扬子克拉通古元古代变质演化--来自黄陵穹窿石榴斜长角闪岩的证据  

Paleoproterozoic metamorphic evolution of the Yangtze Craton: Evidence from the Huangling Dome garnet-amphibolite

作　　者：付强 魏君奇[1] 范堡程 裴康达 FU Qiang;WEI Jun-qi;FAN Bao-cheng;PEI Kang-da(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an 710069,China;Xi'an Mineral Resources Investigation Center of China Geological Survey,Xi'an 710100,China)

机构地区：[1]西北大学地质学系,大陆动力学国家重点实验室,陕西西安710069 [2]中国地质调查局西安矿产资源调查中心,陕西西安710100

出　　处：《岩石矿物学杂志》2023年第2期173-190,共18页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金项目(41572171)。

摘　　要：为探讨扬子克拉通古元古代变质作用特征及其形成的构造背景,对黄陵穹窿北部石榴斜长角闪岩开展了岩相学、地球化学和年代学研究。结果表明,石榴斜长角闪岩中主要矿物有石榴子石、斜长石、角闪石、单斜辉石、石英、钛铁矿等,其中保留有3个阶段的不同变质期次的矿物组合,进变质矿物组合为角闪石+斜长石+石英+钛铁矿,峰期矿物组合为石榴子石+角闪石+斜长石+单斜辉石+石英+钛铁矿,退变质矿物组合为石榴子石+角闪石+斜长石+石英+钛铁矿。石榴斜长角闪岩原岩为亚碱性玄武岩,属于拉斑系列,Mg#较低,表明其原岩经历了一定程度的分异作用。使用传统地质温压计计算不同变质阶段的温压条件分别为:进变质阶段,t=596~625℃,p=0.70~0.82 GPa;峰期变质阶段,t≈760℃,p≈1.35 GPa;退变质阶段,t=692~738℃,p=0.68~0.74 GPa,并建立了一条顺时针的p-t轨迹,显示出先升温升压至峰期阶段,随后发生近等温减压的过程。这一p-t轨迹体现了汇聚板块边缘俯冲-碰撞的构造背景,对石榴斜长角闪岩中的锆石进行U-Pb定年,获得了2 008±11 Ma的谐和年龄,并结合该地区已有的变质年龄,共同揭示了扬子克拉通在古元古代参与了微陆块的拼接,是Columbia超大陆聚合的响应。In order to explore the characteristics of metamorphism and the tectonic setting in the Yangtze Craton, we carried out petrographic, geochemical and chronological studies on the garnet-amphibolite in the north of the Huangling Dome. The results show that the main minerals in the garnet-amphibolite are garnet, plagioclase, amphibole, cliniopyroxene, quartz and ilmenite, in which the mineral assemblages of 3 different metamorphic stages are retained. The prograde metamorphic stage is characterized by the assemblage of amphibolite+plagiospar+quartz+ilmenite and the peak metamorphic stage consists of garnet+amphibole+plagioclase+clinopyroxene+quartz+ilmenite, while the retrograde assemblage contains garnet+amphibole+plagioclase+quartz+ilmenite. The garnet-amphibolite protolith belongs to subalkaline tholeiite with low Mg#, indicating that its protolith has experienced a degree of differentiation. By means of conventional geological thermometer, the temperature and pressure conditions of different metamorphic stages were calculated. We obtained the p-t conditions of 596 ~ 625℃ and 0.70 ~ 0.82 GPa for the prograde metamorphic stage, 760℃ and 1. 35 GPa for the peak metamorphic stage, and 692 ~ 738℃ and 0. 68 ~0.74 GPa for the retrograde metamorphic stage. Meanwhile, a clockwise p-t path was represented from these p-t conditions, showing the process of warming and pressurization to the peak and then a near isothermal decompression. This p-t path reflects the tectonic setting of subduction-collision at the convergent plate margin. U-Pb dating of zircons in the garnet-amphibolite yields a harmonic age of 2 008±11 Ma. Together with the existing metamorphic ages in the region, these ages reveal that the Yangtze Craton was involved in the splicing of microcontinental blocks during the Paleozoic, which might be a response of the Columbia supercontinent assembly.

关 键 词：扬子克拉通 黄陵穹窿 石榴斜长角闪岩 变质演化 变质时代 P-T轨迹 

分 类 号：P588.125[天文地球—岩石学]