胶北平度大金埠含石墨麻粒岩变质演化和石墨结晶形成的研究  

Study on metamorphic evolution and graphite crystallization of graphite-bearing granulites in Dajinbu,Pingdu,Jiaobei

作　　者：玄金卉 孔凡梅 李增胜 李旭平 孙彤 张保瑞 谭凯舰 申颖 XUAN JinHui;KONG FanMei;LI ZengSheng;LI XuPing;SUN Tong;ZHANG BaoRui;TAN KaiJian;SHEN Ying(College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao 266590,China;Shandong Institute of Geological Sciences,Jinan 250013,China)

机构地区：[1]山东科技大学地球科学与工程学院,青岛266590 [2]山东省地质科学研究院,济南250013

出　　处：《岩石学报》2024年第10期3305-3329,共25页Acta Petrologica Sinica

基　　金：国家自然科学基金委山东联合基金重点项目(U1906207)资助.

摘　　要：具有孔兹岩系特征的荆山群主要出露于胶-辽-吉带南段的胶北地体,且普遍经历了高角闪岩相-麻粒岩相变质作用。平度大金埠地区处于平度-莱西石墨成矿带,石墨矿赋存于古元古界荆山群陡崖组徐村段。通过对平度大金埠晶质石墨矿区含石墨泥质麻粒岩进行岩相学、矿物岩石学与地球化学、激光拉曼光谱、年代学等研究,发现大金埠含石墨泥质麻粒岩经历了三个变质演化阶段(M_(1)-M_(3)),且峰期达到高压-超高温变质作用条件。因受超高温变质作用影响,早期进变质阶段(M_(1))矿物信息保留不完整;峰期阶段(M_(2))以黑云母的消失为标志,矿物组合为Grt+Kfs+Pl+Rt+Qz+Liq,该阶段的温压范围为1010~1050℃、1.09~1.20GPa;峰后退变质阶段(M_(3)),黑云母重新出现,矿物组合为Bt+Grt+Kfs+Pl+Rt+Qz,该阶段的温压范围为810~843℃、0.68~0.74GPa,变质演化P-T轨迹具有顺时针特点。拉曼光谱分析显示样品中石墨的结晶程度普遍较高,其拉曼光谱特征与麻粒岩相变质条件下形成的石墨一致,高晶度石墨多结晶于峰期M_(2)向峰后M_(3)退变质作用阶段转变过程中。显然,平度大金埠晶质石墨矿区含石墨麻粒岩中石墨的结晶程度与其结晶时寄主麻粒岩的变质温度密切相关。年代学研究获得变质锆石1830±18Ma的加权平均年龄,与胶-辽-吉带及胶北地体区域上的深熔作用时代一致,代表了大金埠地区高结晶度石墨结晶形成的年龄。本次对石墨结晶形成与寄主变质岩及变质作用的关系探究,对优质晶质石墨矿资源的探矿、找矿具有重要指示意义。The Jingshan Group displaying characteristics typical of khondalite series is located within Jiaobei Terrane,which is the southern section of the Jiao-Liao-Ji belt,and the rocks of the Jingshan Group have generally experienced high amphibolite facies or granulite facies metamorphism.The Dajinbu area in Pingdu is within the Pingdu-Laixi graphite metallogenic belt,and the graphite ore occurs in the Xucun Member of the Douya Formation,which is part of the Paleoproterozoic Jingshan Group.Research results of petrography,mineralogy,petrology,geochemistry,laser Raman spectroscopy and chronology of the graphite-bearing pelitic granulite in the Dajinbu crystalline graphite mining area show that the granulite has undergone three metamorphic evolution stages(M_(1)-M_(3)).During the peak metamorphic stage,the conditions reach high pressure(HP)-ultra high temperature(UHT).The mineral assemblage in the early metamorphic stage(M_(1))is incomplete due to the influence of UHT metamorphism.The peak stage(M_(2))is marked by the disappearance of biotite,with the mineral assemblage of Grt+Kfs+Pl+Rt+Qz+Liq,and the temperature and pressure is in a range of 1010~1050℃and 1.09~1.20GPa.During the retrogressive stage(M_(3)),biotite reappears and the mineral assemblage is Bt+Grt+Kfs+Pl+Rt+Qz,the temperature and pressure conditions of this stage is estimated to be 810~843℃and 0.68~0.74GPa.The graphite-bearing pelitic granulite has a clockwise P-T path.The graphite samples generally exhibit high degree of crystallinity,and their Raman spectra characteristics are in line with those formed under granulite facies metamorphism.The high-crystallinity graphites primarily crystallize during the transition from the peak stage(M_(2))to the retrogressive stage(M_(3)).It is obvious that the degree of graphite crystallinity in the graphite-bearing granulite from the Dajinbu crystalline graphite mining area is closely related to the metamorphic temperature of the host granulites.The weighted mean age of the metamorphic zircons is 1830±18Ma,which is c

关 键 词：含石墨泥质麻粒岩 石墨结晶 超高温变质作用 P-T轨迹 胶-辽-吉带 

分 类 号：P588.347[天文地球—岩石学] P619.252[天文地球—地质学]