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 δ⁵⁶Fe (−0.04‰–0.06‰) that are likely affected by garnet accumulation, tourmaline, and two-mica leucogranites have largely homogeneous δ⁵⁶Fe from 0.13‰ to 0.24‰ irrespective of their highly variable SiO₂, 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 δ⁵⁶Fe relative to the supposed source rocks, represented by metasedimentary rocks and/or metabasite with a δ⁵⁶Fe 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.

中文翻译：

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喜马拉雅浅色花岗岩的岩石成因：从元素和 Fe-Sr-Nd 同位素组合研究的角度来看

喜马拉雅无色花岗岩的岩石成因对于了解喜马拉雅造山带的热和构造演化仍然至关重要。为了了解它们是否主要是地壳深熔的原始熔体或经历了高度的分步结晶 (FC)，我们提供了 30 个具有代表性的喜马拉雅无色花岗岩和 9 个局部变沉积岩的 Fe 同位素数据。除了可能受石榴石堆积影响的三种低 δ ⁵⁶ Fe (-0.04‰–0.06‰) 石榴石白花岗岩外，电气石和二云母白花岗岩的 δ ⁵⁶ Fe基本上均质，范围从 0.13‰ 到 0.24‰，而与其高度可变的 SiO 无关₂、MgO 和 FeOt 含量。结合观察到的矿物组合和可用的分馏因子，这不支持在其岩石形成过程中存在高度的 FC（有或没有同化）。δ ⁵⁶ Fe 相对于假定的烃源岩升高，以变沉积岩和/或 δ ⁵⁶ Fe 值为 0.10‰ 的变质岩为代表，约 0.07‰，可能反映了地壳深熔过程中的 Fe 同位素分馏。这项研究表明，大多数白花岗岩可以对地壳深熔条件以及喜马拉雅造山带的热和构造演化提供强有力的约束。