前寒武纪条带状铁建造(banded iron formation,简称BIF)指全铁含量大于15%,具有由富铁矿物和脉石矿物组成的条带状构造的化学沉积岩。BIF包括两种类型:Algoma型多产于太古代,形成于岛弧、弧后盆地或克拉通内裂谷带,与海底火山活动关系密...前寒武纪条带状铁建造(banded iron formation,简称BIF)指全铁含量大于15%,具有由富铁矿物和脉石矿物组成的条带状构造的化学沉积岩。BIF包括两种类型:Algoma型多产于太古代,形成于岛弧、弧后盆地或克拉通内裂谷带,与海底火山活动关系密切;Superior型多产于早元古代,形成于浅海环境,不含或含有极少量的火山岩(Gross,1980)。几十年来,BIF相关科学问题是地球科学研究的热点与难点。展开更多
On the basis of a comprehensive study on the petrology, trace elements and isotopic geochemistry of the Xiangshan amphibolites, we suggest that the protoliths of the amphibolites were basalts formed in an island\|arc ...On the basis of a comprehensive study on the petrology, trace elements and isotopic geochemistry of the Xiangshan amphibolites, we suggest that the protoliths of the amphibolites were basalts formed in an island\|arc tectonic setting. The basaltic magma was derived from a slightly depleted mantle source with a small amount of crustal contamination. Assemblage of the rock\|forming minerals indicates that these amphibolites underwent a low\|grade metamorphism of amphibolite facies. According to the formation age (1113 Ma) and subsequent metamorphic age (726.6 Ma) of the basalts as well as the geological and geochemical features of these amphibolites, a tectonic model of Proterozoic oceanic island\|arc setting is proposed for central Jiangxi.展开更多
New major element data for coexisting minerals and bulk-rock REE analyses,combined with previously obtained petrologic/geologic information,allow comparison of Archean mafic-ultramafic meta-igneous rocks from adjacent...New major element data for coexisting minerals and bulk-rock REE analyses,combined with previously obtained petrologic/geologic information,allow comparison of Archean mafic-ultramafic meta-igneous rocks from adjacent portions of northeastern Sino-Korean shield .Isotope data published by previous workers document an Early Archean age of formation for metabasaltic rocks now occurring as mafic amphibolite inclusions in tonalitic gneisses west of Bohai Bay(area).Mafic-ultramafic mineral assemblages developed in tonalitic gneisses west of Bohai Bay(areaA).Mafic-ultramafic mineral assemblages developed in amphibolite facies Archean supracrustals east of Bohai Bay(areaB)are chemically similar ,but pre-existing phase associations have been overprinted by the effects of several later metamorphic events.Non0peridotitic area B protoliths appear to be more magnesian ,averaging-12wt.%MgO(versus-7wt.%for area A),and are slightly less fractionated in REE concentrations relative to chondrites(La-Lu=30-8X versus 37-14X for area A),thus perhaps being more mantle-like than area A metabasaltic analogues.The basaltic-komatiitic series east of Bohai Bay probably represents the most ancient crust of that region,being invaded by Archean tonalities,which were subsequently converted to orthogneisses.These observations are compatible with the hypothesis that ,similar to area A metabasaltic rocks now found as amphibolitic inclusions in orthogneisses,are B mafic supracrustals were formed during Early of Middle Archean time ,prior to widespread isofacial amphibolite facies metamorphism(600-700℃,5-7kb,low αH2O).展开更多
Based on their REE features, stratoid or lenticular amphibolites in the Dabie Complex are divided into two types: one is characterized by flat REE distribution patterns and the other by LREE-enrichment. Results of the...Based on their REE features, stratoid or lenticular amphibolites in the Dabie Complex are divided into two types: one is characterized by flat REE distribution patterns and the other by LREE-enrichment. Results of the REE quantitative modelling suggest that the amphibolites were formed from 20% partial melting of garnet lherzolite and 35-56% fractional crystallization of olivine (type THI ) or 14-20% fractional crystallization of olivine and clinopyroxene (type TH2).展开更多
The Shushui Complex can be divided into three rock units based on field investigation,petrography and geochemistry:(1)felsic gneisses,(2)supracrustal rocks consisting of amphibolite,marble and quartzited,and(3)late gr...The Shushui Complex can be divided into three rock units based on field investigation,petrography and geochemistry:(1)felsic gneisses,(2)supracrustal rocks consisting of amphibolite,marble and quartzited,and(3)late granites.Of the complex,felsic gneisses are dominant and formed in the Late Archaean,which were intruded by a basic dyke with a whole-rock Rb-Sr isochron age of 2264±219Ma.The data on rare-earth elements as well as on major and trace elements presented for most of the rock trpes making up the complex suggest that(1)basic gneisses were produced by partial melting of mantle peridotite,followed by fractional crystallization ,and (2)felsic gneisses produced by varying degree of melting of a mafic source.The most suitable tectonic setting to account for the generation of both types would be similar to the underplate setting.展开更多
文摘前寒武纪条带状铁建造(banded iron formation,简称BIF)指全铁含量大于15%,具有由富铁矿物和脉石矿物组成的条带状构造的化学沉积岩。BIF包括两种类型:Algoma型多产于太古代,形成于岛弧、弧后盆地或克拉通内裂谷带,与海底火山活动关系密切;Superior型多产于早元古代,形成于浅海环境,不含或含有极少量的火山岩(Gross,1980)。几十年来,BIF相关科学问题是地球科学研究的热点与难点。
文摘On the basis of a comprehensive study on the petrology, trace elements and isotopic geochemistry of the Xiangshan amphibolites, we suggest that the protoliths of the amphibolites were basalts formed in an island\|arc tectonic setting. The basaltic magma was derived from a slightly depleted mantle source with a small amount of crustal contamination. Assemblage of the rock\|forming minerals indicates that these amphibolites underwent a low\|grade metamorphism of amphibolite facies. According to the formation age (1113 Ma) and subsequent metamorphic age (726.6 Ma) of the basalts as well as the geological and geochemical features of these amphibolites, a tectonic model of Proterozoic oceanic island\|arc setting is proposed for central Jiangxi.
文摘New major element data for coexisting minerals and bulk-rock REE analyses,combined with previously obtained petrologic/geologic information,allow comparison of Archean mafic-ultramafic meta-igneous rocks from adjacent portions of northeastern Sino-Korean shield .Isotope data published by previous workers document an Early Archean age of formation for metabasaltic rocks now occurring as mafic amphibolite inclusions in tonalitic gneisses west of Bohai Bay(area).Mafic-ultramafic mineral assemblages developed in tonalitic gneisses west of Bohai Bay(areaA).Mafic-ultramafic mineral assemblages developed in amphibolite facies Archean supracrustals east of Bohai Bay(areaB)are chemically similar ,but pre-existing phase associations have been overprinted by the effects of several later metamorphic events.Non0peridotitic area B protoliths appear to be more magnesian ,averaging-12wt.%MgO(versus-7wt.%for area A),and are slightly less fractionated in REE concentrations relative to chondrites(La-Lu=30-8X versus 37-14X for area A),thus perhaps being more mantle-like than area A metabasaltic analogues.The basaltic-komatiitic series east of Bohai Bay probably represents the most ancient crust of that region,being invaded by Archean tonalities,which were subsequently converted to orthogneisses.These observations are compatible with the hypothesis that ,similar to area A metabasaltic rocks now found as amphibolitic inclusions in orthogneisses,are B mafic supracrustals were formed during Early of Middle Archean time ,prior to widespread isofacial amphibolite facies metamorphism(600-700℃,5-7kb,low αH2O).
文摘Based on their REE features, stratoid or lenticular amphibolites in the Dabie Complex are divided into two types: one is characterized by flat REE distribution patterns and the other by LREE-enrichment. Results of the REE quantitative modelling suggest that the amphibolites were formed from 20% partial melting of garnet lherzolite and 35-56% fractional crystallization of olivine (type THI ) or 14-20% fractional crystallization of olivine and clinopyroxene (type TH2).
文摘The Shushui Complex can be divided into three rock units based on field investigation,petrography and geochemistry:(1)felsic gneisses,(2)supracrustal rocks consisting of amphibolite,marble and quartzited,and(3)late granites.Of the complex,felsic gneisses are dominant and formed in the Late Archaean,which were intruded by a basic dyke with a whole-rock Rb-Sr isochron age of 2264±219Ma.The data on rare-earth elements as well as on major and trace elements presented for most of the rock trpes making up the complex suggest that(1)basic gneisses were produced by partial melting of mantle peridotite,followed by fractional crystallization ,and (2)felsic gneisses produced by varying degree of melting of a mafic source.The most suitable tectonic setting to account for the generation of both types would be similar to the underplate setting.
