Thermochronological Constraints on the Late Cenozoic Morphotectonic Evolution of the Min Shan, the Eastern Margin of the Tibetan Plateau

Abstract

Strain distribution inferred from rock exhumation history could provide significant insights into the geodynamic models proposed for explaining late Cenozoic outward growth of the Tibetan Plateau. In this work, we present a new thermochronological data set to constrain the exhumation history of the eastern margin of the Tibetan Plateau (i.e., the Min Shan and adjacent areas) and the long-term dip-slip rates of boundary faults, including the Huya fault in the plateau margin and the Minjiang fault in the hinterland. The data set shows evident age diachroneity between different sides of the faults, with dramatically younger ages in their hanging walls than footwalls, suggesting differential exhumation across the faults. Age-elevation plots and inverse thermal history modeling for a vertical profile data set from the plateau margin (west of the Huya fault) indicate the differential exhumation started at late Miocene time (~10 Ma), synchronous with the timing at other sites of the eastern Tibetan Plateau. The magnitude of the differential exhumation is constrained as >0.6 and ~0.2 km/m.y. across the Huya and Minjiang faults, as estimated from age-elevation relationships and one-dimensional modeling of exhumation, providing unique constraints for the dip-slip rates along the faults. These two N-S striking faults, together with the Tazang fault (NWW-striking and left-lateral slipping) to the north and Longmen Shan faults (a set of NE-striking reverse faults with right-lateral components) to the south, forms a large-scale fault system to accommodate the late Cenozoic northeastward upper crustal shortening along a deep-seated hinterland-ward dipping detachment.