TS6.3

The Gulf of Mexico opened as a Late Triassic-Mid Jurassic continental rift that was first largely covered by the Mid-Jurassic Louann Salt and later split apart by a triangular-shaped oceanic crust. Salt in the Gulf of Mexico largely hampers the imaging and interpretation of underlying pre-salt and crustal geometries, which are fundamental for assessing the early kinematic evolution of the margin. To better define these deep geometries and their lateral variations, we built three seismic-based crustal-scale cross-sections across the Florida-Yucatan conjugate margins, in the areas where the Mid-Jurassic salt unit is thinner.

Seismic-based cross-sections image the architecture of rifting and the geometries of the continental and oceanic crusts and the transition between them (ocean-continent transition, OCT). They show a meaningful along-strike variation: the South Florida-East Yucatan area is characterized by a narrower rifted continental crust that evolves sharply to oceanic crust whereas in the North Florida and central-western Yucatan areas, the rifted continental crust is wider and the transition to the oceanic crust corresponds to a narrow magmatic or exhumed mantle domain. In the rifted continental crust, seismic profiles image doubly-verging basement faults organized into decoupled and coupled rift domains. The geometrical and cross-cutting relationships between these basement faults, the Louann Salt and the underlying pre-salt sequence indicates a progressive migration of rifting from proximal to distal domains and from the central and north-eastern to the south-eastern Gulf of Mexico.  

Bulk continental crust extension was determined using the area balancing method. Estimated horizontal extension values vary from a minimum of ∼120 km in the South Florida-East Yucatan conjugate to a minimum of ∼240 km in the North Florida-Central Yucatan conjugate, being systematically larger in the northern margin. Crustal domains identified in the cross-sections were laterally correlated and westwards extended considering gravity and magnetic anomalies data to build a regional-scale, crustal domains map of the Gulf of Mexico. This map, together with the crustal extension estimates, has been used as the reference to carry out a plate-scale reconstruction of the Gulf of Mexico from the early rifting stages to the end of oceanic spreading.

Based on our observations and considering previous models, we propose that the study area evolved from an early rift involving magmatism, to a magma-poor margin, with continental break-up (OCT formation) being characterized by mantle exhumation and associated magmatism along the North Florida and central-western Yucatan areas.

How to cite: Izquierdo-Llavall, E., Ringenbach, J. C., Sapin, F., Rives, T., Callot, J.-P., and Nielsen, C.: Crustal structure and along-strike variations in the Gulf of Mexico conjugate margins: From early rifting to oceanic spreading, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11453, https://doi.org/10.5194/egusphere-egu22-11453, 2022.

With increased geophysical scrutiny of the NE Newfoundland-Irish margin pair (North Atlantic), the previously assumed conjugate relationship and rift-perpendicular extension between the Flemish Cap and Goban Spur are increasingly questioned. We present multichannel reflection profiles along the Flemish Cap, the Porcupine Bank, and the Goban Spur, along which structural domains (proximal, necking, hyperextended, and/or exhumed mantle domains included) are defined. Features of each structural domain along these profiles on the Flemish Cap and the Goban Spur are strikingly different, whereas similar structural features are observed in the necking domains along seismic profiles on the Porcupine Bank and the Flemish Cap. The variability in basement features suggests oblique rifting between the Flemish Cap and the Goban Spur-Porcupine Bank region, as well as a connection between the Porcupine Bank and the Flemish Cap during Early Jurassic rifting. This understanding is consistent with crustal thickness evolution calculated from a deformable plate reconstruction model that is locally updated based on seismic interpretation constraints and previously published plate reconstructions. The updated deformable plate model shows varying extension obliquity between the Porcupine Bank, Goban Spur, and Flemish Cap, which are strongly influenced by inherited Caledonian and Variscan structures, resulting in the conclusion that the Flemish Cap and the Goban Spur were not conjugate margins prior to the opening of the modern North Atlantic Ocean.

How to cite: Yang, P. and Welford, J. K.: Conjugate no more: redefining the pre-rift relationship between the Flemish Cap and the Goban Spur prior to the North Atlantic opening, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2780, https://doi.org/10.5194/egusphere-egu22-2780, 2022.

The Troodos ophiolite of Cyprus hosts a fossil spreading ridge at the Solea graben, whose last magmatic activity has been previously dated to 94.3±0.5 Ma. To study the evolution of a dying ridge, we collected structural geologic data and oriented specimens from the mantle section (serpentinized peridotites, pegmatitic dykes, pyroxenite and wehrlite intrusions) and lower crust (layered gabbros and massive gabbros) for paleomagnetic and rock magnetic analyses. Our results revealed a systematic pattern of horizontal axis rotations (i.e., tilt) in the region to the west of the Solea spreading axis, involving upper crust, lower crust, and upper mantle. Horizontal axis rotations vary in magnitude between ~20° to ~90° within the studied area, with the largest tilts observed to the west of the exposed mantle section at Mt. Olympus, and the smallest tilts observed near the NNW-SSE trending Troodos Forest-Amiandos fault system. This rotation pattern conflicts with previous interpretations considering the Troodos Forest-Amiandos fault as an oceanic detachment, and rather indicates the existence of deep-rooted listric faults that dismembered the Solea spreading ridge after the final phase of spreading.

Paleomagnetic directions from serpentinized peridotites indicate that serpentinization occurred both before and during dismemberment of the ridge by listric faulting. As these directions also record a well-studied regional 90° counter-clock-wise rotation of the Troodos ophiolite, we constrained the timing of ridge dismemberment and associated serpentinization between ~94 Ma and the beginning of the regional microplate rotation in the Turonian, hence encompassing a relatively short period of time of 2-4 Myr that well coincides with hydrothermal alteration in nearby plagiogranites dated at ~92–90 Ma.

How to cite: Advokaat, E., Maffione, M., Burton-Johnson, A., and Dekkers, M.: Anatomy of a dying spreading ridge: paleomagnetic evidence for horizontal axis rotations in the Troodos Ophiolite, Cyprus, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-957, https://doi.org/10.5194/egusphere-egu22-957, 2022.

Throughout Earth’s history, the movement, suturing, and rifting of tectonic plates in the Wilson cycle often takes advantage of lithospheric weaknesses and pre-existing plate boundaries. Continental rifting and subduction initiation represent arduous phases of this cycle for plate divergence and convergence, respectively, where strain is not yet focused into a narrow and mature plate boundary. Here we present an analysis of the Puysegur margin to demonstrate how past tectonic regimes create inherited lithospheric structures that facilitate subsequent stages of the Wilson cycle.

The Puysegur margin is a young subduction zone and forms the northern segment of the Australian-Pacific plate boundary south of New Zealand, which has evolved from divergence to strike-slip and recently to oblique convergence, all in the last ~45 million years. Magnetic anomalies and curved fracture zones located south of the Puysegur segment show the divergent phase involved seafloor spreading and the formation of new oceanic lithosphere. However, these features are not present in the upper Pacific plate at the latitudes of the Puysegur margin, and the lack of quality seismic images in this region hampered our understanding of the local crustal structure, which was assumed to be a northward extension of the oceanic domain. A deep penetrating multichannel reflection (MCS) and ocean-bottom seismometer (OBS) dataset was acquired in 2018 with the R/V Langseth and provided new high-quality seismic images of the crustal structure along the Puysegur margin.

Our seismic images reveal that the overriding Pacific plate contains stretched continental crust with magmatic intrusions, which formed from rifting between Zealandia continental plateaus during AUS-PAC plate divergence. This stretching phase was highly asymmetric and resulted in the opening of the Solander Basin. Rifting was more advanced to the south, yet never proceeded to breakup and seafloor spreading as previously thought. A new southern continent-ocean transition is inferred from potential field data, marking the boundary between stretched continental crust and new oceanic crust formed during the extensional phase.

Along-strike heterogeneity with mixed continental and oceanic domains and asymmetric rift architecture along the Puysegur margin were critical features for following tectonic regimes. Increasingly oblique plate motions sparked strike-slip motion, which localized near the pre-existing spreading center in the south, but along the western edge of the rift zone in relatively unstretched crust at the Puysegur margin in the north. Translational motion juxtaposed weak ~10 Myr old oceanic lithosphere with buoyant continental crust across the strike-slip boundary. Incipient subduction transpired as oceanic lithosphere from the south forcibly underthrust continent lithosphere at an oblique collision zone.

We suggest that subduction initiation at the Puysegur Trench was enabled by inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of continental rifting and strike-slip along the plate boundary. In the global evolution of plate tectonics, strike-slip might be the key component to achieving the Wilson cycle, as it is the most efficient mechanism to offset terranes and juxtapose lithospheric domains of contrasting properties across broad regions, thus generating advantageous conditions for subduction initiation and subsequent closure of oceanic basins.

How to cite: Shuck, B., Van Avendonk, H., Gulick, S., Gurnis, M., Sutherland, R., Stock, J., and Hightower, E.: A Cenozoic Wilson cycle along the Puysegur Margin, New Zealand: The role of rift architecture and strike-slip dynamics enabling subduction initiation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10197, https://doi.org/10.5194/egusphere-egu22-10197, 2022.

The Wilson Cycle of closing and opening of oceans is often schematically portrayed with ‘empty’ oceanic basins. However, bathymetric and geophysical observations outline anomalous topographic features, such as microcontinents and oceanic plateaus, that can be accreted when oceans close in subduction. This implies that numerous rifted margins have formed in regions characterized by the presence of previously accreted continental terranes. The main factors controlling where and how such continental rifts localize in relation to the inherited compressional structures is yet to be explored properly. Potential factors that can influence the evolution and structural style of a rift in such a tectonic setting include the thermo-tectonic age of the accretionary orogen, the number and type (size, rheology) of accreted terranes, the nature of terrane boundaries, as well as the velocity of rifting.

We use 2D finite-element thermo-mechanical models to investigate how the number and size of accreted terranes as well as the duration of tectonic quiescence between orogenesis and extension (i.e., the amount of time available for the thermal re-equilibration of the thickened lithosphere) affect the style of continental rifting. Our results can further understanding of how rifted margins formed after accretionary orogenesis are influenced by the compressional stage such as the Norwegian rifted margin, where the late-Paleozoic to Mesozoic rifting occurred after the early Paleozoic Caledonian orogeny.

We test two hypotheses. According to our first hypothesis, the location of the rift is dependent on the age of the accretion. If extension directly follows accretion, we expect the thick lithosphere of the orogen to be strong in a brittle sense, causing extension to localise adjacent to the orogen. In contrast, if the onset of extension happens after a period of tectonic quiescence, the accretionary orogen has time to heat up and viscously weaken, allowing it to localize deformation more efficiently. We test this hypothesis by varying the amount of time available for thermal re-equilibration.

Secondly, we hypothesize that the degree to which the compressional structures such as terrane boundaries in the accretionary stack reactivate depends on the size and complexity of the accreted assembly (through the number and size of the accreted terrains) as well as the strength of shear zones. We test this hypothesis by varying the number of terranes accreted prior to rifting.

Our preliminary results show that the subduction interface is reactivated in an extensional regime, but without a period of quiescence the reactivation is temporary and rifting occurs in the unthickened foreland basin area.

How to cite: Erdős, Z., Buiter, S., and Tetreault, J.: The influence of accretionary orogenesis on rift dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3220, https://doi.org/10.5194/egusphere-egu22-3220, 2022.

The intracontinental belt of the High Atlas is an aborted rift system along NW Africa, which formed during the Mesozoic break-up of Pangaea and was inverted during the Alpine Orogeny. Although the inversion and orogeny build-up have been extensively studied, the Triassic to Jurassic rifting, synchronous to the opening of the Atlantic and the Tethys, is still poorly understood. True orthogonal rifting is proposed to occur in the Triassic to Early Jurassic, while the end of rifting is controversial and believed to be controlled by oblique extension. Restoration of the Atlantic-Tethys triple junction suggests sinistral motion between Iberia and Africa being active during the Middle Jurassic, which reactivated pre-existing NE-SW trending Hercynian weaknesses in transtension mode. This led to the formation of a series of pull-apart basins involving the basement and localised volcanic activity.

The Atlas system is an excellent field analogue to analyse the role of strike-slip tectonics in extensional systems, especially in the early stages of rifting. Despite the late Cenozoic (Alpine) inversion, the well-exposed syn-rift structures and sediments have been weakly affected by the broad contractional event.

Our study aims to investigate the kinematic and geometry of the oblique rifting phase, the strain variation lengthwise in the Atlas rift system, the relationship between the orthogonal rift structures, the strike-slip structures, and the synchronous volcanism. In this contribution, we will highlight the fieldwork results, which we used to constrain the restoration of the rift sytem, quantify extension vs. transtension, and produce a conceptual model of how strike-slip tectonics can influence the early stages of a rift system.

How to cite: Vasileiou, A., Gouiza, M., Mortimer, E., and Coliier, R.: Analysis of strike-slip tectonics in extensional systems: the case of the Moroccan Atlas system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3597, https://doi.org/10.5194/egusphere-egu22-3597, 2022.

The northwestern margin of the Iberian Peninsula (western Bay of Biscay) is a unique place that gathers several outstanding geological features in a relatively reduced area. Here, a former hyperextended continental margin developed in proximity to a triple point, underwent a subsequent partial tectonic inversion yielding the present Cantabrian margin. For all these reasons, the northwest area of ​​Iberia can be considered as a natural laboratory for the study of the role of tectonic inheritance in the evolution of the extensional continental margins and their subsequent inversion. However, and largely due to the lack of interest from exploration companies, the northwestern margin of Iberia presented a great deficit of geophysical and geological information. Both scientific interest and the lack of information provided the main reasons for the MARIBNO amphibious project (2019-2022). This project is being carried out by a multidisciplinary geoscientific team leaded by the Complutense University of Madrid with the acquisition of offshore and onshore data. The main objectives are focused on the study of the crustal structure, the tectonic control by the structure prior to the alpine stages and the mapping and characterization of the crustal domains, combining geological and geophysical criteria.

A one month-long geophysical cruise was carried out aboard the BO Sarmiento de Gamboa (Spanish Research Council, CSIC) in September-October of 2021. Data acquisition was divided in two cruise legs: The WAS Leg consisted in the acquisition wide-angle seismic data (WAS) along 3 transects with simultaneous offshore-onshore recording in 3 component short-period instruments: Transect WAS-1 (∼320 km) recorded in 14 OBS and 11 land seismometers, Transect WAS-2 (∼260 km) recorded in 12 OBS and 10 land seismometers and Transect WAS-3 (∼255 km) recorded in 9 OBS and 12 land seismometers. The seismic source consisted in an airgun array with 4660 ci and 90 seconds of shot interval. The MCS leg consisted in the acquisition of 2D multichannel seismic reflection data (MCS) along 14 transects (∼1500 km) recorded on a digital streamer with a 12.5 m channel-interval. Several streamer configurations were deployed with 480, 240 and 168 channels and the seismic source consisted in an airgun array with 1960 ci. During both legs, continuous marine acquisition of multibeam bathymetry, gravity, geomagnetics and ultra-high resolution seismic data also were carried out. MARIBNO project is still underway, and the data are being processed and interpreted. Acquired information will be complemented and combined with the additional acquisition of onshore gravity and magnetic data and the information from several geological field mapping studies on seismic transects throughout the Cantabrian Mountains. Here we show some preliminary results and the current development of the MARIBNO amphibious project.

How to cite: Muñoz-Martín, A., Granja-Bruña, J.-L., De la Fuente-Oliver, M. A., Druet, M., De Vicente, G., Gallastegui Suárez, J., and Maestro, A. and the MARIBNO WORKING GROUP: MARIBNO amphibious project: Structure of the northwestern Iberian margin and role of the inherited tectonics in the Alpine extension and inversion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6886, https://doi.org/10.5194/egusphere-egu22-6886, 2022.

Rift-related inheritance plays a key role in orogenic building, by controlling the thermal state and the position of major sedimentary and crustal decollement levels. As recognized by various authors, a switch from thin- to thick-skinned style of deformation in reactivated rifted-margin during convergence occurs where the necking domain of the margin is involved in the subduction. This is observed in the External Crystalline Massifs (Aar, Mont-Blanc, Belledonne, Pelvoux, Argentera) located at the transition between the external and the internal domains of the western Alps corresponding also to the proximal-distal transition (necking domain) of the former Jurassic margin. Necking reactivation during Alpine convergence is accommodated by shear zones, rooted in the ductile middle crust, propagating  the deformation toward the external domain.  This Alpine overprint, which led to a lower greenschist metamorphism (ca. 330°C) in the External Crystalline Massifs, raise the question of the preservation of the rift-related, pre-alpine structures in the western Alps, and their use as fossil-analogues of present-day necking domains.

A case study is the internal Mont-Blanc massif, where preserved pre-rift to syn-rift (Triassic to Mid-Jurassic) cover is observed below the internal nappes, and on top the crustal basement (Mont-Blanc granite). The contact between these deposits and the underlying basement is a fault zone, made of a cataclastic basement overlaid by a black gouge. Above the contact, remnants of allochthonous pre-rift deposits and delaminated carbonates are observed. The syn-rift sandstones (Grès Singuliers Fm), which are either in contact with the fault or located above the pre-rift deposits, contain reworked clasts of cataclasite. Above the contact, in the cataclastic basement, some crinoid-rich sediments of likely Pliensbachian age fill open cracks. Taken together, these observations strongly point to the preservation of a pre-alpine, rift-related detachment fault of Jurassic age.

The petrographical and geochemical analysis of the exhumed fault indicates strong hydration-assisted deformation. In the cataclasite, feldspars breakdown and important element transfer (especially Ba, F, Si, Pb, Zn and REE) suggest fluid circulation in an open system. The black gouge matrix is mostly made of illite, likely recrystallized during the Alpine overprint. In addition, different generations of syn-kinematic veins are observed in the detachment. The first type, composed of graphite precipitated at ~400°C in the cataclasite. Syn-kinematic quartz and quartz hyalophane (Ba-rich feldspars) in the cataclasite and gouge were formed from a fluid above 170°C a salinity of ~9 wt.% NaCl-equivalent. The mobilized elements are the same as those involved in pre-alpine Pb-Zn (Ba-F) ore-deposits of the internal Mont-Blanc (Amône, Mont-Chemin, Catogne), suggesting a genetic link between rift-related faults and mineralisations.

Despite partial Alpine metamorphic overprint, the early tectonic, sedimentary and geochemical records of this rift-related detachment fault are very well preserved, making a good analogue of present-day necking domains. The example of Mont-Blanc massif gives an opportunity to study all these aspects in detail, in particular to understand fluid-mediated element mobility during rifting. Finally, it can be used to better understand the final stages of reactivation of the necking domain in a mature orogenic system.

How to cite: Dall'asta, N., Hoareau, G., Manatschal, G., and Ribes, C.: Preservation of the necking domain in orogens: a case study of the Mont-Blanc massif (Western Alps, France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11778, https://doi.org/10.5194/egusphere-egu22-11778, 2022.

A common observation in plate tectonics is the successive stages of rifting and associated crustal and lithospheric thinning, and subsequent convergence and inversion of sedimentary basins. Rates and style of inversion often vary across the sedimentary basins, influenced by changing stress and thermal fields, different convergence directions, and also controlled by inherited structures, all of which determine the localization and style of the resulting deformation. However, the dynamic feedbacks between lithospheric tectonics and surface processes, and their 3D expressions have not been studied in details by previous models, even though erosion and sediment distribution exerts a significant control on differential vertical movements and thermal evolution.

In this study, we investigate strain partitioning during extension and subsequent structural inversion, and tackle the coupling between tectonics, mantle melting and surface processes. To do so, we apply the 3D thermo-mechanical code I3ELVIS (Gerya 2015; Munch et al. 2020), which is based on staggered finite differences and marker-in-cell techniques to solve the mass, momentum and energy conservation equations for incompressible media. The models also take into account simplified melting processes, as well as erosion and sedimentation by diffusion.

We compare the modeling results with seismic and well data from the Mediterranean back-arc basins, such as the Alboran, Tyrrhenian and Pannonian Basins. The temporal variation of different plate convergence and slab retreat velocities lead to the extensional formation, recent structural inversion and related differential vertical motions of these basins. In fossil extensional basins, plate convergence has ultimately overprinted the former basin structure, and lead to the rise of young orogens, i.e. the Pyrenees or Great Caucasus.

How to cite: Oravecz, É., Balázs, A., Gerya, T., May, D., and Fodor, L.: Structural inversion of sedimentary basins: insights from 3D coupled thermo-mechanical and surface processes models and observations from the Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-542, https://doi.org/10.5194/egusphere-egu22-542, 2022.

The Neuquén Basin is a major Mesozoic sedimentary depocenter located in the foreland of the Andes Mountains in Argentina. The basin hosts world renown inversion systems that have been the target of georesource exploration for the last three decades. The Huincul High is a structurally and economically prominent ~270km long, E-W trending feature that formed by the accretion of exotic Paleozoic terranes influencing subsequent Mesozoic deformation in the basin. Exploration in Huincul High has been mainly focused on the shallow part of the inversion structures leaving a limited understanding of  deep structural architecture and early tectonic evolution. With this research, for the first time a set of 4 3D seismic reflection surveys covering an area of 1400km2 have been analysed and integrated with stratigraphic information from 15 exploratory wells to provide new insights into the tectonostratigraphic and kinematic evolution of the western reaches of the Huincul High.

Detailed horizon and fault interpretation revealed Late Triassic, isolated, 10-50km long NE-SW to NW-SE trending half grabens. These extensional systems are attributed to the Late Triassic cessation of the Andean subduction to the west and intraplate extension regime ensuing. Thickness map of the Lower Jurassic Los Molles unit shows the development of an extensive ~50km  long ~15km wide NE-SW depocentre at that time. It is proposed that Andean subduction was renewed at that time, moving the Neuquén Basin into a backarc environment with hotter, weaker continental lithosphere thinned by mantle underflow which might have caused ductile flexural sag and minimal brittle faulting.

Prominent NE-SW cylindrical inversion anticlines ~17km across and well-developed harpoon structures are observed in the hangingwall of reactivated  ~50km long, NE-SW trending, extensional faults. Growth strata analysis shows thinning of Middle to Lower Cretaceous strata over the crest of these folds suggesting a phase of  NW-SE compression at this time. This compressional phase is attributed to the increase in Andean subduction rate and shallowing of the subduction dip, as the Neuquén Basin is moved into a foreland setting. Fault displacement analysis suggests that the reactivated faults were formed as separate fault segments at the time of extension in the Late Triassic. Additionally, analysis indicates that faults segments with increased reactivation show prominent hangingwall inversion anticlines.

Dip-steered coherency extractions along the Early Cretaceous Vaca Muerta Formation showed en echelon NW-SE transtensional faults occurring directly above Late Triassic non inverted faults; decoupled by the underlying shaly and mechanically weak Los Molles unit. These observations point to a post-inversion tectonic event that might coincide with reconfiguration of subducted plates changing the principal stress orientation and causing strike slip reactivation.

These results highlight the importance of  structural inheritance of a pre-existing  fault architecture in the development of  consequent inversion, and how mechanically weak units can inhibit fault propagation during the later compressional events, acting as a decoupling layer.  A detailed evolutionary model is proposed for the western reaches of the Huincul High which envisages crustal weakening and thermal sag to explain the thickening of the Early Jurassic strata previous to the main Cretaceous inversion.

How to cite: Antonov, I., Scarselli, N., and Adam, J.: Tectonic and geometric assessment of inversion systems in the Huincul High, Neuquén Basin (Argentina) – the role of structural inheritance and mechanical stratigraphy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8244, https://doi.org/10.5194/egusphere-egu22-8244, 2022.

Extensional detachment faults, core complexes and supradetachment basins play major roles in the evolution of 3D rifted margin architecture. The successive incision of basement from early to late stages in the margin evolution is rarely explained in 3D. One reason for this is likely the lack of a unifying model for how very large faults grow and link laterally, and how this, in turn, links to the temporal evolution of the margin. As fault shape exerts a fundamental control on syn-rift basin architecture, the 3D evolution of detachment faults is critical to understand sedimentation in associated basins.

In the proximal margin offshore Norway, one control on lateral variation appears to be the differential exploitation of `extraction´ structures that evolved above the ductile crust. This controlled flips in fault polarity under the proximal margin, and lateral transitions from supradetachment- to half-graben style, Late Paleozoic-Triassic basins. Extensional culminations and core complexes were associated with this deformation pattern at depth.

The growth of an extensional fault past a displacement of a few kilometers will involve a change in 3D fault shape related to the isostatic rollback of parts of the fault plane. As displacement magnitude varies along the fault plane, so will the amount of extensional unloading and associated isostatic compensation. With increasing extension this will enforce a particular shape on the fault plane, with an extensional culmination developing in the area of maximum displacement, and synclinal recesses evolving on the flanks. With continued extension, the culmination evolves into a core complex. Necking domains, where faults propagate into the ductile middle crust appear to be prime locations for this type of faulting. As large-magnitude faults combine into domain-bounding breakaway complexes, this results in intermittent occurrences of core complexes along the main breakaways and lateral transitions into steeper megafaults and fault arrays. At the Mid-Norwegian margin, we interpret the Jurassic-Cretaceous North Møre and south Vøring basins to illustrate this type of evolution. Components of strike-slip may modify this type of pattern, as illustrated by  continental core complexes exposed in areas such as Death Valley and western Norway.

How to cite: Osmundsen, P. T., Péron-Pinvidic, G., Gresseth, J. L., and Braathen, A.: 3D evolution of extensional detachment faults and their effect on the architecture of rifts and rifted margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7480, https://doi.org/10.5194/egusphere-egu22-7480, 2022.

Footwall fault scarp-degradation produces sediments resulting in gravity-driven syn-rift wedge-shaped deposits located on the immediate hangingwall. To understand which aspects control footwall scarp-degradation we propose a model suggesting where, why, and how degradation occurs. We compare five offshore 3D seismic surveys acquired on the Northern Carnarvon Basin (North West Shelf of Australia) calibrated with well data to assess these questions. Two 3D seismic surveys (i.e., Panaeus 2001 East and Fortuna) are located on the Dampier Sub-basin, proximal to the Western Australia coastline and three (i.e., Thebe, Bonaventure and Agrippina) in a more distal position on the Exmouth Plateau. Data show that degradation is more pronounced on the distal surveys compared to the proximal ones. On the proximal surveys, the sedimentation rate is greater than in the distal ones, and footwall scarp-degradation is less pronounced. Answering these questions will help us to predict the style and the amount of footwall scarp-degradation in similar extensional settings.

How to cite: Martinez, C., Chiarella, D., Jackson, C. A.-L., and Scarselli, N.: Regional-scale proximal to distal footwall scarp-degradation variability of extensional faults, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8726, https://doi.org/10.5194/egusphere-egu22-8726, 2022.

Continental extension at mature rifts systems focuses along spreading segments where dominant magmatic activity, diking and minor faulting assist plate divergence. Such processes make adjacent spreading segments grow but also interact at zones where the spreading is transferred from one segment to another. A great variety of tectonic structures has been observed at transfer zones, encompassing parallel strike-slip faults (bookshelf faulting) or conjugate systems of en-echelon oblique faults. Transfer zones can also become transform plate boundaries once continental breakup occurs. However, the role of magma in influencing the deformation at rift-rift transfer zones is unclear as direct observations are rare. In this study, we address this open question by exploiting high-resolution Pléiades-1 tri-stereo imagery to produce the first 1 m DEM of the Afrera Plain transfer zone, between the Erta Ale and Tat Ali spreading segments in Northern Afar. This dataset has been used to conduct a detailed structural analysis of both tectonic and magmatic features and explore their geometrical and spatial relationships. We observed different trends and kinematics: Dikes opens with an extension oriented ~N65°E, consistent with the regional extension; tectonic features have instead an extensional component with direction varying between ~N46°E and ~N68°E. Riedel shears and measurements of fractures opening directions indicate that tectonic deformation occurs along two families of NW-SE- and NS-striking oblique faults having right-lateral and left-lateral components, respectively. At the same time, spatial relationships between faults and lava flows also indicate that magmatic and tectonic activity co-exist in the transfer zone. We explain these observations by two different strain fields acting in the Afrera Plain during magmatic and amagmatic phases. During magmatic phases, dikes open orthogonal to the spreading direction responding to the regional extension. Conversely, during amagmatic phases, the transfer zone is dominated by the interaction between the two spreading segments with counterclockwise rotations of the strain field and shear motions accommodated by conjugate fault systems.

How to cite: La Rosa, A., Pagli, C., Hurman, G., and Keir, D.: Analysis of high-resolution Digital Elevation Model (DEM) of the Afrera Plain (Afar) reveals relationship between magmatism and tectonics in a rift transfer zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1175, https://doi.org/10.5194/egusphere-egu22-1175, 2022.

Quantifying the spatial and temporal evolution of fault systems is crucial in understanding plate boundary deformation and the associated seismic hazard, as well as to help georesources exploration in sedimentary basins. During the last decade, 3D lithospheric-scale geodynamic models have become capable of simulating the evolution of complex fault systems, from the onset of rifting to sea-floor spreading. But since these models describe faults as finite-width shear zones within a deforming continuum, additional efforts are needed to isolate and analyse individual faults, so we can understand the entire life span of normal fault networks.

Here we present 3D numerical forward models using the open-source community software ASPECT. Our thermo-mechanical models include visco-plastic rheology, strain softening as well as lithospheric and asthenospheric layers to capture rift evolution from inception to continental break-up. We quantify normal fault evolution at the surface of the model with a method that describes fault systems as 2D networks consisting of nodes and edges. Building on standard image analysis tools such as skeletonization and edge detection, we establish a hierarchical network structure that groups nodes and edges into components that make up individual evolving faults. This allows us to track fault geometries and kinematics through time enabling us to analyse the growth, linkage and disintegration of faults.

We find that the initial fault network is formed by rapid fault growth and linkage, followed by competition between neighbouring faults and coalescence into a mature fault network. At this stage, faults accumulate displacement without a further increase in length. Upon necking and basin-ward localisation, the first generation of faults shrink and disintegrate successively while being replaced by newly emerging faults in the rift centre. These new faults undergo a localisation process similar to the initial rift stage. We identify several of these basin-ward localisation phases, which all feature this pattern. In oblique rift models, where the extension direction is not parallel to the rift trend, we observe strain partitioning between the rift borders and the centre, with strike-slip faults emerging in the centre even at moderate obliquity. Analysing the spatio-temporal evolution of modelled faults thus allows us to map their entire life span to observed stages of rift system evolution.

How to cite: Brune, S., Wrona, T., Neuharth, D., Glerum, A., and Naliboff, J.: Life and Death of Normal Faults: Quantitative Analysis of Fault Network Evolution in 3D Rift Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6294, https://doi.org/10.5194/egusphere-egu22-6294, 2022.