Petrogenesis of Himalayan Leucogranites: Perspective From a Combined Elemental and Fe‐Sr‐Nd Isotope Study
Qingshang Shi, Yongsheng He, Zhidan Zhao, Dong Liu, Nigel Harris, Di‐Cheng Zhu
Abstract
Abstract The petrogenesis of Himalayan leucogranites remains crucial for understanding the thermal and tectonic evolution of the Himalayan orogen. To understand whether they are largely pristine melts of crustal anatexis or have experienced a high degree of fractional crystallization (FC), we present Fe isotopic data of 30 representative Himalayan leucogranites and 9 local metasedimentary rocks. Excepting three garnet leucogranites with low δ 56 Fe (−0.04‰–0.06‰) that are likely affected by garnet accumulation, tourmaline, and two‐mica leucogranites have largely homogeneous δ 56 Fe from 0.13‰ to 0.24‰ irrespective of their highly variable SiO 2 , MgO, and FeOt contents. Combined with observed mineral assemblages and available fractionation factors, this does not support a high degree of FC (with or without assimilation) in their petrogenesis. The elevated δ 56 Fe relative to the supposed source rocks, represented by metasedimentary rocks and/or metabasite with a δ 56 Fe value of 0.10‰, by ∼0.07‰, may reflect Fe isotope fractionation during crustal anatexis. This study indicates most leucogranites can provide robust constraints on the conditions of crustal anatexis and thus the thermal and tectonic evolution of the Himalayan orogen.