Carbonate rocks are important reservoirs for global petroleum exploration.The largest oilfield in the South China Sea,Liuhua 11-1,is distributed in the massive carbonate reef area of the Zhujiang(Pearl)River Mouth Bas...Carbonate rocks are important reservoirs for global petroleum exploration.The largest oilfield in the South China Sea,Liuhua 11-1,is distributed in the massive carbonate reef area of the Zhujiang(Pearl)River Mouth Basin.Previous studies showed that one 802.17-m-long core from well Xichen-1 in the South China Sea mainly consisted of white and light gray-white organic reefs.Recently,a Miocene whole core(161.9 m long)of well Xiyong-2,near well Xichen-1,was found to contain six layers of yellowish brown,light yellowish gray,iron black,or light yellowish gray-white organic reefs.Scanning electron microscope images of these layers reveal a typical ferroan dolomite rich in Fe(up to 29%),with the high concentrations of Mn,Cu,W,Zn,Cr,Ni,and Co.Systematic X-ray powder diffraction analysis yields a 1.9–6.1 match in phase ratio with ankerite,5.4–26.9 with dolomite,and zero with calcite,which indicate that the samples can be classified as ferroan dolomite.The iron and heavy metals are inferred to be originated from multiple volcanic eruptions of Gaojianshi Island in the Dongdao Atoll during the middle-late Miocene.These elements were dissolved in seawater,likely as a sol,and carried to Yongxing Island in the Xuande Atoll by sea currents and tides enhanced by prevailing winds,and deposited as a part of the sedimentation process in the study area.The ferroan dolomite has Sr content of (125–285)×10^(-6),which is lower than the accepted Sr boundary value of dolomite.This finding suggests that dolomitization occurred during large-scale global glacial regression in the late Miocene.The isolated Xisha carbonate platform,exposed to air,underwent freshwater leaching and dolomitization induced by mixed water,and caused the extensive Fe-Mg exchange along the organic reef profile to form ankerite and ferroan dolomite.These results may help to understand paleoceanographic environmental changes in the South China Sea during the Miocene.展开更多
1 Introduction The widely accepted standard model for the lunar feldspathic crust is:the early Moon was wholly or mostly molten,forming Lunar Magma Ocean(LMO).Olivine and pyroxene crystallized first from that magma oc...1 Introduction The widely accepted standard model for the lunar feldspathic crust is:the early Moon was wholly or mostly molten,forming Lunar Magma Ocean(LMO).Olivine and pyroxene crystallized first from that magma ocean and sank展开更多
In paleogeographic reconstructions of the Columbia and Rodinia Supercontinents,the position of the Greater India landmass is ambiguous.This,coupled with a limited understanding of the tectonic evolution of the mobile ...In paleogeographic reconstructions of the Columbia and Rodinia Supercontinents,the position of the Greater India landmass is ambiguous.This,coupled with a limited understanding of the tectonic evolution of the mobile belts along which the mosaic of crustal domains in India accreted,impedes precise correlation among the dispersed crustal fragments in supercontinent reconstructions.Using structural,metamorphic phase equilibria,chronological and geochemical investigations,this study aims to reconstruct the tectonic evolution of the Chottanagpur Gneiss Complex(CGC)as a distinct crustal block at the eastern end of the Greater Indian Proterozoic Fold Belt(GIPFOB)along which the North India Block(NIB)and the South India Block(SIB)accreted.The study focuses on two issues,e.g.dating the Early Neoproterozoic(0.92 Ga)accretion of the CGC with the NIB contemporaneous with the assembly of Rodinia,and documenting the widespread(>24,000 km^(2))plutonism of1.5-1.4 Ga weakly peraluminous,calc-alkalic to alkali-calcic and ferroan A-type granitoids(±garnet)devoid of mafic microgrannular enclaves and coeval mafic emplacements in the crustal block.These dominantly within-plate granitoids arguably formed by asthenospheric upwelling induced partial melting of garnetbearing anatectic quartzofeldspathic gneisses that dominate the Early Mesoproterozoic basement of the block.The major and trace element chemistry of the granitoids is similar to the 1.35-1.45 Ga A-type granitoids in Laurentia/Amazonia emplaced contemporaneous with the 1.5-1.3 Ga breakup of the Columbia Supercontinent.This study suggests the Chottanagpur Gneiss Complex occured as a fragmented crustal block following the breakup of the Columbia Supercontinent;the crustal block was subsequently integrated within India during the Early Neoproterozoic oblique accretion between the NIB and SIB contemporaneous with the Rodinia Supercontinent assembly.展开更多
The Neoarchean charnockites of North margain of North China Craton(NCC) has become a hot topic into understanding the Early Precambrian basement. Although there is a broad consensus that charnockite is usually related...The Neoarchean charnockites of North margain of North China Craton(NCC) has become a hot topic into understanding the Early Precambrian basement. Although there is a broad consensus that charnockite is usually related to granulite facies metamorphism, whether its petrogenesis and tectonics characteristics remains controversial. Inclusions within hypersthene and garnet in charnockite are used to identify the peak granulite facies mineral assemblage, with the formation of Magnesian-charnockite attributed to anatexis of the protolith associated with this granulite facies metamorphism. The distribution of major and trace elements in charnockite is very uneven, significant depleted in LILEs(eg. Cs, U, Th) and HFSEs(eg. Nb, Ta, P and Ti), riched in Sr. Raising to the coexistence of Eu-enrichment and Eu-depletion type of REE patterns that influenced by the content of plagioclase and the remnants minerals of zircon and apatite. Comparative the petrography, geochemistry and geochronology data of Magnesian-charnockite indicate that the ratios of mafic pellites and basalts involved in anatectic melting are different by the upwelling of mantle magma, also resulting in the Eu anormals characteristics. The formation of the Magnesian-charnockite is closely connected with the subduction of the NCC oceanic crust(About ~2.5 Ga). However, Ferroan-charnockite may be the formed by the crystallization differentiation of the upwelling of mantle-derived shoshonitic magma(About ~2.45 Ga), with the lower crust material addition.展开更多
The lunar ferroan anorthosites,formed by plagioclase flotation from the crystallization of the lunar magma ocean,have an age span of over~200 Ma.However,previous thermal models predicted a much shorter time range.We p...The lunar ferroan anorthosites,formed by plagioclase flotation from the crystallization of the lunar magma ocean,have an age span of over~200 Ma.However,previous thermal models predicted a much shorter time range.We propose that a much smaller thermal conductivity of anorthositic crust due to its high porosity may have delayed the solidification of the lunar magma ocean.Our thermal simulation results,using the thermal conductivity of porous lunar crust,show that crystallization of a 1000 km deep magma ocean could be prolonged to tens of millions of years,and up to 180 Ma under some extreme conditions.The porous crust alone can’t explain the large crustal age span,however.Other circumstances must be taken into consideration,such as a thick lunar soil.展开更多
New geochronologic data from midcontinental Laurentia demonstrate that emplacement of the 1476-1470 Ma Wolf River granitic batholith was not an isolated igneous event,but was accompanied by regional metamorphism,defor...New geochronologic data from midcontinental Laurentia demonstrate that emplacement of the 1476-1470 Ma Wolf River granitic batholith was not an isolated igneous event,but was accompanied by regional metamorphism,deformation,and sedimentation.Evidence for such metamorphism and deformation is best seen in siliciclastic sedimentary rocks of the Baraboo Interval,which were deposited closely following the 1.65-1.63 Ga Mazatzal orogeny.In Baraboo Interval strata,muscovite parallel to slatey cleavage,in hydrothermal veins,in quartzite breccia,and in metamorphosed paleosol yielded ^(40)Ar/^(39)Ar plateau ages of 1493-1465 Ma.In addition,U-Th-total Pb dating of neoblastic overgrowths on detrital monazite gave an age of 1488±20 Ma,and recrystallized hematite in folded metapelite gave a mean U/Th-He age of 1411±39 Ma.Post-Baraboo,arkosic polymictic conglomerate,which contains detrital zircon with a minimum peak age of 1493 Ma,was intruded by a 1470 Ma granite porphyry at the northeastern margin of the Wolf River batholith.This episode of magmatism,regional deformation and metamorphism,and sedimentation,which is designated herein as the Baraboo orogeny,provides a midcontinental link between the Picuris orogeny to the southwest and the Pinware orogeny to the northeast,completing the extent of early Mesoproterozoic(Calymmian)orogenesis for 5000 km along the southern margin of Laurentia.This transcontinental orogen is unique among Precambrian orogenies for its great width(-1600 km),the predominance of ferroan granites derived from partial melting of lower continental crust,and the prevalence of regional high T-P metamorphism related to advective heating by granitic magmas emplaced in the middle to upper crust.展开更多
New geochemical and geochronological data of two types of granites,which are located in Yandangshan area,southeastern Zhejiang Province,were presented to constrain their magma condition,origin and the genetic relation...New geochemical and geochronological data of two types of granites,which are located in Yandangshan area,southeastern Zhejiang Province,were presented to constrain their magma condition,origin and the genetic relationship between them.The SHRIMP zircon U-Pb dating of Dongshan and Hesheng granite in Yandangshan area shows that they were formed at 114±1 and 103±2 Ma,respectively.Samples from the Dongshan granite have high Si O2(76.4 wt.%–76.9 wt.%)and total alkaline(K2O+Na2O=8.35 wt.%–8.47 wt.%)contents,but low Fe OT(0.89 wt.%–1.15 wt.%),Mg O(0.21 wt.%–0.22wt.%),and Ca O(0.24 wt.%–0.34 wt.%)contents and high A/CNK(~1.1)values,belonging to the peraluminous and magnesian granite.The Hesheng granite has high Si O2(72.2 wt.%–77.5 wt.%),total alkaline(K2O+Na2O=8.05 wt.%–9.41 wt.%)and Fe OT contents(1.20–2.06),and high A/CNK values(1.0–1.1),but low in Mg O(0.12 wt.%–0.29 wt.%)and Ca O(0.24 wt.%–0.34 wt.%)contents.Samples from the Hesheng granite also have high Fe OT/Mg O(6.9–10.0)and 10 000×Ga/Al(2.6–3.4)ratios similar to the ferroan/A-type granite.All the samples are enriched in LREE but have produced negative Eu anomalies(Eu/Eu*Dongshan=0.45–0.47;Eu/Eu*Hesheng=0.17–0.55),Ba,Nb,and Ta,while the REE contents of the ferroan/A-type granite(Hesheng)are higher than that of the magnesian granite(Dongshan).The(87Sr/86Sr)i value of the magnesian granite is slightly higher than that of the ferroan/A-type granite and itsεNd(t)value(-6.8)is lower than the latter(-6.0–-5.9).In addition,theεHf(t)value(-11.8–-4.2)of magnesian granite is also lower than that of the ferroan/A-type granite(-8.3–-2.0),indicating that there may be more mantle-derived components in the source area of the ferroan/A-type granite.Zircon saturation thermometer(TZr)and Ti-in-zircon thermometer(TZircon)are used to estimate the temperature of the magma source,and the results show that the magma temperature of the magnesian granite(average TZr=798oC;average TZircon=792oC)is lower than that of the ferroan/A-type granite(average TZr=862oC;average TZircon=859oC).And the oxygen fugacity of magnesian granite(ΔFMQ=1.16–3.47)are also higher than those of the ferroan/A-type granite(ΔFMQ=-0.41–1.14).Our new data indicate that both granites in this study are derived from a mixed source that consists of mantle-derived and crust-derived material.Based on the previous studies,both of the granitic plutons were formed under extension setting,and the granites transformed from magnesian to ferroan in the study area may indicate the extension was enhanced,which may be caused by the roll-back or delamination of the Paleo-Pacific oceanic slab.展开更多
基金Supported by the National Basic Research Program of China(973 Program)(No.2012CB956004)the Science and Technology Basic Resources Investigation Program of China(No.2017FY201407)+1 种基金the National Oil and Gas Major Projects of China(No.2011ZX05025-002)the National Natural Science Foundation of China(NSFC)(No.41106064)
文摘Carbonate rocks are important reservoirs for global petroleum exploration.The largest oilfield in the South China Sea,Liuhua 11-1,is distributed in the massive carbonate reef area of the Zhujiang(Pearl)River Mouth Basin.Previous studies showed that one 802.17-m-long core from well Xichen-1 in the South China Sea mainly consisted of white and light gray-white organic reefs.Recently,a Miocene whole core(161.9 m long)of well Xiyong-2,near well Xichen-1,was found to contain six layers of yellowish brown,light yellowish gray,iron black,or light yellowish gray-white organic reefs.Scanning electron microscope images of these layers reveal a typical ferroan dolomite rich in Fe(up to 29%),with the high concentrations of Mn,Cu,W,Zn,Cr,Ni,and Co.Systematic X-ray powder diffraction analysis yields a 1.9–6.1 match in phase ratio with ankerite,5.4–26.9 with dolomite,and zero with calcite,which indicate that the samples can be classified as ferroan dolomite.The iron and heavy metals are inferred to be originated from multiple volcanic eruptions of Gaojianshi Island in the Dongdao Atoll during the middle-late Miocene.These elements were dissolved in seawater,likely as a sol,and carried to Yongxing Island in the Xuande Atoll by sea currents and tides enhanced by prevailing winds,and deposited as a part of the sedimentation process in the study area.The ferroan dolomite has Sr content of (125–285)×10^(-6),which is lower than the accepted Sr boundary value of dolomite.This finding suggests that dolomitization occurred during large-scale global glacial regression in the late Miocene.The isolated Xisha carbonate platform,exposed to air,underwent freshwater leaching and dolomitization induced by mixed water,and caused the extensive Fe-Mg exchange along the organic reef profile to form ankerite and ferroan dolomite.These results may help to understand paleoceanographic environmental changes in the South China Sea during the Miocene.
基金Funding for this study comes from Chinese NSF projects (41490635, 41530210 and 41573040)
文摘1 Introduction The widely accepted standard model for the lunar feldspathic crust is:the early Moon was wholly or mostly molten,forming Lunar Magma Ocean(LMO).Olivine and pyroxene crystallized first from that magma ocean and sank
基金the financial support provided by UGC(India)fellowshipthe financial support for fieldwork provided through the CPDA funding scheme by Indian Institute of Technology,Kharagpur+2 种基金Invaluable support by Atreyee Bhattacharya(INSTAAR,Boulder)via internal educational initiative grants at University of ColoradoBoulder for the SIMS geochronology work at UCLA is greatly appreciatedThe UCLA Ion Microprobe Laboratory is partially supported by a grant from NSF-EAR’s Instrumentation and Facilities Program(1734856)。
文摘In paleogeographic reconstructions of the Columbia and Rodinia Supercontinents,the position of the Greater India landmass is ambiguous.This,coupled with a limited understanding of the tectonic evolution of the mobile belts along which the mosaic of crustal domains in India accreted,impedes precise correlation among the dispersed crustal fragments in supercontinent reconstructions.Using structural,metamorphic phase equilibria,chronological and geochemical investigations,this study aims to reconstruct the tectonic evolution of the Chottanagpur Gneiss Complex(CGC)as a distinct crustal block at the eastern end of the Greater Indian Proterozoic Fold Belt(GIPFOB)along which the North India Block(NIB)and the South India Block(SIB)accreted.The study focuses on two issues,e.g.dating the Early Neoproterozoic(0.92 Ga)accretion of the CGC with the NIB contemporaneous with the assembly of Rodinia,and documenting the widespread(>24,000 km^(2))plutonism of1.5-1.4 Ga weakly peraluminous,calc-alkalic to alkali-calcic and ferroan A-type granitoids(±garnet)devoid of mafic microgrannular enclaves and coeval mafic emplacements in the crustal block.These dominantly within-plate granitoids arguably formed by asthenospheric upwelling induced partial melting of garnetbearing anatectic quartzofeldspathic gneisses that dominate the Early Mesoproterozoic basement of the block.The major and trace element chemistry of the granitoids is similar to the 1.35-1.45 Ga A-type granitoids in Laurentia/Amazonia emplaced contemporaneous with the 1.5-1.3 Ga breakup of the Columbia Supercontinent.This study suggests the Chottanagpur Gneiss Complex occured as a fragmented crustal block following the breakup of the Columbia Supercontinent;the crustal block was subsequently integrated within India during the Early Neoproterozoic oblique accretion between the NIB and SIB contemporaneous with the Rodinia Supercontinent assembly.
基金financially supported by the National Natural Science Foundation of China (41872194, 41872203)
文摘The Neoarchean charnockites of North margain of North China Craton(NCC) has become a hot topic into understanding the Early Precambrian basement. Although there is a broad consensus that charnockite is usually related to granulite facies metamorphism, whether its petrogenesis and tectonics characteristics remains controversial. Inclusions within hypersthene and garnet in charnockite are used to identify the peak granulite facies mineral assemblage, with the formation of Magnesian-charnockite attributed to anatexis of the protolith associated with this granulite facies metamorphism. The distribution of major and trace elements in charnockite is very uneven, significant depleted in LILEs(eg. Cs, U, Th) and HFSEs(eg. Nb, Ta, P and Ti), riched in Sr. Raising to the coexistence of Eu-enrichment and Eu-depletion type of REE patterns that influenced by the content of plagioclase and the remnants minerals of zircon and apatite. Comparative the petrography, geochemistry and geochronology data of Magnesian-charnockite indicate that the ratios of mafic pellites and basalts involved in anatectic melting are different by the upwelling of mantle magma, also resulting in the Eu anormals characteristics. The formation of the Magnesian-charnockite is closely connected with the subduction of the NCC oceanic crust(About ~2.5 Ga). However, Ferroan-charnockite may be the formed by the crystallization differentiation of the upwelling of mantle-derived shoshonitic magma(About ~2.45 Ga), with the lower crust material addition.
基金financially supported by the National Natural Science Foundation of China (Grants Nos. 41773064, 41931077)the Strategic Priority Program of the Chinese Academy of Sciences (No. XDB41020300)+1 种基金Youth Innovation Promotion Association of CAS, the Key Research Program of the Chinese Academy of Sciences (XDPB11)Beijing Municipal Science and Technology Commission (Z181100002918003)。
文摘The lunar ferroan anorthosites,formed by plagioclase flotation from the crystallization of the lunar magma ocean,have an age span of over~200 Ma.However,previous thermal models predicted a much shorter time range.We propose that a much smaller thermal conductivity of anorthositic crust due to its high porosity may have delayed the solidification of the lunar magma ocean.Our thermal simulation results,using the thermal conductivity of porous lunar crust,show that crystallization of a 1000 km deep magma ocean could be prolonged to tens of millions of years,and up to 180 Ma under some extreme conditions.The porous crust alone can’t explain the large crustal age span,however.Other circumstances must be taken into consideration,such as a thick lunar soil.
基金Detrital zircon analyses were funded in part by the USGS National Cooperative Geologic Mapping Program under award G16AC00143(2016)to EKS.Support for the Arizona LaserChron Center,where detrital zircon analyses of samples 07ES15 and 05ES15 were performed,was provided by NSFEAR 1649254.Support for monazite geochronology was partially provided by an Institute for Lake Superior Geology student research grant and NSF-EAR 0620101 to AVL.
文摘New geochronologic data from midcontinental Laurentia demonstrate that emplacement of the 1476-1470 Ma Wolf River granitic batholith was not an isolated igneous event,but was accompanied by regional metamorphism,deformation,and sedimentation.Evidence for such metamorphism and deformation is best seen in siliciclastic sedimentary rocks of the Baraboo Interval,which were deposited closely following the 1.65-1.63 Ga Mazatzal orogeny.In Baraboo Interval strata,muscovite parallel to slatey cleavage,in hydrothermal veins,in quartzite breccia,and in metamorphosed paleosol yielded ^(40)Ar/^(39)Ar plateau ages of 1493-1465 Ma.In addition,U-Th-total Pb dating of neoblastic overgrowths on detrital monazite gave an age of 1488±20 Ma,and recrystallized hematite in folded metapelite gave a mean U/Th-He age of 1411±39 Ma.Post-Baraboo,arkosic polymictic conglomerate,which contains detrital zircon with a minimum peak age of 1493 Ma,was intruded by a 1470 Ma granite porphyry at the northeastern margin of the Wolf River batholith.This episode of magmatism,regional deformation and metamorphism,and sedimentation,which is designated herein as the Baraboo orogeny,provides a midcontinental link between the Picuris orogeny to the southwest and the Pinware orogeny to the northeast,completing the extent of early Mesoproterozoic(Calymmian)orogenesis for 5000 km along the southern margin of Laurentia.This transcontinental orogen is unique among Precambrian orogenies for its great width(-1600 km),the predominance of ferroan granites derived from partial melting of lower continental crust,and the prevalence of regional high T-P metamorphism related to advective heating by granitic magmas emplaced in the middle to upper crust.
基金funded by the National Natural Science Foundation of China (Nos. 41702047,41541018,41072048)Department of Science and Technology (No. 2014C33023)+1 种基金Geological Exploration Bureau (No. 201531)Department of Land and Resources (No. 2015005)。
文摘New geochemical and geochronological data of two types of granites,which are located in Yandangshan area,southeastern Zhejiang Province,were presented to constrain their magma condition,origin and the genetic relationship between them.The SHRIMP zircon U-Pb dating of Dongshan and Hesheng granite in Yandangshan area shows that they were formed at 114±1 and 103±2 Ma,respectively.Samples from the Dongshan granite have high Si O2(76.4 wt.%–76.9 wt.%)and total alkaline(K2O+Na2O=8.35 wt.%–8.47 wt.%)contents,but low Fe OT(0.89 wt.%–1.15 wt.%),Mg O(0.21 wt.%–0.22wt.%),and Ca O(0.24 wt.%–0.34 wt.%)contents and high A/CNK(~1.1)values,belonging to the peraluminous and magnesian granite.The Hesheng granite has high Si O2(72.2 wt.%–77.5 wt.%),total alkaline(K2O+Na2O=8.05 wt.%–9.41 wt.%)and Fe OT contents(1.20–2.06),and high A/CNK values(1.0–1.1),but low in Mg O(0.12 wt.%–0.29 wt.%)and Ca O(0.24 wt.%–0.34 wt.%)contents.Samples from the Hesheng granite also have high Fe OT/Mg O(6.9–10.0)and 10 000×Ga/Al(2.6–3.4)ratios similar to the ferroan/A-type granite.All the samples are enriched in LREE but have produced negative Eu anomalies(Eu/Eu*Dongshan=0.45–0.47;Eu/Eu*Hesheng=0.17–0.55),Ba,Nb,and Ta,while the REE contents of the ferroan/A-type granite(Hesheng)are higher than that of the magnesian granite(Dongshan).The(87Sr/86Sr)i value of the magnesian granite is slightly higher than that of the ferroan/A-type granite and itsεNd(t)value(-6.8)is lower than the latter(-6.0–-5.9).In addition,theεHf(t)value(-11.8–-4.2)of magnesian granite is also lower than that of the ferroan/A-type granite(-8.3–-2.0),indicating that there may be more mantle-derived components in the source area of the ferroan/A-type granite.Zircon saturation thermometer(TZr)and Ti-in-zircon thermometer(TZircon)are used to estimate the temperature of the magma source,and the results show that the magma temperature of the magnesian granite(average TZr=798oC;average TZircon=792oC)is lower than that of the ferroan/A-type granite(average TZr=862oC;average TZircon=859oC).And the oxygen fugacity of magnesian granite(ΔFMQ=1.16–3.47)are also higher than those of the ferroan/A-type granite(ΔFMQ=-0.41–1.14).Our new data indicate that both granites in this study are derived from a mixed source that consists of mantle-derived and crust-derived material.Based on the previous studies,both of the granitic plutons were formed under extension setting,and the granites transformed from magnesian to ferroan in the study area may indicate the extension was enhanced,which may be caused by the roll-back or delamination of the Paleo-Pacific oceanic slab.
