Zircon LA-ICP-MS U-Pb isotopic dating for Qingshuiquan layered mafic-ulmafic intrusion southern Altun orogen, in northwestern China and its implication

Abstract：Located in Qingshuiquan area neighboring the southern Altun UHP metamorphic belt, the Qingshuiquan mafic-ultramafic intrusion consists of three to four magmatic cycles and exhibits the features of layered mafic-ultramafic intrusion. LA-ICP-MS U-Pb isotopic dating of zircon from hornblende gabbro in the intrusion with Th/U ratios of 0.32~1.16（0.64 on average）and magmatic oscillatory bands was conducted, and the results show that its age is 467.4±1.4 Ma (MSWD=2.5), which is younger than the age of UHP metamorphic rocks (504~487 Ma) and older than the age of A-type granites (~425 Ma) in southern Altun orogen. Meanwhile, the distribution of bimodal magma intrusion at ~465 Ma and contemporary metamorphic thermal events in southern Altun area suggest that the southern Altun orogen was in the tectonic stage of post-collision rifting or extending at ~465Ma.