TS5.1 | Continental rift evolution: from inception to break-up
EDI
Continental rift evolution: from inception to break-up
Co-organized by GD5/GM9
Convener: Frank Zwaan | Co-conveners: Giacomo Corti, Sylvie Leroy, Ameha Muluneh, Carolina Pagli
Orals
| Wed, 26 Apr, 14:00–18:00 (CEST)
 
Room K1
Posters on site
| Attendance Wed, 26 Apr, 10:45–12:30 (CEST)
 
Hall X2
Posters virtual
| Attendance Wed, 26 Apr, 10:45–12:30 (CEST)
 
vHall TS/EMRP
Orals |
Wed, 14:00
Wed, 10:45
Wed, 10:45
Continental rifting is a complex process spanning from the inception of extension to continental rupture or the formation of a failed rift. This session aims at combining new data, concepts and techniques elucidating the structure and dynamics of rifts and rifted margins. We invite submissions highlighting the time-dependent evolution of processes such as: initiation and growth of faults and ductile shear zones, tectonic and sedimentary history, magma migration, storage and volcanism, lithospheric necking and rift strength loss, influence of the pre-rift lithospheric structure, rift kinematics and plate motion, mantle flow and dynamic topography, as well as break-up and the transition to sea-floor spreading. We encourage contributions using multi-disciplinary and innovative methods from field geology, geochronology, geochemistry, petrology, seismology, geodesy, marine geophysics, plate reconstruction, or numerical or analogue modelling. Special emphasis will be given to presentations that provide an integrated picture by combining results from active rifts, passive margins, failed rift arms or by bridging the temporal and spatial scales associated with rifting.

Orals: Wed, 26 Apr | Room K1

Chairpersons: Frank Zwaan, Ameha Muluneh, Giacomo Corti
14:00–14:05
Keynote
14:05–14:25
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EGU23-10023
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solicited
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On-site presentation
Julie Tugend, Nick Kusznir, Geoffroy Mohn, Mark Deptuck, Kristopher Kendell, Fraser D. Keppie, and Natasha Morrison

The isostatic evolution and bathymetry of rifted margins depends on thinning of continental crust, the volume of magmatic additions, lithosphere thermal perturbation during rifting and its post-rift re-equilibration, and sediment loading. Additionally, at some margins, bathymetric evolution may also be affected by basin isolation, where eustatic variations are not controlled by global sea-level changes, and mantle plume dynamic uplift and its collapse. The relative influence of these contributors to rifted margin bathymetric evolution varies from example to example.

Here we investigate the parameters controlling the palaeobathymetric evolution of the Nova Scotian rifted margin during the early stages of the opening of the Central Atlantic Ocean, following Triassic rifting, salt deposition and early Jurassic continental breakup. We use a 3D flexural backstripping technique which incorporates decompaction and post-breakup reverse thermal subsidence modelling to provide palaeobathymetric predictions through the Cretaceous down to the Late Triassic base salt.

Quantitative analysis of seismic reflection and gravity anomaly data together with residual depth anomaly analyses have also been used to determine variations of crustal thickness and crustal type as well as volumes of magmatic addition emplaced during rifting and continental breakup. We show the magma-rich to magma-poor transition of the Nova Scotian margin, characterized by seaward dipping reflectors (SDRs) in the SW, while in the NE mantle is possibly exhumed.

Comparison of our palaeobathymetric predictions with seismic observations and palaeoenvironments deduced from biostratigraphy of drill samples are in good agreement over the continental shelf. As expected, discrepancies exist more distally related to salt withdrawal and sediment gravity-driven sliding. Palaeobathymetries predicted seaward, on the first oceanic crust, range from 2 to 2.5 km; values in the range of those observed at young oceanic ridges.

The oceanic crust of the SW Nova Scotian margin shows well developed sequences of SDRs. Their morphology resembles that of inner SDRs of volcanic margins like the Norwegian and Greenland margins (North Atlantic), where drilling results indicate that they correspond to lava-flows emplaced near or above sea-level. Our predicted palaeobathymetry of top SDRs at breakup is nearly ~2km deeper than the expected near sea-level. This discrepancy suggests that the subsidence of this thick oceanic crust with SDRs requires an additional mechanism in addition to post-rift thermal subsidence.

Mantle plume uplift and collapse likely occurs at volcanic margins and has a long wavelength of the order of 500 km or more. However, the subsidence discrepancy we observe has a shorter wavelength and seems focused along the nascent spreading axis. Thinning of the thick oceanic crust after SDR emplacement by oceanward lateral flow of molten and ductile lower crust is an alternative possibility and may be a common occurrence at volcanic rifted margins after continental breakup.

How to cite: Tugend, J., Kusznir, N., Mohn, G., Deptuck, M., Kendell, K., Keppie, F. D., and Morrison, N.: Palaeobathymetry and anomalous subsidence at rifted margins: Observations from the magma-rich and magma-poor Nova Scotian margin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10023, https://doi.org/10.5194/egusphere-egu23-10023, 2023.

Regular talks - part 1
14:25–14:35
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EGU23-4140
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On-site presentation
Gianreto Manatschal, Simon Tomasi, Pauline Chenin, and Nick Kusznir

The binary magma-rich vs. magma-poor classification of rifted margins was introduced to distinguish between margins showing markedly different crustal architectures, in particular related to the occurrence of magmatic products: the “magma-poor” qualifier is attributed to margins that display a domain of exhumed mantle and whose crustal wedge is exclusively made of continental material, while margins whose continental crust is heavily intruded and overlain by extrusive magmatic flows (e.g., seaward dipping reflections (SDRs) in seismic sections) are regarded as “magma-rich”. Yet, distinguishing between inherited continental crust, newly created magmatic crust and serpentinized mantle in seismic data is challenging due to the comparable geophysical properties (density and seismic velocity). The only interfaces that can usually be identified with some confidence on seismic images are the top of the pre-rift basement and seismic Moho, which allow the determination of the first-order crustal shape of rifted margins. We investigate what the shape of rifted margins can tell us about the timing and volume of magma emplacement during rifting. We use a simple geometric/kinematic model to explore how the volume of magma and the timing of emplacement relative to crustal thinning impact the crustal shape and discuss how this approach may help us to better interpret and understand the tectono-magmatic processes at play during rifting.

We show that crustal shape and inflection points at distal margins can be used to identify magma-poor rifted margins and the occurrence of exhumed mantle. Moreover, the crustal shape and inflection points of magma-poor rifted margins provide direct insights into the dominant processes controlling crustal thinning (e.g., pure-shear stretching, viscoplastic necking, and Coulomb controlled hyperextension) and also the delay of magma emplacement with respect to crustal thinning (e.g., inherited depleted subcontinental mantle, extension rate).

In contrast, shapes of magma-rich margins are more challenging to interpret due to the difficulty to distinguish between continental and magmatic material. We show that different factors may impact the budget and/or timing of magma emplacement and control their distinctive shape, including: (1) the initial conditions from inheritance (e.g., mantle temperature, fertility, and water content); (2) the mode of lithosphere extension (e.g., pure shear vs. depth-dependent lithosphere thinning); and (3) external rift-independent factors (e.g., elevated temperature from mantle plumes).

Crustal shapes allow us to define modes and conditions of crustal thinning at so-called magma-poor rifted margins. In contrast, to interpret crustal shapes of so-called magma-rich rifted margins and understand their tectono-magmatic evolution requires additional information such as timing and budget of magma-emplacement in the crustal wedge, paleo-bathymetry and subsidence history.

How to cite: Manatschal, G., Tomasi, S., Chenin, P., and Kusznir, N.: Linking rifted margin crustal shapes with the timing and volume of magma emplacement, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4140, https://doi.org/10.5194/egusphere-egu23-4140, 2023.

14:35–14:45
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EGU23-3123
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ECS
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On-site presentation
Leonardo Pichel, Ritske Huismans, Rob Gawthorpe, Jan Inge Faleide, and Thomas Theunissen

Rifted margins are often associated with widespread and thick evaporite (salt) deposits, typically formed during the latest stages of rifting, immediately prior to continental breakup. These margins are also characterized by pronounced salt tectonics, which is commonly attributed to gravity-driven salt flow and characterized by kinematically-linked domains of updip extension, translation and downdip shortening. The precise spatial and temporal links between these processes, their relative contributions and the role of rifting and rifted margin architecture on salt deposition and tectonics are still a topic of debate on many margins. We apply 2D thermo-mechanically coupled finite-element modelling of lithospheric extension to investigate the evolution of salt basins along wide rifted margins and the interplay between rifting and salt basin geometry with syn- to post-rift salt tectonics. The models use a geodynamically self-consistent approach where the geometries of the lithosphere and salt basins are not prescribed. They show that late syn-rift salt basins form as a single large basin across both conjugate margins that are later separated by continental breakup and oceanic spreading. This produces syn-depositional salt flow and stretching of the distal salt over an outer margin trough with emplacement of a syn-breakup allochthonous salt nappe over newly-formed seafloor (i.e., oceanic crust and/or exhumed mantle). The post-rift evolution is characterized by updip extension that is balanced by downdip diapir shortening, and pressure-driven nappe advance, which is largely independent of the other two processes. The results are comparable to examples from various salt-bearing rifted margins, including the South Atlantic and Gulf of Mexico, and help us understand their genesis and evolution.

How to cite: Pichel, L., Huismans, R., Gawthorpe, R., Faleide, J. I., and Theunissen, T.: The Inception and evolution of wide salt-bearing rifted margins – insights from numerical modelling and natural systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3123, https://doi.org/10.5194/egusphere-egu23-3123, 2023.

14:45–14:55
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EGU23-13192
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On-site presentation
Thomas Theunissen, Ritske S. Huismans, Delphine Rouby, Sebastian Wolf, and Dave May

Continental rifting is often oblique to the rift axis or plate boundary, comprising many active rifts and mature rifted margins on Earth. Previous research has identified the role of vertical strike-slip and transform structures in oblique extension but has also shown that the initiation of long-distance syn-rift vertical strike-slip motion requires preexisting weaknesses. The Southern part of the Equatorial passive rifted conjugate margins is a typical example that exhibits orthogonal rift segments separating with transform faults with different lengths and orientation. We aim in this study to 1) understand the influence of these inherited weaknesses on the pattern of faulting, 2) to evaluate the consequences of oblique margin formation for rift related topography, and 3) to explore the interaction between tectonic and surface processes in the context of oblique rifting. We use most recent advances in 3-D forward geodynamic modeling coupled with surface processes. Preliminary results support the importance of inherited weak zones in shaping segmented oblique continental margins, with highly contrasting tectonic and subsidence histories in the orthogonal and transform segments. These results compare well with observations from the Equatorial passive rifted conjugate margins and provide insight into the factors that may drive the timing and magnitude of vertical motions and associated sediment flux.

How to cite: Theunissen, T., Huismans, R. S., Rouby, D., Wolf, S., and May, D.: Oblique continental rifting. Insights from 3-D forward coupled geodynamic-surface process modelling and application to the Equatorial passive margins formation., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13192, https://doi.org/10.5194/egusphere-egu23-13192, 2023.

14:55–15:05
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EGU23-9514
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ECS
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On-site presentation
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Malte Froemchen, Ken McCaffrey, Jeroen van Hunen, Mark Allen, and Thomas Phillips

Geodynamic models can aid understanding the evolution of rifting in North China and other rift systems. The North China Craton (NCC) formed by the collision of two Archean blocks in the Paleoproterozoic resulting in a broad collision zone known as Trans-North China Orogen. The NCC shows two different modes of extension that are separated by space and time. Wide, distributed rifts formed during the Paleogene above the Eastern NCC, in the Neogene migrated to the Western NCC forming narrow, localised rifts near the Paleoproterozoic orogens. However, the mechanism that led to development of these fundamentally different rifts and the migration of rifting remains debated. Here we use the geodynamical tool ASPECT to perform 2D thermo-mechanical modelling to explain the role of variable lithospheric strength and inherited lithospheric weaknesses in the development of rift systems. We found that a wide, distributed rift develops over non-cratonic lithosphere, while the adjacent cratonic lithosphere will accommodate little strain. To explain rift migration in North China we require 1.) a period of tectonic quiescence that strengthens the lithosphere following distributed initial rifting 2.) a specific range of relative lithospheric thickness variations and 3) presence of a lithosphere scale weak zone, i.e., an inherited feature. Our results show how lithospheric thickness and strength variations as well as discrete zones of lithospheric weaknesses can influence the style of rifting and facilitate the breakup of an ancient craton. These results are applicable to other multiphase rift systems around the world such as the North Atlantic.

How to cite: Froemchen, M., McCaffrey, K., van Hunen, J., Allen, M., and Phillips, T.: How lithospheric thickness and strength variations facilitate the rifting of ancient cratonic lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9514, https://doi.org/10.5194/egusphere-egu23-9514, 2023.

15:05–15:15
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EGU23-8326
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On-site presentation
Antonio Schettino and Giorgio Ranalli

Continental rifting is one of the four fundamental geological processes of the Wilson cycle. Rifting results from the continuous stretching of a continental mass and involves mechanical, thermodynamic, and rheological processes. It may last several tens Myrs and be followed by a catastrophic breakup stage (drifting), which determines cessation of continuous deformation and the final separation of a continent into two distinct tectonic plates that grow by accretion of oceanic lithosphere. To date, the transition to sea-floor spreading and the conditions for the development of a new ocean have not been fully understood. We present numerical experiments showing that a nonlinear viscoelastic model of the cratonic lithosphere, allowing accumulation of elastic strain over several Myrs, may explain the major features of the rift-drift transition. The model incorporates thermodynamic effects associated with viscous shearing, showing how thermal anomalies generated in the lithosphere during rifting play a major role in the break-up style. A fundamental result of the experiments is that extension is always accompanied by transverse material waves in the lithosphere, with wavelengths of the order of thousands km and periods of several tens kyrs. These waves induce an oscillating topography and could be responsible for high−frequency transgressive–regressive cycles in rift lakes. At sufficiently high extension rates, deformation localizes and these ultra-slow waves determine cyclic shear failure, with formation of X-shaped cross structures through the lithosphere that prelude to the final rupture. A comparison with the Red Sea evolution shows that onset of extension could be older than the widely accepted age of 27-30 Ma and that an older phase of uniform stretching without localization could have preceded the formation of a rift valley.

How to cite: Schettino, A. and Ranalli, G.: Ultra-slow transverse waves during continental extension: A numerical model of the rift-drift transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8326, https://doi.org/10.5194/egusphere-egu23-8326, 2023.

15:15–15:25
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EGU23-2548
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ECS
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On-site presentation
Wei Guan, Lei Huang, Chi-yang Liu, Xu-dong Wang, Li-li Zhang, and Zhe Wu

Detachment faults are developed in different tectonic settings and can record several important tectonic events, such as the rifting and breakup of continents and the spreading of mid-ocean ridges. Megacorrugation is a special structural feature of the detachment fault, characterized by gently domed, overall turtleback shape and prominent undulations of the fault surface that parallel the fault slip direction, corresponds to specific formation conditions. However, the formation mechanism of megacorrugation is still controversial.

To date, there are many controversies regarding the formation mechanism of megacorrugations. Most of these existing models come from the analysis of submarine geomorphic data and onshore field outcrops, lacking direct observation of three-dimensional structures. Therefore, the limitation of adequate datasets might be the main reason for the controversial understanding of the genesis of megacorrugations.

In this study, we finely image the detachment fault in the northern continental margin of the South China Sea using 3D seismic data. Typical megacorrugations are identified on the detachment fault surface. We find that megacorrugations are the result of the superposition of extension-parallel and extension-perpendicular uplifts, and these uplifts are successively controlled by two stages of magma during detachment fault activity. Meanwhile, several accommodation faults, as the key factor controlling the formation of megacorrugations, are discovered on the detachment fault surface for the first time. These accommodation faults control the distribution of early magma and determine the style of megacorrugations. Consequently, the megacorrugations have a formation mechanism dominated by both tectonism and multistage magmatism. This formation mechanism is consistent with the characteristics of the intermediate-type margin. The megacorrugations are the structural features of intermediate-type margins, which are different from the type of magma-poor and magma-rich margins, providing a new constraint for the classification of passive continental margins. Furthermore, we infer that accommodation faults may be widespread in the megacorrugations of mid-ocean ridges; thus, the formation mechanism proposed in this paper is likely common in megacorrugations.

 

References

Brun, J. P. et al. Crustal versus mantle core complexes. Tectonophysics 746, 22–45 (2018).

Cannat, M., Sauter, D., Escartín, J., Lavier, L. & Picazo, S. Oceanic corrugated surfaces and the strength of the axial lithosphere at slow spreading ridges. Earth Planet. Sci. Lett. 288, 174–183 (2009).

Gao, J. et al. The continent–ocean transition at the mid-northern margin of the South China Sea. Tectonophysics 654, 1–19 (2015).

Lister, G., Etheridge, M. A. & Symonds, P. A. Detachment faulting and the evolution of passive continental margins. Geology 14, 246–250 (1986).

Smith, D. K., Cann, J. R. & Escartín, J. Widespread active detachment faulting and core complex formation near 13° N on the Mid-Atlantic Ridge. Nature 442, 440–443 (2006).

Tucholke, B. E., Lin, J. & Kleinrock, M. C. Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid-Atlantic Ridge. J. Geophys. Res. 103, 9857–9866 (1998).

Whitney D. L., Teyssier C., Rey P. & Buck W. R. Continental and oceanic core complexes. Geol. Soc. Am. Bull. 125, 273–298 (2013).

Zhang, C. et al. Syn-rift magmatic characteristics and evolution at a sediment-rich margin: Insights from high-resolution seismic data from the South China Sea. Gondwana Res. 91, 81–96 (2021).

How to cite: Guan, W., Huang, L., Liu, C., Wang, X., Zhang, L., and Wu, Z.: New insight for genesis of megacorrugations in detachment fault: combined control of accommodation fault and magmatism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2548, https://doi.org/10.5194/egusphere-egu23-2548, 2023.

15:25–15:35
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EGU23-11694
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ECS
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Virtual presentation
Hongdan Deng

During rifting, continental crust necks, leading to significant thickness reduction in a few tens of kilometres. However, deformations associated with the necking process remain elusive due to few outcrop examples and a lack of seismic data coverage that clearly images crustal architecture at depth. Here we use deep, high-resolution seismic data across a well-developed necking zone in the northeastern South China Sea passive margin to show the structural style associated with the crustal necking. Seismic stratigraphy in the necking domain can be divided into pre-, syn- and post-rift sequences based on the nature of sequence-bounding unconformities and their relation with faults. Seismic expression of continental crust exhibits two types of reflection characteristics – homogeneous upper crust and layered lower crust. The necking domain shows significant thinning that reduced its thickness from ~30 km to less than over 10 km in a distance of about ~50 km and is characterised by seaward removal of layered lower crust, while the homogeneous upper crust thickness remains largely unchanged in thickness. The necking domain is bounded by inner and outer breakaway complexes that define a portion of flexed crust. Crustal flexure is evidenced by progressive tilting of the necking domain that gradually increases the pre-rift sequence dip from 0° to 10°. Within the tilted necking domain, densely-spaced, landward-dipping minor faults and fractures are organised in a domino configuration, implying a top-to-the-continent movement and a simple shear deformation of the whole continental crust. We suggest that the flexed necking domain could be home to fractured reservoir providing that it is effectively sealed by post-rift sequences.

How to cite: Deng, H.: Crust necking of the northeastern South China Sea: Insights from deep seismic data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11694, https://doi.org/10.5194/egusphere-egu23-11694, 2023.

15:35–15:45
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EGU23-17406
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ECS
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On-site presentation
Thamer Aldaajani and Kevin Furlong

The Arabian Margin experienced intense volcanism over the last 10 Ma, including volcanic eruptions as recent as 600 years ago. What is more, two earthquakes with magnitude > 5 have been recently reported with normal faulting along the Arabian Margin, suggesting that the Arabian Margin is undergoing active deformation. Due to the limited number of GPS stations within the Arabian plate, investigating the intraplate deformation was challenging. A new set of GPS data with 87 stations is used in this work to investigate the Arabian margin rigidity and intraplate deformation (Aldaajani et al., 2021). This new GPS velocities show higher residuals along the Arabian margin that produces dilatational strain rate pattern within the Arabian margin, in the vicinity of the Makkah-Madinah Transtensional zone. The causes of these GPS residuals along the Arabian Margin are unknown. In this work, we use the finite element modeling approach to highlight the mechanical deformation processes along the Arabian margin and test their driving forces. These candidate forces are related either to the edge forces as introduced by the Red Sea rift, the Arabian Margin interior forces as introduced by calculating the Gravitational Potential Energy, or the basal tractions as driven by sub-lithospheric topography and mantle flow. Our results indicate that the GPS residuals are not likely linked with the Gravitational Potential Energy forces. Instead, the basal tractions along an asthenospheric channel, which aligns geographically with the Makkah Madinah Volcanic Line, is the potential driving force for the observed deformation along the Arabian margin.

How to cite: Aldaajani, T. and Furlong, K.: On the driving forces of the rifting processes along the Makkah-Madinah Transform Zone, Western Arabia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17406, https://doi.org/10.5194/egusphere-egu23-17406, 2023.

Coffee break
Chairpersons: Giacomo Corti, Ameha Muluneh, Frank Zwaan
16:15–16:20
Regular talks - part 2
16:20–16:30
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EGU23-5462
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On-site presentation
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Hans Thybo, Irina Artemieva, and Haibin Yang

Formation of new oceans by continental break-up is traditionally understood as a continuous evolution from rifting to ocean spreading. Here we show that already the break-up phase may involve a jump of extensional axis, as earlier observed in e.g. the mature North Atlantic Ocean. The Red Sea is one of few locations on Earth where a new plate boundary presently forms. The new plate boundary is already active in the southern Red Sea oceanic spreading centre, but the north-central segment is still in a continental rifting stage, and the associated magmatism is offset by ca 300 km into Arabia.

This situation is similar to the Baikal Rift Zone, where the rift-related magmatism in the north is offset by 200-300 km into the Sayan-Baikal Fold Belt, but not offset in the south. Our earlier numerical modelling has shown that the location of the magmatism may be controlled by thinning of the lithosphere from the Siberian Craton into the fold belt, whereas the rift location is controlled by pre-existing crustal scale weakness zones (Yang et al., 2018).

Here, we propose a new geodynamic model for the evolution of the Red Sea region which is consistent with all geological and geophysical observations. We demonstrate that the north-central rift is a transient feature that will not develop into coincident ocean spreading. Instead, a new plate boundary forms across Arabia. Our numerical experiments predict that in 1–5 Myr the north-central extensional axis will jump ~300 km eastward into Arabia. The existing Ad Damm strike-slip fault, perpendicular to the central Red Sea rift axis, will evolve into a transform fault between the on-going ocean spreading in the southern Red Sea and the future spreading in north-central Arabia.

We demonstrate that crustal-scale weakness zones can control lithosphere extension and lead to long-distance jumps of extensional axes in continental lithosphere not affected by hotspots. Therefore, our model also provides theoretical basis for understanding dynamics and mechanisms of the transition from rifting to continental break-up at passive continental margins not affected by hotspots.

How to cite: Thybo, H., Artemieva, I., and Yang, H.: New ocean spreading beneath the Arabian Shield controlled by LAB-structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5462, https://doi.org/10.5194/egusphere-egu23-5462, 2023.

16:30–16:40
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EGU23-10156
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On-site presentation
Ian Bastow and Tyrone Rooney

A consensus has emerged over the past two decades that significant extension at crustal depths in the northern East African Rift is achieved not by ductile stretching but by magma intrusion. The implications of this for crustal structure and Moho architecture have all been the focus of intense study. East Africa's deep convecting mantle has also been the focus of intense research, with most workers now accepting of the super-plume model over traditional 'Morgan' plumes (albeit with some ongoing discussion concerning the precise internal architecture of the superplume).  In contrast, our understanding of East Africa's lithospheric mantle and, in particular, the depth to the lithosphere-asthenosphere boundary (LAB), remains remarkably poor.  For example, some studies have postulated that no lithospheric mantle exists below large parts of Afar and the Ethiopian rift where magma-assisted rifting is now underway; others have argued to the contrary, asserting that a melt-rich lithospheric mantle is essential to explain first order observations including mantle seismic anisotropy, and the depth at which melts last re-equilibrated with the mantle prior to eruption. Here we will review some of the seismological and petrological evidence that has featured in this debate, including critically assessing the efficacy of different seismological techniques for determining LAB depth in magmatic versus non-magmatic sectors of the EAR.  We show that petrology contributes strongly to the EAR LAB debate, with the added benefit that it allows the assessment of plate thickness through time.  Finally, we look to recent observations from the Turkana Depression, where a lithosphere thinned during multiple, superposed episodes of rifting, offers the chance to assess lithosphere-asthenosphere interactions in more detail than can be achieved elsewhere along the rift.

How to cite: Bastow, I. and Rooney, T.: East Africa's elusive LAB, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10156, https://doi.org/10.5194/egusphere-egu23-10156, 2023.

16:40–16:50
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EGU23-961
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On-site presentation
Laurent Michon, Vincent Famin, and Xavier Quidelleur

Many continental rifts are subjected to volcanism in tandem with rifting, which has raised a long-standing debate about whether magmatism is the cause or the consequence of plate fragmentation. To re-evaluate this chicken-and-egg question, we took advantage of five decades of research on the East African Rift System (EARS), the largest active continental rift on Earth, to explore the spatial and temporal relationship between rifting and magmatism. By comparing the co-occurrence of tectonics and volcanism since the Eocene with the present-day seismicity, we delimit the EARS as a ~ 5000 km-wide zone of volcano-tectonics made of four branches affecting not only East Africa but also the Mozambique channel and Madagascar. We then developed a quality filtering procedure of published radiometric ages in order to build two independent, robust, and comprehensive age compilations for magmatism and rifting over this extended EARS. Our thorough quality-checked selection of ages reveals that the EARS presents two distinct regimes of volcanism. Since the Upper Eocene, the rift system was affected by (1) pulses of volcanism in 500–1000 km-wide areas, and (2) a discontinuous but remarkably simultaneous volcanic activity, scattered along the four branches of the EARS since 25–27 Ma. Combining this spatio-temporal evolution of volcanism with a critical review of the timing of rifting, we show that the tectonics of the EARS evolves through time from trap-scale to plate-scale rifting. Until the Middle Miocene, extension structures first developed following flood basalt events and plateau uplifts. Then, volcanism resumed synchronously all over the EARS at ca. 12–12.5 Ma, followed by a general extensional deformation. This evolution, which cannot be explained by the sole action of a plume or of tectonics, is therefore interpreted in an intermediate way in which the EARS results from (1) extensive stresses acting on the African lithosphere in the long-lived context of the Gondwana breakup and (2) an overall complex mantle upwelling dynamics arising from the African Large Low Shear Velocity Province (LLSVP). We propose that extension stresses affecting the African lithosphere also modulate the melting of mantle anomalies and/or the collection of magma through the Pan-African belts. This influence explains the synchronous occurrence of many magmatic and tectonic events in the EARS and at the boundaries of the Nubia and Somali plates. Finally, our results suggest that the source of extension stresses affecting the African plate probably evolved from a dominant far-field origin to prevailing variations of gravitational potential energy (GPE) and a diverging basal shear of the Nubia and Somali litho- sphere. This change would stem from an increase of the mantle flux in the Middle Miocene, yielding a change in the EARS’ dynamics from trap-scale to plate-scale rifting.

How to cite: Michon, L., Famin, V., and Quidelleur, X.: Evolution of the East African Rift System from trap-scale to plate-scale rifting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-961, https://doi.org/10.5194/egusphere-egu23-961, 2023.

16:50–17:00
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EGU23-12655
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ECS
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On-site presentation
Rita Kounoudis, Ian Bastow, Cynthia Ebinger, Fiona Darbyshire, Martin Musila, Christopher Ogden, Atalay Ayele, Rebecca Bendick, Garrett Sullivan, Freddie Ugo, Nicholas Mariita, and Gladys Kianji

Continental rifting is currently active in East Africa, where breakup of the African continent is generally occurring in relatively focused rift zones within two uplifted plateaus, with magma intrusions the primary mechanism for strain accommodation throughout the crust and mantle lithosphere. Linking the two narrow rift valleys is the low-lying, and as-yet poorly studied Turkana Depression - an unusually broad 300km-wide region of diffuse faulting, seismicity and magmatism. How the East African Rift has developed here remains elusive and is complicated by the fact the Depression was variably stretched by several superposed episodes of failed rifting since the Mesozoic.

 

Utilising data from the NSF-NERC-funded TRAILS seismic network, we produce the first detailed crustal and uppermost-mantle shear-wave velocity model below the Turkana Depression, illuminating Moho and lithosphere-asthenosphere boundary topography that ultimately shed light on rift development in a multiply-rifted region. We find Turkana’s lithosphere is relatively melt-poor, unlike the Ethiopian rift and Plateau further north, which have undergone extensive lithospheric modification by voluminous Cenozoic flood-basalt magmatism and magma-assisted rifting. The lower crust below rift zones in Turkana is not associated with markedly slow (melt) or fast (cooled gabbroic intrusions) wavespeeds suggesting magmatic extension has not dominated rift development in Turkana. Throughout the Depression, the thinnest crust resides within failed Mesozoic rift zones which the present-day East African Rift appears to circumnavigate, not exploit. Fast uppermost mantle wavespeeds below the thinnest crustal regions indicate post-Mesozoic rifting, re-equilibrated and possibly melt-depleted mantle lithosphere, which now renders the plate stronger and more refractory than regions not previously rifted. Refractory Proterozoic lithosphere also present in southern Ethiopia may have influenced strain localisation and the broad, complex rift zone between Ethiopia and Kenya.

How to cite: Kounoudis, R., Bastow, I., Ebinger, C., Darbyshire, F., Musila, M., Ogden, C., Ayele, A., Bendick, R., Sullivan, G., Ugo, F., Mariita, N., and Kianji, G.: Seismic Imaging of Heterogeneous Lithosphere Beneath the Unusually Broad Turkana Depression, East Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12655, https://doi.org/10.5194/egusphere-egu23-12655, 2023.

17:00–17:10
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EGU23-14948
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ECS
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On-site presentation
Gareth Hurman, Derek Keir, Jonathan Bull, Lisa McNeill, Adam Booth, and Ian Bastow

Traditionally interpretations assume that as magma-rich rift settings mature, the magmatism accommodates greater amounts of extension at the expense of mechanical deformation. However, the importance of faulting in the final stages of magma-rich rifting remains poorly constrained, with the data (e.g. structural geological mapping, seismic reflection and borehole data) from rifts near to break-up a rarity. The Danakil Depression (Northern Afar), is undergoing the final stages of continental break-up, thus providing the ideal natural laboratory to conduct high resolution, quantitative analysis on the architecture, extension and subsidence facilitated by faulting in an active rift setting before seafloor spreading initiates. >500 rift axis faults were identified using remote sensing data (satellite imagery, DEMs), with quantitative analysis showing an increase in fault density, length and connectivity away from magmatic segments. Kinematic and earthquake focal mechanism data demonstrate a transition from transtensional opening in the northern and central sub-regions of the rift to oblique opening in the southern Giulietti Plain and Tat-Ali sub-regions of the Danakil Depression. The oblique opening is attributed to the along-axis step between the Erta-Ale and Harak sub-regions. Integration of seismic reflection and borehole data with the mapped faults shows that extension is primarily accommodated by magmatism within the rift center, with faulting more significant towards the ends of the rift. ~30% of crustal extension is accommodated by axial faulting in areas of low magmatism, highlighting the importance of faulting even in the final stages of magma-rich rifting. Comparing our findings with spreading ridge morphology and structure, which is relevant due to the rift maturity and extensive magmatism present, we conclude that the Danakil Depression is in a transitional stage between continental rifting and seafloor spreading. Spatial changes in the importance of faulting and magmatism in accommodating extension, alongside rift morphology, resemble the relationships observed along spreading ridges. From our observations we have shown that axial faulting still plays a vital role in the final stages of break-up despite the increased importance of magmatism.

How to cite: Hurman, G., Keir, D., Bull, J., McNeill, L., Booth, A., and Bastow, I.: The role of rift axis faulting in the final stages of magma-rich rifting: the Danakil Depression, Afar, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14948, https://doi.org/10.5194/egusphere-egu23-14948, 2023.

17:10–17:20
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EGU23-3935
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ECS
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On-site presentation
Yafet Gebrewold Birhane, Raphael Pik, Nicolas Bellahsen, Lydéric France, Jessica Flahaut, Irene Schimmelpfennig, Dereje Ayalew, and Gezahegn Yirgu

The Afar depression at the northern end of the East African Rift system is the only analog on earth where magmatic continental rifting and associated ongoing break-up processes are exposed onshore. This unique active system presents the key advantage to expose extensional structures related to ocean-continent transition, with magmatic rift segments characterized by contrasted morphologies, and magmato-tectonic styles. The main goal of this study is to identify the location and investigate the functioning and persistence of magma reservoirs at the active magmatic segments in the central Afar depression (Manda Hararo, northern Tendaho grabben), in order to (i) highlight their relationships and potential control with the first- and second-order local segmentation, and (ii) understand the interplay between magmatic and tectonic processes during the generation of such magmatic crust. We combine remote sensing, field investigations, precise and comprehensive mapping of volcanic and tectonic structures, cosmogenic (36Cl) exposure dating of lava surfaces, and geochemical analysis to constrain the temporal frame and the dynamics of magmatic and tectonic processes. The first result of remote sensing analysis allows us to identify two active and self-consistent axial rift subsegments within this extensional system, map detailed lava flow fields which form these segment surfaces and investigate their relationships with caldera formation and focussed fissural activity. Geochemical analysis and dating of lava flows from this Manda Hararo rift system will be conducted to test the integrity of this model of contiguous subsegments.

How to cite: Birhane, Y. G., Pik, R., Bellahsen, N., France, L., Flahaut, J., Schimmelpfennig, I., Ayalew, D., and Yirgu, G.: Detailed Architecture of the Manda Hararo Magmatic Segment in Afar, Ethiopia:, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3935, https://doi.org/10.5194/egusphere-egu23-3935, 2023.

17:20–17:30
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EGU23-2867
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ECS
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Highlight
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On-site presentation
Gabriel Pasquet, Mathieu Duttine, and Isabelle Moretti

The East African Rift (EAR) is a large opening system that allows the observation of all stages of rift evolution from continental opening in the south to oceanization in the north (Ethiopia-Djibouti). Also, the Asal–Ghoubbet active rift, in the Republic of Djibouti, is composed of a magmatic crust and tends to evolve into an oceanic crust. It’s a site of interest for geothermal energy and natural hydrogen. Previous studies have indicated that dihydrogen (H2) emanates from this rift. However, the well-known serpentinization reaction is not the mechanism generating H2 at this site. Rather, the H2 is generated as follows: (1) by alteration of basaltic lava at depth via reaction with seawater flowing from Ghoubbet Bay towards Lake Asal; (2) by simple degassing of the volcanic chamber located a few kilometers below the Fiale Caldera in the rift axis; or (3) as a result of pyritization processes via the oxidation of H2S.

Drill cuttings from the Fiale 1 (F1) and Gale le Goma 1 (Glc1) geothermal wells (located on the inner and outer rift margins, respectively) were analyzed to determine where H2 is generated. Total rock analyses indicated distinct zones at depths of 464 m and 280 m for F1 and Glc1, respectively, representing the boundary between the Asal and Stratoïd Basalts. 57Fe Mössbauer analyses show a decrease in the percentage of Fe3+ at depth, indicating that Fe2+-rich material, particularly in the Stratoïd Basalts, may be a source of H2.

Based on well data from the rift center and the outer rift margin, it is evident that H2 is present at the surface in the rift axis and that this area offers good remnant potential because of the presence of Fe-rich chlorite. Conversely, few H2 emissions were measured at the surface on the outer rift margins, although well data showed some H2 (~0.25%) at depth. The presence of a cap rock in the rift axis has not yet been proven; however, the high loss on ignition and the mineralogy in well Glc1 may indicate that the rocks are sufficiently altered to offer potential as a seal. If so, the rift margins would offer greater exploration potential than the rift center.

How to cite: Pasquet, G., Duttine, M., and Moretti, I.: Early onshore basaltic alteration and its natural hydrogen potential in the Asal–Ghoubbet rift, Republic of Djibouti., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2867, https://doi.org/10.5194/egusphere-egu23-2867, 2023.

17:30–17:40
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EGU23-7681
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ECS
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On-site presentation
Luise Dambly, Friedemann Samrock, Alexander Grayver, and Martin Saar

Active continental rifting in Ethiopia has led to formation of numerous volcanoes and geothermal systems with associated socio-economic potential for generating clean energy.

Aluto and Corbetti are two silicic volcanoes in the Central Main Ethiopian Rift (CMER) that have been closely examined. Past studies provided insights into their formation in the extensional magma-tectonic context of the CMER, into causes of volcanic unrest and surface deformation and seismic activity, as well as their geothermal systems. However, many aspects about the structure of the volcanoes’ underlying transcrustal magmatic system remained unanswered.

Here, we present new 3-D electrical conductivity models of these volcanoes, obtained from inversions of magnetotelluric (MT) data, providing the most detailed images of the associated magmatic and geothermal systems across multiple scales so far.

The models from Aluto and Corbetti provide evidence for several hypothesized properties of the associated magmatic systems. The cross-rift model, enclosing Aluto, shows that the volcano’s lower crustal melt source, west of the rift axis, also feeds volcanos in the western part of the rift, which has been debated in the past.  Our Corbetti model confirms the existence of a shallow magmatic intrusion, as it has been modelled from InSAR and gravimetry studies.

We estimate thermodynamically constrained melt fractions and interpret geothermal flow structures. The inferred melt fractions indicate crystalline magmatic mush systems in rheological lock-up, where melt is extracted slowly through buoyancy processes, while mechanical trapping explains the observed compositional gaps.

How to cite: Dambly, L., Samrock, F., Grayver, A., and Saar, M.: Unraveling the Transcrustal Magmatic Mush and Geothermal Systems of Aluto and Corbetti Volcano in the Main Ethiopian Rift using Magnetotellurics , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7681, https://doi.org/10.5194/egusphere-egu23-7681, 2023.

17:40–17:50
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EGU23-291
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ECS
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Highlight
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On-site presentation
Annelotte Weert, Francesco Vinci, Kei Ogata, Jerome Amory, and Stefano Tavani

In rift basins, the spatial arrangement of extensional faults can influence the facies and the thickness distribution of the syn- and post-sedimentary infill, which can harbour good potential for geothermal systems. In this framework, unravelling the tectono-stratigraphic evolution of a rift basin is decisive, as it can influence one of the key parameters for planning geothermal doublets: aquifer thickness.

In our study, the West Netherlands Basin, located in one of the Netherlands most densely populated areas, is used as a case study. Up to 2022, 14 geothermal doublets were realized in the area, with the main target being the syn-rift deposits of the Late Jurassic Nieuwerkerk Formation. As a NW-SE  oriented transtensional basin, the West Netherlands Basin developed as consequence of Mesozoic extensional tectonics, after which it became inverted during the Late Cretaceous and Cenozoic. Using publicly available seismic 3D and well data, our renewed interpretation of the study area shows two important rift events. The first one during the Early-Mid Jurassic and the second one, partly controlled by structures of the former, during the Late Jurassic, coinciding with the deposition of the Nieuwerkerk Formation.

Our study adds to the understanding of a multiple stage rifting history in the West Netherlands Basin. This is important, as the process influences reservoir thicknesses and with that, the amount of MW that can be extracted from geothermal aquifers. Therefore, this study forms a bridge between providing an integrated picture of the West Netherlands Basin and how the basins geological history affects its geothermal resources.

How to cite: Weert, A., Vinci, F., Ogata, K., Amory, J., and Tavani, S.: How multiple stage rifting influences the planning of geothermal systems: a case study from the West Netherlands Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-291, https://doi.org/10.5194/egusphere-egu23-291, 2023.

17:50–18:00
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EGU23-12967
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ECS
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On-site presentation
Craton control on sediment-hosted metal deposits in continental rifts
(withdrawn)
Anne Glerum, Sascha Brune, Joseph Magnall, Philipp Weis, and Sarah Gleeson

Posters on site: Wed, 26 Apr, 10:45–12:30 | Hall X2

Chairpersons: Giacomo Corti, Ameha Muluneh
X2.193
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EGU23-17194
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ECS
sarah gommery, nicolas Bellahsen, Raphael Pik, Alain Rabaute, and Sebastien Nomade

Central Afar (Ethiopia) is an active example of the final stages of continental rifting. The Stratoid magmatic series (ages between 5 and 1 Ma) were emplaced in a large fissural volcanic province, following an episode of thinning by normal faulting and detachment at 5-6 Ma (Stab et al., 2016). The Gulf Basalt series (0.9-0.4 Ma) later emplaced in more restricted areas attesting for the localisation of the deformation. Current active magmatic axes are even more localized and the most recent lava geochemistry attests for very little crustal contamination (Ayalew et al., 2018) along with recent dyking episodes. This suggests that Central Afar is currently in a late syn-rift stage, possibly close to continental break-up with divergence accommodated by magmatic accretion. The detailed study of the tectono-magmatic evolution of the region will allow us to better constrain the break-up processes active during volcanic margin formation.

Our new mapping of Central Afar has consisted in defining Stratoid sub-series to better follow the interplay between magmatism and deformation during continent-ocean transition. This map is supported by field data, new mapping using satellite multispectral images, and new Ar/Ar dating. We defined three new units: the old Stratoid (5-3 Ma), the intermediate (3-2 Ma) and the young Stratoid (2-1 Ma). This mapping shows that the localisation processes started during the old Stratoid emplacement, which we interpret as an equivalent of Seaward Dipping Reflectors described in magma-rich margins. The detailed mapping of the normal faults in Central Afar is used to quantify the amount of deformation through space and time and discuss the mechanism of divergence accommodation (dyke vs normal faults) in order to track the timing and controlling parameters of the eventual switch from rifting to break-up processes. In the next future, we will study the chemical signature of each series to determine the evolution of magma sources and conditions of melting during the Stratoid phases we defined. Moreover, new dates will provide much needed data on this volcanic series's continuous vs discrete (with pulses) nature.

How to cite: gommery, S., Bellahsen, N., Pik, R., Rabaute, A., and Nomade, S.: Tectono-magmatic evolution of Central Afar since 5 Ma: late syn-rift and break-up processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17194, https://doi.org/10.5194/egusphere-egu23-17194, 2023.

X2.194
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EGU23-9826
Eleonora Braschi, Alessandro Bragagni, Andrea Orlando, Luisa Guarnieri, Giacomo Corti, and Simone Tommasini

The East African Rift System (EARS) is the classic example of an active continental rift where extensional tectonics and lithospheric thinning have been closely associated to the generation of large volumes of magmas and represents the environment with the largest range of erupted magma types all over the world. The geochemical signature of erupted magmas testifies the involvement of different mantle domains and depths (i.e., subcontinental lithosphere, asthenosphere and deeper mantle sources). The aim of this contribution is to investigate the variable involvement of different mantle domains in the genesis of the EARS magmas through space and time, considering not only the geochemical signature of erupted magmas but also the geochemical message of mantle xenoliths. The main goal is to provide a large-scale view of the common process driving the origin of magmas in the EARS beyond the local peculiarities linked to specific settings. We screened an exhaustive geochemical database of basalts and mantle xenoliths from the EARS, together with original trace elements and Sr-Nd isotope data of new samples collected from the Main Ethiopian Rift and Turkana depression, subdivided according to spatial and temporal criteria. From a spatial point of view, the samples were ascribed to five groups (Afar, Ethiopia, Turkana, Eastern Branch, and Western Branch) and from a temporal point of view, the magmatic activity of the EARS was subdivided into three main temporal intervals (45-25 Ma, 25-10 Ma and 10-0 Ma). The geochemical and radiogenic isotope (Sr, Nd, Pb) signature of the selected basalts denotes the variable contributions of a mantle plume, a more depleted asthenospheric mantle (DMM), and different SubContinental Lithospheric Mantle (SCLM) domains, depending on their temporal and spatial distribution. The geochemistry of the selected basalts shows a marked correspondence with the compositional heterogeneity of mantle xenoliths, whose isotopic systematics (Sm-Nd, Re-Os) indicates the formation of the local SCLM in the Archean and during the Pan-African orogeny. Both SCLM domains contributed significantly to magma genesis in the Western Branch (whose signature points towards a contribution of the Pan-African lithosphere) and Eastern Branch (which is also affected by Archean SCLM domains) magmas. We outline that the contribution of the SCLM generally increases with time, possibly related to an increase of the geothermal gradient in response to the arrival and flattening of the plume head at the base of the lithosphere and later extension, thinning and shallower melting. Our interpretation supports a pivotal role of the different SCLM domains in magma genesis that is able to fully explain the large compositional heterogeneity of the EARS basalts and represents a reasonable alternative to the putative presence of multiple mantle plumes or a heterogeneous mantle upwelling.

How to cite: Braschi, E., Bragagni, A., Orlando, A., Guarnieri, L., Corti, G., and Tommasini, S.: Time-space variations in the East African Rift magmatism: the role of different mantle domains, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9826, https://doi.org/10.5194/egusphere-egu23-9826, 2023.

X2.195
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EGU23-12595
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ECS
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Pauline Gayrin, Thilo Wrona, and Sascha Brune

Mapping and characterisation of crustal faults represent one of the contemporary challenges for both tectonic understanding and seismic hazard assessment. Given the high resolution of satellite-derived digital elevation models and remote-sensing imagery, the development of an automatic method of fault extraction is a critical turning point. Here we present a Python-based, open-source workflow,  which is able to extract and characterize individual faults as well as entire fault networks from various datasets. 

Our workflow consists of four main steps: (1) The DEM contains different types of noise, which we reduce using Gaussian smoothing. (2) Then we use the Canny edge detection to highlight topographic discontinuities, such as faults. (3) These edges are simplified in single pixel-wide lines through the skeletonization algorithm. (4) Finally, we create a network consisting of nodes and edges from this skeleton. After a few post-processing steps we obtain a fault network of the sample area. 

We use the toolbox to study faulting in the East African Rift system, especially the Magadi Natron basin. The workflow was applied to a TanDEM-X digital elevation model with 12 m horizontal resolution and the Copernicus GLO-30 dataset with 30 m average horizontal resolution. The strike analysis shows four main directions from distinct fault populations. Moreover, we derive the fault displacement distribution throughout the basin, which allows us to calculate the total orthogonal extension of each geological unit and to compute the overall amount of extension of the region during geologically recent times.

Our workflow is designed to evaluate topographic data of target sites in nature, it can, however, also be used to analyze analogue models and numerical simulations. To this aim, specific functions can be added in a modular way to suit the particularity of the area and of available data types. This workflow allows us to imagine a very wide range of applications and subjects of interest.

How to cite: Gayrin, P., Wrona, T., and Brune, S.: Semi-automated fault extraction and quantitative structural analysis from DEM data, a comprehensive tool for fault network analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12595, https://doi.org/10.5194/egusphere-egu23-12595, 2023.

X2.196
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EGU23-6197
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ECS
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Mohammed Jabir and Mohammed Ali

The continental lithosphere stretches and ultimately splits during extension resulting in rifted margins that may transform into passive margins depending on their mechanical and thermal state. The heating and thinning of the continental lithosphere during the rifting process causes contemporaneous subsidence that accumulates syn-rift deposits. The extension of the lithosphere plays a critical role in plate dynamics as it occurs both in oceans and continents. The passive margin of northeast Arabia provides a unique geodynamic system for the full development of a continental rift into a mature passive margin. Here, this margin is buried under 5-7-kilometer-thick foreland basin sequences. The basement beneath the passive margin sequences has not been imaged by seismic nor sampled by deepest exploration wells. Therefore, the evolution remains enigmatic due to the lack of resolving data and the deep burial cover. This signifies the need for a powerful innovative approach to characterize the lithospheric stretching that occurred and its ever-since evolution. Here we integrate seismic reflection profiles and 3D seismic volumes, with compiled biostratigraphic data from 260 exploration wells to remove the sediment and water loads effect to acquire terms due to tectonic mechanisms. Seismic stratigraphy loosely identifies the top of the passive margin sequences based on the seismic reflection configurations, reflector geometry, and reflection termination. The bottom of these rifted sequences however cannot be determined. Additionally, the structural configuration of the rifting that occurred was severely obscured by the Ophiolite emplacement in the Late Cretaceous and the collision along the Zagros suture in the Miocene. As result, the faults were highly inverted negatively due to the emplacement of significant orogenic loads and crustal shortening. On the basis of backstripping, we suggest the occurrence of at least two phases of continental rifting during the Permian-Jurassic time spanning combined age of ~147 Ma. The initial phase commenced in the Early Permian (ca. 272 Ma) and is linked to the initial Tethys opening. The final rifting phase took place in the Late Jurassic (ca. 160 Ma) and is associated with the culmination of the continental break-up of Gondwana. The anomalous tectonic subsidence coupled is related to the heating and thinning that caused the thermal contraction of the crust. A uniform depth extension model implies that the lithosphere was thinned to 88% during the initial rifting and by 1% during the final rifting based on modeled stretching factors of 1.13 to 1.27 and 1.11 to 1.17, respectively. Spatial modeling of the stretching factors yielded critical insight into the lithospheric and crustal necking that occurred in the area. The identified evolution of northeast Arabia’s passive margin and its implications contributes to efforts in determining the hydrocarbon prospectivity of deep plays in the area.

How to cite: Jabir, M. and Ali, M.: Evolution from continental rifting to passive margin in northeast Arabia; evidence from exploration wells in the United Arab Emirates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6197, https://doi.org/10.5194/egusphere-egu23-6197, 2023.

X2.197
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EGU23-15687
Anna Maria Marotta, Riccardo Barzaghi, Arcangela Bollino, Alessandro Regorda, and Roberto Sabadini

We perform a new gravity analysis in the Gulf of Aden with the aim to find new constraints on the geodynamic evolution of the area. Our analysis is developed within the frame of the new GO_CONS_EGM_TIM_RL06 global gravity model solution (Brockmann et al., 2021) that reflects the Earth’s static gravity field as observed by GOCE (Gravity field and steady-state Ocean Circulation Explorer). We analyzed the solution at different harmonic degree, to account for different depths of the sources. Terrain correction has been performed by means of a spherical tesseroidal methodology (Marotta and Barzaghi, 2017) and the obtained residual gravity pattern has been compared to the gravity disturbance predicted by means of a 2D visco-plastic finite element thermo-mechanic model that simulates the evolution of the Gulf of Aden, from rifting to oceanization, for different crust thickness and initial thermal configuration of the lithosphere (Bollino et al., 2022). The formation of oceanic crust and serpentinite due to the hydration of the uprising mantle peridotite has been also accounted. To be compliant with the geodetic residual gravity, we define a model normal Earth in terms of a horizontally uniform density distribution that, vertically, coincides with the density distribution predicted at the sides of the 2D model domain at the same time of the comparison. In order to perform the comparison between observed and predicted gravity features, data have been extracted along six profiles crossing the Gulf of Aden at different sectors, from the south-east to the north west. Our preliminary results indicate that the Gulf of Aden developed as a slow passive rift of a hot lithosphere with a thick crust, fixing the upper bound of crustal thickness in the surrounding of the Gulf of Aden to 40 km.

References

Bollino, A., Regorda, A., Sabadini, R., & Marotta, A. M. (2022). From rifting to oceanization in the Gulf of Aden: Insights from 2D numerical models. Tectonophysics838, 229483.

Brockmann, J. M., Schubert, T., & Schuh, W. D. (2021). An improved model of the Earth’s static gravity field solely derived from reprocessed GOCE data. Surveys in Geophysics42(2), 277-316.

Marotta, A. M., & Barzaghi, R. (2017). A new methodology to compute the gravitational contribution of a spherical tesseroid based on the analytical solution of a sector of a spherical zonal band. Journal of Geodesy91(10), 1207-1224.

How to cite: Marotta, A. M., Barzaghi, R., Bollino, A., Regorda, A., and Sabadini, R.: New constraints on the geodynamics of the Gulf of Aden from gravity field analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15687, https://doi.org/10.5194/egusphere-egu23-15687, 2023.

X2.198
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EGU23-4733
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ECS
Gilbert M George, Munukutla Radhakrishna, and Kanchan Pande

Laccadive Ridge located off the southwest continental margin of India, is identified as part of highly extended continental crust that is heavily intruded by volcanics or as an aseismic ridge formed by the Reunion hotspot trace. Although there is a growing body of evidence suggesting it as a continental fragment, there has not been a clear identification of rift related structures at the margin. In this study, we use multichannel seismic and gravity data to decipher the nature of the Laccadive Ridge. The multichannel seismic reflection data reveal fault structures in the Laccadive Basin which separates the Laccadive Ridge from the western continental margin of India indicating that the basin is underlain by extended continental crust. Two rifting directions are evident from the seismic data that are aligned with the Precambrian NW-SE to NNW-SSE Dharwar trend and the ENE-WSE Satpura trend of the Indian shield. These trends are conformable with the trends in the gravity anomaly map which matches very well with the identified graben structures on the Ridge. We suggest that the magma travelled through the faults in the highly extended crust and gave rise to the numerous intrusions which are present all along the ridge. To restore the pre- India Madagascar geometry of the Laccadive Ridge, the gravity anomalies have been inverted to estimate the depth to Moho beneath the ridge. The volcanic addition to the crust due to magmatism and possible underplating was calculated using the adiabatic decompression melt generation models, and used to estimate the final crustal thickness. Stretching factors were calculated from these crustal thickness values and used to understand the pre-rift extent of the continental fragment. The results altogether give important information about the rift-related structures along the ridge and insights into the importance of this continental fragment in the evolution of India and Madagascar. 

How to cite: George, G. M., Radhakrishna, M., and Pande, K.: Laccadive Ridge as a Continental Fragment: Pre-rift Geometry, Rifting style and Volcanism based on Multi-channel Seismic and Gravity Interpretation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4733, https://doi.org/10.5194/egusphere-egu23-4733, 2023.

X2.199
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EGU23-682
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ECS
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Pattabhiram Kondepudi, Kanchan Pande, and Radhakrishna Munukutla

The breakup of Gondwanaland led to the creation of many rift basins, of which the Kutch basin is one. Previous geochronological studies of the Kutch onshore rocks have established multiple episodes of magmatism ranging from 124-60 Ma. The wells drilled on the Kutch offshore basin also encountered magmatic rocks at various depths, but their temporal relationship is not constrained.

                The present study reports the Ar-Ar ages of 5 igneous rocks from the Kutch offshore wells. As determined by petrographical and geochemical analysis, these samples comprise two basalts(b), two dolerites(d), and a rhyolite(r). The plateau ages of the samples are 80.5 ± 0.5(b), 81.4 ± 0.5(r), 100.3 ± 0.6(b), 72.6 ± 0.4(d), and 67.1 ± 0.6(d) (errors quoted at 2σ level). These ages establish magmatism offshore from 100 to 67 Ma. There are several levels where magmatic rocks occur in these wells. Dolerite stringers in Early Cretaceous to middle Jurassic sedimentary rocks have been reported from a few wells.

                The geochronology data from the Kutch onshore and adjoining areas in Rajasthan show a magmatic record from 190-60 Ma. There is a possibility that some magmatic rocks in the Kutch offshore basin encountered in different wells may also record the older magmatism and events from the break-up of Gondwana to Seychelles, thereby unfolding the tectono-magmatic history of this region.

How to cite: Kondepudi, P., Pande, K., and Munukutla, R.: Does the Kutch offshore basin record India's Continental breakup history from Africa to Seychelles?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-682, https://doi.org/10.5194/egusphere-egu23-682, 2023.

X2.200
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EGU23-7518
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ECS
Kai Li, Sascha Brune, Derek Neuharth, Geoffroy Mohn, Anne Glerum, and Zoltan Erdös

Cenozoic rifting in the South China Sea developed after a Mesozoic Andean-type orogeny (i.e., Yanshanian orogen) which led to structural, compositional, and thermal inheritance.These inherited lithospheric weaknesses can control the inception and evolution of rifting, as well as the final architecture of the rifted continental margin. In order to better understand these processes, recent studies have utilized seismic profiles, drill cores, and geochronological analysis to identify Mesozoic strata, magmatic rocks related to a former arc, and pre-Cenozoic fault systems in the region. These findings reveal that the pre-rift lithosphere was heterogeneous and that inherited structures affected the subsequent Cenozoic rift evolution.

Here we use multi-stage models to investigate the impact of tectonic inheritance on the spatiotemporal evolution and final rift margin architecture in the South China Sea. We employ a numerical forward model that includes a two-way coupling strategy (Neuharth et al., 2022) linking the geodynamic code ASPECT and the landscape evolution model FastScape. We reproduce the first-order kinematic evolution of the South China Sea by imposing accordion type models of continental collision, followed by extension. We present a reference model that incorporates orogenic topography, thrust fault distribution, and the architecture of the rifted margin, while also accounting for realistic crustal thicknesses, heat flow, and lithosphere-asthenosphere boundary (LAB) properties. This model was derived by conducting a systematic evaluation of a suite of models that varied in terms of lithosphere rheology, convergence velocity, heat production, erosion rate, and random initial noise distribution.

Our reference model reproduces a range of observations including continental collision, post-orogenic collapse, continental rifting and lithospheric breakup. During orogeny, the lithosphere undergoes thrust faulting, and crustal thickening, leading to the formation of inherited weakness in the crust. From orogenic collapse to continental rifting, pre-existing thrust faults serve as nucleation sites for normal faults, and their interaction with later rift-related normal faults can locally modify the regional stress field. During rifting, low-angle detachment faults which connect the reactivated thrust faults contribute to the overall deformation of the lithosphere. In this model, crustal thickening led to increasing temperature, which resulted in a more ductile lower crust with a rheological transition from brittle to ductile deformation. This thermal weakening of the lower crust allows for increased deformation and strain accommodation during lithospheric stretching. The presence of pre-existing thrust faults and a more ductile lower crust ultimately led to the formation of wide rifted margin of the South China Sea. We suggest that this finding is applicable to other post-orogenic, wide rifts worldwide, such as the Basin and Range Province, the Aegean Sea and the West Anatolian extensional system.

[1] Neuharth, D., Brune, S., Wrona, T., Glerum, A., Braun, J., & Yuan, X. (2022). Evolution of rift systems and their fault networks in response to surface processes. Tectonics, 41(3), e2021TC007166.

How to cite: Li, K., Brune, S., Neuharth, D., Mohn, G., Glerum, A., and Erdös, Z.: From orogeny to rifting: the role of inherited structures during the formation of the South China Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7518, https://doi.org/10.5194/egusphere-egu23-7518, 2023.

X2.201
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EGU23-15242
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Mateus Rodrigues de Vargas, Julie Tugend, Geoffroy Mohn, and Nick Kusznir

The wide rifting mode that preceded the opening of the South China Sea in the Cenozoic generated a complex network of sedimentary basins, whose structure is currently being investigated. Until now, most studies focused on the Pearl River Mouth segment. Comparatively, towards Taiwan, the crustal structure of the north-easternmost part of the South China Sea margin (Tainan-Taixinan Basin sensu lato) is less explored.

To investigate the crustal structure of this segment, an extensive open access data set was used, including (a) 07 offshore well logs with biostratigraphic information, (b) over 15,000-line km of two-dimensional reflection seismic (c) over 4,100-line km of refraction seismic, (d) satellite free-air gravity anomaly data, and (e) bathymetry (GEBCO 15 seconds grid in meters). We interpreted seismic data together with the results of a gravity inversion scheme that provides three-dimensional variations of Moho depth and crustal thickness. The joint inversion of interpreted seismic and gravity-inverted Moho enabled the determination of crustal basement density variations along a set of 2D profiles.

This integrated approach enables us to distinguish at least five crustal domains from the continental shelf towards the ocean (i.e., north to south) showing contrasted stratigraphic and structural style, crustal thicknesses, and basement densities. (a) The proximal margin is characterized by a continental basement between 19 and 37 km thick, likely including thick Mesozoic to Paleozoic sediments and numerous intrusive rocks. (b) The necking zone is associated with the deepening of the top basement and increasing crustal thinning. This domain widens toward the northeast and is controlled by counter-regional faults that created half grabens filled by polyphasic syn-rift sediments. (c) To the south, the hyper-thinned crust (<~10 km thick) is controlled by regional low-angle normal faulting related to rifting prior to the South China Sea opening in the Oligocene. These rift structures seem to control the formation of NE trending wedge-shaped basins infilled by thin syn-rift deposits, possibly of Eocene and younger age. (d) Seawards, a domain of thicker crust is observed (10 to 16 km thick), characterized by an average high-density crust (>2900 kg/m-3), the scarceness or absence of faulting, and the onlap of Miocene sediments. The transition towards the unambiguous oceanic domain is characterized by an array of outer highs of likely dominantly magmatic origin. (e) Unambiguous oceanic crust is characterized by chaotic high-amplitude crust with an average thickness of ~6 km, passively draped by post-Oligocene sediments.

This segment of the South China Sea margin is characterized by the presence of a failed rift axis, underlain by hyper-thinned crust. The age of rifting is not directly constrained, but this basin likely preserves the oldest rift phase preceding the opening of the South China Sea. Further south, the peculiar high-average density crustal domain appears most likely of magmatic origin, where Mesozoic to Cenozoic basalts have been dredged.

These new results on the crustal structure of the north-easternmost part of the South China Sea margin point toward a polyphase magmatic activity and more complex tectonic history than previously assumed.

How to cite: Rodrigues de Vargas, M., Tugend, J., Mohn, G., and Kusznir, N.: Crustal structure of the NE continental margin of the South China Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15242, https://doi.org/10.5194/egusphere-egu23-15242, 2023.

X2.202
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EGU23-13096
Geoffroy Mohn, Etienne Legeay, Jean-Claude Ringenbach, William Vetel, and François Sapin

This contribution explores the formation and evolution of hyper-extended basins controlled by low-angle normal faults active at <30°. Such extensional structures are documented worldwide in different geodynamic settings (e.g., continental passive margins, collapsing orogens) but contradict classical fault mechanic models questioning how such extensional structures can form. Based on a recent industrial 3D seismic reflection survey along Sabah (southern margin of the SCS, Dangerous Ground), here we investigate the 3D structure of low angle normal faults and the related pre-, syn- and post-tectonic stratigraphic architecture of hyper-extended rift basins. We mapped and analyzed in 3D the surface of several normal fault systems active at low-angle associated with the interpretation of an array of seismic profiles across the basins.

The mapped faults show an average dip angle of 30° and appear planar, characterized by continuous reflections with no clear steepening at depth and sole-out at variable depths. They controlled the formation of two main depocenters (southern and northern basins) filled by up to 6 km of sediments including pre- to post-rift sequences. Intra-basement seismic reflectors dipping towards the north-west are observed, onto which extensional structures often seem to sole out. These reflectors are interpreted as interleaved thrust sheets from a dismantled accretionary wedge of the former Mesozoic active margin (Yanshan Arc).

Results show polyphased syn-rift infill during the development of the low-angle normal faults. The first syn-tectonic sequence appears as chaotic and discontinuous packages that has been dismembered during the activity of extensional structures. The second syn- tectonic sequence represent the main filling succession associated with numerous second order normal faults that become gradually younger towards the central depocenter. Antithetic to the main extensional structure, secondary normal fault soling out at the top of the pre-rift succession is observed. It controls the formation of growth strata showing a thickening opposite to the low-angle normal faults. The overall structure describes the geometry of an extensional fishtail.

Our results provide some key new elements on the 3D mechanisms of low-angle normal faulting and its control on sedimentary evolution as well as coeval crustal deformation.

How to cite: Mohn, G., Legeay, E., Ringenbach, J.-C., Vetel, W., and Sapin, F.: 3D structure of low-angle normal faulting and related tectono-sedimentary processes in the SE South China Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13096, https://doi.org/10.5194/egusphere-egu23-13096, 2023.

X2.203
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EGU23-12341
Nick Kusznir and Júlia Gómez-Romeu

The geometry and evolution of extensional faults with large offsets during rifting leading to continental breakup is hotly debated. We examine, using flexural isostatic modelling, extensional fault geometry evolution within the hyperextended domain and the transition to exhumed mantle during magma-poor rifted margin formation. Flexural response modelling is used to predict the isostatic rotation and bending of the active fault plane and also the geometries of earlier faults within footwall and hanging-wall. Faults are assumed to have an initial steep dip of 60 at the surface. In the case of progressive in-sequence faulting, we show that sub-horizontal reflectors imaged on seismic reflection data, often interpreted as seismically active low angle faults, can be generated by the flexural isostatic rotation of faults with initially high angle geometry; modelling results show that there is no requirement for sub-horizontal active faulting. With increase in fault extension, flexural isostatic rotation results in the decrease in fault dip at the point of footwall emergence (i.e. the rolling hinge effect). The emergence angle  decreases to asymptotic values of ~ 30 , the precise value depending on Te and whether the initial fault geometry is listric or planar. Shallow emergent fault angles result in fault locking and the development of new high-angle short-cut fault segments within the hanging-wall. This results in the transfer and isostatic rotation of triangular pieces of hanging-wall onto exhumed fault footwall, forming extensional allochthons which our modelling predicts are typically limited to a few km in lateral extent and thickness. Our modelling results show that a sequence of extensional listric or planar faults with identical parameters (i.e. location, heave, surface dip, Te) produce very similar sea-bed bathymetric relief. This indicates that sea-bed relief cannot be used to distinguish listric from planar fault geometry. Listric and planar fault geometries do however produce distinct Moho and allochthon shapes. Extensional faulting and thinning of hyper-extended continental crust may eventually lead to mantle exhumation. Where extensional faulting is in-sequence, this results in a smooth bathymetric transition from thinned continental crust to exhumed mantle. In contrast out-of- sequence faulting results in a transition to exhumed mantle with bathymetric relief. We illustrate these model predictions with examples from seismic reflection data.

How to cite: Kusznir, N. and Gómez-Romeu, J.: Fault Geometry Evolution During Hyper-Extension: Formation of Sub-horizontal Reflectors and Allochthons , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12341, https://doi.org/10.5194/egusphere-egu23-12341, 2023.

X2.204
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EGU23-9265
Laurent Beccaletto and Sylvie Bourquin

From the end of the Carboniferous onwards, the over-thickened and hot Variscan crust collapsed (late-orogenic collapse), accompanied by the rise of high-grade metamorphic domes along low-angle detachment faults and the development of mainly half-graben or pull-apart type asymmetric intramountain coal basins.

These Carboniferous-Permian late orogenic basins widely developed around 300 Ma and were filled with siliciclastic continental material, accompanied by a widespread intrusive and extrusive magmatic activity. These basins crop out in the internal parts of the belt south of the Variscan Front in several limited locations in and around the Variscan basement of Western Europe (Massif Central, Vosges-Black Forest, Alps, Harz). They occur as small isolated and disconnected “basins” with incomplete sedimentary series. Their present-day area does not reflect their initial extent and thickness, which can be explored by studying their subsurface prolongation beneath their Meso-Cenozoic sedimentary covers.

We propose a geological overview of the late Variscan Carboniferous-Permian Brécy basin (SW Paris basin, France), based on the reprocessing and interpretation of vintage seismic lines and related deep boreholes. We aim (i) to discuss its sedimentary filling, which is hidden beneath the Meso-Cenozoic cover of the Paris basin, (ii) to present thickness maps of its 3.9 km-thick sedimentary filling, and (iii) to describe its structural extensional features related to a syn- to post-rift tectonic scenario. We finally compared our new results to other Carboniferous-Permian deposits in France (to discuss its lateral correlation with neighboring basins) and northwest Europe, suggesting that the Brécy Basin may represent - due to its thickness and location - a missing link between late Variscan basins in southern and northern Europe.

How to cite: Beccaletto, L. and Bourquin, S.: The 3.9 km-thick Carboniferous-Permian Brécy Basin (SW Paris Basin, France), a missing link between late Variscan basins in southern and northern Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9265, https://doi.org/10.5194/egusphere-egu23-9265, 2023.

X2.205
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EGU23-16077
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ECS
Soukaina Ajrhough, Manuel Garcia-Avila, Houssine Boutarouine, José B. Diez, and El Hassane El Arabi

The Berrechid sub-basin contains records of the opening history of the Central Atlantic Margin (CAM) during the late Triassic-Early Jurassic. This syn-rift sub-basin encompasses (i) a Lower Salt-Mudstone Formation (LSM Fm), (ii) tholeiitic basalt flows related to the Central Atlantic Magmatic Province (CAMP), and (iii) an Upper Salt-Mudstone Formation (USM Fm). Significant tectonic, sedimentary, and climatic episodes have determined the depositional environment of the (USM Fm) which remains a matter of debate. We thoroughly investigate the sedimentological and mineralogical features of core materials, mine, and field outcrops covering the Hettangian evaporites, dated recently using palynological assemblage, and red beds of the Lower and Upper Members that constitute the (USM Fm). The following interpretations were based on the identified lithology, mineralogy, sedimentary structures, and textures. Particular consideration was also given to the lithostratigraphic variation along the sub-basin.

The Lower Member comprises a repetitive sequence of alternating primary bedded halite and syn-depositional displacive halite, whereas the Upper Member consists of bedded anhydrite/gypsum and siliciclastic mudstone. The bedded halite displays chevron and cumulate crystals, implying precipitation in shallow saline brines. The displacive halite encloses cubic crystals, randomly oriented in mudstone, suggesting the deposition in a wet saline mudflat. The siliciclastic mudstone associated with the bedded anhydrite/gypsum has various sedimentary aspects, characteristic of a subaerial dry mudflat environment. The distinct diagenetic features recognizable throughout the (USM Fm) include grey reduction spots and dissolution pipes filled with blocky clear halite cement. All these lithologies have registered periods of flooding, evapoconcentration, and desiccation, suggesting deposition in an arid continental setting. The absence of distinctive marine lithofacies and the lack of carbonates are additional evidence for our inference.

Both Lower and Upper Members are affected by a network of NNE-SSW to NE-SW normal faults. They show a varying thickness along the cores and outcrops, indicating the syn-sedimentary tectonic character of the studied Formation during the Early Jurassic time. The lateral migration of the paleoenvironments mentioned above is hence mainly controlled by the sub-basin’s architecture as half-graben jointly with the ongoing subsidence and sediments supply.

These interpretations of the USM Fm’s paleoenvironment highlight the continental context of the series during the Early Jurassic time. These results provide new insights on the paleogeography of the late syn-rift phase of the Moroccan Central Atlantic Margin.

How to cite: Ajrhough, S., Garcia-Avila, M., Boutarouine, H., B. Diez, J., and El Arabi, E. H.: Moroccan Central Atlantic Margin: Paleoenvironment reconstruction of a late syn-rift series (Berrechid sub-basin), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16077, https://doi.org/10.5194/egusphere-egu23-16077, 2023.

X2.206
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EGU23-5793
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ECS
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Julia C. L. G. Fonseca, César R. Ranero, Paola Vannucchi, Helenice Vital, and David Iacopini

    The formation of the >1000 km long Brazilian Equatorial Margin (BEM) is not yet understood. Limited accessibility of data has caused its classification as a transform margin based on its geodynamic situation during the separation of Africa and South America. However, a newly available grid of seismic reflection lines imaging the entire crust along ~500 km of the BEM provides a comparatively high-resolution map of its structure that questions the classic interpretation of the system, but also does not agree with end-member models of Atlantic Margin rifting. The dataset consists of ~10k  km of 2D seismic reflection lines and several exploration wells provided by the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP). The area covered by the grid extends from the south of the Romanche Fracture Zone to Touros High. The imaged domains extend under the continental shelf, the continental slope, and the deep-water basin. The aim of this work is to discuss the crustal structure, the distribution and age of syn-rift sediment and how syn-rift deformation styles vary along the BEM

     We have interpreted and mapped the Moho reflection along most of the region, as well as the base of the sediment cover, defining the geometry of the possibly crystalline basement. The basement thickness thins from ~7-4 s Two-Way Time (TWT) under the continental shelf to ~4-2 s TWT under the continental slope and from ~2.0-1.5 s TWT to under the deep-water basin where the basement thickness ranges 4.9-2.2 s (TWT). We have mapped and age-calibrated syn-rift sediment deposits from under the continental shelf to the deep-water basin.

   The style of deformation and distribution of syn-rift strata changes from south to north along the study region. At the Touros High Plateau, the southernmost region of the Equatorial Margin, the basement and syn-rift strata across the continental slope and deep-water basin are cut by steep faults with a deformation pattern that may indicate a strike-slip transform-type kinematic opening. On the central to northern sectors of the study area, syn-rift strata fill the space created by normal faults. These faults, that define a complex pattern, can dip landward or seaward and cause blocks to be tilted. Apparently, most faults exhibit small offsets and only a few cut and offset (>0.3 s TWT) the top of the basement by a significant amount.

     The style of crustal thinning and the syn-tectonic strata and fault geometry indicate that only the southernmost sector of Touros High contains structures supporting transform tectonics. The central and north sectors display a gradual seaward crustal thinning and lack evidence of significant syn-rift magmatism. The often-well-imaged Moho suggests a deep-water margin floored by a fairly constant-thickness basement, which indicates the lack of mantle exhumation. The seismic structure supports a transition from faulted and gradually thinned crust overlaid by syn-rift strata to a constant-thickness basement that lacks significant faulting and syn-tectonic deposits, which may be interpreted as the first formed oceanic crust during the Cretaceous Magnetic Quiet Zone.

 

How to cite: Fonseca, J. C. L. G., Ranero, C. R., Vannucchi, P., Vital, H., and Iacopini, D.: Rift and COT structure of the Brazilian Equatorial Margin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5793, https://doi.org/10.5194/egusphere-egu23-5793, 2023.

X2.207
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EGU23-13153
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ECS
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Alberto Pastorutti, Magdala Tesauro, Carla Braitenberg, Florence Colleoni, Laura De Santis, and Martina Busetti

Continental Rift systems often involve narrow regions, which accommodate all the stretching. In some cases, the initial extension occurs with a diffuse style and may successively produce a narrow rift. An example is the West Antarctica Rift System, bearing evidence of the concurrent formation of multiple basins normal to the rift axis. This rift system has undergone extension between the Cretaceous and the middle Neogene age (105 to 11 Ma [1, 2]), due to the sea floor spreading in the northwestern Ross Sea. It is composed of three main basins (Victoria Land Basin, Central Trough, and Eastern Basin), which cover a present-day length of 900-1000 km, encompassing the lateral contact between the cratonic domains of East Antarctica and West Antarctica Phanerozoic lithosphere. The different basins, bounded by structural highs, exhibit significant variations in the thickness and thinning of the underlying crust and lithosphere. This multiple-basin pattern suggests that, at least for some part of the rifting, the deformation occurred in a diffuse way, instead of being localized in a small portion of the rift system [3].

The factors controlling these deformation styles have been identified in the inheritance of structures and thermal/rheological heterogeneities [4], which acted concurrently with the extensional kinematics in shaping the present-day rift architectures. Therefore, an improved knowledge on how different thermo-structural initial conditions (e.g. lateral contacts, thermal transients, accumulated strain softening) influence the outcome of rifting may help identify the most likely state at the onset of rifting. To this purpose, we implement a series of numerical models, testing several starting structural conditions (rheology, temperature, prior damage) and distribution of extensional velocity (a single phase or multiple pulses, for the same total extension) that could trigger this peculiar diffuse deformation pattern.

To build a 2-D simplified geometry of the structures of the rift system, we took as a reference the seismic profiles BGR-02 and ACRUP2, normal to the rift axis, along the 77° S parallel [5].  We assumed an initial crustal thickness of about 50 km and a kinematic pattern consisting of two main distinct extension phases, covering the Cretaceous-Cenozoic interval [1, 6].

Modelling was carried out using the open source Underworld2 code [7], which relies on Lagrangian integration point finite element approach and provides a Python API to construct, run, and visualize the output of geodynamic models. The results show that the models that are more consistent with the observations require the existence of peculiar a-priori inherited features. In addition to the role of inheritance, diffuse patterns are favoured, for the same extension amount, by slow and long-lasting rifting phases, with respect to fast and short time pulses.

This work was carried out in the context of PNRA project "Onset of Antarctic Ice Sheet Vulnerability to Oceanic conditions (ANTIPODE)".

[1] Behrendt et al. (1991) https://doi.org/10.1029/91TC00868

[2] Granot & Dyment (2018) https://doi.org/10.1038/s41467-018-05270-w

[3] Huerta & Harry (2007) https://doi.org/10.1016/j.epsl.2006.12.011

[4] Perron et al. (2021) https://doi.org/10.1051/bsgf/2020038

[5] Trey et al. (1999) https://doi.org/10.1016/S0040-1951(98)00155-3

[6] Davey & De Santis (2006) https://doi.org/10.1007/3-540-32934-X_38

[7] Mansour et al. (2020) https://doi.org/10.21105/joss.01797

How to cite: Pastorutti, A., Tesauro, M., Braitenberg, C., Colleoni, F., De Santis, L., and Busetti, M.: Diffuse Cretaceous-Cenozoic rifting in the Southern Ross Sea: the influence of inheritance and kinematics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13153, https://doi.org/10.5194/egusphere-egu23-13153, 2023.

Posters virtual: Wed, 26 Apr, 10:45–12:30 | vHall TS/EMRP

Chairpersons: Ameha Muluneh, Giacomo Corti
vTE.3
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EGU23-8328
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ECS
Kitti Váradi, László Fodor, Márk Szijártó, and László Bereczki

The Danube Basin is a prominent sub-basin of the Pannonian Basin, forming a transitional zone of the Eastern Alps and the Western Carpathians on the border of Slovakia, Hungary, and Austria. During the Miocene, the lithosphere of the Pannonian Basin underwent extensive rifting, leading to the formation of the Danube Basin (Tari, 1994). During this process, several grabens and half-grabens were opened, the timing of which has been investigated by previous studies (Tari et al., 2020; Šujan et al., 2021; Váradi and Bereczki, 2022) in both the Slovakian, the Austrian and the Hungarian part of the Basin.

The aim of this research was to quantify the extension that took place in the Danube Basin during the Miocene. Using seismic sections crossing the particular grabens which were interpreted in previous research (Váradi and Bereczki, 2022), we carried out 2D balancing of the sections, which is an area-preserving structural modeling method used for the reconstruction of the status of the geological layers before its deformations.

With the outcome of this research, we were able to define the scale of the horizontal lengthening along the sections in meters and percentages, thereby giving an estimation of the scale of the stretching of the upper crust suffered in the study area during the Miocene rifting. Based on the preliminary results, the scale of the extension can be estimated at approximately 20­–40%. This value is in line with the results of Bereczki et al. (2018), and can be compared with the results of Lenkey (1999) and Horváth (2007). In the future, our result can be refined by integrating balanced outcrop sections and by 3D balancing for the entire area.

The research was supported by the National Research, Fund of Hungary (NKFIH) OTKA in framework of projects No. PD 142660 and No. 134873.

 

References:

Bereczki, L., G. Markos, D. Gärtner, Z. Friedl, B. Musitz, B. Székely, and G. Maros, 2018, Structural modelling of some synrift sub-basins in the Pannonian Basin: EGU General Assembly Conference Abstracts, 13144.

Horváth, F., 2007, A Pannon-medence geodinamikája - Eszmetörténeti tanulmány és geofizikai szintézis. Dissertation, Eötvös Loránd University, 240 p.

Lenkey, L., 1999, Geothermics of the Pannonian basin and its bearing on the tectonics of basin evolution. PhD Thesis, Vrije University, Amsterdam, 215 p.

Šujan, M., S. Rybár, M. Kováč, M. Bielik, D. Majcin, J. Minár, D. Plašienka, P. Nováková, and J. Kotulová, 2021, The polyphase rifting and inversion of the Danube Basin revised: Global and Planetary Change, 196, 103375.

Tari, G., 1994, Alpine tectonics of the Pannonian basin. PhD Thesis, Rice University, Houston (Texas), 510 p.

Tari, G. C., I. Gjerazi, and B. Grasemann, 2020, Interpretation of vintage 2D seismic reflection data along the Austrian-Hungarian border: Subsurface expression of the Rechnitz metamorphic core complex: Interpretation, 8, SQ73–SQ91.

Váradi, K., and L. Bereczki, 2022, The polyphase Miocene extensional formation of the Hungarian and Slovakian part of the Danube Basin: Young Researchers in Structural Geology and Tectonics (Yorsget) 2022 Abstract Book, 37.

How to cite: Váradi, K., Fodor, L., Szijártó, M., and Bereczki, L.: Quantification of the scale of Miocene extension in the Danube Basin based on 2D balancing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8328, https://doi.org/10.5194/egusphere-egu23-8328, 2023.

vTE.4
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EGU23-9970
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ECS
Ghizlane Jarif, Khalid Amrouch, Abderrahmane Soulaimani, Mark Bunch, and Hamza Skikra

The Gippsland basin is part of the Australian southern margin rift system. It is a world class oil and gas producing province located about 200 km east of the city of Melbourne, and covers about 46 000 km2 onshore and offshore. The offshore part is a post orogenic continental margin basin formed during Jurassic-cretaceous resulting from the breakup of Gondwana supercontinent in the Mesozoic and the separation of Antarctica and Australia. A second rifting phase occurred with a NE-SW associated with the development of the Tasman Sea. Gippsland basin is filled by three major lithostratigraphic groups, namely: the Strzelecki group, Latrobe and Seaspray groups. The sedimentary fill unconformably overlies a Paleozoic basement made up of igneous and folded sedimentary rocks of the Lachlan orogenic. The objective of this study is to help constraining the tectonostratigraphic evolution and the structural evolution model of the basin based on 2D seismic interpretation as reflection seismic data.  The interpretation of seismic reflection data is a fundamental method for determining the geometry and displacement of faults in the subsurface which is primordial in studying structural events in sedimentary basins.

How to cite: Jarif, G., Amrouch, K., Soulaimani, A., Bunch, M., and Skikra, H.: 2D Seismic Analysis for unraveling the structural and tectonostratigraphic evolution of the Gippsland basin, southern Australia., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9970, https://doi.org/10.5194/egusphere-egu23-9970, 2023.