U-Pb ages and Hf isotopes of detrital zircons from mica quartz schist in Guixi area of northeastern Jiangxi Province and their geological significance

Abstract：Detailed LA-ICP-MS U-Pb dating and LAM-MC-ICPMS Lu-Hf isotope analysis were carried out for zircons in a mica quartz schist sample from Guixi area of northern Cathaysia Block, South China. These zircons are characterized by zoning, higher Th/U ratios (>0.4), HREE enrichment and positive Ce and negative Eu anomalies, and are similar to magmatic zircons in some aspects. Zircon U-Pb geochronological results of the mica quartz schist show a peak at ~775 Ma and a secondary peak at ~840 Ma, probably corresponding to two large-scale magmatic events. εHf(t) values for the ~840 Ma zircons could be divided into two intervals with both negative or positive values, whereas εHf(t) values for the ~775 Ma zircons are all negative values. Combined with previous zricon U-Pb dating and Hf isotopic results, the authors conclude that the Neoproterozoic magmatism in the Cathyasia Block mainly found expression in recycling of ancient crustal components. Nine zircon grains from the mica quartz schist with the other secondary peak at around 1770 Ma have very constant U-Pb ages and Hf isotopic composition, implying that they were most probably captured from the Paleoproterozoic basement rock.