Two-phase orogen-wide extension of the Himalaya since Miocene

Geodynamic studies of active collisional orogens suggest that exhumation patterns and pathways of the deep-seated rocks are dictated by coupled systems of thrust tectonics and climate-induced erosion in the orogenic fronts. However, the intensities of these couplings are less in the interior of the orogens because of the least effect of precipitation-induced erosion. Here, we use a dataset of thermochronologic cooling ages to constrain thermo-kinematic models of the extensional gneiss domes existing in the interior of the Himalayan orogen. We hypothesize that extensional collapse linked to dissipation of the gravitational potential energy of the Himalayan orogen at ~7-3 Ma significantly controlled the exhumation pathways of the gneiss dome rocks. Our modelling results suggest that the Himalayan Orogen has undergone two stages of extensional collapse, i.e., ~21-13 Ma in the ductile and ~7-3 Ma in the brittle regimes, respectively. Thus, we propose that events of extensional collapse are repetitive orogenic-scale phenomena in active orogens. Notably, the patterns of cooling ages do not correlate with precipitation, lithology, topographic relief, or channel steepness index, suggesting that topography and geomorphology have limited control over the cooling and exhumation patterns of rocks in the interior of the Himalayan orogen.