青海祁漫塔格小盆地北基性岩墙群地质特征及意义

Geological features and implication of mafic dykes swarm at northern Qimantag small basin in Qinghai

祁漫塔格小盆地北首次发现的北西-南东向基性岩墙群,侵入于早志留世花岗闪长岩中及晚奥陶世祁漫塔格群碎屑岩组中。对辉绿(玢)岩墙进行了LA-MC-ICP-MS锆石U-Pb测年,年龄为(396.5±3.1)Ma,时代中泥盆世;岩石化学和地球化学表明,基性岩墙为上地幔部分熔融的产物,显示的是具富铁演化特征的拉斑玄武岩系列,基性岩浆的分异演化未受陆壳物质混染;小盆地北基性辉绿(玢)岩墙的发现,进一步证明了在中泥盆世该地区经历了多次强烈挤压碰撞及其之间的相对松弛伸展,为祁漫塔格地区的构造岩浆旋回演化过程提供了重要的地质信息。

It has been discovered that mafic dykes swarm with NW-SE trend at northern Qimantag small basin intruded into the Early Silurian granodiorite Middle and Late Ordovician clastic Qimantage group.LA-MC-ICP-MS zircon U-Pb dating of diabase dykes(porphyrites) revealed that the age is(396.5 ± 3.1) Ma and belongs to Middle Devonian.Lithochemistry and geo-chemistry shows that mafic dykes are the products of partial melting of upper mantle.They belong to tholeiitic series with iron-rich evolutional characteristics and the differentiation and evolution of mafic magma has not been contaminated by continental crust.The discovery of diabase dykes(porphyrites) at northern Qimantag small basin further proves that this area undergone strong compression and collision and relative relaxation and extension repeatedly in Middle Devonian.The foundlings provide important geological information for the cycling and evolving process of tectonic magmatic in Qimantag area.