Thermal diffusivity(D)and thermal conductivity(κ)of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil apparatus...Thermal diffusivity(D)and thermal conductivity(κ)of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil apparatus.The results show that the values of D andκof both samples systematically decrease with increasing temperature and increase with increasing pressure.By combination of the thermal physical data of rocks and minerals and geophysical constraints,we performed numerical simulation on the thermal evolution of Tibet vary over depth,distance and geologic ages.The present results provide new constraints on occurrence of partial melting and its geophysical significance beneath Tibetan crust.展开更多
The Luobusa Ophiolite,Southern Tibet,lies in the eastern portion of Indus–Yarlung Zangbo suture zone that separates Eurasia from the Indian continent.An aeromagnetic reconnaissance survey has revealed an EWtrending Y...The Luobusa Ophiolite,Southern Tibet,lies in the eastern portion of Indus–Yarlung Zangbo suture zone that separates Eurasia from the Indian continent.An aeromagnetic reconnaissance survey has revealed an EWtrending Yarlung Zangbo River aeromagnetic anomaly zone,and it is considered to be caused mainly by the Indus–Yarlung Zangbo Ophiolite.The Luobusa Ophiolite reflects the eastern portion of the Yarlung Zangbo River aeromagnetic anomaly zone.Conventionally,the ultramafic rock in the Luobusa Ophiolite is considered as the origin of the high magnetic anomalies.However,results from the surface magnetic survey and the magnetic susceptibility measurements from drill cores indicate that the high magnetic anomalies are distributed inhomogeneously in the Luobusa Ophiolite.In some cases,the susceptibility exhibits more than 30 times difference between two sides of the same sample.A fact emerged that the susceptibility of dunite with serpentinization is higher than that of fresh dunite,harzburgite and chromite when we analyzed the measurement results.In order to understand the origin of the high magnetic anomalies,we measured the density and susceptibility of 17 samples,microscopic and electron probe analyses have been performed as well.The result indicates the presence of dunite with serpentinization containing an abundant of micro-fissures filled with magnetite.Olivine has a susceptibility of about 2.7–351(910-5SI),pyroxene about 16–320,and chromite about200–800.All these units feature relatively low susceptibility in ultramafic rock,and only the magnetite is characterized by a high susceptibility of about 200,000(910-5SI).Based on these observations,we conclude that the precipitation of magnetite in the process of serpentinization of the olivine caused by the geological process in the Luobusa Ophiolite is the origin of high magnetic anomalies.展开更多
Geophysics offers an important means to investigate the physical processes occurring inside the earth.In particular,since the 1960s,electromagnetic(EM)methods have played important roles in mineral exploration and eng...Geophysics offers an important means to investigate the physical processes occurring inside the earth.In particular,since the 1960s,electromagnetic(EM)methods have played important roles in mineral exploration and engineering investigation.Such investigation requires extensive data acquisition and experimental analysis based on geophysical techniques.However,high-performance geophysical equipment,particularly EM exploration equipment,has been dominated by large geophysical companies from the United States,Canada,Germany,and other European countries for decades.This has limited the development of deep exploration technology in China.Recently,we have developed a high-resolution acquisition system with a wireless control unit and a high-power transmitting system for surface EM prospecting(SEP).The new system has been tested in the high-intensity,noisy environment in Jian-sanjiang area,Heilongjiang Province.We then conducted a field survey on the western edge of Qaidam Basin,Qinghai Province.A highly conductive anomaly was found in the upper mantle below the Qinmantage Mountains,which indicates a possible northward fluid channel that runs from below the Qinmantage Mountains to the bottom of the western crust of the Qaidam Basin.Identification of this significant feature was made possible by the new SEP for its better resolution than the previous systems.Also,geophysical analysis confirmed that the thick Cenozoic sediments of the Qaidam Basin are underlain by rigid Precambrian basement rocks and are characterized by a series of folds.The resistivity profile indicates that the Qaidam Basin was formed due to the folding structures in the northern part of the Qinghai-Tibet Plateau which provided an additional evidence for the uplifting of the Qinghai-Tibet Plateau.展开更多
基金Key Research Program of Frontier Sciences of CAS(ZDBS-LY-DQC015)National Natural Science Foundation of China(Nos.41973056,41773056,41303048)Science Foundation of Guizhou Province(2017-1196,2018-1176).
文摘Thermal diffusivity(D)and thermal conductivity(κ)of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil apparatus.The results show that the values of D andκof both samples systematically decrease with increasing temperature and increase with increasing pressure.By combination of the thermal physical data of rocks and minerals and geophysical constraints,we performed numerical simulation on the thermal evolution of Tibet vary over depth,distance and geologic ages.The present results provide new constraints on occurrence of partial melting and its geophysical significance beneath Tibetan crust.
基金supported by the National Natural Science Foundation of China (U1262206)Chinese Geological Survey Geological Prospecting Fund (12120113095200)the National Science and Technology Program (2011ZX05019-007)
文摘The Luobusa Ophiolite,Southern Tibet,lies in the eastern portion of Indus–Yarlung Zangbo suture zone that separates Eurasia from the Indian continent.An aeromagnetic reconnaissance survey has revealed an EWtrending Yarlung Zangbo River aeromagnetic anomaly zone,and it is considered to be caused mainly by the Indus–Yarlung Zangbo Ophiolite.The Luobusa Ophiolite reflects the eastern portion of the Yarlung Zangbo River aeromagnetic anomaly zone.Conventionally,the ultramafic rock in the Luobusa Ophiolite is considered as the origin of the high magnetic anomalies.However,results from the surface magnetic survey and the magnetic susceptibility measurements from drill cores indicate that the high magnetic anomalies are distributed inhomogeneously in the Luobusa Ophiolite.In some cases,the susceptibility exhibits more than 30 times difference between two sides of the same sample.A fact emerged that the susceptibility of dunite with serpentinization is higher than that of fresh dunite,harzburgite and chromite when we analyzed the measurement results.In order to understand the origin of the high magnetic anomalies,we measured the density and susceptibility of 17 samples,microscopic and electron probe analyses have been performed as well.The result indicates the presence of dunite with serpentinization containing an abundant of micro-fissures filled with magnetite.Olivine has a susceptibility of about 2.7–351(910-5SI),pyroxene about 16–320,and chromite about200–800.All these units feature relatively low susceptibility in ultramafic rock,and only the magnetite is characterized by a high susceptibility of about 200,000(910-5SI).Based on these observations,we conclude that the precipitation of magnetite in the process of serpentinization of the olivine caused by the geological process in the Luobusa Ophiolite is the origin of high magnetic anomalies.
基金supported by the National Key Research and Development Program(Grant No.2018YFC0603200)the Research and Development Program of Scientific Research Instruments and Equipment of the Chinese Academy of Sciences(Grant No.ZDZBGCH2018006)+1 种基金the Key Program of National Natural Science Foundation of China(Grant No.42030106)the Second Tibetan Plateau Scientific Expedition and Research Program(Grant No.2019QZKK0804).
文摘Geophysics offers an important means to investigate the physical processes occurring inside the earth.In particular,since the 1960s,electromagnetic(EM)methods have played important roles in mineral exploration and engineering investigation.Such investigation requires extensive data acquisition and experimental analysis based on geophysical techniques.However,high-performance geophysical equipment,particularly EM exploration equipment,has been dominated by large geophysical companies from the United States,Canada,Germany,and other European countries for decades.This has limited the development of deep exploration technology in China.Recently,we have developed a high-resolution acquisition system with a wireless control unit and a high-power transmitting system for surface EM prospecting(SEP).The new system has been tested in the high-intensity,noisy environment in Jian-sanjiang area,Heilongjiang Province.We then conducted a field survey on the western edge of Qaidam Basin,Qinghai Province.A highly conductive anomaly was found in the upper mantle below the Qinmantage Mountains,which indicates a possible northward fluid channel that runs from below the Qinmantage Mountains to the bottom of the western crust of the Qaidam Basin.Identification of this significant feature was made possible by the new SEP for its better resolution than the previous systems.Also,geophysical analysis confirmed that the thick Cenozoic sediments of the Qaidam Basin are underlain by rigid Precambrian basement rocks and are characterized by a series of folds.The resistivity profile indicates that the Qaidam Basin was formed due to the folding structures in the northern part of the Qinghai-Tibet Plateau which provided an additional evidence for the uplifting of the Qinghai-Tibet Plateau.
