柴达木盆地北缘全吉地块东端变基性岩体LA-ICP-MS锆石U-Pb年龄:中元古代陆块裂解的证据

全吉地块东端古元古代二长花岗片麻岩中普遍发育变质的基性岩体,它们的形成时代、变质作用时代和对地块基底构造演化的指示意义尚不清楚。应用LA-ICP-MS技术测定其中的一个变基性岩体的锆石U-Pb年龄,获得的10个测点数据显示,锆石受到热事件的强烈改造而发生严重铅丢失,但拟合的不一致线仍给出相关性较好的上交点年龄1712Ma±47Ma和下交点年龄472Ma±29Ma,MSWD=1.4。这表明,变质基性岩的原岩形成于中元古代早期,是全吉地块在古元古代末期汇入Columbia超大陆之后于中元古代早期初始裂解而侵位的基性岩体。这些基性岩体在早古生代卷入了柴北缘碰撞带而发生角闪岩相变质作用,并受到构造肢解。

LA-ICP-MS zircon U-Pb age of meta-basic plutons in eastern Quanji massif: evidence for Mesoproterozoic continental break-up

The meta-basic plutons are extensively developed within the Paleoproterozoic monzogranitic gneiss in the eastern most Quanji massif; however, their formation and metamorphic ages and implications for the basement tectonic evolution remain unclear. In this paper, the zircon U-Pb age of one of the meta-basic plutons was determined with LA-ICP-MS. Ten analytical data show strong lead loss due to thermal events, but their discordant line remains well correlated with the upper intercept age of 1712±47 Ma and lower intercept age of 472±29 Ma, MSWD=1.4. The dating result indicates that the protolith of this pluton was formed in the early Mesoproterozoic, being the product of the initial break-up process after the assembly of the Quanji massif with the supercontinent Columbia in the Late Paleoproterozoic. The proton then underwent amphibolite facies metamorphism and structural dismantling resulting from its being involved into the North Qaidam Collision Zone in the Early Paleozoic.