Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process

Abstract

The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U–Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979–711Ma), Paleozoic (507–400Ma), and Early (252–185Ma) and Late (158–100Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979–911Ma, weakly deformed I-type granites at 894–815Ma, and A-type granites at 759–711Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507–470Ma, 460–422Ma and ∼415–400Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507–470Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460–422Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ∼415–400Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185Ma, with the cluster in 225–200Ma. It took place predominantly in the western part of the South Qinling Belt. The 250–240Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction of the Mianlue Ocean between the South Qinling Belt and the South China Block. Voluminous late-stage (225–185Ma) magmatism evolved from early I-type to later I-A-type granitoids associated with contemporaneous lamprophyres, representative of a transition from syn- to post-collisional setting in response to the collision between the North China and the South China blocks. Late Mesozoic (158–100Ma) granitoids, located in the southern margin of the North China Block and the eastern part of the North Qinling Belt, are characterized by I-type, I- to A-type, and A-type granitoids that were emplaced in a post-orogenic or intraplate setting. The first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process. These suggest that the tectonic evolution of the Qinling Orogen is very complicated.