DETRITAL MUSCOVITE PROVENANCE OF THE INDUS BASIN, WESTERN LADAKH, INDIA: IMPLICATIONS ON THE NATURE AND TIMING OF INDIA-ASIA COLLISION

The India-Asia collision zone records the depositional, tectonic, geodynamic and geomorphological processes that ensued in the Himalayan orogenic interior after the onset of collision between India and Asia continental plates in early Cenozoic time. The Indus Basin sedimentary rocks, which are exposed along the India-Asia continental suture in Ladakh, northwest India, present a natural laboratory to test models of deposition and collision in the Himalayan orogenic system. We present new detrital muscovite ⁴⁰Ar/³⁹Ar age data from the Indus Basin formations in western Ladakh to determine the possible source regions contributing sediments to the Indus Basin at the time of deposition of these formations. Presence of Asian and Indian detrital muscovite in the early – middle Eocene formations of the Indus Basin indicate the the onset of India-Asia collision by that time. Late Eocene – early Oligocene muscovite dominate the uppermost formation of the Indus Basin stratigraphy in western Ladakh, suggesting their derivation from metamorphic source regions on the Indian plate (e.g., Tso Morari complex). Comparing our results with the published detrital zircon U-Pb and detrital muscovite ⁴⁰Ar/³⁹Ar age data from the Indus Basin, we address the ongoing debate on whether the Ladakh arc collided first with India or Asia in northwest India.