新疆吐尔库班套蛇绿混杂岩的发现及其地质意义

摘要

Ophiolite, as a well record of ocean-crust relic, plays an important role in the study of paleo-plate tectonics and its evolution. The newly-found Tuerkubantao ophiolitic mélange is located in the south of the Buerjin, Altay area, China. It is composed of ultramafic rock, gabbro, diabase, basalt and flysch formation. The zircon U-Pb ages of the gabbro and gneissic granite are 363 Ma and 355 Ma, respectively. It suggests that the generation of the ophiolite and ocean-crust subduction was at the end of the Late Devonian. The geochemical characteristics of ultramafic-mafic rocks and basalt suggest tbat they may belong to low alkali, low Ti and Mgrich tholeiite series and that the basalt may have been formed in MORB-like tectonic setting. The gneissie granite in the mélange belt may belong to sodium or low-K series and occurred in volcanic arc or syn-collision tectonic setting that was also related with the ocean-crust subduction. Tuerkubantao ophiolite, together with Kekesentao, Qiaoxiahala anc Buergen ophiolites constitute an ophiolitic mélange belt along the Irtys fault, which belongs to the Zaysan-Kekesentao-South Mongolia geosuture zone dividing the Siberian plate from the Kazakhstan-Junggar plate.%蛇绿岩作为残留洋壳的良好记录,对于研究古板块构造及其演化具有重要意义.新发现的吐尔库班套蛇绿混杂岩位于新疆阿尔泰布尔津南部,主要由超镁铁岩、辉长岩、辉绿岩、玄武岩、复理石建造等构成.其中辉长岩和片麻状花岗岩的锆石U-Pb年龄在363～355 Ma,指示蛇绿岩的形成、洋壳俯冲时代在晚泥盆世晚期.岩石地球化学特征表明,该蛇绿岩套的镁铁-超镁铁岩和玄武岩属低碱、低钛、富镁的拉斑玄武岩系列,具有较典型的幔源岩石特征,玄武岩形成于类似洋中脊的构造环境.混杂岩带中的片麻状花岗岩属于钠质的低钾岩石系列,形成于火山孤或同碰撞构造环境,亦为洋壳俯冲的结果.吐尔库班套蛇绿岩与科克森套、乔夏哈拉、布尔根蛇绿岩一起构成了沿额尔齐斯分布的蛇绿混杂岩带,构成了分割西伯利亚板块和哈萨克斯坦-准噶尔板块的斋桑-科克森套-南蒙古缝合带.