新疆三塘湖早石炭世玄武岩地球化学特征及构造环境意义

GEOCHEMICAL CHARACTERISTICS OF EARLY CARBONIFEROUS BASALTS IN SANTANGHU REGION,XINGJIANG AND THEIR SIGNIFICANCE IN TECTONIC SETTINGS

三塘湖地区早石炭世火山活动强烈，发育以安山岩类为主的玄武岩、安山岩、英安流纹岩的岩石组合。玄武岩类具有Ａｌ２Ｏ３含量高，铁含量低，ＴｉＯ２含量低，大离子亲石元素及轻稀土元素富集的钙碱性系列特点。微量元素比值蛛网图和稀土元素配分型式具有岛弧钙碱性玄武岩的特征。利用不同构造环境玄武岩的ＮｂＺｒＹ图式、ＣｒＣｅ／Ｙ图式判别出三塘湖地区在早石炭世为岛弧构造环境。

Volcanicity was violent during the Early Carboniferous in Santanghu region.The volcanic rocks consist of basalts,andesites and dacite liparite,with andesites playing the main part.Geochemical analysis indicates that the basalts are characterized by high content of Al 2O 3,low contents of FeO+0.9Fe 2O 3 and TiO 2,rich macroion lithophile element(LIL)and LREE.The spider diagram of trace element ratio and the REE distribution patterns show the characteristics of the island arc calc alkaline series.In addition,basalt discrimination diagrams,such as Nb Zr Y and Cr Ce/Sr,suggest that Santanghu area was in an island arc envirnment during the Early Carboniferous.