Oct. 16, 2019,
noon - 1 p.m.
The Main Central Thrust (MCT) shear zone is one of the major Himalayan fault systems that is largely responsible for the generation of its high topography. Garnets collected across the MCT record their growth history in the crust through changes in their chemistry. These chemical changes can be extracted and modeled. Here, we report detailed pressure-temperature paths recorded by garnets collected across the MCT, which is exposed along the Marsyangdi River in central Nepal. The paths track evolving conditions in the Earth’s crust when the MCT was active during the growth of the Himalayas. The results suggest the fault system formed as individual rock packages moved at distinct times. Further modeling of the P-T paths makes predictions about how the Himalayas developed, including that the MCT have may have ceased motion 18-15 million years ago, as other faults closer to the Indian subcontinent became active, and that it re-activated 8-2 million years ago, leading to the generation of high Himalayan topography. In addition, the modeling suggests very high erosion rates occurred within the range after re-activation. Although garnets have long been used to understand how fault systems evolve, we provide details of an approach that allows higher-resolution data to be extracted from them, and show how they could be used to track rates of large-scale erosion.