The Khorat Plateau on the Indochina Terrane is known to have formed during the closure of the Tethys Ocean, although the origin of its potash mineral deposits is a topic of current debate. Data from a borehole on Sava...The Khorat Plateau on the Indochina Terrane is known to have formed during the closure of the Tethys Ocean, although the origin of its potash mineral deposits is a topic of current debate. Data from a borehole on Savannakhet Basin is used in this study to re-define the evaporation processes of the study area. Geochemical analyses of halite from various borehole-derived evaporite strata have elucidated the fluid sources from which these ores formed. Measured δ11B indicated that ore deposits formed primarily due to evaporation of seawater, although non-marine fluids affected the later stages of the evaporation process. Fluctuations in B and Br concentrations in carnallite- and sylvite-rich strata indicate the influence of fresh water. Boron concentration in carnallite unit indicated the influence of hydrothermai fluids. From the relative timings of these various fluid influxes, the evolution of these evaporates can be divided into four stages： （1） an initial marine evaporation at the beginning of the deposit＇s formation, where seawater （and minor fresh water） trapped on the uplifted Khorat Plateau produced sediments and salts with Br contents lower than those of normal marine-derived evaporites; （2） a transgression stage, where seawater recharged the basin; （3） a hydrothermal infiltration stage, which was coeval with the late Yanshan movement; and （4） a stage of fresh water supply, as recorded by fluctuations in B and Br contents, inferring intermittent fresh water influx into the basin. Thus, although evaporites on the Savannakhet Basin primarily formed via marine evaporation, they were also influenced to a significant degree by the addition of non-marine fresh water and hydrothermal fluids.展开更多
The Qilian Block(QB)is a Precambrian micro-continent located in the northeastern Qinghai–Tibet Plateau.Prevalent Lower Paleozoic granitic magmatic rocks crop out in the QB.A new integrated study of zircon U-Pb ages a...The Qilian Block(QB)is a Precambrian micro-continent located in the northeastern Qinghai–Tibet Plateau.Prevalent Lower Paleozoic granitic magmatic rocks crop out in the QB.A new integrated study of zircon U-Pb ages and systematic whole-rock geochemical data for the Xindian,Dongjiazhuang and Xiaogaoling granites in the eastern segment of the QB constrains their emplacement ages,petrogenesis,and regional evolutionary history.U-Pb dating reveals that the Xindian granite was emplaced 454 Ma,and both the Dongjiazhuang and Xiaogaoling granites were emplaced ca.440 Ma.Geochemical study shows that all granites belong to the high-K calc-alkaline to shoshonitic series and are S-type granites formed by partial melting of continental crust,mainly metagraywacke.We infer that these ca.454–445 Ma granites formed in a syn-collisional setting during the continental collisional between the Qaidam and Qilian blocks.展开更多
In this study,the compressive,split tensile,and flexural strengths of concrete with nano-CaCO_(3) only were compared with those of concrete with nano-CaCO_(3) and basalt fibers through field experiments,and the underl...In this study,the compressive,split tensile,and flexural strengths of concrete with nano-CaCO_(3) only were compared with those of concrete with nano-CaCO_(3) and basalt fibers through field experiments,and the underlying mechanisms were analyzed by the Scanning Electron Microscope (SEM) techniques.On the mesoscale,a damage model of concrete was established based on the continuum progressive damage theory,which was used to investigate the influence of different lengths and contents of fibers on the mechanical properties of concrete.Then,the experimental and numerical simulation results were compared and analyzed to verify the feasibility of model.The results show that nano-CaCO_(3) can enhance the compressive strength of the concrete,with an optimal content of 2.0%.Adding basalt fibers into the nano-CaCO_(3) reinforced concrete may further enhance the compressive,split tensile,and flexural strengths of the concrete;however,the higher content of basalt fiber can not lead to higher performance of concrete.The optimal length and content of fiber are 6 mm and 0.20%,respectively.The SEM result shows that the aggregation of basalt fibers is detrimental to the mechanical properties of concrete.The numerical simulation results are in good agreement with the experimental results.展开更多
基金funded by the National Natural Science Foundation of China(grant No.40903024)the National Natural Science Foundation of China(grant No.41602086)
文摘The Khorat Plateau on the Indochina Terrane is known to have formed during the closure of the Tethys Ocean, although the origin of its potash mineral deposits is a topic of current debate. Data from a borehole on Savannakhet Basin is used in this study to re-define the evaporation processes of the study area. Geochemical analyses of halite from various borehole-derived evaporite strata have elucidated the fluid sources from which these ores formed. Measured δ11B indicated that ore deposits formed primarily due to evaporation of seawater, although non-marine fluids affected the later stages of the evaporation process. Fluctuations in B and Br concentrations in carnallite- and sylvite-rich strata indicate the influence of fresh water. Boron concentration in carnallite unit indicated the influence of hydrothermai fluids. From the relative timings of these various fluid influxes, the evolution of these evaporates can be divided into four stages： （1） an initial marine evaporation at the beginning of the deposit＇s formation, where seawater （and minor fresh water） trapped on the uplifted Khorat Plateau produced sediments and salts with Br contents lower than those of normal marine-derived evaporites; （2） a transgression stage, where seawater recharged the basin; （3） a hydrothermal infiltration stage, which was coeval with the late Yanshan movement; and （4） a stage of fresh water supply, as recorded by fluctuations in B and Br contents, inferring intermittent fresh water influx into the basin. Thus, although evaporites on the Savannakhet Basin primarily formed via marine evaporation, they were also influenced to a significant degree by the addition of non-marine fresh water and hydrothermal fluids.
基金financially supported by the Qinghai Science and Technology Department(Grant No.2016-ZJ752)Qinghai Salt Lake Industry(Grant No.E050DZ0801)。
文摘The Qilian Block(QB)is a Precambrian micro-continent located in the northeastern Qinghai–Tibet Plateau.Prevalent Lower Paleozoic granitic magmatic rocks crop out in the QB.A new integrated study of zircon U-Pb ages and systematic whole-rock geochemical data for the Xindian,Dongjiazhuang and Xiaogaoling granites in the eastern segment of the QB constrains their emplacement ages,petrogenesis,and regional evolutionary history.U-Pb dating reveals that the Xindian granite was emplaced 454 Ma,and both the Dongjiazhuang and Xiaogaoling granites were emplaced ca.440 Ma.Geochemical study shows that all granites belong to the high-K calc-alkaline to shoshonitic series and are S-type granites formed by partial melting of continental crust,mainly metagraywacke.We infer that these ca.454–445 Ma granites formed in a syn-collisional setting during the continental collisional between the Qaidam and Qilian blocks.
基金Funded by the National Natural Science Foundation of China (No. 51969026)the Natural Science Foundation of Qinghai Province in China (No. 2018-ZJ-750)。
文摘In this study,the compressive,split tensile,and flexural strengths of concrete with nano-CaCO_(3) only were compared with those of concrete with nano-CaCO_(3) and basalt fibers through field experiments,and the underlying mechanisms were analyzed by the Scanning Electron Microscope (SEM) techniques.On the mesoscale,a damage model of concrete was established based on the continuum progressive damage theory,which was used to investigate the influence of different lengths and contents of fibers on the mechanical properties of concrete.Then,the experimental and numerical simulation results were compared and analyzed to verify the feasibility of model.The results show that nano-CaCO_(3) can enhance the compressive strength of the concrete,with an optimal content of 2.0%.Adding basalt fibers into the nano-CaCO_(3) reinforced concrete may further enhance the compressive,split tensile,and flexural strengths of the concrete;however,the higher content of basalt fiber can not lead to higher performance of concrete.The optimal length and content of fiber are 6 mm and 0.20%,respectively.The SEM result shows that the aggregation of basalt fibers is detrimental to the mechanical properties of concrete.The numerical simulation results are in good agreement with the experimental results.
