TS8.1

EDI
Transform plate boundaries and strike-slip tectonics

Transform faults are one of the three types of plate boundaries required for Earth-like plate tectonics to operate. In these locations, plates move laterally in relation to each other without significant creation or destruction of plate material. Transform plate boundaries played a fundamental role in the development of the theory of plate tectonics. The concept of transform fault was introduced by Tuzo Wilson as the final piece of a puzzle that allowed connecting ridges to convergent zones and close the circumference of lithospheric plates. Wilson recognized that transform faults were different from the already known continental transcurrent faults (or nonlithospheric strike-slip faults). The term transform plate boundary is since then been used to define a lithospheric strike-slip fault zone that constitutes a plate boundary. The term is also used more loosely to define strike-slip boundaries of diffuse tectonic blocks or microplates. At smaller orders, strike-slip faults exist in all kinds of environments and at all scales, accommodating the lateral movement of tectonic blocks and linking other kinds of faults. Transform plate boundaries can exist in both continental or oceanic lithosphere, leading to markedly different strain distribution patterns and seismic activity. This is particularly true for the case of oceanic transform faults, which result from the own growth of the plates. Due to their remote locations, the rheological structure and behavior of oceanic transform faults are still largely unknown. The fact that they exist in oceanic environments suggests that they are prone to constant fluid circulation and alteration, potentiated by the chemical reactions between rocks and circulating fluids. Transform faults have also traditionally been perceived as places of low to moderate magnitude seismicity, but recent events have shown that these structures can generate very high magnitude hazardous events. Examples include the 2010 Haiti earthquake and the 1941 M 8.4 earthquake along the Gloria Fault. In this session, we aim to discuss the evolution of oceanic and continental transform and strike-slip faults. We welcome studies on structural geology, marine geology, geochemistry, petrology, remote sensing, tectonics, seismology and hazards, as well as modelling studies, using both analogue and numerical approaches. Associated processes such as shear localization, serpentinisation, biogenic activity, fluid migration and extrusion are also very welcome.

Co-organized by GM9/NH4
Convener: João Duarte | Co-conveners: Christian Hensen, Lea Beloša
Presentations
| Wed, 25 May, 10:20–11:38 (CEST)
 
Room K2

Presentations: Wed, 25 May | Room K2

Chairpersons: João Duarte, Christian Hensen, Lea Beloša
10:20–10:26
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EGU22-1979
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ECS
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On-site presentation
Yu Ren, Jacob Geersen, and Ingo Grevemeyer

Oceanic transform faults are among the most prominent morphologic features in ocean basins, offsetting mid-ocean ridges by tens to hundreds of kilometers. Since the inception of plate tectonics, transform faults have been assumed to be simple, two-dimensional strike-slip, conservative plate boundaries, where lithosphere is neither created nor destroyed. This concept nurtured an over-simplified understanding of oceanic transform faults for many decades. New advances in seafloor mapping revealed that the morphology of oceanic transform faults is difficult to explain exclusively by strike-slip faulting and differential thermal subsidence. We compiled ship-based bathymetric data of 94 oceanic transform faults, and parameterized their morphological characteristics (e.g., length, width, depth, etc.) using quantitative geomorphologic methods. A prominent feature of most oceanic transform plate boundaries is a deep valley extending along the active transform fault. Our statistical analysis indicates that these valleys are generally deeper and wider at slow- and ultraslow-slipping rates than at faster slipping rates. However, the key feature that governs structural variability, seems to be age-offset across a transform fault rather than spreading rate. While the correlation between transform morphology and spreading rate turns out to be rather weak, our statistical results consistently show that transform valleys get deeper and wider with increasing age-offset. The surface deformation pattern observed therefore supports the tectonic extension scaling with age-offset predicted by recent geodynamic simulations (Grevemeyer et al., 2021). Furthermore, at small age-offsets (< 5 Myr), scatters especially in the depth of transform valley increase, indicating that small-age-offset transforms corresponding to weak lithospheric strength are easily affected by secondary tectonic processes, such as nearby hotspots and changes in plate motion. Now, five decades after Wilson (1965) published his seminal paper on transform faults, our quantitative submarine geomorphologic study emphasizes that oceanic transform faults are not simple conservative strike-slip plate boundaries, but that tectonic extension is an integral process affecting their morphology. The larger age-offset causes greater extension at OTFs and hence wider and deeper valleys as evidenced by our statistics on transform morphology.

References

Wilson, J. T. (1965), A new class of faults and their bearing on continental drift. Nature, 207, 343–347. doi: 10.1038/207343a0

Grevemeyer, I., Rüpke, L. H., Morgan, J. P., Iyer, K., & Devey, C. W. (2021), Extensional tectonics and two-stage crustal accretion at oceanic transform faults. Nature, 591, 402–407. doi: 10.1038/s41586-021-03278-9

How to cite: Ren, Y., Geersen, J., and Grevemeyer, I.: Extensional tectonics at oceanic transform plate boundaries: evidence from seafloor morphology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1979, https://doi.org/10.5194/egusphere-egu22-1979, 2022.

10:26–10:32
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EGU22-2279
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Highlight
Ingo Grevemeyer, Dietrich Lange, Ingo Klaucke, Anouk Beniest, Laura Gómez de la Peña, Yu Ren, Helene-Sophie Hilbert, Yuhan Li, Louisa Murray-Bergquist, Katharina Unger, Colin W. Devey, and Lars Ruepke

Fracture zones were recognized to be an integral part of the seabed long before plate tectonics was established. Later, plate tectonics linked fracture zones to oceanic transform faults, suggesting that they are the inactive and hence fossil trace of transforms. Yet, scientist have spent little time surveying them in much detail over the last three decades. Recent evidence (Grevemeyer, I., Rüpke, L.H., Morgan, J.P., Iyer, K, and Devey, C.W., 2021, Extensional tectonics and two-stage crustal accretion at oceanic transform faults, Nature, 591, 402–407, doi:10.1038/s41586-021-03278-9) suggests that the traditional concept of transform faults as being conservative (non-accretionary) plate boundary faults might be wrong. Instead, transform faults are always deeper than the associated fracture zones and numerical modelling results suggest that transform faults seem to suffer from extensional tectonics below their strike-slip surface fault zone. During the cruise M170 of the German research vessel METEOR early in 2021, we aimed to test this hypothesis by collecting, in a pilot study, micro-seismicity data from the Oceanographer transform fault which offsets the Mid-Atlantic Ridge by 120-km south of the Azores near 35°N. Preliminary analysis of 10-days of seismicity data recorded at 26 ocean-bottom-seismometers and hydrophones showed 10-15 local earthquakes per day. Along the transform fault the distribution of micro-earthquakes and focal mechanisms support strike-slip motion. However, at both ridge-transform intersections seismicity does not mimic a right-angular plate boundary; instead, seismicity occurs below the inside corner and focal mechanism indicate extensional tectonics. Therefore, micro-seismicity supports features found in numerical simulations, revealing that transform faults have an extensional as well as a strike-slip component.

How to cite: Grevemeyer, I., Lange, D., Klaucke, I., Beniest, A., Gómez de la Peña, L., Ren, Y., Hilbert, H.-S., Li, Y., Murray-Bergquist, L., Unger, K., Devey, C. W., and Ruepke, L.: The Oceanographer transform fault revisited – preliminary results from a micro-seismicity survey reveals extensional tectonics at ridge-transform intersections, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2279, https://doi.org/10.5194/egusphere-egu22-2279, 2022.

10:32–10:38
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EGU22-4993
Christian Heine, Myron Thomas, Jimmy van Itterbeeck, Ilya Ostanin, Andrey Seregin, Michael Spaak, Tamara Morales, and Tess Oude Essink

Oceanic Transform faults are one of the three major tectonic plate boundaries and yet their evolution and deformational mechanism is not well understood. They are broadly considered to be dominated by strike-slip displacement along simple planar vertical faults and to be conservative in nature with no magmatic addition. Observations from Pre-Stack depth-migrated (PSDM) 3D seismic of Cretaceous-aged transforms in the eastern Gulf of Guinea allow complex internal architectures to be described, including crustal scale detachments and rotated packages of volcanics.

These insights demonstrate additional complexity previously only predicted in numerical simulations of spreading ridge-transform interaction, namely intra-transform extension at a high angle to the spreading orientation, and the addition of significant extrusive volcanic material. In the study area of São Tomé and Príncipe, several Oceanic Fracture Zones (OFZ) are identified, consisting of a broad deformational zones that can be described from top to base crust. OFZ scarps are observed to connect at depth with zones of low angle reflectivity which dip into the OFZ and perpendicular to the spreading orientation. At depth they detach onto the Moho below, necking the adjacent crust along the length of the OFZ in the manner of extensional shear zones. Thickly stacked and tilted reflectors, interpreted as extrusive lava flows, are common above the shear zones and infill up to 75% of the crustal thickness. The entire OFZ stratigraphy is overlain and sealed by late-stage lavas that are continuous from the abyssal hills of the trailing spreading ridge. This constrains a process of oblique extension at a high angle to the spreading orientation along a low angle shear zone which also acts as a conduit for decompression related melt.

We demonstrate that transforms in São Tomé and Príncipe were both non-conservative and not a simple strike slip fault zone, contradicting the current understanding of modern systems. This style of deformation has similarities with anomalously deep and smooth nodal basins which form at slow spreading inside-corner crust. Our model adds strong observational constraints to complement recent numerical models that predict oblique extension within transform zones.

How to cite: Heine, C., Thomas, M., van Itterbeeck, J., Ostanin, I., Seregin, A., Spaak, M., Morales, T., and Oude Essink, T.: A new model for the evolution of oceanic transform faults based on 3D PSDM Seismic observations from São Tomé and Príncipe, eastern Gulf of Guinea., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4993, https://doi.org/10.5194/egusphere-egu22-4993, 2022.

10:38–10:44
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EGU22-8005
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ECS
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On-site presentation
Attila Balazs, Taras Gerya, Dave May, and Gabor Tari

Passive and transform margins emerging during continental rifting and opening of oceanic basins are fundamental elements of plate tectonics. It has been suggested that inherited structures, variable plate divergence velocities and surface processes exert a first order control on the topographic, bathymetric and magmatic evolution and thermal history of these margins and related sedimentary basins. We conducted 3D thermo-mechanical numerical experiments with the code I3ELVIS coupled to surface processes modelling (FDSPM) to simulate the dynamics of continental rifting, continental transform fault zone formation and persistent oceanic transform faulting. Numerical modelling results allow to explain the first order observations from passive and transform margins, such as diachronous rifting, strain localization into individual oblique rift basins and the opening of structurally separate oceanic basins connected in an open marine environment. In addition, the models reproduce the rise of transform marginal ridges and submarine plateaus, continental crustal slivers within oceanic transforms and their interaction with erosion and sedimentation. Model results are compared and validated by seismic and well data from passive and transform margin segments of the Atlantic.

How to cite: Balazs, A., Gerya, T., May, D., and Tari, G.: Contrasting passive and transform margin tectonic history and sedimentation: insights from 3D numerical modelling and observations from the Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8005, https://doi.org/10.5194/egusphere-egu22-8005, 2022.

10:44–10:50
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EGU22-1070
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ECS
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Virtual presentation
Anthony Jourdon, Charlie Kergaravat, Guillaume Duclaux, and Caroline Huguen

Transform margins represent ~30% of nonconvergent margins worldwide. Their formation and evolution have traditionally been addressed through kinematic models that do not account for the mechanical behaviour of the lithosphere. In this study, we use high-resolution 3D numerical thermo-mechanical modelling to simulate and investigate the evolution of intra-continental strain localization under oblique extension. The obliquity is set through velocity boundary conditions that range from 15 (high obliquity) to 75 (low obliquity) every 15 for rheologies of strong and weak lower continental crust. Numerical models show that the formation of localized strike-slip shear zones leading to transform continental margins always follows a thinning phase during which the lithosphere is thermally and mechanically weakened. For low- (75) to intermediate-obliquity (45) cases, the strike-slip faults are not parallel to the extension direction but form an angle of 20 to 40 with the plate motion vector, while for higher obliquities (30 to 15) the strike-slip faults develop parallel to the extension direction. Numerical models also show that during the thinning of the lithosphere, the stress and strain re-orient while boundary conditions are kept constant. This evolution, due to the weakening of the lithosphere, leads to a strain localization process in three major phases: (1) initiation of strain in a rigid plate where structures are sub-perpendicular to the extension direction; (2) distributed deformation with local stress field variations and formation of transtensional and strikeslip structures; (3) formation of highly localized plate boundaries stopping the intra-continental deformation. Our results call for a thorough re-evaluation of the kinematic approach to studying transform margins.

How to cite: Jourdon, A., Kergaravat, C., Duclaux, G., and Huguen, C.: Looking beyond kinematics: 3D thermo-mechanical modelling reveals the dynamics of transform margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1070, https://doi.org/10.5194/egusphere-egu22-1070, 2022.

10:50–10:56
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EGU22-12463
Vincent Roche, Sylvie Leroy, Jean-Claude Ringenbach, François Sapin, Sidonie Revillon, François Guillocheau, William Vetel, and Louise Watremez

Gondwana splitting started during the Early Jurassic (ca. 180 Ma) with the separation of Antarctica and Madagascar from Africa, followed by the separation of South America and Africa during the Middle Jurassic. Thanks to recent seismic profiles for petroleum exploration, the architecture of rifted margins and the transform faults zones, which developed as a result of the relative motion between tectonic plates have been recently evidenced and studied along the whole eastern and south-eastern Africa (i.e., in the Western Somali Basin, the Mozambique Basin, the Natal Basin, and the Outeniqua Basin). Yet, the structure and overall kinematic evolution of the three major transform faults zones together – i.e., the Agulhas, the Davie, and the Limpopo Fracture Zones – that control the opening of these major oceanic basins remain poorly studied. The interpretation of an extensive regional multichannel seismic dataset coupled with recent studies allows us to propose an accurate regional mapping of the crustal domains and major structural elements along the rifted margins along the whole eastern and south-eastern Africa. We provide new constraints on the structuration and evolution of these three transform systems. Although our findings indicate common features in transform style (e.g., a right-lateral transform system, a wide sheared corridor), the deformation and the thermal regime along these systems appear quite different. In particular, we show that the Davie and Agulhas Fracture Zones recorded spectacular inversions during the transform stage whereas transtensional deformation is observed along the Limpopo Fracture Zone during its activity. This suggests that faults activity controls vertical displacements along transform margins, minimising other processes such as thermal exchanges between the oceanic and continental lithospheres across the transform fault and flexural behaviour of the lithosphere. This different style of deformation may be explained by two main forcing parameters: (i) the magmatic conditions that may modify the rheology of the crust, and (ii) the far-field forces that may induce a rapid change of regional tectonic stress. Further, in the Davie and Agulhas cases, the major transform faults postdate the development of the rift zone-controlling faults. Thus, there are no pre-existing structures that control the initiation of a transform fault zone. Conversely, the Limpopo margin shows an intracontinental transform faulting stage. In both cases, a minimum of several Ma is required to establish a complete kinematic linkage between the two-active spreading centers. During this period, the rifted segments opening possibly triggered rift-parallel mantle flow, which progressively favors the decoupling in-between the continental domain and the future oceanic domain. In the post-drift history, rapid changes of regional tectonic stress are recorded and show that some transform margins are excellent recorders of large plate kinematic changes.

How to cite: Roche, V., Leroy, S., Ringenbach, J.-C., Sapin, F., Revillon, S., Guillocheau, F., Vetel, W., and Watremez, L.: East African Fracture Zones: a long lifespan since the breakup of Gondwana, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12463, https://doi.org/10.5194/egusphere-egu22-12463, 2022.

10:56–11:02
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EGU22-11355
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ECS
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On-site presentation
Alana Oliveira de Sa, Sylvie Leroy, Elia D'Acremont, Sara La Fuerza, and Bernard Mercier de Lepinay

The northern boundary of the Caribbean plate is characterized by the oblique collision between the Caribbean (CAR) and North American (NOAM) tectonic plates. The progressive counterclockwise rotation of the two plates accompanying the eastward translation of NOAM vs. CAR is responsible for the increasing obliquity of the collision between these two plates. Consequently, successive southward jumps of major strike-slip faults accommodate the eastward escape of the Caribbean plate and the collisional indentation against the Bahama Banks. During this process, Cuba was progressively welded to the North American Plate. Several strike-slip corridors record this diachronous collision as major left-lateral transfer zones in Cuba: Eastern Yucatan Margin (Upper Cretaceous), Pinar-Varadero (Paleocene), La Trocha (early Eocene), Cauto-Nipe (middle/late Eocene), and Oriente Fault Zone (early Oligocene). The nature and age of the related tectonic events of these tectonic corridors were widely studied onshore. However, offshore northern Cuba remains relatively unknown. We provided a first offshore description of northeastern Cuba based on a multi-channel seismic reflection and swath-bathymetric dataset from the Haiti-SIS cruise. The seismic reflection profiles show that the structural and sedimentary architecture of the insular slope varies significantly from central to eastern Cuba. This lateral variability seems mainly influenced by the proximity with the Bahama Banks, which act as a succession of local indenters. The width of the insular slope varies from 5-10km in central Cuba to more than 50km in width towards the east off the Guacanayabo-Nipe tectonic corridor. In this region, the insular slope shows a thick sedimentary cover suggesting a main subsiding regional block related to the middle/late Eocene onset of the Guacanayabo-Nipe tectonic corridor. Contrasting lateral deformation patterns in this region are probably related to the diachronous strike-slip events related to the activity of the Cauto-Nipe fault. The coexistence of folds, transtensive and transpressive structures affecting the sedimentary infill attests that the local stress regimes of this fault have gradually changed. Our study correlates offshore deformation phases recorded in the offshore northeastern coast of Cuba, with major deformation episodes recorded onshore Cuba from Eocene to present-day. Our tectonostratigraphic evolution of the eastern offshore of Cuba provides new constraints to improve the knowledge of the geodynamics of the northern boundary of the Caribbean plate.

How to cite: Oliveira de Sa, A., Leroy, S., D'Acremont, E., La Fuerza, S., and Mercier de Lepinay, B.: Cuba's northern offshore: a witness to geodynamics evolution of the northern boundary of the Caribbean plate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11355, https://doi.org/10.5194/egusphere-egu22-11355, 2022.

11:02–11:08
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EGU22-10112
Kevin P. Furlong and Kirsty A. McKenzie

The faults that accommodate Pacific - North America plate motion along the San Andreas plate boundary occupy a region that previously served as part of the upper plate of the Cascadia subduction zone plate boundary. After the passage of the Mendocino triple junction (MTJ), several fault systems develop within the newly formed Pacific-North America plate margin, with one fault system eventually evolving to become the primary plate boundary structure (termed the San Andreas Fault in central California). As a result of the northward migration of the MTJ, the Cascadia subduction zone, undergoing NNW-directed shortening at a rate of ~ 50 km/Ma, replaced by the equivalent lengthening of the San Andreas system.  In northern California, three primary fault systems are identified:  on the west (along the western margin of the North America plate) is the San Andreas fault (which does not serve as major component of the lithospheric scale plate boundary structure in northern California; moving inland (eastward) is the Maacama - Rodgers Creek (M-RC) fault system; further east is the Lake Mountain - Bartlett Springs (LM-BS) fault system.  These latter two faults primarily accommodate Pacific -North America motion in the region just to the south of the MTJ. 

New tomography imagery of this region of northern California provides crustal constraints on deformation and fault localization, both within Cascadia, north of the MTJ, and south of the transition from subduction to translation. Using these tomographic images and analyses of GPS data within the region, we have developed a tectonic model that both explains the present fault systems north and south of the MTJ, and helps us understand why one of these fault systems - the M-RC fault system - develops to become the primary plate boundary structure over several million years after MTJ passage. Two fundamental aspects of the North America and Pacific plates control the location of these primary fault systems - the existence of relatively rigid upper-plate backstops  (the Great Valley and Klamath blocks), and a small remnant (the Pioneer fragment) of the subducted Farallon plate accreted to the eastern margin of the Pacific plate and migrating northward with it. As a result of these structures, the LM-BS fault system develops as an upper-crust (brittle) fault system, while the M-RC system initially forms as a shear zone (ductile) along the eastern margin of the Pioneer fragment, with the upper-crustal faults developing in response to the deeper plate boundary shear zone. This lithospheric shear zone localizes the plate boundary development and leads to the M-RC system becoming the main plate boundary fault.

How to cite: Furlong, K. P. and McKenzie, K. A.: Formation and Development of the San Andreas Fault System with Migration of the Mendocino Triple Junction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10112, https://doi.org/10.5194/egusphere-egu22-10112, 2022.

11:08–11:14
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EGU22-2128
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ECS
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On-site presentation
Jakub Fedorik, Abdulkader Afifi, Frank Zwaan, and Guido Schreurs

The southern Dead Sea Transform (SDST) is an active left-lateral transform plate boundary that extends from the Sinai triple junction to the Lebanon restraining bend, separating the Arabian and Sinai plates. In this study, we analyze structural variations along the SDTS, and reproduce these variations in a 4D analogue model.  

From south to north, the structural styles along the SDTS indicate (1) rotational transtension within the Gulf of Aqaba, (2) pure strike-slip in Wadi Araba and Jordan River valley, and (3) pull-apart basins in the Dead Sea, Sea of Galilee and Hula basin. These different structural styles were replicated experimentally in an analogue model incorporating transtension with minor rotation along a kinked plate boundary. Our 4D model produced a deep southern depression with en echelon faults corresponding to the Gulf of Aqaba, a simple strike-slip fault system without vertical displacement reflecting the Wadi Araba and Jordan Valley, and a set of pull-apart basins reminiscent of the Dead Sea, Sea of Galilee and Hula basins. The accurate reproduction of the structural styles along this 600km-long plate boundary segment constrains the relative movement between the Arabian and Sinai plates to a simple combination of transtension with minor rotation, thereby negating the earlier hypothesis of Euler pole shift during the tectonic evolution of the SDST. 

How to cite: Fedorik, J., Afifi, A., Zwaan, F., and Schreurs, G.: A kink in the plate boundary, rotation and transtension: new 4d insights into the tectonics of the southern Dead Sea Transform, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2128, https://doi.org/10.5194/egusphere-egu22-2128, 2022.

11:14–11:20
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EGU22-5427
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ECS
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On-site presentation
Esther Heckenbach, Sascha Brune, Anne Glerum, and Derek Neuharth

The region around the Dead Sea Transform represents a unique example of the structures that form around restraining and releasing bends in a strike-slip environment. With our 3D numerical models, we aim to understand the processes that shaped the region including the Dead Sea Basin, the Dead Sea Transform Fault, and the Lebanese Restraining Bend.

In our study, we employ geodynamic modelling using the software ASPECT coupled to the surface processes code FastScape. Our model setup includes a compressive and a tensional stepover along a strike-slip fault with periodic along-strike boundary conditions. Even though we use a simplistic setup with horizontally homogeneous rock layers, we can reproduce many of the present-day features of the Dead Sea Transform region, including the sediment thicknesses in the Dead Sea basin, heat flow patterns, relative topographical height differences, and the general outlines and activity of the main faults along the Dead Sea basin, the Mount Lebanon and Anti Lebanon ranges.

With our models we can investigate the influence of surface processes on the underlying stepover strike-slip tectonics and the resulting crustal-scale flower structures: (1) Along the tensional stepover, the horizontal distance between the bounding faults of the pull-apart basin increases with greater efficiency of surface processes due to an increasing sediment load filling the basin. The sediments hinder the border faults in approaching each other at the surface, thereby enforcing basin-ward fault dip, resulting in wider and deeper basins with greater surface process efficiency. (2) In the uplifted compressive stepover, the erosional efficiency has a direct feedback on the longevity of faults and the rheological state of the crust through its influence on the uplift rate. Elevated erosion-induced uplift rates lead to a connection of the brittle parts of lower and upper crust, because the upper crustal viscous part is moved into a zone of lower temperatures and thus becomes brittle. This drastic change of the underlying rheology manifests in the formation of a new fault, which cuts through the centre of the compressional area. When no erosion is assumed a similar fault is observed in map view, but cross sections reveal that without erosion this fault has a different origin and the flower structure is more complex and more symmetric than for models that include erosion.

How to cite: Heckenbach, E., Brune, S., Glerum, A., and Neuharth, D.: 3D geodynamic evolution of strike-slip restraining and releasing bends modulated by surface processes: application to the Dead Sea Transform, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5427, https://doi.org/10.5194/egusphere-egu22-5427, 2022.

11:20–11:26
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EGU22-3802
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ECS
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On-site presentation
Kristóf Porkoláb, Ernst Willingshofer, Dimitrios Sokoutis, Eszter Békési, and Fred Beekman

The localization of the North Anatolian Fault in the northern Aegean Sea (North Aegean Trough) is an intriguing example of continental transform fault propagation. Understanding this process critically depends on quantifying the amount of strike-slip displacement and the superposition of normal and strike-slip faulting in the region, which is the aim of this study. In particular, we unravel and quantify normal and dextral faulting along the Alonnisos fault system, at the south-western margin of the North Aegean Trough (Sporades Basin), in order to constrain the spatial and temporal evolution of the basin and the North Anatolian Fault. We present detailed structural data collected from Messinian strata of Alonnisos to infer the amount of tilting and shortening and to constrain normal and dextral faulting along the Alonnisos fault system through simple analytical half-space models of dislocations. The Messinian rocks of Alonnisos record significant tilting and gentle folding close to the termination zone of the main fault segment. The tilting of the Messinian rocks implies footwall uplift in the order of 6-7 km (vertical displacement) during normal faulting on the boundary fault system, which lead to post 5 Ma substantial deepening of the Sporades Basin. The post-Messinian folding accommodated ~ 1 km shortening at the footwall termination zone of the Alonnisos fault, which implies a dextral slip of 3-4 km. Our results support the models of currently distributed dextral strain in the North Aegean in response to the propagation of the North Anatolian Fault. However, similarities with the evolution of the Sea of Marmara might suggest that dextral shear could yet become fully localized in the NAT in the next few Myrs.

How to cite: Porkoláb, K., Willingshofer, E., Sokoutis, D., Békési, E., and Beekman, F.: Post-5 Ma rock deformation on Alonnisos (Greece) constrains the propagation of the North Anatolian Fault, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3802, https://doi.org/10.5194/egusphere-egu22-3802, 2022.

11:26–11:32
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EGU22-12062
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ECS
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On-site presentation
Erick Prince, Kamil Ustaszewski, Sumiko Tsukamoto, Christoph Grützner, and Marko Vrabec

The Periadriatic Fault System (PAF) is one of the most important tectonic and geomorphological features in the Alps. It has accommodated between 150-300 km of right-lateral strike-slip motion between the European and Adriatic plates from about 35 Ma until 15 Ma. However, for such a large-scale feature, the eastern PAF reveals relatively little instrumental and historical seismic activity, especially when compared to nearby structures in the adjacent Southern Alps. With this project, we aim to show which fault segments of the eastern PAF system accommodated seismotectonic deformation in the Quaternary by applying trapped charge dating methods to fault gouges produced by its activity. We use optically stimulated luminescence (OSL) and electron spin resonance (ESR). The principle for both is the accumulation of unpaired electrons in lattice defects of quartz and feldspar, due to natural radiation product of the decay of radiogenic nuclides, which are then released during an earthquake due to shear heating allowing the system to reset (Fukuchi 1992, Aitken 1998, Tsukamoto et al., in Tanner 2019). Due to their dating range (a few decades to ~1Ma) and low closing temperature, trapped charge methods provide a unique opportunity to date earthquake activity during the Quaternary at near-surface conditions. During our field campaigns, we collected 19 fault gouge samples from 15 localities along the PAF, the Labot/Lavanttal fault, and the Šoštanj fault. From each locality, we controlled the structures found in the field, which allowed us to relate the observed deformation features in outcrop scale to the activity along each fault. Aside from the fault gouge in the cores of the large-scale structures at the sampled localities, we additionally found gouge and cataclasites formed within the host rocks in small-scale faults presenting the orientation of the respective regional fault, providing supplementary evidence of activity.

How to cite: Prince, E., Ustaszewski, K., Tsukamoto, S., Grützner, C., and Vrabec, M.: Quaternary Seismogenic Activity Along the Eastern Periadriatic Fault System: Dating of Fault Gouges via Trapped Charge Methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12062, https://doi.org/10.5194/egusphere-egu22-12062, 2022.

11:32–11:38
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EGU22-10205
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Virtual presentation
Paola Cianfarra, Francesco Salvini, Laura Crispini, Michele Locatelli, and Laura Federico

The North Victoria Land structural framework is characterized by the long-lived tectonic activity along major crustal lineaments, including the NNW-SSE and NW-SE trending Rennick Graben Fault (RGF) system and Aviator Fault (AF). This tectonic corridor is characterized by an important strike-slip component that is easily connected to the main strike-slip fracture zone that characterizes the Southern Ocean between Australia and East-Antarctica. Structural analysis of field data along the RGF evidences a poly-phased activity with multiple reactivations related to the Paleozoic juxtaposition of NVL to the East Antarctic craton (as resulting from the Gondwana breakup) and to the Meso-Cenozoic plate tectonics associated to the Australia-East Antarctica separation and characterized by both offshore and onshore crustal strike-slip deformation. Both the northward, offshore propagation of the RGF system and its southward prosecution and link with the AF are inferred but still need to be proved/better framed.

During the XXXVII Italian Antarctic campaign in the framework of the LARK project 92 field measurement sites have been surveyed between latitude 71.5°S and 73.5°S. To better frame the link between the RGF and AF the evidence of brittle deformation (including faults with the associated kinematic indicators and fracture attitude, dimension and sets) have been measured. This deformation involve rocks with ages ranging from Lower Paleozoic to Lower Jurassic. Where time constraints from stratigraphy are lacking and to better frame the age of the tectonics with its associated vertical displacement, ad hoc field samples have been collected for thermochronology dating.

Open, un-mineralized fracture sets are important indicator of recent paleo-stress (tectonic) activity, since their formation is limited to shallow depth and their presence testify a short erosion time, thus representing a good indicator of the last, recent stress regime. The intensity of brittle deformation associated to this last tectonic setting can be quantified by the H/S adimensional parameter, where H represents the size of the fracture and S is the spacing between nearest fractures belonging to the same azimuthal family and having comparable dimensions. This parameter has been proved (Cianfarra & Salvini 2016) to be proportional to the total energy released by the stress during fracture generation though time. The analysis of the recently collected field structural data is still in progress and will allow to prepare both a map of the spatial distribution of H/S values and to infer the (multiple) paleostress responsible for the observed brittle deformations by the application of original methodologies that include the inversion of fault and near orthogonal fracture systems. The latter inversion methodology solves both the identification and grouping of the fractures into the two systematic and non-systematic families, and the orientation of the responsible paleostress by a Monte Carlo approach.

Results from the central RGF system area shows the increase of the H/S values by approaching the RGF central zone, due to the increase of the local stress produced by its kinematics.

Cianfarra P. and Salvini F., (2016). Quantification of fracturing within fault damage zones affecting Late Proterozoic carbonates in Svalbard. Rend. Fis. Acc. Lincei, 27(19), 229-241. DOI 10.1007/s12210-016-0527-5

How to cite: Cianfarra, P., Salvini, F., Crispini, L., Locatelli, M., and Federico, L.: Linking the strike-slip kinematics of the Rennick Graben Fault system and the Aviator Fault from field structural data, North Victoria Land, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10205, https://doi.org/10.5194/egusphere-egu22-10205, 2022.