Foster, G.; Vance, D.; Argles, T. and Harris, N.
The Tertiary collision-related thermal history and tectonic evolution of the NW Himalaya.
Journal of Metamorphic Geology, 20(9),
Garnet-whole rock Sm-Nd data are presented for several samples from the Indian plate in the NW Himalaya. These dates, when combined with the P-T evolution of the Indian plate rocks, allow a thorough reconstruction of the prograde thermal evolution of this region (including the Nanga Parbat Haramosh Massif) during the early Cenozoic. Combining these data with Rb-Sr mineral separate ages, enables us to constrain the post-peak cooling history of this region of the Himalaya.
The data presented here indicate that the upper structural levels of the cover rocks of the Nanga Parbat Haramosh Massif, and similar rocks in the Kaghan Valley to the south-west, were buried to pressures of c. 10 kbar and heated to temperatures of c. 650 °C at 46–41 Ma. The burial of the lower structural levels of the cover rocks of the Nanga Parbat Haramosh Massif, to similar depths but at higher temperatures of c. 700 °C, occurred slightly later at 40–36 Ma, synchronous with the imbrication and exhumation of the amphibolite- and eclogite-grade rocks of the Kaghan Valley. In contrast, the cover rocks of the Nanga Parbat Haramosh Massif were not imbricated or exhumed at this time, remaining buried beneath the Kohistan-Ladakh Island Arc until the syntaxis-forming event that occurred in the last 10 Myr. The timing of tectonic events in the north-western Himalaya differs from that experienced by the rocks of the Central Himalaya in that the earliest stage of burial in the NW Himalaya predates that of the Central Himalaya by c. 6 Myr. This difference may result from the diachronous nature of the Indo-Asian collision or may simply be a reflection of differing timing at different structural levels.
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