Possible thermal buffering by crustal anatexis in collisional orogens: Thermobarometric evidence from the Nepalese Himalaya

One-dimensional thermal models suggest that large thrust faults may exert first-order control on the thermal structure of collisional orogenic belts, and an increasing body of petrologic data may be interpreted as consistent with these models. We present new thermobarometric data from the central Nepalese Himalaya which imply that large sections of the Himalayan orogen may have been at roughly uniform temperatures during active thrusting, a phenomenon that is not predicted by existing models. We attribute this phenomenon to thermal buffering as a consequence of widespread in situ anatexis. If this process is common in the intermediate and lower crust of active orogens and if it is localized spatially, one-dimensional thermal models may produce an extremely oversimplified picture of heat transfer processes during collisional orogenesis.