TS6.1

TS6 EDI
Continental rift evolution: from inception to break-up 

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.

Co-organized by GD1/GM9/SM4/SSP1
Convener: Frank Zwaan | Co-conveners: Carolina Pagli, Sylvie Leroy, Derek Keir, Giacomo Corti
Presentations
| Mon, 23 May, 15:10–18:26 (CEST)
 
Room D1

Session assets

Session materials

Presentations: Mon, 23 May | Room D1

Chairpersons: Frank Zwaan, Carolina Pagli, Derek Keir
15:10–15:13
1.1. East African Rift System
15:13–15:23
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EGU22-7155
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ECS
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solicited
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Highlight
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Virtual presentation
Anne Glerum, Sascha Brune, and Walid Ben Mansour

The East African Rift System (EARS) is the largest active continental rift on Earth. Inherited lithospheric strength variations have played a large role in forming the system’s current geometry. The partly overlapping eastern and western EARS branches encompass the large Victoria continental microplate that rotates counter-clockwise with respect to Nubia, in striking contrast to its neighboring plates.

Both the forces driving rifting in the EARS as a whole and the rotation of Victoria in particular are debated. Whereas some studies largely ascribe the rifting to horizontal mantle tractions deriving from plume-induced flow patterns (e.g., Ghosh et al., 2013), or to more equal contributions of mantle tractions and gravitational potential energy (e.g., Kendall and Lithgow-Bertelloni, 2016), recent work by Rajaonarison et al. (2021) points to a dominant role for lithospheric buoyancy forces in the opening of the rift system. Similarly, other numerical modeling (Glerum et al., 2020) has shown that Victoria’s rotation can be induced through drag of the major plates along the edges of the microplate transmitted along stronger lithospheric zones, with weaker regions facilitating the rotation, without the need for plume-lithosphere interactions (e.g., Koptev et al., 2015; Calais et al., 2006).

With unprecedented data-driven, regional spherical geodynamic numerical models spanning the EARS and the upper 660 km of mantle, we aim to identify the individual contributions of lithosphere and mantle drivers of deformation in the EARS and of Victoria’s rotation. Observational data informs the model setup in terms of crustal and lithospheric thickness, sublithospheric mantle density structure and plate motions. Comparison to separate observations of the high-resolution model evolution of strain localization, melting conditions, horizontal stress directions, topography and horizontal plate motions allows us to identify the geodynamic drivers at play and quantify the contributions of large-scale upper mantle flow to the local deformation of the East African crust.

 

Calais et al. (2006). GSL Special Publications, 259(1), 9–22.

Ghosh et al. (2013). J. Geophys. Res. 118, 346–368.

Glerum et al. (2020). Nature Communications 11 (1), 2881.

Koptev et al. (2015). Nat. Geosci. 8, 388–392.

Rajaonarison et al. (2021). Geophys. Res. Letters, 48(6), 1–10.

How to cite: Glerum, A., Brune, S., and Ben Mansour, W.: Geodynamic Drivers of the East African Rift System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7155, https://doi.org/10.5194/egusphere-egu22-7155, 2022.

15:23–15:24
15:24–15:29
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EGU22-4683
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ECS
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Virtual presentation
Rita Kounoudis, Ian Bastow, Cynthia Ebinger, Christopher Ogden, Atalay Ayele, Rebecca Bendick, Nicholas Mariita, Gladys Kianji, Martin Musila, and Garrett Sullivan

Multiple geoscientific studies along the Main Ethiopian and Eastern rifts have revealed that extension via magma intrusion now prevails over plate stretching as the primary mechanism for strain accommodation throughout the crust and mantle lithosphere. However, problematic in this picture is where the Main Ethiopian and Eastern rifts meet, across the low-lying, broadly-rifted, and as-yet poorly-studied Turkana Depression which separates the elevated Ethiopian and East African plateaus. We have so far revealed through body-wave tomography (Kounoudis et al., 2021), that the Depression does not lack mantle dynamic support in comparison to the plateaus, suggesting a significantly thinned crust, resulting from superposed Mesozoic and Cenozoic rifting, most likely explains its low elevations. Slow uppermost-mantle wavespeeds imply the presence of either melt-intruded mantle lithosphere or ponded asthenospheric material below lithospheric thin-spots induced by the region’s multiple rifting phases. To better illuminate the Depression’s lithosphere-asthenosphere system, we conduct a surface-wave analysis to image crust and uppermost-mantle structure using data from the NSF-NERC funded Turkana Rift Arrays Investigating Lithospheric Structure (TRAILS) project broadband seismic network. In particular, we investigate the presence of melt, whether the lithosphere is melt-rich, melt-poor, and/or if ponded zones of asthenosphere exist below variably thinned lithosphere. Group velocity dispersion curves, measured using data from local and regional earthquakes, yield the first high resolution fundamental mode Rayleigh-wave group velocity maps for periods between 4 and 40s for the Turkana Depression. In collaboration with the ongoing TRAILS GPS project, we explore how these results relate to present-day versus past episodes of extension.

 

Kounoudis, R., Bastow, I.D., Ebinger, C.J., Ogden, C.S., Ayele, A., Bendick, R., Mariita, N., Kiangi, G., Wigham, G., Musila, M. & Kibret, B. (2021). Body-wave tomographic imaging of the Turkana Depression: Implications for rift development and plume-lithosphere interactions. G3, 22, doi:10.1029/2021GC009782.

How to cite: Kounoudis, R., Bastow, I., Ebinger, C., Ogden, C., Ayele, A., Bendick, R., Mariita, N., Kianji, G., Musila, M., and Sullivan, G.: The Crust and Uppermost-Mantle Structure of the Turkana Depression: Insights from Surface-Wave Analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4683, https://doi.org/10.5194/egusphere-egu22-4683, 2022.

15:29–15:30
15:30–15:35
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EGU22-11973
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On-site presentation
Eleonora Braschi, Simone Tommasini, Giacomo Corti, and Andrea Orlando

The East African Rift System (EARS) is the classic example of an active continental rift associated with extension, deformation, lithosphere thinning, and generation of magmas from different mantle domains and depths. Magmatism and tectonics have always been closely linked and their mutual relationships concern many processes such as the kinematics and rates of extension, the passive versus active role of mantle upwelling and magma genesis. In addition, the spatial and temporal variations of the geochemical signature of magmas varies in response to different mantle domains contributing to their genesis (subcontinental lithosphere, asthenosphere and deeper mantle sources).

In this study we carefully screened an exhaustive geochemical database of basalts (including authors’ unpublished data) emplaced in the EARS to decipher the possible connection between different mantle domains, and the evolution and tectonic characteristics of the EARS. The geochemical data were subdivided according to spatial and temporal criteria: from a spatial point of view, the samples were ascribed to five groups, namely Afar, Ethiopia, Turkana depression, Kenya and Tanzania. From a temporal point of view, the magmatic activity of the EARS was subdivided into three main temporal sequences: 45-25 Ma, 25-10 Ma and 10-0 Ma.

The geochemical signature and radiogenic isotopes (Sr, Nd, Pb) of the selected basalts reveal significant spatial and temporal variations and permits to place important constraints on the contribution of subcontinental lithosphere, asthenosphere, and lower mantle in magma genesis

How to cite: Braschi, E., Tommasini, S., Corti, G., and Orlando, A.: Spatial and temporal variation of magmatism in the East African Rift System: influence of tectonics and different mantle domains, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11973, https://doi.org/10.5194/egusphere-egu22-11973, 2022.

15:35–15:36
15:36–15:41
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EGU22-1696
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On-site presentation
Laurent Jolivet, Cécile Allanic, Thorsten Becker, Nicolas Bellahsen, Justine Briais, Anne Davaille, Claudio Faccenna, Eric Lasseur, and Barbara Romanowicz

The origin of the Eocene-Oligocene European Cenozoic Rift System (ECRIS) is debated in terms of driving forces, far-field or near field, Alpine slab-pull or active plume. An analysis of residual (non-isostatic) topography over Africa and Europe reveals domains elongated parallel to the absolute motion of plates in a hot-spot reference frame. The East African Rift (EAR) and the ECRIS sit on top of such positive anomalies. A recent whole mantle tomographic model (French et al., 2013; French & Romanowicz, 2015; Davaille & Romanowicz, 2020) shows in addition that the low shear-wave velocity zones of the lower and upper mantle are organized with a bundle of vertical plumes and horizontal fingers pointing in the same direction parallel to the absolute motion of Africa and Eurasia, thus parallel to the main rifts. The case of the EAR and its magmatic extension toward the north across the Arabian Plate is particularly clear with several levels of such fingers. The northward migration of the first volcanism from Ethiopia to Armenia between the Eocene and the Late Miocene suggests that the asthenosphere moves faster than the plates and thus drives plate motion (Faccenna et al., 2013). We propose a simple model where plates are driven by basal drag, following an upwelling from the low-velocity anomalies below Africa and toward subduction zones. The EAR develops as lithospheric weak zones on top of the positive anomalies of residual topography due to the underlying low velocity anomalies elongated parallel to the absolute motion. This indicates an interplay between large-scale convection, a small-scale fingering instability, and lithospheric deformation. The development of the Eocene-Oligocene short-lived ECRIS and its interference with Mediterranean slab dynamics are then discussed in the framework of this simple model.

How to cite: Jolivet, L., Allanic, C., Becker, T., Bellahsen, N., Briais, J., Davaille, A., Faccenna, C., Lasseur, E., and Romanowicz, B.: Continental rifts and mantle convection: Insights from the East African Rift and a new model of the West European Rift System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1696, https://doi.org/10.5194/egusphere-egu22-1696, 2022.

15:41–15:42
15:42–15:47
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EGU22-2208
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ECS
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Highlight
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On-site presentation
Valentin Rime, Anneleen Foubert, Balemwal Atnafu, and Tesfaye Kidane

The Afar Depression forms a triple junction between three rift systems: the Red Sea Rift, the Gulf of Aden Rift and the Main Ethiopian Rift. Rifting began in the Oligocene after the eruption of the Ethiopian Flood Basalts. It represents a unique modern example of hotspot-influenced continental breakup. Its emerged position allows detailed field and remote sensing investigations. Important mapping efforts in the area during the 60s and 70s provided very valuable input for the understanding of the local geology but also for the development of global tectonic, volcanological and sedimentary concepts in continental rift settings.

This study presents the compilation of a new geological map which covers the complete Afar depression and includes its Phanerozoic sedimentary and magmatic cover. The map is based on extensive literature research, remote sensing and fieldwork. The geological history of the Afar Depression has also been reviewed. The map evidences the complexity of the rift system with the interaction of distinct tectonic plates, blocks, rift segments, sedimentary basins and volcanic areas that evolve through time and space. This integrative geological map and review is used to reassess and discuss aspects of the style, evolution, kinematics and dynamics of this rift system. Studying this unique modern example of active rifting will help in the better comprehension of rift processes and passive margin development worldwide.

How to cite: Rime, V., Foubert, A., Atnafu, B., and Kidane, T.: New mapping of the Afar Depression: towards the better understanding of rift dynamics in a hotspot-influenced continental rift zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2208, https://doi.org/10.5194/egusphere-egu22-2208, 2022.

15:47–15:48
15:48–15:53
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EGU22-2290
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ECS
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On-site presentation
Kevin Wong, David Ferguson, Penny Wieser, Daniel Morgan, Marie Edmonds, Amdemichael Zafu Tadesse, and Gezahegn Yirgu

Rifting in Ethiopia is predominantly driven by magmatic intrusion into the rifting crust. Unravelling the dynamics of lithospheric melt migration and storage is paramount to understanding the late-stage development of continental rifts. In particular, extensive geophysical observations of the structure and composition of rifting crust must be supported by petrology to provide a complete picture of rift-related magmatism. We present major element, trace element, and volatile element compositional data for olivine-hosted melt inclusions from the Boku Volcanic Complex (BVC), a monogenetic cone field in the north Main Ethiopian Rift. Through combined CO2-density-calibrated Raman spectroscopy and secondary ion mass spectrometry we assess the total CO2 concentrations within the melt inclusions allowing us to estimate pressures of entrapment via CO2-H2O solubility models. Our results show that primitive BVC melts carry up to 0.58 wt% CO2 (mean ~0.2 wt%), with as much as half of the CO2 in the melt inclusion present within shrinkage bubbles. Volatile solubility models suggest that these melts are stored over a narrow range of depths (10-15 km), consistent with geophysical data and implying the existence of focussed zone of magma intrusion at mid-crustal depths. The expansive range of trace element concentrations in the inclusions illustrate that, at the time of entrapment, compositional heterogeneity remains extant, and melts must therefore be stored in discrete magmatic bodies with limited mixing. Our results have implications for understanding the interplay between magma intrusion and extensional tectonics during continental break-up, such as magmatic compensation of crustal thinning and the thermo-mechanical effects of melt emplacement into the rifting crust.

How to cite: Wong, K., Ferguson, D., Wieser, P., Morgan, D., Edmonds, M., Tadesse, A. Z., and Yirgu, G.: Petrological evidence for focussed mid-crustal magma intrusion in the Main Ethiopian Rift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2290, https://doi.org/10.5194/egusphere-egu22-2290, 2022.

15:53–15:54
1.2. Young oceans, back-arcs and marginal seas
15:54–15:59
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EGU22-7186
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On-site presentation
Tihana Pensa, Abdulkader Afifi, Antoine Delaunay, and Guillaume Baby

Fossil carbonate reefs are common along rifts and rifted passive margins. They provide valuable paleoecological and paleogeographical information. Moreover, porous reef buildups are targeted as potential oil and gas reservoirs and sites for gas storage.

The Red Sea and Gulf of Suez contain several generations of reef deposits: (1) syn-rift Early and Middle Miocene reefs that formed along the eroded footwalls of normal faults, and (2) post-rift Pliocene-Holocene coastal reefs that split apart, subsided, and aggraded to form carbonate platforms by salt-driven raft tectonics. The Late Miocene lacks reefs due to evaporitic conditions. This study focuses on the uplifted Early-Middle Miocene reef deposits, which outcrop sporadically along the Arabian and African margins of the Red Sea, particularly the northern half, over a distance of ~1000 km. They are exhumed along the coastal plain at elevations of 50-150 meters. We studied several reefs on the Arabian side and carried out age determination implementing a revised planktonic foraminifera zonation and paleoenvironmental interpretation. We also used satellite images to identify and map similar exhumed reefs on the African side.

The Miocene reefs are located along the eroded footwalls of normal fault scarps that form the first or second marginal half grabens, usually sitting unconformably over the basement. The flat reef and back-reef lagoonal facies are often removed by erosion, but the dipping thick fore-reef talus breccias are preserved. The breccias are an unsorted mix of coral reef and back reef debris and also contain basement clasts. The linear fore-reef talus deposits follow along the fault scarps, revealing paleo-valleys incised into the hanging wall. Placing the reef on the basin-scale helps us distinguish the tectonic influence, accompanied by climate and eustatic sea-level variation, on shallow marine carbonates during rifting.

Mapping all published, newly discovered, and inferred outcrops along the African and Arabian coast of the Red Sea allow us to develop a new tectono-sedimentary model for reef evolution in the syn-rift setting. The proposed model explains the absence of the reef outcrops in the southern areas of the Arabian Red Sea and predicts subsurface zones where reef growth possibly took place. Nature of the contact between reef carbonates and the underlying Precambrian basement in conjunction with the consistently preserved fore-reef zone disclose the uplift history and erosion events prior and post reef growth. In addition, following the reef distribution, we developed a syn-rift paleogeographic model of the Red Sea.

How to cite: Pensa, T., Afifi, A., Delaunay, A., and Baby, G.: Tectonic control on the reef evolution in the Red Sea syn-rift basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7186, https://doi.org/10.5194/egusphere-egu22-7186, 2022.

15:59–16:00
16:00–16:05
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EGU22-1405
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ECS
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On-site presentation
Antoine Delaunay, Abdulkader Alafifi, Guillaume Baby, Jakub Fedorik, Paul Tapponnier, and Jérôme Dyment

This presentation describes the structure and morphologies associated with seafloor spreading in the Red Sea inferred from bathymetric, gravity, magnetic and seismic data. We show that the orientation of the structures is consistent with an Arabia-Nubia Euler pole located within the 95% confidence of Ar-Rajehi et al, (2010) Euler pole and with the tectonic model initially proposed by Girdler (1984). At the Red Sea scale, our model shows that a spreading axis extends along its entire length, even though it is mostly covered by allochthonous Middle Miocene salt and Late Miocene minibasins flowing inward from the margins. In the northern Red Sea, oceanic basement is only exposed through small windows within the salt, forming a series of deeps. The seafloor segments symmetrically bisect the new ocean in the south. Right-stepping transform faults that cluster near Jeddah, Zabargad and Ikhwan Islands offset the ridge axis as spreading is getting more oblique towards the Euler Pole. The northern, central and southern Red Sea segments display a well-developed mid-ocean ridge flanked by landward-dipping volcanic basement, typical of slow spreading ridges. In the northern magma poor spreading segment, mantle exhumation is likely at the transition between continental and oceanic crust. Transpression and transtension along transform faults accounts for the exhumation of the mantle on Zabargad Island as well as the collapse of a pull-apart basin in the Conrad deep.

We propose a new structural model for the Red Sea constrained by the geodetic rules of tectonic plates movements on a sphere. Finally, we discuss the effect of the Danakil microplate on the ridge morphology and show that the Arabia-Nubia-Danakil triple junction is likely located further north than previously described, around 18±0.5°N, where we observe a shift in the ridge axis orientation as well as in the spreading orientation.

How to cite: Delaunay, A., Alafifi, A., Baby, G., Fedorik, J., Tapponnier, P., and Dyment, J.: Structure and Morphology of the Mid-Ocean-Ridge in the Red Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1405, https://doi.org/10.5194/egusphere-egu22-1405, 2022.

16:05–16:06
16:06–16:11
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EGU22-10866
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ECS
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On-site presentation
Michael Andrés Avila Paez, Andreas Kammer, Camilo Andres Conde Carvajal, Alejandro Piraquive Bermudez, and Cristhian Nicolas Gomez Plata

Since the middle Triassic the long-lived convergent margin of western Gondwana evolved from a relatively steeply inclined into a flat lying slab setting that combined an extensional regime on the backarc side with the telescoping of crustal slices at the continental margin. In the Northern Andes the opening of Late Triassic basins is practically contemporaneous with the outwedging of lower crustal slices, that often alternate with intrusive sheets of S-type granites and mark the limit to a  non-metamorphic roof. A tectonic coupling between backarc collapse and the escape of lower crustal slices can be examined in detail in the northwestern flank of the Sierra Nevada de Santa Marta, a northern-most outlier of the North Andean basement. Remnants of a Late Triassic graben fill attest here to a block tilted toward the hinterland. Its tri-partite sedimentary sequence recycled material sourced from external parts of the continental margin. The basement of a more foreland-oriented block of the Sevilla belt is affected by outward-verging folds, which have formed under greenschist facies conditions in its upper and lower amphibolite conditions in its lower part. The succeeding Inner Santa Marta Metamorphic Belt consists of a stack of high-grade metamorphic basement slices separated by siliciclastic wedges metamorphosed under lower amphibolite conditions. The soles of the basement slices consist of migmatites with remobilized granitic pods and resulting folds oriented in a dip-slip direction. These structures are overprinted by a flattening and a second migmatitic event, which records peak P-T conditions of a lowest crustal level. Accordingly, they contain inclusions of ultramafic rocks. The time-equivalent correspondence between a supracrustal  backarc extension and a foreland-directed stacking of crustal slices suggests some similarity to the model  of a low-viscosity channel of a thickened orogenic crust. An important difference of this flat-slab setting resides, however, in a wholesale mobility of a strongly heated crust that constitutes the backarc and frontal position of this active margin.

How to cite: Avila Paez, M. A., Kammer, A., Conde Carvajal, C. A., Piraquive Bermudez, A., and Gomez Plata, C. N.: Backarc rifting as a response to a crustal collapse at the western Gondwana margin: The Triassic tectonic setting of the Sierra Nevada de Santa Marta, Northern Andes of Colombia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10866, https://doi.org/10.5194/egusphere-egu22-10866, 2022.

16:11–16:12
16:12–16:17
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EGU22-8715
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On-site presentation
Geoffroy Mohn, Jean-Claude Ringenbach, Michael Nirrengarten, Julie Tugend, Anders McCarthy, and Chao Lei

Marginal Seas are extensional basins formed in a convergent setting near active subduction zones. They are characterized by a short life (<25 Ma), as well as unstable and changing directions of seafloor spreading. However, the underlying processes involved in their formation from rifting to seafloor spreading initiation are still debated (supra-subduction convection/extension, slab-pull). This problem is further compounded by the fact that our understanding of continental breakup is primarily derived from the evolution of magma-poor and magma-rich Continent-Ocean Transitions (COT) of the Atlantic margins.

In this contribution, we characterize the tectono-magmatic processes acting during continental breakup by investigating the COT structures of three main Marginal Seas located in the Western Pacific, namely the South China Sea, the Coral Sea and the Woodlark Basin. All three examples formed under rapid extension rates and propagation of seafloor spreading. Although each marginal basin has its uniqueness, we show that these three marginal basins are characterized by a narrow COT (typically <~20 km), documenting the sharp juxtaposition of continental crust against igneous oceanic crust. The COT of the three basins shows that final extension is accommodated by the activity of one major low-angle normal fault. This extension is contemporaneous with important magmatic activity expressed by volcanic edifices, dykes and sills emplaced in the distalmost part of these margins. Such narrow COT suggests that a rapid shift from rifting to spreading.

The rapid localization of extensional deformation in a narrow area has major implications for partial melting generation. The evolution of extensional structures is controlled by the interplay of lithospheric thinning, asthenosphere upwelling and decompression melting. High extension rate prevents conductive cooling and lead to focus volcanic activity in a narrow area evolving rapidly in space and time to magmatic accretion. Causes for the fast extensions rates of Marginal Sea rifting are likely controlled by kinematic boundary conditions directly or indirectly controlled by nearby subduction zones. Such mode of breakup is probably not limited to marginal Seas but only enhanced in such settings.

How to cite: Mohn, G., Ringenbach, J.-C., Nirrengarten, M., Tugend, J., McCarthy, A., and Lei, C.: Continental breakup style of Marginal Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8715, https://doi.org/10.5194/egusphere-egu22-8715, 2022.

16:17–16:18
1.3. Continental and intercratonic rifts
16:18–16:23
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EGU22-9480
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On-site presentation
Maria Smirnova, Anton Latyshev, Ivan Panchenko, Petr Kulikov, Alexey Khotylev, and Rustam Garipov

Permian-Triassic rifts of the West Siberian basin compose one of the largest continental rift systems in the world. The Koltogor-Urengoy and Khudosey rifts of meridional strike are the main structures in the eastern part of the basin and are filled mainly by basaltic lavas with clastic sediments. However, in the central part of the West Siberian plate felsic lavas are widespread along with mafic volcanics. Here we present the detailed data on composition of lavas, whole-rock geochemistry, geophysical features and U-Pb ages from the Frolov-Krasnoleninsky region in the central part of the West Siberian basin.

Within the studied region, Permian-Triassic rifts of NW and NE strike are predominant. The main structure is Rogozhnikov-Nazym graben of NW strike, composed of rhyolite-dacitic lavas.  According to the seismic data, this volcanic area comprises multiple local eruptive centers (1-5 km in diameter). Lavas constitute the major part of the volcanic pile, while tuffs are subordinate (up to 15%). Deep boreholes did not reach the base of volcanic sequence, but its thickness exceed 0.5 km.

The main geochemical features of the Rogozhnikov-Nazym volcanics are: 1) acidic composition and increased alkali content; 2) signs of supra-subduction setting: Ta-Nb and Pb anomalies; 3) high ratios of all incompatible trace elements. According to these features, volcanic rocks of the Rogozhnikov-Nazym graben were formed in the setting of post-collisional extension. Furthermore, coeval felsic lavas are widespread in smaller structures of the Frolov-Krasnoleninskiy region and demonstrate similar geochemical characteristics.

We obtained 9 U-Pb (SHRIMP) ages from felsic lavas of the Rogozhnikov-Nazym graben and other rift structures. All samples yielded ages in the range from 254±2 to 248.2±1.3 Ma (Late Permian – Early Triassic). Thus, volcanic activity in the Frolov-Krasnoleninsky region was nearly synchronous to the main phase of Siberian Traps magmatism in the Siberian platform.

Volcanic rocks of the Frolov-Krasnoleninsky region constitute rifts of NW strike (mainly felsic lavas, including the Rogozhnikov-Nazym graben) and NE strike (mainly mafic lavas, geochemically similar to the Siberian Traps basalts). We suggest that orientation of rifts inherits two conjugate strike-slip fault systems, which mark the W-E compression during the preceding collisional event in the Early-Middle Permian, and the mechanism of extension is similar to pull-apart model. The contrasting composition of volcanics can be caused by different-depth zones of magma generation.

The Permian-Triassic volcanics are overlain by continental coal-bearing coarse-grained volcanoclastic sediments of the Chelyabinsk Group (Middle Triassic – Early Jurassic). These deposits fill the local depressions in the paleotopography. The Middle Jurassic clastic Tyumen Formation overlays both volcanic rocks and Chelyabinsk Group, covers almost the entire territory of the Frolov-Krasnoleninsky region and marks the initiation of post-rift subsidence in the West Siberian basin.

How to cite: Smirnova, M., Latyshev, A., Panchenko, I., Kulikov, P., Khotylev, A., and Garipov, R.: Permian-Triassic rifts of the West Siberian basin: evidence of voluminous felsic volcanic activity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9480, https://doi.org/10.5194/egusphere-egu22-9480, 2022.

16:23–16:24
16:24–16:29
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EGU22-6172
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Virtual presentation
Natalia Pravikova, Alexander Tevelev, Alexey Kazansky, Irina Kosheleva, Ivan Sobolev, Alexandra Borisenko, Egor Koptev, Petr Shestakov, and Jiří Žák

Early Carboniferous igneous rocks are widespread in the Southern Urals. We have obtained new stratigraphic and isotopic data on plutonic and volcanic complexes, allowing us to determine correlation of their age and to construct a new geodynamic model.

The prevailing tectonic setting in the Southern Urals during the Early Carboniferous was sinistral transtension. Volcanic and plutonic complexes in transtensional zones were synchronously formed along large submeridional orogen-parallel strike-slip faults, but are particularly abundant within two N–S-trending zones: Magnitogorsk and East Ural.

The upper Tournaisian–lower Visean sequence in the Magnitogorsk zone consists mainly of moderately alkaline volcanic rocks, basalt and rhyolite are predominant, but pyroclastic, volcano-sedimentary, terrigenous, and carbonate rocks are also widespread. The middle Visean sequence consists of moderately alkaline basalt, andesite, dacite including lavas, tuffs and tuffites. The thickness of the Lower Carboniferous volcanic group varies from 1200 to 5500 m. The age of the volcanic rocks has been proved by findings of foraminifera in limestone interbeds. The oldest volcanic rocks appear in upper Tournaisian, while the youngest are found in the middle upper Visean. New U–Pb zircon dating using SHRIMP is now in progress.

Volcanic rocks in the East Ural zone occur within a few tectonic sheets. The sequence consists of lavas and tuffs of basalt, basaltic andesite, andesite and rhyolite. The total thickness of the sequence varies from 800 to 1500 m. The age of the sequence is determined by findings of fossil plants as middle Visean.

We studied eight plutons in the Magnitogorsk and six in the East Ural zones. Most of them record several intrusive phases. The composition of the rocks varies from gabbro to granodiorites and granites from normal to moderately alkaline series. We combined our new isotopic data on zircons (SHRIMP) with published ages and came to the following conclusions.

  • Two main stages of Early Carboniferous plutonism can be distinguished in the Southern Ural. The first began simultaneously in both zones at the Devonian/Carboniferous boundary (ca. 356–357 Ma) and then changed to volcanic activity at around 346 Ma in the Magnitogosk zone and at around 340 Ma in the East Ural zone, respectively. The second stage began after the termination of volcanic activity and corresponds to 334–327 Ma interval in both zones. So, stages of active volcanism and plutonism alternate in time.
  • Early Carboniferous rifting began with intrusion of plutons, usually associated with transtensional zones under oblique collision. The subsequent volcanic stage corresponds to local extension. The next stage of plutonism began just after volcanism termination and marked a cessation of tectonic activity.

The reported study was funded by RFBR and Czech Science Foundation according to the research project № 19-55-26009. Centre of collective usage ‘Geoportal’, Lomonosov Moscow State University (MSU), provided access to remote sensing data.

How to cite: Pravikova, N., Tevelev, A., Kazansky, A., Kosheleva, I., Sobolev, I., Borisenko, A., Koptev, E., Shestakov, P., and Žák, J.: Early Carboniferous rifting in the Southern Urals: New isotopic dating of plutonic and volcanic complexes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6172, https://doi.org/10.5194/egusphere-egu22-6172, 2022.

16:29–16:30
16:30–16:35
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EGU22-9962
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Virtual presentation
Jordi Julià, Miro Döring, and Thabita Barbosa

NE Brazil is scarred by a number of aborted rift basins that developed from the same extensional stresses that lead to the opening of the South Atlantic. Extension started in Late Jurassic times, with the formation of an AfroBrazilian Depression south of the Patos Lineament, and continued through the Early Berriasian along two NS trending axes of deformation: Recôncavo-Tucano-Jatobá (RTJ) and Gabon-Sergipe-Alagoas (GSA). In the Late Berriasian - Early Barremian, rifting jumped North of the Pernambuco Lineament to progress along the NE-SW trending Cariri-Potiguar (CP) axis. In the Late Barremian, approximately coinciding with the opening of the Equatorial Atlantic, rifting aborted along the RTJ and CP axes and continued along the GBA trend eventually resulting in continental break-up. Extension-related magmatic activity seems to have been restricted to break-up along the marginal basins, although dyke swarms bordering the Potiguar basin (Rio Ceará-Mirim) seem to be associated to early extension stages in NE Brazil and three subparallel dolerite dykes, with K-Ar dates of 105±9 Ma, were inferred indirectly from aeromagnetic and outcrop data East of the RTJ axis. Aiming at better understanding the structure and evolution of the syn-rift basins of NE Brazil, a total of 20 seismic stations were deployed between October 2018 and January 2021 along the CP and RTJ trends. The deployment, funded by the national oil company Petrobras, included both broadband and short-period stations borrowed from the Pool de Equipamentos Geofísicos do Brasil. These stations complemented a number of permanent broadband stations belonging to the Rede Sismográfica do Brasil. Receiver functions were obtained for each of the seismic stations from teleseismic P-wave recordings and S-wave velocity models were developed from their joint inversion with dispersion velocities from an independent tomographic study. In the RTJ basins, our results show that the crust is about 41 km thick and displays a thick (5-8 km) layer of fast-velocity material (> 4.0 km/s) at its bottom; in the Potiguar basin, our results show a thinner crust of about 30-35 km underlain by an anomalously slow (4.3-4.4 km/s) uppermost mantle. We argue that those anomalous layers are the result of syn-rift and/or post-rift magmatic intrusions, which would have had the effect of increasing velocity at lower crustal levels under the RTJ basins and decreasing velocity at uppermost mantle depths under the Potiguar basin. If correct, ou interpretation would imply that, in spite of an overall lack of evidence at shallow levels, deep magmatic processes have played a role in the formation and evolution of the syn-rift basins of NE Brazil.

How to cite: Julià, J., Döring, M., and Barbosa, T.: Crustal architecture under the NE Brazil syn-rift basins from receiver functions: Evidence of deep magmatic processes., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9962, https://doi.org/10.5194/egusphere-egu22-9962, 2022.

16:35–16:36
16:36–16:40
Coffee break
Chairpersons: Giacomo Corti, Sylvie Leroy, Frank Zwaan
17:00–17:03
2.1. Rifted margins
17:03–17:13
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EGU22-11260
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solicited
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Virtual presentation
Francois Sapin

Rifted margins are the result of the successful process of thinning and breakup of continents leading to the formation of new oceanic lithosphere. Observations on rifted margins are now integrating an increasing amount of multi-channel seismic data and drilling of several Continent-Ocean Transitions. Based on large scale geometries and domains observed on high-quality long-offset seismic lines, we illustrate a simple classification based on mechanical behavior and magmatic production. Therefore, rifted margins are not divided into opposing types, but described as a combination and continuum that can evolve through time and space from ductile to brittle mechanical behavior on one hand and from magma-poor to magma-rich on the other hand.

For instance, margins such as the Mauritania-Senegal Basin evolve north to south from a magma-poor to a magma-rich margin. Margins such as the Vøring one suffered different rifting episodes evolving from ductile deformation in the Devonian to more brittle and magma-poor rifting in the Cretaceous prior to a final magma-rich breakup in the Paleogene.

Thanks to these examples and to some others, we show the variability of the rifted margins worldwide but also along strike of a single segment and through time along a single margin in order to explore and illustrate some of the forcing parameters that can control the initial rifting conditions but also their evolution through time.

How to cite: Sapin, F.: Rifted margins classification and forcing parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11260, https://doi.org/10.5194/egusphere-egu22-11260, 2022.

17:13–17:14
17:14–17:19
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EGU22-13043
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ECS
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On-site presentation
Nicholas Montiel, Emmanuel Massini, Luc Lavier, and Othmar Müntener

A holistic understanding of rift initiation, evolution, and variation is made complicated by the difficulties of deep seismic imaging, limited modern examples of continental rifting, and few accessible outcrops of fossil rifted margins. In particular, The temporal structural and rheological evolution of the mantle lithosphere during riftingis poorly constrained. The mantle lithosphere rheology controls lithospheric strength at initiation, but how deformation is partitioned between the crust and mantle,  and how the paths for melt migration from the asthenosphere to the rift surface evolve during rifting is fundamental for our understanding of the rift-to-drift evolution .
Here, we use elastoplastic-viscoelastoplastic modeling in concert with published deep seismic profiles of Atlantic rifted margins and geological insights from the Lanzo peridotite outcrops in the Alps to propose a new mode of extensional tectonics in the subcontinental mantle. We run a series of dynamic models varying initial conditions and mechanisms of deformation localization in the mantle lithosphere consistent with mechanisms of ductile shear zone formation observed at slow spreading centers. Models and geophysical surveys show homologous, sigmoidal reflectors in the mantle, a reversal of fault vergence as seafloor spreading develops, exhumation of the mantle, and increasing magmatic accretion. Geological evidence, along with the coincidence of magmatic accretion and extensional structures in the mantle, suggests that faults in the mantle may serve as conduits for melt, resulting in bright reflectors on seismic profiles.

How to cite: Montiel, N., Massini, E., Lavier, L., and Müntener, O.: Characterizing mantle deformation processes during the rift-to-drift transition at magma-poor margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13043, https://doi.org/10.5194/egusphere-egu22-13043, 2022.

17:19–17:20
17:20–17:25
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EGU22-8003
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ECS
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On-site presentation
Julie Linnéa Sehested Gresseth, Per Terje Osmundsen, and Gwenn Péron-Pinvidic

Within rifted margins, the necking domain corresponds to the area where drastic reduction in basement thickness leads the crust to attain a wedge-shape. The crustal thinning occurs along detachment fault systems typically recording displacements in the order of 10s of kilometers. These systems commonly shape the crustal taper and eventually the taper break, where crustal thickness is thinned to 10 km or less. In recent years, it has become clear that evolutionary models for detachment fault systems remain unsatisfactory as the well-known principles for smaller magnitude fault systems are not fully applicable to these large-magnitude systems. Consequently, the detailed responses in the foot- and hanging walls and associated basin sedimentation within detachment fault systems and necking domains remain poorly understood compared to those observed in extensional half-graben basins.

We use interpretation of 3D- and 2D seismic reflection data from the Mid-Norwegian rifted margin to discuss the effects of lateral interaction and linkage of extensional detachment faults on the necking domain configuration. We investigate how the structural evolution of these detachment faults interact with the effects of isostatic rollback to produce complex 3D geometries and control the configuration of the associated supradetachment basins. The study area demonstrates how successive incision may induce a complex structural relief in response to faulting and folding. In the proximal parts of the south Vøring and northeastern Møre basins, the Klakk and Main Møre Fault Complexes form the outer necking breakaway complex and the western boundary of the Frøya High. We interpret the previously identified metamorphic core complex within the central Frøya High as an extension-parallel turtleback-structure. The now eroded turtleback is flanked by a supradetachment basin with two synclinal depocenters resting at the foot of the necking domain above the taper break. We attribute footwall and turtleback exhumation to Jurassic-Early Cretaceous detachment faulting along the Klakk and Main Møre Fault Complexes. The study area further demonstrates how detachment fault evolution may lead to the formation of younger, successively incising fault splays locally. Consequently, displacement may occur along laterally linked fault segments generated at different stages in time. Implicitly, the detachment fault system may continue to change configuration and therefore re-iterate itself and its geometry during its evolution.

How to cite: Gresseth, J. L. S., Osmundsen, P. T., and Péron-Pinvidic, G.: Evolution of detachment fault systems within necking domains: insights from the Frøya and Gossa Highs, mid-Norwegian margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8003, https://doi.org/10.5194/egusphere-egu22-8003, 2022.

17:25–17:26
17:26–17:31
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EGU22-1799
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Virtual presentation
Gaël Lymer, Conrad Childs, and John Walsh

Corrugated detachments are fundamental crustal structures found in many extensional systems and plate tectonic boundaries, including mid-oceanic ridges and rifted margins. Direct observations of the complete geometry of extensional detachments are rare and our understanding of detachment fault structures and the mechanisms of development of high-angle normal faults and their rotation to lower angles mainly relies on proxy observations, for example seismicity trends, and numerical modelling.

We present interpretations of a high-resolution 3D seismic reflection survey from the hyperextended domain of the Porcupine Basin, Offshore West of Ireland. The 3D data image a highly reflective corrugated surface, the P reflector, that we interpret as an extensional detachment preserved in its slip position that likely developed at the top mantle surface during Jurassic hyperextension of the basin. Within the 3D data, the P reflector covers an area 95 km long and 35 km wide and has a domal shape that is elongate in the N-S direction with a crest at ~6.3 s two way travel time. It is the first time to our knowledge that 3D seismic data has imaged a complete detachment in the hyperextended area of a rifted margin, including its domal shape, the breakaway structures, and the linkage between the steep and shallow segments of the detachment. The resolved texture and geometry of the detachment and its relationship with overlying faults provide a basis for refining current models of detachment formation accommodating extreme extension.

Steep west-dipping faults mark the western frontal margin of the detachment. The steep faults pass eastward into shallower, predominantly west-dipping faults that appear to merge downwards with the P reflector. The P reflector has pronounced E-W corrugations, interpreted to indicate the detachment slip vector. The reflector is also characterised by abrupt changes in dip across N-S transverse ridges. These ridges are spaced on average 10 km apart, they coincide with lines of intersection between the P reflector and large overlying faults, and they often mark the termination of detachment corrugations. We interpret these ridges as recording former locations of the western boundary of the detachment so that they indicate a step-wise westward propagation of the P reflector. While it is generally accepted that detachments develop by oceanward propagation, we suggest that the faceted nature of the detachment indicates that this process is a punctuated one and that the clearly imaged transverse ridges record the oceanward stepping of the detachment with the initiation of a new family of steep faults.

We propose a new concept for the growth of detachments that may be applicable to other detachments that accommodate extreme extension, for example at mid-oceanic slow and ultra-slow spreading ridges.

How to cite: Lymer, G., Childs, C., and Walsh, J.: Punctuated propagation of a corrugated extensional detachment offshore West of Ireland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1799, https://doi.org/10.5194/egusphere-egu22-1799, 2022.

17:31–17:32
17:32–17:37
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EGU22-3259
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On-site presentation
Rachid Essamoud, Abdelkrim Afenzar, and Ahmed Belqadi

The continental deposits of the Triassic basins developed along the eastern margin of the Central and North Atlantic show a similar sedimentological evolution, as those of the western margin resulting from the interaction of various processes.

The examples chosen in this work are those of the Mohammedia-Benslimane-ElGara-Berrechid basin MBEB in the Moroccan meseta that we studied in detail in the field, and that we tried to compare with Portugal which is on the same East Atlantic margin.

At the begininig of the Mesozoic, the northwestern part of the African continent was affected by an initial fracturing associated with the early stages of the opening of the Central Atlantic (Atlantic rift) during which several Moroccan Triassic basins are open.

The Mohammedia-Benslimane-ElGara-Berrechid basin is part of the Moroccan western Triassic province, which corresponds to all the basins of the Moroccan Atlantic margin in direct relation with the Atlantic rift. In this basin, an asymmetric rift is set up on the old Hercynian structures during the Carnien-Norien, the paroxysm is reached at the Trias-Lias passage with the installation of basalts (CAMP: Central Atlantique Magmatic Province).

During rifting (syn-rift stage in the Upper Triassic), the MBEB basin experienced three major phases of sediment filling. The first phase is purely continental, the first deposits to arrive in the opening basin are of proximal fluvial origin. Subsequently, the decrease of the paleopente and the rise of the base level generated paleoenvironmental changes in the basin (2nd phase), and the deposition system evolved towards distal environments. During the third phase, the syn-rift sedimentary series recorded a marine incursion in the late Triassic with saliferous sedimentation. This marine intervention is deduced from the presence of a thick saliferous series with a large lateral extension and whose isotopic ratios of sulfur and bromine contents indicate their marine origin. These marine waters are probably of Tethysian origin and are also linked to the opening of the Proto-Atlantic.

In Portugal, the Upper Triassic is represented by two formations in the north of the Lusitanian basin (Palain, 1976): Silves Fm which is fluvial sandstone and Dagorda Fm which includes first dolomites and then evaporites. In this Portuguese basin, the proximal-distal fluvial transition took place at the Norien-Rhétien limit. This also rift-type basin was filled with continental fluvial and alluvial clastic rocks of the Silves Formation, largely derived from the adjacent Iberian highlands of the Meseta. Locally, black shales are present at the top of the Silves and may represent the first marine incursion into the basin.

The comparison between the two basins shows that they followed a similar evolution at the base and in the middle of the series but at the top the MBEB basin presented thick layers of evaporites while that of Portugal presented mainly dolomites attributed to paralic facies.

Palain, C., 1976. Une série détritique terrigene; 'les grès de silves'; Trias et Lias inférieur du Portugal. Mem. Serv. Geol. Portugal, p. 25 (377 pp.)

How to cite: Essamoud, R., Afenzar, A., and Belqadi, A.: Triassic sedimentation on the Eastern Atlantic margin: two examples from Moroccan Meseta and Portugal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3259, https://doi.org/10.5194/egusphere-egu22-3259, 2022.

17:37–17:38
17:38–17:43
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EGU22-11336
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On-site presentation
Mohamed Gouiza

The breakup of Pangaea in Early Mesozoic times initiated first in the Central Atlantic region, where Triassic to Early Jurassic lithosphere extension led to continental breakup and oceanic accretion. The Central Atlantic rifted margins of NW Africa and eastern North America exhibit complex along-strike variations in structural configuration, crustal geometries, and magmatic budget at breakup. Quantifying these lateral changes is essential to understand the tectonic and geodynamic processes that dominated rifting and continental breakup. The existing seismic refraction lines along the African side and its American conjugate provide good constraints on the 2D crustal architecture of several Central Atlantic margins. However, they are insufficient to quantify the ambiguous lateral variations.

This work examines the central segment of the Moroccan Atlantic margin, which is named here the Sidi Ifni-Tan Tan margin. Using 2D seismic reflection and well data, we quantify the stratigraphic and structural architecture of the margin. We then use this to constrain 2D and 3D gravity models, to predict crustal thickness and types. Ultimately, our results are integrated with previous findings from the conjugate Nova Scotia margin, on the Canadian side, to propose a rift to drift model for this segment of the Central Atlantic and discuss the tectonic processes that dominated rifting and decided the fate of continental breakup.

How to cite: Gouiza, M.: Rift to drift evolution and crustal structure of the Central Atlantic: the Sidi Ifni-Nova Scotia conjugate margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11336, https://doi.org/10.5194/egusphere-egu22-11336, 2022.

17:43–17:44
17:44–17:49
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EGU22-5938
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On-site presentation
Julie Tugend, Nick Kusznir, Geoffroy Mohn, Mark Deptuck, Kris Kendell, Fraser Keppie, Natasha Morrison, and Russell Dmytriw

The palaeobathymetric evolution of rifted margins during continental breakup is complex. We investigate the subsidence of Late Triassic to Early Jurassic evaporitic sequences in the proximal and distal parts of the Scotian margin that formed during the opening of the Central Atlantic Ocean.

We use a 3D flexural backstripping technique, which incorporates decompaction and post-breakup reverse thermal subsidence modelling applied to key stratigraphic intervals through the Jurassic down to the Late Triassic base salt. The isostatic evolution of rifted margins depends on crustal thinning, lithosphere thermal perturbation and melt production during rifting and breakup. Quantitative analysis of seismic reflection and gravity anomaly data together with subsidence analysis have also been used to determine crustal thickness variations and ocean–continent transition structure, and to constrain the along strike variability in breakup related magmatism and crustal composition.

Reverse post-breakup subsidence modelling to the Late Triassic base salt restores this horizon at breakup time to near sea level in the proximal domains of the Scotian margin where the continental crust was only slightly thinned during rifting. In contrast, predicted palaeobathymetry of the base salt surface restored to breakup time is greater than 2 to 3 km in the distal parts of the margin where the continental crust was highly thinned (<10km) close to the ocean-continent-transition. One possible interpretation of this is that while the proximal salt underwent post-rift thermal subsidence only, the distal salt was deposited during the latest stage of rifting focused along the distal domains of the Scotian margin, where it underwent additional tectonic subsidence from crustal thinning. This observed difference between the subsidence of proximal and distal salt has been observed elsewhere on the South Atlantic margins (e.g., the Angolan Kwanza margin) and illustrates the complexity of the subsidence and palaeobathymetric evolution of distal rifted margins during breakup.

The deposition of Triassic evaporites occurred before and after the emplacement of the Central Atlantic Magmatic Province (CAMP). The impact of the CAMP on rifting, crustal structure and palaeobathymetric evolution of the Nova Scotia remains to be determined. We do not exclude an additional positive dynamic topography effect at breakup time related to the CAMP magmatic event.

How to cite: Tugend, J., Kusznir, N., Mohn, G., Deptuck, M., Kendell, K., Keppie, F., Morrison, N., and Dmytriw, R.: Palaeobathymetric evolution of the Nova Scotia rifted margin during the Central Atlantic Ocean opening, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5938, https://doi.org/10.5194/egusphere-egu22-5938, 2022.

17:49–17:50
2.2. Geodynamic modelling
17:50–17:55
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EGU22-9052
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Presentation form not yet defined
Oblique continental rifting. Insights from 3-D forward geodynamic modelling coupled with surface processes and application to the Equatorial passive margins formation.
(withdrawn)
Ritske S. Huismans, Thomas Theunissen, Delphine Rouby, Sebastian G. Wolf, and Dave May
17:55–17:56
17:56–18:01
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EGU22-5758
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ECS
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Virtual presentation
Derek Neuharth, Sascha Brune, Thilo Wrona, Anne Glerum, Jean Braun, and Xiaoping Yuan

During the formation of rifted continental margins, a rift evolves through a number of stages that produce major sedimentary basins and distinct rifted margin domains. While these domains have been classified based on the resulting structures and crustal thickness seen in geophysical data, the evolution of the fault network that produces these domains is not as well understood. Further, margin architecture may be influenced by erosion and sedimentation. Previous studies have qualitatively examined how faults respond to sedimentation during rifting, but there has not been a quantitative study on how variable surface processes efficiency affects fault network properties and the effect this has on rift evolution.

In this study we use a two-way coupling between the geodynamic code ASPECT (Kronbichler et al., 2012) and the surface processes code FastScape (Braun and Willett, 2013) to run 12 high-resolution 2D rift models that represent asymmetric, symmetric, and wide rift types (Neuharth et al., in review). For each rift type, we vary the surface process efficiency by altering the bedrock erodibility (Kf) from no surface processes to low (Kf = 10-6 m0.2/yr), medium (10-5), and high efficiency (10-4). To analyze these models, we use a novel quantitative fault analysis toolbox that extracts discrete faults from our continuum models and correlates them through space and time (https://github.com/thilowrona/fatbox). This toolbox allows us to track faults and their properties such as the number of faults, their displacement, and cumulative length, to see how they evolve through time, as well as how these properties change given different rifting types and surface processes efficiency.

Based on the evolution of fault network properties, we find that rift fault networks evolve through 5 major phases: 1) distributed deformation and coalescence, 2) fault system growth, 3) fault system decline and basinward localization, 4) rift migration, and 5) continental breakup. Each of these phases can be correlated to the rifted margin domains defined from geophysical data (e.g., proximal, necking, hyperextended, and oceanic). We find that surface processes do not have a large impact on the overall evolution of a rift, but they do affect fault network properties by enhancing strain localization, increasing fault longevity, and reducing the total length of a fault system. Through these changes, they can prolong rift phases and delay continental breakup with increasing surface process efficiency. To summarize, we find that surface processes do not change the overall evolution of rifts, but they do affect fault growth and as a result the timing of rifting.

 

Braun, J., and Willett, S.D., 2013, A very efficient O(n), implicit and parallel method to solve the stream power equation governing fluvial incision and landscape evolution: Geomorphology, v. 180–181, p. 170–179, doi:10.1016/j.geomorph.2012.10.008.

Kronbichler, M., Heister, T., and Bangerth, W., 2012, High Accuracy Mantle Convection Simulation through Modern Numerical Methods.: Geophysical Journal International, v. 191, doi:doi:10.1111/j.1365-246x.2012.05609.x.

Neuharth, D., Brune, S., Wrona, T., Glerum, A., Braun, J., and Yuan, X.P., (in review at  Tectonics), Evolution of rift systems and their fault networks in response to surface processes, [preprint], doi: https://doi.org/10.31223/X5Q333

How to cite: Neuharth, D., Brune, S., Wrona, T., Glerum, A., Braun, J., and Yuan, X.: Evolution of rift systems and their fault networks in response to surface processes , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5758, https://doi.org/10.5194/egusphere-egu22-5758, 2022.

18:01–18:02
18:02–18:07
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EGU22-12619
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ECS
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On-site presentation
Raghu Gudipati, Marta Pérez-Gussinyé, Miguel Andres-Martinez, Mario Neto-Araujo, and Jason Phipps Morgan

When continental lithosphere is extended to break-up it forms two conjugate passive margins. In many instances, these margins are asymmetric: while one is wide and extensively faulted, the conjugate thins more abruptly and exhibits little faulting. Recent studies have suggested that this asymmetry results from the formation of an oceanward-dipping sequential normal fault array and rift migration leading to the observed geometry of asymmetric margins. Numerical models have shown that fault sequentiality arises as a result of asymmetric uplift of the hot mantle towards the hanging wall of the active fault. The preferential localization of strain reinforced by strain weakening effects is random and can happen on either conjugate. However, along the long stretch of the South Atlantic margins, from the Camamu-Gabon to the North Santos-South Kwanza conjugates, the polarity can be very well correlated with the distance of the rift to nearby cratonic lithosphere. Here, we use numerical experiments to show that the presence of a thick cratonic root inhibits asthenospheric flow from underneath the craton towards the adjacent fold belt, while flow from underneath the fold belt towards the craton is favoured. This enhances and promotes sequential faulting and rift migration towards the craton and resulting in a wide faulted margin on the fold belt and a narrow conjugate margin on the craton side, thereby determining the polarity of asymmetry, as observed in nature.

How to cite: Gudipati, R., Pérez-Gussinyé, M., Andres-Martinez, M., Neto-Araujo, M., and Phipps Morgan, J.: Passive margin asymmetry and its polarity in the presence of a craton, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12619, https://doi.org/10.5194/egusphere-egu22-12619, 2022.

18:07–18:08
18:08–18:13
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EGU22-9420
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On-site presentation
Gang Lu and Ritske Huismans

Breakup volcanism along rifted passive margins is highly variable in time and space. The factors controlling magmatic activity during continental rifting and breakup are not resolved and controversial. Here we use numerical models to investigate melt generation at rifted margins with contrasting rifting styles corresponding to those observed in natural systems. Our results demonstrate a surprising correlation of enhanced magmatism with margin width. This relationship is explained by depth-dependent extension, during which the lithospheric mantle ruptures earlier than the crust, and is confirmed by a semi-analytical prediction of melt volume over margin width. The results presented here show that the effect of increased mantle temperature at wide volcanic margins is likely over-estimated, and demonstrate that the large volumes of magmatism at volcanic rifted margin can be explained by depth-dependent extension and very moderate excess mantle potential temperature in the order of 50-80 °C, significantly smaller than previously suggested.

How to cite: Lu, G. and Huismans, R.: Melt volume at Atlantic volcanic rifted margins controlled by depth-dependent extension and mantle temperature, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9420, https://doi.org/10.5194/egusphere-egu22-9420, 2022.

18:13–18:14
18:14–18:19
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EGU22-8663
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ECS
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Highlight
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Virtual presentation
Gaetano Ferrante, Eleonora Rivalta, and Francesco Maccaferri

Continental rifting can be accompanied by a large amount of volcanism, which is often observed to shift from the inside of the rift basin to its flanks and conversely, but the controls on this variability are still unclear. Maccaferri et al. (2014) proposed that elastic stresses under rifts are dominated by gravitational unloading due to the excavation of the graben. According to this model, off-rift volcanism follows the creation of a stress barrier below the rift that drives dikes diagonally away from the rift axis, or stops their ascent altogether so that they get stuck as lower crustal sills. The Maccaferri et al. (2014) model is however based on simplyfied assumptions that need to be relaxed to further test its validity. In particular, the model neglects the effect of the accumulating crustal intrusions on ascending dikes. Here we build on this model to explain the spatio-temporal evolution of rift volcanism in terms of the reorientation of principal stresses in the crust due to the progressive unloading of a rift basin with time. To do so, we extend the dike propagation boundary element code used by Maccaferri et al. (2014) to account for the stresses generated by previously ascended dikes. We find that volcanism in rift zones starts inside the rift depression for small values of basin depth. The deepening of the rift is accompanied by the development of a stress barrier under the basin which deflects ascending dikes, causing a shift of surface volcanism from the inside to the flanks. The intensification of the barrier due to further deepening of the basin promotes the formation of lower crustal sill-like structures that pile up under the rift, shallowing the depth at which magma is injected. This eventually leads to dikes being injected from above the stress barrier, moving surface volcanism back to the axial part of the rift. We compare the results of our model to observations of evolving volcanism and crustal structure for rifts of different graben width and depth.

How to cite: Ferrante, G., Rivalta, E., and Maccaferri, F.: Spatio-temporal evolution of rift volcanism driven by progressive crustal unloading, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8663, https://doi.org/10.5194/egusphere-egu22-8663, 2022.

18:19–18:20
18:20–18:25
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EGU22-12955
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Virtual presentation
Thomas Theunissen, Ritske S. Huismans, Gang Lu, and Nicolas Riel

The choice of crustal and mantle densities in numerical geodynamic models is usually based on convention. The isostatic component of the topography is, however, in most if not all cases not calibrated to fit observations resulting in not very well constrained elevations. The density distribution on Earth is not easy to constrain because it involves multiple variables (temperature, pressure, composition, and deformation). We provide a review and global analysis of the topography of the Earth showing that elevation of stable continents and active mid-ocean ridges far from hotspots on average is +400 m and -2750 m respectively. We show that density values for the crust and mantle, commonly used for isostatic modeling result in highly inaccurate prediction of topography. We use thermodynamic calculations to constrain the density distribution of the continental lithospheric mantle, sub-lithospheric mantle, the mid-ocean ridge mantle, and review data on crustal density. We couple the thermo-dynamic consistent density calculations with 2-D forward geodynamic modelling including melt prediction and calibrate crustal and mantle densities that match the observed elevation difference. Our results can be used as a reference case for geodynamic modeling that accurately fits the relative elevation between continents and mid-ocean ridges consistent with geophysical observations and thermodynamic calculations. 

How to cite: Theunissen, T., Huismans, R. S., Lu, G., and Riel, N.: Relative continent/mid-ocean ridge elevation: a reference case for isostasy in geodynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12955, https://doi.org/10.5194/egusphere-egu22-12955, 2022.

18:25–18:26
End Block 2
End session