蚌埠隆起区石榴辉石岩变质PT轨迹及年代学研究  

Analysis of metamorphic P-T conditions and zircon U-Pb age for garnet-pyroxenite in Bengbu uplift tectonic

作　　者：王娟[1] 宋传中[1] 

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《地质科学》2016年第4期1223-1245,共23页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目（编号：41272073）和国家科技重大专项“准噶尔盆地晚古生代构造格架与演化”（编号：2011ZX05008-001-31）资助 致谢 本文得到中国科学院大学吴春明老师,中国科学院地质与地球物理研究所陈意老师与林伟老师的指导,并提出宝贵的修改意见.合肥工业大学聂峰同学、赵俊先同学和李仪兵同学给予本文校稿,在此一并表示感谢.

摘　　要：蚌埠隆起位于华北克拉通东部陆块的胶—辽—吉造山带的最南缘，由于侧重点和关注度的差异，对于该地区的变质演化过程的探究一直较为缺乏，制约了人们对该隆起形成过程的理解。为此，本文通过对该隆起的石榴辉石岩及其退变的黑云斜长片麻岩详细的野外观测、岩相学分析、热力学评价和年代学的研究，较为充分地探讨了该隆起的形成机制。研究显示这两类岩石记录了5个变质阶段：阶段-Ⅰ的平均温压为：^-T=672±17 ℃和^-P=1.05±0.02 GPa；阶段-Ⅱ的平均温压为：^-T=805±30 ℃和^-P=1.21±0.04 GPa；阶段-Ⅲ的平均温压为：^-T=615±13 ℃和^-P=0.93±0.02 GPa； 阶段-Ⅳ的平均温压为：^-T=632±6 ℃和^-P=0.50±0.01 GPa；阶段-Ⅴ的温压为推测值：T=400 ℃～450 ℃和P=0.2～0.4 GPa。其中阶段-Ⅰ～阶段-Ⅲ表象为角闪岩相→麻粒岩相→角闪岩相的过程，显示了一个近等压的可能的快速升温和降温的过程。而阶段-Ⅲ～阶段-Ⅳ表现为一个近于等温降压的快速过程，直至阶段-Ⅴ表现为可能的缓慢降温降压过程。结合背景资料和前人年龄数据，以及本次对退变黑云斜长片麻岩的锆石U-Pb定年（1 885±16 Ma）研究，推测该全过程可能反映的是两期变质事件。其中，早期的变质以阶段-Ⅰ、阶段-Ⅱ和阶段-Ⅲ为代表，揭示了大约在2.5 Ga时期，蚌埠隆起经历了大规模岩浆上侵及紧密相伴的高温麻粒岩相变质事件；而晚期变质以阶-Ⅲ→阶段-Ⅳ等温降压为代表，可能反映的是大约1.9 Ga时期，胶—辽—吉造山带的形成过程。Bengbu uplift tectonic located in the south of Jiao-Liao-Ji orogenic belt in the North China Craton（NCC）,the study of metamorphic evolution process in this area is still relatively weak. That restrict the people＇s understanding of the region. The paper cast a detail analysis in field observation,petrographic,thermodynamic evaluation and chronology for garnet pyroxenite and deteriorated amphibolite hornblende. And we give a more fully discussion to the mechanism formation of the uplift. According,this two kind of rocks record five periods metamorphic,as follows：The average P-T condition of Stage-Ⅰ：^-T=672±17 ℃ and ^-P=1.05±0.02 GPa; The average P-T condition of Stage-Ⅱ：^-T=805±30 ℃ and P=1.21±0.04 GPa;The average P-T condition of Stage-Ⅲ：=^-T 615±13 ℃ and ^-P =0.93±0.02 GPa; The average P-T condition of Stage-Ⅳ：^-T =632±6 ℃ and ^-P=0.50±0.01 GPa;The average P-T condition of speculated Stage-V：T=400 ℃～450 ℃ and P=0.2～0.4 GPa. Stage-Ⅰ to stage-Ⅲ has been show a course of amphibolite facies → granulite facies → amphibolite facies,and it likely revealed a rapid heating and cooling process with nearly constant pressure. Stage-Ⅲ to stage-Ⅳ indicated a rapidly isothermal decompression process,and stage-V probably is a slowly cooling step down process. Summarized background information,predecessors＇ research and the zircon U-Pb chronology data（1 885±16 Ma）from deteriorated amphibolite hornblende in study area,we suggested that the five metamorphic stage of rocks revealed two events of metamorphic. Early phase represented by the stage-Ⅰ,stage-Ⅱ and stage-Ⅲ,Bengbu uplift tectonic may be gone through massive assault on the magma and the high temperature granulite facies metamorphic following in ～2.5 Ga. Later period show as a process of isothermal decompression from stage-Ⅲ to stage-Ⅳ,and it suggest the formation of Jiao-Liao-Ji orogenic belt in ～1.9 Ga in some degree.

关 键 词：蚌埠隆起区 石榴辉石岩 PT条件评价 锆石U-PB定年 

分 类 号：P588.34[天文地球—岩石学] P597.3[天文地球—地质学]