河南洛宁太华变质杂岩区早元古代变质作用P-T-t轨迹及其大地构造意义  

Paleoproterozoic metamorphic P-T-t path and tectonic significance of the Luoning metamorphic complex at the southern terminal of the Trans-North China Orogen, Henan Province

作　　者：蒋宗胜[1,2] 王国栋[2] 肖玲玲[3] 第五春荣[1] 卢俊生[2] 吴春明[1,2] 

机构地区：[1]大陆动力学国家重点实验室,西北大学地质学系,西安710069 [2]中国科学院研究生院地球科学学院,北京100049 [3]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2011年第12期3701-3717,共17页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40872125);西北大学大陆动力学国家重点实验室联合资助

摘　　要：太华变质杂岩广泛出露于华北克拉通南缘,总体呈SW-NE向展布。在河南洛宁地区,太华变质杂岩以TTG片麻岩、斜长角闪片麻岩和变泥质片麻岩为主。斜长角闪片麻岩中可识别出三个阶段的变质矿物组合:进变质阶段矿物组合(M1)为石榴子石变斑晶内部的包裹体矿物组合(Amp1+Pl1+Qtz),变质高峰期矿物组合(M2)为石榴子石变斑晶边部和基质矿物组合(Grt2+Amp2+Pl2+Qtz),退变质阶段矿物组合(M3)为"白眼圈"状后成合晶组合(Amp3+Pl3+Qtz)。运用矿物温度计与压力计估算三个阶段的P-T条件分别为:进变质阶段约600～680℃/7.0～7.6kbar,变质高峰期为680～790℃/9.5～10.7kbar,退变质阶段为580～720℃/6.5～7.6kbar。变泥质片麻岩中保留了进变质阶段(M1)包裹体矿物组合(Bt1+Pl1+Qtz)和峰期变质阶段(M2)矿物组合(Grt2+Bt2+Pl2+Qtz)两个阶段。其中未发现后期退变质反应结构,石榴子石中也未发现成分环带。P-T条件估算结果分别为:M1阶段620～710℃/4.9～5.6kbar,M2阶段710～760℃/7.3～8.3kbar。洛宁地区太华变质杂岩记录了顺时针的近等温降压型的P-T轨迹,可能经历了与华北中部造山带其它杂岩类似的变质演化过程,推测其形成于华北克拉通东部陆块和西部陆块沿中部造山带的拼合过程中。SIMS与ICP-MS锆石U-Pb定年表明,斜长角闪片麻岩记录了1938～1967Ma的变质事件,比华北中部造山带其它变质杂岩区所广泛记录的～1850Ma变质事件早了约100Ma,暗示中部造山带的拼合可能是一个长期的、复杂的过程。The NW-SE-striking Taihua metamorphic complex crop out discretely along the southern margin of the Trans-North China Orogen （TNCO）, among which the Luoning metamorphic terrane is mainly composed of TTG-like gneisses, amphibolitic gneisses and metapelitic gneisses. Garnets in amphibolitic gneisses are commonly embayed and surrounded by amphibole＋plagioclase＋quartz symplectites. Three generations of mineral assemblages have been recognized in the amphibolites： the prograde assemblage （M1） is represented by plagioclase＋amphibole±biotite±epidote＋quartz enclosed in garnet porphyroblasts, the peak metamorphic assemblage （M2） is dominantly composed of garnet porphyroblasts and the matrix minerals plagioclase＋amphibole＋biotite＋quartz, and the retrograde metamorphic assemblage （M3） is represented by the symplectitic intergrowth of amphibole＋plagioclase＋quartz rimming garnet porphyroblasts. Thermodynamic computation shows that the metamorphic conditions of the plagioclase-amphibole gneisses are 600~680℃ at 7.0~7.6kbar for the M1 stage, 680~790℃ at 9.5~10.7kbar for the metamorphic peak M2 stage and 580~720℃ at 6.5~7.6kbar for the retrograde M3 stage, respectively. Two stages of metamorphic assemblages are preserved in the metapelitic gneisses, the prograde metamorphic assemblages （M1） and the peak metamorphic assemblages （M2）. Calculated metamorphic P-T conditions of these two stages are 620~710℃ at 4.9~5.6kbar and 710~760℃ at 7.3~8.3kbar, respectively. The Taihua metamorphic complex is deciphered to have undergone metamorphism characterized by clockwise P-T paths including the nearly isothermal decompression （ITD） segments, which are inferred to be related to the final amalgamation of North China Craton （NCC） along the TNCO. SIMS and ICP-MS U-Pb dating of metamorphic zircons extracted from amphibolitic gneisses yielded metamorphic ages ranging from 1938Ma to 1967Ma, ca. 100Ma earlier than the ubiquitous ~1850Ma metamorphic event recorded in most of the metamor

关 键 词：温压计 P-T轨迹 变质作用时代 太华变质杂岩 中部造山带 华北克拉通 

分 类 号：P588.345[天文地球—岩石学]