The Changning-Menglian Belt represents the main Paleo-Tethyan Suture in the southeastern Tibetan Plateau,which divides Gondwana-and Eurasia-derived continental fragments from each other.The belt contains ultramafic-ma...The Changning-Menglian Belt represents the main Paleo-Tethyan Suture in the southeastern Tibetan Plateau,which divides Gondwana-and Eurasia-derived continental fragments from each other.The belt contains ultramafic-mafic volcanic rocks that provide evidence of the tectonic processes which operated during the evolution of the Paleo-Tethyan Ocean.New geochemical data for Early Carboniferous volcanics in the southern Changning-Menglian Belt show that wehrlites have cumulate and poikilitic textures,and contain low-Fo(84.2-87.2)olivine,clinopyroxene with low Mg#values(79.4-85.6),and spinel with high Cr#values(67.8-72.4).Estimated equilibrium temperatures obtained using olivine-spinel Fe-Mg exchange geothermometry range from 978℃ to 1373℃(mean=1205℃;n=3).These observations combined with a lack of reaction or melt impregnation textures indicate that these units represent magmatic cumulates rather than having formed as a result of mantle-melt reactions.Both wehrlites and basalts in the belt have subparallel rare earth element(REE)-and primitive-mantle-normalized multi-element patterns with slightly positive Nb-Ta anomalies,but negligible Eu and Zr-Hf anomalies.The volcanics have similar Sr-Nd-Pb isotopic compositions withεNd(t)values of 4.2-4.5(mean=4.3;n=3)and 4.0-4.4(mean 4.2;n=4),respectively,and also have similar immobile element ratios,such as Nb/La,Nb/U,Th/La,Zr/Nb,Th/Ta,La/Yb,Nb/Th,Nb/Y,and Zr/Y.These characteristics indicate both units have ocean island basalt(OIB)-like geochemical affinities,consistent with the fact that the clinopyroxene in the wehrlites is compositionally similar to OIB-related cumulus clinopyroxene.This suggests that both the wehrlites and basalts were derived from similar parental magmas that underwent generally closed-system magmatic differentiation dominated by fractionation of the olivine and clinopyroxene.This parental magma was likely generated in an oceanic seamount setting from an OIB-type mantle source(i.e.,asthenospheric mantle)containing garnet-spinel lherzolite material.Com展开更多
With the definition and adoption of the Global Stratotype Section and Point （GSSP） for base of the Visean in China, the newly synthesized zonations and correlation of some significant fossil groups： foraminifera, c...With the definition and adoption of the Global Stratotype Section and Point （GSSP） for base of the Visean in China, the newly synthesized zonations and correlation of some significant fossil groups： foraminifera, conodont, coral and brachiopoda near the Tournaisian-Visean boundary beds are reviewed, which help in the recognition of the boundary in various sedimentary facies. The occurrence of two physical events, one pre- and one post- the Tournaisian-Visean boundary is emphasized, which allows for recognition of the position close to the Tournaisian-Visean boundary in the field. The regional correlation in southern China and international correlation throughout Eurasia around the Tournaisian-Visean boundary beds with the GSSP is proposed.展开更多
A stratotype section, boundary point and conodont sign have been recommended for GSSP of the Tournaisian-Visean boundary, based on studies of sectional sedimentology, conodont facies and phylogeneses in South China. T...A stratotype section, boundary point and conodont sign have been recommended for GSSP of the Tournaisian-Visean boundary, based on studies of sectional sedimentology, conodont facies and phylogeneses in South China. Two areas representing margin and inner of the Yangtzi Plate and three sections of different facies were chosen, i.e. the Longdianshan sec-tion of the platform facies in Liuzhou of Guangxi, the Yudong section of the ramp facies in Shidian of Yunnan and the Pengchong section of the basin facies in Liuzhou of Guangxi. Stratigraphic frameworks of two areas were set up by systematical studies of carbonate facies and cycles. Conodont facies-distribution and paleoecologic conditions were researched on statistics of fossil variation and richness, and a kind of planktonic conodont, gnathodids that were widespread, is chosen to select the sign-fossil from it. Seven conodont pedigrees were supplemented or erected by studies of statistics and transitional forms. Conodont evolution in the Early Carboniferous could be divided into three stages, i.e. the Siphonodella stage, the Gnathodus typicus stage and the Gnathodus bilineatus stage. The transform-surface between the later two stages could be put as the Tournaisian-Visean boundary. Finally, this paper proposes that the Pengchong section can be the stratotype candidate of the Tournaisian-Visean boundary, the boundary point be put at the bottom of bed 58 and the stratotype sign of conodont be the first occurrence of Gnathodus praebilineatus of the Gnathodus semiglaber branch.展开更多
基金This study was financially supported by the Major Science and Technology Special Plan of Yunnan Province(Grant No.202202AG050006)the National Natural Science Foundation of China(Grant No.41603032)+1 种基金the Applied Basic Research Foundation of Yunnan Province(Grant No.2017FB075)the Yunnan Key Research and Development Program(Grant No.2015CB452601),and the China Geological Survey(Grant No.12120114064301).
文摘The Changning-Menglian Belt represents the main Paleo-Tethyan Suture in the southeastern Tibetan Plateau,which divides Gondwana-and Eurasia-derived continental fragments from each other.The belt contains ultramafic-mafic volcanic rocks that provide evidence of the tectonic processes which operated during the evolution of the Paleo-Tethyan Ocean.New geochemical data for Early Carboniferous volcanics in the southern Changning-Menglian Belt show that wehrlites have cumulate and poikilitic textures,and contain low-Fo(84.2-87.2)olivine,clinopyroxene with low Mg#values(79.4-85.6),and spinel with high Cr#values(67.8-72.4).Estimated equilibrium temperatures obtained using olivine-spinel Fe-Mg exchange geothermometry range from 978℃ to 1373℃(mean=1205℃;n=3).These observations combined with a lack of reaction or melt impregnation textures indicate that these units represent magmatic cumulates rather than having formed as a result of mantle-melt reactions.Both wehrlites and basalts in the belt have subparallel rare earth element(REE)-and primitive-mantle-normalized multi-element patterns with slightly positive Nb-Ta anomalies,but negligible Eu and Zr-Hf anomalies.The volcanics have similar Sr-Nd-Pb isotopic compositions withεNd(t)values of 4.2-4.5(mean=4.3;n=3)and 4.0-4.4(mean 4.2;n=4),respectively,and also have similar immobile element ratios,such as Nb/La,Nb/U,Th/La,Zr/Nb,Th/Ta,La/Yb,Nb/Th,Nb/Y,and Zr/Y.These characteristics indicate both units have ocean island basalt(OIB)-like geochemical affinities,consistent with the fact that the clinopyroxene in the wehrlites is compositionally similar to OIB-related cumulus clinopyroxene.This suggests that both the wehrlites and basalts were derived from similar parental magmas that underwent generally closed-system magmatic differentiation dominated by fractionation of the olivine and clinopyroxene.This parental magma was likely generated in an oceanic seamount setting from an OIB-type mantle source(i.e.,asthenospheric mantle)containing garnet-spinel lherzolite material.Com
基金supported by the Ministry of Science and Technology (Grant No. 2006FY120300-7)the National Commission on Stratigraphy of China (No. 2006CB80640)the China Geological Survey (No. 1212010916059)
文摘With the definition and adoption of the Global Stratotype Section and Point （GSSP） for base of the Visean in China, the newly synthesized zonations and correlation of some significant fossil groups： foraminifera, conodont, coral and brachiopoda near the Tournaisian-Visean boundary beds are reviewed, which help in the recognition of the boundary in various sedimentary facies. The occurrence of two physical events, one pre- and one post- the Tournaisian-Visean boundary is emphasized, which allows for recognition of the position close to the Tournaisian-Visean boundary in the field. The regional correlation in southern China and international correlation throughout Eurasia around the Tournaisian-Visean boundary beds with the GSSP is proposed.
基金This work was supported by the National Natural Science Foundation of China(Grant No.40242001).
文摘A stratotype section, boundary point and conodont sign have been recommended for GSSP of the Tournaisian-Visean boundary, based on studies of sectional sedimentology, conodont facies and phylogeneses in South China. Two areas representing margin and inner of the Yangtzi Plate and three sections of different facies were chosen, i.e. the Longdianshan sec-tion of the platform facies in Liuzhou of Guangxi, the Yudong section of the ramp facies in Shidian of Yunnan and the Pengchong section of the basin facies in Liuzhou of Guangxi. Stratigraphic frameworks of two areas were set up by systematical studies of carbonate facies and cycles. Conodont facies-distribution and paleoecologic conditions were researched on statistics of fossil variation and richness, and a kind of planktonic conodont, gnathodids that were widespread, is chosen to select the sign-fossil from it. Seven conodont pedigrees were supplemented or erected by studies of statistics and transitional forms. Conodont evolution in the Early Carboniferous could be divided into three stages, i.e. the Siphonodella stage, the Gnathodus typicus stage and the Gnathodus bilineatus stage. The transform-surface between the later two stages could be put as the Tournaisian-Visean boundary. Finally, this paper proposes that the Pengchong section can be the stratotype candidate of the Tournaisian-Visean boundary, the boundary point be put at the bottom of bed 58 and the stratotype sign of conodont be the first occurrence of Gnathodus praebilineatus of the Gnathodus semiglaber branch.
