Surface processes and inherited structures are widely regarded as factors that strongly influence the evolution of mountain belts. The first-order effects of these parameters have been studied extensively throughout the last decades, but their relative importance remains notoriously difficult to assess and document. We use lithospheric scale plane-strain thermomechanical model experiments to study the effects of surface processes and extensional inheritance on the internal structure of contractional orogens and their foreland basins. Extensional inheritance is modeled explicitly by forward modeling the formation of a rift basin before reversing the velocity boundary conditions to model its inversion. Surface processes are modeled through the combination of a simple sedimentation algorithm, where all negative topography is filled up to a prescribed reference level, and an elevation-dependent erosion model. Our results show that (1) extensional inheritance facilitates the propagation of basement deformation in the retro-wedge and (2) increases the width of the orogen; (3) sedimentation increases the length scale of both thin-skinned and thick-skinned thrust sheets and (4) results in a wider orogen; (5) erosion helps to localize deformation resulting in a narrower orogen and a less well-developed retro-wedge. A comparison of the modeled behaviors to the High Atlas, the Pyrenees, and the Central Alps, three extensively studied natural examples characterized by different degrees of inversion, is presented and confirms the predicted controls of surface processes and extensional inheritance on orogenic structure.

The first-order characteristics of collisional mountain belts and the potential feedback with surface processes are predicted by critical taper theory. While the feedback between erosion and mountain belt structure has been fairly extensively studied, less attention has been given to the potential role of synorogenic deposition. For thin-skinned fold-and-thrust belts, recent studies indicate a strong control of syntectonic deposition on structure, as sedimentation tends to stabilize the thin-skinned wedge. However, the factors controlling basement deformation below fold-and-thrust belts, as evident, for example, in the Zagros Mountains or in the Swiss Alps, remain largely unknown. Previous work has suggested that such variations in orogenic structure may be explained by the thermotectonic "age" of the deforming lithosphere and hence its rheology. Here we demonstrate that sediment loading of the foreland basin area provides an additional control and may explain the variable basement involvement in orogenic belts. When examining the role of sedimentation, we identify two end-members: (1) sediment-starved orogenic systems with thick-skinned basement deformation in an axial orogenic core and thin-skinned deformation in the bordering forelands and (2) sediment-loaded orogens with thick packages of synorogenic deposits, derived from the axial basement zone, deposited on the surrounding foreland fold-and-thrust belts, and characterized by basement deformation below the foreland. Using high-resolution thermomechanical models, we demonstrate a strong feedback between deposition and crustal-scale thick-skinned deformation. Our results show that the loading effects of syntectonic sediments lead to long crustal-scale thrust sheets beneath the orogenic foreland and explain the contrasting characteristics of sediment-starved and sediment-loaded orogens, showing for the first time how both thin-and thick-skinned crustal deformations are linked to sediment deposition in these orogenic systems. We show that the observed model behavior is consistent with observations from a number of natural orogenic systems.

Abstract. We use two-dimensional thermomechanical models to investigate the potential role of rapid filling of foreland basins in the development of orogenic foreland fold-and-thrust belts. We focus on the extensively studied example of the Western European Alps, where a sudden increase in foreland sedimentation rate during the mid-Oligocene is well documented. Our model results indicate that such an increase in sedimentation rate will temporarily disrupt the formation of an otherwise regular, outward-propagating basement thrust-sheet sequence. The frontal basement thrust active at the time of a sudden increase in sedimentation rate remains active for a longer time and accommodates more shortening than the previous thrusts. As the propagation of deformation into the foreland fold-and-thrust belt is strongly connected to basement deformation, this transient phase appears as a period of slow migration of the distal edge of foreland deformation. The predicted pattern of foreland-basin and basement thrust-front propagation is strikingly similar to that observed in the North Alpine Foreland Basin and provides an explanation for the coeval mid-Oligocene filling of the Swiss Molasse Basin, due to increased sediment input from the Alpine orogen, and a marked decrease in thrust-front propagation rate. We also compare our results to predictions from critical-taper theory, and we conclude that they are broadly consistent even though critical-taper theory cannot be used to predict the timing and location of the formation of new basement thrusts when sedimentation is included. The evolution scenario explored here is common in orogenic foreland basins; hence, our results have broad implications for orogenic belts other than the Western Alps.

We present a new method that can be used to quantitatively evaluate the consistency between balanced section restorations and thermochronological data sets from orogenic belts. We have applied our method to a crustal-scale area-balanced cross-section restoration along a profile in the Central Pyrenees. This restoration is well constrained and supported by a wide variety of geological and geophysical data. Moreover, an extensive thermochronological data set has been collected independently in the area. We use the structural-kinematic software 2D-Move ™ to constrain a set of velocity fields that describes the kinematics of the Central Pyrenees. Using these velocity fields as input for the thermokinematic code PECUBE, we derive predictions of the thermal history and a range of thermochronometric ages for the modeled area. We find that the kinematic history of the belt as inferred from section balancing is in good agreement with the published thermochronological data. High-temperature (zircon fission-track and K-feldspar Ar-Ar) data constrain the thermal structure of the belt as well as the timing of underplating. Low-temperature (apatite fission-track and (U-Th)/He) data require late synorogenic sedimentary burial of the southern flank of the Pyrenees between late Eocene (40 Ma) to late Miocene (9 Ma) times, consistent with previous studies, and imply that no such burial occurred on the northern flank.

Subduction interface strength has important role in back-arc stress-state; Back-arc extension in 2D is facilitated by weak overriding plate rheology; The subduction of narrow oceanic domains can generate enough slab-pull to create back-arc breakup;

Back‐arc basins such as the ones behind the island‐arcs of the Western Pacific Ocean or the ones in the Mediterranean Sea are ubiquitous structures of the Earth. They are extensional basins forming in the overriding plate behind subduction zones and similarly to continental rifts, they can exhibit different structural styles from narrow, localized rifting to wide‐rift extension. While these different structural styles have been long recognized, the factors controlling the style of extension in these basins have not been explored properly. We use thermo‐mechanical models to investigate how the relative rates of progressive build‐up of slab‐pull force and of convective thinning and thermal weakening of the overriding plate control the style of back‐arc rifting. Following subduction‐initiation, a high subducting plate velocity results in rapid build‐up of the slab‐pull force. The relatively low rate of convectively thinning and associated moderate weakening of the overriding plate require slab‐pull to build up to close to its maximum value to overcome the high back‐arc integrated strength resulting in a narrow back‐arc rift. In turn a low subducting plate velocity in comparison with the timescale of convective thinning of the overriding plate allows for significant back‐arc weakening before the slab‐pull force becomes large enough to drive back‐arc extension. In this case, the back‐arc exhibits a wide rifting style as extension occurs at significantly reduced overriding plate integrated strength. Our model results provide an explanation why some subduction zones exhibit wide, distributed extension in the overriding plate such as for instance observed in the Pannonian basin.

Venus is a terrestrial planet with dimensions similar to the Earth, but a vastly different geodynamic evolution, with recent studies debating the occurrence and extent of tectonic‐like processes happening on the planet. The precious direct data that we have for Venus is very little, and there are only few numerical modeling studies concerning lithospheric‐scale processes. However, the use of numerical models has proven crucial for our understanding of large‐scale geodynamic processes of the Earth. Therefore, here we adapt 2D thermomechanical numerical models of rifting on Earth to Venus to study how the observed rifting structures on the Venusian surface could have been formed. More specifically, we aim to investigate how rifting evolves under the Venusian surface conditions and the proposed lithospheric structure. Our results show that a strong crustal rheology such as diabase is needed to localize strain and to develop a rift under the high surface temperature and pressure of Venus. The evolution of the rift formation is predominantly controlled by the crustal thickness, with a 25 km‐thick diabase crust required to produce mantle upwelling and melting. The surface topography produced by our models fits well with the topography profiles of the Ganis and Devana Chasmata for different crustal thicknesses. We therefore speculate that the difference in these rift features on Venus could be due to different crustal thicknesses. Based on the estimated heat flux of Venus, our models indicate that a crust with a global average lower than 35 km is the most likely crustal thickness on Venus.

<p align="justify">Venus is a terrestrial planet with dimensions similar to the Earth and, although it is generally assumed that it does not host plate-tectonics, there are indications that Venus might have experienced, or still does experience, some form of tectonics. In fact, there are widespread observations of rifts on Venus called ‘chasma’ (plural ‘chasmata’), from radar-image interpretation of normal-fault-bounded graben structures (Harris & Bédard, 2015).</p> <p align="justify">The rifts on Venus have been likened to continental rifts on Earth such as the East African (e.g., Basilevsky & McGill, 2007) and Atlantic rift system prior to ocean opening (Graff et al., 2018), even if they are commonly wider than their terrestrial equivalent (e.g., Foster & Nimmo, 1996). However, despite being a prominent feature on its surface, little is known about the mechanisms responsible for creating rifts on Venus beyond the assumption that they are extensional features (Magee & Head, 1995).</p> <p align="justify">Since rifting on Earth in both continental and oceanic settings has been extensively studied through modeling, we adapted 2D thermo-mechanical numerical models of rifting on Earth to Venus in order to study how rifting structures observed on the Venusian surface could have been formed. More specifically, we investigated how rifting evolves under the high pressure and temperature conditions of the Venusian surface and the lithospheric structure proposed for Venus.</p> <p align="justify">Our results show that a strong crustal rheology such as diabase is needed to localize strain and to develop a rift under the harsh surface conditions of Venus. The evolution of the rift formation is predominantly controlled by the crustal thickness, with a 25 km-thick diabase crust required to produce mantle upwelling and melting. Lastly, we compared the surface topography produced by our models with the topography profiles of different Venusian chasmata. We observed a good fit between models characterised by different crustal thicknesses and the Ganis and Devana Chasmata, suggesting that differences in rift features on Venus could be due to different crustal thicknesses.</p> <p align="justify"> </p> <p align="justify"><strong>References</strong></p> <p align="justify">Basilevsky, A. T., & McGill, G. E. (2007). Surface evolution of Venus. In Exploring Venus as a terrestrial planet (p. 23-43). American Geophysical Union. doi: 10.1029/176GM04</p> <p align="justify">Foster, A., & Nimmo, F. (1996). Comparisons between the rift systems of East Africa, Earth and Beta Regio, Venus. Earth and Planetary Science Letters, 143 (1), 183-195. doi: 10.1016/0012-821X(96)00146-X</p> <p align="justify">Graff, J., Ernst, R., & Samson, C. (2018). Evidence for triple-junction rifting focussed on local magmatic centres along Parga Chasma, Venus. Icarus, 306 , 122-138. doi: 10.1016/j.icarus.2018.02.010</p> <p align="justify">Harris, L. B., & Bédard, J. H. (2015). Interactions between continent-like ‘drift’, rifting and mantle flow on Venus: gravity interpretations and Earth analogues. In: Volcanism and Tectonism Across the Inner Solar System. Geological Society of London. doi: 10.1144/SP401.9</p> <p align="justify">Magee, K. P., & Head, J. W. (1995). The role of rifting in the generation of melt: Implications for the origin and evolution of the Lada Terra-Lavinia Planitia region of Venus. Journal of Geophysical Research: Planets, 100 (E1), 1527-1552. doi: 10.1029/94JE02334</p>