准噶尔北部科克森套蛇绿岩中辉长岩年代学、岩石化学特征及地质意义

Chronology and Lithochemistry of Gabbro from Kekesentao Ophiolite in the Northern Junggar,Xinjiang and Its Geological Significance

新疆西准噶尔北部科克森套蛇绿岩由辉长岩、辉橄岩、橄辉岩、辉石岩、蛇纹岩、玄武岩、硅质岩、含放射虫硅质板岩及片岩、片麻岩组成。辉长岩化学特征表现为富Al2O3、CaO、MgO,贫K2O、TiO2特点,与岛弧玄武岩相似。稀土元素与E-MORB特征基本一致,反映岩浆来源于富集地幔。微量元素具大离子亲石元素Rb,Th,K,Sr相对富集,高场强元素Nb,Ta,Ti相对亏损特征,显示与俯冲带流体交代有关。辉长岩锆石年龄(405±4)Ma,代表洋壳形成年代。在构造环境上,科克森套蛇绿混杂岩显示富集洋脊玄武岩特征,形成于岛弧环境,与岛弧消减带扩张环境相一致,因此,科克森套蛇绿混杂岩应形成于早泥盆世。从时间、空间分布及构造环境上,科克森套蛇绿岩与库尔提蛇绿岩、沙尔布拉克蛇绿岩及布尔根蛇绿岩具相似性,为早泥盆世古亚洲洋在准噶尔北缘向西伯利亚板块俯冲所形成的沟-弧-盆体系下的弧后系统,与相邻哈萨克斯坦斋桑蛇绿岩带、蒙古比基蛇绿岩带共同构成西伯利亚与准噶尔板块间的缝合带。

The kekesengtao ophiolite is located at the north part of western Junggar,Xinjiang,which is composed of gabbro,peridotite,pyroxenite,serpentine,basalt,siliceous rock,radiolarian siliceous slate,schist and gneiss.The petrochemical characteristics of gabbro are rich in Al2O3,CaO,MgO and poor in K2O and TiO2.Similar to island arc basalt.The characteristics of rare earth elements are basically consistent with e-MORB.It indicates that magma originates from the enriched mantle.Trace elements are characterized by the relative enrichment of large ion lithophile elements Rb,Th,K and Sr,and the relative loss of high field strong elements Nb,Ta and Ti.It is related to subduction zone fluid replacement.Zircons from gabbro are(405±4)Ma old,indicating the age of oceanic crust.From the perspective of tectonic environment,the kekesengtao ophiolite hybrid shows the characteristics of rich oceanic ridge basalt.It also shows that it was formed in the island arc,which is consistent with the expansion environment of the island arc subduction zone.Therefore,the kekesengtao ophiolite hybrid should have formed in the early devonian.From time,space distribution and tectonic environment.Kekesengtao ophiolite is similar to kurti ophiolite sarbraque ophiolite and burgen ophiolite.It is a back-arc system formed under the trench-arc-basin system formed by the devonian paleo-asian ocean subducting to the Siberian plate in the northern margin of junggar.Together with the adjacent isaimulberry ophiolite belt in kazakhstan and the biki ophiolite belt in Mongolia,it forms the suture belt between the Siberian and junggar plates.