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There has been considerable debate concerning the petrogenesis of Cenozoic highly felsic, strongly peraluminous, leucogranites within the Himalayan–Tibetan orogen, with two contrasting viewpoints regarding their origin, either as primary melts from parting melting or magmatic differentiation. This debate hampers our understanding of the tectono‐magmatic evolution and associated uplift and exhumation processes during Himalayan orogenesis. This study attempts to resolve this debate by means of an integrated petrographic, geochronological, and geochemical study on the Cenozoic Cuonadong leucogranites (including two‐mica granites, garnet‐bearing granites, and tourmaline‐bearing granites) in the eastern part of the south Himalayan–Tibetan orogen. One SHIRIMP zircon U–Pb dating of two‐mica granites and four LA–ICP–MS monazite U–Th–Pb dating of all three types of granites yield ages of ca. 21.9–19.7 Ma. Combined with previous published continuous U–Th–Pb zircon/monazite ages varying from 16.5 to 21.8 Ma, indicating that Cuonadong leucogranites have experienced continuously multiple episodes of intrusion and long‐term crystallization from ca.16 to 22 Ma, and lasted for ca. 6 Myrs. Major and trace element geochemistry combined with whole‐rock Sr–Nd isotope data suggest that the Cuonadong's three types of leucogranites are highly fractionated and garnet‐ and tourmaline‐bearing granites are more evolved. The Cuonadong leucogranite melts are mainly derived from metapelites within the High Himalayan Crystalline Sequence, and underwent fractional crystallization of biotite, monazite, and plagioclase during melt migration. This study indicates Cuonadong leucogranites are Cenozoic highly fractionated strongly peraluminous leucogranites, which, combined with previous intermittent documentations of fractionated leucogranites, point to an increasing maturation of the continental crust composition during continental orogenesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Mazhala Au-Sb deposit in South Tibet was constrained at ca. 35 Ma. • Mazhala apatite belongs to fluorapatite having F contents of 2–4%. • Mazhala apatite is rich in MREE but depleted in LREE- and HREE. • Mazhala apatite have δ18O values in the range of 16-19‰. • The Mazhala Au-Sb deposit was mainly precipitated from metamorphic water. Due to lack of suitable datable minerals, timing of the Mazhala Au-Sb deposit in South Tibet remains unresolved. Also, previous geochemical studies suggest an ambiguous conclusion on the source of ore-forming fluid, with diverse viewpoints of magmatic water, mixed magmatic–meteoric water or mixed metamorphic-meteoric water, respectively. In this study, hydrothermal apatite U-Pb dating constrains the Mazhala Au-Sb deposits to have formed at ca. 35 Ma, consistent with the timing of Eocene leucogranite intrusions in South Tibet. The Mazhala Au-Sb mineralization occurred during the main collision stage to late collision stage in Eocene to Oligocene, and predates the Cuonadong Sn mineralization in South Tibet which occurred during the crustal extension stage in Miocene. An EPMA analysis shows the apatite belongs to fluorapatite that have F contents in the dominant range of 2–4%. The Mazhala apatite displays an overall MREE enrichment and LREE- and HREE depletion distribution pattern with positive Eu anomalies, and have δ18O values dominantly in the range of 16-19‰ with a mean δ18O‰ value of 17.74 ± 0.15‰ (2σ), which suggest a relatively homogenous chemical composition for the ore forming fluids with a relatively stable temperature regime. In combination with previous temperature estimates, the ore forming fluids are inferred to have a dominant δ18O fluid value of 13-16‰, which overlap with metamorphic water. The combined age and geochemical data suggest Eocene leucogranite intrusion induced metamorphic fluid circulation within Paleozoic-Mesozoic metamorphic sedimentary rocks around the study area, which prompted precipitation of fluorapatite together with Au-Sb bearing pyrite and arsenopyrite in the Mazhala Au-Sb deposit. This study puts an emphasis on the contribution of metamorphic water as the dominant ore-forming fluid origin in the Mazhala Au-Sb deposit. In contrast, the close spatial and temporal association of the Cuonadong Sn polymetallic mineralization with the Miocene leucogranite intrusion-induced hydrothermal activity in the Cuonadong dome demonstrates that their genetic links, as was also evidenced by C-H-O-S-Pb isotope data that point to a dominant contritution of Miocene leucogranite to ore-forming fluid and materials for the Cuonadong Sn polymetallic ore deposits. As such, from a perspective of ore-forming model in South Tibet it be seen that during the main collision stage to late collision stage ore-forming fluid and materials were mainly derived from metamorphic water, whereas during the crustal extension stage, ore-forming fluid and materials were dominantly sourced from magmatic water. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Eocene Gumu sodic lamprophyres (GSLs) are identified in the Southern Qiangtang Orogen. • The GSLs belong to the sodic alkaline series with OIB-like affinity. • The GSLs are likely originated from asthenosphere mantle modified by slab fluids. • The GSLs were generated during the upwelling of asthenosphere triggered by delamination of the lithosphere. Sodic lamprophyres have important implications on crust-mantle interactions and tectonic evolutionary processes. This study presents detailed mineralogical and geochemical dataset to elucidate the origin of the sodic lamprophyres in the Gumu area and geodynamic implications for the Southern Qiangtang Orogen. The Gumu sodic lamprophyres (GSLs)with a zircon 206Pb/238U age of 42 Ma are primarily composed of amphibole (45%-57%), plagioclase (20%-30%) and clinopyroxene (10%). They exhibit sodic alkaline series affinity with high Na 2 O content (3.65 wt% on average) and Na 2 O/K 2 O ratio (2.26 on average). The GSLs show OIB-like geochemistry, including enrichment in LREEs and LILEs, positive zircon ε Hf (t) (+1.16 to + 7.39), slightly higher ε Nd (t) (−0.38 to + 0.9), and lower initial 87Sr/86Sr (0.70522 to 0.70589) values), and they were likely derived by the partial melting of an asthenosphere mantle source previously modified by slab fluids under spinel-garnet facies at about 1,321 °C-1,399 °C and 2.1–2.7 GPa. Integrating published regional contemporaneous mafic–intermediate rocks from the Qiangtang Orogen and this study, we propose that the GSLs formed in an intracontinental setting during asthenosphere upwelling triggered by delamination of the lithosphere. The GSLs provide new perspective for reconstructing the Eocene tectonomagmatic process in the Southern Qiangtang Orogen. [ABSTRACT FROM AUTHOR]