Zircon U-Pb age, geochemistry and Hf isotopic compositions of quartzdiorite from the Xinliaodong Cu polymetallic deposit in eastern Guangdong Province

The Xinliaodong Cu polymetallic deposit is a newly-discovered copper ore deposit in eastern Guangdong Province. In this paper, zircon U-Pb age, geochemistry and zircon Hf isotope of the ore-related quartz-diorite from the Xinliaodong Cu polymetallic ore district were studied to constrain its geochronology and petrogenesis. The zircon LA-ICP-MS dating yielded a concordant age of 161±1Ma (n=25, MSWD=0.57), which is interpreted as the petrogenic age of quartz-diorite. Geochemical data show that the quartz-diorite is magnesium-enriched in composition (MgO=4.53%~4.91%) with moderate content of alkali (Na₂O+K₂O=3.99%~5.05%). It is a metaluminous granite and belongs to the calc-alkaline series. Its REE and trace elements are characterized by enrichment of LREE and large ion lithophile elements (K, Rb, Ba, Th and U) and depletion of HREE and high-field strength elements (Nb, Ta, Ti and P), with slightly weak negative anomalies of Eu (δEu=0.68~0.76). The results of the electron microprobe analysis show that the biotite from the quartz-diorite belongs to magnesian biotite, whereas the zoned plagioclase belongs to labradorite. The Hf isotope shows that the εHf (t) values of the quartze-diorite range from -5.8 to 2.7, with t_DM2 ages between 1.03Ga and 1.58Ga. Geochemistry and zircon Hf isotopic compositions indicate that the parental magmas of the quartz-diorite are rather complex. The diagenetic mass of the pluton was derived from the source of crust-mantle mixture and it might have originated from partial melting of a subducted slab which reacted with mantle wedge peridotites. Besides, the magma was intermingled with ancient crustal material during magmatic ascent. According to petrogeochemistry, mineral chemistry and Hf isotope, combined with the tectonic evolution of the eastern Guangdong Province as well as previous achievements, the authors infer that the quartz-diorite was generated in an active continental margin setting triggered by slab subduction.