Water(or H) in the silicate mantle is a key element in influencing Earth's climate, habitability, geochemical evolution, geophysical properties and geodynamical processes, and has received increasing attention in ...Water(or H) in the silicate mantle is a key element in influencing Earth's climate, habitability, geochemical evolution, geophysical properties and geodynamical processes, and has received increasing attention in the past decades. Experimental work under simulated high-pressure and high-temperature conditions is a powerful tool in characterizing the species, distribution, storage capacity and various physicochemical impacts of water in the mantle. In recent years, significant approaches have been acquired about some key physical, chemical and dynamical properties of water in the mantle and their various impacts, as a result of extensive studies by high-pressure and temperature experiments, and our knowledge of Earth's water cycle, especially the deep water cycle, on both temporal and spatial scales has been greatly enhanced. In this paper, a brief review based mainly on experimental studies is presented concerning the current understanding and some recent approaches of water in the silicate mantle, such as the possible origin, amount, storage and the effect on mantle properties.展开更多
The Qinling-Dabie accretionary fold belt in east-central China represents the E-W trending suture zone between the Sino-Korean and Yangtze cratons. A portion of the accretionary complex exposed in northern Hubei Provi...The Qinling-Dabie accretionary fold belt in east-central China represents the E-W trending suture zone between the Sino-Korean and Yangtze cratons. A portion of the accretionary complex exposed in northern Hubei Province contains a high-pressure / low-temperature metamorphic sequence progressively metamorphosed from the blueschist through greenschist to epidote-amphibolite / eclogite facies. The Hongan metamorphic belt can be divided into three metamorphic zones,based on progressive changes in mineral assemblages: Zone Ⅰ,in the south,is characterized by transitional blueschist-greenschist facies; ZoneⅡis characterized by greenschist facies; ZoneⅢ,in the northern most portion of the belt,is characterized by eclogite and epidote-amphibolite facies sequences. Changes in amphibole compositions from south to north as well as the appearance of increasingly higher pressure mineral assemblages toward the north document differences in metamorphic P-T conditions during formation of this belt. Preliminary P-T estimates for Zone I metamorphism are 5 ~ 7 kbar,350 ~ 450℃; estimates for Zone III eclogites are 10 ~ 22 kbar,500 ±50℃. The petrographic,chemical and structural characteristics of this metamorphic belt indicate its evolutionin a northward-dipping subduction zone and subsequent uplift prior to and during the final collisionbetween the Sino-Korean and Yangtze cratons.展开更多
After the integration of petrographic study, geothermobarometry and Gibbs method, the synthetic P-T paths for the rocks from different geological profiles in the North Qilian, China, have been derived. The composite P...After the integration of petrographic study, geothermobarometry and Gibbs method, the synthetic P-T paths for the rocks from different geological profiles in the North Qilian, China, have been derived. The composite P-T paths from different methods indicate that all the high-pressure rocks in the Qilian area recorded P-T paths with clockwise loops starting at the blueschist facies, later reaching peak metamorphism at the blueschist facies, eclogite fades or epidote-amphibolite facies and ending up with the greenschist facies. The incremental Ar-Ar dating shows that the plateau ages for the high-pressure rocks range from 410 to 443 Ma. The plateau ages could be used as a minimum age constraint for the subduction that resulted in the formation of these high-pressure rocks in the Qilian area. It is proposed that the late-stage decompressional and cooling P-T paths with ends at the greenschist facies for these high-pressure rocks probably reflect the uplift process which could occur after shifting the arc-trench tectonic system to the system of continental orogenic belts. The retrograde paths for the high-pressure rocks in the North Qilian tectonic belt are characterized by dramatic decompression with slight cooling, which suggests very rapid exhumation. Petrography supports that the mountain-building for the Qilian mountain range could undergo a very fast process which caused rapid uplift and denudation.展开更多
Eclogitic garnet-amphibole rocks are scattered around me Songshugou ultramafic bodies in Qinling Mountains . Three metamorphic stages are recognized in terms of petrography, mineral chemistry and geothermobarometry . ...Eclogitic garnet-amphibole rocks are scattered around me Songshugou ultramafic bodies in Qinling Mountains . Three metamorphic stages are recognized in terms of petrography, mineral chemistry and geothermobarometry . The first alhite-amphibole stage was of greenschist facies metamorphism with typical mineral assemblage of actinolite+epidote+chlorite+albite ; the pressure and temperature conditions were equal to or lower than 500MPa and about 400 ℃ .The second prograde eclogitic garnet-amphibole stage was of amphibole-eclogite fades metamorphism with typical mineral assemblage of garnet+hornblende± clinopyroxene+ruffle without ptagioclase ,the pressure condition was at least 1000- 1200MPa and the temperature about 600 ℃ .The third retrograde epidote-amphibole stage was of epidote-amphibolite fecies with assemblage of plagioclase+hornblende+epidote+ilmenite/titanite , the temperature was 500-600 ℃ and the pressure from 800MPa down to 500MPa .All three stages took place in one single tectonothermal event called Jinningian movement at about 1000Ma .The p-T path shows a hairpin shape and thus indicates a metamorphism in the sobduction environment. The metamorphk processes of the garnet- amphibole rocks thus provides a significant evidence for the pbte tectonic movement prevailing in the late Middle Proterozoic period.展开更多
The experimental study on the melting of potassic basalt and eclogite with about 2% waterat 800-1300℃ and 1.0-3.5 GPa shows that the solidi of both rocks are significantly lower thanthose obtained from the previous e...The experimental study on the melting of potassic basalt and eclogite with about 2% waterat 800-1300℃ and 1.0-3.5 GPa shows that the solidi of both rocks are significantly lower thanthose obtained from the previous experiments of the same type of rocks under dry conditions,and the former which is enriched in potassium has a lower melting point than the latter. It is con-sistent with the previous study. The melting temperature of eclogite increases with pressure,whereas potassic basalt has similar properties only at 1.5—2.5 GPa and>3.0 GPa, and at 2.5—3.0 GPa the melting temperature decreases with pressure. This can be explained as follows: (1)eclogite only has one hydrous mineral amphibole and the dehydous temperature is lower than thewet solidus of the rock. (2) Amphibole exists in potassic basalt at the pressures lower than 2.5GPa and phlogopite exists at pressures higher than 2.5 GPa, and the special compositions of bothminerals determine that amphibole has a dehydration temperature higher than or close to that ofthe wet solidus of the rocks, while phlogopite has a dehydration temperature lower than that ofthe wet solidus. On the other hand the features of the continuous solidus in the experiment ofhydrous eclogite were produced by the fact that the dehydration temperature of its amphibolelower than or close to the melting temperature of the hydrous conditions. So the melting tempera-ture lowers at higher pressures. Therefore, the composition of the rocks in the lithosphere and thetypes of hydrous minerals and their stable P-T conditions are the important factors controllingthe solidi of rocks. It can quite well explain the partial melting of rocks and the origin of the lowvelocity zone in the deep lithosphere.展开更多
基金supported by the National Basic Research Program of China(Grant Nos.2014CB845904 and 41590622)the National Natural Science Foundation of China(Grant No.41372041)+1 种基金the Recruitment Program of Global Young Experts(China)the Fundamental Research Funds for the Central Universities(China)
文摘Water(or H) in the silicate mantle is a key element in influencing Earth's climate, habitability, geochemical evolution, geophysical properties and geodynamical processes, and has received increasing attention in the past decades. Experimental work under simulated high-pressure and high-temperature conditions is a powerful tool in characterizing the species, distribution, storage capacity and various physicochemical impacts of water in the mantle. In recent years, significant approaches have been acquired about some key physical, chemical and dynamical properties of water in the mantle and their various impacts, as a result of extensive studies by high-pressure and temperature experiments, and our knowledge of Earth's water cycle, especially the deep water cycle, on both temporal and spatial scales has been greatly enhanced. In this paper, a brief review based mainly on experimental studies is presented concerning the current understanding and some recent approaches of water in the silicate mantle, such as the possible origin, amount, storage and the effect on mantle properties.
基金supported by the Stanford-Hubei Bureau of Geology and Mineral Resources co-operative projectMost of the field and analytical data were collected and supported by the GSA and Mc Gee funds ( E. A. E. ),the Stanford China Industrial Affiliates programme and NSF EAR 89-17319
文摘The Qinling-Dabie accretionary fold belt in east-central China represents the E-W trending suture zone between the Sino-Korean and Yangtze cratons. A portion of the accretionary complex exposed in northern Hubei Province contains a high-pressure / low-temperature metamorphic sequence progressively metamorphosed from the blueschist through greenschist to epidote-amphibolite / eclogite facies. The Hongan metamorphic belt can be divided into three metamorphic zones,based on progressive changes in mineral assemblages: Zone Ⅰ,in the south,is characterized by transitional blueschist-greenschist facies; ZoneⅡis characterized by greenschist facies; ZoneⅢ,in the northern most portion of the belt,is characterized by eclogite and epidote-amphibolite facies sequences. Changes in amphibole compositions from south to north as well as the appearance of increasingly higher pressure mineral assemblages toward the north document differences in metamorphic P-T conditions during formation of this belt. Preliminary P-T estimates for Zone I metamorphism are 5 ~ 7 kbar,350 ~ 450℃; estimates for Zone III eclogites are 10 ~ 22 kbar,500 ±50℃. The petrographic,chemical and structural characteristics of this metamorphic belt indicate its evolutionin a northward-dipping subduction zone and subsequent uplift prior to and during the final collisionbetween the Sino-Korean and Yangtze cratons.
文摘After the integration of petrographic study, geothermobarometry and Gibbs method, the synthetic P-T paths for the rocks from different geological profiles in the North Qilian, China, have been derived. The composite P-T paths from different methods indicate that all the high-pressure rocks in the Qilian area recorded P-T paths with clockwise loops starting at the blueschist facies, later reaching peak metamorphism at the blueschist facies, eclogite fades or epidote-amphibolite facies and ending up with the greenschist facies. The incremental Ar-Ar dating shows that the plateau ages for the high-pressure rocks range from 410 to 443 Ma. The plateau ages could be used as a minimum age constraint for the subduction that resulted in the formation of these high-pressure rocks in the Qilian area. It is proposed that the late-stage decompressional and cooling P-T paths with ends at the greenschist facies for these high-pressure rocks probably reflect the uplift process which could occur after shifting the arc-trench tectonic system to the system of continental orogenic belts. The retrograde paths for the high-pressure rocks in the North Qilian tectonic belt are characterized by dramatic decompression with slight cooling, which suggests very rapid exhumation. Petrography supports that the mountain-building for the Qilian mountain range could undergo a very fast process which caused rapid uplift and denudation.
基金The project is supported by National Nature Science Fountation of China No.48900015
文摘Eclogitic garnet-amphibole rocks are scattered around me Songshugou ultramafic bodies in Qinling Mountains . Three metamorphic stages are recognized in terms of petrography, mineral chemistry and geothermobarometry . The first alhite-amphibole stage was of greenschist facies metamorphism with typical mineral assemblage of actinolite+epidote+chlorite+albite ; the pressure and temperature conditions were equal to or lower than 500MPa and about 400 ℃ .The second prograde eclogitic garnet-amphibole stage was of amphibole-eclogite fades metamorphism with typical mineral assemblage of garnet+hornblende± clinopyroxene+ruffle without ptagioclase ,the pressure condition was at least 1000- 1200MPa and the temperature about 600 ℃ .The third retrograde epidote-amphibole stage was of epidote-amphibolite fecies with assemblage of plagioclase+hornblende+epidote+ilmenite/titanite , the temperature was 500-600 ℃ and the pressure from 800MPa down to 500MPa .All three stages took place in one single tectonothermal event called Jinningian movement at about 1000Ma .The p-T path shows a hairpin shape and thus indicates a metamorphism in the sobduction environment. The metamorphk processes of the garnet- amphibole rocks thus provides a significant evidence for the pbte tectonic movement prevailing in the late Middle Proterozoic period.
基金Note:This study was supported by China National Natural Science Foundation Grant No.49070087.
文摘The experimental study on the melting of potassic basalt and eclogite with about 2% waterat 800-1300℃ and 1.0-3.5 GPa shows that the solidi of both rocks are significantly lower thanthose obtained from the previous experiments of the same type of rocks under dry conditions,and the former which is enriched in potassium has a lower melting point than the latter. It is con-sistent with the previous study. The melting temperature of eclogite increases with pressure,whereas potassic basalt has similar properties only at 1.5—2.5 GPa and>3.0 GPa, and at 2.5—3.0 GPa the melting temperature decreases with pressure. This can be explained as follows: (1)eclogite only has one hydrous mineral amphibole and the dehydous temperature is lower than thewet solidus of the rock. (2) Amphibole exists in potassic basalt at the pressures lower than 2.5GPa and phlogopite exists at pressures higher than 2.5 GPa, and the special compositions of bothminerals determine that amphibole has a dehydration temperature higher than or close to that ofthe wet solidus of the rocks, while phlogopite has a dehydration temperature lower than that ofthe wet solidus. On the other hand the features of the continuous solidus in the experiment ofhydrous eclogite were produced by the fact that the dehydration temperature of its amphibolelower than or close to the melting temperature of the hydrous conditions. So the melting tempera-ture lowers at higher pressures. Therefore, the composition of the rocks in the lithosphere and thetypes of hydrous minerals and their stable P-T conditions are the important factors controllingthe solidi of rocks. It can quite well explain the partial melting of rocks and the origin of the lowvelocity zone in the deep lithosphere.
