DOES GEOMETRY MATTER? USING A COUPLED KINEMATIC-THERMAL MODEL TO LINK THE GEOMETRY AND KINEMATICS OF A BALANCED CROSS SECTION TO COOLING AGES

Advancements in thermochronology, and the range of mineral systems available to document the cooling history of rocks have allowed us to link the age of thermochronologic samples to both exhumational and deformational processes. However, in compressional orogens it is unclear how much of this temperature-time path is a function of active folding and faulting, or erosional processes that continue after folding and faulting have ceased. Because of uncertainty in how cooling ages are linked to fault displacement, particularly in fold-thrust belts where multiple generations of structures deform and / or transport a package of rocks, accurate assignment of an age and rate to thrust displacement is an ongoing challenge. We present a kinematic deformation model that is coupled to an advection diffusion thermal model that allows us to test the effect of geometry and kinematics on cooling ages. Many current numerical experiments use a static décollement geometry combined with an underplating and/or accretion parameter to transfer material from below the decollement to a growing wedge above the decollement. However, these models fall short in that they cannot evaluate if and how the décollement changes with time (location and magnitude of ramps), or if cooling ages are linked to specific structures, because these models disconnect the thermal history from the attributes of structures that facilitated that history. In contrast, a kinematically viable model of a sequentially restored cross section predicts the location and magnitude of footwall ramps and how the decollement may be changing with time. For a viable linked kinematic-thermal model, the locations of footwall ramps predicted by the balanced cross section must provide modeled cooling ages that match the observed ages for the kinematic scenario to be considered valid. We test the coupled thermal-kinematic model along a structural transect across the Himalaya in eastern Bhutan and compare modeled cooling ages to published cooling ages. This approach allows for a way to directly test how the geometry and rate of deformation effect location, magnitude and age of erosion as well as the recycling and preservation of foreland basin sediments.