西准噶尔谢米斯台山东段早石炭世玄武安山岩的成因及意义

摘要

本文对西准噶尔谢米斯台山东段早石炭世的火山岩进行了 Ar-Ar 年代学、岩石学和地球化学研究。Ar-Ar 定年结果显示,这些火山岩喷发时间为338.7±6.9 Ma。在地球化学方面,它们显示钙碱性的特征,富集大离子亲石元素(LILE)和轻稀土元素(LREE),亏损高强场元素(HFSE,如Nb和Ta)以及具有高的Rb/Y和Ba/Nb比值,显示岛弧岩浆的特征。而在Th-Hf/3-Nb/16环境判别图中,所有样品落在岛弧玄武岩区域。结合古地理、古地磁、岩浆岩以及大地构造研究成果,作者认为西准噶尔地区在早石炭世处于岛弧环境,即准噶尔洋向西北侧和东南侧的双向俯冲。在亚洲洋的构造演化过程中,还存在斋桑洋、北天山洋和准噶尔洋等多个洋内俯冲系统。%This paper presents new Ar-Ar age and geochemical data for the early Carboniferous volcanic rocks in the eastern part of the Xiemisitai Mountain, northern West Junggar. 40Ar/39Ar dating of the basaltic andesite yielded a well-defined plateau age of 338.7±6.9 Ma. In geochemistry, the basaltic andesite exhibits calc-alkaline characteristics, enriched in LILE and LREE, depleted in HFSE (e.g. Nb and Ta) with high Rb/Y and Ba/Nb ratios, which is consistent with the geochemical characteristics of arc-related magmas. Furthermore, all rocks plot in the island arc basalt field in the Th-Hf/3-Nb/16 tectonic discrimination diagram. Combined with previous results of palaeogeography, palaeomagnetism, magmatic rocks and structural geology, we consider that the basaltic andesite was likely generated in an island arc setting. Subduction of Junggar Ocean was bidirectional, toward the northwest and southeast, respectively. Paleo-Asian Ocean might have experienced multiple intra-oceanic subduction (i.e, North Tianshan Ocean, Junggar Ocean, Irtysh-Zaysan Ocean, etc.) during its tectonic evolution.