Recent progress in the study of the UHP metamorphic belt in southwestern Tianshan,China,is summarized in this paper.This about 80-km-long and over 10-km-wide UHP belt has been recognized by the discovery of coesite,co...Recent progress in the study of the UHP metamorphic belt in southwestern Tianshan,China,is summarized in this paper.This about 80-km-long and over 10-km-wide UHP belt has been recognized by the discovery of coesite,coesite pseudomorphs and other UHP minerals.It is the largest oceanic-type UHP metamorphic belt reported so far.It has formed due to northward subduction of the Tianshan Paleo-Ocean.U-Pb dating of metamorphic rims of zircons from a coesite-bearing garnet-phengite schist yields a peak UHP metamorphic ages of 320±3.7 Ma.Combined with ages of 233–226 Ma obtained from rims of zircons from retrograded eclogites,a long retrograde metamorphic evolution(>70 Ma)has been revealed.According to phase equilibria modeling,the P-T paths of both coesite-bearing eclogites and garnet-phengite schists are characterized by thermal relaxation,i.e.,the metamorphic temperature peak lags behind the pressure peak,indicating that the UHP rocks experienced slow and long heating and decompression during exhumation in the subduction channel.On the basis of the field observation that a small amount of eclogite lenses is wrapped in large volumes of metapelites,and the similar P-T paths of both rock types,we propose that the exhumation of the UHP eclogites from southwestern Tianshan,China,may have resulted from the exhumation of large volumes of low-density metapelites,which carried the denser eclogites to the Earth’s surface.展开更多
Coesite provides direct evidence for ultrahigh pressure metamorphism. Although coesite has been found as inclusions in zircon in paragneiss of the north Qaidam Mountains, it has never been identified in eclogite. In t...Coesite provides direct evidence for ultrahigh pressure metamorphism. Although coesite has been found as inclusions in zircon in paragneiss of the north Qaidam Mountains, it has never been identified in eclogite. In this contribution, based on petrographic observations and in situ Raman microprobe spectroscopy, coesite was identified as inclusions in garnet of eclogite from the Aercituoshan, Dulan UHP metamorphic unit, north Qaidam Mountains. Coesite is partly replaced by quartz, showing a pali-sade texture. This is the first report on coesite in eclogite from the north Qaidam Mountains, and is also supported by garnet-omphacite-phengite geothermobarometry (2.7―3.25 GPa, 670―730℃). Coesite and its pseudomorphs have not been found in eclogites and associated rocks of other units of the north Qaidam Mountains. Further studies are required to confirm if all metamorphic units in the north Qaidam Mountains underwent the ultrahigh-pressure metamorphism.展开更多
Coesite is a polymorph of Si O2formed at speci?c high-pressure conditions, and its presence in some crustal rocks as relicts marks the exhumation of deep subducted material to mantle depths, thus providing robust evid...Coesite is a polymorph of Si O2formed at speci?c high-pressure conditions, and its presence in some crustal rocks as relicts marks the exhumation of deep subducted material to mantle depths, thus providing robust evidence for the hypothesis on ultrahigh pressur (UHP) metamorphism [1]. The discovery of coesite and other展开更多
Coesite is an indicator mineral of ultra-high-pressure metamorphism. Since coesite was reported in the Habutengsu Valley, we have also found it in eclogite and schist from the Atantayi Valley in the southwestern Tians...Coesite is an indicator mineral of ultra-high-pressure metamorphism. Since coesite was reported in the Habutengsu Valley, we have also found it in eclogite and schist from the Atantayi Valley in the southwestern Tianshan, China. Petrographic and micro-Raman analyses were carried out for the Atantayi metamorphic rocks and coesite was recognized in the predominant rock types, i.e. schist and eclogite, from three sections. The coesite-bearing schist consists mainly of garnet, Na-Ca amphibole, quartz, white mica and albite; the coesite-bearing eclogite is mainly composed of omphacite, garnet, glaucophane and zoisite. The coesite occurs as various mineral inclusions within porphyroblastic garnet. Findings of coesite in eclogite and associated schist indicate not only the regional in situ formation of the Atantayi ultra-high-pressure eclogite, but also the large areal extent of ultra-high-pressure metamorphism in southwestern Tianshan, extending up to 10 km north-south and 60-80 km east-west.展开更多
基金supported by the National Basic Research Program of China(2009CB825007)the National Natural Science Foundation of China(41121062 and41272069)
文摘Recent progress in the study of the UHP metamorphic belt in southwestern Tianshan,China,is summarized in this paper.This about 80-km-long and over 10-km-wide UHP belt has been recognized by the discovery of coesite,coesite pseudomorphs and other UHP minerals.It is the largest oceanic-type UHP metamorphic belt reported so far.It has formed due to northward subduction of the Tianshan Paleo-Ocean.U-Pb dating of metamorphic rims of zircons from a coesite-bearing garnet-phengite schist yields a peak UHP metamorphic ages of 320±3.7 Ma.Combined with ages of 233–226 Ma obtained from rims of zircons from retrograded eclogites,a long retrograde metamorphic evolution(>70 Ma)has been revealed.According to phase equilibria modeling,the P-T paths of both coesite-bearing eclogites and garnet-phengite schists are characterized by thermal relaxation,i.e.,the metamorphic temperature peak lags behind the pressure peak,indicating that the UHP rocks experienced slow and long heating and decompression during exhumation in the subduction channel.On the basis of the field observation that a small amount of eclogite lenses is wrapped in large volumes of metapelites,and the similar P-T paths of both rock types,we propose that the exhumation of the UHP eclogites from southwestern Tianshan,China,may have resulted from the exhumation of large volumes of low-density metapelites,which carried the denser eclogites to the Earth’s surface.
基金Supported by National Natural Science Foundation of China (Grant Nos.41772138, 40472102 and 40272095)Program of Excellent Young Scientists of the Ministry of Land and Resources of ChinaGeological Survey Project of China Geological Survey (Grant No. 1212010611811)
文摘Coesite provides direct evidence for ultrahigh pressure metamorphism. Although coesite has been found as inclusions in zircon in paragneiss of the north Qaidam Mountains, it has never been identified in eclogite. In this contribution, based on petrographic observations and in situ Raman microprobe spectroscopy, coesite was identified as inclusions in garnet of eclogite from the Aercituoshan, Dulan UHP metamorphic unit, north Qaidam Mountains. Coesite is partly replaced by quartz, showing a pali-sade texture. This is the first report on coesite in eclogite from the north Qaidam Mountains, and is also supported by garnet-omphacite-phengite geothermobarometry (2.7―3.25 GPa, 670―730℃). Coesite and its pseudomorphs have not been found in eclogites and associated rocks of other units of the north Qaidam Mountains. Further studies are required to confirm if all metamorphic units in the north Qaidam Mountains underwent the ultrahigh-pressure metamorphism.
基金supported by funds from the Key Project of National Natural Science Foundation of China (41430209)the Major State Basic Research Development Projects (2015CB856103)+2 种基金Most Special Fund from the State Key Laboratory of Continental Dynamics, Northwest University (BJ081331, 201210133)the National Natural Science Foundation of China (41020201, 41402045, 41602052)the Gold Geological Party of Chinese Armed Police Force Project (DD20160079)
文摘Coesite is a polymorph of Si O2formed at speci?c high-pressure conditions, and its presence in some crustal rocks as relicts marks the exhumation of deep subducted material to mantle depths, thus providing robust evidence for the hypothesis on ultrahigh pressur (UHP) metamorphism [1]. The discovery of coesite and other
基金supported by the National Natural Science Foundation of China (40730314, 41002019, and 40821002)the National Basic Research Program of China (2009CB825007)the National Science Foundation for Postdoctoral Scientists of China
文摘Coesite is an indicator mineral of ultra-high-pressure metamorphism. Since coesite was reported in the Habutengsu Valley, we have also found it in eclogite and schist from the Atantayi Valley in the southwestern Tianshan, China. Petrographic and micro-Raman analyses were carried out for the Atantayi metamorphic rocks and coesite was recognized in the predominant rock types, i.e. schist and eclogite, from three sections. The coesite-bearing schist consists mainly of garnet, Na-Ca amphibole, quartz, white mica and albite; the coesite-bearing eclogite is mainly composed of omphacite, garnet, glaucophane and zoisite. The coesite occurs as various mineral inclusions within porphyroblastic garnet. Findings of coesite in eclogite and associated schist indicate not only the regional in situ formation of the Atantayi ultra-high-pressure eclogite, but also the large areal extent of ultra-high-pressure metamorphism in southwestern Tianshan, extending up to 10 km north-south and 60-80 km east-west.
