青岛连三岛地区“荆山岩群”高压变质岩的变质时代和变质演化特征  

Geochronology and metamorphic evolution of the HP metamorphic rocks of“Jingshan Group”from Liansandao area,Qingdao

作　　者：郜源 曹玉亭 王淞杰 李旭平 孔凡梅 GAO Yuan;CAO YuTing;WANG SongJie;LI XuPing;KONG FanMei(Shandong Prorincial Key Laboratory of Depositional Mineralization&Sedimentary Minerals,College of Earth Science&Engineering,ShandongUnitersity of Science and Technology,Qingdao 266590,China;Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China.)

机构地区：[1]山东省沉积成矿作用与沉积矿产重点实验室,山东科技大学地球科学与工程学院,青岛266590 [2]自然资源部深地动力学重点实验室,中国地质科学院地质研究所,北京100077

出　　处：《岩石学报》2021年第5期1347-1371,I0001-I0006,共31页Acta Petrologica Sinica

基　　金：NSFC-山东联合基金重点支持项目(U1906207);国家自然科学青年基金项目(41803031);山东省自然科学基金项目(ZR2019BD046);自然资源部深地动力学重点实验室开放课题(J1901-16)联合资助。

摘　　要：青岛连三岛地区原划为古元古界荆山岩群中出露各类片岩、片麻岩。本文在前人研究的基础上,对连三岛地区出露的含榴黑云母斜长片麻岩、含榴云母片岩和含榴黑云母钾长片麻岩,进行详细的岩相学和矿物化学研究,确定其变质温压条件及其P-T演化轨迹,并采用LA-ICP-MS锆石U-Pb定年,获得了3个样品的原岩时代和变质时代,为全面深入认识其变质属性提供了进一步的重要依据。根据岩相学和矿物化学成分可以识别出两期矿物组合:第一期(峰期变质阶段)为Grt1+Kfs+Aln+Ph+Qtz;第二期(退变质阶段)为Grt2+Pl+Ep+Bt+Qtz;依据多硅白云母Si压力计、锆石Ti温度计以及GB-GBPQ矿物温压计,确定其峰期变质和退变质的温压条件分别为T=600~817℃、P=2.4~2.6GPa和T=431~456℃、P=0.48~0.82GPa。结合白云母部分熔融现象,上述两个变质阶段构成了一个折返早期升温降压,后穿过多硅白云母熔融反应线,最后降温降压的顺时针型演化的P-T轨迹。CL图像显示3个样品的锆石均具有典型的岩浆核-变质边结构;结合LA-ICP-MS锆石原位微区U-Pb定年和微量元素分析,3个样品分别获得了769~756Ma、~223Ma和213~216Ma三组年龄,分别与苏鲁造山带其他高压-超高压变质岩的新元古代原岩时代(700~800Ma)、峰期变质时代(240~225Ma)和角闪岩相退变质时代(215~205Ma)一致。对样品含榴黑云母斜长片麻岩(17LSD-1)和含榴云母片岩(18LSD-2)进行锆石Hf同位素分析,获得样品17LSD-1的ε_(Hf)(t)=-23.2~2.8、t_(DM2)~C(Hf)=1712~2845Ma,表明其原岩主要来源于古元古代陆壳重熔;样品18LSD-2的ε_(Hf)(t)=-13.9~8.6、t_(DM2)~C(Hf)=1113~2358Ma,表明样品形成时壳源物质成分占主导地位,同时部分幔源或新生地壳物质的加入,导致少部分ε_(Hf)(t)偏正值。Hf同位素结果表明连三岛变质岩原岩的形成与扬子板块新太古代-早古元古代的陆壳重熔有关。对比前人的相关数据,无论是原岩时代�Various types of schist and gneiss are exposed in the Liansandao area in Qingdao,which was originally classified as the Paleoproterozoic Jingshan Group.This paper,on the basis of previous studies,conducts detailed studies of petrography,mineral chemistry,LA-ICP-MS zircon U-Pb dating and Hf isotope analysis on the garnet-bearing biotite plagioclase gneiss,garnet-bearing mica schist and garnet-bearing biotite K-feldspar gneiss from the Liansandao area.The results are used to determine the metamorphic P-T-t path and clarify the protolith properties of these metamorphic rocks,which contributes to improve our current understanding on the metamorphic evolution of the rocks from the Liansandao area.Two stages of the mineral assemblages can be identified according to petrography and mineral chemical composition:The peak metamorphic phase is suggested by the occurrence of Grt1+Kfs1+Aln+Ph+Qtz,which is overprinted by a retrograded assemblage of the retrograded metamorphic phase of Grt2+Pl+Ep+Bt+Qtz.According to Si-in-phengite geobarometry,Ti-in-zircon thermometry and GB-GBPQ thermobarometry,the P-T conditions for the peak and retrograde metamorphic stages were constrained to be 2.4~2.6 GPa/600~817℃and 0.48~0.82 GPa/431~456℃,respectively.The above two metamorphic stages showing a clockwise P-T path,with early heating and decompression after peak metamorphism,subsequently followed by the dehydration melting reaction of phengite,and finally cooling and decompression.Zircon CL images show that the zircons from the three samples all exhibit the inherited magmatic core-metamorphic rim internal microstructure.Based on LAICP-MS U-Pb dating,three groups of ages were yielded,including(I)769~756 Ma;(Ⅱ)c.223 Ma;and(Ⅲ)213~216 Ma,which are consistent with the Neoproterozoic protolith ages(700~800 Ma),the peak metamorphic and retrograde metamorphic ages of the high pressure/ultra-high pressure metamorphic rocks in the Sulu orogen,respectively.Hf isotope analysis of the Sample 17 LSD-1 obtainedεHf(t)=-23.2~2.8,tDM2C(Hf)=1712~2845

关 键 词：苏鲁造山带 古元古代荆山岩群 变质岩 锆石U-PB定年 P-T演化轨迹 

分 类 号：P588.3[天文地球—岩石学]