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.

Keywords

Early Jurassic / Erlanghe Formation / Paleo-Pacific Plate / subduction / volcanic rocks

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2026 Geological Society of China.