柴北缘前寒武纪岩体（地层）变质年龄及其对早古生代造山作用的指示

柴北缘前寒武纪岩体（地层）分布广泛。为确定柴北缘地区前寒武纪岩体（地层）受早古生代碰撞造山作用的影响，采用LA-ICP-MS技术，对大柴旦地区前寒武纪黑云斜长片麻岩、斜长角闪岩及石榴子石斜长角闪岩中的锆石进行了U-Pb同位素定年。黑云斜长片麻岩获得479~472Ma的变质年龄，斜长角闪岩获得440Ma和470Ma 2个变质年龄，石榴子石斜长角闪岩获得418.8Ma±3.0Ma的变质年龄。初步确定，柴北缘早古生代造山作用对前寒武纪岩体构成了3次强度不等的变质作用叠加，分别为大洋俯冲末期阶段(495~467Ma)岛弧花岗岩弱热烘烤变质作用、大陆碰撞造山阶段(467~423Ma)区域变质作用、S型花岗岩热动力变质作用和大陆后碰撞造山阶段(423~371Ma) I型花岗岩强烈接触热变质作用。

The metamorphic age of Precambrian rocks in North Qaidam margin and its implications for Early Paleozoic orogeny

Precambrian rocks are widely distributed in the northern margin of the Qaidam Basin. In order to determine the influence of the early Paleozoic collisional orogeny on Precambrian rocks, the authors employed LA-ICP-MS technology to conduct zircon U-Pb dating. Biotite-plagioclase gneiss has 206Pb/238U metamorphic age of (479~472)Ma, amphibolite has two peaks of 206Pb/238U metamorphic age of 440Ma and 470Ma respectively, and garnet-amphibolite has 206Pb/238U metamorphic age of 418.8Ma±3.0Ma. Preliminary determination shows that there existed three times of influences of metamorphism on Precambrian rocks, i.e., thermal contact metamorphism of island arc granite at the late stage of oceanic subduction (495~467Ma), regional metamorphism and thermal contact metamorphism of S type granite at the continental collision stage (467~423Ma) and I type granite thermal contact metamorphism at the post-collisional stage (423~371Ma).