大杨树盆地双峰式火山岩的地球化学特征及构造环境

LA-ICP-MS zircon U-Pb age and tectonic environment of bimodal volcanic rocks in Dayangshu basin

为探究大杨树盆地的演化过程,基于阿荣旗地区实测资料,分析双峰式火山岩的地球化学特征及构造环境。结果表明,大杨树盆地早白垩世晚期发育一套由玄武-玄武安山岩和英安-流纹岩组成的双峰式火山岩,二者在空间上紧密伴生,形成时代基本一致。玄武-玄武安山和英安-流纹岩岩的LA-ICP-MS锆石U-Pb年龄分别为123±2、117. 68±0. 60 Ma,岩石中Si O2的质量分数分别为50. 80%～57. 10%、65. 46%～72. 58%。玄武-玄武安山岩的δEu为0. 74～0. 98,Sr、P、Ti弱亏损,英安-流纹岩的δEu为0. 34～0. 68,强烈亏损Sr、P、Ti。大杨树盆地早白垩世时期是一个规模宏大的陆内裂谷,该裂谷控制双峰式火山岩的形成。

This paper is an attempt to explore the evolution process of Dayangshu basin by analyzing the geochemical characteristics and tectonic environment of bimodal volcanic rocks based on the regional geological mineral surveys in Arong Banner area.The results show that the Dayangshu basin in late early cretaceous stage witnessed a series of bimodal volcanic rocks composed by a set of basalt-basaltic andesite and dacite-rhyolite,both of which are closely associated in the space and of almost identical formation time.Basalt-basalt andesite and ying'an-rhyolite have the LA-ICP-MS zircon U-Pb ages of 123±2 and 117.68±0.60 Ma,respectively and the mass fractions of SiO 2 in the rocks in the range of 50.80%-57.10%and 65.46%-72.58%,respectively.The basalt-basalt andesite hasδEu ranging from 0.74 to 0.98,and is weakly depleted in Sr,P and Ti;Yingan-rhyolite hasδEu ranging from 0.34 to 0.68,and is strongly depleted in Sr,P and Ti.Dayangshu basin,a large-scale intracontinental rift in Early Cretaceous stage controls the formation of bimodal volcanic rocks.