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).