阿尔泰山东部阿尔沙特地区酸性火山岩锆石U-Pb定年及地质意义

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

阿尔泰山东部诺尔特—阿尔沙特地区晚古生代火山岩十分发育,其中阿尔沙特一带出露一套片理化蚀变流纹岩与含凝灰质英安流纹岩的岩石组合,呈北西—南东向带状展布,前人将其划为石炭系红山嘴组a段,其岩性组合明显区别于红山嘴组b、c段地层,且稳定成规模出露。本次工作笔者对其进行了LA-ICPMS锆石U-Pb测年,获得锆石的^(206)Pb/^(238)U和^(207)Pb/^(235)U谐和年龄为(400.5±4.6)Ma,^(206)Pb/^(238)U年龄加权平均值为(400.4±3.6)Ma,代表岩浆结晶年龄,时代为早泥盆世,较前人认为的石炭纪早。结合区域地质资料分析认为,(400.4±3.6)Ma区内古大洋俯冲已达到顶峰阶段,该火山岩形成于活动大陆边缘构造环境。

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 H from Member b and c ong of shanzui Formation, but itslithologic characteristics is obviously different Hongshanzui Formation. The altered rhyolitesare selected to determine for LA-ICP-MS zircon U-Pb ages. The result shows that the 206 ^pb/238^U and 207 ^pb/235^U concordia age is （400.5 ± 4.6） Ma, the 206^Pb/238^U we the rock crystallization age were formed in igh the ted average age is （400.4 ± 3.6） Ma, indicatin Early Devonian, not Carboniferous. Combine g d with the data of southern margin of Altay, the volcanic rocks were generated in a continental arc setting of active continental margin.