Re-Evaluating A-Type Granite Petrogenesis: Formation during Ocean Opening

Abstract

A-type granites are commonly emplaced in extensional settings, including post-collisional, intraplate, and back-arc environments. This study delves into the early Permian A-type granite and its felsic enclaves from the southern Beishan orogenic belt, a critical segment of the Central Asian Orogenic Belt (CAOB). Through detailed SHRIMP zircon U–Pb dating, trace element analysis, whole-rock geochemistry, and Sr–Nd and zircon Hf–O isotope investigations, we offer new insights into the petrogenesis of these igneous rocks and their tectonic implications. The results indicate that the Caohu K-feldspar granites and its felsic enclaves, dated at 286–289 Ma, are A-type granites. These granites were sourced from the partial melting of juvenile lower crust triggered by mantle-derived magma upwelling, followed by crust-mantle magma mixing and fractional crystallization. Based on a synthesis of regional magmatic and sedimentary records, we propose an origin for these A-type granites not in a post-orogenic setting, but in association with Early Permian oceanic opening in the Liuyuan area. This finding underscores the complex interplay between magmatic and tectonic processes during the evolution of the southern Beishan orogenic belt, further highlights the significance of Permian magmatism for understanding the dynamic tectonic history of the CAOB and provides fresh perspectives on the formation and development of A-type granites in accretionary settings.