东天山卡拉塔格石炭纪安山岩地球化学、年代学研究及地质意义

Geochemistry,Geochronology and Its Implication of Carboniferous Andesite in the Kalatage Area,East Tianshan,Xinjiang

通过对东天山卡拉塔格石炭纪安山岩进行详细岩石学、地球化学、锆石U-Pb年代学和Lu-Hf同位素研究,精确厘定了该火山岩成岩时代,探讨了岩浆来源及构造背景,进一步约束了古亚洲洋闭合时限。卡拉塔格石炭纪地层为一套火山碎屑岩夹火山岩,其中火山岩以安山岩为主。对安山岩进行LA-ICPMS锆石U-Pb测年,获得年龄(309.0±3.3)Ma为晚石炭世。岩石地球化学特征显示,安山岩为钠质、过铝质、钙碱性系列;稀土元素富集LREE,(La/Yb)_(N)为3.10~4.13,δEu呈弱的负异常;微量元素Zr/Yb(6.78~8.76)、Hf/Yb(1.47~1.83)、Zr/Nb(32.06~34.60)的值均接近于岛弧安山岩;元素蛛网图上具富集大离子亲石元素Rb,Ba,U,K等,亏损Nb,Ta,Ti特征,表明其形成于岛弧环境。样品εHf(t)变化范围较大为-13.1~+14.8,且具高Sr,Yb和Y含量,低Sr/Y值,Ba/La>13,表明安山岩源区以俯冲流体交代的地幔楔部分熔融为主。

Through the detailed study of petrology,geochemistry,zircon U-Pb chronology and Lu Hf isotope of the Carboniferous andesite in Kalatag,East Tianshan,the diagenetic age of the volcanic rock is accurately determined,the magmatic source and tectonic background are discussed,and the closure time of the paleo Asian Ocean is further con-strained.The Kalatage Carboniferous strata are a set of pyroclastic rock intercalated volcanic rocks,in which the volcanic rocks are dominated by andesite.The LA-ICP MS zircon U-Pb dating of andesite obtained(309.0±3.3)Ma,which be-long to the late Carboniferous.The geochemical characteristics show that the andesite is mainly composed of sodium,peraluminous and calc-alkaline series,and displays LREE enrichment and negative Eu anomalies with(La/Yb)_(N) ratio of 3.10~4.13,Zr/Yb of 6.78~8.76,Hf/Yb of 1.47~1.83,Zr/Nb of 32.06~34.60 which are close to that of arc andesite.The samples have affinities to an arc setting which possess the signature of enrichment in large ionic lithophilic element of Rb、Ba、U、K and depletion in Nb、Ta、Ti on the primitive-mantle normalized trace element multi-variation diagrams.The andesite display large range ofεHf(t)(-13.1~+14.8),high Sr,Yb and Y content,low Sr/Y,Ba/La>13.These charac-teristics indicate that they were mainly derived from a partial melting of mantle wedges mixed with subduction fluid.