LA-ICP-MS U-Pb dating of zircon from granitic gneiss of the Nierong microcontinent: The discovery of the Neoproterozoic basement rock and its significance
聂荣微陆块花岗片麻岩锆石LA-ICP-MS U-Pb定年——新元古代基底岩石的发现及其意义

The Nierong microcontinent was a micro-lens gripping in the Bangong Co-Nujiang River suture zone, there are monzonite-gneiss and biotite-monzonite-gneiss in the Nierong microcontinent. We report LA-ICP-MS U-Pb zircon dating results for the granitic gneiss in the Nierong microcontinent. The CL images of the granitic gneiss zircons show distinct oscillatory zoning, indicative most of the zircons were crystallized in granite. Sixteen analyses have high Th/U ratios, the Th/U ratios range from 0.58 to 1.24, with an average of 0.79, their U-Pb results form a single, essentially concordant group with a mean 206Pb/238U age of 819±5.2Ma. Reflect that the granitic gneiss was emplaced in the ages of 819.6±5.2Ma. We got the same chronology data (809Ma) from the clastic zircon in the south Qiangtang also. We think the ages of 507Ma show that the Nierong microcontinent was effected by another tectonics thermal event after the Late Pan-African motion.