新疆西部巴楚地区晋宁期的洋岛火山岩

Volcanic Rocks of Jinningian Oceanic Islands in the Bachu Area,Western Xinjiang

塔里木盆地中部有一条近东西向的重磁高异常带,火成岩露头仅见于西部的巴楚地区。采集25件晋宁期火山岩样品进行研究,地球化学特征表明岩石形成的大地构造背景为洋岛,且可清楚地区分出洋岛碱性玄武岩(亚速尔型洋岛)和洋岛拉斑玄武岩(夏威夷型洋岛),两者反映了洋盆发育的不同阶段。一件晋宁期超基性岩样品显示出岛弧岩浆岩的性质,与塔里木中部地区的闪长岩和花岗闪长岩应同为晋宁期岛弧的记录。它们可能指示一条横贯塔里木盆地中部的晋宁期古缝合线,原称的塔里木板块(克拉通)是由两个原先分隔的地块在晋宁运动时碰撞拼合而形成的,并成为罗迪尼亚超大陆的一部分。该古缝合线在震旦纪—中生代构造活动性较强,尤其是二叠纪—三叠纪的构造—岩浆事件规模较大。据此讨论了晋宁期构造—岩浆活动在认识基底形成、区域演化和油气勘探中的意义。

There was a gravity-magnetic abnormal belt traversing the middle part of Tarim Basin. The igneous rocks in ages of Proterozoic and Paleozoic outcropped only in the Bachu area, western Xinjiang, with the Jinningian（the latest Mesoproterozoic-Early Neoproterozoic）one being characterized by deformation and metamorphism. The FeO^＊/MgO vs. TiO2 diagram, MnO-TiO2-P2O5, Zr-Nb-Y and Th-Hf-Ta triangular diagrams showed the tectonic setting of the Jinningian volcanic rocks being oceanic island. The REE features and trace element spidergrams indicated further that the oceanic island volcanic rocks could be divided into two groups： the alkaline basalt being a record of Azores-type oceanic island, and the tholeiite （as well as subordinate weakly alkaline basalt） interlayered with andesite（or andesitic basalt）being a record of Hawaii-type one, which reflected varied evolution phases of an oceanic basin. One sample of uhramafic rock seemed to be a product of Jinningian island arc, which was discovered by drilling in central Tarim. Both the igneous rocks of oceanic islands and island arc meant that there might be a Jinningian fossil suture in the middle part of Tarim Basin. In other words, the Tarim plate（craton） might be amalgamated by two originally separated the Jinningian orogeny. The fossil suture activated blocks and become a part of the Rodinia supercontinent in repeatedly and became a pathway of magmatism in Sinian-Paleozoic, especially, the basalt eruption and alkalic rock intrusion during Early Permian（the Cisuralian）. Based on it, the implications of the Jinningian tectono-magmatism in basement structural pattern, tectonic evolution and oil-gas potentials in the Tarim Basin were discussed.