Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu-Nujiang suture zone,the Dongmozhazhua and Mohailaheng Pb-Zn deposits in the Yushu area of Qinghai Province are...Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu-Nujiang suture zone,the Dongmozhazhua and Mohailaheng Pb-Zn deposits in the Yushu area of Qinghai Province are representative Pb-Zn deposits of the Pb-Zn-Cu polymetallic mineralization belt in the northern part of the Nujiang-Lancangjiang-Jinshajiang area,which are in the front belt of the Yushu thrust nappe system.The formed environments of these two deposits are different from those of sediment-hosted base metal deposits elsewhere in the world.The authors hold that they were formed during the Indian-Asian continental collision and developed within the fold-thrust belt combined with thrust and strike-slip-related Cenozoic basins in the interior of the collisional zone.Studying on the metallogenic epochs of these two deposits is helpful to the understanding of ore-forming regularity of the regional Pb-Zn-Cu mineralization belt and also to the search for new deposits in this region.The age of the Dongmozhazhua deposit has been determined by the Rb-Sr isochron method for sphalerite residues,whereas the age of the Mohailaheng deposit has been determined by the Rb-Sr isochron method for sphalerite residues and the Sm-Nd isochron method for fluorite.The age of the Dongmozhazhua deposit is 35.0-±0.0 Ma ((87Sr/86Sr)0=0.708807) for sphalerite residues.The age of the Mohailaheng deposit is 32.2±0.4 Ma ((87Sr/86Sr)o=0.708514) for sphalerite residues and 31.8±0.3 Ma ((143Nd/144Nd)o=0.512362) for fluorite with an average of 32.0 Ma.Together with the regional geological setting during mineralization,a possible tectonic model for metallogeny of the Dongmozhazhua and Mohailaheng Pb-Zn deposits has been established.These two ages are close to the ages of the Pb-Zn deposits in the Lanping and Tuotuohe basins,indicating that it is possible that the narrow 1000-kilometer-long belt controlled by a thrust nappe system on the eastern and northern margins of the Tibetan plateau could be a giant Pb-Zn mineralized belt.展开更多
Sm Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold bearing shear zone on western Hainan Island, are measured. The Sm Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd)0=0.512...Sm Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold bearing shear zone on western Hainan Island, are measured. The Sm Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd)0=0.512094, εNd(t) ranges from +1.80 to +2.00 and TDM from 982 Ma to 1196 Ma (average: 1060 Ma). The authors point out that the whole rock Sm Nd isochron age (495.98±13.14 Ma) really represents the petrogenetic age of lamprophyre and the time of magmatism during subsequent subduction.展开更多
The characterstic of the basement of Junggar block has been a topic of long-standingdebate.Based on the data of gravity and magnetic anomaly,some researchers deduced thatthere were Precambrian basic-ultrabasic complex...The characterstic of the basement of Junggar block has been a topic of long-standingdebate.Based on the data of gravity and magnetic anomaly,some researchers deduced thatthere were Precambrian basic-ultrabasic complex on the basement of Junggar block.However,others maintained that the basement of Junggar block was probably the Paleozoicoceanic crust because of the lack of isotopic evidence and older outcrops aroundthe Junggar Basin. In recent years,molecules of fossil community were discovered from Aleandao Groupat the Qingshuiquan and Kamuster of eastern Junggar.Most of the fossils,such asPylocorpus,Retincnlafopora,Asteropyla,were found at the boundary between Cambrianand Sinian in Qinling and South China.An isotopic age of 1908 Ma for leuco-pink graniticgneiss from the lower Huangcaopo Group was gained by evaporated Pb-isotope method forsingle zircon in Xiaoluigou of eastern Junggar by Zhang et al.But all of these results onlyindicate a possibility that the basement of Junggar block consists of展开更多
An ophiolite belt is exposed to the northern edge of Altun Tagh Mountain. Geochronological researches were made on gabbro and basalt. Sm-Nd isochron age of gabbro is (829 ± 60) Ma, while the age of gabbro mixed b...An ophiolite belt is exposed to the northern edge of Altun Tagh Mountain. Geochronological researches were made on gabbro and basalt. Sm-Nd isochron age of gabbro is (829 ± 60) Ma, while the age of gabbro mixed basalt is (949 ± 62) Ma. The dating of Sm-Nd isochron proves that ophiolite formed in (829 ± 60) Ma, which implies that the northern half of Tarim (or north Tarim Block) had been separated by an ocean from the southern half of Tarim and Qaidam (or south Tarim Block) until (829 ± 60) Ma. The south Tarim Block could accrete to the north Tarim Block at the beginning of Sinian,thereby forming the north Altun Tagh suture. The Sinian system would be the first cover on the amalgamated Tarim craton.展开更多
The ophiolite suite in Shexian County, Anhui Province extends more than 40 km in NE orientation. It is called Fuchuan ophiolite because its outcrop is the most complete in Fuchuan. This ophiolite which upthrusts over ...The ophiolite suite in Shexian County, Anhui Province extends more than 40 km in NE orientation. It is called Fuchuan ophiolite because its outcrop is the most complete in Fuchuan. This ophiolite which upthrusts over the Precambrian Shexian granodiorite body is composed of dunite, harzburgite, cumulate pyroxenite, spilite, keratophyre and tuffaceous phyllite (Fig. 1).展开更多
The REE patterns of the basic volcanic rocks in Mangya area, Altun, are slight rich in LREE with (La/Ya)-N=1.69-3.20, (La/Sm)-N=1.37-1.87, other trace element ratios of the rocks are Th/Ta≈1 (for a few samples greate...The REE patterns of the basic volcanic rocks in Mangya area, Altun, are slight rich in LREE with (La/Ya)-N=1.69-3.20, (La/Sm)-N=1.37-1.87, other trace element ratios of the rocks are Th/Ta≈1 (for a few samples greater than 1.5), Nb/Y=0.34-0.62, Ti/Y=310-443 (on the average: 381), Ti/V=37-62, Zr/Nb=9.4-12.4, Sr/Rb=12-80 (on the average: 37), and Nb/Th=7.7-16.8. These features are similar to that of E-MORE or OIB. The ε Nd(t) value, being 3.95- 4.12, shows that the source of the volcanic rocks is derived from depleted asthenosphere mantle mixed with materials from enriched mantle. These, together with the information of geological setting and rock assemblages, indicate that the basic volcanic rocks are of ophiolite. The Sm-Nd isotope ages for the eight basic volcanic rock samples construct a straight line with good correlation, and the calculated isochron age is (481.3±53) Ma. Besides, the eight calculated ε Nd(t) and model ages are close to each other, which suggests that they are homologous, so the isochron is not a mixed line. In the meantime, the isochron age ((481.3±53) Ma) is lower than the model ages (T DM=1 004-1 534 Ma) of the samples, suggeting that the isochron age represents the formation age of the basic volcanic rocks and the ophiolite belt in Mangya area, Altun is formed in the early Paleozoic (Cambrian-Ordovician). In spite of the greater uncertainty of the age, it is still reliable because it is consistent with the age constrained by the regional strata.展开更多
The Jinchuan ultramafic rock body mainly consists of lherzolites and a small amount of dunites and websterites. The largest Cu-Ni sulphide ore in China occurs in the rock body. Its original age remains equivocal now b...The Jinchuan ultramafic rock body mainly consists of lherzolites and a small amount of dunites and websterites. The largest Cu-Ni sulphide ore in China occurs in the rock body. Its original age remains equivocal now because the available age data are in disorder. This note reports the dating result obtained with Sm-Nd internal isochron method.展开更多
GEOLOGICAL scientists have paid much attention to the suture zones formed by collision between the Sino-Korean and Yangtze blocks because of the discovery of the ultrahigh pressue metamorphic (UHPM) rocksfrom northern...GEOLOGICAL scientists have paid much attention to the suture zones formed by collision between the Sino-Korean and Yangtze blocks because of the discovery of the ultrahigh pressue metamorphic (UHPM) rocksfrom northern Jiangsu Province (Su), southern Shandong Province (Lu) and the Dabie Mountains.Although the age of 200-240 Ma is probably the best estimation for UHPM metamorphism in the DabieMountains, the primary intrusive and metamorphic ages of the complex from northern Jiangsu Provincehave not been determined before. Using the Sm-Nd isotopic dating method, our study is aimed at datingthe UHPM metanorphic event of northern Jiangsu Province and researching a probable relation between theUHPM rocks from the Dabie Mountains and the UHPM rocks from northern Jiangsu Province.展开更多
1 Geologic background THE volcanic U-deposits are generally associated with felsic to intermediate volcanic rock and their sedimentary derivatives. However, uranium mineralization has been found to be spatially associ...1 Geologic background THE volcanic U-deposits are generally associated with felsic to intermediate volcanic rock and their sedimentary derivatives. However, uranium mineralization has been found to be spatially associated with thebasalt of bimodal volcanic associations in Baimianshi uranium ore field. Baimianshi uranium ore-field islocated in Baimianshi volcanic-sedimentary basin of south Jiangxi Province. The cover rocks of the basinconsist of a suite of bimodal volcanic-sedimentary sequences. Its basement rocks are two-mica granites ofBaimianshi rock body. The basalt of cover rocks is interbedded with arkoses in lower sequence, and rhyolite or rhyolitic tuff in upper sequence. Uranium minerals mainly occur as disseminations in the展开更多
Geologists have been paying much attention to the characteristics and age of the basement of the Tarim Block. Recently, some isotopic ages for the Precambrian rocks in the margin areas of the Tarim Block have been obt...Geologists have been paying much attention to the characteristics and age of the basement of the Tarim Block. Recently, some isotopic ages for the Precambrian rocks in the margin areas of the Tarim Block have been obtained. The oldest age presented by the above study is 2487±5.1 Ma determined with evaporated Pb-isotope method for zircons of the blue quartz-bearing granite from the Kuruktag area. However, the possibility of the Archaean basement of Tarim Block was only deduced. In this study the age of 3.3 Ga展开更多
Diagenetic-metallogenic ages of pyritic cherts formed by the syn-sedimentation of hydrothermal vent and ages of the Jinchang Rock Formation in the Mojiang large nickel-gold deposit in the Ailaoshan gold metallogenic b...Diagenetic-metallogenic ages of pyritic cherts formed by the syn-sedimentation of hydrothermal vent and ages of the Jinchang Rock Formation in the Mojiang large nickel-gold deposit in the Ailaoshan gold metallogenic belt have been discussed on the basis of chronology of isotopic geochemistry. Nickel-gold-bearing pyritic cherts in the mining were formed by syn-sedimentation of hydrothermal vent in the Late Devonian, i.e. age by Sm-Nd isochronal method (t) = (358±8.6) (2σ) Ma and age by Rb-Sr isochronal method (t) = (354.7±0.72) (2σ) Ma. On the other hand, deep-water cherts from the Jinchang Rock Formation of the Upper Devonian in the area were initiated at the same time; that is, age by Sm-Nd isochronal method (t) = (359(+21) (2(7) Ma and age by Rb-Sr isochronal method (t) = (358.02±0.30) (2σ) Ma.展开更多
Emplacement ages of lamproites that comprise lamproite and olivine lamproite in Zhenyuan County, Guizhou Province, China, have been constrained by the whole-rock Sm-Nd and Rb-Sr isochron methods and the whole rock K-A...Emplacement ages of lamproites that comprise lamproite and olivine lamproite in Zhenyuan County, Guizhou Province, China, have been constrained by the whole-rock Sm-Nd and Rb-Sr isochron methods and the whole rock K-Ar method. Intrusive activities of lamproites in the Sinantang area of Zhenyuan County, Guizhou Province, took place during the Late Cambrian, as indicated by the Sm-Nd isochron ages (t) = (503±17) (2σ) Ma and by the Rb-Sr isochron ages (t) = (501.2±4.6) (2σ) Ma. Intrusive activities of olivine lamproites at the Maping with Ⅱ -type diamond and Xitou in Zhenyuan County, Guizhou Province, took place from the Late Cambrian to the Early Ordovician, as evidenced by the Sm-Nd isochron ages (t) = (502±27) (2σ) Ma and by the Rb-Sr isochron age (t) = (502± 27) (2σ) Ma. This suggests that the upwelling hot materials derived from the deep mantle were emplaced from the Late Cambrian to the Early Ordovician (503-497 Ma), while the time terminal of cooling of the geothermal event of展开更多
A new stepwise dissolution scheme, involving acids with different properties, enables the selective recovery of radiogenic and common Pb from a mineral, and makes single-mineral Pb-Pb dating possible. Garnet from a gr...A new stepwise dissolution scheme, involving acids with different properties, enables the selective recovery of radiogenic and common Pb from a mineral, and makes single-mineral Pb-Pb dating possible. Garnet from a granulite sample from Huangtuling, northern Dabie Mountain yields a Pb-Pb isochron age of (1098 ± 35) Ma, which is interpreted as the timing of peak metamorphism of granulite facies.展开更多
A study of the Sm-Nd isotope composition of Honguleleng ophiolite in Xinjiang, China, isochron age ((626±25)Ma),εNd(t) = 8.40,and its model age (TNdDM) in the range of 1 180-1 208 Ma, indicates that the ophiolit...A study of the Sm-Nd isotope composition of Honguleleng ophiolite in Xinjiang, China, isochron age ((626±25)Ma),εNd(t) = 8.40,and its model age (TNdDM) in the range of 1 180-1 208 Ma, indicates that the ophiolite was formed in the late stage of the Upper Sinian. In combination with its facies association, petrochemistry, REE patterns, trace elements展开更多
We report a combined internal and whole-rock Sm-Nd isochron age, and Nd and Pb isotopic data for gabbro dikes of the Luobusha ophiolite in Tibet. The Sm-Nd isochron of data for two whole rocks and plagioclase and clin...We report a combined internal and whole-rock Sm-Nd isochron age, and Nd and Pb isotopic data for gabbro dikes of the Luobusha ophiolite in Tibet. The Sm-Nd isochron of data for two whole rocks and plagioclase and clinopyroxene separates from one of the rocks yields a Middle Jurassic age of (177±31) Ma (with an initial εNd(t) = +8), which provides a significant bound on the time of formation of the Luobusha ophiolite. The Nd and Pb isotopic charac-teristics of the dike indicate an Indian-Ocean-type isotopic affinity, and we conclude that the Luobusha ophiolite formed in an oceanic setting during the Middle Jurassic.展开更多
The middle-lower reaches of the Yangtze River are a famous copper-ironmetallogenic belt, but many vital basic geologic problems about lithogenesis andmineralization are hard to be solved, since the metamorphic basemen...The middle-lower reaches of the Yangtze River are a famous copper-ironmetallogenic belt, but many vital basic geologic problems about lithogenesis andmineralization are hard to be solved, since the metamorphic basement has not beendiscovered. Although Dongling Group metamorphic rock series outcrops in Huaining,Anhui Province, and Huangxu System metamorphic rock series outcrops in NingzhenMountain in Jiangsu Province, they are generally considered to be of the Sinian, dueto their low metamorphism and the lack of convincible isotopic age data.展开更多
Ⅰ. GEOLOGICAL SETTING AND MAJOR ROCK TYPES The metamorphic belt occurs along a series of islands and peninsulas of the west bank of the Taiwan Strait between Pingtan and Nan’ao, about 370 km in length and 10—25 km ...Ⅰ. GEOLOGICAL SETTING AND MAJOR ROCK TYPES The metamorphic belt occurs along a series of islands and peninsulas of the west bank of the Taiwan Strait between Pingtan and Nan’ao, about 370 km in length and 10—25 km in width. Volcanic and intrusive rocks of the Mesozoic are widely distributed on the west side of the metamorphic belt. The rocks of metamorphic belt suffered from amphibolite facies metamorphism. Migmatite and migmatitic granite are well developed.展开更多
文摘Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu-Nujiang suture zone,the Dongmozhazhua and Mohailaheng Pb-Zn deposits in the Yushu area of Qinghai Province are representative Pb-Zn deposits of the Pb-Zn-Cu polymetallic mineralization belt in the northern part of the Nujiang-Lancangjiang-Jinshajiang area,which are in the front belt of the Yushu thrust nappe system.The formed environments of these two deposits are different from those of sediment-hosted base metal deposits elsewhere in the world.The authors hold that they were formed during the Indian-Asian continental collision and developed within the fold-thrust belt combined with thrust and strike-slip-related Cenozoic basins in the interior of the collisional zone.Studying on the metallogenic epochs of these two deposits is helpful to the understanding of ore-forming regularity of the regional Pb-Zn-Cu mineralization belt and also to the search for new deposits in this region.The age of the Dongmozhazhua deposit has been determined by the Rb-Sr isochron method for sphalerite residues,whereas the age of the Mohailaheng deposit has been determined by the Rb-Sr isochron method for sphalerite residues and the Sm-Nd isochron method for fluorite.The age of the Dongmozhazhua deposit is 35.0-±0.0 Ma ((87Sr/86Sr)0=0.708807) for sphalerite residues.The age of the Mohailaheng deposit is 32.2±0.4 Ma ((87Sr/86Sr)o=0.708514) for sphalerite residues and 31.8±0.3 Ma ((143Nd/144Nd)o=0.512362) for fluorite with an average of 32.0 Ma.Together with the regional geological setting during mineralization,a possible tectonic model for metallogeny of the Dongmozhazhua and Mohailaheng Pb-Zn deposits has been established.These two ages are close to the ages of the Pb-Zn deposits in the Lanping and Tuotuohe basins,indicating that it is possible that the narrow 1000-kilometer-long belt controlled by a thrust nappe system on the eastern and northern margins of the Tibetan plateau could be a giant Pb-Zn mineralized belt.
文摘Sm Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold bearing shear zone on western Hainan Island, are measured. The Sm Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd)0=0.512094, εNd(t) ranges from +1.80 to +2.00 and TDM from 982 Ma to 1196 Ma (average: 1060 Ma). The authors point out that the whole rock Sm Nd isochron age (495.98±13.14 Ma) really represents the petrogenetic age of lamprophyre and the time of magmatism during subsequent subduction.
基金Project supported by the National "305" Project in the Eighth Five-year Plan.
文摘The characterstic of the basement of Junggar block has been a topic of long-standingdebate.Based on the data of gravity and magnetic anomaly,some researchers deduced thatthere were Precambrian basic-ultrabasic complex on the basement of Junggar block.However,others maintained that the basement of Junggar block was probably the Paleozoicoceanic crust because of the lack of isotopic evidence and older outcrops aroundthe Junggar Basin. In recent years,molecules of fossil community were discovered from Aleandao Groupat the Qingshuiquan and Kamuster of eastern Junggar.Most of the fossils,such asPylocorpus,Retincnlafopora,Asteropyla,were found at the boundary between Cambrianand Sinian in Qinling and South China.An isotopic age of 1908 Ma for leuco-pink graniticgneiss from the lower Huangcaopo Group was gained by evaporated Pb-isotope method forsingle zircon in Xiaoluigou of eastern Junggar by Zhang et al.But all of these results onlyindicate a possibility that the basement of Junggar block consists of
文摘An ophiolite belt is exposed to the northern edge of Altun Tagh Mountain. Geochronological researches were made on gabbro and basalt. Sm-Nd isochron age of gabbro is (829 ± 60) Ma, while the age of gabbro mixed basalt is (949 ± 62) Ma. The dating of Sm-Nd isochron proves that ophiolite formed in (829 ± 60) Ma, which implies that the northern half of Tarim (or north Tarim Block) had been separated by an ocean from the southern half of Tarim and Qaidam (or south Tarim Block) until (829 ± 60) Ma. The south Tarim Block could accrete to the north Tarim Block at the beginning of Sinian,thereby forming the north Altun Tagh suture. The Sinian system would be the first cover on the amalgamated Tarim craton.
基金Project supported by the National Natural Science Foundation of China
文摘The ophiolite suite in Shexian County, Anhui Province extends more than 40 km in NE orientation. It is called Fuchuan ophiolite because its outcrop is the most complete in Fuchuan. This ophiolite which upthrusts over the Precambrian Shexian granodiorite body is composed of dunite, harzburgite, cumulate pyroxenite, spilite, keratophyre and tuffaceous phyllite (Fig. 1).
文摘The REE patterns of the basic volcanic rocks in Mangya area, Altun, are slight rich in LREE with (La/Ya)-N=1.69-3.20, (La/Sm)-N=1.37-1.87, other trace element ratios of the rocks are Th/Ta≈1 (for a few samples greater than 1.5), Nb/Y=0.34-0.62, Ti/Y=310-443 (on the average: 381), Ti/V=37-62, Zr/Nb=9.4-12.4, Sr/Rb=12-80 (on the average: 37), and Nb/Th=7.7-16.8. These features are similar to that of E-MORE or OIB. The ε Nd(t) value, being 3.95- 4.12, shows that the source of the volcanic rocks is derived from depleted asthenosphere mantle mixed with materials from enriched mantle. These, together with the information of geological setting and rock assemblages, indicate that the basic volcanic rocks are of ophiolite. The Sm-Nd isotope ages for the eight basic volcanic rock samples construct a straight line with good correlation, and the calculated isochron age is (481.3±53) Ma. Besides, the eight calculated ε Nd(t) and model ages are close to each other, which suggests that they are homologous, so the isochron is not a mixed line. In the meantime, the isochron age ((481.3±53) Ma) is lower than the model ages (T DM=1 004-1 534 Ma) of the samples, suggeting that the isochron age represents the formation age of the basic volcanic rocks and the ophiolite belt in Mangya area, Altun is formed in the early Paleozoic (Cambrian-Ordovician). In spite of the greater uncertainty of the age, it is still reliable because it is consistent with the age constrained by the regional strata.
文摘The Jinchuan ultramafic rock body mainly consists of lherzolites and a small amount of dunites and websterites. The largest Cu-Ni sulphide ore in China occurs in the rock body. Its original age remains equivocal now because the available age data are in disorder. This note reports the dating result obtained with Sm-Nd internal isochron method.
文摘GEOLOGICAL scientists have paid much attention to the suture zones formed by collision between the Sino-Korean and Yangtze blocks because of the discovery of the ultrahigh pressue metamorphic (UHPM) rocksfrom northern Jiangsu Province (Su), southern Shandong Province (Lu) and the Dabie Mountains.Although the age of 200-240 Ma is probably the best estimation for UHPM metamorphism in the DabieMountains, the primary intrusive and metamorphic ages of the complex from northern Jiangsu Provincehave not been determined before. Using the Sm-Nd isotopic dating method, our study is aimed at datingthe UHPM metanorphic event of northern Jiangsu Province and researching a probable relation between theUHPM rocks from the Dabie Mountains and the UHPM rocks from northern Jiangsu Province.
文摘1 Geologic background THE volcanic U-deposits are generally associated with felsic to intermediate volcanic rock and their sedimentary derivatives. However, uranium mineralization has been found to be spatially associated with thebasalt of bimodal volcanic associations in Baimianshi uranium ore field. Baimianshi uranium ore-field islocated in Baimianshi volcanic-sedimentary basin of south Jiangxi Province. The cover rocks of the basinconsist of a suite of bimodal volcanic-sedimentary sequences. Its basement rocks are two-mica granites ofBaimianshi rock body. The basalt of cover rocks is interbedded with arkoses in lower sequence, and rhyolite or rhyolitic tuff in upper sequence. Uranium minerals mainly occur as disseminations in the
文摘Geologists have been paying much attention to the characteristics and age of the basement of the Tarim Block. Recently, some isotopic ages for the Precambrian rocks in the margin areas of the Tarim Block have been obtained. The oldest age presented by the above study is 2487±5.1 Ma determined with evaporated Pb-isotope method for zircons of the blue quartz-bearing granite from the Kuruktag area. However, the possibility of the Archaean basement of Tarim Block was only deduced. In this study the age of 3.3 Ga
基金This work was supported by the National Natural Science Foundation of China (Grants No. 49925309)the State Key Project of Fundamental Research Planning (Grants No. 1999043200) and the Yunnan Province-Chinese Academy of Sciences Corporation Project (G
文摘Diagenetic-metallogenic ages of pyritic cherts formed by the syn-sedimentation of hydrothermal vent and ages of the Jinchang Rock Formation in the Mojiang large nickel-gold deposit in the Ailaoshan gold metallogenic belt have been discussed on the basis of chronology of isotopic geochemistry. Nickel-gold-bearing pyritic cherts in the mining were formed by syn-sedimentation of hydrothermal vent in the Late Devonian, i.e. age by Sm-Nd isochronal method (t) = (358±8.6) (2σ) Ma and age by Rb-Sr isochronal method (t) = (354.7±0.72) (2σ) Ma. On the other hand, deep-water cherts from the Jinchang Rock Formation of the Upper Devonian in the area were initiated at the same time; that is, age by Sm-Nd isochronal method (t) = (359(+21) (2(7) Ma and age by Rb-Sr isochronal method (t) = (358.02±0.30) (2σ) Ma.
基金This work was jointly supported by the National Outstanding Young Scientist Foundation of China (Grant No. 49925309) the State Key Project of Fundamental Research Planning (Grants No. 1999043200) and 95-Y-25.
文摘Emplacement ages of lamproites that comprise lamproite and olivine lamproite in Zhenyuan County, Guizhou Province, China, have been constrained by the whole-rock Sm-Nd and Rb-Sr isochron methods and the whole rock K-Ar method. Intrusive activities of lamproites in the Sinantang area of Zhenyuan County, Guizhou Province, took place during the Late Cambrian, as indicated by the Sm-Nd isochron ages (t) = (503±17) (2σ) Ma and by the Rb-Sr isochron ages (t) = (501.2±4.6) (2σ) Ma. Intrusive activities of olivine lamproites at the Maping with Ⅱ -type diamond and Xitou in Zhenyuan County, Guizhou Province, took place from the Late Cambrian to the Early Ordovician, as evidenced by the Sm-Nd isochron ages (t) = (502±27) (2σ) Ma and by the Rb-Sr isochron age (t) = (502± 27) (2σ) Ma. This suggests that the upwelling hot materials derived from the deep mantle were emplaced from the Late Cambrian to the Early Ordovician (503-497 Ma), while the time terminal of cooling of the geothermal event of
文摘A new stepwise dissolution scheme, involving acids with different properties, enables the selective recovery of radiogenic and common Pb from a mineral, and makes single-mineral Pb-Pb dating possible. Garnet from a granulite sample from Huangtuling, northern Dabie Mountain yields a Pb-Pb isochron age of (1098 ± 35) Ma, which is interpreted as the timing of peak metamorphism of granulite facies.
文摘A study of the Sm-Nd isotope composition of Honguleleng ophiolite in Xinjiang, China, isochron age ((626±25)Ma),εNd(t) = 8.40,and its model age (TNdDM) in the range of 1 180-1 208 Ma, indicates that the ophiolite was formed in the late stage of the Upper Sinian. In combination with its facies association, petrochemistry, REE patterns, trace elements
基金This work was supportedby both the National Natural Science Foundation of China and the National Key Project for Basic Research on the Tibetan Plateau (Grant Nos. 49772107, 49802005 and G1998040800) the U.S. National Science Foundation (EAR-9805318)
文摘We report a combined internal and whole-rock Sm-Nd isochron age, and Nd and Pb isotopic data for gabbro dikes of the Luobusha ophiolite in Tibet. The Sm-Nd isochron of data for two whole rocks and plagioclase and clinopyroxene separates from one of the rocks yields a Middle Jurassic age of (177±31) Ma (with an initial εNd(t) = +8), which provides a significant bound on the time of formation of the Luobusha ophiolite. The Nd and Pb isotopic charac-teristics of the dike indicate an Indian-Ocean-type isotopic affinity, and we conclude that the Luobusha ophiolite formed in an oceanic setting during the Middle Jurassic.
文摘The middle-lower reaches of the Yangtze River are a famous copper-ironmetallogenic belt, but many vital basic geologic problems about lithogenesis andmineralization are hard to be solved, since the metamorphic basement has not beendiscovered. Although Dongling Group metamorphic rock series outcrops in Huaining,Anhui Province, and Huangxu System metamorphic rock series outcrops in NingzhenMountain in Jiangsu Province, they are generally considered to be of the Sinian, dueto their low metamorphism and the lack of convincible isotopic age data.
文摘Ⅰ. GEOLOGICAL SETTING AND MAJOR ROCK TYPES The metamorphic belt occurs along a series of islands and peninsulas of the west bank of the Taiwan Strait between Pingtan and Nan’ao, about 370 km in length and 10—25 km in width. Volcanic and intrusive rocks of the Mesozoic are widely distributed on the west side of the metamorphic belt. The rocks of metamorphic belt suffered from amphibolite facies metamorphism. Migmatite and migmatitic granite are well developed.