Here we report the first direct Rb-Sr dating of pyrites and ores using sub-sampling from lode gold deposits in Linglong, Jiaodong Peninsula, which is a supra-large lode gold deposit and propose this as a useful geochr...Here we report the first direct Rb-Sr dating of pyrites and ores using sub-sampling from lode gold deposits in Linglong, Jiaodong Peninsula, which is a supra-large lode gold deposit and propose this as a useful geochronological technique for gold mineralization with poor age constraint. The Rb-Sr data of pyrites yield an isochron age of (121.6±8.1) Ma, whereas those of ore and ore-pyrite spread in two ranges from 120.0 to 121.8 Ma and from 110.0 to 111.7 Ma. Studies of characteristic of gold deposit and microscopy of pyrite and quartz indicate that the apparent ages of ore and ore-pyrite are not isochron ages, only mixed by two end members, i.e. the primitive hydrothermal fluids and wall rocks, whereas the isochron age of pyrite sub-samples constrains the age of gold mineralization (121.6±8.1) Ma, i.e. early Cretaceous, which is in good agreement with the published SHRIMP zircon U-Pb ages.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 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 Pengjiakuang, Dazhuangzi and Fayunkuang gold deposits, located on the northern margin of the Mesozoic Jiaolai Basin, east of Shandong Province, are controlled by a low-angle normal fault. Gold ores are typically b...The Pengjiakuang, Dazhuangzi and Fayunkuang gold deposits, located on the northern margin of the Mesozoic Jiaolai Basin, east of Shandong Province, are controlled by a low-angle normal fault. Gold ores are typically brecciated, veinlet and disseminated. The Ar-Ar and Rb-Sr isochron dating methods were adopted to date ores and lamprophyre dike. The results indicate that the age of the Pengjiakuang gold deposit is 117.33—118.42 Ma, that of the Dazhuangzi gold deposit is 117.39 Ma, and that of the Fayunkuang gold deposit is (128.49±7.2) Ma. The consistency in metallogenic age between the gold deposits on the margin of the Jiaolai Basin and the gold deposits (115—126 Ma) of the northern uplift area suggests that both were formed in the same metallogenic period. That is to say, the large-scale metallogeny of the Jiaodong region took place in late-Yanshannian ((120±10) Ma).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
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
Using laser 40Ar/39Ar dating method,we have gotten the metamorphic ages of lawsonite blueschist and epidote blueschist from Jiuquan,northern Qilian Mountain,NW China.The high quality laser 40Ar/39Ar dating of glaucoph...Using laser 40Ar/39Ar dating method,we have gotten the metamorphic ages of lawsonite blueschist and epidote blueschist from Jiuquan,northern Qilian Mountain,NW China.The high quality laser 40Ar/39Ar dating of glaucophane from lawsonite blueschist gives an isochron age of 413±5 Ma.The isochron age obtained from phengite in epidote blueschist is 415±7 Ma.These data,combining with peak metamorphic P-T conditions and regional geological setting,allow us to infer that the lower limit of the ages of the prograde subduction metamorphism from lawsonite blueschist facies to epidote blueschist facies occurred at ca.413-415 Ma,which also suggests that the formation of lawsonite blueschist in the northern Qilian Mountain maybe resulted from the corner flow in the cold subduction zone.This study shows that the final closing time of the northern Qilian remnant oceanic basin is about 413-415 Ma,which also represents the convergent age between the North China Craton and the Qaidam block.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 mafic dykes are composed of a series of northwest-trending diabase in Kuokesu of the Kuruktag region, Xinjiang. Four whole-rock samples of the mafic dykes in the region give an 40Ar/36Ar–40K/36Ar isochron age of ...The mafic dykes are composed of a series of northwest-trending diabase in Kuokesu of the Kuruktag region, Xinjiang. Four whole-rock samples of the mafic dykes in the region give an 40Ar/36Ar–40K/36Ar isochron age of 282 Ma with the initial 40Ar/36Ar = 507. The characteristics of the major, trace and rare earth elements of the dyke rocks indicate that they belong to the calc-alkaline series and were emplaced in extensional structures at an intermediate depth of the crust. This shows that there was a large-scale extension in the Permian Period, which might be associated with the post-collisional extension of the ancient Tianshan Mountains.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
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 min展开更多
Lead isotopic analytic data of 30 ores gathered from the Zhuanmiao boron deposit, Wengquangou boron (iron) deposit and its Dongtaizi Ore Member constitute three isochrons, the corresponding ages of which are 1902 ...Lead isotopic analytic data of 30 ores gathered from the Zhuanmiao boron deposit, Wengquangou boron (iron) deposit and its Dongtaizi Ore Member constitute three isochrons, the corresponding ages of which are 1902 ± 12 Ma, 1852 ± 9 Ma and 1917 ± 48 Ma. Lead isotopic analyses of marble from the Xiquegou Member of the Qingchenzi orefield yield a Pb-Pb isochron age of 1844 ± 27 Ma. 40Ar-39Ar quick neutron activation dating of phlogopites and microclines coexisting with ore minerals in the Wengquangou boron (iron) and Zhuanmiao boron deposits shows that: (1) the phlogopite from the Wengquangou has a plateau age of 1923 ± 1.5 Ma and an isochron age of 1924 ± 2.5 Ma; (2) the microcline from the Wengquangou has the plateau age of 1407 ± 5.4 Ma and 220 ± 12 Ma and an isochron age of 1403 ± 19 Ma; (3) the phlogopites from the Zhuanmiao yield a plateau age 1918 ± 1.3 Ma and an isochron age of 1918 ± 2.9 Ma; (4) the microclines from the Zhuanmiao yield the plateau age of 1420 ± 16 Ma and 250 ± 8 Ma and an isochron age of 1425 ± 19 Ma and 269 ± 16 Ma. These ages indicate that the eastern Liaoning area happened around 1900 Ma, an important tectonomagmatic event, which is consistent with the worldwide Mid-Proterozoic tectonomagmatic event. During this period, the Proterozoic Liaohe Group was folded and underwent strong normal metamorphism, and the (hydrothermal) sedimentary boron deposits (or source beds) formed earlier were strongly superimposed by mineralization, resulting in enrichment of boron; later regional geological processes made little contribution to the formation of the boron deposits. Lead isotopic components show that the U-Pb and Th-Pb isotopic system reached homogenization in the ores whereas only the U-Pb isotopic system reached homogenization in the marble from the Xiquegou district, which indicates that the boron deposits superimposed in the studied area endured a relatively strong process of hydrothermal migmatization during the end phase of early Proterozoic metamorphism.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
Up to now, there were no systematic studies of geochemistry and isotopic age for the Yixian （义县） fluorite deposit, western Liaoning （辽宁） Province, China. Based on the analysis of metallogenic geological settin...Up to now, there were no systematic studies of geochemistry and isotopic age for the Yixian （义县） fluorite deposit, western Liaoning （辽宁） Province, China. Based on the analysis of metallogenic geological setting, we studied the REE, Rb-Sr and Sm-Nd isotopes. The chondrite-normalized REE patterns of fluorite are characterized by moderate LREE depletion （LREE/HREE=0.95-3.57, （La/Yb）N=0.08-2.84） and enrichment of Sr （146×10^-6-596×10^-6） and moderately positive Eu anomalies （δEu=1.10-1.34）, which are similar to those of the host Mesoproterozoic carbonate rocks. The fluorite display （^87Sr/^86Sr）t=-0.708 5, （^143Nd/^144Nd）t=-0.511 785, and δNd（t）=-12.8, which are similar to those of the host Mesoproterozoic carbonate rocks and volcanic rocks of Middle Jurassic Lanqi （蓝旗） Formation. The REE and Sr-Nd isotope geochemistry suggest that the source of the ore-forming material may be the volcanic rocks of Lanqi Formation and host carbonate rocks. The Sm-Nd isochron age of 154±14 Ma （MSWD=0.23） indicates that the Yixian fluorite mineralization nearly corresponds to the period of Lanqi Formation. Based on the integrated geological and geochemical studies, coupled with previous studies, we suggest that Yixian fluorite deposit formed in the extension setting of postcoilisional stage and may be attributed to the partial melting of ancient basaltic rocks in the lower crust induced by underplating of basic magma and to the reaction between the F-rich ore-forming fluids and the host carbonate rocks.展开更多
The black shale series that formed in the Edi- acaran-Cambrian transition are important stratigraphic records of the co-evolution of the paleo-ocean, -climate, and -biology. In this study, we measured Re-Os isotopic c...The black shale series that formed in the Edi- acaran-Cambrian transition are important stratigraphic records of the co-evolution of the paleo-ocean, -climate, and -biology. In this study, we measured Re-Os isotopic compositions of the black shale in the Niutitang Formation from the Gezhongwu section in Zhijin, Guizhou Province. The samples had high Re and Os contents, with Re ranging from 21.27 to 312.78 ng/g and Os ranging from 0.455 to 7.789 ng/g. The Re-Os isotope isochron age of 522.9 ± 8.6 Ma implies deposition of the Niutitang black shale predated the Chengjiang Fauna, providing an age constraint for the expansion of oceanic anoxia in the study area. The initial ^187Os/^188Os ratio of 0.826 ± 0.026 indi- cates that enhanced continental weathering might have triggered the expansion of the oceanic anoxia.展开更多
文摘Here we report the first direct Rb-Sr dating of pyrites and ores using sub-sampling from lode gold deposits in Linglong, Jiaodong Peninsula, which is a supra-large lode gold deposit and propose this as a useful geochronological technique for gold mineralization with poor age constraint. The Rb-Sr data of pyrites yield an isochron age of (121.6±8.1) Ma, whereas those of ore and ore-pyrite spread in two ranges from 120.0 to 121.8 Ma and from 110.0 to 111.7 Ma. Studies of characteristic of gold deposit and microscopy of pyrite and quartz indicate that the apparent ages of ore and ore-pyrite are not isochron ages, only mixed by two end members, i.e. the primitive hydrothermal fluids and wall rocks, whereas the isochron age of pyrite sub-samples constrains the age of gold mineralization (121.6±8.1) Ma, i.e. early Cretaceous, which is in good agreement with the published SHRIMP zircon U-Pb ages.
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 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.
基金This work was supported by the Chinese Academy of Sciences(Grant Nos.KZCX1-Y-03 and KZ951-A1-404).
文摘The Pengjiakuang, Dazhuangzi and Fayunkuang gold deposits, located on the northern margin of the Mesozoic Jiaolai Basin, east of Shandong Province, are controlled by a low-angle normal fault. Gold ores are typically brecciated, veinlet and disseminated. The Ar-Ar and Rb-Sr isochron dating methods were adopted to date ores and lamprophyre dike. The results indicate that the age of the Pengjiakuang gold deposit is 117.33—118.42 Ma, that of the Dazhuangzi gold deposit is 117.39 Ma, and that of the Fayunkuang gold deposit is (128.49±7.2) Ma. The consistency in metallogenic age between the gold deposits on the margin of the Jiaolai Basin and the gold deposits (115—126 Ma) of the northern uplift area suggests that both were formed in the same metallogenic period. That is to say, the large-scale metallogeny of the Jiaodong region took place in late-Yanshannian ((120±10) Ma).
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
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.
基金supported by the National Natural Science Foundation of China (40821002)the National Basic Research Pro-gram of China (2009CB825007)
文摘Using laser 40Ar/39Ar dating method,we have gotten the metamorphic ages of lawsonite blueschist and epidote blueschist from Jiuquan,northern Qilian Mountain,NW China.The high quality laser 40Ar/39Ar dating of glaucophane from lawsonite blueschist gives an isochron age of 413±5 Ma.The isochron age obtained from phengite in epidote blueschist is 415±7 Ma.These data,combining with peak metamorphic P-T conditions and regional geological setting,allow us to infer that the lower limit of the ages of the prograde subduction metamorphism from lawsonite blueschist facies to epidote blueschist facies occurred at ca.413-415 Ma,which also suggests that the formation of lawsonite blueschist in the northern Qilian Mountain maybe resulted from the corner flow in the cold subduction zone.This study shows that the final closing time of the northern Qilian remnant oceanic basin is about 413-415 Ma,which also represents the convergent age between the North China Craton and the Qaidam block.
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This study was supported by the State"Ninth Five-Year Plan"Key Project No.96-915-05-02.
文摘The mafic dykes are composed of a series of northwest-trending diabase in Kuokesu of the Kuruktag region, Xinjiang. Four whole-rock samples of the mafic dykes in the region give an 40Ar/36Ar–40K/36Ar isochron age of 282 Ma with the initial 40Ar/36Ar = 507. The characteristics of the major, trace and rare earth elements of the dyke rocks indicate that they belong to the calc-alkaline series and were emplaced in extensional structures at an intermediate depth of the crust. This shows that there was a large-scale extension in the Permian Period, which might be associated with the post-collisional extension of the ancient Tianshan Mountains.
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 min
基金supported by the National 973 Project of China(G1999043201)
文摘Lead isotopic analytic data of 30 ores gathered from the Zhuanmiao boron deposit, Wengquangou boron (iron) deposit and its Dongtaizi Ore Member constitute three isochrons, the corresponding ages of which are 1902 ± 12 Ma, 1852 ± 9 Ma and 1917 ± 48 Ma. Lead isotopic analyses of marble from the Xiquegou Member of the Qingchenzi orefield yield a Pb-Pb isochron age of 1844 ± 27 Ma. 40Ar-39Ar quick neutron activation dating of phlogopites and microclines coexisting with ore minerals in the Wengquangou boron (iron) and Zhuanmiao boron deposits shows that: (1) the phlogopite from the Wengquangou has a plateau age of 1923 ± 1.5 Ma and an isochron age of 1924 ± 2.5 Ma; (2) the microcline from the Wengquangou has the plateau age of 1407 ± 5.4 Ma and 220 ± 12 Ma and an isochron age of 1403 ± 19 Ma; (3) the phlogopites from the Zhuanmiao yield a plateau age 1918 ± 1.3 Ma and an isochron age of 1918 ± 2.9 Ma; (4) the microclines from the Zhuanmiao yield the plateau age of 1420 ± 16 Ma and 250 ± 8 Ma and an isochron age of 1425 ± 19 Ma and 269 ± 16 Ma. These ages indicate that the eastern Liaoning area happened around 1900 Ma, an important tectonomagmatic event, which is consistent with the worldwide Mid-Proterozoic tectonomagmatic event. During this period, the Proterozoic Liaohe Group was folded and underwent strong normal metamorphism, and the (hydrothermal) sedimentary boron deposits (or source beds) formed earlier were strongly superimposed by mineralization, resulting in enrichment of boron; later regional geological processes made little contribution to the formation of the boron deposits. Lead isotopic components show that the U-Pb and Th-Pb isotopic system reached homogenization in the ores whereas only the U-Pb isotopic system reached homogenization in the marble from the Xiquegou district, which indicates that the boron deposits superimposed in the studied area endured a relatively strong process of hydrothermal migmatization during the end phase of early Proterozoic metamorphism.
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
基金supported by the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT)the 111 Project (No.B07011)
文摘Up to now, there were no systematic studies of geochemistry and isotopic age for the Yixian （义县） fluorite deposit, western Liaoning （辽宁） Province, China. Based on the analysis of metallogenic geological setting, we studied the REE, Rb-Sr and Sm-Nd isotopes. The chondrite-normalized REE patterns of fluorite are characterized by moderate LREE depletion （LREE/HREE=0.95-3.57, （La/Yb）N=0.08-2.84） and enrichment of Sr （146×10^-6-596×10^-6） and moderately positive Eu anomalies （δEu=1.10-1.34）, which are similar to those of the host Mesoproterozoic carbonate rocks. The fluorite display （^87Sr/^86Sr）t=-0.708 5, （^143Nd/^144Nd）t=-0.511 785, and δNd（t）=-12.8, which are similar to those of the host Mesoproterozoic carbonate rocks and volcanic rocks of Middle Jurassic Lanqi （蓝旗） Formation. The REE and Sr-Nd isotope geochemistry suggest that the source of the ore-forming material may be the volcanic rocks of Lanqi Formation and host carbonate rocks. The Sm-Nd isochron age of 154±14 Ma （MSWD=0.23） indicates that the Yixian fluorite mineralization nearly corresponds to the period of Lanqi Formation. Based on the integrated geological and geochemical studies, coupled with previous studies, we suggest that Yixian fluorite deposit formed in the extension setting of postcoilisional stage and may be attributed to the partial melting of ancient basaltic rocks in the lower crust induced by underplating of basic magma and to the reaction between the F-rich ore-forming fluids and the host carbonate rocks.
基金supported by the China Geological Survey (DD20160346)the National Natural Science Foundation of China (41472089)the Guizhou Geological Prospecting Fund (2016091)
文摘The black shale series that formed in the Edi- acaran-Cambrian transition are important stratigraphic records of the co-evolution of the paleo-ocean, -climate, and -biology. In this study, we measured Re-Os isotopic compositions of the black shale in the Niutitang Formation from the Gezhongwu section in Zhijin, Guizhou Province. The samples had high Re and Os contents, with Re ranging from 21.27 to 312.78 ng/g and Os ranging from 0.455 to 7.789 ng/g. The Re-Os isotope isochron age of 522.9 ± 8.6 Ma implies deposition of the Niutitang black shale predated the Chengjiang Fauna, providing an age constraint for the expansion of oceanic anoxia in the study area. The initial ^187Os/^188Os ratio of 0.826 ± 0.026 indi- cates that enhanced continental weathering might have triggered the expansion of the oceanic anoxia.
