TY - JOUR A1 - Ballato, Paolo A1 - Brune, Sascha A1 - Strecker, Manfred T1 - Sedimentary loading–unloading cycles and faulting in intermontane basins BT - Insights from numerical modeling and field observations in the NW Argentine Andes JF - Earth & planetary science letters N2 - 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 Maria 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. (C) 2018 Elsevier B.V. All rights reserved. KW - sedimentary loading and unloading cycles KW - intermontane basins KW - intrabasinal faulting KW - Argentinean broken foreland KW - 2D numerical experiments KW - Andes Y1 - 2019 U6 - https://doi.org/10.1016/j.epsl.2018.10.043 SN - 0012-821X SN - 1385-013X VL - 506 SP - 388 EP - 396 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Ulvrova, Martina M. A1 - Brune, Sascha A1 - Williams, Simon E. T1 - Breakup Without Borders BT - How Continents Speed Up and Slow Down During Rifting JF - Geophysical research letters N2 - 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. Y1 - 2018 U6 - https://doi.org/10.1029/2018GL080387 SN - 0094-8276 SN - 1944-8007 VL - 46 IS - 3 SP - 1338 EP - 1347 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Dielforder, Armin A1 - Frasca, Gianluca A1 - Brune, Sascha A1 - Ford, Mary T1 - Formation of the Iberian-European convergent plate boundary fault and its effect on intraplate deformation in Central Europe JF - Geochemistry, geophysics, geosystems N2 - With the Late Cretaceous onset of Africa-Iberia-Europe convergence Central Europe experienced a pulse of intraplate shortening lasting some 15-20 Myr. This deformation event documents area-wide deviatoric compression of Europe and has been interpreted as a far-field response to Africa-Iberia-Europe convergence. However, the factors that governed the compression of Europe and conditioned the transient character of the deformation event have remained unclear. Based on mechanical considerations, numerical simulations, and geological reconstructions, we examine how the dynamics of intraplate deformation were governed by the formation of a convergent plate boundary fault between Iberia and Europe. During the Late Cretaceous, plate convergence was accommodated by the inversion of a young hyperextended rift system separating Iberia from Europe. Our analysis shows that the strength of the lithosphere beneath this rift was initially sufficient to transmit large compressive stresses far into Europe, though the lithosphere beneath the rift was thinned and thermally weakened. Continued convergence forced the formation of the plate boundary fault between Iberia and Europe. The fault evolved progressively and constituted a lithospheric-scale structure at the southern margin of Europe that weakened rheologically. This development caused a decrease in mechanical coupling between Iberia and Europe and a reduction of compressional far field stresses, which eventually terminated intraplate deformation in Central Europe. Taken together, our findings suggest that the Late Cretaceous intraplate deformation event records a high force transient that relates to the earliest strength evolution of a lithospheric-scale plate boundary fault. KW - intraplate deformation KW - orogeny KW - plate boundary fault KW - plate coupling force KW - Pyrenees KW - lithosphere dynamics Y1 - 2019 U6 - https://doi.org/10.1029/2018GC007840 SN - 1525-2027 VL - 20 IS - 5 SP - 2395 EP - 2417 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Lescoutre, Rodolphe A1 - Tugend, Julie A1 - Brune, Sascha A1 - Masini, Emmanuel A1 - Manatschal, Gianreto T1 - Thermal Evolution of Asymmetric Hyperextended Magma-Poor Rift Systems: Results From Numerical Modeling and Pyrenean Field Observations JF - Geochemistry, geophysics, geosystems N2 - We investigate the thermal and structural evolution of asymmetric rifted margin using numerical modeling and geological observations derived from the Western Pyrenees. Our numerical model provides a self-consistent physical evolution of the top basement heat flow during asymmetric rifting. The model shows a pronounced thermal asymmetry that is caused by migration of the rift center toward the upper plate. The same process creates a diachronism for the record of maximum heat flow and maximum temperatures (T-max) in basal rift sequences. The Mauleon-Arzacq basin (W-Pyrenees) corresponds to a former mid-Cretaceous asymmetric hyperextended rift basin. New vitrinite reflectance data in addition to existing data sets from this basin reveal an asymmetry in the distribution of peak heat (T-max) with respect to the rift shoulders, where highest values are located at the former upper- to lower-plate transition. This data set from the Arzacq-Mauleon field study confirms for the first time the thermal asymmetry predicted by numerical models. Numerical modeling results also suggest that complexities in synrift thermal architecture could arise when hanging-wall-derived extensional allochthons and related T-max become part of the lower plate and are transported away from the upper- to lower-plate transition. This study emphasizes the limitations of the common approach to integrate punctual thermal data from pre-rift to synrift sedimentary sequences in order to describe the rift-related thermal evolution and paleothermal gradients at the scale of a rift basin or a rifted margin. KW - Thermal evolution KW - Asymmetric rifting KW - Numerical model KW - Field analogue KW - Pyrenees KW - Heat flow Y1 - 2019 U6 - https://doi.org/10.1029/2019GC008600 SN - 1525-2027 VL - 20 IS - 10 SP - 4567 EP - 4587 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Döhmann, Maximilian J.E.A. A1 - Brune, Sascha A1 - Nardini, Livia A1 - Rybacki, Erik A1 - Dresen, Georg T1 - Strain Localization and Weakening Processes in Viscously Deforming Rocks BT - Numerical Modeling Based on Laboratory Torsion Experiments JF - Journal of geophysical research : JGR N2 - Localization processes in the viscous lower crust generate ductile shear zones over a broad range of scales affecting long‐term lithosphere deformation and the mechanical response of faults during the seismic cycle. Here we use centimeter‐scale numerical models in order to gain detailed insight into the processes involved in strain localization and rheological weakening in viscously deforming rocks. Our 2‐D Cartesian models are benchmarked to high‐temperature and high‐pressure torsion experiments on Carrara marble samples containing a single weak Solnhofen limestone inclusion. The models successfully reproduce bulk stress‐strain transients and final strain distributions observed in the experiments by applying a simple, first‐order softening law that mimics rheological weakening. We find that local stress concentrations forming at the inclusion tips initiate strain localization inside the host matrix. At the tip of the propagating shear zone, weakening occurs within a process zone, which expands with time from the inclusion tips toward the matrix. Rheological weakening is a precondition for shear zone localization, and the width of this shear zone is found to be controlled by the degree of softening. Introducing a second softening step at elevated strain, a high strain layer develops inside the localized shear zone, analogous to the formation of ultramylonite bands in mylonites. These results elucidate the transient evolution of stress and strain rate during inception and maturation of ductile shear zones. KW - dislocation creep KW - torsion KW - 2-D numerical model KW - rheological weakening KW - two phase aggregates KW - strain localization Y1 - 2018 U6 - https://doi.org/10.1029/2018JB016917 SN - 0148-0227 SN - 2169-9356 VL - 124 IS - 1 SP - 1120 EP - 1137 PB - Union CY - Washington, DC ER -