Fluid–rock–deformation interactions in the fossil Zanskar detachment footwall (NW India) revealing Early Miocene exhumation, and high-altitude ancient rainfall

Abstract

The South Tibetan Detachment (STD) is parallel to the east–west-trending axis of the Himalayan range over >1500 km and represents an untapped source of information for understanding the coupling between multi-scale deformation processes, fluid flow, exhumation of high-grade rocks and topography. Here, we present hydrogen isotope ((Formula presented.) 2H) geochemistry, quartz c-axis fabric deformation thermometry and electron microprobe micro-analyser data from a strand of the STD exposed in NW India (the Zanskar Detachment). Our data document intense meteoric fluid–rock–deformation interactions within the upper part of the hot (>400°C) mylonitic footwall to the detachment, which was active at 22–20 Ma. Calculated (Formula presented.) 2Hwater values ranging from −115 to −95‰ suggest that the Zanskar area was standing at least above 2500–3000 m mean topographic elevation during the early Miocene. When compared with previous data obtained from Mt Everest, our results suggest that high topography along the Himalayan range was diachronous, occurring at c. 20 Ma in the western Himalaya (>3000) and at c. 15 Ma in the Central Himalaya (>5000 m). This study highlights the close relationships between topography, meteoric fluid flow, high heat flux and exhumation of the Himalayan Crystalline Core.