Volcanic-intrusive connections and crystal-melt segregation in the Dulan tilted crustal section: Insights from accessory mineral evolution

Abstract

The volcanic-intrusive connection is critical for understanding the formation of transcrustal magma systems and the mechanisms driving magma eruption. Yet, the genetic links between abyssal intrusive rocks and acidic volcanic rocks remain poorly understood. Here, we present new data from the Dulan volcanic-intrusive complex, a tilted section of the East Kunlun orogenic belt, integrating zircon UPb dating, trace elements, apatite and zircon Hf isotope geochemistry, and whole-rock geochemistry to investigate volcanic-intrusive connections and track crystal-melt segregation processes. The Dulan complex comprises rhyolite, granite porphyry, and granodiorite, all showing consistent zircon UPb ages, rare earth element (REE) patterns, and εHf(t) values, suggesting a shared magma source. Glomerocrysts of plagioclase, alkali feldspar, and hornblende, along with antecrystic zircon and apatite, imply a cumulate affinity in granodiorite and granite porphyry. Compositional variations in whole-rock and accessory minerals indicate that plagioclase, apatite, and zircon fractionation significantly influenced magma evolution. We propose a two-stage crystal segregation process in a ∼ 2 Myr-long magma reservoir system. In the early stage, at ∼33 km depth, aqueous fluid influx initiated crystal-melt segregation, forming the Dulan granodiorite from residual mush. In the later stage, mafic melt and fluid injections caused crystal-melt segregation in a shallower reservoir at ∼12 km depth, with high-silica magma producing rhyolite, while residual mush consolidated into granite porphyry. Our findings suggest that volcanic-intrusive connections are more complex than mere compositional equivalence or complementarity, requiring multidimensional analysis through accessory minerals and whole-rock geochemistry.