Deciphering high-pressure granulite-facies metamorphism and anatexis within a collisional orogeny can provide crucial constraints on geodynamic evolution and melt activity during subduction and exhumation.Combining pe...Deciphering high-pressure granulite-facies metamorphism and anatexis within a collisional orogeny can provide crucial constraints on geodynamic evolution and melt activity during subduction and exhumation.Combining petrographic observations,mineral chemistry,REE in Grt-Cpx thermobarometry,and previous work,at least four stages are suggested for the metamorphic evolution of the mafic granulites in the South Altun,including the protolith stage,the high-pressure granulite-facies stage(909-1037℃and 17.3-30 kbar),medium-pressure granulite-facies overprint(9.1-11.9 kbar and 753-816℃),and subsequent late amphibolite-greenschist-facies metamorphism.Zircon U-Pb dating shows that the mafic granulites underwent high-pressure granulite-facies metamorphism at 497.2±3.7 Ma,while the leucosome formed at 498.2±2.9 Ma.Thus,the leucosomes from the host mafic granulite may have been formed at the high-pressure granulite-facies metamorphic event.The characteristics of zircon morphology,mineral inclusions,low Th/U values,HREE enrichment,and negative Eu anomalies indicate that these zircons from the leucosome were formed from the metamorphic melts.The characteristics of whole-rock major and trace elements as well as Hf isotopic features of zircons between the leucosomes and the host mafic granulite indicate that the melt may have been generated by the partial melting of the host mafic granulite.展开更多
准噶尔是新疆北部古生代造山带的重要组成部分,以广泛发育晚古生代后碰撞花岗岩为特征,是中亚造山带中显生宙陆壳生长作用非常显著的地区之一。根据新近获得的SHRIMP锆石U-Pb年龄,并参考已经发表的锆石U-Pb年龄,本文重新厘定了准噶尔晚...准噶尔是新疆北部古生代造山带的重要组成部分,以广泛发育晚古生代后碰撞花岗岩为特征,是中亚造山带中显生宙陆壳生长作用非常显著的地区之一。根据新近获得的SHRIMP锆石U-Pb年龄,并参考已经发表的锆石U-Pb年龄,本文重新厘定了准噶尔晚古生代后碰撞深成岩浆活动的时限。按照最新的国际地质年表中石炭纪和二叠纪划分方案(Gradstein et al．,2004),准噶尔后碰撞深成岩浆活动是从早石炭世中-晚维宪期开始、于早二叠世末期结束的。东准噶尔后碰撞深成岩浆活动发生在330～265Ma之间,而西准噶尔后碰撞深成岩浆活动的时限在340～275Ma之间,持续时间分别约65Ma。但是,在东准噶尔,后碰撞深成岩浆活动集中在330～310Ma和305～280Ma两个时段发生,而在西准噶尔,后碰撞深成岩浆活动的高峰发生在310～295Ma之间。准噶尔晚古生代后碰撞深成岩浆活动在空间上没有受到重要地质界线(如蛇绿岩带)的分隔控制,在有的地方花岗岩还可以侵位在蛇绿岩带之中。而晚古生代后碰撞深成岩浆活动不但在准噶尔分布广泛,而且在准噶尔北邻的阿尔泰造山带和南邻的天山造山带中均有出现,具有广泛的区域性。展开更多
基金financially supported by the Basic Foundation of Tianjin University of Commercethe Fund from the Key Laboratory of Continental Dynamics of Ministry of Natural Resources(J2306)。
文摘Deciphering high-pressure granulite-facies metamorphism and anatexis within a collisional orogeny can provide crucial constraints on geodynamic evolution and melt activity during subduction and exhumation.Combining petrographic observations,mineral chemistry,REE in Grt-Cpx thermobarometry,and previous work,at least four stages are suggested for the metamorphic evolution of the mafic granulites in the South Altun,including the protolith stage,the high-pressure granulite-facies stage(909-1037℃and 17.3-30 kbar),medium-pressure granulite-facies overprint(9.1-11.9 kbar and 753-816℃),and subsequent late amphibolite-greenschist-facies metamorphism.Zircon U-Pb dating shows that the mafic granulites underwent high-pressure granulite-facies metamorphism at 497.2±3.7 Ma,while the leucosome formed at 498.2±2.9 Ma.Thus,the leucosomes from the host mafic granulite may have been formed at the high-pressure granulite-facies metamorphic event.The characteristics of zircon morphology,mineral inclusions,low Th/U values,HREE enrichment,and negative Eu anomalies indicate that these zircons from the leucosome were formed from the metamorphic melts.The characteristics of whole-rock major and trace elements as well as Hf isotopic features of zircons between the leucosomes and the host mafic granulite indicate that the melt may have been generated by the partial melting of the host mafic granulite.
文摘准噶尔是新疆北部古生代造山带的重要组成部分,以广泛发育晚古生代后碰撞花岗岩为特征,是中亚造山带中显生宙陆壳生长作用非常显著的地区之一。根据新近获得的SHRIMP锆石U-Pb年龄,并参考已经发表的锆石U-Pb年龄,本文重新厘定了准噶尔晚古生代后碰撞深成岩浆活动的时限。按照最新的国际地质年表中石炭纪和二叠纪划分方案(Gradstein et al．,2004),准噶尔后碰撞深成岩浆活动是从早石炭世中-晚维宪期开始、于早二叠世末期结束的。东准噶尔后碰撞深成岩浆活动发生在330～265Ma之间,而西准噶尔后碰撞深成岩浆活动的时限在340～275Ma之间,持续时间分别约65Ma。但是,在东准噶尔,后碰撞深成岩浆活动集中在330～310Ma和305～280Ma两个时段发生,而在西准噶尔,后碰撞深成岩浆活动的高峰发生在310～295Ma之间。准噶尔晚古生代后碰撞深成岩浆活动在空间上没有受到重要地质界线(如蛇绿岩带)的分隔控制,在有的地方花岗岩还可以侵位在蛇绿岩带之中。而晚古生代后碰撞深成岩浆活动不但在准噶尔分布广泛,而且在准噶尔北邻的阿尔泰造山带和南邻的天山造山带中均有出现,具有广泛的区域性。
