Extensional inheritance and surface processes as controlling factors of mountain belt structure

Abstract

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.

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…In most of these examples thin-skinned thrusting propagated generally speaking outward (in-sequence), while thick-skinned thrusting progressed downwards. These observations correspond partly to the results of numerical experiments: [292] report that the thin-skinned style detachment of cover was driven by successive thick-skinned thrusts emerging from the model crust; this process propagated outward. [293] observed in their model with two décollement layers that activation of décollement propagated downward and outward.…”

Testing the effects of topography, geometry, and kinematics on modeled thermochronometer cooling ages in the eastern Bhutan Himalaya

“…The process of linking kinematic models of deformation derived from balanced cross sections to advection-diffusion thermal models in order to calculate the evolving subsurface temperatures and predict cooling ages has been explored recently by several research groups Erdös et al, 2014;Mora et al, 2015;McQuarrie and Ehlers, 2015;Castelluccio et al, 2016;Rak et al, 2017). The level of kinematic detail modeled in each of these examples varies greatly, as does how depths of measured samples were projected backwards in time.…”

“…Each kinematic step can range from 5 to 30 km over estimated time steps of 0.25-15 Myr. The flexural response of deformation has either been cal-604 M. E. Gilmore et al: Testing the effects of topography, geometry, and kinematics culated explicitly in the reconstruction software (McQuarrie and Ehlers, 2015;Rak et al, 2017) or estimated based on reconstructed paleodepths, foreland basin history, and/or perceived flexural response by using the flexural-slip unfolding algorithm in Move (Erdös et al, 2014;Mora et al, 2015;Castelluccio et al, 2016). Due to this growing method of linking cross section kinematics to thermal models, it is critical to examine how sensitive the predicted ages are to how flexural isostasy and topography are calculated because both control the depth and thus the thermal history of rocks through time .…”

“…A two-dimensional grid of points spaced 0.5 km apart was distributed across the section and sequentially deformed with the cross section to generate high-resolution displacement vectors describing how the kinematics of the system evolve in ∼ 10 km increments. By assigning an age to each step, the displacement field is converted into a velocity field that is used in the thermal and cooling age prediction model Pecube (Erdös et al, 2014;McQuarrie and Ehlers, 2015;Rak et al, 2017). Each model presented in this study was run using four to seven different suites of velocities to (1) see predominant trends in the predicted cooling ages and (2) determine which combination of velocities resulted in predicted cooling ages that best matched the measured data.…”

“…The shape of subsurface isotherms and the cooling history of minerals are also controlled by the evolution of topography, something that is largely unknown and often modeled either as a steady-state topography that matches modern topography (e.g., Coutand et al, 2014;Erdös et al, 2014;Herman et al, 2010;Whipp et al, 2007) or as an evolving topography in which relief increases or decreases with time as indicated by geologic datasets (e.g., Erdös et al, 2014). The spa-tial and temporal changes in cooling rate due to topographic relief depend on topographic wavelength and amplitude, exhumation rate and duration, and the thermochronometer systems recording the change (Ehlers and Farley, 2003;Braun et al, 2003;Mancktelow and Grasemann, 1997;Stüwe et al, 1994).…”