Multistage Fractional Crystallization in the Continental Arc Magmatic System: Constraints from the Appinites in Tengchong Block, Southeastern Extension of Tibet

Abstract The petrogenesis and evolution process of continental arc magmatism provide insight into discovering the formation differentiation crust. Therefore, geochemical, isotopic, mineralogical analyses were conducted for coeval igneous rocks in Tengchong Block to clarify their magmatic systems. Middle Triassic appinites Block, southeastern extension Tibet, generated at subduction setting with zircon U-Pb age ca. 243 Ma. Nb/Yb, Zr/Yb, Ta/Yb ratios along depleted Hf isotopic compositions indicate a source an N-MORB affinity appinites. However, relatively enriched whole-rock Sr-Nd characteristic high Sr/Nd, Ba/Th, Th/La, Th/Nd suggest was metasomatized by ~2% subducted sediment-derived fluid. According REE modeling, primary magma Nabang due 5-10% partial melting such mantle source. are characterized variable compositions, as SiO2 contents 47.82-61.74 wt.% MgO 10.61-2.61 wt.%, which resulted from polybaric multistage fractional crystallization slightly hydrous thick At lower crustal pressures, clinopyroxene main fractionating phase, middle amphibole+magnetite dominant phases; predominant plagioclase fractionation occurred emplacement level. This could be effective mechanism induce amphibole, accompanied suppressing lower-middle induces alumina evolved melt forms high-alumina basaltic andesitic magma.