Geochemistry and geochronology of metamorphic rocks in Kanas Group, Altay orogenic belt

Kanas Group is composed of a set of thick low pressure type shallow metamorphic rocks, mainly comprising schist, gneiss, and metamorphic sandstone; nevertheless, its formation time is in debate, resulting in the controversy concerning the tectonic evolution of Altay tectonic belt. The restoration of Kanas metamorphic protolith reveals that the metamorphic rocks are parametamorphic rocks. In consideration of the influence of inheriting parent rock features of rock materials and degree of metamorphism of metamorphic rocks, the authors investigated the element geochemical characteristics of clastic rocks by using research methods for clastic rocks, and the results show that the protolith of Kanas Group metamorphic rocks was formed in an environment of continental arc and also had characteristics of active continental margin. CIA, ICV indexes show that the original rocks experienced relatively warm and humid weathering process, with low maturity. The zircon U-Pb data show that the youngest zircon age is(500 ±3.0)Ma, which represents the upper limit age of Kanas Group, and that the strata were formed before late Cambrian, being a flysch formation produced in an environment of continental island arc or active continental margin. The breakup of Neoproterozoic Qingbaikouan early basement suggests that the Altay tectonic belt had Precambrian continental crust basement.