Identifying crystal accumulation and melt extraction during formation of high-silica granite

Abstract High-silica (>70 wt% SiO2) magmas are usually believed to form via shallow crustal–level fractional crystallization of intermediate magmas. However, the broad applicability this model is controversial, because required crystal-melt separation processes have rarely been documented globally up now. The ca. 50 Ma Nyemo composite pluton Gangdese batholith belt in southern Tibet, which comprises intrusive rocks with intermediate- high-silica compositions (65–78 wt%), offers a unique opportunity for substantiating coexistence extracted melts and complementary silicic cumulates one Earth's most complete transcrustal magmatic systems. exhibit similar zircon Hf isotopic compositional ranges (mean ?Hf(t) = +5.7 +8.3), suggesting common, non-radiogenic magma source crustal assimilation deep crust. Yet, these distinct geochemical characteristics. miarolitic rapakivi granites strongly depleted Ba, Sr, Eu, their trace elements show extremely low Eu/Eu* Dy/Yb. In contrast, monzogranite relatively enriched Ba Sr minor Eu anomalies, characterized by high Therefore, we propose that represent highly fractionated melt from mush reservoir at unusually storage pressure (?99–119 MPa), constitutes residual cumulates.