胶西北丛家花岗闪长岩体SHRIMP锆石U-Pb年代学研究

摘要

Northwest Jiaodong area is the most important gold mineralization concentration area in China. The relationship between Mesozoic granitoid and gold deposits in northwest Jiaodong area is very imtimate. In this paper, the authors studied the geological background and zircon SHRIMP geochronology of Congjia intrusion from Guojialing sequence. The dating result of zircons from porphyritic granodiorite is (127±1) Ma, suggesting that it was an early Cretaceous intrusion. The difference between ages from each intrusions of Guojialing sequence is very insignificant, indicating that they were emplaced almost at the same time at ca. 127.9 Ma. Multiple stage inherited zircon ages of Ar3, Pt1, J3 obtained from zircons in Congjia intrusion and former researches imply that the magma source regions of Guojialing sequence are very complicated. There are Precambrian basement and late Jurassic Linglong sequence from Jiaoliao block, Triassic syn-collision granitoid from Jiaonan–Weihai orogenic belt, and the addition of mantle-derived components. Crust-derived components are mainly made up of Linglong sequence. There exists very imtimate relationship between Guojialing sequence and gold deposits in northwest Jiaodong area. From the aspect of time, Guojialing sequence was formed 5~10 Ma earlier than gold deposits in northwest Jiaodong area, in good accordance with the diagenesis-mineralization time gap between gold deposits and their cognate magmatites. From the aspect of space, it is inferred that insidious Guojialing sequence exists under every three main ore-controlling fault zones in northwest Jiaodong area, and gold deposits occur always together with Guojialing sequence. From the aspect of material composition, Guojialing sequence is relatively richer in sodium than other early Cretaceous magmatites, which might have resulted from segregation of gold-bearing potassium-rich hydrothermal solution before its emplacement. Thus, Guojialing sequence is closer in time to the mother rock of gold deposits in northwest Jiaodong area.%胶西北地区是我国最重要的金矿集中区,区内大量展布的中生代花岗岩与金矿关系十分密切,本文通过对郭家岭序列的丛家花岗闪长岩体的地质背景和 SHRIMP锆石年代学研究,获得该岩体的成岩年龄为(127±1) Ma,地质时代属早白垩世。郭家岭序列各个岩体所测得的年龄值相差不大,表明它们近于同时侵位,侵位时间为127.9 Ma。丛家岩体锆石样品中测得Ar3、Pt1、J3等多个期次的继承锆石年龄。结合前人研究,表明郭家岭序列岩浆源区成分非常复杂,既有来自胶辽陆块的前寒武纪基底、晚侏罗世玲珑序列,也有来自胶南—威海造山带的三叠纪同碰撞花岗岩类,还有幔源组分的加入。其中,壳源组分以玲珑序列为主。郭家岭序列与胶西北地区金矿的关系十分密切。从时间上看,郭家岭序列的形成年龄早于胶西北地区金矿的形成年龄5~10 Ma,符合同源岩浆成因金矿的成岩成矿时间差。从空间上看,胶西北地区三条主要控矿断裂带下均有隐伏郭家岭序列存在,金矿与郭家岭序列形影不离。从物质成分上看,与其他早白垩世岩浆岩类相比,郭家岭序列相对富 Na,有可能是郭家岭序列在侵位之前,经历了含 Au 的富 K 热液组分分离的结果。因此,郭家岭序列更接近于胶西北地区金矿的成矿母岩。