阿尔泰晚古生代早期长英质火山岩的地球化学特征及构造背景

Geochemistry and Tectonic Setting of Early Late Paleozoic Felsic Volcanic Rocks from the Altai Orogenic Belt,North Xinjiang

新疆北部哈巴河一带出露的一套晚古生代早期长英质火山岩主要由英安质一流纹质火山岩组成。其Rb-Sr等时线年龄为405±57Ma，为早泥盆世。地球化学特征显示它们具有Ti含量低，Mg^含量中等-富集（42．2～88．7），Th／Ta为8．6～16．4，低-中等Ti／Zr值（介于4．9～53.46）；稀土配分型式为LREE富集，无Eu或中等的负Eu异常；且在蜘蛛网图上显示LlLE富集，Nb和Ta亏损的特征。Y-Nb和Rb-（Y＋Nb）构造判别图解显示这些长英质火山岩形成于岛弧环境。结合前人的研究成果，认为新疆北部哈巴河晚占牛代早期长英质火山岩是在古亚洲洋北侧岛弧构造环境下形成的，足作为古亚洲洋从SW至NE方向朝西伯利亚古板块俯冲的产物。

The Habahe felsic volcanic rocks, outcropped in the Habahe area, north Xinjiang with age of early Late Paleozoic, are mainly composed of dacitic to ryolitic rocks. The Rb-Sr i sochronal dating is 405±57 Ma, and belongs to Early Devonian. Geochemical character shows that the Habahe felsic volcanic rocks are dacitic and ryolitic composition and are low Ti content, intermediate to enriched Mg^# （42.2～88.7）, Th/Ta ratios of 8.6～16.4 and lower to intermediate Ti/Zr ratios （4.9～53.5）. These rocks have enriched LREE with lack or negative Eu anomalies. Enrichment in LILE and depletion in Nb and Ta in the trace spider diagram as well as volcame arc character in the Y-Nb and Rb-（Y ＋ Nb） discrimitive diagram reflect that formation of the Habahe felsie volcanic rocks has tectonic affinity of island arc. Based on present stucly combined with the previous study, the authors suggest the Habahe felsic volcanic rocks were formed under tectonic setting of island arc developed in the north side of the Paleo-Asian Ocean in the age of early Late Palcozoic and were as products when the Paleo-Asian Ocean subducted towards the Siberian Paleo-Plate from the SW towards NE direction.