We report the petrology and oxygen isotopic composition,using a Cameca Nano SIMS 50L ion microprobe,of a plagioclase-olivine inclusion,C#1,found in the Ningqiang carbonaceous chondrite.In addition to major phases(plag...We report the petrology and oxygen isotopic composition,using a Cameca Nano SIMS 50L ion microprobe,of a plagioclase-olivine inclusion,C#1,found in the Ningqiang carbonaceous chondrite.In addition to major phases(plagioclase,spinel and olivine),C#1 is also surrounded by a pyroxene rim(64 vol%Ca-rich and 36 vol%Ca-poor pyroxenes).On a three-isotope oxygen diagram,δ^(17)O vs.δ^(18)O,the compositions of individual minerals analyzed in C#1 fall along the carbonaceous chondrite anhydrous mineral line(CCAM),and oxygen isotopic compositions in C#1 show significant variability in δ^(18)O and δ^(17)O.The oxygen isotopic compositions of the pyroxene rim minerals are similar to those of the other host minerals,which suggests that the rim likely formed from the same melting process as the host.The rim is considered to have formed as a result of interaction between an ^(16)O-poor gas and a melt.Some spinel grains are typically ^(16)O-rich and likely of relict origin,which is similar to ^(16)O-rich Ca-,Al-rich inclusions,which are probably a precursor of C#1.The inclusion then likely melted in an ^(16)O-poor region where chondrules form,accompanied by oxygen isotope exchange with an ^(16)O-poor gas.Some anorthite,pyroxene and spinel might have undergone fluid-assisted thermal metamorphism on the Ningqiang chondrite parent body.The oxygen isotope data and evolution of the C#1 plagioclase-olivine inclusion are similar with those of Al-chondrules in chondrites.展开更多
The types of chondrules in the Boxian meteorite have been determined Electron microprobe nalvsis ofvarious textural types of chondrules in the meteorite has revealed the composition ofglassy chondrules and oftheir gla...The types of chondrules in the Boxian meteorite have been determined Electron microprobe nalvsis ofvarious textural types of chondrules in the meteorite has revealed the composition ofglassy chondrules and oftheir glassy matrix,Also presented in this paper are the related explanations.In addition.the genesis,texturaldiversity and evolution of the chondrules as well as the olivine girdles observed in the chondrules arediscussed.展开更多
Aluminum-rich chondrules （ARCs）, which share mineralogic and chemical properties with both Ca, Al-rich inclusions （CAIs） and ferromagnesian chondrules, play an important role in revealing their temporal and petrog...Aluminum-rich chondrules （ARCs）, which share mineralogic and chemical properties with both Ca, Al-rich inclusions （CAIs） and ferromagnesian chondrules, play an important role in revealing their temporal and petrogenetic relationships. In this work, seven ARCs were found in three ordinary chondrites GRV 022410 （H4）, GRV 052722 （H3.7） and Julesburg （L3.6）. They contain bulk Al2O3 - 17%-33% and exhibit igneous textures composed of olivine, high- and low-Ca pyroxene, plagioclase, spinel and glass. In situ SIMS analyses show that ARCs have oxygen isotopic compositions （δ18O=-6.1‰-7.1‰; δ17O= -4.5‰-5.1‰） close to ferromagnesian chondrules but far more depleted in 160 than CAIs （δ18O=-40‰; δ17O=-40‰）. Most ARCs plot close to the terrestrial mass fractionation （TF） line, and a few between the TF and carbonaceous chondrite anhydrous mixing （CCAM） lines. Plagioclase, nepheline and glass suffered O-isotopic exchanges during the metamorphism processes in the parent body. Spinel, olivine and pyroxene represent the primary O-isotopic compositions of ARCs, and define a fitted line with a slope of- 0.7±0.1. Compared with the results of previous studies, shallower slope as well as more depleted 160 compositions further demonstrates that ARCs in ordinary chondrites are not a simple mixing product of ferromagnesian chondrules and CAIs. Instead, they probably experienced higher-degree oxygen isotope exchange with a δ6O-poor nebular gas reservoir during multiple melting episodes.展开更多
The mineralogy and petrography of EET 14017 were studied using optical microscope,scanning electron microscope,electron microprobe,and micro-Raman.The mineral chemistry of olivine,pyroxene,plagioclase,spinel,and Fe-Ni...The mineralogy and petrography of EET 14017 were studied using optical microscope,scanning electron microscope,electron microprobe,and micro-Raman.The mineral chemistry of olivine,pyroxene,plagioclase,spinel,and Fe-Ni metal in EET 14017 is comparable to that of previously studied L/LL3.0x chondrites.In particular,the Cr2O3 content in the ferroan chondrule olivine and the excess silica component,[]Si4O8,in the plagioclase lead us to conclude that EET 14017 belongs to subtype 3.05.Raman spectral data of carbonaceous matter from the matrix of EET 14017 suggest a higher degree of thermal metamorphism,probably due to terrestrial weathering in Antarctica.EET 14017 and some of the other L/LL3.0x chondrites from the EET region are possibly a pair,since they have similar Cr2O3 contents of ferroan chondrule olivines and Raman spectral data,and moreover they were also found in a restricted region of the blue ice field.The plagioclase in some chondrules is a late crystal phase in the chondrule melt,which may constrain the timing of chondrule formation and cooling rate.If more L/LL3.0x chondrites like EET 14017 from Antarctica are identified,they would be excellent source material for studying the early evolution of the Solar System.展开更多
The Dergaon fall represents a shock-melted H4-5 （S5） ordinary chondrite which includes at least ten textural varieties of chondrules and belongs to the high chondrule-matrix ratio type. Our study reveals that the ch...The Dergaon fall represents a shock-melted H4-5 （S5） ordinary chondrite which includes at least ten textural varieties of chondrules and belongs to the high chondrule-matrix ratio type. Our study reveals that the chondrules are of diverse mineralogy with variable olivine-pyroxene ratios （Type Ⅱ）, igneous melt textures developed under variable cooling rates and formed through melt fractionations from two different melt reservoirs. Based on the experimental analogues, mineralogical associations and phase compositions, it is suggested that the Dergaon chondrules reflect two contrasting environments： a hot, dust-enriched and highly oxidized nebular environment through melting, without significant evapora- tion, and an arrested reducing environment concomitant with major evaporation loss of alkali and highly volatile trace elements. Coexistence of chlorapatite and merrillite suggests formation of the Dergaon matrix in an acidic accretionary environment. Textural integration and chemical homogenization occurred at - I atmospheric pressure and a mean temperature of 765 ℃ mark the radiogenic thermal event. Equilibrated shock features （olivine mosaicism, diaplectic plagioclase, polycrystalline troilite） due to an impact-induced thermal event reflect a shock pressure 〉45 GPa and temperature of 600 ℃. By contrast, the local disequilibrium shock features （silicate melt veins comprising of olivine crystallites, troilite melt veins and metal droplets） correspond to a shock pressure up to 75 GPa and temperature 〉950 ℃.展开更多
The Boxian meteorite (LL3-4), fallen in October 1977, possesses low degree of thermal metamorphism and good chondrule texture. A Ca-Al-rich chondrule （CA chondrule） was found in this chondrite. This chondrule is ca....The Boxian meteorite (LL3-4), fallen in October 1977, possesses low degree of thermal metamorphism and good chondrule texture. A Ca-Al-rich chondrule （CA chondrule） was found in this chondrite. This chondrule is ca. 0.36 mm in diame ter. There is only one light red euhedral spinel crystal, ca. 34％ in volume of this chondrule, while prismatic fassaite crystals occupy ca. 29％ and only one small crystal of olivine and light brown intergranular glass of the above minerals, ca. 37％ （Fig. 1）.展开更多
基金supported by the Natural Science Foundation of China(Grant Nos.41673070,41103032,41503062)the Hunan Provincial Natural Science Foundation of China(Grant No.2021JJ30242)the Scientific Research Fund of Hunan Provincial Education Department(Grant No.18A204)。
文摘We report the petrology and oxygen isotopic composition,using a Cameca Nano SIMS 50L ion microprobe,of a plagioclase-olivine inclusion,C#1,found in the Ningqiang carbonaceous chondrite.In addition to major phases(plagioclase,spinel and olivine),C#1 is also surrounded by a pyroxene rim(64 vol%Ca-rich and 36 vol%Ca-poor pyroxenes).On a three-isotope oxygen diagram,δ^(17)O vs.δ^(18)O,the compositions of individual minerals analyzed in C#1 fall along the carbonaceous chondrite anhydrous mineral line(CCAM),and oxygen isotopic compositions in C#1 show significant variability in δ^(18)O and δ^(17)O.The oxygen isotopic compositions of the pyroxene rim minerals are similar to those of the other host minerals,which suggests that the rim likely formed from the same melting process as the host.The rim is considered to have formed as a result of interaction between an ^(16)O-poor gas and a melt.Some spinel grains are typically ^(16)O-rich and likely of relict origin,which is similar to ^(16)O-rich Ca-,Al-rich inclusions,which are probably a precursor of C#1.The inclusion then likely melted in an ^(16)O-poor region where chondrules form,accompanied by oxygen isotope exchange with an ^(16)O-poor gas.Some anorthite,pyroxene and spinel might have undergone fluid-assisted thermal metamorphism on the Ningqiang chondrite parent body.The oxygen isotope data and evolution of the C#1 plagioclase-olivine inclusion are similar with those of Al-chondrules in chondrites.
文摘The types of chondrules in the Boxian meteorite have been determined Electron microprobe nalvsis ofvarious textural types of chondrules in the meteorite has revealed the composition ofglassy chondrules and oftheir glassy matrix,Also presented in this paper are the related explanations.In addition.the genesis,texturaldiversity and evolution of the chondrules as well as the olivine girdles observed in the chondrules arediscussed.
基金supported by the Natural Science Foundation of Jiangsu Province(Grant No.BK20131040)the National Natural Science Foundation of China(Grants Nos.41403056,41173076,41273079,41003026)the Minor Planet Foundation of China
文摘Aluminum-rich chondrules （ARCs）, which share mineralogic and chemical properties with both Ca, Al-rich inclusions （CAIs） and ferromagnesian chondrules, play an important role in revealing their temporal and petrogenetic relationships. In this work, seven ARCs were found in three ordinary chondrites GRV 022410 （H4）, GRV 052722 （H3.7） and Julesburg （L3.6）. They contain bulk Al2O3 - 17%-33% and exhibit igneous textures composed of olivine, high- and low-Ca pyroxene, plagioclase, spinel and glass. In situ SIMS analyses show that ARCs have oxygen isotopic compositions （δ18O=-6.1‰-7.1‰; δ17O= -4.5‰-5.1‰） close to ferromagnesian chondrules but far more depleted in 160 than CAIs （δ18O=-40‰; δ17O=-40‰）. Most ARCs plot close to the terrestrial mass fractionation （TF） line, and a few between the TF and carbonaceous chondrite anhydrous mixing （CCAM） lines. Plagioclase, nepheline and glass suffered O-isotopic exchanges during the metamorphism processes in the parent body. Spinel, olivine and pyroxene represent the primary O-isotopic compositions of ARCs, and define a fitted line with a slope of- 0.7±0.1. Compared with the results of previous studies, shallower slope as well as more depleted 160 compositions further demonstrates that ARCs in ordinary chondrites are not a simple mixing product of ferromagnesian chondrules and CAIs. Instead, they probably experienced higher-degree oxygen isotope exchange with a δ6O-poor nebular gas reservoir during multiple melting episodes.
基金supported by Korea Polar Research Institute project PE24050.
文摘The mineralogy and petrography of EET 14017 were studied using optical microscope,scanning electron microscope,electron microprobe,and micro-Raman.The mineral chemistry of olivine,pyroxene,plagioclase,spinel,and Fe-Ni metal in EET 14017 is comparable to that of previously studied L/LL3.0x chondrites.In particular,the Cr2O3 content in the ferroan chondrule olivine and the excess silica component,[]Si4O8,in the plagioclase lead us to conclude that EET 14017 belongs to subtype 3.05.Raman spectral data of carbonaceous matter from the matrix of EET 14017 suggest a higher degree of thermal metamorphism,probably due to terrestrial weathering in Antarctica.EET 14017 and some of the other L/LL3.0x chondrites from the EET region are possibly a pair,since they have similar Cr2O3 contents of ferroan chondrule olivines and Raman spectral data,and moreover they were also found in a restricted region of the blue ice field.The plagioclase in some chondrules is a late crystal phase in the chondrule melt,which may constrain the timing of chondrule formation and cooling rate.If more L/LL3.0x chondrites like EET 14017 from Antarctica are identified,they would be excellent source material for studying the early evolution of the Solar System.
文摘The Dergaon fall represents a shock-melted H4-5 （S5） ordinary chondrite which includes at least ten textural varieties of chondrules and belongs to the high chondrule-matrix ratio type. Our study reveals that the chondrules are of diverse mineralogy with variable olivine-pyroxene ratios （Type Ⅱ）, igneous melt textures developed under variable cooling rates and formed through melt fractionations from two different melt reservoirs. Based on the experimental analogues, mineralogical associations and phase compositions, it is suggested that the Dergaon chondrules reflect two contrasting environments： a hot, dust-enriched and highly oxidized nebular environment through melting, without significant evapora- tion, and an arrested reducing environment concomitant with major evaporation loss of alkali and highly volatile trace elements. Coexistence of chlorapatite and merrillite suggests formation of the Dergaon matrix in an acidic accretionary environment. Textural integration and chemical homogenization occurred at - I atmospheric pressure and a mean temperature of 765 ℃ mark the radiogenic thermal event. Equilibrated shock features （olivine mosaicism, diaplectic plagioclase, polycrystalline troilite） due to an impact-induced thermal event reflect a shock pressure 〉45 GPa and temperature of 600 ℃. By contrast, the local disequilibrium shock features （silicate melt veins comprising of olivine crystallites, troilite melt veins and metal droplets） correspond to a shock pressure up to 75 GPa and temperature 〉950 ℃.
文摘The Boxian meteorite (LL3-4), fallen in October 1977, possesses low degree of thermal metamorphism and good chondrule texture. A Ca-Al-rich chondrule （CA chondrule） was found in this chondrite. This chondrule is ca. 0.36 mm in diame ter. There is only one light red euhedral spinel crystal, ca. 34％ in volume of this chondrule, while prismatic fassaite crystals occupy ca. 29％ and only one small crystal of olivine and light brown intergranular glass of the above minerals, ca. 37％ （Fig. 1）.
