GD5.1 | Towards new understandings of complex continental margins and oceans

GD5.1

It is becoming increasingly apparent that continental rifting, breakup, and ocean spreading involve complexities not easily explained by standard models, especially in oblique and transform settings. The unexpected discovery of continental material far offshore, e.g. at the Rio Grande Rise, and realisation of the importance of obliquity and time-dependence in rifting, challenge conventional tectonic models. This session aims to bring together new observations, models, and ideas to help us understand the complex factors influencing continental rifting, breakup and ocean spreading, including oblique and transform settings. Works investigating time-dependant controls on rifting mechanisms, plate kinematics, strain localisation, obliquity, plate interior deformation, inherited lithospheric structures, interaction and feedbacks of rift processes, lithospheric and mantle derived driving forces, magmatism, syn-rift sedimentation, and other controls on rifting, are therefore welcomed to this session. Contributions from any geoscience discipline, including marine geophysics, seismology, ocean drilling, geochemistry, petrology, plate kinematics, tectonics, structural geology, numerical and analogue modelling, sedimentology and geochronology etc., are sought. We particularly encourage cross-disciplinarity, the spanning of spatio-temporal scales, and thought-provoking studies that challenge conventions from any and all researchers.

Co-organized by SM4/SSP1/TS5
Convener: Jordan J. J. Phethean | Co-conveners: Patricia Cadenas Martínez, Alexander L. Peace, Christian SchifferECSECS, Frank Zwaan
Orals
| Thu, 27 Apr, 08:30–10:15 (CEST)
 
Room -2.91
Posters on site
| Attendance Thu, 27 Apr, 14:00–15:45 (CEST)
 
Hall X2
Orals |
Thu, 08:30
Thu, 14:00

Orals: Thu, 27 Apr | Room -2.91

The oral presentations are given in a hybrid format supported by a Zoom meeting featuring on-site and virtual presentations. The button to access the Zoom meeting appears just before the time block starts.
Chairpersons: Jordan J. J. Phethean, Patricia Cadenas Martínez
08:30–08:35
08:35–08:45
|
EGU23-15682
|
GD5.1
|
On-site presentation
|
Catherine Hill, Peter Webb, and Sheona Masterton

The Fram Strait (North-eastern Atlantic Ocean) developed along a narrow transform margin that separates the Arctic Basin in the north from the Atlantic Basins in the south. The transform margin developed from the Miocene to Present Day and provided the first oceanic gateway between the Arctic Basin and the Atlantic Basins, allowing the ventilation of a previously closed Arctic Basin and a dramatic shift in global ocean circulation. Existing tectonic models are over-simplified and do not account for new data acquired from 2017 onward. Understanding the tectonic complexity of the Fram Strait and reconciling the fine details in a globally robust plate model is critically important for global ocean circulation models but may also provide an important insight into the development of paleo-transform margins further back in time.  

Potential fields data provide a particularly useful screening tool, especially at high latitudes where sea-ice makes the acquisition of seismic and well data more difficult. Detailed analysis of the structural and crustal architecture of the Fram Strait was conducted using potential fields data for structural mapping, 2D gravity and magnetic models, and 3D inversions for depth-to-basement and depth-to-Moho; these all combine for a new, high-resolution, tectonic model for the region. The results reveal the geometries of ocean basins under transtension, where the ultra-slow and non-volcanic opening have no currently established thermal driver. The crust is low-density and formed by faulting, exhumation and serpentinization of deeper mantle layers.  This mode results from tectonically forced opening where transtension accommodates plate motion at established offset spreading ridges to the north in the Arctic Basin and to the south in the North-eastern Atlantic Ocean.  

Of particular importance is the arrangement of early fracture zones and the location of bathymetric ridges, which illustrate the segmented nature of early transform margins and variability of crustal type and evolution within individual segments. This variability has dramatically affected paleo-bathymetry and, therefore, has exerted significant control on ocean circulation and sediment transport.  

An incomparable advantage of globally available gravity and magnetic data is the ability to draw upon global analogues when investigating new or frontier areas. Analogues can be made between conjugate margins, but also between different systems around the planet. Younger, developing tectonic systems may provide important insights into the early evolution of more complicated areas, where poly-phase tectonic histories may have since matured or been subsequently overprinted. The Fram Strait model shares similarities with other examples of global transform margins, such as the Equatorial Atlantic. This provides an opportunity to re-examine the crustal architecture and structural relationships within other transform margin settings, using the Fram Strait as an analogue for early opening history.  

How to cite: Hill, C., Webb, P., and Masterton, S.: Challenging our understanding of the early evolutionary history of transform margins using a revised, high-resolution model of the Fram Strait, North-eastern Atlantic Ocean. , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15682, https://doi.org/10.5194/egusphere-egu23-15682, 2023.

08:45–08:55
|
EGU23-9465
|
GD5.1
|
ECS
|
On-site presentation
Laura Gómez de la Peña, César R. Ranero, Manel Prada, Valentí Sallares, and Donna Shillington

Models of continental margins evolution are largely based on incomplete information, much of it built on research that is now >20 years old. Recent developments in parallel computing and novel geophysical approaches provide now the means to obtain a new look at the structure with radically superior resolution seismic models and a mathematically-robust analysis of the data uncertainty, that was formerly difficult, if not unfeasible, to achieve.

We focused on the Newfoundland margin and applied bleeding-edge methodologies to a high-quality dataset acquired in 2000. The SCREECH data includes three primary transects with coincident multichannel seismic reflection data acquired on a 6-km streamer and wide-angle data recorded by short-period OBS and OBH spaced at ~10-20 km. This dataset was processed >15 years ago with now outdated methodologies. This re-processing in an HPC environment provided the high-resolution images that are needed to fulfill the characterization of this margin.

In particular, we performed the join inversion of multichannel and wide-angle seismic data, which radically improved the resolution of the velocity model and allow to perform a Pre-Stack Depth Migration of the multichannel data. The higher resolution of these images allows to characterize the different crustal domains of the margin in detail, as well as the tectonic structure.

Our results support a more complex structure than previously suggested, with crustal characteristics that change over short distances. In addition, reprocessing of the MCS data allowed to a better understanding of the crustal structure, as the Moho is imaged for the first time along the necking domain. Altogether, these results provide the high-resolution images needed to understand the formation and evolution of the Newfoundland margin.

Comparison of these results on the Newfoundland margin with the most novelty data on the West Iberian margin, acquired during the cruises FRAME (2018) and ATLANTIS (2022) (PI: C. Ranero, streamer data and coincident closely-spaced OBS data), provides a unique opportunity to further understand the evolution of the North Atlantic opening.

How to cite: Gómez de la Peña, L., R. Ranero, C., Prada, M., Sallares, V., and Shillington, D.: A revision of the Newfoundland Margin: new results from revisited legacy seismic datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9465, https://doi.org/10.5194/egusphere-egu23-9465, 2023.

08:55–09:05
|
EGU23-3394
|
GD5.1
|
On-site presentation
|
Marta Neres and César R. Ranero

The conceptual models of magma-poor rifted margins are greatly influenced by the continent-to-ocean transition structure of the archetypal magma-poor West Iberia Margin. Some previous works with West Iberia magnetic data have been used to constrain the structure and interpret the transition from the exhumed mantle domain to the oceanic crust formed at a spreading center. However, it is found that the resolution uncertainty of the geophysical data was generally overlooked, leading to over-detailed interpretations. In this work we use synthetic magnetic modelling to show that magnetic data acquired at sea-level cannot resolve sub-horizontal lithological layering in deep-water continental margins. Then, we present a new magnetic model guided by a refined velocity model of the wide-angle seismic IAM-9 profile in the Iberia Abyssal Plain. This new model supports that the J-anomaly is caused by a ~6 km thick oceanic crustal structure with locally increased magnetization compared to regular oceanic crust. This J-anomaly crust abuts the exhumed mantle across a nearly vertical boundary, and is the oldest accreted oceanic crust. These results support that mantle exhumation was abruptly terminated by the accretion of oceanic crust. Mantle melting creating oceanic crust was probably not driven by gradual lithospheric thinning and asthenospheric upwelling, but may be the result of seafloor spreading center propagation cutting across the lithosphere and creating the abrupt structure.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL. Support from FCT (PTDC/CTA-GEF/1666/2020), Spanish Ministry of Science and Innovation (CTM2015-71766-R, PID2019-109559RB-I00) and Spanish Research Agency (CEX2019-000928-S) is also acknowledged.

How to cite: Neres, M. and R. Ranero, C.: An appraisal using magnetic data of the Continent to Ocean Transition Structure West of Iberia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3394, https://doi.org/10.5194/egusphere-egu23-3394, 2023.

09:05–09:15
|
EGU23-9908
|
GD5.1
|
Virtual presentation
Mansour M. Abdelmalak, Sébastien Gac, Jan Inge Faleide, Grace E. Shephard, Filippos Tsikalas, Stéphane Polteau, Dmitry Zastrozhnov, and Trond H. Torsvik

The formation of the NE Atlantic conjugate margins is the result of multiple rifting phases spanning from the Late Paleozoic and culminating in the early Eocene when breakup was accompanied with intense magmatic activity. The pre-breakup configuration of the NE Atlantic continental margins is controlled by crustal extension, magmatism, and sub-lithospheric processes, all of which need to be quantified for the pre-breakup architecture to be restored. Key parameters that need to be extracted from the analysis of crustal structures and sediment record include stretching factors, timing of rifting phases, and nature of the deep crustal structures. The aim of this study is to quantify the pre-drift extension of the NE Atlantic conjugate margins using interpreted crustal structure and forward basin modeling. We use a set of eight 2D conjugate crustal transects and corresponding stratigraphic models, constrained from an integrated analysis of 2D and 3D seismic and well data. The geometry and thickness of the present-day crust is compared to a reference thickness which has experienced limited or no crustal extension since Permian time allowing the quantification of crustal stretching. Based on the eight conjugate crustal transects, the total pre-drift extension is estimated to range between 181 and 390 km with an average of 270–295 km. These estimates are supported by the results of forward basin modeling, which predict total extension between 173 and 325 km, averaging 264 km. The cumulative pre-drift extension estimates derived from basin modeling are in turn used to calculate the incremental crustal stretching factors at each of the three main rifting phases between the conjugate Greenland-Norwegian margins. The mid-Permian early Triassic rifting phase represents 32% of the total extension, while the equivalent values are 41% for the mid-Jurassic to mid-Cretaceous and 27% for the Late Cretaceous-Paleocene rifting phases. These values are used to establish and present at first, a full-fit palinspastic plate kinematic model for the NE Atlantic since the mid-Permian and will be the base for future work on more elaborated models in order to build accurate paleogeographic and tectonic maps.

How to cite: Abdelmalak, M. M., Gac, S., Faleide, J. I., Shephard, G. E., Tsikalas, F., Polteau, S., Zastrozhnov, D., and Torsvik, T. H.: Quantification and Restoration of the Pre-Drift Extension Across the NE Atlantic Conjugate Margins During the Mid-Permian-Early Cenozoic Multi-Rifting Phases, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9908, https://doi.org/10.5194/egusphere-egu23-9908, 2023.

09:15–09:25
|
EGU23-2710
|
GD5.1
|
ECS
|
On-site presentation
|
Michael King, J. Kim Welford, and John Waldron

Atlantic Canada and its conjugate margins, the Irish, Iberian, and Moroccan margins, were subject to rifting and eventual breakup during the Mesozoic, following prior Appalachian Orogenesis from the early to mid-Paleozoic. The complexities of that older orogenesis, involving accretion and collision of Laurentian and peri-Gondwanan terranes during the closing of the Iapetus Ocean, contributed to the heterogeneous pre-rift template of the modern southern North Atlantic Ocean and the timing and extent of subsequent rift-related deformation.

In this work, we present newly-derived offshore and onshore present-day crustal thickness estimates of Atlantic Canada that are calculated using constrained 3-D gravity inversion and later reconstructed back to the onset of rifting and beyond, using GPlates and pyGPlates. In addition, deformable plate reconstructions are also used to reconstruct present-day magnetic anomalies, both onshore and offshore, back through time to track Appalachian orogenic trends beyond what can be deduced from geological field mapping alone. With the pre-rift template of the southern North Atlantic Ocean restored, we then attempt to extend these reconstructions further back in time to the Paleozoic to investigate strain localization within and between Appalachian terranes. Our results clearly reveal the fundamental influence of orogenic inheritance on subsequent rift events and the present-day variations in the crustal architecture that are observed along rifted margins. This study also provides the first quantitative assessment of Atlantic Canada’s crustal evolution from a compressive regime, to an extensional regime, to passive margin development.

How to cite: King, M., Welford, J. K., and Waldron, J.: Deformable plate reconstructions of Atlantic Canada and its conjugates back to the Paleozoic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2710, https://doi.org/10.5194/egusphere-egu23-2710, 2023.

09:25–09:35
|
EGU23-2721
|
GD5.1
|
On-site presentation
Richard F. Katz and Peter Huybers

Topographic spectra of abyssal hills from fast-spreading mid-ocean ridges have concentrations of power at Milankovitch frequencies and, in particular, around 1/(41 ka) [1].  This frequency corresponds to variations in Earth’s obliquity and is prominent in many climate records, including Pleistocene sea-level variations. Sea-level variations are understood to induce variations in magma supply to the ridge axis [2]. How might these magma-supply variations pace the faulting that creates abyssal hills?  We hypothesise that magma-supply variations introduce a perturbation to elastic plate thickness that is correlated with crustal thickness [3]. Building on Roger Buck’s theory for plate unbending and faulting at fast-spreading ridges [4], we show how thickness perturbations lead to concentrations in bending stresses in thinner parts of the plate.  These concentrations can be significant relative to background unbending stresses and may therefore pace faulting, depending on their amplitude and wavelength.  Using perturbation analysis and numerical solutions of Euler-Bernoulli beam theory, we develop predictions for fault spacing as a function of spreading rate, amplitude of magma supply variations, and other physical parameters.

[1] Huybers, Peter, et al. "Influence of late Pleistocene sea-level variations on mid-ocean ridge spacing in faulting simulations and a global analysis of bathymetry." PNAS https://doi.org/10.1073/pnas.2204761119 

[2] Cerpa, Nestor G., David W. Rees Jones, and Richard F. Katz. "Consequences of glacial cycles for magmatism and carbon transport at mid-ocean ridges." EPSL https://doi.org/10.1016/j.epsl.2019.115845 

[3] Boulahanis, Bridgit, et al. "Do sea level variations influence mid-ocean ridge magma supply? A test using crustal thickness and bathymetry data from the East Pacific Rise." EPSL https://doi.org/10.1016/j.epsl.2020.116121 

[4] Buck, W. Roger. "Accretional curvature of lithosphere at magmatic spreading centers and the flexural support of axial highs." JGR https://doi.org/10.1029/2000JB900360 

How to cite: Katz, R. F. and Huybers, P.: Unbending connects sea level to faulting at fast-spreading mid-ocean ridges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2721, https://doi.org/10.5194/egusphere-egu23-2721, 2023.

09:35–09:45
|
EGU23-13436
|
GD5.1
|
ECS
|
On-site presentation
Crustal geometries of the Eastern North American Margin and a comparison with the West African conjugate
(withdrawn)
Mike Shotton, Estelle Mortimer, Mohamed Gouiza, Chris Green, and Richard Collier
09:45–09:55
|
EGU23-13753
|
GD5.1
|
ECS
|
On-site presentation
Valentin Rime, Anneleen Foubert, Joël Ruch, and Tesfaye Kidane

Oceanic plateaus are traditionally considered as oceanic crust thickened by magmatic processes. In the last decades, however, continental material significantly older than the surrounding oceanic crust has been recovered from drillings on oceanic plateaus (e.g. Rio Grande Rise, Mauritius and Mascarene Plateau, Elan Bank), leading to numerous questions about the origin of these structures.

The Central Afar region is part of the Afro-Arabian Rift System. It witnessed the eruption of the Ethiopian Flood Basalts approx. 30 My ago followed by rifting. Mapping, plate kinematic modelling and geophysical data show that, despite important extension, the area features relatively thick crust. This crust is characterized by important magmatic underplating, intrusions, and volcanic material with isolated continental fragments. Therefore, it might represent an analogue for the development of oceanic plateaus. Numerous rift jumps and magma-compensated thinning linked to the presence of the Afar hotspot can explain the structure of the Central Afar. Unlike Central Afar, the Danakil Depression in northern Afar shows more classical structures and will probably develop into a magma-rich margin. The Afar depression thus constitute a unique example of the early development of different types of passive margins and oceanic plateaus.

How to cite: Rime, V., Foubert, A., Ruch, J., and Kidane, T.: The Central Afar region as an analogue for the development of oceanic plateaus?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13753, https://doi.org/10.5194/egusphere-egu23-13753, 2023.

09:55–10:15
|
EGU23-5784
|
GD5.1
|
solicited
|
On-site presentation
Colin Reeves

The mid-ocean ridges of the Atlantic and Indian oceans remain essentially fixed with respect to a constellation of mantle plumes throughout Gondwana dispersal.  The Bouvet plume is central to the dispersal process.  A model for the complex early Bouvet (Africa-Antarctica-South America) triple junction provides a link between the relatively simple tectonic histories of the South Atlantic and Indian oceans.  The model is based on interpretation of ocean-floor topography and repeated, meticulous and iterative animation in ‘Atlas’ plate-modelling software.

East and West Gondwana started to separate at   ̴184 Ma (Toarcian) with a 2000-km-long dextral transtensional rift between Africa and Antarctica.  The earliest triple junction was initiated south of Africa as the Malvinas plateau started to move west along the Agulhas fault at   ̴165 Ma (Callovian).  Limpopia, a micro-fragment, at first remained attached to Antarctica while the Maurice Ewing Bank (MEB) retained its attachment to Africa.  New dynamism initiated rifting in the South Atlantic Ocean and between India and Antarctica-Australia early in the Cretaceous.  Complex reorganisation of micro-fragments near the Bouvet plume head led, by   ̴129 Ma (Hauterivian), to a triple junction configuration with the present outline of South America intact (including the MEB fixed off the Malvinas plateau) and with Limpopia, the continental core of the Mozambique Ridge (supplemented by copious Cretaceous volcanism) fixed to Africa.  This configuration was to prove long-lived.

It is interesting to speculate whether the large Morokweng meteorite impact in southern Africa (J/K boundary) could have triggered tectonic acceleration.

The model is illustrated in animation at https://www.reeves.nl/gondwana/aac-anim-1

How to cite: Reeves, C.: The Bouvet triple junction: a model of Gondwana fragmentation in Jurassic and Early Cretaceous times, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5784, https://doi.org/10.5194/egusphere-egu23-5784, 2023.

Posters on site: Thu, 27 Apr, 14:00–15:45 | Hall X2

The posters scheduled for on-site presentation are only visible in the poster hall in Vienna. If authors uploaded their presentation files, these files are linked from the abstracts below, but only on the day of the poster session.
Chairpersons: Jordan J. J. Phethean, Patricia Cadenas Martínez
X2.219
|
EGU23-1937
|
GD5.1
Gong Jianming, Liao Jing, Lei Baohua, Liang Jie, Chen Jianwen, and Li Sen

According to the geotectonic analysis and seismic data interpretation, the Offshore Indus Basin is the extension of the Lower Indus Basin in the sea area, with a double-layer structure of "lower fault and upper depression" similar to that of the Lower Indus Basin in the land area. That is, the Mesozoic is a fault basin and the Cenozoic is a depression basin. On the 2D seismic profile, the Mesozoic strata are characterized by many faults, large fault throw, steep dip angle and the development of transport system. There is a great difference between the shallow water area of the northern continental shelf and the deep water area of the southern part of the Cenozoic strata. In the northern part, there are more gravity slumping faults, larger fault throw, and more developed transport systems, while in the southern part, there are fewer faults, smaller fault throw, and less developed transport systems. By comparing and analyzing the small normal faults in the passive continental margin basin of Guyana, South America, and their reservoir forming models, it can be inferred that there may be many "invisible" normal faults with small fault throw, large density and steep dip angle developed in the Cenozoic slope break area of the offshore Indus Basin. In addition, in the strike slip area of Murray Ridge in the west of the basin, the Mesozoic and Cenozoic fault transport systems are developed. The results of sea land correlation and offshore drilling core analysis show that there may be three sets of widely distributed source rocks in the Offshore Indus Basin, which are Cretaceous, Paleo-Eocene and Lower Miocene mudstones. According to comprehensive analysis, the formation of oil and gas reservoirs in the Offshore Indus Basin is mainly controlled by Mesozoic large fault transportation, Mesozoic-Cenozoic fault relay transportation, Cenozoic collapse fault transportation and "hidden" fault transportation. The types of oil and gas pools may mainly include Mesozoic "self generated and self stored" or "side generated and side stored", Cenozoic "lower generated and upper stored" in the north and east of the basin, and "lower generated and upper stored" and "self generated and self stored" in the west of the basin.

How to cite: Jianming, G., Jing, L., Baohua, L., Jie, L., Jianwen, C., and Sen, L.: Fault Transportation and Hydrocarbon Accumulation in Offshore Indus Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1937, https://doi.org/10.5194/egusphere-egu23-1937, 2023.

X2.220
|
EGU23-1612
|
GD5.1
Lei Baohua, Gong Jianming, Liao Jing, Liang Jie, Chen Jianwen, and Li Sen

Due to the lack of drilling confirmation and the poor imaging quality of the early seismic data in deeper part, there was a great controversy on the understanding of the strata under the Cenozoic in the offshore Indus Basin: some scholars thought that the Deccan volcanic rocks were widely distributed; It is also believed to be Mesozoic sedimentary strata, but its stratigraphic framework, distribution and structural characteristics are not clear. This directly affects the evaluation of exploration potential in this area. Using the latest multi-channel seismic data, we have clearly identified Mesozoic sedimentary strata in the offshore Indus Basin. The offshore Indus basin is composed of the underlying Mesozoic rifting basin and the overlying Cenozoic passive continental margin sedimentary basin. It is a two-stage superimposed basin developed on the stretched and thinned crust of the Indian plate, drifting from the southern hemisphere to the present position together with the Indian continent. Through correlation of sea and land strata, it is found that the Mesozoic offshore Indus Basin is an offshore extension of the lower Indus Basin, and has similar stratigraphic distribution characteristics and structural characteristics to the lower Indus Basin. The correlation of seismic wave sets indicates that the Jurassic, Sembar Formation and Lower Goru Formation of Lower Cretaceous and the Upper Goru Formation of Upper Cretaceous were also deposited in the sea area. The Jurassic and Lower Cretaceous have the stratigraphic characteristics of eastern faulted and western overlapped, and the Upper Cretaceous has the characteristics of east-west double faulted. The basin rifting area expanded westward continuously during the Mesozoic. The Mesozoic strata were controlled by nearly N-S trending faults,the northern near-shore strata partially reformed by Cenozoic near E-W fault, and the western strata was influenced by the near N-S uplifting and strike-slip structure of Murray Ridge. The average thickness of Mesozoic strata is about 2000m, and the thickest can reach 12000m. The Mesozoic major depocenter is located in the southeast of the basin, the second one is in the northwest. The favorable structural types such as faulted nose, faulted anticline and anticline are mainly developed. These structures were mainly formed during the late Mesozoic compressive uplift period. Therefore, the Mesozoic in the Offshore Indus Basin has the material basis and structural geological conditions for the formation of oil and gas fields. If the favorable structure in Mesozoic can be configured with the depocenter, it will be conducive to hydrocarbon near-source charging. Like the Lower Indus Basin, the Mesozoic is also a favorable direction for petroleum exploration.

How to cite: Baohua, L., Jianming, G., Jing, L., Jie, L., Jianwen, C., and Sen, L.: Mesozoic structural characteristics and exploration potential of the offshore Indus Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1612, https://doi.org/10.5194/egusphere-egu23-1612, 2023.

X2.221
|
EGU23-12199
|
GD5.1
|
ECS
Athanasia Vasileiou, Mohamed Gouiza, Estelle Mortimer, and Richard Collier

The High Atlas is an aborted rift system along NW Africa that formed during the Mesozoic break-up of Pangaea and was inverted during the Alpine Orogeny. In contrast to the well-studied inversion, the Triassic-Jurassic rifting, synchronous to the Atlantic and the Tethyan opening, is still not fully understood. Orthogonal rifting is proposed to be active during the Triassic to early Early Jurassic, and was followed by an oblique extensional phase. The timing of this change in the kinematic of rifting is poorly constrained. Restoration of the Atlantic-Tethys triple junction suggests sinistral motion during the Middle Jurassic, which reactivated NE-SW trending Hercynian structures in a transtensional manner.

The Atlas system is a great field analogue to study and analyse extensional systems influenced by strike-slip tectonics since the well exposed syn-rift structures and sediments have been weakly affected by the contraction during the late Cenozoic Alpine inversion.

This work investigates the kinematic and geometry of the oblique rifting phase, the stress and strain variation lengthwise along the Atlas rift system, the relationship between the Triassic-Early Jurassic orthogonal rift structures, the Middle Jurassic strike-slip structures, and the potential synchronous volcanism occurring during the Middle Jurassic. This contribution highlights the fieldwork results of significant outcrops that we used to constrain the restoration of the rift system, evaluate extension and transtension, and produce a conceptual model of how strike-slip tectonics can influence the evolution of continental rifting.

How to cite: Vasileiou, A., Gouiza, M., Mortimer, E., and Collier, R.: Strike-slip influenced rift systems: the case study of the Moroccan Atlas system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12199, https://doi.org/10.5194/egusphere-egu23-12199, 2023.

X2.222
|
EGU23-12348
|
GD5.1
|
ECS
Przemyslaw Domel, Vera Schlindwein, Andreia Plaza-Faverola, and Stefan Bünz

The Fram Strait opening is associated with a complex stress regime that results from the oblique relation between two ultra-slow spreading mid-ocean ridges, the Molloy ridge (MR) and the Knipovich Ridge (KR), offset by the Molloy Transform Fault (MTF). Gas-charged thick sedimentary deposits developed over both oceanic and continental crust. Sedimentary faulting reveals recent stress transfer into the sub-surface. However, the mechanisms by which stress accommodates across the west Svalbard margin and its effect on fluid flow and seepage dynamics remain poorly understood. An analysis of earthquake occurrence and focal mechanisms can shed light on the present state of tectonic forces in the area, their origin and potential influence on nearby faults. Conventional studies using land instrumentation provide incomplete seismological records even for such comparatively land proximal settings, due to still large distances to the nearest permanent observatories and a poor azimuthal coverage. We deployed 10 ocean bottom seismometers (OBS) for 11 months between 2020-2021 about 10 km north of the northern termination of KR to investigate patterns of stress transfer off the ridge and the influence on the sedimentary system. OBSs are spaced by about 10 km around an area characterized by fault-related seepage and sedimentary slumps visible on the bathymetry. Using partially automated routines we built a catalogue of local earthquakes and computed their epicenters and magnitudes. Earthquake locations roughly follow the plate boundaries and better focus seismicity along their bathymetric imprint versus the land observations. Along the MTF, we observe that the earthquakes are concentrated southwards on the North American plate and seismicity across the west-Svalbard margin is limited. A large number of earthquakes extend beyond the MTF and KR corner and concentrate at a bathymetric depression, adjacent to the recently revised continental-oceanic transition boundary. Focal mechanisms from past observations show a gradual change from strike-slip movement along the MTF to extensional faulting at the corner. The distribution of earthquakes correlates with highly faulted sedimentary overburden interpreted in high resolution seismic data, and with major structures in gravity and magnetic maps. This suggests an efficient stress release at the plate boundary and little to no transfer northward from the KR termination onto the Eurasian plate. We detected only a few events recorded along the Vestnesa contourite drift and on the continental shelf. These earthquakes may indicate reactivation of crustal faults under the weight of thick sedimentary deposits or other processes such as glacial isostacy. The inferred stress distribution in the region has implications for understanding fault-related gas transport and methane seepage at Arctic margins.

How to cite: Domel, P., Schlindwein, V., Plaza-Faverola, A., and Bünz, S.: Local seismicity in the obliquely spreading setting of Fram Strait constrained from ocean bottom seismometers: Implications for fluid flow and methane seepage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12348, https://doi.org/10.5194/egusphere-egu23-12348, 2023.

X2.223
|
EGU23-6339
|
GD5.1
|
ECS
Marie-Andrée Dumais, Laurent Gernigon, Odleiv Olesen, Ståle E. Johansen, and Anna Lim

The interest for the polar regions and complex continental margins and ocean has increased during the last few decades. New technologies allow to conduct research in this hostile environment, permitting to investigate the tectonic and geodynamic history of the North Atlantic and Arctic oceans. In particular, the crustal and lithospheric structure of the Fram Strait and the transition from the Knipovich Ridge to the Barents Sea shelf and Svalbard are still poorly understood. Several multi-geophysical investigations from various campaigns since the 90s along the Western Barents Sea margin and the Northeast Greenland margin resulted in limited and contradicting interpretations of the crust and upper mantle. In this work, we study the spreading of the Knipovich Ridge and the regional tectonic of the Fram Strait and the Svalbard Margin.

Our new KRAS-16 aeromagnetic data survey the complexity of the seafloor spreading history of the Fram Strait region. The high-resolution data identified the magnetic isochrons around the Knipovich Ridge and suggest the presence of several oceanic fracture zones and lineaments in the Fram Strait. The Knipovich ridge spreading initiated at C6 (20 Ma) and a ridge jump occurred at C5E. The oceanic crustal domain was consequently delineated. This new survey suggests that the continent-ocean boundary on the east Barents margin should be relocated up to 150 km farther west compared to previous studies. A 3-D magnetic inversion modelling identified zone with weak magnetization along the rift valley correlated with the absence of volcanic or bathymetric rise evidence. Combined with seismicity data available along the Knipovich Ridge, amagmatic and magmatic accretions show a segmentation of the seafloor spreading that correlates with the variation in magnetization along the rift valley. Furthermore, the new location of the continent-ocean boundary prompted to revise the existing 2-D seismic interpretations in terms of crustal interpretation and tectonic. This is tested further using joint 2-D gravity and magnetic field modelling and electromagnetic/magneto-telluric (CSEM/MT) data. A wide transition lithospheric domain likely comprising an exhumed lower crust or mantle is delineated from our interpretation. These results provide insights of the regional and structural nature of the Knipovich Ridge and its intricate development.

How to cite: Dumais, M.-A., Gernigon, L., Olesen, O., Johansen, S. E., and Lim, A.: Complex seafloor spreading Knipovich Ridge and its crustal structure: insights from aeromagnetic data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6339, https://doi.org/10.5194/egusphere-egu23-6339, 2023.

X2.224
|
EGU23-12301
|
GD5.1
Laurent Gernigon, Claudia Haase, Sofie Gradmann, Marie-Andrée Dumais, Trond Slagstad, Frode Ofstad, Aziz Nasuti, and Marco Bronner

We integrated high-resolution aeromagnetic data and 2D/3D seismic data from the Norwegian Southwestern Barents Sea. The main objective is to address the long-standing question on the role of pre-existing basement structures in controlling strain accommodation and extension in the Finnmark Platform and adjacent rift basins. The thorough qualitative analysis of the high-resolution magnetic data reveals fault geometries, regional kinematics, magmatism and inheritance of older Precambrian/Caledonian structures. Through the application of second order derivative filters and depth-to-magnetic-source modelling, the trends of the Caledonian metamorphic fabrics are identified and correlated with the structure of buried basement faults and shear zones also imaged at the same level of resolution on 2D/3D seismic data. The magnetic data reveal an unprecedented detail of the basement fabrics dominated by high-frequency NW-SE trending magnetic lineaments associated with the semi-regional Sørøya-Ingøya Shear Zone. The high-frequency magnetic lineaments are superimposed by lower frequency NNW-SSE trending magnetic lineaments that reflect the inheritance of older Precambrian structures. At the edge of the Tromsø Basin, the new magnetic data highlight sill intrusions also visible on seismic data. Fault geometries, regional kinematics, and spatial distribution of the magnetic sources suggest that old detachments and younger Mesozoic faults reactivated the basement fabrics found along the graben borders. Focusing of strain accommodation at the edge of the Hammerfest Basin is helped as well as modulated by the presence of back-thrusted Caledonian nappes interpreted on the Finnmark Platform. Offshore, surface ruptures associated with graben formation align with the dominant NNW-SSE trending magnetic lineaments defining steeper normal faults that are characterised by right-stepping segments along the southern flank of the Hammerfest Basin. Based on potential field models, we finally quantify the crustal architecture of the rift and platform system. At upper crustal level, we test the presence and significance of potential Palaeozoic basin preserved at the edge of the basement hinge-zones. Potential field modelling also highlights and quantifies several rift domains defined by moderate to extreme thinning of the crust (low-β stretched domain, necking, and high-β hyperextended regions). The development of the necking zone is clearly influenced by the existence of former first-order and multi-scale inherited basement features preserved in the Finnmark Platform.

How to cite: Gernigon, L., Haase, C., Gradmann, S., Dumais, M.-A., Slagstad, T., Ofstad, F., Nasuti, A., and Bronner, M.: Onshore-offshore relationship and anatomy of a necking zone: insights from high-resolution aeromagnetic survey on the Finnmark Platform (Norwegian Barents Sea), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12301, https://doi.org/10.5194/egusphere-egu23-12301, 2023.

X2.225
|
EGU23-10392
|
GD5.1
Jeremy Rimando, Peace Alexander, Ai Gusti Guna, and Katsuichiro Goda

Earthquakes in the offshore Grand Banks region of Newfoundland pose a risk to lives and property in nearby coastal communities and to crucial commercial infrastructure and operations in offshore areas. The 1929 M7.2 Grand Banks earthquake, which was associated with a tsunamigenic landslide, devastated the coastal communities in southern Newfoundland and ruptured several trans-Atlantic telecommunications cables. Despite this event, we still know little about the structural setting and neotectonics of the area. In this study, we identified potentially active tectonic structures, and associated secondary deformation features, affecting the youngest strata and the seabed in this region through the interpretation of offshore two-dimensional (2D) seismic reflection profiles. Analysis of these profiles also allowed us to interpret the relationship of the younger, potentially seismogenic structures to inherited passive margin structures at depth. Our findings on the locations and geometries of potentially active faults can be utilized as a basis for seismic hazard inputs for the modelling of earthquake scenarios, which are useful for estimating the potential impacts of the rupture of faults/fault segments on certain populations and assets.

How to cite: Rimando, J., Alexander, P., Guna, A. G., and Goda, K.: Subsurface evidence for potentially seismogenic structures in the offshore Grand Banks region of Newfoundland, eastern Canada: present-day reactivation of inherited passive margin structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10392, https://doi.org/10.5194/egusphere-egu23-10392, 2023.

X2.226
|
EGU23-7509
|
GD5.1
|
ECS
|
Ai Gusti Guna and Alexander L. Peace

The Flemish Pass Basin is a Mesozoic basin offshore Newfoundland in Eastern Canada. This basin has proven petroleum systems, and formed via multiple rifting episodes as a part of the wider North Atlantic rift system during Pangaea’s disintegration. We utilise the Bay du Nord 3D seismic survey to derive 3D fault models, which include throws profile. The aim of this was to investigate fault nucleation and growth history, and how this may relate to previous interpretations of multi-stage rifting, plus the possible role of structural inheritance in controlling basin evolution.

Through our interpretation of the 3D volume, we identified three fault systems (1: NE-SW, 2: NW-SE & 3: NNE-SSW), plus one distinctive basin-bounding fault (trending E-W). The NE-SW basement-involved system typically comprises 12 – 17 km long faults dipping 10–25o, with throws of 250–1250 m. This fault system exhibits throws of 600–1250 m between the hanging wall and footwall of the interpreted Pre–Mesozoic cut–off horizon. We interpret this observation of large throw values to relate to the initiation of extension following the Pre-Mesozoic horizon, which likely coincides with the previously interpreted regional Late Triassic–Early Jurassic rift phase. Moreover, although lower throws (≤200 m) were recorded between the Base Upper Tithonian and Late Jurassic horizons, evidence of reactivation of this fault system is interpreted from the throw values, which range from 300–750 m between the Base Upper Tithonian and the Aptian horizons. We interpret this to result from further reactivation due to the previously interpreted 2nd regional rift phase in the Late Jurassic – Early Cretaceous. The NW-SE fault system constitutes 3 – 10 km long planar normal faults, with throws ranging from 50–300 m scattered between the Base Upper Tithonian and Late Cretaceous cut-off lines. We interpret that this fault set propagated downward and linked with pre-existing basement-involved faults, and that the nucleation of this fault set occurred during the 2nd rift phase. The NNE-SSW planar normal fault system is interpreted to be younger based on stratigraphic relationships and comprises 2–8 km long faults. This fault system was interpreted to correspond with the 3rd rift phase during the Cretaceous, and has throw values between the Base Upper Tithonian and the Base Cretaceous horizons ranging from 100–350 m. Finally, the distinct E-W striking basin-bounding normal fault revealed throws of 250–4000 m. This fault acts as a sub-basin confinement on the southern part of the 3D survey area, with throw variation distributed in the Pre-Mesozoic horizon from 1000–4000 m and between Base Upper Tithonian–Aptian Cretaceous horizons with values of 250-800 m.

Overall, our results demonstrate that: 1) in the Flemish Pass basin, there are three fault systems, and one distinctive basin-bounding fault, all of which display variable throw values corresponding to three rift phases (Late Triassic-Early Jurassic, Late Jurassic–Early Cretaceous, and Cretaceous) and 2) pre-existing structures influenced basin development by providing an initial seed for subsequent faulting and may have possibly formed a mechanical link aiding propagation.

How to cite: Guna, A. G. and Peace, A. L.: Geometries and kinematics of fault systems in the Flemish Pass Basin: Insights from the Bay du Nord 3D seismic survey, offshore Newfoundland, Eastern Canada, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7509, https://doi.org/10.5194/egusphere-egu23-7509, 2023.

X2.227
|
EGU23-16613
|
GD5.1
Alexander Peace, Jordan Phethean, Yang Li, and Gillian Foulger

In recent years, unexpected continental crust in areas presumed to be purely oceanic in nature has been discovered, indicated by the presence of Paleozoic zircons in rock samples. Notable examples include the Rio Grande Rise, Mauritius, and potentially also the Comoros islands, which have all previously been interpreted as mantle plume edifices. Iceland is also often interpreted as a hotspot of mantle plume origin, however the presence of a deep seated consistent thermal anomaly with depth has long been challenged, with implications for the wider regional geodynamic evolution.

Previous reports of Mesozoic and Paleozoic zircons from Iceland may allude to the presence of continental material at depth, although these are sometimes suggested to be the result of contamination. Nonetheless, geochemical evidence from erupted material at Öræfajökull may indicate a continental contribution to melts beneath SE Iceland, and the nearby Jan Mayen microcontinent readily demonstrates the ability of continental material to make its way to the ocean interior, coincident with hotspot volcanism. Furthermore, continental material in the NE Atlantic Ocean is perhaps more common than previously thought, with recent work suggesting that substantial components of the Greenland-Iceland-Faeroes region may be continental in nature.

Here, we test the hypothesis that the basaltic upper crust of Iceland is underlain by older continental crust. To do this, we have undertaken extensive, targeted sampling of Icelandic rocks and sediments using robust collection approaches to eliminate the possibility of contamination. Over a 3-week period in summer 2022, we collected samples from across the entirety of Iceland. We sampled both intrusive and extrusive rocks with a wide range of ages (both felsic and mafic, but with an emphasis on felsic rocks), as well as river sediments from above 250 m elevation (to avoid potential contamination from Greenland glacial debris). Zircons will be separated from these samples using contamination-safe approaches, and then U-Pb and Hf isotopic age analysis will be completed. The results from this preliminary study will be used to guide further sampling in summer 2023, allowing evaluation of the competing hypothesises for the origin of Iceland.

How to cite: Peace, A., Phethean, J., Li, Y., and Foulger, G.: Iceland: mantle plume or microcontinent? A zircon study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16613, https://doi.org/10.5194/egusphere-egu23-16613, 2023.

X2.228
|
EGU23-8482
|
GD5.1
Laetitia Le Pourhiet, Thomas Francois, Anthony Jourdon, and Tiphaine Larvet

While a lot of literature exist modelling the effect of former tectonic structure faults, stacking of different lithologies with a dip or former lacolithes, little has been done in modelling the effect of heterogeneous thermal properties in the lithosphere and particularly in the crust and these contributions are old enough that some of their main results need to be reminded and extended using current modelling tools.  

I will first recall how much periodic variations in heat production rate in the crust may affect the temperature at the Moho and the thickness of the lithosphere using analytical solution, I will then use thermo-mechanical simulation to demonstrate how important are these effects in 2 and 3D at tectonic timescale especially while reactivating former post orogenic collapse structures such as metamorphic core complexes and migmatite domes. I will illustrate how the simulation might apply to the West European rift, the Menderes massif or the South China Sea.

I will finally show using 2D numerical simulations how much the repartition of heat production in the crust influences the long-term survival of mobile belts and can explain partly why the European lithosphere keeps large heat flow despites its thermos-tectonic age.

How to cite: Le Pourhiet, L., Francois, T., Jourdon, A., and Larvet, T.: Thermal inheritance in continental rifting., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8482, https://doi.org/10.5194/egusphere-egu23-8482, 2023.

X2.229
|
EGU23-6881
|
GD5.1
|
ECS
Tiphaine Larvet, laetitia le Pourhiet, Philippe Agard, and Manuel Pubellier

Although slab pull is recognized as the main driving force of tectonic plates, marginal basins formation is generally explained by slab roll back or mantle plume impingement. The link between the slab pull force and the continental breakup of the lower plate is still poorly investigated, maybe due to the scarcity of proven examples? The goal of this study is to identify the mechanical conditions for which the slab pull force can be transmitted to the continental lithosphere of the lower plate and generates a continental rifting and breakup. The first condition requires to transfer the slab pull force across the oceanic domain and generate tensional setting into the attached continental margin. Then the ocean needs to be free of any Mid-oceanic ridge, which means that the continental breakup of the lower plate can only happen after the subduction or the inactivation of the ridge. The other conditions cannot be assessed as easily, and therefore motivates our modelling.

We perform a set of 2D thermo-mechanical regional-scale simulations of ridge-free subduction with slab pull evolving self-consistently during the sinking of the slab. The aim is to understand how, when and where slab pull can lead to continental breakup. Two parametric studies are presented. One investigates the tectonic plates kinematic relatively to the upper mantle and another one focused on the strength of both the oceanic and the continental part of the lower plate. In the simulations, the continental rifting is driven by tensional forces internally generated by the subduction zone. Kinematic conditions are only prescribed to the boundaries of the simulation domains to simulate convergent setting and promote subduction. Our numerical simulations reveal that a significant increase of the slab pull induced by the crossing of the 410 km phase transition is responsible for the lower plate breakup. If the oceanic domain is weaker than the continental margin, the slab pull leads to the slab break-off. On the contrary, if the continental domain is weaker, we observe a continental breakup at around 500 km apart from the passive margin. If the lower plate moves compared to the asthenosphic mantle below it, the horizontal basal shear at the LAB prevents the localization of the deformation and leads to an aborted rift.

To synthetize in natural examples, we show that the slab pull can lead to continental breakup when the Mid-oceanic ridge is already subducted, the continental domain is weaker than the oceanic domain, and the horizontal displacement of the lower plate is the same as that of the astenospheric mantle underneath. In light of this new constrains, we discuss the plate reconstruction models proposed for (1) the Cimmerian blocks detachment from the Gondwana during the Permian and (2) the Oligocene South China Sea opening.

How to cite: Larvet, T., le Pourhiet, L., Agard, P., and Pubellier, M.: Continental breakup and slab pull driving force, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6881, https://doi.org/10.5194/egusphere-egu23-6881, 2023.

X2.230
|
EGU23-9462
|
GD5.1
Lower plate retreat and opening of an Andean backarc basin
(withdrawn)
Andreas Kammer
X2.231
|
EGU23-16556
|
GD5.1
|
ECS
Júlia Gómez-Romeu, Nick Kusznir, Andy Alvey, and Emmanuel Masini

The Guyana-Suriname-Western Demerara (G-S-WD) continental margins are located at the junction of the Central Atlantic and proto-Caribbean oceanic basins as they developed in the Jurassic. The emplacement of the later Caribbean subduction partly destroyed the Jurassic record of the proto-Caribbean basin which implies that the Jurassic kinematics of this region are still debated. However, the G-S-WD margins escaped from subduction and preserve most of the Jurassic record. We investigate the architecture of the G-S-WD margins and the distribution of Jurassic oceanic crust. This allows us to determine the margins tectonic styles and gain insights into the Jurassic regional plate kinematics during the southward propagation of the Central Atlantic, the opening of the proto-Caribbean basin and its link with the development of the Gulf of Mexico (GoM).

We use 3D gravity inversion to map Moho depth, crustal basement thickness and continental lithosphere thinning factor. Input data for the gravity inversion is sediment thickness from seismic reflection grids, satellite free-air gravity data and digital bathymetry. From the resulting 3D Moho depth volume we produce margin crustal cross-sections to determine the structure and architecture of the G-S-WD margins. The Guyana segment shows a transform architecture, the Suriname segment a rift-transform architecture and the Western Demerara segment a magma-rich rifted margin with SDRs up to 20 km thick.

We also use crustal thickness mapping from gravity inversion together with regional magnetic anomaly superimposed satellite gravity anomaly data to determine the extent of Jurassic oceanic crust and delineate its boundary with Cretaceous Equatorial Atlantic oceanic crust. The boundary between Jurassic and Cretaceous oceanic crust is identified as running from the NW corner of the Demerara Plateau to Barbados. This boundary has the same orientation as the Guyana transform margin.

Plate reconstructions of crustal thickness from gravity inversion have been used to examine the relationship between the Jurassic opening of the Central Atlantic, the development and opening of the GoM and the formation of the Jurassic crust offshore G-S-WD.

A new plate reconstruction of the opening of the GoM based on transform fault small circles observed in satellite free-air gravity data shows that before the rotational opening of GoM at ~165 Ma, the early GoM and oceanic crust offshore G-S-WD formed a co-linear linked rift/sea-floor spreading system offset by a sinistral transform to the west of Florida.

How to cite: Gómez-Romeu, J., Kusznir, N., Alvey, A., and Masini, E.: The Jurassic rifted margins and ocean basin, offshore Guyana-Suriname-Demerara and its link with Gulf of Mexico opening, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16556, https://doi.org/10.5194/egusphere-egu23-16556, 2023.

X2.232
|
EGU23-8472
|
GD5.1
|
ECS
Michelle Graça, Nick Kusznir, and Natasha Stanton

We have processed the EMAG2v3 observed full field magnetic anomaly (Meyer et al., 2017) using the magnetic potential transformation to make a pseudo-gravity anomaly map for the South Atlantic between 15° S and 40° S. A pseudo-gravity transformation attempts to remove the dipolar complexity of a magnetic anomaly and produce the equivalent gravity anomaly assuming a constant ratio of magnetization to density contrast. We assume that magnetization is induced. Our South Atlantic study area encompasses the major bathymetric features of the Rio Grande Rise (RGR) and Walvis Ridge (WR), as well as the Brazilian and African rifted margins.

On the Brazilian continental margin, there are high positive pseudo-gravity anomalies on the São Paulo Plateau (SPP) in the Santos Basin, as well as on the Florianópolis Ridge (FR). The distal Campos Basin also shows high positive pseudo-gravity anomaly. The southern Pelotas Brazilian rifted margin shows negative pseudo-gravity anomaly becoming positive oceanward on the Torres High. In the oceanic domain the Rio Grande Rise (RGR) shows three units of high positive pseudogravity anomalies. Although the RGR presents high amplitude pseudo-gravity anomalies, they are not homogeneous. The Eastern RGR has the most intense and linear N-S anomaly, while its Central unit has a circular pseudo-gravity anomaly and is more constrained in area. The Western RGR has a lower amplitude pseudo-gravity anomaly. The C34 magnetic anomaly region, separating the Eastern and Central RGR, shows a negative pseudo-gravity anomaly. Negative pseudo-gravity anomalies indicate that the assumption of entirely induced magnetization used in the pseudo gravity transformation is invalid and that significant long wavelength remnant magnetization exists. This may indicate heterogeneity of the magnetized layer as well as the effects of magnetic field reversals.

On the African plate, very strong positive pseudo-gravity anomalies occur on the inner WR and the SW African continental margin. The positive pseudo-gravity anomalies of the WR and the beginning of the outer SW trending WR “tail” create a very strong continuous positive pseudo-gravity anomaly. Together with the South African rifted margin, it forms a strong positive anomaly with a “7” shape. Westwards of the C34 magnetic anomaly there are no significant large amplitude pseudo-gravity anomalies.

The map of the pseudo-gravity has been restored using the GPlates reconstruction software. At 110 Ma, the SPP is near the inner WR and both show high amplitude positive pseudo-gravity anomalies. At 110 Ma, the FR is close to the most distal portion of the inner WR, both showing positive pseudo-gravity anomalies. At 85 Ma, the Central RGR, the western extremity of the inner WR and the start of the WR “tail” show conjugate positive pseudo-gravity anomalies. After the C34 anomaly, seen as an intense negative pseudo-gravity anomaly, the Eastern RGR and its conjugate WR “tail” both show positive pseudo-gravity anomalies and separate at ~ 65 Ma. The pseudo-gravity anomaly map indicates that the RGR and WR comprise distinct units which are correlated across the ocean and which correspond to the multiple oceanic ridge jumps reported in Graça et al. (2019).

How to cite: Graça, M., Kusznir, N., and Stanton, N.: A Pseudo-Gravity Magnetic Anomaly Transformation Map for the Central South Atlantic: Implications for Ocean Development after Breakup, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8472, https://doi.org/10.5194/egusphere-egu23-8472, 2023.

X2.233
|
EGU23-11824
|
GD5.1
Gabriela Fernandez Viejo, Carlos Lopez-Fernandez, and Patricia Cadenas

The analysis of two decades (2003-2022) of seismicity recorded by the Spanish and Portuguese seismic networks along the West Iberian passive margin results in a picture of the clustered and moderate seismicity observed in this intraplate submarine area.

The study precise the trend of specific alignments, providing an accurate depiction of event distribution along two stripes 700 km long through the ocean floor in WNW-ESE direction. These alignments are parallel to the Africa-Eurasia plate boundary, but distinctly separated from its related seismicity ≈300 and ≈700 km respectively, enough distance to be considered as intraplate.

When trying to relate this seismicity to structural, and/or geophysical features, it doesn’t arise a conclusive picture. The earthquakes occur indiscriminately across thinned continental, hyperextended, and exhumed mantle rift domains. They fade out in the proximity of undisputed oceanic crust, but some events extend beyond. The hypocentral depths signal a considerable amount of events nucleating in the upper mantle. The focal mechanisms are predominantly strike-slip and a superposition of the event map with geophysical data shows a puzzling lack of affinity with any of them.

Considering these observations, different hypothesis are discussed to explain this relatively anomalous distribution of seismicity. Some of them previously advanced in the literature do not portray convincing arguments. Others are too unspecific. None of them are completely flawless, suggesting that maybe there is several factors at play. Despite being one of the most probed passive margins in the world, the present geodynamical state of the West Iberian Margin manifested in its modern seismicity, seems to remain unknown.

Interpreting these data within a global tectonic plate framework, together with the potential addition of sea bottom seismometers may give the key to understand this activity along one of the most archetypical margins of the Atlantic Ocean.

How to cite: Fernandez Viejo, G., Lopez-Fernandez, C., and Cadenas, P.: Two decades of seismicity in the West Iberian Margin: current hypothesis and new ideas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11824, https://doi.org/10.5194/egusphere-egu23-11824, 2023.