Origin and Magmatic Evolution Characteristics of the Dala Granite in the Eastern Himalayas: Evidence From Plagioclase and Mica Mineralogy
Hang Liu, Wenchang Li, Huawen Cao, Xiangfei Zhang, Ling Xing, Haoran ChenABSTRACT
Magmatic rocks with adakite affinity are used to constrain crustal thickness. Eocene adakitic rocks were recently discovered in the eastern Himalayas. However, both the timing and evidence of crustal thickening and the petrogenetic origin of adakitic rocks remain contentious. The Dala two‐mica granite was analysed using zircon/monazite U–(Th)–Pb dating, Hf isotopes, whole‐rock major/trace elements and feldspar/mica electron microprobes. Granite was emplaced ca. 41 Ma. It had high SiO 2 , Al 2 O 3 and K 2 O contents, classified as high‐potassium, calc‐alkaline, peraluminous granite, with adakitic signatures; enriched large‐ion lithophile elements (LILEs, e.g., Ba, Sr), depleted high‐field‐strength elements (HFSEs, e.g., Nb, Ta, Zr, Y) and weak or no Eu anomalies. Depletions in Nb/U, Nd/Sm, MgO, Mg # , Cr, Ni, plus zircon ε Hf ( t ) values (−25.7 to −7.1, average −10.8) and two‐stage depleted mantle model ages ( T DM2 , 1562–2723 Ma) indicate an origin of ancient thickened lower crust. The study confirmed that granite formed via partial melting of the thickened lower crust, with melt formation linked to fluid‐present muscovite melting. It may have experienced biotite metasomatism during its ascent, with the Himalayan crust reaching a thickness of ∼50 km in the early Eocene.