High-precision geothermobarometry across the High Himalayan metamorphic sequence, Langtang Valley, Nepal

One of the long recognized features of Himalayan geology is the apparent in version of metamorphic sequences, as evidenced in both metamorphic paragene ses and thermobarometric data. With the aid of an extended thermobarometric dataset from the Langtang Valley section of the Higher Himalayan Crystalli nes, it can be demonstrated that the relatively large uncertainties associa ted with traditional thermobarometric techniques severely limit the tectoni c interpretation of metamorphic gradients across the Himalayas. We apply th e recently developed Delta PT approach, which significantly improves the pr ecision to which pressure and temperature differences between samples may b e calculated. High-precision thermobarometric data reveal an isothermal, ra ther than inverted, temperature array at Langtang, while the pressure data suggest significant structural complexity, with the Higher Himalayan Crysta llines in the Langtang section comprising two distinct, possibly duplicated sequences, each having experienced considerable structural attenuation fol lowing metamorphism.