The Middle Triassic Meiwu Batholith, West Qinling, Central China: Implications for the Evolution of Compositional Diversity in a Composite Batholith

An integrated study involving whole-rock and Sr–Nd–Hf isotope geochemistry and zircon geo-chronology and trace element combined with detailed field investigation was carried out for the composite Meiwu batholith in the West Qinling orogenic belt of central China to probe the origins of its compositional diversity and its emplacement history. The batholith is composed of quartz diorite, granodiorite and biotite granite, with abundant mafic magmatic enclaves and minor tonalitic enclaves in the granodiorite. The crystallization age of the batholith is 240–245 Ma. Geochemical and Sr–Nd–Hf isotopic data indicate that the magmas that formed the quartz diorite and the mafic enclaves were derived by partial melting of enriched lithosphere mantle, followed by variable degrees of hybridization with crustal magmas in deep crustal hot zones. These ini-tially heterogeneous, hybrid magmas successively intruded into the upper crust and coalesced into a large magma chamber. Zircon trace element and Hf isotopic compositions suggest that the outer fine-grained part of the quartz diorite pluton crystallized from a less differentiated magma as a result of rapid cooling and thus preserved its initial heterogeneities, whereas the inner me-dium-grained part of the quartz diorite pluton crystallized from a convecting, isotopically homo-