This paper is supported by the Special Doctoral Grant of the Ministry of Education of China （No. 98049114） and the National Natural Science Foundation of China （No. 49972023）.
The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites, ***qüartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian an...The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites, ***qüartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian and less commonly the Sinian and Upper Palaeozoic. They have been subjected at least to two epochs of metamorphism. The early epoch belongs to progressive metamorphism which is centered on high amphibolite-granulite fades in the Fuping area and changed outwards into low amphibolite facies (staurolite-kyanite zone), epidote amphibolite facies (garnet zone) and greenschist facies (chlorite and biotite zones), the metamorphic age of which is about 220–260 Ma. This early-epoch metamorphism belongs to different pressure types: the rocks from greenschist to low amphibolite facies belong to the typical medium-pressure type which shows geothermal gradients of about 17–20 ***C/km and was probably produced by a crustal thickening process related to continental collision, and the high amphibolite-granulite facies belongs to the low-pressure type which shows geothermal gradients of about 25–38 ***C/km and was probably affected by some magmatic heats. Based on the basic characteristics of the P-T paths of the different facies calculated from the garnet zonations, it can be deduced that the metamorphism of medium-pressure facies series took place during an imbricated thickening process, rather than during the uplifting process after thickening. The late-epoch metamorphism belongs to dynamic metamorphism of greenschist facies which is overprinted on the early-epoch metamorphic rocks and is Yanshanian or Himalayan in age, probably related to intracontinental orogeny.展开更多
变质程度达角闪岩相及麻粒岩相的各类变质岩石在变质作用高峰期后,如果降温速率比较慢,往往发生退变质性质的离子再交换反应与纯转换反应。这两类退变质反应不可避免地改造了变质高峰期的矿物成分,使岩石不能准确记录变质作用各阶段的...变质程度达角闪岩相及麻粒岩相的各类变质岩石在变质作用高峰期后,如果降温速率比较慢,往往发生退变质性质的离子再交换反应与纯转换反应。这两类退变质反应不可避免地改造了变质高峰期的矿物成分,使岩石不能准确记录变质作用各阶段的矿物成分和变质作用p T轨迹。对这两类反应的研究已成为近年来变质岩石学研究的热点之一。本文通过研究实例,简要综述了基性麻粒岩中石榴子石-斜方辉石之间的Fe-Mg再交换反应、酸性麻粒岩中斜长石-碱性长石之间的K-Na再交换反应、泥质片麻岩中石榴子石变斑晶边部的部分分解(纯转换)反应,以及恢复变质高峰期矿物成分和计算变质高峰期p T条件的方法。指出只有在准确恢复变质高峰期变质矿物成分的基础上,获得的变质作用p T t轨迹才能反映客观地质事实。展开更多
The Kadui blueschist is located in the central section of Yarlung Zangbo suture zone （YZSZ）, southern Tibet, and has been subjected to the subduction of the Neo-Tethyan Ocean below the Asian Plate and provides impor...The Kadui blueschist is located in the central section of Yarlung Zangbo suture zone （YZSZ）, southern Tibet, and has been subjected to the subduction of the Neo-Tethyan Ocean below the Asian Plate and provides important clues for better understanding the evolution of the India-Asia convergence zone. In this paper, the systematical petrographic and mineral chemical studies were carried out on the Kadui blueschist, which reveal a mineral assemblage of sodic amphibole, chlorite, epidote, albite and quartz with accessory minerals of titanite, calcite and zircon. Electron microprobe analyses demonstrate that amphibole shows zoned from actinolite core to ferrowinchite/riebeckite rim composition indicating that the sodic amphibole has formed during a prograde metamorphic event. The protolith of the blueschist is an intermediate-basic pyroclastic rock. The calculated pseudosection indicates a clockwise P-T path and constrains peak metamorphic conditions of about 5.9 kbar at 345 ℃. This condition is transitional between pumpellyite-actinolite, greenschist and blueschist facies with a burial depth of 20-22 km and a thermal gradient of 15-16 ℃/km. This thermal gradient belongs to high pressure intermediate P/T facies series and is possibly related to a warm subduction setting of young oceanic slabs. Our new findings indicate that the Kadui blueschist in the central part of YZSZ experienced a rapid subduction and exhumation process as a response to a northward subduction of the Neo-Tethyan oceanic lithosphere during the initial India-Asia collision stage.展开更多
The high-pressure （HP） eclogite in the western Dabie Mountain encloses numerous hornblendes, mostly barroisite. Opinions on the peak metamorphic P-T condition, PT path and mineral paragenesis of it are still in disp...The high-pressure （HP） eclogite in the western Dabie Mountain encloses numerous hornblendes, mostly barroisite. Opinions on the peak metamorphic P-T condition, PT path and mineral paragenesis of it are still in dispute. Generally, HP eclogite involves garnet, omphacite, hornblendes and quartz, with or without glaucophane, zoisite and phengite. The garnet has compositional zoning with XMg increase, XCa and XMn decrease from core to rim, which indicates a progressive metamorphism. The phase equilibria of the HP eclogite modeled by the P-T pseudosection method developed recently showed the following： （1） the growth zonation of garnet records a progressive metamorphic PT path from pre-peak condition of 1.9-2.1 GPa at 508~C-514~C to a peak one of 2.3-2.5 GPa at 528~C-531~C for the HP eclogite; （2） the peak mineral assemblage is garnet＋omphacite＋glaucophane＋quartz_＋phengite, likely paragenetic with lawsonite; （3） the extensive hornblendes derive mainly from glaucophane, partial omphacite and even a little garnet due to the decompression with some heating during the post-peak stage, mostly representing the conditions of about 1.4-1.6 GPa and 580~C-640~C, and their growth is favored by the dehydration of lawsonite into zoisite or epidote, but most of the garnet, omphacite or phengite in the HP eclogite still preserve their compositions at peak condition, and they are not obviously equilibrious with the hornblendes.展开更多
The mafic granulites in Dinggye,as various scale lense-shaped enclaves within the high Himalayan crystalline rock series,occur along mylonitic foliations at the junction between the Southern Tibetan Detachment System(...The mafic granulites in Dinggye,as various scale lense-shaped enclaves within the high Himalayan crystalline rock series,occur along mylonitic foliations at the junction between the Southern Tibetan Detachment System(STDS)and the Xainza-Dinggye normal fault system.The main lithological assemblage comprises garnet plagioclase pyroxenite,garnet two-pyroxene granulite,pyroxene garnet amphibolite and so on.The detailed petrological analyses show that these mafic granulites underwent at least four-stage metamorphic evolution.The first metamor-phic stage,the garnet+clinopyroxene+quart mineral assemblage(M1)was probably formed un-der eclogite facies,the second stage,the plagioclase+clinopyroxene symplectite mineral as-semblage(M2)was produced under high-pressure granulite facies by the early decompressive breakdown of M1 mineral assemblage,the third stage,the plagioclase+clinopyroxene+hypersthene symplectite mineral assemblage(M3)was formed at granulite facies by the late period decompressive breakdown of M1 and M2 mineral assemblages and the final stage,pla-gioclase+hornblende mineral assemblage(M4)was formed by hydrolysis of earlier mineral as-semblages during late uplifting.The detailed mineral composition analyses suggest that garnets and clinopyroxenes within M1 and M2 mineral assemblages display similar compositions to the equivalents in the B and C types of eclogites,whereas the M3 clinopyroxenes are akin to these of the same kind of minerals in the granulite.These mineral chemistry features and P-T estimates calculated by mineral thermometers and barometers indicate that the early stage relic porphyro-blasts(M1)could be formed at the eclogite facies,the early decompressive breakdown(M2)occurred at the high-pressures granulite facies of 1.35―1.48 GPa and 625―675℃,the M3 mineral assemblage recorded the granulite facies of 0.7―0.95 GPa and 775―900℃and M4 plagioglase+hornblende retrograde mineral assemblage was produced under the amphibolite facies metamorphism with pressure of 0.4 to 0.75 GPa and temperature at between 660 and 700℃.These construct P-T paths from crustal subduction overthickening to tectonic uplift tectono-thermal evolution.The mineral chemical characteristics and P-T condition at every metamorphic stage of these granulites indicate that these rocks experienced the eclogite facies metamorphism during the early stage.Subsequently,these mafic granulites underwent the three-stage exhuma-tion of the eclogite facies tectonic uplift,isostatic uplift related to the transformation from ec-logite/high-pressure granulite to granulite facies and extensional uplift.展开更多
基金This paper is supported by the Special Doctoral Grant of the Ministry ofEducation of China(No.98049114)and the National Natural Science Foundation of China(No.49972023).
文摘This paper is supported by the Special Doctoral Grant of the Ministry of Education of China （No. 98049114） and the National Natural Science Foundation of China （No. 49972023）.
文摘The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites, ***qüartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian and less commonly the Sinian and Upper Palaeozoic. They have been subjected at least to two epochs of metamorphism. The early epoch belongs to progressive metamorphism which is centered on high amphibolite-granulite fades in the Fuping area and changed outwards into low amphibolite facies (staurolite-kyanite zone), epidote amphibolite facies (garnet zone) and greenschist facies (chlorite and biotite zones), the metamorphic age of which is about 220–260 Ma. This early-epoch metamorphism belongs to different pressure types: the rocks from greenschist to low amphibolite facies belong to the typical medium-pressure type which shows geothermal gradients of about 17–20 ***C/km and was probably produced by a crustal thickening process related to continental collision, and the high amphibolite-granulite facies belongs to the low-pressure type which shows geothermal gradients of about 25–38 ***C/km and was probably affected by some magmatic heats. Based on the basic characteristics of the P-T paths of the different facies calculated from the garnet zonations, it can be deduced that the metamorphism of medium-pressure facies series took place during an imbricated thickening process, rather than during the uplifting process after thickening. The late-epoch metamorphism belongs to dynamic metamorphism of greenschist facies which is overprinted on the early-epoch metamorphic rocks and is Yanshanian or Himalayan in age, probably related to intracontinental orogeny.
文摘变质程度达角闪岩相及麻粒岩相的各类变质岩石在变质作用高峰期后,如果降温速率比较慢,往往发生退变质性质的离子再交换反应与纯转换反应。这两类退变质反应不可避免地改造了变质高峰期的矿物成分,使岩石不能准确记录变质作用各阶段的矿物成分和变质作用p T轨迹。对这两类反应的研究已成为近年来变质岩石学研究的热点之一。本文通过研究实例,简要综述了基性麻粒岩中石榴子石-斜方辉石之间的Fe-Mg再交换反应、酸性麻粒岩中斜长石-碱性长石之间的K-Na再交换反应、泥质片麻岩中石榴子石变斑晶边部的部分分解(纯转换)反应,以及恢复变质高峰期矿物成分和计算变质高峰期p T条件的方法。指出只有在准确恢复变质高峰期变质矿物成分的基础上,获得的变质作用p T t轨迹才能反映客观地质事实。
基金financially supported by the National Natural Science Foundation of China(No.41572044)the SDUST Research Fund(No.2015TDJH101)
文摘The Kadui blueschist is located in the central section of Yarlung Zangbo suture zone （YZSZ）, southern Tibet, and has been subjected to the subduction of the Neo-Tethyan Ocean below the Asian Plate and provides important clues for better understanding the evolution of the India-Asia convergence zone. In this paper, the systematical petrographic and mineral chemical studies were carried out on the Kadui blueschist, which reveal a mineral assemblage of sodic amphibole, chlorite, epidote, albite and quartz with accessory minerals of titanite, calcite and zircon. Electron microprobe analyses demonstrate that amphibole shows zoned from actinolite core to ferrowinchite/riebeckite rim composition indicating that the sodic amphibole has formed during a prograde metamorphic event. The protolith of the blueschist is an intermediate-basic pyroclastic rock. The calculated pseudosection indicates a clockwise P-T path and constrains peak metamorphic conditions of about 5.9 kbar at 345 ℃. This condition is transitional between pumpellyite-actinolite, greenschist and blueschist facies with a burial depth of 20-22 km and a thermal gradient of 15-16 ℃/km. This thermal gradient belongs to high pressure intermediate P/T facies series and is possibly related to a warm subduction setting of young oceanic slabs. Our new findings indicate that the Kadui blueschist in the central part of YZSZ experienced a rapid subduction and exhumation process as a response to a northward subduction of the Neo-Tethyan oceanic lithosphere during the initial India-Asia collision stage.
基金funded by the National Natural Science Foundation of China (No.40525006 and 40372032).
文摘The high-pressure （HP） eclogite in the western Dabie Mountain encloses numerous hornblendes, mostly barroisite. Opinions on the peak metamorphic P-T condition, PT path and mineral paragenesis of it are still in dispute. Generally, HP eclogite involves garnet, omphacite, hornblendes and quartz, with or without glaucophane, zoisite and phengite. The garnet has compositional zoning with XMg increase, XCa and XMn decrease from core to rim, which indicates a progressive metamorphism. The phase equilibria of the HP eclogite modeled by the P-T pseudosection method developed recently showed the following： （1） the growth zonation of garnet records a progressive metamorphic PT path from pre-peak condition of 1.9-2.1 GPa at 508~C-514~C to a peak one of 2.3-2.5 GPa at 528~C-531~C for the HP eclogite; （2） the peak mineral assemblage is garnet＋omphacite＋glaucophane＋quartz_＋phengite, likely paragenetic with lawsonite; （3） the extensive hornblendes derive mainly from glaucophane, partial omphacite and even a little garnet due to the decompression with some heating during the post-peak stage, mostly representing the conditions of about 1.4-1.6 GPa and 580~C-640~C, and their growth is favored by the dehydration of lawsonite into zoisite or epidote, but most of the garnet, omphacite or phengite in the HP eclogite still preserve their compositions at peak condition, and they are not obviously equilibrious with the hornblendes.
基金This work was suppotted by the Ministry of Saance and Techmology of the People's Republic of China(Gant No 2002CB412608)the Specific Project for the Aunthos of Best Dissertations of Chimese Univarsities and Colleges(Grant No.200022).
文摘The mafic granulites in Dinggye,as various scale lense-shaped enclaves within the high Himalayan crystalline rock series,occur along mylonitic foliations at the junction between the Southern Tibetan Detachment System(STDS)and the Xainza-Dinggye normal fault system.The main lithological assemblage comprises garnet plagioclase pyroxenite,garnet two-pyroxene granulite,pyroxene garnet amphibolite and so on.The detailed petrological analyses show that these mafic granulites underwent at least four-stage metamorphic evolution.The first metamor-phic stage,the garnet+clinopyroxene+quart mineral assemblage(M1)was probably formed un-der eclogite facies,the second stage,the plagioclase+clinopyroxene symplectite mineral as-semblage(M2)was produced under high-pressure granulite facies by the early decompressive breakdown of M1 mineral assemblage,the third stage,the plagioclase+clinopyroxene+hypersthene symplectite mineral assemblage(M3)was formed at granulite facies by the late period decompressive breakdown of M1 and M2 mineral assemblages and the final stage,pla-gioclase+hornblende mineral assemblage(M4)was formed by hydrolysis of earlier mineral as-semblages during late uplifting.The detailed mineral composition analyses suggest that garnets and clinopyroxenes within M1 and M2 mineral assemblages display similar compositions to the equivalents in the B and C types of eclogites,whereas the M3 clinopyroxenes are akin to these of the same kind of minerals in the granulite.These mineral chemistry features and P-T estimates calculated by mineral thermometers and barometers indicate that the early stage relic porphyro-blasts(M1)could be formed at the eclogite facies,the early decompressive breakdown(M2)occurred at the high-pressures granulite facies of 1.35―1.48 GPa and 625―675℃,the M3 mineral assemblage recorded the granulite facies of 0.7―0.95 GPa and 775―900℃and M4 plagioglase+hornblende retrograde mineral assemblage was produced under the amphibolite facies metamorphism with pressure of 0.4 to 0.75 GPa and temperature at between 660 and 700℃.These construct P-T paths from crustal subduction overthickening to tectonic uplift tectono-thermal evolution.The mineral chemical characteristics and P-T condition at every metamorphic stage of these granulites indicate that these rocks experienced the eclogite facies metamorphism during the early stage.Subsequently,these mafic granulites underwent the three-stage exhuma-tion of the eclogite facies tectonic uplift,isostatic uplift related to the transformation from ec-logite/high-pressure granulite to granulite facies and extensional uplift.
