蚌埠隆起区镁铁质麻粒岩变质PT及变质作用演化  

Metamorphism and metamorphic evolution of mafic granulite in Bengbu Uplift

作　　者：刘玉娟 张妍[2] 王娟[2] 彭春蕾 宋传中[2] 石永红[2] Liu Yujuan;Zhang Yan;Wang Juan;Peng Chunlei;Song Chuanzhong;Shi Yonghong(Anhui Technical College of Industry and Economy,Hefei 230009;School of Resource and Environment Engineering,Hefei University of Technology,Hefei 230009)

机构地区：[1]安徽工业经济职业技术学院,合肥230009 [2]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《地质科学》2022年第3期835-860,共26页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金青年项目(编号:42102052);安徽省高校自然科学研究重点项目(编号:KJ2021A1537)资助。

摘　　要：华北克拉通作为世界上最古老的克拉通之一,初始地壳的形成年代为~3.8 Ga,由东部陆块、西部陆块和中央造山带组成。蚌埠隆起区位于华北克拉通东南缘,胶—辽—吉造山带的南端,构造位置重要。前人对蚌埠隆起区进行了大量的锆石U-Pb年代学、同位素地球化学、变质温压条件及P-T轨迹等研究,但变质PT条件存在较大差异。本文主要通过对石榴麻粒岩进行详细的岩相学、矿物化学成分、锆石U-Pb年代学、温压条件及变质期次分析,进一步探讨蚌埠隆起区的变质演化过程及变质时代。依据矿物组合及成分差异,进行多种温压计联合计算,最终确定其记录了两期峰期后变质作用:1)变质阶段-Ⅰ:■=765±34℃,■=1.22±0.04 GPa;2)变质阶段-Ⅱ:■=609±22℃,■=0.98±0.05 Ga;揭示东芦山地区经历了麻粒岩相→角闪岩相的快速冷却过程,其中变质阶段-Ⅰ应为峰期变质PT条件的下限。通过大量变质PT条件对比研究可知,对于具有中、下地壳物质属性的镁铁质麻粒岩而言,由于其经历了较高级别的变质作用,相平衡模拟法、平均温压法及微量元素温度计等对峰期PT条件的恢复可能更具优势,而传统地质温压计的离子交换作用在一定程度上受控于后期变质改造及再平衡作用,更可能获得峰期后的变质PT条件。锆石U-Pb年代学及锆石内部包体分析结果揭示,其具有多期次变质/生长特征,其中1.84~1.74 Ga(变质锆石年龄)、~2.1 Ga(岩浆锆石年龄)与~2.5 Ga(变质/岩浆锆石年龄)分别代表了石榴麻粒岩的角闪岩相退变质阶段(M3)变质时代、原岩形成时代及华北克拉通的主期生长阶段与紧随其后的高温变质事件。多期变质作用和岩浆作用的年代学证据,契合华北陆块的地壳生长和演化历史,锆石内的包体特征为多期、不同级别的变质作用记录提供了另一角度的证据。As one of the oldest cratons in the world, the North China Craton(NCC)has an initial crustal age of~3.8 Ga, which is composed of eastern continental block, the western block and the central orogenic belt. The Bengbu Uplift, located in the southeast of the North China Craton and the most southern part of the Jiao-Liao-Ji orogenic belt, is of an important structural position. Previous studies on zircon U-Pb chronology, isotope geochemistry, metamorphic PT and P-T path, etc., have been performed. However, there are great differences in metamorphic PT conditions. We have done detailed analyses on petrography, mineral chemistry, zircon U-Pb isotopic geochronology, metamorphic PT conditions and stages of garnet pyroxenolite, trying to place the metamorphic evolution of the Bengbu Uplift. Combined with the analytical results of petrography, mineral chemistry and various thermobarometers calculation finally determined that it records two post peak metamorphism stages: 1)stage-Ⅰ: ■= 765±34 ℃and ■= 1.22±0.04 GPa;2)stage-Ⅱ: ■= 609±22 ℃ and ■= 0.98±0.05 GPa. It is revealing that Donglushan area has experienced a rapid cooling process from granulite facies to amphibolite facies, in which metamorphic stage-Ⅰ should be the lower limit of peak metamorphism PT conditions.Through the comparative study of large number of metamorphic PT conditions, it can be seen that for the mafic granulite with the material properties of the middle and lower crust, due to its high-level metamorphism, P-T pseudosection method, PT average method and trace element thermometer have more advantages in the restoration of peak metamorphic PT conditions.While the ion exchange of the traditional geological thermometer is controlled by the later metamorphic transformation and rebalancing, it is more likely to obtain post peak metamorphic PT conditions. Results of the zircon U-Pb isotopic dating and zircon inclusion analysis show that it has multi-stage metamorphic/growth characteristics. Among them, 1.84~1.74 Ga(metamorphic zircon age,

关 键 词：蚌埠隆起 石榴麻粒岩 PT条件 锆石包体 锆石U-PB定年 

分 类 号：P588[天文地球—岩石学] P597[天文地球—地质学]