Thermochronological constraints on Eocene deformation regime in the Long-Men Shan: Implications for the eastward growth of the Tibetan Plateau

Abstract

Understanding the spatio-temporal distribution of strain during Cenozoic growth of the Tibetan Plateau is important for constraining the geodynamic processes underpinning plateau formation. Offset Quaternary landforms and historic earthquake data suggest an along-strike change in deformation style for the eastern margin of the Tibetan Plateau, characterized by a transition from ESE-verging shortening to right-lateral shear from the southern to northern segment of the Long-Men Shan fault zone within a distance of ca. 500 km. When and how this along-strike deformation pattern formed is central to understanding the uplift history and spatio-temporal distribution of strain in the eastern margin of the Tibetan Plateau, and the underpinning geodynamics. To address this, we report a suite of low-temperature thermochronology data from the northern segment of Long-Men Shan fault zone that show a contrast in post late Cretaceous cooling and exhumation histories between the hinterland (west of the marginal Yingxiu-Beichuan fault) and foreland sides (east of the fault). Prior to the Eocene (ca. 40 Ma), the hinterland experienced significant exhumation in contrast to minor exhumation on the foreland side, but, post Eocene exhumation accelerated on the foreland side. This change reflects a switch in the deformation regime from shortening to strike-slip-dominated. This switch reduced hinterland rock uplift and tectonic and topographic loading over the foreland basin, leading to accelerated foreland exhumation through isostatic adjustments. A compilation of fault deformation history for the eastern Tibetan Plateau shows a second tectonic transition in the late Miocene, characterized by formation of the south-striking Huya and Minjiang faults. Our results highlight the importance of progressive late Eocene and late Miocene tectonic transitions in shaping the eastern margin of the Tibetan Plateau. • The hinterland and foreland sides of the eastern Tibetan Plateau margin experienced differential Eocene exhumation. • The differential evolution indicates a coeval tectonic transition from shortening-dominated to strike-slip-dominated. • A second tectonic transition is characterized by the late Miocene formation of the Huya and Minjiang faults. • The eastern margin of the Tibetan Plateau is shaped by progressive late Eocene and late Miocene tectonic transitions.