Exhumation History Along the Muli Thrust—Implication for Crustal Thickening Mechanism in Eastern Tibet

Abstract

Thrusting implication in the crustal thickening history of eastern Tibet is highly debated. The ∼250 km-long Muli thrust of the Yalong thrust belt in SE Tibet is a major Miocene structure with a pronounced topographic step (∼2,000 m). Using thermo-kinematic modeling based on thermochronology data, we constrain the crustal geometry of the thrust as being steep (>70°) at the surface, in agreement with field observations, and flattening at depth (≥20 km) on an intra-crustal décollement. Thrusting motion on the fault shows a velocity of 0.2 ± 0.06 km/Ma since 50 Ma, followed by an acceleration at a rate of 0.6 ± 0.08 km/Ma starting at 12.5 ± 1 Ma, yielding a total of ∼15 km of exhumed crust. Deeper, deformation may be localized through a ductile shear zone, and be related to the ∼15 km Moho step and shear wave velocity contrast imaged by tomography beneath the Yalong thrust belt.