The Magmatic Plumbing System for Mesozoic High‐Mg Andesites, Garnet‐bearing Dacites and Porphyries, Rhyolites and Leucogranites from West Qinling, Central China

&NA; An integrated study of the petrography, mineral composition, zircon geochronology, whole‐rock geochemistry and Sr‐Nd‐Hf isotopes was carried out for an unusual suite of igneous rocks, including high‐Mg andesites, garnet‐bearing dacites and porphyries, rhyolites and leucogranites, from West Qinling, central China. These data, particularly observations from garnets, are used to demonstrate the petrogenetic links among the associated magmatic components which eventually formed the observed lithologies, evaluate the influence of recycling crystal populations and reconstruct the whole magmatic plumbing system. The crystallization ages of these igneous rocks are ˜239–244 Ma. The high‐Mg andesites are phenocryst‐rich and characterized by high Mg# (>40; Mg#=100*mol. MgO/(MgO + FeO)), Cr and Ni abundances, low Sr/Y and (La/Yb)N ratios, and relatively high ISr and negative &egr;Nd(t) and &egr;Hf(t) values. The petrography, mineral chemistry and geochemical data indicate that the high‐Mg andesites were generated by mixing between mantle‐derived magmas and crustal melts, with subsequent entrainment of xenocrysts (e.g. high Mg# pyroxenes, high An plagioclase and some glomerocrysts) from various sources within the crust. The chemical compositions of the garnet‐bearing dacites and porphyries and crystal‐poor rhyolites define a common differentiation trend. They become more strongly peraluminous and have more evolved Sr‐Nd‐Hf isotopic compositions with increasing SiO2 content. Petrological and geochemical data indicate that these peraluminous magmas were likely produced by fractional crystallization of andesitic magma, accompanied by assimilation of crustal materials and, or, entrainment of various phenocryst/xenocryst assemblages. Four types of garnets have been identified, including antecrysts, orthocrysts, peritectic phases and xenocrysts, and the variations in mineral composition and inclusion assemblage indicate a complicated history of magma mixing and mineral‐melt interaction/re‐equilibrium. The leucogranites are strongly depleted in HREE ((La/Yb)N > 300) and show remarkable negative Eu anomalies (Eu/Eu* = 0·42–0·52). These geochemical features are indicative of the presence of both residual garnet and plagioclase in the magma source resulting from muscovite dehydration melting of metapelitic rocks. Together, all these observations consistently reflect magma evolution in several dispersed but interconnected magma reservoirs which formed a complicated trans‐crustal magmatic plumbing system. Local magma compositions have been influenced by multiple processes, including crystallization and accumulation, recharging, anatexis, magma mixing and mingling, assimilation, remobilization of crystal mushes and random entrainment of various phenocryst assemblages and crustal xenoliths. Therefore, detailed petrographic information and mineral composition data are needed for interpreting the whole‐rock geochemistry properly. The rapid ascent and eruption of crystal‐rich and garnet‐bearing magmas have been closely associated with an extensional regime in a post‐collisional tectonic setting and facilitated by active fault systems.