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0000-0003-4985-1810
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GFZ Potsdam
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Oceanography not elsewhere classified | Geology | Marine Geoscience | Geodynamics
Publisher: American Geophysical Union (AGU)
Date: 02-2020
DOI: 10.1029/2019JB018560
Publisher: Springer Science and Business Media LLC
Date: 25-03-2021
Publisher: Geological Society of America
Date: 10-01-2014
DOI: 10.1130/G35082.1
Publisher: Frontiers Media SA
Date: 22-08-2019
Publisher: Elsevier BV
Date: 07-2019
Publisher: Springer International Publishing
Date: 19-08-2013
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-7155
Abstract: & & 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& #8217 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& #8217 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 in idual contributions of lithosphere and mantle drivers of deformation in the EARS and of Victoria& #8217 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& #8211 .& & & & Ghosh et al. (2013). J. Geophys. Res. 118, 346& #8211 .& & & & Glerum et al. (2020). Nature Communications 11 (1), 2881.& & & & Koptev et al. (2015). Nat. Geosci. 8, 388& #8211 .& & & & Rajaonarison et al. (2021). Geophys. Res. Letters, 48(6), 1& #8211 .& &
Publisher: Springer Science and Business Media LLC
Date: 06-06-2014
DOI: 10.1038/NCOMMS5014
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-7518
Abstract: Cenozoic rifting in the South China Sea developed after a Mesozoic Andean-type orogeny (i.e., Yanshanian orogen) which led to structural, compositional, and thermal inheritance.These inherited lithospheric weaknesses can control the inception and evolution of rifting, as well as the final architecture of the rifted continental margin. In order to better understand these processes, recent studies have utilized seismic profiles, drill cores, and geochronological analysis to identify Mesozoic strata, magmatic rocks related to a former arc, and pre-Cenozoic fault systems in the region. These findings reveal that the pre-rift lithosphere was heterogeneous and that inherited structures affected the subsequent Cenozoic rift evolution.Here we use multi-stage models to investigate the impact of tectonic inheritance on the spatiotemporal evolution and final rift margin architecture in the South China Sea. We employ a numerical forward model that includes a two-way coupling strategy (Neuharth et al., 2022) linking the geodynamic code ASPECT and the landscape evolution model FastScape. We reproduce the first-order kinematic evolution of the South China Sea by imposing accordion type models of continental collision, followed by extension. We present a reference model that incorporates orogenic topography, thrust fault distribution, and the architecture of the rifted margin, while also accounting for realistic crustal thicknesses, heat flow, and lithosphere-asthenosphere boundary (LAB) properties. This model was derived by conducting a systematic evaluation of a suite of models that varied in terms of lithosphere rheology, convergence velocity, heat production, erosion rate, and random initial noise distribution.Our reference model reproduces a range of observations including continental collision, post-orogenic collapse, continental rifting and lithospheric breakup. During orogeny, the lithosphere undergoes thrust faulting, and crustal thickening, leading to the formation of inherited weakness in the crust. From orogenic collapse to continental rifting, pre-existing thrust faults serve as nucleation sites for normal faults, and their interaction with later rift-related normal faults can locally modify the regional stress field. During rifting, low-angle detachment faults which connect the reactivated thrust faults contribute to the overall deformation of the lithosphere. In this model, crustal thickening led to increasing temperature, which resulted in a more ductile lower crust with a rheological transition from brittle to ductile deformation. This thermal weakening of the lower crust allows for increased deformation and strain accommodation during lithospheric stretching. The presence of pre-existing thrust faults and a more ductile lower crust ultimately led to the formation of wide rifted margin of the South China Sea. We suggest that this finding is applicable to other post-orogenic, wide rifts worldwide, such as the Basin and Range Province, the Aegean Sea and the West Anatolian extensional system.[1] Neuharth, D., Brune, S., Wrona, T., Glerum, A., Braun, J., & Yuan, X. (2022). Evolution of rift systems and their fault networks in response to surface processes.& Tectonics,& (3), e2021TC007166.
Publisher: American Geophysical Union (AGU)
Date: 06-2009
DOI: 10.1029/2009GC002491
Publisher: American Geophysical Union (AGU)
Date: 2019
DOI: 10.1029/2018JB016917
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-4047
Abstract: & & Understanding how normal faults grow is critical to an accurate assessment of seismic hazards, for successful exploration of natural (including low-carbon) resources and for safe subsurface carbon storage. Our current knowledge of fault growth is, in large parts, derived from seismic reflection data of continental rifts and margins. These seismic datasets do however suffer from limited data coverage and resolution. In addition, detailed fault mapping in increasingly large seismic reflection data requires a large amount of expertise and time from interpreters. Here we map faults across the entire northern North Sea rift using a combination of supervised deep learning and broadband 3-D seismic reflection data. This approach requires us to interpret & .1% of the data for training and allows us to extract almost 8000 in idual normal faults across a 161 km wide (E-W), 266 km long (N-S) and 20 km deep volume. We find that rift faults form incredibly complex networks revealing a previously-unrecognised variability in terms of fault length, density and strike. For instance, while we observe up to 75.9 km long faults extending from the Stord Basin and Bj& #248 rgvin Arch in the south into the Uer and Lomre Terrace to the north, most faults (& %) are closely spaced (& 5 km) and relatively short (& km long). Moreover, these faults show a large range of strikes varying from NW-SE to NE-SW with two dominant fault strikes (NE-SW & NW-SE) almost perpendicular to each other. This observation is difficult to reconcile with previous studies on the extension directions during rifting of the northern North Sea. While previous studies suggest that pre-existing shear zones control faulting in the northern North Sea, we only observe faults aligning with the southern parts of the Lomre shear zone and the eastern parts of the Ninian shear zones, but none of the other eight previously mapped shear zones. Instead we think that these variations in fault strike could occur naturally through the complex evolution of fault networks. As such our innovative approach allows us to map faults across the entire northern North Sea revealing complex networks, which challenge many conventional views of fault growth during continental rifting.& &
Publisher: California Digital Library (CDL)
Date: 19-09-2018
Publisher: Elsevier
Date: 2019
Publisher: Elsevier BV
Date: 02-2019
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-8187
Abstract: & & The impingement of a hot buoyant mantle plume onto the lithosphere can result in either breaking of the lithosphere, which might results in subduction initiation or in under-plating of the plume beneath the lithosphere. Key natural ex les of the former and latter are formation of subduction along the southern margin of Caribbean and northwestern South America in the late Cretaceous as well as the hotspot chains of Hawaii, respectively. In previous studies the interaction of a buoyant mantle plume with lithosphere was investigated either for the case of stationary lithosphere or for moving lithosphere but ignoring the effect of magmatic weakening of the lithosphere above the plume head. In this study we aim to investigate the response of a moving lithosphere to the arrival of a stationary mantle plume including the effect of magmatic lithospheric weakening. To do so we use 3d thermo-mechanical models employing the finite difference code I3ELVIS. Our setup consists of an oceanic lithosphere, mantle plume and asthenosphere till depth of 400 km. The moving plate is simulated by imposing a kinematic boundary condition on the lithospheric part of the side boundaries. The mantle plume in our models has a mushroom shape. The experiments differ in the age of the lithosphere, rate of the plate motion and size of the mantle plume. For different combinations of these parameters model results show either (1) breaking of the lithosphere and initiation of subduction above the plume head or (2) asymmetric spreading of the plume material below the lithosphere without large deformation of the lithosphere. We find that the critical radius of the plume that breaks the lithosphere and initiates subduction depends on plume buoyancy and the lithospheric age, but not on the plate speed. In general, the modeling results for the moving plate are similar to the results for a stationary plate, but the shapes of the region of the deformed lithosphere differ.& &
Publisher: Elsevier BV
Date: 06-2015
Publisher: Copernicus GmbH
Date: 10-03-2029
DOI: 10.5194/EGUSPHERE-EGU22-2743
Abstract: & & Continental break-up at Rift-Rift-Rift triple junctions commonly represents the & #8220 requel& #8221 of oceanic basin formation. Currently, the only directly observable ex le of a Rift-Rift-Rift setting is the Afar triple junction where the African, Arabian and Somalian plates interact to form three rift branches, two of which are experiencing oceanization (the Gulf of Aden and the Red Sea). The younger of the three (the Main Ethiopian Rift) is still undergoing continental extension. We performed analogue and numerical models simulating continental rifting in a Rift-Rift-Rift triple junction setting to investigate the resulting structural pattern and evolution. By adopting a parametrical approach, we modified the ratio between plate velocities, and we performed single-phase (all the three plates move) and two-phase models (with a first phase where only one plate moves and a second phase where all the three plates move). Additionally, the direction of extension was changed to induce orthogonal extension only in one of the three rift branches. Our single-phase models suggest that differential extension velocities in the rift branches determine the localization of the triple junction, which is located closer to the rift branch experiencing slower extension velocities. Furthermore, imposed velocities affect the distribution of deformation and the resulting pattern of faults. The effect of a faster plate is to favour the formation of structures trending orthogonal to dominant velocity vectors, while faults associated with the movement of the slower plates remain subordinate. In contrast, imposing similar velocities in all rift arms leads to the formation of a symmetric fault pattern at the triple junction, where the distribution of deformation is similar in the three rift branches. Two-phase models reveal high-angle faults interacting at the triple junction, confirming that differential extension velocities in the three rift branches strongly affect the fault pattern development and highlighting geometrical similarities with the Afar triple junction.& &
Publisher: American Geophysical Union (AGU)
Date: 08-2014
DOI: 10.1002/2014GC005446
Publisher: American Geophysical Union (AGU)
Date: 24-02-2022
DOI: 10.1029/2021TC007166
Abstract: Continental rifting is responsible for the generation of major sedimentary basins, both during rift inception and during the formation of rifted continental margins. Geophysical and field studies revealed that rifts feature complex networks of normal faults but the factors controlling fault network properties and their evolution are still matter of debate. Here, we employ high‐resolution 2D geodynamic models (ASPECT) including two‐way coupling to a surface processes (SP) code (FastScape) to conduct 12 models of major rift types that are exposed to various degrees of erosion and sedimentation. We further present a novel quantitative fault analysis toolbox (Fatbox), which allows us to isolate fault growth patterns, the number of faults, and their length and displacement throughout rift history. Our analysis reveals that rift fault networks may evolve through five major phases: (a) distributed deformation and coalescence, (b) fault system growth, (c) fault system decline and basinward localization, (d) rift migration, and (e) breakup. These phases can be correlated to distinct rifted margin domains. Models of asymmetric rifting suggest rift migration is facilitated through both ductile and brittle deformation within a weak exhumation channel that rotates subhorizontally and remains active at low angles. In sedimentation‐starved settings, this channel satisfies the conditions for serpentinization. We find that SP are not only able to enhance strain localization and to increase fault longevity but that they also reduce the total length of the fault system, prolong rift phases and delay continental breakup.
Publisher: Elsevier BV
Date: 2019
Publisher: Elsevier BV
Date: 2019
Publisher: Wiley
Date: 09-08-2016
Publisher: Deutsches GeoForschungsZentrum (GFZ)
Date: 2014
Publisher: American Geophysical Union (AGU)
Date: 03-07-2020
DOI: 10.1029/2019GL086611
Publisher: Elsevier BV
Date: 12-2016
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-11050
Abstract: Understanding how normal fault networks initiate and evolve is important for quantifying plate boundary deformation, assessing seismic hazard and finding natural resources. In recent years, 3D numerical models have been developed that can simulate the entire process of normal fault formation, from the start of rifting to the creation of new ocean floor. However, state-of-the-art methods treat faults as finite-width shear zones not as discrete entities, so additional work is needed to isolate in idual faults and their characteristics in order to better understand fault system dynamics over geological scales.We present 3D numerical rift models of moderately oblique extension using the ASPECT software. These models reproduce the thermo-mechanical behavior of Earth's lithosphere and simulate fault system dynamics from inception to breakup accounting for visco-plastic rheology, strain softening and surface processes. We use a method that extracts surficial fault systems as 2D networks of nodes and edges to study the evolution of normal faulting. By applying data analysis techniques, we group nodes and edges into components that represent in idual faults and track their geometry and movement over time.We find that the initial fault network forms through rapid fault growth and linkage, followed by competition between neighboring faults that leads to their coalescence into a stable network. At this point, modelled normal faults continue to accumulate displacement but do not grow any longer. As deformation localizes towards the center of the rift, the initial border faults shrink and disintegrate, being replaced by new faults in the center of the rift. During that transition, we document strain partitioning between predominantly dip-slip border faults and oblique-slip or strike-slip intra-basin faults. The longevity of faulting is thereby controlled by crustal rheology and surface process efficiency. Quantitative analysis of fault evolution allows us to deduce fault growth and linkage as well as fault tip retreat and disintegration in unprecedented detail.
Publisher: Springer Science and Business Media LLC
Date: 18-07-2016
DOI: 10.1038/NATURE18319
Abstract: Rifted margins are formed by persistent stretching of continental lithosphere until breakup is achieved. It is well known that strain-rate-dependent processes control rift evolution, yet quantified extension histories of Earth's major passive margins have become available only recently. Here we investigate rift kinematics globally by applying a new geotectonic analysis technique to revised global plate reconstructions. We find that rifted margins feature an initial, slow rift phase (less than ten millimetres per year, full rate) and that an abrupt increase of plate ergence introduces a fast rift phase. Plate acceleration takes place before continental rupture and considerable margin area is created during each phase. We reproduce the rapid transition from slow to fast extension using analytical and numerical modelling with constant force boundary conditions. The extension models suggest that the two-phase velocity behaviour is caused by a rift-intrinsic strength--velocity feedback, which can be robustly inferred for erse lithosphere configurations and rheologies. Our results explain differences between proximal and distal margin areas and demonstrate that abrupt plate acceleration during continental rifting is controlled by the nonlinear decay of the resistive rift strength force. This mechanism provides an explanation for several previously unexplained rapid absolute plate motion changes, offering new insights into the balance of plate driving forces through time.
Publisher: American Geophysical Union (AGU)
Date: 08-2012
DOI: 10.1029/2011JB008860
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-10695
Abstract: & & Continental rifts show surface expressions of deep crustal processes, such as faulting and volcanism. The East African Rift System (EARS) is one of the most prominent ex les of an active continental rift driven by tectonics and magmatism. Nonetheless, we still struggle to quantify the amount of extension due to these processes on a kyr- to Myr-time-scale. In particular, the distribution of extension within low-offset normal fault networks within rift basin interiors is challenging to determine.& & & & To address these issues, we develop a semi-automated workflow to extract normal faults from the TanDEM-X science DEM data (12 m horizontal resolution, 0.4 m average height error) of the Magadi-Natron Region of the Eastern branch of the EARS, limited to the north by the Suswa caldera (1.15& #176 S) and to the south by Gelai and Oldoinyo Lengai volcanoes (2.75& #176 S). This data allows us to quantify brittle surface deformation that occurred since the last deposition of widespread volcanic lavas in& these basins. Our workflow consists of five steps: (1) gradient calculation, (2) thresholding, (3) skeletonization, (4) Hough transformation, and (5) clustering. Because the surface faults appear as topographic discontinuities, we first calculate the gradient of the DEM to detect them. Then we use an adaptive threshold (Otsu) to distinguish faults from unfaulted areas. Next, we skeletonize the threshold to extract line segments and perform a Hough transformation to determine the orientation of these segments. Finally, we use a density-based clustering algorithm (DBSCAN) to group these segments into faults. This algorithm is considering proximity between the segment, similarity in dip and strike direction.& & & & A strike analysis applied on the fault data of the whole basin shows four main directions from distinct fault populations. Each direction cluster corresponds to a geological layer and a time interval. For ex le, the azimuth N20& #176 , corresponds to present and recent rift direction, mostly on the ~1Myr old Magadi trachyte. A direction of N170& #176 is mostly represented in earlier,& Mio-Pliocene volcanic units of the rift. Moreover, we derive the fault displacement distribution throughout the basin.This allows us to calculate the total extension of each geological unit and to compute the overall amount of extension of the region during geologically recent times.& & & & We provide a new high-resolution fault map that depicts strike direction and throw even of small-offset normal faults. This characterization helps us increase our understanding of recent brittle deformation within the Magadi-Natron region and thus the propagation of rifting in the eastern branch of the East African Rift System.& &
Publisher: Copernicus GmbH
Date: 16-07-2018
DOI: 10.5194/SE-2018-63
Abstract: Abstract. Movements of tectonic plates often induce oblique deformation at ergent plate boundaries. This is in striking contrast with traditional conceptual models of rifting and rifted margin formation, which often assume 2D deformation where the rift velocity is oriented perpendicular to the plate boundary. Here we quantify the validity of this assumption by analysing the kinematics of major continent-scale rift systems in a global plate tectonic reconstruction from the onset of Pangea breakup until present-day. We evaluate rift obliquity by joint examination of relative extension velocity and local rift trend using the script-based plate reconstruction software pyGPlates. Our results show that the global mean rift obliquity amounts to 34° with a standard deviation of 24°, using the convention that the angle of obliquity is spanned by extension direction and rift trend normal. We find that more than ~ 70 % of all rift segments exceeded an obliquity of 20° demonstrating that oblique rifting should be considered the rule, not the exception. In many cases, rift obliquity and extension velocity increase during rift evolution (e.g. Australia-Antarctica, Gulf of California, South Atlantic, India-Antarctica), which suggests an underlying geodynamic correlation via obliquity-dependent rift strength. Oblique rifting produces 3D stress and strain fields that cannot be accounted for in simplified 2D plane strain analysis. We therefore highlight the importance of 3D approaches in modelling, surveying, and interpretation of most rift segments on Earth where oblique rifting is the dominant mode of deformation.
Publisher: American Geophysical Union (AGU)
Date: 2017
DOI: 10.1002/2016GC006645
Publisher: American Geophysical Union (AGU)
Date: 02-2020
DOI: 10.1029/2019GC008663
Publisher: Springer Science and Business Media LLC
Date: 20-12-2009
Publisher: Copernicus GmbH
Date: 13-04-2023
Abstract: Abstract. Continental rifts evolve by linkage and interaction of adjacent in idual segments. As rift segments propagate, they can cause notable re-orientation of the local stress field so that stress orientations deviate from the regional trend. In return, this stress re-orientation can feed back on progressive deformation and may ultimately deflect propagating rift segments in an unexpected way. Here, we employ numerical and analog experiments of continental rifting to investigate the interaction between stress re-orientation and segment linkage. Both model types employ crustal-scale two-layer setups wherein pre-existing linear heterogeneities are introduced by mechanical weak seeds. We test various seed configurations to investigate the effect of (i) two competing rift segments that propagate unilaterally, (ii) linkage of two opposingly propagating rift segments, and (iii) the combination of these configurations on stress re-orientation and rift linkage. Both the analog and numerical models show counterintuitive rift deflection of two sub-parallel propagating rift segments competing for linkage with an opposingly propagating segment. The deflection pattern can be explained by means of stress analysis in numerical experiments wherein stress re-orientation occurs locally and propagates across the model domain as rift segments propagate. Major stress re-orientations may occur locally, which means that faults and rift segment trends do not necessarily align perpendicularly to far-field extension directions. Our results show that strain localization and stress re-orientation are closely linked, mutually influence each other, and may be an important factor for rift deflection among competing rift segments as observed in nature.
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5427
Abstract: & & The region around the Dead Sea Transform represents a unique ex le 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.& &
Publisher: California Digital Library (CDL)
Date: 12-07-2018
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-7783
Abstract: & & The formation of new subduction zones is a key component of global plate tectonics. Initiation of subduction following the impingement of a hot buoyant mantle plume is one of the few scenarios that allow breaking the lithosphere and recycling a stagnant lid without requiring any pre-existing weak zones. According to this scenario, upon arrival of a hot and buoyant mantle plume beneath the lithosphere, the lithosphere breaks apart and the hot mantle plume materials flow atop of the broken parts of the lithosphere. This leads to bending of the lithosphere and eventually initiation of subduction. Plume-lithosphere interaction can lead to subduction initiation provided that the plume causes a critical local weakening of the lithospheric material above it, which depends on the plume volume, its buoyancy, and the thickness of the lithosphere. Previous modeling studies showed that plume-lithosphere interaction can result in initiation of multi- or single-slab subduction zones around the newly formed plateau. However, they did not explore the parameters playing key roles in discriminating between the single- and multi-slab subduction scenarios. Here, we investigate factors controlling the number and shape of retreating subducting slabs formed by plume-lithosphere interaction. Using 3d thermo-mechanical models we show that the response of the lithosphere to arrival of a mantle plume beneath it depends on several parameters such as age of oceanic lithosphere, thickness of the crust, large-scale lithospheric extension rate, relative location of plume head and plateau edge and mantle temperature. The numerical experiments reveal that plume-lithosphere interaction in present day Earth can result in three different deformation regimes: (a) multi-slab subduction initiation, (b) single-slab subduction initiation and (c) plateau formation without subduction initiation. On early Earth (in Archean times) plume-lithosphere interaction could result in formation of either multi-slab subduction zones, very efficient in production of new crust, or episodic short-lived circular subduction. Extension eases subduction initiation caused by plume-lithosphere interaction. Plume-induced subduction initiation of old oceanic lithosphere with a plateau with thick crust is only possible if the lithosphere is subjected to extension.& &
Publisher: American Geophysical Union (AGU)
Date: 09-2017
DOI: 10.1002/2017TC004739
Publisher: Elsevier BV
Date: 12-2018
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-2573
Abstract: The tectonic exhumation of mantle material is a well-known phenomenon and may occur during both rifting and subsequent (large-scale) basin inversion. However, the processes leading to the exhumation of dense and therefore negatively buoyant (sub-)lithospheric mantle material remain poorly understood. We therefore conducted a series of thermomechanical simulations using the geodynamics code ASPECT (coupled with FastScape for the inclusion of surface processes) testing the impact of various parameters on mantle exhumation in inverted rift systems.We find that rift duration strongly impacts mantle exhumation, both during the rift phase, as well as during subsequent inversion. When only limited rifting is applied, the dense mantle material cannot reach the surface as the overlying crustal layers remain connected. Basin inversion then tends to create a symmetric pop-up structure by reactivating rift boundary faults, and the dense mantle material is forced down by the thickening of low-density crustal layers on top of it. Only after certain amount of extension, the crust is sufficiently thinned so that mantle material can be exhumed. This mantle material may then remain near the surface or be further exhumed during basin inversion. Such further mantle exhumation is favoured if asymmetric reactivation of the rift basin occurs, so that mantle material is thrust on top of the downgoing plate.The establishment of such asymmetric orogenic systems allowing for efficient mantle exhumation is further promoted by having only short-lived tectonic quiescence between rifting and inversion, so that no thermal equilibration of the exhumed mantle domain can occur. As a result, the rift basin remains a weakness that is readily exploited during inversion. Longer periods of tectonic quiescence restore the strength of the lithosphere, so that delayed inversion generates more symmetric structures, with limited opportunities for mantle exhumation.Within this tectonic context, erosion efficiency is another key factor. First, more efficient erosion during inversion removes crustal material so that the mantle can be exhumed (even in symmetric orogenic systems). Second, efficient erosion also leads to the development of asymmetric orogenic systems, thus doubly contributing to mantle exhumation. Somewhat similarly, high plate velocities during inversion introduce larger amounts of crustal material into the system, which erosion cannot remove in a timely manner, whereas slow plate velocities allow erosion more time to remove material. Hence, mantle exhumation is positively correlated to erosion efficiency, and is negatively correlated to plate velocities during inversionFinally, serpentinization of mantle material can occur close to the Earth& #8217 s surface (i.e. in the uppermost kilometres) and strongly reduces the material& #8217 s density and brittle strength. Although our models so far only show a limited effect of serpentinization, the overall weakness of serpentinized mantle material at the rift basin floor seems to reduce localization of inversion-related deformation, thus generating more symmetric inversion systems with limited mantle exhumation.
Publisher: American Geophysical Union (AGU)
Date: 08-2020
DOI: 10.1029/2020GC009119
Publisher: California Digital Library (CDL)
Date: 17-03-2021
DOI: 10.31223/X5S60M
Publisher: Copernicus GmbH
Date: 28-11-2022
DOI: 10.5194/EGUSPHERE-2022-1190
Abstract: Abstract. Understanding where normal faults are is critical to an accurate assessment of seismic hazard, the successful exploration for and production of natural (including low-carbon) resources, and for the safe subsurface storage of CO2. Our current knowledge of normal fault systems is largely derived from seismic reflection data imaging intra-continental rifts and continental margins. However, exploitation of these data is limited by interpretation biases, data coverage and resolution, restricting our understanding of fault systems. Applying supervised deep learning to one of the largest offshore 3-D seismic reflection data sets from the northern North Sea allows us to image the complexity of the rift-related fault system. The derived fault score volume allows us to extract almost 8000 in idual normal faults of different geometries, which together form an intricate network characterised by a multitude of splays, junctions and intersections. Combining tools from deep learning, computer vision and network analysis allows us to map and analyse the fault system in great detail and a fraction of the time required by conventional interpretation methods. As such, this study shows how we can efficiently identify and analyse fault systems in increasingly large 3-D seismic data sets.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-13336
Abstract: & & The removal, redistribution, and transient storage of sediments in tectonically active mountain belts is thought to exert a first-order control on shallow crustal stresses, fault activity, and hence on the spatiotemporal pattern of regional deformation processes. Accordingly, sediment loading and unloading cycles in intermontane sedimentary basins may inhibit or promote intrabasinal faulting, respectively, but unambiguous evidence for this potential link has been elusive so far.& & & & Here we combine 2D numerical experiments that simulate contractional deformation in a broken-foreland setting (i.e., a foreland where shortening is diachronously absorbed by spatially disparate, reverse faults uplifting basement blocks) with field data from intermontane basins in the NW Argentine Andes. Our modelling results suggest that thicker sedimentary fills (& 0.7-1.0 km) may suppress basinal faulting processes, while thinner fills (& 0.7 km) tend to delay faulting. Conversely, the removal of sedimentary loads via fluvial incision and basin excavation promotes renewed intrabasinal faulting.& & & & These results help to better understand the tectono-sedimentary history of intermontane basins that straddle the eastern border of the Andean Plateau in northwestern Argentina. For ex le, the Santa Mar& #237 a and the Humahuaca basins record intrabasinal deformation during or after sediment unloading, while the Quebrada del Toro Basin reflects the suppression of intrabasinal faulting due to loading by coarse conglomerates. We conclude that sedimentary loading and unloading cycles may exert a fundamental control on spatiotemporal deformation patterns in intermontane basins of tectonically active broken forelands.& &
Publisher: Copernicus GmbH
Date: 26-10-2018
Abstract: Abstract. Movements of tectonic plates often induce oblique deformation at ergent plate boundaries. This is in striking contrast with traditional conceptual models of rifting and rifted margin formation, which often assume 2-D deformation where the rift velocity is oriented perpendicular to the plate boundary. Here we quantify the validity of this assumption by analysing the kinematics of major continent-scale rift systems in a global plate tectonic reconstruction from the onset of Pangea breakup until the present day. We evaluate rift obliquity by joint examination of relative extension velocity and local rift trend using the script-based plate reconstruction software pyGPlates. Our results show that the global mean rift obliquity since 230 Ma amounts to 34° with a standard deviation of 24°, using the convention that the angle of obliquity is spanned by extension direction and rift trend normal. We find that more than ∼ 70 % of all rift segments exceeded an obliquity of 20° demonstrating that oblique rifting should be considered the rule, not the exception. In many cases, rift obliquity and extension velocity increase during rift evolution (e.g. Australia-Antarctica, Gulf of California, South Atlantic, India-Antarctica), which suggests an underlying geodynamic correlation via obliquity-dependent rift strength. Oblique rifting produces 3-D stress and strain fields that cannot be accounted for in simplified 2-D plane strain analysis. We therefore highlight the importance of 3-D approaches in modelling, surveying, and interpretation of most rift segments on Earth where oblique rifting is the dominant mode of deformation.
Publisher: American Geophysical Union (AGU)
Date: 04-2009
DOI: 10.1029/2008GC002292
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-7763
Abstract: & & Subduction zones are key components of plate tectonics and plate tectonics could not begin until the first subduction zone formed. Plume-induced subduction initiation, which has been proposed as triggering the beginning of plate tectonics (Gerya et al., 2015), is one of the few scenarios that can break the lithosphere and recycle a stagnant lid without requiring any pre-existing weak zones. So far, two natural ex les of plume-induced subduction initiation have been recognized. The first was found in southern and western margins of the Caribbean Plate (Whattam and Stern 2014). Initiation of the Cascadia subduction zone in Eocene times has been proposed to be the second ex le of plume-induced subduction initiation (Stern and Dumitru, 2019).& & & & The focus of previous studies was to inspect plume-lithosphere interaction either for the case of stationary lithosphere (e.g., Gerya et al., 2015) or for moving lithosphere without considering the effect of lithospheric magmatic weakening above the plume head (e.g., Moore et al., 1998). In present study we investigate the response of moving oceanic lithosphere to the arrival of a rising mantle plume head including the effect of magmatic lithospheric weakening. We used 3D numerical thermo-mechanical modeling. Using I3ELVIS code, which is based on finite difference staggered grid and marker-in-cell with an efficient OpenMP multigrid solver (Gerya, 2010), we show that plate motion may affect the plume-induced subduction initiation only if a moderate size plume head (with a radius of 140 km in our experiments) impinges on a young but subductable lithosphere (with the age of 20 Myr). Outcomes indicate that lithospheric strength and plume buoyancy are key parameters in penetration of the plume and subduction initiation and that plate speed has a minor effect. We propose that eastward motion of the Farallon plate in Late Cretaceous time could play a key role in forming new subduction zones along the western and southern margin of the Caribbean plate.& & & & & & & & & References:& & & & Gerya, T., 2010,& Introduction to Numerical Geodynamic Modelling.. Cambridge University Press.& & & & Gerya, T.V., Stern, R.J., Baes, M., Sobolev, S.V. and Whattam, S.A., 2015. Plume-induced subduction initiation triggered Plate Tectonics on Earth. Nature, 527, 221& #8211 .& & & & Moore, W. B., Schubert, G. and Tackley, P., 1998, Three-dimensional simulations of plume-lithosphere interaction at the Hawaiian swell. Science, 279, 1008-1011.& & & & Stern, R.J., and Dumitru, T.A., 2019, Eocene initiation of the Cascadia subduction zone: A second ex le of plume-induced subduction initiation? Geosphere, v. 15, 659-681.& & & & Whattam, S.A. and Stern, R.J., 2014. Late Cretaceous plume-induced subduction initiation along the southern margin of the Caribbean and NW South America: The first documented ex le with implications for the onset of plate tectonics. Gondwana Research, 27, doi: 10.1016/j.gr.2014.07.011.& &
Publisher: Springer Science and Business Media LLC
Date: 07-03-2023
Publisher: American Geophysical Union (AGU)
Date: 10-2022
DOI: 10.1029/2022TC007491
Abstract: Rift‐Rift‐Rift triple junctions are key features of emergent plate boundary networks during fragmentation of a continent. A key ex le of such a setting is the Afar triple junction where the African, Arabian and Somalian plates interact. We performed analog and numerical models simulating continental break‐up in a Rift‐Rift‐Rift setting to investigate the resulting structural pattern and evolution. We modified the ratio between plate velocities, and we performed single‐stage (with all plates moving at the same time) and two‐stage (where one plate first moves alone and then all the plates move simultaneously) models. Additionally, the direction of extension was changed to induce orthogonal extension in one of the three rift branches. Our models suggest that differential extension velocities in the rift branches determine the localization of the structural triple junction, which is located closer to the rift branch experiencing slower extension velocities. Furthermore, imposed velocities affect the deformation resulting in end‐member fault patterns. The effect of applying similar velocities in all rift arms is to induce a symmetric fault pattern (generating a Y‐shaped geometry). In contrast, a faster plate generates structures trending orthogonal to dominant velocity vectors, while faults associated with the movement of the slower plates remain subordinate (generating a T‐shaped pattern). Two‐stage models reveal high‐angle faults interacting at the triple junction, confirming that differential extension velocities strongly affect fault patterns. These latter models show large‐scale similarities with fault patterns observed in the Afar triple junction, providing insights into the factors controlling the structural evolution of this area.
Publisher: American Geophysical Union (AGU)
Date: 04-2021
DOI: 10.1029/2021GC009681
Abstract: Seafloor spreading at slow rates can be accommodated on large‐offset oceanic detachment faults (ODFs), that exhume lower crustal and mantle rocks in footwall domes termed oceanic core complexes (OCCs). Footwall rocks experience large rotation during exhumation, yet important aspects of the kinematics—particularly the relative roles of solid‐block rotation and flexure—are not clearly understood. Using a high‐resolution numerical model, we explore the exhumation kinematics in the footwall beneath an emergent ODF/OCC. A key feature of the models is that footwall motion is dominated by solid‐block rotation, accommodated by the nonplanar, concave‐down fault interface. A consequence is that curvature measured along the ODF is representative of a neutral stress configuration, rather than a “bent” one. Instead, it is in the subsequent process of “apparent unbending” that significant flexural stresses are developed in the model footwall. The brittle strain associated with apparent unbending is produced dominantly in extension, beneath the OCC, consistent with earthquake clustering observed in the Trans‐Atlantic Geotraverse at the Mid‐Atlantic Ridge.
Publisher: Copernicus GmbH
Date: 23-03-2017
DOI: 10.5194/SE-2017-26
Abstract: Abstract. We evaluate the spatial and temporal evolution of Earth’s long-wavelength surface dynamic topography since the Jurassic, using a series of high-resolution global mantle convection models. These models are Earth-like in terms of convective vigour, thermal structure, surface heat-flux and the geographic distribution of heterogeneity. The models generate a degree-2 dominated spectrum of dynamic topography, with negative litudes above subducted slabs (i.e. circum-Pacific regions and southern Eurasia) and positive litudes elsewhere (i.e. Africa, north-west Eurasia and the central Pacific). Model predictions are compared with published observations and subsidence patterns from well data, both globally and for the Australian and South African regions. We find that our models reproduce the long-wavelength component of these observations, although observed smaller-scale variations are not reproduced. We subsequently define “geodynamic rules” for how different surface tectonic settings are affected by mantle processes: (i) locations in the vicinity of a subduction zone show large negative dynamic topography litudes (ii) regions far away from convergent margins feature long-term positive dynamic topography (iii) rapid variations in dynamic support occur along the margins of overriding plates (e.g. Western US) and at points located on a plate that rapidly approaches a subduction zone (e.g. India and Arabia). Our models provide a predictive quantitative framework linking mantle convection with plate tectonics and sedimentary basin evolution, thus improving our understanding of how subduction and mantle convection affect the spatio-temporal evolution of basin architecture.
Publisher: Elsevier BV
Date: 2017
Publisher: American Geophysical Union (AGU)
Date: 09-2016
DOI: 10.1002/2016GC006471
Publisher: American Geophysical Union (AGU)
Date: 14-02-2019
DOI: 10.1029/2018GL080387
Abstract: Relative plate motions during continental rifting result from the interplay of local with far‐field forces. Here we study the dynamics of rifting and breakup using large‐scale numerical simulations of mantle convection with self‐consistent evolution of plate boundaries. We show that continental separation follows a characteristic evolution with four distinctive phases: (1) an initial slow rifting phase with low ergence velocities and maximum tensional stresses, (2) a synrift speed‐up phase featuring an abrupt increase of extension rate with a simultaneous drop of tensional stress, (3) the breakup phase with inception of fast sea‐floor spreading, and (4) a deceleration phase occurring in most but not all models where extensional velocities decrease. We find that the speed‐up during rifting is compensated by subduction acceleration or subduction initiation even in distant localities. Our study illustrates new links between local rift dynamics, plate motions, and subduction kinematics during times of continental separation.
Publisher: Copernicus GmbH
Date: 21-04-2021
Abstract: Abstract. Assessing the size of a former ocean of which only remnants are found in mountain belts is challenging but crucial to understanding subduction and exhumation processes. Here we present new constraints on the opening and width of the Piemont–Liguria (PL) Ocean, known as the Alpine Tethys together with the Valais Basin. We use a regional tectonic reconstruction of the Western Mediterranean–Alpine area, implemented into a global plate motion model with lithospheric deformation, and 2D thermo-mechanical modeling of the rifting phase to test our kinematic reconstructions for geodynamic consistency. Our model fits well with independent datasets (i.e., ages of syn-rift sediments, rift-related fault activity, and mafic rocks) and shows that, between Europe and northern Adria, the PL Basin opened in four stages: (1) rifting of the proximal continental margin in the Early Jurassic (200–180 Ma), (2) hyper-extension of the distal margin in the Early to Middle Jurassic (180–165 Ma), (3) ocean–continent transition (OCT) formation with mantle exhumation and MORB-type magmatism in the Middle–Late Jurassic (165–154 Ma), and (4) breakup and mature oceanic spreading mostly in the Late Jurassic (154–145 Ma). Spreading was slow to ultra-slow (max. 22 mm yr−1, full rate) and decreased to ∼5 mm yr−1 after 145 Ma while completely ceasing at about 130 Ma due to the motion of Iberia relative to Europe during the opening of the North Atlantic. The final width of the PL mature (“true”) oceanic crust reached a maximum of 250 km along a NW–SE transect between Europe and northwestern Adria. Plate convergence along that same transect has reached 680 km since 84 Ma (420 km between 84–35 Ma, 260 km between 35–0 Ma), which greatly exceeds the width of the ocean. We suggest that at least 63 % of the subducted and accreted material was highly thinned continental lithosphere and most of the Alpine Tethys units exhumed today derived from OCT zones. Our work highlights the significant proportion of distal rifted continental margins involved in subduction and exhumation processes and provides quantitative estimates for future geodynamic modeling and a better understanding of the Alpine Orogeny.
Publisher: Deutsches GeoForschungsZentrum GFZ
Date: 2016
Publisher: Geological Society of America
Date: 12-2014
DOI: 10.1130/G36085.1
Publisher: Copernicus GmbH
Date: 22-11-2022
DOI: 10.5194/EGUSPHERE-2022-1203
Abstract: Abstract. Continental rifts evolve by linkage and interaction of adjacent in idual segments. As rift segments propagate, they can cause notable re-orientation of the local stress field so that stress orientations deviate from the regional trend. In return, this stress re-orientation can feed back on progressive deformation and may ultimately deflect propagating rift segments in an unexpected way. Here, we employ numerical and analog experiments of continental rifting to investigate the interaction between stress re-orientation and segment linkage. Both model types employ crustal-scale two-layer setups where pre-existing linear heterogeneities are introduced by mechanical weak seeds. We test various seed configurations to investigate the effect of i) two competing rift segments that propagate unilaterally, ii) linkage of two opposingly propagating rift segments, and iii) the combination of these configurations on stress re-orientation and rift linkage. Both the analog and numerical models show counter-intuitive rift deflection of two rift segments competing for linkage with an opposingly propagating segment. The deflection pattern can be explained by means of stress analysis in numerical experiments where stress re-orientation occurs locally and propagates across the model domain as rift segments propagate. Major stress re-orientations may occur locally, which means that faults and rift segment trends do not necessarily align perpendicularly to far-field extension directions. Our results show that strain localization and stress re-orientation are closely linked, mutually influence each other and may be an important factor for rift deflection among competing rift segments as observed in nature.
Publisher: Copernicus GmbH
Date: 19-04-2022
DOI: 10.5194/EGUSPHERE-2022-139
Abstract: Abstract. Continental rifts can form when and where continents are stretched. If the driving forces can overcome lithospheric strength, a rift valley forms. Rifts are characterised by faults, sedimentary basins, earthquakes and/or volcanism. With the right set of weakening feedbacks, a rift can evolve to break a continent into conjugate rifted margins such as those found along the Atlantic and Indian Oceans. When, however, strengthening processes overtake weakening, rifting can stall and leave a failed rift, such as the North Sea or the West African Rift. A clear definition of continental break-up is still lacking because the transition from continent to ocean can be complex, with tilted continental blocks and regions of exhumed lithospheric mantle. Rifts and rifted margins not only shape the face of our planet, they also have a clear societal impact, through hazards caused by earthquakes, volcanism, landslides and CO2 release, and through their resources, such as fertile land, hydrocarbons, minerals and geothermal potential. This societal relevance makes an understanding of the many unknown aspects of rift processes as critical as ever.
Publisher: Copernicus GmbH
Date: 26-02-2023
DOI: 10.5194/EGUSPHERE-EGU23-12967
Abstract: & & Many large sediment-hosted base metal deposits occur in failed continental rifts and the passive margins of successful rifts, e.g., in the MacArthur Basin (Australia), and in the Selwyn Basin (Canada). The large-scale geodynamics control the parameters involved in metal leaching and deposition on smaller spatial and temporal scales. Such parameters include 1) the supply of syn-rift siliciclastic sediments from the rift shoulders to form potential source rocks, 2) elevated temperatures and heat flows supporting metal leaching by fluids, 3) fault networks facilitating hydrothermal fluid flow, and 4) organic rich siliciclastic host rocks.& & & & Analysis of the occurrence of base metal deposits and lithospheric thickness has shown that the majority of deposits are located within 200 km of a craton edge (Hoggard et al. 2020). Numerical models have also shown that a craton close enough to an incipient rift controls the asymmetry of the rift system (Andres-Martinez 2016). We therefore investigate how the presence of a craton controls the development of environments favorable for metal leaching and deposition in rift basins.& & & & To this end, we use the geodynamic code ASPECT (Kronbichler et al. 2012 Heister et al. 2017) coupled to the landscape evolution model FastScape (Braun and Willett 2013 Neuharth et al. 2022) to model 2D rift systems from inception to break-up in the presence of a craton. With these high-resolution (~150 m) simulations, we investigate the relationship between craton distance and thickness and the area of potential source rock and host rock, where metals could be leached and deposited, respectively. We subsequently analyse the co-occurrence of such source and host rock and potential faulting events connecting them (e.g., Rodr& #237 guez et al. 2021).& & & & Preliminary results show that the close presence of a craton leads to predominantly asymmetric systems with a narrow craton-side margin (as shown by Andres-Martinez 2016). A craton also increases the amount of potential source and host rock. Whereas the amount of source rock increases with distance between craton and rift, the total area of potential host rock decreases. Furthermore, the co-occurrence of source, host and faults in one subbasin is rare.& & & & & & & & & Andres-Martinez, M. 2016. PhD thesis, Royal Holloway University of London.& & & & Braun, J. and S. D. Willett. 2013. & em& Geomorphology& /em& 180& #8211 : 170& #8211 . DOI: 10.1016/j.geomorph.2012.10.008.& & & & Heister, T. et al. 2017. & em& Geophys. J. Int.& /em& 210 (2): 833& #8211 . DOI: 10.1093/gji/ggx195.& & & & Hoggard, M. et al. 2020. & em& Nature Geoscience& /em& 13 (7): 504& #8211 . DOI: 10.1038/s41561-020-0593-2.& & & & Kronbichler, M. et al. 2012. & em& Geophys. J. Int.& /em& 191 (1): 12& #8211 . DOI: 10.1111/j.1365-246X.2012.05609.x.& & & & Neuharth, D. et al. 2022. & em& Tectonics& /em& 41 (3): e2021TC007166. DOI: 10.1029/2021TC007166.& & & & Rodr& #237 guez, A. et al. 2021. & em& GCubed& /em& 22 (6). DOI: 10.1029/2020GC009453.& &
Publisher: American Geophysical Union (AGU)
Date: 07-2020
DOI: 10.1029/2020GC008935
Abstract: We combine numerical modeling of lithospheric extension with analysis of seismic moment release and earthquake b‐value in order to elucidate the mechanism for deep crustal seismicity and seismic swarms in the Main Ethiopian Rift (MER). We run 2‐D numerical simulations of lithospheric deformation calibrated by appropriate rheology and extensional history of the MER to simulate migration of deformation from mid‐Miocene border faults to ∼30 km wide zone of Pliocene to recent rift floor faults. While currently the highest strain rate is localized in a narrow zone within the rift axis, brittle strain has been accumulated in a wide region of the rift. The magnitude of deviatoric stress shows strong variation with depth. The uppermost crust deforms with maximum stress of 80 MPa, at 8–14 km depth stress sharply decreases to 10 MPa and then increases to a maximum of 160 MPa at ∼18 km depth. These two peaks at which the crust deforms with maximum stress of 80 MPa or above correspond to peaks in the seismic moment release. Correspondingly, the drop in stress at 8–14 km correlates to a low in seismic moment release. At this depth range, the crust is weaker and deformation is mainly accommodated in a ductile manner. We therefore see a good correlation between depths at which the crust is strong and elevated seismic deformation, while regions where the crust is weaker deform more aseismically. Overall, the bimodal depth distribution of seismic moment release is best explained by the rheology of the deforming crust.
Publisher: Springer Science and Business Media LLC
Date: 22-07-2010
Publisher: American Geophysical Union (AGU)
Date: 05-2021
DOI: 10.1029/2020TC006553
Abstract: Complex, time‐dependent, and asymmetric rift geometries are observed throughout the East African Rift System (EARS) and are well documented, for instance, in the Kenya Rift. To unravel asymmetric rifting processes in this region, we conduct 2D geodynamic models. We use the finite element software ASPECT employing visco‐plastic rheologies, mesh‐refinement, distributed random noise seeding, and a free surface. In contrast to many previous numerical modeling studies that aimed at understanding final rifted margin symmetry, we explicitly focus on initial rifting stages to assess geodynamic controls on strain localization and fault evolution. We thereby link to geological and geophysical observations from the Southern and Central Kenya Rift. Our models suggest a three‐stage early rift evolution that dynamically bridges previously inferred fault‐configuration phases of the eastern EARS branch: (1) accommodation of initial strain localization by a single border fault and flexure of the hanging‐wall crust, (2) faulting in the hanging‐wall and increasing upper‐crustal faulting in the rift‐basin center, and (3) loss of pronounced early stage asymmetry prior to basinward localization of deformation. This evolution may provide a template for understanding early extensional faulting in other branches of the East African Rift and in asymmetric rifts worldwide. By modifying the initial random noise distribution that approximates small‐scale tectonic inheritance, we show that a spectrum of first‐order fault configurations with variable symmetry can be produced in models with an otherwise identical setup. This approach sheds new light on along‐strike rift variability controls in active asymmetric rifts and proximal rifted margins.
Publisher: Copernicus GmbH
Date: 08-10-2020
Publisher: Geological Society of America
Date: 02-2018
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5879
Abstract: & & The growth of faults is well studied with field methods, experiments and theoretical models. Fault evolution is largely established from a geometrical and kinematic point of view with respect to the growth of isolated faults and their mutual interaction. However, the dynamics of fault growth (e.g. stress shadowing, damage zone evolution, energy budgets) and the emergence of interactions over various spatial and temporal scales in larger fault networks is a topic of recent interest less illuminated so far. We here introduce a new experimental setup allowing to study & #8220 large-n& #8221 fault networks evolving in crustal-scale brittle and brittle-ductile analogue models. We document preliminary results helping to demonstrate and verify the capability of the approach.& & & & The setup, called & #8220 The Expander& #8221 , builds on a traditional extensional setup with a basal rubber sheet expanded in one direction. The aspect ratio of the rubber sheet controls its lateral contraction (& #8220 Poisson& #8217 s effect& #8221 ) and thus the bulk strain ratio under pure shear conditions. We can thus realize constrictional (prolate) to plane to flattening (oblate) kinematic basal boundary conditions depending on the sheet& #8217 s aspect ratio and whether we expand or relax the sheet. Evolving fault networks vary from anastomosing fold-and-thrust belts to conjugate sets of strike-slip fault networks to quasi-parallel normal fault populations, respectively. We apply digital image correlation (DIC) to track the kinematic surface evolution and photogrammetry (structure from motion, SFM) for topography evolution.& & & & First observations suggest that strike-slip fault networks in a purely brittle crust under basal pure shear conditions evolve into compartments of synthetic faults, the size of which scale with brittle layer thickness similar to fault spacing. The scaling seems to be controlled by slip partitioned onto the in idual faults and mediated by stress shadows. Numerical simulation of the experiment suggests that the compartmentalization might evolve further through sequential de-activation of smaller faults and collapse of deformation into a single regional scale master fault with or without prescribing a zone of crustal weakness (a & #8220 seed& #8221 ). Further experiments are planned to test the fault pattern evolution for different mechanical stratigraphy (brittle-viscous layers, seeds) and kinematic boundary conditions.& &
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5758
Abstract: & & 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 (K& sub& f& /sub& ) from no surface processes to low (K& sub& f & /sub& = 10& sup& -6 & /sup& m& sup& .2& /sup& /yr), medium (10& sup& -5& /sup& ), and high efficiency (10& sup& -4& /sup& ). 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 (hilowrona/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& #8211 , p. 170& #8211 , 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: 0.31223/X5Q333& &
Publisher: American Geophysical Union (AGU)
Date: 05-2019
DOI: 10.1029/2018GC007840
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-5674
Abstract: Destination Earth initiative pursues the implementation of a digital model of the Earth. With the aim to help understand and simulate the evolution and behavior of the Earth system components, to aid in better forecasting the impacts on human system processes, ecosystem processes and their interaction. The current state of the art technologies in numerical computations (HPC), data infrastructures (involving data storage, data access, data analysis), enable the possibility of developing numerical clones mimicking Earth& #8217 s geophysical extreme phenomena.A Digital Twin for GEOphysical extremes (DT-GEO),is a new EU project funded under the Horizon Europe programme (2022-2025), with the objective of developing a prototype for a digital twin on geophysical extremes including earthquakes, volcanoes, tsunamis, and anthropogenic-induced extreme events. It will enable analyses, forecasts, and responses to & #8220 what if& #8221 scenarios for natural hazards from their genesis phases and across their temporal and spatial scales. The project consortium brings together world-class computational and data Research Infrastructures (RIs), operational monitoring networks, and leading-edge research and academia partnerships in various fields of geophysics. It mergesthe latest outcomes from other European projects and, Centers of Excellence. DT-GEO will deploy and test 12 Digital Twin Components (DTCs). These will be self-contained entities embedding flagship simulation codes, Artificial Intelligence layers, large volumes of (real-time) data streams from and into data-lakes, data assimilation methodologies, and overarching workflows for deployment and execution of single or coupled DTCs in centralized HPC and virtual cloud computing Ris. (DT-GEO: A Digital Twin for GEOphysical extremes, project ID 101058129)
Publisher: Copernicus GmbH
Date: 11-09-2017
Abstract: Abstract. We evaluate the spatial and temporal evolution of Earth's long-wavelength surface dynamic topography since the Jurassic using a series of high-resolution global mantle convection models. These models are Earth-like in terms of convective vigour, thermal structure, surface heat-flux and the geographic distribution of heterogeneity. The models generate a degree-2-dominated spectrum of dynamic topography with negative litudes above subducted slabs (i.e. circum-Pacific regions and southern Eurasia) and positive litudes elsewhere (i.e. Africa, north-western Eurasia and the central Pacific). Model predictions are compared with published observations and subsidence patterns from well data, both globally and for the Australian and southern African regions. We find that our models reproduce the long-wavelength component of these observations, although observed smaller-scale variations are not reproduced. We subsequently define geodynamic rules for how different surface tectonic settings are affected by mantle processes: (i) locations in the vicinity of a subduction zone show large negative dynamic topography litudes (ii) regions far away from convergent margins feature long-term positive dynamic topography and (iii) rapid variations in dynamic support occur along the margins of overriding plates (e.g. the western US) and at points located on a plate that rapidly approaches a subduction zone (e.g. India and the Arabia Peninsula). Our models provide a predictive quantitative framework linking mantle convection with plate tectonics and sedimentary basin evolution, thus improving our understanding of how subduction and mantle convection affect the spatio-temporal evolution of basin architecture.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-6999
Abstract: & & The Victoria plate in the East African Rift System (EARS) is one of the largest continental microplates on Earth. The partly overlapping eastern and western EARS branches encompassing Victoria follow the inherited lithospheric weaknesses of the Proterozoic mobile belts. Multiple lines of evidence show that Victoria rotates counter-clockwise with respect to Nubia, in striking contrast to its neighboring plates. Previous numerical modeling (Glerum et al., under review) has shown that this rotation is induced through the & #8216 edge-driven& #8217 mechanism (Schouten et al., 1993), where stronger lithospheric zones transmit the drag of the major plates along the edges of the microplate, while weaker regions facilitate the rotation.& & & & The current work enhances the previous 3D box models with a spherical domain, detailed data-driven lateral thickness variations and the inclusion of mantle structure in terms of temperature and density. Crustal and lithospheric thickness variations are taken from recent geophysical datasets of the present-day African continent (Tugume et al., 2013 Globig et al., 2016). Mantle structure is either scaled from seismic tomography models or generated through the addition of thermal upwellings mimicking the East African Superplume (e.g. Ebinger and Sleep, 1998). Preliminary results show that the counterclockwise rotation of Victoria, its rotation pole and its angular velocity as observed through GPS are consistently reproduced through the data-driven lithospheric strength distribution. With subsequent models we will demonstrate the effect of mantle structure on dynamic topography, strain localization and stress distribution in the EARS.& & & & & & & & & Ebinger, C.J. and Sleep, N.H. (1998), Cenozoic magmatism throughout East Africa resulting from impact of a single plume. & em& Nature& /em& 395 (6704), 788& #8211 .& & & & & Glerum, A., Brune, S., St s, D. S. and Strecker, M. (under review), Why does Victoria rotate? Continental microplate dynamics in numerical models of the East African Rift System.& & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & Globig, J., Fern& #224 ndez, M., Torne, M., Verg& #233 s, J., Robert, A. and Faccenna, C. (2016), New insights into the crust and lithospheric mantle structure of Africa from elevation, geoid, and thermal analysis, & em& J. Geophys. Res. Solid Earth& /em& , 121, 5389& #8211 .& & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & Schouten, H., Klitgord, K. D. and Gallo, D. G. (1993), Edge-driven microplate kinematics. & em& J. Geophys. Res.& /em& 98, B4, 6689& #8211 .& & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & Tugume, F., Nyblade, A., Juli& #224 , J. and van der Meijde, M. (2013), Precambrian crustal structure in Africa and Arabia: Evidence lacking for secular variation. & em& Tectonophysics& /em& 609, 250& #8211 .& &
Publisher: Springer Science and Business Media LLC
Date: 13-11-2017
Publisher: Springer Science and Business Media LLC
Date: 21-03-2018
DOI: 10.1038/S41467-019-09335-2
Abstract: Continental rift systems form by propagation of isolated rift segments that interact, and eventually evolve into continuous zones of deformation. This process impacts many aspects of rifting including rift morphology at breakup, and eventual ocean-ridge segmentation. Yet, rift segment growth and interaction remain enigmatic. Here we present geological data from the poorly documented Ririba rift (South Ethiopia) that reveals how two major sectors of the East African rift, the Kenyan and Ethiopian rifts, interact. We show that the Ririba rift formed from the southward propagation of the Ethiopian rift during the Pliocene but this propagation was short-lived and aborted close to the Pliocene-Pleistocene boundary. Seismicity data support the abandonment of laterally offset, overlapping tips of the Ethiopian and Kenyan rifts. Integration with new numerical models indicates that rift abandonment resulted from progressive focusing of the tectonic and magmatic activity into an oblique, throughgoing rift zone of near pure extension directly connecting the rift sectors.
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-6294
Abstract: & & 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 in idual 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 in idual 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.& &
Publisher: American Geophysical Union (AGU)
Date: 03-2021
DOI: 10.1029/2020GC009577
Publisher: Copernicus GmbH
Date: 23-03-2017
Publisher: Wiley
Date: 06-02-2021
Publisher: Elsevier BV
Date: 09-2013
Publisher: American Geophysical Union (AGU)
Date: 02-2020
DOI: 10.1029/2019JB018910
Publisher: Springer Science and Business Media LLC
Date: 08-06-2020
DOI: 10.1038/S41467-020-16176-X
Abstract: The Victoria microplate between the Eastern and Western Branches of the East African Rift System is one of the largest continental microplates on Earth. In striking contrast to its neighboring plates, Victoria rotates counterclockwise with respect to Nubia. The underlying cause of this distinctive rotation has remained elusive so far. Using 3D numerical models, we investigate the role of pre-existing lithospheric heterogeneities in continental microplate rotation. We find that Victoria’s rotation is primarily controlled by the distribution of rheologically stronger zones that transmit the drag of the major plates to the microplate and of the mechanically weaker mobile belts surrounding Victoria that facilitate rotation. Our models reproduce Victoria’s GPS-derived counterclockwise rotation as well as key complexities of the regional tectonic stress field. These results reconcile competing ideas on the opening of the rift system by highlighting differences in orientation of the far-field ergence, local extension, and the minimum horizontal stress.
Publisher: American Geophysical Union (AGU)
Date: 30-09-2010
DOI: 10.1029/2009JB007100
Publisher: Research Square Platform LLC
Date: 17-10-2023
Publisher: Frontiers Media SA
Date: 11-10-2019
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-3343
Abstract: & & & & & & & & & & & & & span& The Afar rift, at the northern part of the East African Rift System (EARS), is a classic natural laboratory to study the formation of sea-floor spreading centers. Several geo-physical monitoring studies have been conducted mainly following the 2005 Dabbahu-Manda Harraro (DMH) and the 1978 Asal segments volcano-seismic crises. The two segments are located at the tips of the Red Sea and the Gulf of Aden rifts, respectively, hence how the two segments propagate towards each other is crucial to our understanding on deformation during rift linkage. To this end, we use GPS data from central Afar to model the strain and rotation rates in the region. Our results show that both the DMH and Asal segments are characterized by high shear strain and rotation rates, in agreement with independent geophysical and geological observations. No significant strain concentration occurs between the two rift propagators. By combining our results with previous geophysical observations, we suggest that linkage between the DMH and Asal segments occurs via & /span& & span& & #8764 E-W & /span& & span& oriented strike-slip fault at the tip of DMH and a broad region of NW-SE oriented normal fault bounded en echelon grabens, which are almost parallel to the Asal segment. Our preliminary results show that the style of deformation in the central Afar region is more complex and distributed than at ocean ridges where rift segments connect with localized transform faults. However, our results may inform on how transform faults initiate.& & /span& & & & / & & / & & / & & / & & / &
Publisher: Copernicus GmbH
Date: 26-03-2010
DOI: 10.5194/NHESS-10-589-2010
Abstract: Abstract. The Indonesian archipelago is known for the occurrence of catastrophic earthquake-generated tsunamis along the Sunda Arc. The tsunami hazard associated with submarine landslides however has not been fully addressed. In this paper, we compile the known tsunamigenic events where landslide involvement is certain and summarize the properties of published landslides that were identified with geophysical methods. We depict novel mass movements, found in newly available bathymetry, and determine their key parameters. Using numerical modeling, we compute possible tsunami scenarios. Furthermore, we propose a way of identifying landslide tsunamis using an array of few buoys with bottom pressure units.
Publisher: Elsevier
Date: 2023
Publisher: Elsevier BV
Date: 11-2013
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-12595
Abstract: Mapping and characterisation of crustal faults represent one of the contemporary challenges for both tectonic understanding and seismic hazard assessment. Given the high resolution of satellite-derived digital elevation models and remote-sensing imagery, the development of an automatic method of fault extraction is a critical turning point. Here we present a Python-based, open-source workflow,& which is able to extract and characterize in idual faults as well as entire fault networks from various datasets.& Our workflow consists of four main steps: (1) The DEM contains different types of noise, which we reduce using Gaussian smoothing. (2) Then we use the Canny edge detection to highlight topographic discontinuities, such as faults. (3) These edges are simplified in single pixel-wide lines through the skeletonization algorithm. (4) Finally, we create a network consisting of nodes and edges from this skeleton. After a few post-processing steps we obtain a fault network of the s le area.& We use the toolbox to study faulting in the East African Rift system, especially the Magadi Natron basin. The workflow was applied to a TanDEM-X digital elevation model with 12 m horizontal resolution and the Copernicus GLO-30 dataset with 30 m average horizontal resolution. The strike analysis shows four main directions from distinct fault populations. Moreover, we derive the fault displacement distribution throughout the basin, which allows us to calculate the total orthogonal extension of each geological unit and to compute the overall amount of extension of the region during geologically recent times.Our workflow is designed to evaluate topographic data of target sites in nature, it can, however, also be used to analyze analogue models and numerical simulations. To this aim, specific functions can be added in a modular way to suit the particularity of the area and of available data types. This workflow allows us to imagine a very wide range of applications and subjects of interest.
Publisher: American Geophysical Union (AGU)
Date: 04-2021
DOI: 10.1029/2020GC009615
Abstract: Continental microplates are enigmatic plate boundary features, which can occur in extensional and compressional regimes. Here we focus on microplate formation and their temporal evolution in continental rift settings. To this aim, we employ the geodynamic finite element software ASPECT to conduct 3D lithospheric‐scale numerical models from rift inception to continental breakup. We find that depending on the strike‐perpendicular offset and crustal strength, rift segments connect or interact through one of four regimes: (1) an oblique rift, (2) a transform fault, (3) a rotating continental microplate or (4) a rift jump. We highlight that rotating microplates form at offsets km in weak to moderately strong crustal setups. We describe the dynamics of microplate evolution from initial rift propagation, to segment overlap, vertical‐axis rotation, and eventually continental breakup. These models may explain microplate size and kinematics of the Flemish Cap, the Sao Paulo Plateau, and other continental microplates that formed during continental rifting worldwide.
Publisher: Copernicus GmbH
Date: 08-10-2020
DOI: 10.5194/SE-2020-161
Abstract: Abstract. Assessing the size of a former ocean, of which only remnants are found in mountain belts, is challenging but crucial to understand subduction and exhumation processes. Here we present new constraints on the opening and width of the Piemont-Liguria (PL) Ocean, known as the Alpine Tethys together with the Valais Basin. We use a regional tectonic reconstruction of the Western Mediterranean-Alpine area, implemented into a global plate motion model with lithospheric deformation, and 2D thermo-mechanical modelling of the rifting phase to test our kinematic reconstructions for geodynamic consistency. Our model fits well with independent datasets (i.e. ages of syn-rift sediments, rift-related fault activity and mafic rocks) and shows that the PL Basin opened in four stages: (1) Rifting of the proximal continental margin in Early Jurassic (200–180 Ma), (2) Hyper-extension of the distal margin in Early-Middle Jurassic (180–165 Ma), (3) Ocean-Continent Transition (OCT) formation with mantle exhumation and MORB-type magmatism in Middle-Late Jurassic (165–154 Ma), (4) Break-up and mature oceanic spreading mostly in Late Jurassic (154–145 Ma). Spreading was slow to ultra-slow (max. 22 mm/yr, full rate) and decreased to ~ 5 mm/yr after 145 Ma while completely ceasing at about 130 Ma due to motion of Iberia relative to Europe during the opening of the North Atlantic. The final width of the PL Ocean reached a maximum of 250 km along a NW–SE transect between Europe and Adria (Ivrea). In the Cretaceous and Cenozoic, the amount of plate convergence between Adria (Ivrea) and Europe during Alpine subduction (84–35 Ma, 420 km) and collision (35–0 Ma, 260 km) largely exceeded the width of the ocean. We suggest that at least 63 % of the subducted and accreted material was highly thinned continental lithosphere and most of the Alpine Tethys Ophiolites exhumed today derived from OCT zones. Our work highlights the importance of distal rifted continental margins during subduction and exhumation processes and provides quantitative estimates for future geodynamic modelling and a better understanding of the Alpine Orogeny.
Publisher: American Geophysical Union (AGU)
Date: 10-2019
DOI: 10.1029/2019GC008600
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-11421
Abstract: The Main Ethiopian Rift (MER) is characterized by a significant along-strike variation in rift evolution and strain accommodation mechanisms. The northern MER is at a transitional stage, whereas the central MER is at an intermediate stage of rifting. Previous geophysical and geological observations suggest that rift obliquity, age of onset of rifting and/or presence/absence of magma could be responsible for the observed difference in deformation style. Here, we use the geodynamic modelling software ASPECT that has recently been coupled with the landscape evolution model FastScape to understand the role that surface processes (such as erosion and sedimentation) play in controlling the style of deformation at the central and northern sectors of the MER. Our results show that& the deformation in the central MER can be well explained by efficient surface processes. However, our models fail to fully capture the deformation in the northern MER implying that magma plays a significant role in this sector of the rift. We show that& the MER is a unique plate boundary where surface and magmatic processes control the style of deformation at different sectors within the same tectonic setting.&
Publisher: Research Square Platform LLC
Date: 08-12-2021
DOI: 10.21203/RS.3.RS-986686/V1
Abstract: Diamonds are erupted at Earth’s surface in volatile-rich magmas called kimberlites 1,2,3 . These enigmatic magmas, originating from depths exceeding 150 kilometres in Earth’s mantle 1 , occur in stable cratons and in pulses broadly synchronous with supercontinent cyclicity 4 . Whether their mobilization is driven by mantle plumes 5 or mechanical weakening of cratonic lithosphere 4,6 remains unclear. Here we show that most kimberlites spanning the past billion years erupted approximately 25 million years after the onset of continental fragmentation, suggesting an association with rifting processes. Our dynamic models show that physically steep lithosphere-asthenosphere boundaries formed during terminal rifting (necking) generate convective instabilities in the asthenosphere that slowly migrate many hundreds of kilometres inboard of the rift, causing destabilization of cratonic mantle keel tens of kilometres thick. Displaced lithosphere is replaced by hot, upwelling asthenosphere in the return flow, causing partial melting of carbonated mantle and variable assimilation of lithospheric material. The resulting small-volume kimberlite magmas ascend rapidly and adiabatically, exsolving amounts of carbon dioxide (CO 2 ) that are consistent with independent constraints 7 . Our model reconciles diagnostic kimberlite features including association with cratons and geochemical characteristics that implicate a common asthenospheric mantle source contaminated by cratonic lithosphere 8 . Together, these results provide a quantitative and mechanistic link between kimberlite episodicity and supercontinent cycles via progressive disruption of cratonic keels.
Publisher: Springer Science and Business Media LLC
Date: 26-07-2023
Location: Germany
Start Date: 07-2018
End Date: 06-2022
Amount: $446,340.00
Funder: Australian Research Council
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