胶西北地区北截金矿闪长玢岩锆石SHRI MP年龄及其地质意义

摘要

山东省招远市北截金矿是胶西北地区发现较早的金矿之一，主要赋存于严格受NEE向断裂控制的黄铁绢英岩化蚀变带内，是典型的破碎带蚀变岩型金矿。本文通过对矿区内切穿矿体的闪长玢岩、郭家岭序列下属北截岩体的地质背景和SHRIMP锆石U-Pb年代学研究，得出闪长玢岩形成年龄为117±2Ma，北截岩体形成年龄为129±1Ma，限定北截金矿成矿年龄在117～129Ma之间，属早白垩世。锆石样品中测得Ar3、Z、J3等多个期次的继承锆石年龄，表明北截岩体和闪长玢岩形成过程具有多重继承演化性。根据同源岩浆的成岩成矿时间差及岩体与金矿的空间位置，判断郭家岭序列与金矿关系更为密切。讨论了胶东金矿的成矿期次和构造环境，认为其形成于俯冲造山带的弧后伸展环境，其形成与演化受中生代以来中国东部岩石圈大规模减薄、地幔上涌或陆缘裂谷的影响，最终成因可能与地幔柱有关。%The Beijie gold deposit in Zhaoyuan city is one of the earliest discovered gold deposit in the northwest Jiaodong area.It is a typical altered tectonite-type gold deposit which lies in beresitization alteration zone strictly controlled by an NEE fault.This article studies geological background and zircon SHRIMP geochronology of diorite-porphyrite cutting through orebody and Beijie intrusion from Guojialing sequences.Dating result of zircons from diorite-porphyrite is 117 ±2Ma and Beijie intrusion is 129 ±1Ma,suggesting that the Beijie gold deposit was formed in early Cretaceous with an age of 117~129Ma.Multiple stages of inherited zircon age of Ar3 ,Z,J3 gained from zircons in Beij ie intrusion and diorite-porphyrite imply that the process of rock forming was very complicated and inherited.Guojialing sequence is 5~10Ma earlier than gold deposits in the Jiaodong area,and it is more closer to gold deposits in space distribution,suggesting that it is much more closer to a magma source of ore-forming fluid in the Jiaodong area.Ore-forming stage and tectonic environment of Jiaodong gold deposits are also discussed.It is conclucled that the Jiaodong gold concentration area was formed in an environment of back-arc extending.Its formation and evolution were controlled by large-scale lithospheric thinning,mantle upwelling,and continental margin rift in east China in Mesozoic.It was very probably related to a mantle plume.