大别造山带宿松变质杂岩变质演化过程  

Metamorphic Evolution of Susong Metamorphic Complex in Dabie Orogenic Belt,China

作　　者：周安泰 石永红[1] 赵俊先[1] 杨根山 ZHOU An-tai;SHI Yong-hong;ZHAO Jun-xian;YANG Gen-shan(School of Resources and Environment Engineering,Hefei University of Technology,Hefei 230009,Anhui,China)

机构地区：[1]合肥工业大学资源与环境工程学院,安徽合肥230009

出　　处：《地球科学与环境学报》2018年第6期727-738,共12页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(41641016)

摘　　要：宿松变质杂岩位于大别造山带最南端,是该造山带重要组成部分之一。由于其变质程度相对较低,记录的变质演化信息相对较少,所以其变质P-T轨迹的构建一直是研究难点,制约了对大别造山带形成过程的全面理解。针对宿松变质杂岩特征性岩石——石榴斜长角闪岩展开了细致的岩相学、矿物化学研究和热力学评价。结果表明:该类岩石具有切尔马克闪石+绿帘石+石英+金红石(Ts+Ep+Qz+Rt)、石榴石+斜长石+切尔马克闪石+石英+绿帘石+金红石(Grt+Pl+Ts+Qz+Ep+Rt)、斜长石+切尔马克闪石+石英+磁铁矿(Pl+Ts+Qz+Mag)及以绿泥石+石英(Chl+Qz)为代表等4个变质阶段矿物组合,其温压范围依次为591℃～620℃、0.48～0.56GPa,606℃～636℃、1.01～1.12GPa,600℃～619℃、0.79～0.91GPa,400℃～500℃、0.1～0.3GPa,展现了一个近等温升压→近等温降压→降温降压的变质P-T轨迹。P-T轨迹的构建表明宿松变质杂岩经历了早期快速俯冲、折返和晚期缓慢抬升过程,暗示了作为扬子板块前缘块体——宿松变质杂岩在大洋板片拖曳作用下迅速俯冲,由于板片断离在浮力作用下迅速回返,并长时间停滞在上地壳层次,再缓慢上升至地表。Susong metamorphic complex is located at the southernmost end of Dabie orogenic belt, and is one of the important components of the orogenic belt. Due to the relatively low degree of metamorphism and relatively little information of metamorphic evolution, the construction of metamorphic P-T path has challenged geologists for many years, which restricts the full understanding of the formation mechanism of Dabie orogenic belt. The detailed petrographic, mineralogical and thermodynamic evaluation of garnet-plagioclase amphibolite, which was a typical rock from Susong metamorphic complex, were carried out. the results show that this kind of rocks has four metamorphic stage mineral assemblages including Ts＋Ep＋Qz＋Rt, Grt＋Pl＋Ts＋Qz＋Ep＋Rt, Pl＋Ts＋Qz＋Mag and mainly Chl＋Qz, and the corresponding temperatures and pressures are 591 ℃-620 ℃, 606 ℃-636 ℃, 600 ℃-619 ℃ and 400 ℃-500 ℃, and 0.48-0.56 GPa, 1.01-1.12 GPa, 0.79-0.91 GPa and 0.1-0.3 GPa, showing a metamorphic P-T pattern of near-isothermal pressure lift→near-isothermal pressure reduction→temperature reduction and depressuri-zation. The establishment of this P-T path indicates that Susong metamorphic complex experiences rapid subduction and exhumation in the early stage, and slow uplift in the late stage, suggesting that Susong metamorphic complex, as the leading edge block of Yangtze plate, subducts rapidly under the dragging action of the oceanic plate, returns rapidly due to the buoyancy of the plate fragments, stays at the upper crustal level for a long time, and then rises slowly to the surface.

关 键 词：变质杂岩 变质作用 石榴斜长角闪岩 峰期变质条件 P-T 轨迹 地质温压计 大别造山带 扬子板块 

分 类 号：P588.34[天文地球—岩石学]