西天山温泉地区奥陶纪侵入岩地球化学特征及成因探讨

Geochemical Characteristics and Origin of Ordovician Intrusive Rocks in Wenquan Area in Western Tianshan Mountains

西天山温泉地区是以温泉岩群为基底的古老地块,岩浆活动强烈,发育大量不同期次花岗岩类,奥陶纪侵入岩为一套准铝质—过铝质钙碱性岩石,(La/Yb)_(N)值为6.22~13.02,轻稀土元素富集,δEu为0.77~0.96,具轻微负Eu异常,微量元素中富集Sr、Ba等大离子亲石元素,亏损Th、Nb、P、Ti等高场强元素,属于中等分异的Ⅰ型花岗岩,具有壳幔混源岩浆特征。岩石地球化学特征指示,奥陶纪侵入岩形成于洋壳俯冲作用下的火山弧环境,是古亚洲洋俯冲作用在本区的体现,对认识天山地区古生代构造演化具有重要指示意义。

As an ancient block with Wenquan group as its basement,magmatic activity is strong in Wenquan area in western Tianshan mountains.It has developed a large number of granitoids of different stages.The Ordovician intrusive rocks are a set of quasi aluminousperaluminous and calcalkaline rocks.The(La/Yb)_(N) value is 6.22~13.02.The LREE enrichment.δEu value is 0.77~0.96,and shows a slight negative Eu anomaly.The trace elements are enriched in large ion lithophile elements,such as Sr and Ba,and depleted in high field strength elements,such as Th,Nb,P and Ti.They belong to moderately differentiated"Ⅰ"type granite,which is characterized by crust mantle mixed source magma.The geochemical characteristics of the rocks indicate that the Ordovician intrusions are formed in volcanic arc environment under the subduction of oceanic crust,which is the embodiment of the subduction of the Paleo Asian Ocean in this area.It is of great significance for understanding the Paleozoic tectonic evolution of Tianshan mountains.