Characteristics and zircon U-Pb dating of the Kumdaban rock mass swarm on the northern margin of the Azhong block

Abstract：The Kumdaban rock mass swarm distributed in an uplift of medium- and low-grade metamorphic rocks on the northern margin of the Azhong block is a large-scale composite rock mass, in which the contact relationships between different rock types are very clear. From early to late, their emplacement order is fine-grained biotitic monzogranite→medium-grained biotite monzogranite containing phenocrysts. The geochemical data of the rocks testify that the rock mass swarm is similar to the continental island-arc granite (CAG) and displays the features of crust-derived granite. The single-zircon U-Pb age of 449.7±5.8 Ma obtained from the rock mass swarm indicates a Late Ordovician age for the emplacement of the rock mass swarm. The formation of the rock mass may be related to the southward subduction of the Early Paleozoic oceanic crust in Hongliugou-Lapeiquan.