胶东半岛构造演化及金成矿作用

发布时间：2018-05-30 23:24

  本文选题：胶东半岛 + 构造演化　； 参考：《中国地质大学(北京)》2016年博士论文

【摘要】：胶东半岛晚中生代花岗质岩浆活动可分为-160 Ma,～130 Ma,～115 Ma三期。三期侵入岩极端负的全岩εNd(t)和锆石εHf(t)及非常老的锆石铪TDM2年龄表明其母岩浆源区主要为古老下地壳。元素和同位素地球化学特征说明三期侵入岩母岩浆形成深度逐渐变浅,形成于伸展构造环境,可能是受太平洋板块俯冲控制。通过对花岗质岩石继承锆石的研究,认为三叠纪碰撞时扬子下地壳俯冲到胶北地体之下至少～40 km的深度,形成类似鳄鱼嘴式构造；俯冲的扬子下地壳是胶北地体和苏鲁造山带内晚中生代花岗岩母岩浆的主要源区。胶莱盆地沉积岩碎屑锆石U-Pb年龄显示出-2500 Ma,～1850 Ma,～770 Ma,～230 Ma和～120 Ma五个主要峰值,反映区域五期主要构造-热事件。～120 Ma的峰值年龄与胶东半岛金成矿的年代一致。盆地顶底部沉积物源区存在差别,从底到顶白垩纪年龄越来越多,而白垩纪之前的越来越少,且白垩纪峰值年龄逐渐变年轻。胶莱盆地中新元古代碎屑锆石具岩浆成因特征,源自苏鲁造山带,其年龄频谱与扬子克拉通西缘和北缘岩浆活动时限一致,推测沿扬子克拉通西缘和北缘的俯冲活动可能向东延伸到苏鲁地区。三叠纪或以前形成的交代地慢和俯冲的扬子板块为区域金成矿提供流体、挥发份及成矿物质。锆石、磷灰石裂变径迹研究表明在～30-80 Ma胶东地壳经历明显隆升,隆升时间段与周缘盆地最大沉降及华北克拉通东部玄武岩形成时间吻合,说明华北克拉通东部在晚白垩世-古近纪经历显著地壳隆升,形成地堑-地垒构造系统。胶东半岛金矿主要赋存于晚中生代花岗岩中,通过花岗岩锆石和磷灰石裂变径迹数据约束的地壳隆升剥蚀量估算出该区域金矿化深度为～6-11 km。胶东金矿省蚀变岩型金矿床的蚀变包括钾长石化、绢云母化、碳酸盐化,不同蚀变之间具有成因上的联系,前一阶段蚀变能诱发下一期次蚀变,同一期次蚀变不同反应相互促进,各种蚀变、矿化如同多米诺链,起始于富K+、H+和Au流体与含斜长石的花岗岩相遇。从钾长石化到碳酸盐化阶段,不同热液蚀变导致蚀变岩石、矿石样品具有不同矿物组合及地球化学特征。蚀变类型和强度控制元素在空间的分布,断裂、节理等构造也控制元素迁移富集,构造发育部位,蚀变矿化强烈,成矿元素含量呈现峰值,金矿体亦在此部位产出。
[Abstract]:The late Mesozoic granitic magmatism in Jiaodong Peninsula can be divided into three phases of -160 Majiao 130 Majiao 115 Ma. The TDM2 age of zircon and very old zircon hafnium indicates that the parent magmatic source region is mainly of the ancient lower crust. The geochemical characteristics of elements and isotopes indicate that the formation depth of the intrusive mother magma gradually shallowes in the extensional tectonic environment and may be controlled by the subduction of the Pacific plate. Based on the study of inherited zircon from granitic rocks, it is considered that the lower crust of Yangtze subducted to a depth of at least 40 km below the Jiaobei terrain during the Triassic collision, forming a similar crocodile beak structure. The subducted lower crust of Yangtze is the main source of late Mesozoic granitic mother magma in Jiaobei terrane and Sulu orogenic belt. The zircon U-Pb age of depositional rocks in Jiaolai Basin shows five main peaks of -2500 Ma / 1850 Ma / 770 Ma / 230Ma and / or 120Ma respectively, which reflect that the peak age of the five major tectonic-thermal events (120Ma) is consistent with the age of gold mineralization in Jiaodong Peninsula. There are differences in the source regions of the sediments at the top and bottom of the basin. The age of Cretaceous is increasing from bottom to top, but less and less before Cretaceous, and the peak age of Cretaceous becomes younger and younger. The MesoNeoproterozoic clastic zircon in the Jiaolai Basin is of magmatic origin and originated from the Sulu orogenic belt. The age spectrum of the zircon is consistent with the time limit of magmatic activity in the western margin of the Yangtze craton and the northern margin of the Yangtze craton. It is inferred that the subduction along the western and northern margin of the Yangtze craton may extend eastward to the Sulu area. The Yangtze plate formed during the Triassic or before the metasomatism and subduction provides fluids, volatiles and ore-forming materials for regional gold mineralization. The study of fission track of zircon and apatite shows that the crust of Jiaodong experienced obvious uplift at 30-80 Ma, and the uplift time coincided with the maximum subsidence of the peripheral basin and the formation time of basalt in the eastern part of the North China Craton. It is concluded that the eastern North China Craton experienced a significant crustal uplift during the late Cretaceous to Paleogene and formed a graben-barrier tectonic system. The gold deposits in Jiaodong Peninsula are mainly located in late Mesozoic granites. The depth of gold mineralization in this area is estimated to be 6-11 km by crustal uplift and denudation restricted by fission track data of zircon and apatite. The alteration of the altered rock type gold deposit in Jiaodong gold deposit includes potassium feldspar, sericite, carbonization, and there is a genetic relationship among the different alterations. The alteration in the previous stage can induce the next secondary alteration. In the same period, different reactions promote each other, and all kinds of alteration and mineralization are like dominoes, which originated from the encounter of K-rich H and au fluids with plagioclase bearing granite. Different hydrothermal alteration results in altered rocks, and the ore samples have different mineral assemblages and geochemical characteristics. The distribution of alteration type and strength control elements in space, faults, joints and other structures also control the migration and enrichment of elements, structural development site, strong alteration mineralization, metallogenic elements content of peak value, gold orebody also occurred in this area.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P618.51;P548
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本文编号：1957290