福建省紫金山铜金矿田石帽山群下组火山岩锆石LA-ICP-MS U-Pb测年与白垩纪岩浆活动期次

摘要

The ages of the volcanic rocks from the bottom of lower Fm. Of the Shimaoshan Group in the Zijinshan Cu-Au orefield, Fujian province, were dated using in-situ LA-ICP-MS zircon U-Pb method. The 206Pb/238U weighted average ages of the zircons are 113.0 ± 1.9 Ma(n= 16, MSWD = 1.02)and 110. 1 ±0.7 Ma (n = 16, MSWD = 0. 16) , respectively. Combined with previous results, the Cretaceous magmatic activities in the Zijinshan Cu-Au orefield can be divided into three stages; (1) 115 ~ 110 Ma is the early stage of volcanic eruption-overflow, (2) 110 ~ 105 Ma is the middle stage of volcanic overflow-concealed explosive-filling the volcano channels and intrusion of the Sifang pluton, (3) 105 ~95 Ma is the late stage of emplacement of multistage porphyry granite and formation of hydrothermal-porphyry mineralization. The dating results provide new information for further study of the Cretaceous magmatism and ore-formation of the Zijinshan Cu-Au orefield.%通过对石帽山群下组底部火山岩两组原位锆石进行LA-ICP-MS U-Pb测年,准确厘定了福建省紫金山铜金矿田中石帽山群下组火山岩的时代,获得206pb/238U加权平均年龄分别为113.0±1.9 Ma(n =16,MSWD =1.02)和110.1±0.7 Ma(n=16,MSWD =0.16),并取得了131.8～ 162.7 Ma和501.3 Ma的捕获锆石或继承锆石的年龄信息.结合近年前人发表的锆石测年成果,将紫金山铜金矿田白垩纪岩浆活动划分为三个阶段:(1) 115～110 Ma为早期火山爆发-溢流阶段；(2) 110～105 Ma为中期岩浆溢流-隐爆-填塞火山通道及四坊岩体侵位阶段；(3)105～ 95 Ma为晚期多阶段花岗闪长斑岩侵位与斑岩-热液成矿作用阶段.这为紫金山铜金矿田白垩纪岩浆活动期次与成矿时代研究提供了重要新资料.