Geochemical and isotopic investigations have been carded out on the Chebu gabbroite in southern Jiangxi Province, southeast China and these results are compared with gabbro bodies along the coast of Fujian Province in...Geochemical and isotopic investigations have been carded out on the Chebu gabbroite in southern Jiangxi Province, southeast China and these results are compared with gabbro bodies along the coast of Fujian Province in order to understand their magma sources and tectonic implications. The Chebu intrusion formed at the beginning of the Middle Jurassic （172~4.3 Ma）. These rocks are Ti-rich and Al-poor in major elements, characterized by strong enrichment in large-ion lithophile elements （LILE） and moderate enrichment in high field strength elements （HFSE） and light rare-earth elements CLREE）, without pronounced Nb or Ta anomalies. Age-correlated Sr-Nd isotope ratios show moderately high ranges of （^87Sr/^86Sr）i from 0.7065 to 0.7086 and 0.5124 to 0.5125 of （^143Nd/^144Nd）i. The geochemical characteristics of the Chebu gabbroite suggest that it is notably different from island-arc basalt and similar to intra-plate basaltic rocks. By combining interpretations of its geological and geochemical characteristics and the regional geological development history, the Chebu gabbroitic intrusion is thought to be the product of asthenosphere upwelling and rapid lithosphere extension during a transition of tectonic systems in southeast China. The tectonic environment and source characteristics of the intrusion are different from Cretaceous gabbro bodies along the coast of Fujian Province, The former formed in a tectonic environment of rapid intra-plate lithospheric extension and the source characteristics were of a weakly enriched primitive mantle, whereas the latter originated mainly in a volcanic-magmatic arc extensional tectonic environment and the nature of the source was an enriched mantle with more subduct subducted components.展开更多
The pyrite-type FeO2 H-Fe O2 system has been experimentally confirmed to be stable in Earth's lowermost mantle but there is limited information about its physical properties at high pressures constraining our unde...The pyrite-type FeO2 H-Fe O2 system has been experimentally confirmed to be stable in Earth's lowermost mantle but there is limited information about its physical properties at high pressures constraining our understanding of its potential geophysical implications for the deep Earth.Here,static calculations demonstrate that the pyrite-type FeO2 H-FeO2 system has a high density and Poisson's ratio and ultra-low seismic velocities at conditions of Earth's lowermost mantle.It provides a plausible mechanism for the origin of ultra-low velocity zones at Earth's D″layer.The incorporation of hydrogen in the pyrite-type FeO2H-FeO2 system tends to decrease the S wave velocity(VS)but increase the bulk sound velocity(VΦ),and can potentially explain the observed anti-correlation of VS and VΦin the lowermost mantle.Additionally,FeO2 H exhibits nearly isotropic whereas Fe O2 is highly anisotropic,which may help understand some seismic anisotropies at the core-mantle boundary.展开更多
基金supported jointly by the National National Science Foundation of China(Grant Nos 40402011 and 40434011)China Postdoctoral Science Foundation and Chinese Academy of Sciences(KZCX3-SW-125)the Ministry of Science and Technology of China(G1999043211)
文摘Geochemical and isotopic investigations have been carded out on the Chebu gabbroite in southern Jiangxi Province, southeast China and these results are compared with gabbro bodies along the coast of Fujian Province in order to understand their magma sources and tectonic implications. The Chebu intrusion formed at the beginning of the Middle Jurassic （172~4.3 Ma）. These rocks are Ti-rich and Al-poor in major elements, characterized by strong enrichment in large-ion lithophile elements （LILE） and moderate enrichment in high field strength elements （HFSE） and light rare-earth elements CLREE）, without pronounced Nb or Ta anomalies. Age-correlated Sr-Nd isotope ratios show moderately high ranges of （^87Sr/^86Sr）i from 0.7065 to 0.7086 and 0.5124 to 0.5125 of （^143Nd/^144Nd）i. The geochemical characteristics of the Chebu gabbroite suggest that it is notably different from island-arc basalt and similar to intra-plate basaltic rocks. By combining interpretations of its geological and geochemical characteristics and the regional geological development history, the Chebu gabbroitic intrusion is thought to be the product of asthenosphere upwelling and rapid lithosphere extension during a transition of tectonic systems in southeast China. The tectonic environment and source characteristics of the intrusion are different from Cretaceous gabbro bodies along the coast of Fujian Province, The former formed in a tectonic environment of rapid intra-plate lithospheric extension and the source characteristics were of a weakly enriched primitive mantle, whereas the latter originated mainly in a volcanic-magmatic arc extensional tectonic environment and the nature of the source was an enriched mantle with more subduct subducted components.
基金financial support from the National Natural Science Foundation of China (Nos. 41473056 and 41472037)
文摘The pyrite-type FeO2 H-Fe O2 system has been experimentally confirmed to be stable in Earth's lowermost mantle but there is limited information about its physical properties at high pressures constraining our understanding of its potential geophysical implications for the deep Earth.Here,static calculations demonstrate that the pyrite-type FeO2 H-FeO2 system has a high density and Poisson's ratio and ultra-low seismic velocities at conditions of Earth's lowermost mantle.It provides a plausible mechanism for the origin of ultra-low velocity zones at Earth's D″layer.The incorporation of hydrogen in the pyrite-type FeO2H-FeO2 system tends to decrease the S wave velocity(VS)but increase the bulk sound velocity(VΦ),and can potentially explain the observed anti-correlation of VS and VΦin the lowermost mantle.Additionally,FeO2 H exhibits nearly isotropic whereas Fe O2 is highly anisotropic,which may help understand some seismic anisotropies at the core-mantle boundary.
