Radiogenic Heating as the Thermal Driver of Himalayan Crustal Heating During Prolonged Thickening

The thermal evolution of the crust during continental collision evolves from cold to hot with time, which impacts crustal reworking and differentiation. However, it remains elusive as to the mechanism driving the crust to be hot during the protracted collision. Here, we describe crust thermal evolution via detailed petrographic and geochronological analyses, and P−T calculations on different metamorphic rocks from east‐central Himalaya, which record a wide range of P−T conditions and ages from the early to the late collision stage. The Eocene (ca. 44 Ma) metamorphism, represented by the Kangmar garnet amphibolite, exhibits P = ∼12 kbar, T = 670°−690°C, and a geothermal gradient of 17.0°–17.4°C/km. Rocks in the Tsona area yield metamorphic ages of 39–36 Ma and peak P−T conditions of 13.0–14.5 kbar and 760°−770°C (16.0°−17.9°C/km). Mafic granulites recorded variable peak conditions of 18–25 kbar and 720°−870°C (8.72°−14.6°C/km) and were overprinted by granulite‐facies metamorphism of ∼8 kbar, 916°−932°C (∼33.3°C/km) at ∼15 Ma. These results indicate that the Himalayas exhibited elevated thermal gradients during protracted collisions. Given the thick felsic crust and high rate of heat production, thermal modeling results indicate that radiogenic heating during prolonged collision caused the Himalayan crust to be hot, even to ultra‐high temperature conditions, and led to the elevated geothermal gradients. As a premier example of continental orogenesis, the Himalaya is distinctly hotter than the cold Alpine‐type orogens. This thermal difference could stem from a reduced convergence rate, low‐angle underthrusting, vigorous felsic magmatism, and persistent shear heating.