past years that need to be updated, re-analysed and re-interpreted in the light of our present knowledge of the subductions processes. Moreover it is needed to better clarify the temporal and spatial evolution of those processes in order to much precise our geodynamic ideas of mountain building, sedimentary basins formation, subduction, the transition from oceanic to continental subductions (collision) or the reverse from collision to subduction...
Among other global places, the zone from Japan, Taiwan to the Philippines is a key area to study such subduction/collision transition due to the rapid convergence between Eurasian and Philippine Sea plates. There are geodynamic inversion of the east dipping Manila oceanic subduction, that evolves northward, first, into a Continental Subduction (so called collision) onshore Taiwan, then secondly, east of Taiwan, into the north dipping Ryukyu arc/continent subduction. Due to the so rapid Plates shortening rate (10cm.y-1), those active Oceanic to Continental Subductions processes in Taiwan creates 1/8 of the annual seismicity in the World !
There are other places in the World active or not, that should also be taken into careful consideration in order to reveal and lead us to better understand new tectonic processes (e.g.: Alpes, Pyrénées, Cascades and so on).
In this EGU session, we aim to discuss and update the existing geodynamic processes and state of the art of the oceanic to continental subductions processes after so numerous data that had been collected recently and all the works that had been done on this subject. Therefore this EGU Session should help us to much better understand the geodynamic of plate convergence, the role of oceanic crust and the transition between subduction and collision.

Co-organized by GM9/TS7
Convener: Benoit Deffontaines | Co-conveners: Ho-Han HsuECSECS, S. K. Hsu
vPICO presentations
| Wed, 28 Apr, 13:30–15:00 (CEST)

Session assets

Session materials

vPICO presentations: Wed, 28 Apr

Chairperson: Benoit Deffontaines
13:30–13:35
13:35–13:40
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EGU21-2441
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ECS
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solicited
Eleonora Ficini, Marco Cuffaro, and Carlo Doglioni

The lithospheric sinking along subduction zones is part of the mantle convection. Therefore, computing the volume of lithosphere recycled within the mantle by subducting slabs quantifies the equivalent amount of mantle that should be displaced, for the mass conservation criterion. Starting from the analysis of the subduction hinge kinematics, that could either move towards (H-convergent) or away (H-divergent) with respect to the fixed upper plate, we compute the amount of lithosphere currently subducting below 31 subduction zones worldwide. Our results show that ~190 km3/yr and ~88 km3/yr of lithosphere are currently subducting below H-divergent and H-convergent subduction zones, respectively. This volume discrepancy is principally due to the difference in the two end-members subduction rate, that takes into account the hinge kinematics. We also propose supporting numerical models providing asymmetric volumes of subducted lithosphere, using the subduction rate, instead of plate convergence, as boundary condition. Subduction zones show a worldwide asymmetry from geological and geophysical observations, such as slab dip, structural elevation, gravity anomalies, heat flow, metamorphic evolution, subsidence and uplift rates or depth of the décollement planes. This asymmetry is expressed also in the behaviour of the subduction hinge, so that H-divergent subduction zones appears to be coincident with subduction zones having “westward”-directed slabs, whereas H-convergent are compatible with those that have “eastward-to-northeastward”-directed slabs. On the basis of this geographical polarity of subducting slabs, the obtained lithospheric volume estimation gives ~214 km3/yr and ~88 km3/yr of subducting lithosphere for subduction zones with W-directed and E-to-NE-directed slabs, respectively. This imply that W-directed subduction zones contribute more than twice in lithospheric sinking into the mantle with respect to E-to-NE-directed ones. In accordance with the conservation of mass principle, this volumetric asymmetry in the mantle suggests a displacement of ~120 km3/yr of mantle material from the west to the east, providing a constrain for a global asymmetric mantle convection.

How to cite: Ficini, E., Cuffaro, M., and Doglioni, C.: Asymmetric dynamics at subduction zones: from plate kinematic constraints to global mantle convection, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2441, https://doi.org/10.5194/egusphere-egu21-2441, 2021.

13:40–13:42
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EGU21-2922
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ECS
Kai Xue, Wouter P. Schellart, and Vincent Strak

Overriding plate deformation (OPD) and topography vary at different subduction zones, with some subduction zones showing mainly overriding plate extension and low topography (e.g. Mariana, Tonga, Izu-Bonin subduction zones), while some showing mainly shortening and elevated topography (e.g. Makran, southern Manila subduction zones). Here we investigate how different subduction modes, namely trench retreat and trench advance, affect OPD and generate corresponding topography with fully dynamic analogue models of time-evolving subduction in three-dimensional space. We conduct two sets of experiments, one of which is characterized by trench retreat and slab rollback, and the other characterized by trench advance and slab rollover. We compute the mantle flow, the overriding plate strain and topography during subduction using the particle image velocimetry technique (PIV). The overriding plate in the experiments showing continuous trench retreat experiences overall extension, while in the experiments with trench advance following trench retreat it experiences overall shortening. The overriding plate in both trench retreat and trench advance subduction modes present fore-arc shortening and intra-arc extension. Our experiments indicate that the overall OPD except in the fore-arc region is mainly driven by the horizontal mantle flow at the base of the OP inducing a viscous drag force (FD), and is determined by the gradient of the horizontal mantle flow velocity (dvx/dx). Furthermore, a large-scale trenchward overriding plate tilting and an overall subsidence of the overriding plate were observed in the experiments showing continuous trench retreat, while a landward tilting and an overall uplift of the overriding plate were observed during long-term trench advance. The two types of topography during the two different subduction modes can be ascribed to the large-scale trenchward and landward mantle flow, respectively, and thus represent forms of dynamic topography. Our models showing trench advance provide a possible mechanism for OPD in the Makran subduction zone, which has experienced overall trench-normal tectonic shortening in the overriding plate, but shows extension in a local region of the coastal Makran that is spatially comparable to that in our experiments.  In addition, these models might also provide an explanation for the regional topography at the Makran subduction zone, which shows a long-wavelength topographic high in the overriding plate near the trench that decreases northward.

How to cite: Xue, K., Schellart, W. P., and Strak, V.: Overriding plate deformation and topography during slab rollback and slab rollover: insights from subduction experiments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2922, https://doi.org/10.5194/egusphere-egu21-2922, 2021.

13:42–13:44
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EGU21-1420
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ECS
Zhibin Lei and Huw Davies

Trench retreat, or slab roll-back, has been proposed to account for various degrees of extensional deformation within the overriding plate in subduction zones, eg. Izu-Bonin-Mariana, Tonga etc. However, the relationship between trench retreat rate and the degree of extension has not been rigorously tested. Here we obtain a wide range of trench retreat rate by varying the initial age of subducting plate (SP, Age0SP) and overriding plate (OP, Age0OP) met at trench. Then we investigate how much trench retreat rate is needed to initiate rifting in the OP.

The results show that models would evolve from a non-steady state towards a steady state as the SP sinks to the transition zone at 660 km.

Before the SP starts to interact with the transition zone, the trench retreat rate accelerates with time reaching a maximum value (vmax), which can be very high but only lasts a short time (~0.5 Myr). For models with a given OP, vmax is Age0SP-dependent. The trench retreat rate, on the other hand, determines the extensional extent within the OP. With increasing Age0SP, a minimum trench retreat rate (vrift) is needed to initiate rifting within the OP. For models with Age0OP = 20 Myr and Age0OP = 25 Myr, vrift is ~19 cm/yr and ~27 cm/yr separately. This implies that an older OP is more resistant to extensional stress field driven by trench retreat. In all, three types of stretching states are observed within the OP in our models: i) minor extension, where vmax<vrift and the OP lithosphere has little extension; ii) rift, where vmax≈vrift and the OP would rift but not be torn apart; iii) break-up, where vmax>vrift and the OP would rift when the trench retreat rate reaches vrift, then breaks up into two parts after it exceeds vrift. We note all three states involve different extents of mantle wedge erosion at ~100 km away from the trench underneath the OP, while rifting and break-up occur >700 km away from the trench. In the break-up cases, the two parts of the OP can be ~250 km apart.

After the SP reaches the transition zone, the trench retreat rate would drop to a constant magnitude around 2 cm/yr and lose the Age0SP-dependency. This is because the viscosity jump at the transition zone prevents the SP from accelerating into the lower mantle. Meanwhile, the Age0SP-dependent negative buoyancy loses its dominant role in driving the trench retreat.

We discuss two driving mechanisms to relate the initiation of extension with rapid trench retreat (trench suction): 1) focused upwelling from the transition zone; 2) horizontal basal drag. We conclude that the transient rapid trench retreat can lead to an extensional stress field through basal drag which is strong enough to initiate rifting or even break-up within a mobile overriding plate. A high negative SP buoyancy could play the driving force to generate this transient rapid trench retreat.

How to cite: Lei, Z. and Davies, H.: Investigating the role of transient rapid trench retreat in initiating rifting of a mobile overriding plate during subduction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1420, https://doi.org/10.5194/egusphere-egu21-1420, 2021.

13:44–13:46
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EGU21-13972
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ECS
Yaguang Chen, Hanlin Chen, Taras Gerya, and Mingqi Liu

Vertical tearing of subducting oceanic slabs plays an important role in the subduction dynamic worldwide, accommodating slabs motion and segmentation in subduction zones. In previous studies, several models have been proposed for the origin of vertical slab tearing – they were related to variations in the slab age, rollback rate, buoyancy, moving direction, etc. However, the physical mechanism of vertical slab tearing remains elusive. Here, we propose a new model that stable vertical tearing of subducting oceanic slabs can be generated by inversion of transform margins and controlled by the strain-weakening rheology of subducting oceanic plates that facilitate out of plane (mode-III) shear deformation inside subducting slabs. Through 3D thermo-mechanical numerical modeling, we systematically investigate the effects of transform margins length and the rheology of subducting oceanic plates on the vertical slab tearing. Numerical results show that (1) interaction between two neighboring subducting slabs decreases as the transform margins length and the resulting trench offset increase. Once the offset reaches the critical offset, sustained vertical slab tearing occurs spontaneously. (2) Strain weakening parameters are crucial in the lithospheric deformation. An intense strain weakening, with a strong and rapid lowering of internal friction coefficient, greatly facilitates the initial slabs tear and makes it sustained. (3) Slab age is also an important factor in vertical slab tearing. A longer critical offset is required for the older oceanic lithosphere. (4) The vertical tear and resulting slab segmentation can operate as a self-sustained dynamical process (i.e., can be defined as dynamical instability of oblique subduction that gives preference to segmented slabs). Once a vertical tear is formed, it can propagate steadily for a long time.

How to cite: Chen, Y., Chen, H., Gerya, T., and Liu, M.: Vertical slab tearing controlled by the rheology of subducting oceanic plates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13972, https://doi.org/10.5194/egusphere-egu21-13972, 2021.

13:46–13:48
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EGU21-13160
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ECS
Abdul Qayyum, Nalan Lom, Eldert L Advokaat, Wim Spakman, and Douwe J.J van Hinsbergen

Much of our understanding of the dynamics of slab break-off and its geological signatures rely on numerical models with a simplified set-up, in which slab break-off follows arrival of a continent in a mantle-stationary trench, the subsequent arrest of plate convergence, and after a delay time of 10 Ma or more, slab break off under the influence of slab pull. However, geological reconstructions show that plate tectonic reality deviates from this setup: post-collisional convergence is common, trenches are generally not stationary relative to mantle, neither before nor after collision, and there are many examples in which the mantle structure below collision zones is characterized by more, or fewer slabs than collisions.

A key example of the former is the India-Asia collision zone, where the mantle below India hosts two major, despite the common view of a single collision. Kinematic reconstructions reveal that post-collisional convergence amounted 1000s of kms, and was associated with ~1000 km of trench/collision zone advance. Collision between India-Asia collision zone may provide a good case study to determine the result of post-collisional convergence and absolute lower and upper plate motion on mantle structure, and to evaluate to what extent commonly assumed diagnostic geological phenomena of slab break-off apply.

In addition to the previously identified major India, Himalaya, and Burma slabs, we here map smaller slabs below Afghanistan and the Himalaya that reveal the latest phases of break-off. We show that west-dipping and east-dipping slabs west and east of India, respectively, are dragged northward parallel to the slab, slabs subducting north of India are overturned, and that the shallowest slab fragments are found in the location where the horizontally underthrust Indian lithosphere below Tibet is narrowest. Our results confirm that northward Indian absolute plate motion continued during two episodes of break-off of large (>1000 km wide) slabs, and decoupling of several smaller fragments. These slabs are currently found south of the present day trench locations. The slabs are located even farther south (>1000 km) of the leading edge of the Indian continental lithosphere, currently underthrust below Tibet, from which the slabs detached, signalling ongoing absolute Indian plate motion. We conclude that the multiple slab break-off events in this setting of ongoing plate convergence and trench advance is better explained by shearing off of slabs from the downgoing plate, possibly at a depth corresponding to the base of the Indian continental lithosphere, are not (necessarily) related to the timing of collision. A recently proposed, detailed diachronous record of deformation, uplift, and oroclinal bending in the Himalaya that was liked to slab break-off fits well with our kinematically reconstructed timing of the last slab shear-off, and may provide an important reference geological record for this process. We find that the commonly applied conceptual geological signatures of slab break-off do not apply to the India-Asia collision zone, or to similar settings and histories such as the Arabia-Eurasia collision zone. Our study provides more realistic boundary conditions for future numerical models that aim to assess the dynamics of subduction termination and its geological signatures.

How to cite: Qayyum, A., Lom, N., Advokaat, E. L., Spakman, W., and van Hinsbergen, D. J. J.: Geological signatures of slab shear-off during ongoing India-Asia convergence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13160, https://doi.org/10.5194/egusphere-egu21-13160, 2021.

13:48–13:50
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EGU21-3615
Santanu Bose, Wouter P Schellart, Vincent Strak, João C. Duarte, and Zhihao Chen

The Himalaya and the Tibetan plateau, the highest mountain range on Earth, have been growing continuously for the last 55 Myrs since India collided with Eurasia. The forces driving this protracted mountain building process are still not fully understood, and continue to puzzle Earth Scientists. Although it is now well accepted that subduction zones are the main driver for plate motion, plate boundary migration, and mantle flow in the asthenosphere, their role in driving Indian indentation into the Asian landmass has never been tested with geodynamic models. This study uses four-dimensional geodynamic physical models to test the role of lateral subduction zones in driving the India-Asia collision. The objective of our study is to investigate if the slab pull force of the Sunda and Makran slabs have any role to play in the dynamics of the ongoing India-Asia convergence, particularly after the complete disappearance of the Tethyan slab, which was primarily steering the northward travel of the Indian plate since late Jurassic. To address this issue, we performed three experiments by varying the size and configuration of the subducting plate in the initial model setup.  Our experimental results show that active subduction of the Indo-Australian plate along the Sunda subduction zone is the main driver of the India-Asia convergence, Indian indentation, the growth of the Himalaya-Tibet mountains, and the eastward extrusion of southeast Asia. Our work further suggests that the protracted growth of collisional mountains on Earth requires nearby active subduction zones and, therefore, Himalayan-type orogens may have been rare in the Earth’s history.

How to cite: Bose, S., Schellart, W. P., Strak, V., Duarte, J. C., and Chen, Z.: What is driving India-Asia convergence?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3615, https://doi.org/10.5194/egusphere-egu21-3615, 2021.

13:50–13:52
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EGU21-10611
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ECS
Nipaporn (Nidnueng) Nakrong, Wim Spakman, Fangqin Chen, and Gordon Lister

Slab tearing in subducting plates is widely implicated in terms of the factors that control the evolution of the structural geology of the over-riding crust, here illustrated by interactions between the subducting Nazca plate and the overlying overthrust western continental margin of South America. We examine the different ways that structures above the bounding megathrusts are linked to the ripping and tearing of the subducting plate beneath, in particular focussed on the Andean orogeny at the Arica bend during the formation of the Bolivian orocline. We can create models for slab tearing by integrating seismotectonic analysis, seismic tomography, and morphotectonics. There are many features in the UU-P07 tomographic model that we cannot yet relate to the evolution of surface structure, for example, the gaps and tears beneath the Bolivian Orocline, or the separation of the detached slab we interpret as a paleo-segment of the Nazca plate, illustrating traces of an ancient subduction system. However, we can link the evolution of some surface structures to the growth of the giant kink of the Nazca slab that connects to the surface near the Arica bend. This may have driven strike-slip faulting with opposing sense-of-shear, northern south of the Bolivian Orocline. Megathrust rupture segments may be related to the polygonal kinked trace of the orogen, which is not at all a continuously curved arc. In this contribution, we relate the growth and accentuation of the Arica Bend to the evolution of the giant kink in the Nazca plate using a 4-D tectonic reconstruction.

How to cite: Nakrong, N. (., Spakman, W., Chen, F., and Lister, G.: Slab tearing of the Nazca plate in the Central Andes and its interaction with the overriding plate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10611, https://doi.org/10.5194/egusphere-egu21-10611, 2021.

13:52–13:54
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EGU21-10959
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ECS
Alexandra Skrubej, Audrey Galve, Mireille Laigle, Andreas Rietbrock, Philippe Charvis, Sandro Vaca, Hans Agurto-Detzel, Laure Schenini, Felix Bogelspacher, Davide Oregioni, Damien Vignon, Andreas Brotzer, Maria Muñoz Muñoz, and Mayra Moreno Piña

The Ecuadorian subduction regularly hosts large earthquakes. Among them, the Mw 8.8 1906 earthquake is the 7th biggest known event. Following the recent 2016 Mw 7.8 Pedernales earthquake, a large deployment of onshore/offshore seismological stations, in addition to the permanent seismological/geodetical network, revealed a complex slip behavior including the presence  of  seismic and aseismic slip.

During the geophysical experiment HIPER, in march 2020, 47 Ocean Bottom Seismometers (OBS), were densely deployed along a 93-km-long trench-perpendicular profile, recording airgun shots (4990 cu.inch.) performed by R/V Atalante to obtain a high-resolution P-wave velocity image. The profile was located north of the 2016 Pedernales rupture zone passing through an area experiencing aseismic slip and a region of contrasted geodetic interseismic coupling.    

We used the traveltime tomography code « tomo2d » (Korenaga et al., 2000) to invert first arrivals and reflected phases recorded by our OBS.  A joint 2D-seismic-reflection profile was acquired (abstract by L. Schenini) and provides details on the oceanic basement topography and on Vp velocities in shallow sedimentary layers.

Regarding the structural complexity in the region, we decided to start the inversion  using an a priori 2D velocity model. Several geophysical experiments have already been conducted offshore-onshore Ecuador (SISTEUR, 2000 ; SALIERI, 2001 and ESMERALDAS, 2005). Compilation of velocity models from tomographic images were used to build two a priori 1D Vp velocity models for both the Nazca oceanic crust and the forearc seismic structure. A 2D a priori Vp velocity model was built by merging the results of the two localized inversions using a selection of OBS on each side of the trench.

We obtain the crustal structure of the upper and subducting plates down to 20 km depth. Beneath the trench, a ~30-km-wide low-Vp anomaly is observed at lithospheric scale. This velocity is 10% lower than the typical Vp values observed for hydrated Pacific-type oceanic crust near the trench (Grevemeyer et al., 2018). Recorded PmP phases will allow us to further constrain the crustal thickness. While we observe PmP phases in areas of low-Vp, the Moho reflectivity weakens and even disappears from the coincident MCS line. This intriguing observation could highlight processes, such as the presence of fluids or serpentinization, that need to be identified and better understood.

How to cite: Skrubej, A., Galve, A., Laigle, M., Rietbrock, A., Charvis, P., Vaca, S., Agurto-Detzel, H., Schenini, L., Bogelspacher, F., Oregioni, D., Vignon, D., Brotzer, A., Muñoz Muñoz, M., and Moreno Piña, M.: Travel-time tomography imaging the Ecuadorian subduction, north of the Mw 7.8 Pedernales earthquake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10959, https://doi.org/10.5194/egusphere-egu21-10959, 2021.

13:54–13:56
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EGU21-8378
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ECS
Cemil Arkula, Nalan Lom, John Wakabayashi, Grant Rea-Downing, Mark Dekkers, and Douwe van Hinsbergen

The western edge of the North America plate contains geological records that formed during the long-lived convergence between plates of the Panthalassa Ocean and North America. The geology of different segments along western North America indicates different polarities (eastward and westward) for subducted slabs and thereby various tectonic histories and settings. The western United States (together with Mexico) plays a key role in this debate, many geologic interpretations assume continuous eastward subduction in contrast to observations within proximal geologic segments and tomographic images of the lower mantle below North America and the eastern Pacific Ocean which suggest a more complex subduction history. In this study, we aim to evaluate the plate tectonic setting in which the Jurassic ophiolites of California formed. Geochemical data from these ophiolites suggest that they formed above a nascent intra-oceanic or continental margin subduction zone. We first developed a kinematic reconstruction of the western US geology back to the Jurassic based on published structural geological data. Importantly, we update the reconstruction of the various branches of the San Andreas fault system to determine the relative position of the ophiolite fragments and adopt a previous restoration of Basin and Range extension which we expand northward towards Washington state. We then reconstruct North American margin deformation associated with Cretaceous to Paleogene shortening and strike-slip faulting. We find no clear candidates in the geological record that may have accommodated major subduction between the Jurassic ophiolite belt and the North American margin and consequently concur with the school of thought that considers that the ophiolite belt, as well as the underlying subduction-accretionary Franciscan Complex, likely formed in the North American fore-arc. We collected paleomagnetic data to reconstruct the spreading direction of the Jurassic Californian ophiolites, by providing new paleomagnetic data from sheeted dykes of the Josephine and Mt. Diablo Ophiolites. These suggest a NE-SW paleo-ridge orientation, oblique to the North American margin which may be explained by partitioning of a dextral component of subduction obliquity relative to North America. We used this spreading direction in combination with published ages of the ophiolites and our restoration of the relative position of these ophiolites prior to post-Jurassic deformation to construct a ridge-transform system at which the Jurassic ophiolites accreted. The results will be used to evaluate which parts of the subduction systems that existed in the eastern Panthalassa Ocean may reside in the western US, and which parts may be better sought in the northern Canadian Segment or/and in the southern Caribbean region.

How to cite: Arkula, C., Lom, N., Wakabayashi, J., Rea-Downing, G., Dekkers, M., and van Hinsbergen, D.: A Kinematic Reconstruction of Jurassic ocean spreading from the ophiolites of California, the western U.S. using structural geology and paleomagnetism., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8378, https://doi.org/10.5194/egusphere-egu21-8378, 2021.

13:56–13:58
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EGU21-8328
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ECS
Leny Montheil, Douwe Van Hinsbergen, Philippe Münch, Pierre Camps, and Mélody Philippon

Since the Eocene, the northeastern corner of the Caribbean plate is shaped by the indentation of the buoyant Bahamas platform with the Greater Caribbean Arc, the suture of a portion of the Antillean subduction zone along Cuba and Hispaniola and the subsequent relocation of the plate boundary along the strike slip Cayman Trough. Puzzlingly enough, these major re-arrangements followed a plate motion reorganization (Boschmann et al., 2014). During this kinematic reorganization, the Lesser Antilles trench initiated (or subduction intensified) along the eastern boundary of the Caribbean plate and progressively bent, resulting in an increase of subduction obliquity from south to north (Philippon et al., 2020a). This curvature has been, and still may be, associated with deformation within the Caribbean plate. Interestingly, in the 10-15 Ma following the plate reorganization, a hypothetical, now submerged “landbridge” allowed the dispersion of terrestrial fauna from South America to the Greater Antilles: the GAARlandia landbridge (land of Greater Antilles and Aves Ridge). Although it has been recently shown that Puerto Rico and the Northern Lesser Antilles where connected once forming a land mass called GrANoLA around 33-35 Ma (Philippon et al., 2020b), these rapids and drastics geodynamical changes may have impacted the regional paleogeography, which remains to be constrained. The intraplate deformation in the north-est Caribbean region associated with the plate reorganization, the Bahamas indentation, and the plate boundary curvature likely hold the key to (part of) the evolution of this landbridge.
At present day, the N-Eastern border of the Caribbean plate shows parallel to the trench faults dissecting the plate in a sliver-like manner. This “sliver” is cross cutted by perpendicular to the trench faults in four crustal blocks: Gonave, Hispaniola, Puerto Rico and the Northern Lesser Antilles. Present-day and past kinematics of these blocks, and even their existence, are still debated.

In this study, in the course of the French GAARAnti project, we focus on paleomagnetically determined vertical axis rotations that affected Puerto Rico and the Northern Lesser Antilles blocks since the Eocene, and use these to inform kinematic reconstructions constrained by regional structural analysis and Ar40-Ar39 geochronology. These reconstructions will be used to refine the paleogeographic evolution of the NEastern edge of the Caribbean plate since the Eocene in order test the GAARlandia hypothesis.

A new set of paleomagnetic data (180 Oligo-Miocene specimens of sediments sampled in 18 sites) indicates that the Puerto Rico block underwent an early to mid-Miocene 10° counterclockwise (CCW) rotation. This result clearly differs from those of Reid et al., 1991 who concluded a Late Miocene 25° CCW rotation and that is currently used by the community to interpret the tectonic history of the northeastern Caribbean plate. The use of a larger dataset, that geographically covers the entire island, and of a more recent reference frame explain the difference observed between the two results. This new result will lead to a re-interpretation of the tectonic evolution of the region that will be integrated in a regional kinematic reconstruction.

How to cite: Montheil, L., Van Hinsbergen, D., Münch, P., Camps, P., and Philippon, M.: Paleomagnetic and structural study of the NEastern Caribbean plate as mean to give paleogeographic constrains for fauna dispersal., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8328, https://doi.org/10.5194/egusphere-egu21-8328, 2021.

13:58–14:03
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EGU21-10993
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ECS
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solicited
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Highlight
Clément Garrocq, Serge Lallemand, Boris Marcaillou, Jean-Frédéric Lebrun, Crelia Padron, Frauke Klingelhoefer, Mireille Laigle, Philippe Münch, Aurélien Gay, Laure Schenini, Marie-Odile Beslier, Jean-Jacques Cornée, Bernard Mercier de Lépinay, Frédéric Quillévéré, and Marcelle BouDagher-Fadel

The Grenada Basin separates the active Lesser Antilles Arc from the Aves Ridge, described as a Cretaceous-Paleocene remnant of the “Great Arc of the Caribbean.” Although various tectonic models have been proposed for the opening of the Grenada Basin, the data on which they rely are insufficient to reach definitive conclusions. We present a large set of deep-penetrating multichannel seismic reflection data and dredge samples acquired during the GARANTI cruise in 2017. By combining them with published data including seismic reflection data, wide-angle seismic data, well data and dredges, we refine the understanding of the basement structure, depositional history, tectonic deformation and vertical motions of the Grenada Basin and its margins as follows: (1) rifting occurred during the late Paleocene- early Eocene in a NW-SE direction and led to seafloor spreading during the middle Eocene; (2) this newly formed oceanic crust now extends across the eastern Grenada Basin between the latitude of Grenada and Martinique; (3) asymmetrical pre-Miocene depocenters support the hypothesis that the southern Grenada Basin originally extended beneath the present-day southern Lesser Antilles Arc and probably partly into the present-day forearc before the late Oligocene-Miocene rise of the Lesser Antilles Arc; and (4) the Aves Ridge has subsided along with the Grenada Basin since at least the middle Eocene, with a general subsidence slowdown or even an uplift during the late Oligocene, and a sharp acceleration on its southeastern flank during the late Miocene. Until this acceleration of subsidence, several bathymetric highs remained shallow enough to develop carbonate platforms.

How to cite: Garrocq, C., Lallemand, S., Marcaillou, B., Lebrun, J.-F., Padron, C., Klingelhoefer, F., Laigle, M., Münch, P., Gay, A., Schenini, L., Beslier, M.-O., Cornée, J.-J., Mercier de Lépinay, B., Quillévéré, F., and BouDagher-Fadel, M.: Genetic Relations Between the Aves Ridge and the Grenada Back-Arc Basin, East Caribbean Sea , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10993, https://doi.org/10.5194/egusphere-egu21-10993, 2021.

14:03–14:05
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EGU21-11712
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Highlight
Crelia Padron, Frauke Klingelhoefer, Boris Marcaillou, Jean-Frédéric Lebrun, Serge Lallemand, Clément Garrocq, Mireille Laigle, Walter Roest, Marie-Odile Beslier, Laure Schenini, David Graindorge, Aurelien Gay, Franck Audemard, and Philippe Münch

Studying back-arc basins, where sedimentation is less deformed than in the forearc, provides complementary information about formation and tectonic evolution of subduction zones. At the Lesser Antilles subduction zone, the North and South American plates are subducting underneath the Caribbean plate at a velocity of 2 cm per year. The crescent-shaped Grenada back-arc basin is located between the Aves Ridge, which hosted the remnant Early Paleogene “Great Caribbean Arc”, and the Eocene to present Lesser Antilles Arc. In this study, based on wide-angle data, we provide constraints about lateral variations in basement thickness and velocity structure in the Lesser Antilles back-arc, and to a lesser extend in the arc and forearc domain, constraining for the first time the extent of oceanic crust in the Grenada Basin and shed light on the structure and compositions of the basin’s margins.

Three combined wide-angle and reflection seismic profiles, together with gravity and bathymetric data, were acquired in the Lesser Antilles back-arc basin. Direct modeling techniques were applied to the wide-angle seismic data in order to include shallow structures imaged by the coincident reflection seismic data. The resulting velocity models were additionally constrained by gravity modeling and synthetic seismogram calculation. The final models from direct modeling image variations in thickness and velocity structure of the sedimentary and crustal layers to a depth of up to 35 km. The sedimentary cover has a variable thickness from less than a kilometer on top of the ridges to nearly 10 km in the basin. North of Guadeloupe Island, the crust is ~20 km thick from back-arc to forearc, without significant change between the Aves Ridge, the Eocene and present Lesser Antilles volcanic arc. While based on the seismic velocities, the southern part of the basin is underlain by a 6.5-7 km thick crust of of mainly magmatic origin over a width of ~80 km, the northern part is underlain by thinned continental crust. At the western flank of the Lesser Antilles Arc, the crust is 17.5-km thick, about 5 km thinner than north of Martinique island. The velocity structure is typical of volcanic arcs or oceanic plateaus. Between Aves Ridge and the Grenada basin the crust thins in a 80-100 km wide transition zone. No anomalous high velocities indicating the presence of exhumed upper mantle material were detected at the transition zone. This narrow E-W arc-ocean transition zone suggests that opening might have proceeded in a direction highly oblique to the main convergence.

How to cite: Padron, C., Klingelhoefer, F., Marcaillou, B., Lebrun, J.-F., Lallemand, S., Garrocq, C., Laigle, M., Roest, W., Beslier, M.-O., Schenini, L., Graindorge, D., Gay, A., Audemard, F., and Münch, P.: Deep structure of the Grenada Basin from wide-angle seismic, bathymetric and gravity data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11712, https://doi.org/10.5194/egusphere-egu21-11712, 2021.

14:05–14:07
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EGU21-6452
Mihai Tatu and Elena Luisa Iatan

The first magmatic event that post-dates the Meso-Cretaceous orogeny in the Carpatho-Balkan area took place in the Upper Cretaceous at the same time and after the formation of Gosau-type molasses basins, the whole being controlled by an extensional tectonic transpressive-transtensive type (Schuller, 2004; Schuller et al., 2009; Drew, 2006; Georgiev et al., 2009). This tectonic regime controlled the spatial and temporal distribution of both magmatites and metallogenesis associated with the main feature discontinuity.

This aspect is suggested by gravimetry and magnetism studies (Andrei et al., 1989), and also structural studies (Schuller et al., 2009; Drew, 2006; Georgiev et al., 2009).

The age data attest to the temporal sequentially of Upper Cretaceous magmatism's evolution in the Carpathians and the Balkans. The most accurate age data (using geochronometers of zircon U-Pb and molybdenite Re-Os) suggest a very narrow evolutionary range (70.2-83.98 Ma, after Nicolescu et al., 1999; Galhofer, 2015 and 72.36-80.63 Ma, after Ciobanu et al., 2002; Zimmerman et al., 2008), which is characteristic to short-lived magmatism. In contrast, the same magmatism exists between 84-86 Ma in Serbia (Bor-Madjanpek district) and between 86-92 Ma and 67-70 Ma in Bulgaria (Srednogorie massif) in the Rhodope massif (von Quadt et al., 2007).

The magma volumes have been significant several times, so much so that we have circumstances such as that in Vlǎdeasa (Apuseni Mts), and not only, in which sedimentary deposits of the Gosau type are "suspended" at high altitude, "behind" the granodiorite intrusions. According to Lin & Wang (2006), there are two approaches to explain this situation in the Carpathians during Upper Cretaceous: (1) mechanical convective ablation of the lithosphere, as suggested by Bird (1979) for North American mountain ranges, or (2) detachment of a large piece of the lithospheric mantle, as suggested by Houseman et al. (1981). The thin crust can be explained in an extensional context, regardless of the adopted model, which facilitates rapid ascents of magmas induced by adiabatic detente at the base of the lithosphere and/or in the asthenosphere.

Irregular variations in LaN/YbN, Eu/Eu*, Ce/Ce*, and initial 87Sr/86Sr, and 143Nd/144Nd ratios that are in the range between 0.704957-0.706774 and 0.512456-0.512538 respectively, suggest that the banatites were generated by partial melting of the LCC, with the involvement of mantle-derived magmas.

The metallogenesis associated with banatitic magmatism is characterized by a great typological variety of metalliferous accumulations forming mineral deposits with main commodities of Fe, Cu, Pb, Zn, ± Au, Ag, W, Mo, B, Mg, Te, Bi, Sb, spatially dominated by transpressive-transtensive tectonics. The most common forms of mineralization is skarn, porphyry copper, massive sulfide, and veins. These mineral deposits exibit complex paragenesis of more than 200 minerals, some of which were first described: ludwigite, szaibelyite, dognacskaite, rezbanyite, veszelyite and csiklovaite. The main mineral deposits associated with the Romanian banatites are Baita Bihor (Mo-Bi-W-Cu-U-Pb-Zn-B), Baisoara (Fe-Zn-Pb), Ocna de Fier-Dognecea (Fe-Cu-Pb-Zn-Bi), Moldova Noua (porphyry Cu±Au-Ag-Mo), Oravita-Ciclova (Cu-Mo-W-Bi) and Sasca (Cu-Mo).

 

 

Acknowledgments
This work was supported by two PNCDI III grants of the Romanian Ministry of Research and Innovation, PN-III-P1-1.2-PCCDI-2017-0346/29 and PN-III-P4-ID-PCCF-2016-4-0014.

 

How to cite: Tatu, M. and Iatan, E. L.: Late Cretaceous short-lived magmatism and related metallogenesis in the Carpathian area (Romania): connections with Balkans  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6452, https://doi.org/10.5194/egusphere-egu21-6452, 2021.

14:07–14:09
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EGU21-11195
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ECS
Aleksandr D. Savelev, Andrei K. Khudoley, and Sergey V. Malyshev

Sette-Daban LIP-related event [1] was dated by U-Pb baddeleyite and Sm-Nd isochron methods, but very limited information has been published on the geochemical and isotopic compositions of the associated igneous rocks. This work presents a new dating and the largest geochemical base of samples from the Sette-Daban event.

Mafic sills of the Sette-Daban event are most widespread in the upper part of the Lakhanda Group and lower part of the Uy Group (Maya-Kyllakh zone). Two intrusions were dated by the U-Pb baddeleyite method, yielding ages of 1005 ± 4 Ma - Sakhara river and 974 ± 7 Ma - Allakh-Yun river [2]. Isotope dating of a sublatitudinal dike in the Belaya River area gave an age which overlaps the already known dating along the Sakhara river.

Studied samples from the rivers Yudoma and Allah-Yun confirmed the already obtained result from the previous work [3]. The Sette-Daban dolerite sills resemble low-Ti lavas of intraplate flood basalt provinces (e.g., Karoo, Siberian Traps) and possess IAB-like trace element patterns.

In turn, samples from the Belaya River are enriched more strongly and closer to the OIB distribution. The rare earth elements contents (e.g., La, Ce, Pr, Nd, Sm) in Belaya samples is 2-5 times higher than in Yudoma. However, εNd(T) values vary from 4.3 to 6.3 which corresponds to the already known range of values for the Sette-Daban complex.

Thus, detailed geochemical studies made it possible to identify a new zone (Belaya) in the Sette-Daban complex, which has significant differences from the previously obtained values.

The studies were supported by the Russian Science Foundation grant No. 19-77-10048.

 

References:

[1] Ernst, R.E. Large Igneous Provinces. In Large Igneous Provinces; Ernst, R.E., Ed.; Cambridge University Press: Cambridge, UK, 2014; p. 653. ISBN 9780521871778.

[2] Rainbird, R.H.; Stern, R.A.; Khudoley, A.K.; Kropachev, A.P.; Heaman, L.M.; Sukhorukov, V.I. U-Pb geochronology of Riphean sandstone and gabbro from southeast Siberia and its bearing on the Laurentia-Siberia connection. Earth Planet. Sci. Lett. 1998, 164, 409–420.

[3] Savelev, A.D.; Malyshev, S.V.; Savatenkov, V.M.; Ignatov, D.D.; Kuzkina, A.D. Meso-Neoproterozoic Mafic Sills along the South-Eastern margin of the Siberian Craton, SE Yakutia: Petrogenesis, Tectonic and Geochemical features. Minerals 2020, 10, 805.

How to cite: Savelev, A. D., Khudoley, A. K., and Malyshev, S. V.: Variations in the geochemical composition of dolerites of the Sette-Daban event, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11195, https://doi.org/10.5194/egusphere-egu21-11195, 2021.

14:09–15:00