摘要
西准噶尔松树沟地区地层主要由碎屑沉积岩和火山岩组成,以玄武岩、安山岩和火山碎屑岩为主,其中玄武岩属于钙碱性系列,安山岩属于拉斑系列。对岩石中锆石开展LA-ICP-MS锆石U-Pb年代学研究,安山岩锆石年龄表明其形成于（317.1±6.4）Ma,粗砂岩56颗锆石中仅有1颗锆石年龄（（389±9）Ma）属于中泥盆世,其余主要集中在319~359 Ma,最小年龄（319±6）Ma。因此,该套地层并非形成于中泥盆世,很可能形成于晚石炭世早期。地球化学研究表明,玄武岩和安山岩具有相似的稀土配分曲线,轻稀土富集的右倾REE分配模式,富集大离子亲石元素K、Rb、Ba、Sr等,亏损高场强元素Nb、Ta、Th、Zr、Hf等,呈现出Ta、Nb、Ti负异常,认为该火山岩形成于岛弧环境,岩浆来源于俯冲板片脱水产生的流体不均一交代的地幔楔。该套岛弧火山岩的形成时代限定了斋桑洋盆的关闭时限（晚于317.1 Ma）。
Songshugou strata in the west of the Junggar Basin are made up of elastic sedimentary rocks and volcanic rocks. The volcanic rocks are mainly basalt, andesite and volcanic elastic rock, in which basalt belongs to calc-alkaline series and andesite belongs to porphyry series. Zircon U - Pb dating of these rocks shows that the age of zircon in andesite is （317.1±6.4）Ma. In 56 zircon samples, only one age is （389±9）Ma, suggesting the middle Devonian, whereas all other ages are concentrated in 319 -359 Ma, with the youngest one being （319±6）Ma. It is thus held that the strata were probably formed at the early stage of the late Carboniferous rather than in the middle Devonian. Geochemical studies show that the basalt and andesite have similar REE partition curves as well as right-oblique REE patterns of rich light rare earth elements, and are enriched in high ionic elements such as K, Rb, Ba, Sr and depleted in high field strength elements such as Nb, Ta, Th, Zr and Hf, with Ta, Nb, Ti negative anomalies. It is concluded that the volcanic rocks were formed in an island-arc environment and the magma was derived from mantle wedge formed by metasomatism of subducting plate dehydration that produced fluid. The formation of island arc volcanic rock restricted the closing time of the zhaisang basin（later than 317.1 Ma）.
出处
《中国地质》
CAS
CSCD
北大核心
2014年第5期1438-1451,共14页
Geology in China
基金
中国地质调查局项目“阿尔泰-准噶尔北缘成矿带基础地质综合研究”(1212011085009)、“天山成矿带基础地质综合研究”(1212011085055)及“西北基础地质调查成果集成与综合研究”(1212011220649)联合资助
