Discovery of the Indosinian aluminum A-type granite in Zhejiang Province and its geological significance

Abstract

Zircon LA-ICP-MS U-Pb dating of the Jingju syenogranites in the southwestern part of Zhejiang Province shows that these rocks were crystallized in the Late Triassic at 215±2 Ma, rather than in the Cretaceous as previously proposed. The Jingju syenogranites are characterized by relatively high K2O and FeO*, and low MgO. They have high concentrations of large ion lithophile elements (LIL) and LREE, such as K, Th, La, and Ce, but are depleted in high field strength elements (HFSE) such as Nb, Ta, and Ti. Their 104Ga/Al ratios and (Zr+Nb+Ce+Y) contents are also high. These characteristics are similar to those of A-type granites. The syenogranites have high ISr (0.7179–0.7203), low ɛNd(t) (from −14.2 to −13.2), and relatively old T2DM ages, similar to those of the ancient metamorphic basement in the Cathaysia Block. It is suggested that the Jingju syenogranites were formed by partial melting of the Cathaysia basement rocks during tectonic extension. This identification of Indosinian A-type granite in Jingju has significant implications for understanding the early Mesozoic tectonic evolution of South China.