粤东新寮岽铜多金属矿区石英闪长岩锆石U-Pb年龄、地球化学及Hf同位素组成

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

新寮岽铜多金属矿是近年来在粤东地区新发现的一个铜矿床。对该矿床中与成矿关系密切的石英闪长岩进行了锆石U-Pb年龄、地球化学、Hf同位素研究，以约束其形成时代和岩石成因。测得石英闪长岩LA-ICP-MS锆石U-Pb年龄为161±1Ma（n=25，MSWD=0.57），被解释为岩体的成岩年龄。地球化学数据显示，石英闪长岩具有碱含量中等（Na2O+K2O=3.99%~5.05%），高镁（MgO=4.53%~4.91%）的特征，属准铝质钙碱性系列。稀土和微量元素特征表明，其富集轻稀土元素和大离子亲石元素（K、Rb、Ba、Th、U），亏损重稀土元素和高场强元素（Nb、Ta、Ti、P），具弱负Eu异常（δEu=0.68~0.76）。电子探针分析结果表明，石英闪长岩中黑云母为镁质黑云母，具环带结构，斜长石为拉长石。锆石Hf同位素分析结果表明，石英闪长岩εHf（t）为-5.8~2.7，tDM2=1.03~1.58Ga。岩石地球化学和锆石Hf同位素组成特征表明，石英闪长岩源区较复杂，为壳幔混合源，可能为俯冲板片部分熔融并与楔形地幔橄榄岩相互作用形成，且岩浆上侵过程中有古老地壳物质的混染。综合岩石地球化学、矿物化学及Hf同位素特征，结合区域构造演化史和前人研究成果，推测岩体形成于俯冲背景下的活动大陆边缘环境。

The Xinliaodong Cu polymetallic deposit is a newly-discovered copper ore deposit in eastern Guangdong Province. Inthis paper, zircon U-Pb age, geochemistry and zircon Hf isotope of the ore-related quartz-diorite from the Xinliaodong Cu polyme?tallic ore district were studied to constrain its geochronology and petrogenesis. The zircon LA-ICP-MS dating yielded a concordantage of 161±1Ma (n=25, MSWD=0.57), which is interpreted as the petrogenic age of quartz-diorite. Geochemical data show that thequartz-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 enrich?ment 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. TheHf isotope shows that the εHf (t) values of the quartze-diorite range from -5.8 to 2.7, with tDM2 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. Thediagenetic mass of the pluton was derived from the source of crust-mantle mixture and it might have originated from partial meltingof a subducted slab which reacted with mantle wedge peridotites. Besides, the magma was intermingled with ancient crustal materialduring magmatic ascent. According to petrogeochemistry, mineral chemistry and Hf isotope, combined with the tectonic evolution ofthe eastern Guangdong Province as well as previous achievements, the authors infer that the quartz-diorite was generated in an activecontinental margin setting triggered by slab subduction.