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The spatiotemporal interaction of large‐ and regional‐scale upper mantle forces can prevail in collisional settings. To better understand the role of these forces on post‐subduction tectonics, we focus on mantle dynamics in the East Anatolian Plateau, a well‐documented segment of the Arabian‐Eurasian continental collision zone. Specifically, we analyze multiple forces in the upper mantle, which have not been considered in previous studies in this region. To this end, we use a state‐of‐the‐art 3D instantaneous geodynamic model to quantify the dynamics of thermally defined upper mantle structures derived from seismic tomography data. Results reveal a prominent SW‐NE‐oriented mantle flow from the Arabian foreland to the Greater Caucasus–a plumelet–through a lithospheric channel under the East Anatolian Plateau. This plumelet induces localized dynamic topography (∼500 m) around the extensional Lake Van province, favoring NE‐directed compression and westward escape of the Anatolian plate. We suggest that the Lake Van region is an active magma‐rich intraplate rift in the Africa‐Arabia‐Anatolian plume‐rift system. The rift zone was probably initiated by Neotethyan subduction‐related forces and has been reactivated and/or sustained by the plumelet‐induced convective support. Our findings are consistent with numerous observations, including the recent low‐ultralow seismic velocities with a SW‐NE splitting anisotropy pattern, geochemical and petrological studies, and local kinematics showing upper mantle‐induced extensional tectonics in the collisional region. Plain Language Summary: Our goal is to better understand the active deformations of post‐subduction tectonics. To this end, we ran a 3D thermomechanical model of the East Anatolian Plateau, one of the most intriguing segments of the Arabian‐Eurasian continental collision zone. The model integrates seismically defined upper mantle structures and uses an open‐source code (ASPECT). Results reveal the significant role of large‐ and regional‐scale upper mantle forces in the study region. At long wavelengths, we find SW‐NE‐oriented mantle flow and associated dynamic topography. We interpret that such flow—a plumelet (regional upper‐mantle plume migration with neither a significant tail extending to the lower mantle nor a mushroom head reaching the hot spots on the surface)—is linked to the large‐scale mantle flow from the Arabian plate to the Greater Caucasus. At short wavelengths, we find localized dynamic topography and high stress and strain anomalies in the Lake Van zone. We argue that the plumelet, which became more forceful after the removal of the subducted Neotethyan slab, may have generated mantle tractions that contribute to magma‐rich‐intraplate rifting in the Lake Van region. Our results are in good agreement with local kinematics, low‐speed seismic velocities with SW‐NE anisotropy patterns, and geochemical‐petrological studies. Key Points: We present the 3D numerical model and observations related to the Africa‐Arabia‐Anatolian plume‐rift systemOur thermomechanical model provides new insight into the magma‐rich intraplate active rifting in collisional settingsIntegrated analyses from the 3D geodynamic model and observations reveal a SW‐NE‐oriented plumelet and its regional implications [ABSTRACT FROM AUTHOR]

Central Afar is shaped by the interaction between the Red Sea (RS) and Gulf of Aden (GoA) rifts. While there have been several studies conducted in the region, we know surprisingly little about the mechanism of connection between these two rift branches. Here we use high‐resolution 3D lithospheric scale geodynamic modeling to capture the evolution of linkage between the RS and GoA rifts in central Afar. Our results demonstrate that the two rifts initially overlap and interact across a broad zone of faulting and vertical axis block rotation. However, through time, rift overlap is abandoned in favor of direct linkage which generates a series of localized en‐echelon basins. The present‐day direct linkage between the two rifts is supported by geodetic observations. Our study reconciles previously proposed models for the RS and GoA rift connection by considering spatial and temporal evolution of the rifts. Plain Language Summary: Rifts are places where tectonic plates move away from each other. They normally start as short, isolated features, and then grow and connect together to eventually form oceans. Central Afar in East Africa is a great location to study how these rifts form and grow by connecting with other rifts. In this area, the Red Sea (RS) and Gulf of Aden (GoA) rifts interact, but it is not clear how this happened through time. Some studies suggest that the two rifts form an overlap zone where blocks within the overlap rotate, while others argue that the two rifts directly link and form a continuous rift zone. To resolve this debate, we conducted a high‐resolution computer simulation of the evolution of the RS and GoA rifts in central Afar. We compared our model results with earthquake positions and satellite data that constrain the present‐day motion of the plates. Our results demonstrate that the RS and GoA rifts first overlapped for a few millions of years, and then formed a direct linkage. Our study suggests that both conceptual models can be reconciled when we consider the temporal evolution of the two rifts through geological times. Key Points: Analyzing the spatiotemporal evolution of rifts can address the controversial issue on the connection between propagating riftsWe present results from InSAR and geodynamic models to describe the connection between Red Sea (RS) and Gulf of Aden (GoA) rifts in central AfarThe connection between the two rifts evolves from rift overlap to direct linkage elucidating the observed deformation in the region [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Continental rifting is responsible for breaking apart continents and forming new oceans. Rifts generally evolve according to three types: wide rift, symmetric rift, and asymmetric rifts, which also shape the final geometry of the continental rifted margin. Geophysical data shows that the evolution of rifts depends on a multitude of factors including the complex interactions between fault networks that accommodate extension and the processes of erosion and sediment deposition. Here we run 2D computer simulations to investigate fault network evolution during active rifting that include changes to the surface through erosion and sedimentation. By using a new python tool box, we extract the fault network from the simulation and determine individual fault properties like the number of faults, displacement, age, and length through time. We find that regardless of the rift type, rifts evolve according to five phases that can be assessed through the evolution of the fault network properties. Additionally, we find that greater erosion and sedimentation can prolong rift phases and delay the breakup of continents. Key Points: We apply a new fault analysis toolbox to coupled numerical models of tectonics and surface processesFault network evolution of the major symmetric, asymmetric, narrow, and wide rift types can be described in five distinct phasesSurface processes reduce fault network complexity and delay breakup by enhancing strain localization and increasing fault longevity [ABSTRACT FROM AUTHOR]

The lithosphere is often assumed to reside in a thermal steady‐state when quantitatively describing the temperature distribution in continental interiors and sedimentary basins, but also at active plate boundaries. Here, we investigate the applicability limit of this assumption at slowly deforming continental rifts. To this aim, we assess the tectonic thermal imprint in numerical experiments that cover a range of realistic rift configurations. For each model scenario, the deviation from thermal equilibrium is evaluated. This is done by comparing the transient temperature field of every model to a corresponding steady‐state model with an identical structural configuration. We find that the validity of the thermal steady‐state assumption strongly depends on rift type, divergence velocity, sampling location, and depth within the rift. Maximum differences between transient and steady‐state models occur in narrow rifts, at the rift sides, and if the extension rate exceeds 0.5–2 mm/a. Wide rifts, however, reside close to thermal steady‐state even for high extension velocities. The transient imprint of rifting appears to be overall negligible for shallow isotherms with a temperature less than 100°C. Contrarily, a steady‐state treatment of deep crustal isotherms leads to an underestimation of crustal temperatures, especially for narrow rift settings. Thus, not only relatively fast rifts like the Gulf of Corinth, Red Sea, and Main Ethiopian Rift, but even slow rifts like the Kenya Rift, Rhine Graben, and Rio Grande Rift must be expected to feature a pronounced transient component in the temperature field and to therefore violate the thermal steady‐state assumption for deeper crustal isotherms. Plain Language Summary: Temperature distribution is a key factor when studying Earth's interior. Here, we quantify the influence of rift velocity on temperature distribution with numerical simulations. As a continent begins to split, forming a rift, hot material beneath the rift center moves upwards increasing the temperatures at shallow crustal depth. However, simple thermal models often assume an equilibrated, constant temperature field. To evaluate tectonically induced changes in temperatures, we compare lithosphere‐scale dynamic models to models with the same material configuration but with a steady‐state temperature distribution and no deformation. We find that the latter approach well represents locations outside the rift valley and shallow crustal depths where comparably low temperatures prevail. Contrarily, at the sides of the rift valley, or for deeper‐lying isotherms like 400°C, the assumption of an equilibrated thermal field leads to an underestimation of crustal temperatures. Furthermore, we show that temperatures in narrow rifts like the Kenya Rift and the Rhine Graben are more strongly modified by tectonic movements than temperatures in wide rifts, like the Basin and Range Province. Finally, we conclude that the assumption of constant temperatures is only valid for wide rifts and very slowly extending narrow rifts with a speed limit of <0.5–2 mm/a. Key Points: We use numerical forward modeling to quantify the transient thermal imprint of continental extensionThe validity of the thermal steady‐state assumption in narrow rifts is limited to extension velocities less than 0.5–2 mm/aTransient thermal effects are particularly significant for deep isotherms, narrow rifts, and beneath the rift shoulders [ABSTRACT FROM AUTHOR]

It has recently been demonstrated that the interaction of a mantle plume with sufficiently old oceanic lithosphere can initiate subduction. However, the existence of large lithospheric heterogeneities, such as a buoyant plateau, in proximity to a rising plume head may potentially hinder the formation of a new subduction zone. Here, we investigate this scenario by means of 3‐D numerical thermomechanical modeling. We explore how plume‐lithosphere interaction is affected by lithospheric age, relative location of plume head and plateau border, and the strength of the oceanic crust. Our numerical experiments suggest four different geodynamic regimes: (a) oceanic trench formation, (b) circular oceanic‐plateau trench formation, (c) plateau trench formation, and (d) no trench formation. We show that regardless of the age and crustal strength of the oceanic lithosphere, subduction can initiate when the plume head is either below the plateau border or at a distance less than the plume radius from the plateau edge. Crustal heterogeneity facilitates subduction initiation of old oceanic lithosphere. High crustal strength hampers the formation of a new subduction zone when the plume head is located below a young lithosphere containing a thick and strong plateau. We suggest that plume‐plateau interaction in the western margin of the Caribbean could have resulted in subduction initiation when the plume head impinged onto the oceanic lithosphere close to the border between plateau and oceanic crust. Key Points: Plume‐plateau interaction can lead to four different deformation regimesCrustal heterogeneity facilitates subduction of old oceanic lithosphereHigh crustal strength hampers subduction initiation when the plume head interacts with a young lithosphere containing a thick and strong plateau [ABSTRACT FROM AUTHOR]

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 divergence 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. Plain Language Summary: While the continents are spread out across the Earth at present day, we know that at various times in Earth's history these same continents were assembled together in larger "supercontinents". These supercontinents eventually fragment by a process called continental rifting, but certain aspects of the kinematic evolution of this process remained elusive so far. We created a series of sophisticated computer simulations of mantle convection in which continental rifts emerge naturally when the forces acting on assembled continents become large enough to break them apart. The simulations show that continental breakup involves a positive feedback loop, where the faster the continents move apart, the more quickly the connection between them weakens—similar to a rope that is stretched until it yields and eventually snaps. This speed‐up of the continents can trigger the formation of new plate boundaries elsewhere on Earth, even at large distance to the rift. We also find that the continents often slow down again once the continents are separated and a new ocean basin is formed. Key Points: We investigate rift dynamics without imposed lateral boundaries using 2‐D spherical annulus numerical modelsContinental rupture exhibits a multiphase evolution: (1) slow rifting, (2) sudden acceleration and breakup, (3) fast drifting, and (4) drift slow‐downAbrupt plate speed‐up during rifting generates enhanced convergence at existing plate boundaries or induces subduction initiation [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sedimentary loading–unloading cycles control deformation in intermontane basins. • Loading delays fault nucleation and intrabasinal faulting. • Unloading promotes fault nucleation and intrabasinal faulting. 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 modeling 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 example, the Santa María 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. [ABSTRACT FROM AUTHOR]

Break-up--related extrusive magmatism, imaged in reflection seismic data as seaward-dipping reflectors (SDRs), extends symmetrically along the volcanic margins of the Atlantic Ocean. Recent research found distinct along-margin variations in the distribution of SDRs, and abundance of volcanic material was found to be spatially linked to transfer fault systems. These segmented the propagating rift that later developed into the ocean, and are interpreted as rift propagation barriers. Based on these observations, we develop a numerical model, which shows that rift-parallel mantle flow and locally enhanced rates of volcanism are the result of delays in rift propagation and segmented opening. Our model suggests that segmentation is one of the major factors in the distribution and localization of rift-related extrusive magmatism. We conclude that in addition to mantle temperature and inherited crustal structures (e.g., weaknesses from previous rift episodes), rift propagation delay plays an important role in the distribution of extrusive volcanism at volcanic passive margins by controlling the mantle flow beneath the rift axis. [ABSTRACT FROM AUTHOR]

The article offers information on the numerical modeling of continental and oceanic rifts. Topics discussed include the forces that are involved in rift dynamics including local and far-field forces; the impact of asthenospheric flow on surface stress; and the geodynamics of rift modeling. Also mentioned is a study in the issue focusing on rotational rifting.

Localization processes in the viscous lower crust lead to the formation of deformation zones over a broad range of scales. Weakening mechanisms on the grain scale cause strength reduction of rocks during localization. To gain insight into the processes involved, we conduct centimeter-scale numerical models with the finite element software SLIM3D. Our 2D models are benchmarked to high-temperature and high-pressure torsion experiments on Carrara marble samples containing a single weak Solnhofen limestone inclusion (Nardini et al., 2018). Bulk stress-strain evolution and final strain distribution are successfully reproduced by the numerical models. In order to mimic rheological weakening, a simple, strain dependent softening law is applied that alters the pre-exponential factor of the flow law. By varying softening parameter values within this modeling framework, the impact of rheological weakening on localization and shear zone formation is quantified.We find that strain localization inside the host matrix is initiated by local stress concentrations at the inclusion tips. Rheological weakening is a precondition for shear zone formation within the matrix. At the tip of the propagating shear zone, weakening occurs within a process zone that evolves in four phases (P1) pre-weakening, (P2) onset and acceleration of weakening, (P3) deceleration of weakening and (P4) steady-state. The degree of softening controls the shear zone width. With the introduction of a second softening step at elevated local strain, a high strain layer develops inside the already localized shear zone, analogue to the formation of ultramylonite bands in mylonites.ReferenceNardini, L., Rybacki, E., Döhmann, M. J., Morales, L. F., Brune, S., & Dresen, G. (2018). High-temperature shear zone formation in Carrara marble: The effect of loading conditions. Tectonophysics, 749, 120-139. [ABSTRACT FROM AUTHOR]

Abstract Linking deep seismic profiles with regional-scale gravity inversion is a powerful tool to deduce the architecture of rifted margins and their structural evolution. Here we map upper and lower crustal thicknesses of the northern South China Sea (SCS) margin in order to investigate the occurrence of depth-dependent crustal extension from the proximal to the distal margin. By comparing upper and lower crustal stretching factors, we find that the northern margin of the SCS is segmented in three parts: (1) sedimentary basins where upper crust is stretched more than lower crust, (2) distal margin where lower crust is stretched more than upper crust, (3) mostly proximal margin regions where the two layers have similar stretching factors. Our results suggest that sedimentary basins and distal margin prominently feature depth-dependent extension, however accommodated by different processes. While differential thinning within sedimentary basins appears to be governed by lateral pressure variations inducing lower crustal flow, we suggest the distal margin to be affected by a combination of mantle flow-induced lower crustal shearing and sequential fault activity during crustal hyper-extension. Graphical abstract Unlabelled Image Highlights • Regional stretching factor contrasts between the upper and lower crust are mapped in the northern margin of the SCS. • Pressure variations are the main mechanisms for depth-dependent stretching in the sedimentary basins • Mantle upwelling, basin-ward localization and crustal hyper-extension contribute to depth-depend stretching at distal margin. [ABSTRACT FROM AUTHOR]