Late Jurassic Volcanism Deduced from Geochemical, Geochronological, and Sr‐Nd‐Hf Isotopic Composition Characteristics of the Nanyuan Formation, South China

Abstract

AbstractThe Nanyuan Formation contains information related to the Mesozoic tectonic transformation. In this study, three representative profiles were surveyed from the Nanyuan Formation, and multiple analyses were conducted. Zircon U‐Pb dating yielded their ages as approximately 158–146 Ma. The volcanic rocks are enriched in Rb, Th, U, K, and Pb and depleted in Nb, Ta, P, and Ti, implying their affinity for I‐type granites. The εNd(t) values (–8.3 to −6.0), (87Sr/86Sr)i values (0.7077–0.7094) of the volcanic rock, and εHf(t) values (–8.71 to 0.12) of the Mesozoic zircons suggest that the Nanyuan Formation magma originated in the lower crust with the involvement of depleted mantle materials. The parent rocks of the rhyolitic and dacitic volcanic rocks formed by partial melting of basement rocks in South China and the andesitic volcanic rocks were derived from partial melting of the metasomatites generated by slab‐mantle interaction. The fractional crystallization also played an important role in later stage. Discrimination diagrams of the volcanic rocks indicated that they formed in a volcanic arc environment. Combined with previous data, the Nanyuan Formation recorded subduction of the Paleo‐Pacific Plate before regional tectonic transformation. The compressive stress field endured until the end of the Late Jurassic.