浙西北平水铜矿细碧角斑岩成岩年龄及其地质意义

文章对浙西北平水铜矿赋矿围岩双溪坞群平水组细碧角斑岩中锆石进行了LA-ICP-MS U-Pb同位素年龄测定。结果显示锆石Th/U比值为0.42~2.28,明显高于Th/U比值小于0.1的变质成因的锆石,为典型岩浆成因锆石。几乎所有的锆石颗粒样品都投影在谐和曲线上及其附近,细碧岩年龄加权平均值为(952±5)Ma(n=18,MSWD=0.19),角斑岩年龄加权平均值为(954±8)Ma(n=15,MSWD=0.51);结合锆石自形、发育岩浆环带等特点,该年龄是平水组细碧角斑岩的形成年龄。结合前人研究及地质事实,本次研究确定双溪坞群平水组细碧角斑岩的成岩年龄为新元古代(950 Ma左右);认为江南造山运动发生的上、下限虽还没有最终限定,但它东端的造山运动很可能介于1.0~0.9 Ga;钦杭成矿带北东段地区有寻找同类矿床的潜力。

Chronology and geological significance of spillite-keratophyre in Pingshui Formation, northwest Zhejiang Province

This paper reports LA-ICP-MS zircon U-Pb ages of spillite-keratophyre in Pingshui Formation, northwest Zhejiang Province. The Th/U ratios in the range of 0.42-2.28 show that the zircon is a typical magmatic mineral. Analytical results show that the weighted mean ,²⁰⁶Pb/²³⁸U age of the spillite is (952±5) Ma (n=18, MSWD=0.19), and that of the keratophyre is (954±8) Ma (n=15, MSWD=0.51). Combined with previous studies and geological facts, the authors hold that the diagenetic epoch of the spillitekeratophyre in the Pingshui Formation was the Neoproterozoic (about 950 Ma). It is further suggested that the amalgamation between the Yangtze and Cathaysia Blocks in the eastern segment of the Jiangnan orogen was completed between 1.0 Ga and 0.9 Ga. It can be inferred that the Pingshui area and even Qin-Hang metallogenic belt have the potential in search for VMS deposits.