新疆察布查尔山早石炭世火山岩构造环境判别

察布查尔山位于伊犁-伊赛克湖微板块的南部,出露最老地层为下石炭统大哈拉军山组一套浅海相-陆相基性-酸性火山岩建造.通过岩石学,岩石地球化学分析,该火山岩整体碱度较高,碱性和亚碱性系列共存,正常类型和钾质类型共存,SiO2过饱和或低度不饱和.K2O平均含量3.4%,K2O/Na2O值多大于0.6,中基性岩Al2O3含量多大于16%.玄武岩RbN/YbN值4.5~19.9,属强不相容元素富集型.酸性岩CeN/YbN在5.2~7.2之间,显示地壳熔融特点.结合图解判别,确定早石炭世火山岩形成环境为活动大陆边缘.

GEOCHEMICAL FEATURES OF EARLY-CARBONIFEROUS VOLCANITES FROM THE CHABUCHAER MOUNTAIN, YILI REGION, XINJIANG

Chabuchaer Mountain area is in the south part of the micro-plate of Yili-yisaike lake. The oldest outcropping strata is the Dahalajunshan group of Early Carboniferous Period with shallow-sea eruption as well as subaerial eruption of basic and intermediate and acidic volcanic rocks. According to comprehensive research of lithogengesis and lithogeochemisty, all these volcanic rocks have higher alkalinity, alkalis with sub-alkalis series, normal type with akali type have coexisted, and SiO2 have oversaturated rock with under saturate. The K2O mean content of the volcanic rocks is equal to 3.4% and most K2O/Na2O exceed 0.6. The large quantities of Al2O3 of volcanic rocks exceed 16%. The trace elements RbN/YbN values of basalt are 4.7-1.99 show enriched ICE type. The CeN/YbN values of acid rocks are 5.2-7.2 are melted crust type. Graphic interpretations are integrated and we conclude that these volcanic activities occurred in a marginal arc.