Early Oligocene partial melting in the Main Central Thrust Zone (Arun valley, eastern Nepal Himalaya)

Microstructural observations combined with P-T pseudosection analysis show that dehydration partial melting occurred in the kyanite-field. After reaching peak conditions at about 820 °C, 13 kbar, the studied sample experienced decompression accompanied by cooling down to 805 °C, 10 kbar, which caused in situ melt crystallization. SHRIMP monazite and zircon geochronology provides evidence that the anatexis affecting the upper portion of the MCTZ occurred during Early Oligocene (∼ 31 Ma). These results demonstrate that in the upper MCTZ, at least in the eastern Himalaya, crustal anatexis was earlier than, and not a consequence of, decompression linked to exhumation along the MCT.