新疆东准噶尔滴水泉一带早石炭世火山岩年龄及地球化学特征

    Age and geochemical characteristics of the Early Carboniferous volcanic rocks in Dishuiquan area of East Junggar Basin, Xinjiang

    • 摘要: 滴水泉一带早石炭世火山岩分布于卡拉麦里蛇绿岩带南侧、准噶尔盆地东缘。岩石类型有玄武岩、玄武安山岩、安山岩、安山质角砾熔岩。岩石系列为碱性系列和拉斑玄武岩系列,LA-ICP-MS锆石U-Pb年龄为(336.6±3.7)Ma~(338.3±5.2)Ma,时代为早石炭世。火山岩富集LILE和轻稀土元素((La/Yb)N=3.3~8.5),Nb、Ta略显亏损, Isr值在0.70354~0.70411之间,εNd(t)值为+4.9~+6.6,源区可能是受到俯冲板片脱水流体交代的大陆地幔楔。地球化学特征表明,火山岩形成于板内环境,为后碰撞岩浆活动的产物,暗示准噶尔盆地东缘地区后碰撞岩浆活动至少从早石炭世就已经开始。火山岩中捕获的老锆石指示,准噶尔盆地东部可能存在古老基底。

       

      Abstract: The Early Carboniferous volcanic rocks in Dishuiquan area are distributed in southern Kalamaili ophiolite belt on the eastern margin of the Junggar Basin. The volcanic rocks are mainly composed of basalts, basaltic andesites, andesite and andesitic breccia lava, belonging to alkaline series and tholeiite series. The LA-ICP-MS zircon U-Pb ages of the volcanic rocks are (336.6±3.7)Ma~(338.3±5.2)Ma, indicating that they were formed in early Carboniferous. These volcanic rocks are enriched in LILE and REE ((La/Yb)N = 3.3~8.5), depleted in Nb and Ta slightly, with relatively low Isr (0.70354~0.70411) and positive εNd(t) (+4.9~+6.6). They were probably derived from a continental mantle wedge source metasomatized by dehydration fluids produced by a subducted slab. Geochemical features indicate that volcanic rocks were formed in an intraplate environment and produced in the post-collisional extensional period. These volcanic rocks suggest that post-collision magmatic activity had already begun at least in the Early Carboniferous in the eastern margin of the Junggar Basin. The captured ancient zircons in volcanic rocks indicate the presence of the old basement in eastern Junggar Basin.

       

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