Characteristics of Early Jurassic Volcanic Rocks of the Erlanghe Formation in the Southern Zhangguangcai Range and their Response to Paleo‐Pacific Plate Subduction

ABSTRACT The main lithologies of the volcanic rocks in the Erlanghe Formation of the southern Zhangguangcai Range are andesite and rhyolite. Zircon laser ablation multi‐collector inductively coupled plasma mass spectrometer (LA‐MC‐ICP–MS) isotopic dating yields weighted average ages of 190 ± 2.8 and 187 ± 1.7 Ma, indicating their formation during the Early Jurassic. The Erlanghe Formation volcanic rocks exhibit geochemical characteristics, including enrichment in large‐ion lithophile elements (LILEs) and depletion in high‐field‐strength elements (HFSEs). In situ zircon Hf isotopic results show that andesite and rhyolite samples have consistent Hf isotopic compositions, with high positive ε Hf ( t ) values (+6.5 to +9.6, +8.5 to +11.8) and similar two‐stage model ages ( T DM2 = 619−818 and 477−684 Ma). The intermediate volcanic rocks are derived from a depleted mantle source and formed by partial melting of the thickened lower crust—a process induced by the underplating of depleted mantle‐derived magmas. In contrast, the felsic volcanic rocks form via partial melting of crustal materials. The discovery of the 190−187 Ma calc‐alkaline volcanic assemblage reveals a compositional polarity of volcanic rocks along the transect from the continental margin to the continental interior. This finding provides reliable constraints on the initiation timing of Paleo‐Pacific Plate subduction within the tectonic system of the southern Zhangguangcai Range.