不同变质条件下变基性岩中磷灰石地球化学特征:以古元古代华北中部造山带为例  

Geochemical characteristics of apatite in metabasic rocks under different metamorphic conditions:a case study from the Paleoproterozoic Trans-North China Orogen

作　　者：杨钰清 高彭 张健[3] 刘晓光[4] 程昌泉 尹常青 钱加慧 YANG Yuqing;GAO Peng;ZHANG Jian;LIU Xiaoguang;CHENG Changquan;YIN Changqing;QIAN Jiahui(School of Earth Sciences and Engineering,Sun Yat-sen University,Zhuhai 519082,Guangdong,China;CAS Key Laboratory of Crust-Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,Anhui,China;Department of Earth Sciences,The University of Hong Kong,Hong Kong 999077,China;Key Lab of Submarine Geosciences and Prospecting Techniques,and College of Marine Geosciences,Ocean University of China,Qingdao 266100,Shandong,China)

机构地区：[1]中山大学地球科学与工程学院,广东珠海519082 [2]中国科学院壳幔物质与环境重点实验室中国科学技术大学地球和空间科学学院,安徽合肥230026 [3]香港大学地球科学系,中国香港999077 [4]海底科学与探测技术教育部重点实验室中国海洋大学海洋地球科学学院,山东青岛266100

出　　处：《地质力学学报》2024年第6期991-1011,共21页Journal of Geomechanics

基　　金：国家自然科学基金项目(42025204)。

摘　　要：磷灰石是一种常见的副矿物,在各种岩石类型中均有产出,其U-Pb年龄、微量元素(特别是REE、Th、U和Sr等)和Sr-Nd同位素组成可提供重要的年代学和地球化学信息。目前对于其在造山过程中不同变质级别下的地球化学行为的研究并不清楚。作为古元古代典型的陆-陆碰撞造山带,华北克拉通中部造山带记录了一套从绿片岩相、经角闪岩相至麻粒岩相的完整变质岩石组合,因而是研究基性岩变质演化过程磷灰石地球化学属性的理想区域。文章在中部造山带的五台—恒山地区系统采集了绿片岩、斜长角闪岩和基性麻粒岩样品,并对不同变质级别变基性岩中的磷灰石进行了详细的岩相学和微量元素研究。研究结果表明,绿片岩样品中含有岩浆成因和变质成因2种类型的磷灰石,斜长角闪岩样品中主要为变质成因磷灰石,而基性麻粒岩样品中主要为深熔型磷灰石,表现出岩浆成因磷灰石的微量元素特征,可能结晶自深熔熔体。研究表明磷灰石的微量元素变化能够清晰地反映变质演化过程中随温压条件变化而出现的熔体和共存结晶矿物的影响,为了解造山作用过程中的元素迁移和平衡提供了新的约束。[Objective]Apatite is a common accessory mineral that is widely distributed in various rock types.Its U-Pb age,trace elements(particularly REE,Th,U,and Sr),and Sr-Nd isotopic compositions provide important information on its chronology and magmatism.However,the geochemical behavior at different metamorphic levels during orogenesis remains unclear.As a typical continent-to-continent collisional orogenic belt in the Paleoproterozoic,the Trans-North China Orogen(TNCO)has recorded an integrated metamorphic sequence ranging from greenschist to amphibolite to granulite facies.Therefore,it is an ideal area to study the geochemical behavior of apatite during various grades of metamorphism involving the orogenic process.[Methods]In this study,we systematically collected metabasic samples of different metamorphic grades,including greenschist,amphibolite,and mafic granulite,in the Wutai-Hengshan area of the TNCO.We conducted detailed petrographic observations and geochemical analyses of apatite grains from metabasic rocks with different metamorphic grades.[Results]Our results showed that the apatite grains from the greenschist samples had both magmatic and metamorphic origins.The apatite grains in the amphibolite samples were mainly of metamorphic origin.In contrast,the grains from the granulite samples were closely related to crustal anatexis,exhibiting geochemical characteristics of magmatic-origin apatite.[Conclusion]This study shows that trace element variations in apatite can clearly reflect the influence of metamorphic grades,crustal anatexis,and coexisting rock-forming minerals with variations in temperature and pressure conditions during metamorphism.[Significance]The results of this study provide new constraints to our understanding of elemental migration and the geochemical balance within apatite during orogeny.

关 键 词：华北克拉通 中部造山带 变基性岩 变质作用 磷灰石 微量元素 

分 类 号：P584[天文地球—岩石学] P588.3[天文地球—地质学]