Neoproterozoic and Paleozoic tectonic evolution in north Qaidam, northeastern Tibetan Plateau recorded by magmatism and metamorphism

Abstract

In order to better understand the Neoproterozoic and Paleozoic magmatism, metamorphism and tectonic evolution of the whole Tibetan Plateau, here we report the field observations, LA-ICP-MS zircon U-Pb dating, whole-rock geochemistry, Sr-Nd isotopes, and LA-MC-ICP-MS zircon Lu-Hf isotopes of the amphibolites, volcanic rocks, and granitoids from the north Qaidam UHPM belt of the northeastern Tibetan Plateau. The Neoproterozoic mafic rocks (protolith of amphibolites) with zircon U-Pb age of 959 Ma are subduction-related magmatic rocks formed in a failed continental back arc rift above an oceanic-continental subduction zone by melting of an enriched mantle. These mafic rocks underwent Paleozoic metamorphism as revealed by metamorphic zircons that crystallized at 430 Ma during the retrogression from eclogite to amphibolite facies metamorphism. The Neoproterozoic granitoids are strongly peraluminous muscovite granites with LA-ICP-MS zircon U-Pb ages of 918–875 Ma. The formation of these granitoids occurred at high to low temperatures and low oxygen fugacities, and was possibly derived by partial melting of Paleo- to Meso-Proterozoic crustal rocks during the orogenic collapse. The Paleozoic magmatism, including 454 Ma arc-type dacites, 412 Ma collisional muscovite granite, and the post-collisional 370 Ma biotite monzogranite and 368 Ma diorite, records a detailed tectonic evolution history from oceanic subduction, through continental collision, to post-collision in the north Qaidam UHPM belt.