胶东辽上金矿荆山群U-Pb年代学特征及其记录的多期地质事件  

U-Pb geochronology of Jingshan Group,Liaoshang gold deposit,Jiaodong Peninsula,and its records of multi-stage geological and metallogenic events

作　　者：陈燕平 李增胜 李旭平 李洪奎 陈妍蓉 孔凡梅 CHEN YanPing;LI ZengSheng;LI XuPing;LI HongKui;CHEN YanRong;KONG FanMei(Shandong Provincial Key Laboratory of Depositional Mineralization and Sedimentary Minerals,Shandong University of Science and Technology,Qingdao 266510,China;Shandong Institute of Geological Sciences,Jinan 250013,China)

机构地区：[1]山东省沉积成矿作用实验室,山东科技大学地球科学与工程学院,青岛266510 [2]山东省地质科学研究院,济南250013

出　　处：《岩石学报》2024年第11期3643-3662,共20页Acta Petrologica Sinica

基　　金：国家自然科学基金地质联合基金(U2244206)和国家自然科学基金项目(42272104)联合资助.

摘　　要：辽上金矿是近年来在胶东新发现的一类金矿,即黄铁矿碳酸盐脉型金矿。它明显区别于同地区焦家式破碎带蚀变岩型金矿和玲珑式石英脉型金矿,主要赋存于古元古代荆山群和晚侏罗世玲珑二长花岗岩接触带。矿区荆山群岩石的年代学研究,有助于理解辽上金矿成矿地质背景。在辽上金矿的钻孔岩心中采集5个荆山群样品,分别为黑云变粒岩、碎裂岩、透辉石变粒岩、浅粒岩和透辉石大理岩,这些岩石均遭遇了晚期成矿流体的交代作用,发生了不同程度的碳酸盐化和黄铁矿化。获取的锆石在阴极发光图像中多呈核-边结构,结合LA-ICP-MS锆石U-Pb年龄和原位微量元素特征显示,该地区荆山群变沉积岩系中碎屑锆石主要为岩浆锆石,年龄分布在2.6~2.0Ga之间,对应的年龄主峰为~2.11Ga,次峰为~2.46Ga,其中最年轻的碎屑锆石的207 Pb/206 Pb年龄为2024±33.6Ma,表明沉积物源主要来源于胶东地区出露的太古宙基底和古元古代中期岩浆岩,且沉积时间不早于2.02Ga。由于变质增生边较窄,获取的变质年龄相对较少,其中最古老的一组变质锆石年龄为~1.95Ga,结合碎屑锆石的年龄,推测该地区荆山群岩系的沉积时间介于2.02G~1.95Ga之间的某一时期。这些变质年龄主要分为两阶段,分别为~1.93Ga和~1.84Ga,与胶东地区古元古代经历的高压麻粒岩相峰期变质作用和峰期后近等压降温变质作用发生的时间一致。对碳酸盐透辉石变粒岩样品中磷灰石进行U-Pb定年,获取的变质年龄为252.5±2.4Ma,表明辽上地区荆山群岩系卷入到二叠纪末期华南板块和华北板块俯冲造山过程中。此外,在该样品的锆石中识别出一组热液锆石,年龄为132.4±3.2Ma,早于辽上金矿的主成矿年龄和胶东半岛其他金矿的成矿年龄,代表成矿前的热液活动,表明辽上金矿成矿作用至少持续了~20Myr。Liaoshang gold deposit is a newly discovered type of gold deposits in Jiaodong in recent years,namely,the pyrite carbonate vein type gold deposit.It is significantly different from the Jiaojia type(altered rock-type)and the Linglong type(quartz vein-type)gold deposits in the same area.The ores mainly occur in the contact zone between the Paleoproterozoic Jingshan Group and the Late Jurassic Linglong monzonitic granite.Through the chronological study upon the Jingshan Group rocks in the mining area,the geological backgrounds related to the formation of the Liaoshang gold deposit are well understood.Five samples of the Jingshan Group rocks were collected from the drilling cores of the Liaoshang gold mine,and they were all subjected to the metasomatism of mineralization fluids,resulting in varying degrees of carbonation and pyrite mineralization.The obtained zircons in cathodoluminescence(CL)images mostly exhibit clear core-rim structure.Combined with LA-ICP-MS zircon U-Pb ages and in-situ trace element characteristics,it is shown that the inherited detrital zircons in the metamorphic sedimentary rocks of the Jingshan Group in this region are mainly magmatic zircons,with ages ranging from 2.6Ga to 2.0Ga,with a major peak at 2.11Ga and a shoulder at 2.46Ga.The youngest detrital zircons have an averaged 207 Pb/206 Pb age of 2024±33.6Ma,indicating that the sediment source is mainly from the exposed Archean basement and Mid-Paleoproterozoic magmatic rocks in the Jiaobei terrane,and the deposit time was not earlier than 2.02Ga.Due to the narrow metamorphic overgrowth/recrystallization rims,limited metamorphic ages were obtained.Among them,the oldest set of metamorphic zircons has an age of~1.95Ga.Combined with the ages of inherited detrital zircons,it is speculated that the deposit time of the Jingshan Group in this area was 2.02~1.95Ga.Besides,these metamorphic ages were mainly divided into two groups of~1.93Ga and~1.84Ga respectively,which were consistent with the peak metamorphic process of high-pressure granulite fa

关 键 词：辽上金矿 荆山群 锆石U-Pb定年 磷灰石U-Pb定年 多期地质事件 

分 类 号：P588.34[天文地球—岩石学] P597.3[天文地球—地质学]