Zircon U-Pb Dating of Volcanic Rocks from Aershate Area in Eastern Altay and Its Geological Implications

The Nurt-Aershate area is located in the eastern part of Altay, where Late Paleozoic volcanic rocks are well developed. There exists a set of rock assemblages of altered rhyolite and tuff dacite rhyolite in Aershate area, which isextensively and stably distributed distribution from northwest to southeast with a zoned shape. This set of rock assemblages was originally assigned to the Member a of Hongshanzui Formation, but itslithologic characteristics is obviously different from Member b and c of Hongshanzui Formation. The altered rhyolitesare selected to determine for LA-ICP-MS zircon U-Pb ages. The result shows that the ²⁰⁶Pb/²³⁸U and ²⁰⁷Pb/²³⁵U concordia age is(400.5±4.6)Ma, the ²⁰⁶Pb/²³⁸U weighted average age is(400.4±3.6)Ma, indicating the rock crystallization age were formed in the Early Devonian, not Carboniferous. Combined with the data of southern margin of Altay, the volcanic rocks were generated in a continental arc setting of active continental margin.