大兴安岭塔源地区中生代火山岩锆石U-Pb年代学、地球化学及构造环境

大兴安岭塔源地区广泛出露一套中生代中酸性火山岩,文章在详细的野外调查基础上对其进行岩石地球化学、U-Pb年代学研究。确定塔源地区中生代火山岩为钙碱性过铝质的中酸性火山岩,稀土配分曲线呈现轻稀土元素相对富集的右倾分布特征,具有较弱的Eu负异常,富集Rb、Th、K等大离子亲石元素,亏损Sr、P、Ti等高场强元素,初步认为火山岩主要来源于地壳的部分熔融。通过锆石LA-ICP-MS U-Pb定年获得火山岩底部英安岩~(206)Pb/~(238)U加权平均年龄为154.6 Ma,结合前人获得顶部流纹岩~(206)Pb/~(238)U加权平均年龄128.7 Ma,表明火山岩形成于晚侏罗世-早白垩世。结合区域地质资料,认为其可能是蒙古-鄂霍茨克洋闭合之后的后造山阶段产物。

Zircon U-Pb dating, geochemistry and tectonic setting of the Mesozoic intermediate-acid volcanic rocks in Tayuan area, Greater Khingan Range

A set of Mesozoic intermediate-acid volcanic rocks is widely outcropped in Tayuan area, Greater Khingan Range. Based on the abundant information from detailed field investigation, the authors study the petrogeochemistry and zircon U-Pb geochronology of the volcanic rocks. The petrogeochemistry indicates that the volcanic rocks belong to the calcium alkaline peraluminous and intermediate-acid volcanic rocks, and the REE distribution patterns of these rocks decline to right with relatively enriched LREE and a weak negative Eu anomaly, the LILE including Rb, Th and K are enriched, while the HFSE including Sr, P and Ti are depleted. Therefore, it is considered that the volcanic rocks are mainly derived from the partial melting of the Crust. The zircon LA-ICP-MS U-Pb dating results show that the ²⁰⁶Pb/²³⁸U weighted mean age of the dacite from the bottom of the volcanic rocks is 154.6 Ma, combined with the previous ²⁰⁶Pb/²³⁸U weighted mean age of 128.7 Ma of the rhyolite at the top of the volcano rocks, it is considered that the volcanic rocks were formed from the Late Jurassic to Early Cretaceous. According to regional geological data, the volcanic rocks may be the post-orogenic products after the closure of the Mongolia-Okhotsk ocean.