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

The South Tibetan Detachment (STD) is parallel to the east–west-trending axis of the Himalayan range over &gt;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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 2 H) 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 (&gt;400°C) mylonitic footwall to the detachment, which was active at 22–20 Ma. Calculated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 2 H water 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 (&gt;3000) and at c . 15 Ma in the Central Himalaya (&gt;5000 m). This study highlights the close relationships between topography, meteoric fluid flow, high heat flux and exhumation of the Himalayan Crystalline Core.