Discontinuous ophiolite suites along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet representing remnants of the Neo-Tethyan oceanic lithosphere are considered to be formed between Late Jurassic and Early Creta...Discontinuous ophiolite suites along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet representing remnants of the Neo-Tethyan oceanic lithosphere are considered to be formed between Late Jurassic and Early Cretaceous.Older ophiolite or ophiolitic mélange(e.g.Triassic)to reveal the initial evolution the Neo-Tethyan ocean within the YZSZ have rarely been documented so far.The western YZSZ extending from the Saga to Ladakh area are composed of the northern ophiolitic subbelt,the Zhongba terrane and the southern ophiolitic sub-belt.In this study,we document structural,petrological and geochronological data of mafic intrusions from the Mayoumu massif in the southern ophiolitic sub-belt of the western YZSZ.Two lithos-tectonic sub-units,the southern ophiolitic complex and the northern ophiolitic mélange,are recognized in the Mayoumu massif in terms of structural pattern and petrology.LA-ICP-MS zircon U-Pb dating of gabbro from the ophiolitic mélange yields an age of 243±1 Ma with zirconεHf(t)values of+7.9 to+13.2.Two samples of diabase samples from the ophiolite yield ages of 131±1 Ma and 124±1 Ma with zirconεHf(t)values ranging from+10.8 to+15.0 and+12.3 to+15.4,respectively.Geochemically,rare earth elements(REEs)patterns show that these mafic intrusions are similar to those of the normal mid-ocean-ridge basalt(N-MORB).Enrichment of fluidmobile elements(e.g.Rb and Ba)and depletion of Nb,and Ta suggest that these intrusions were possibly originated from melting of a depleted mantle source influenced by subducted slab.Our data strongly confirms that the Neo-Tethyan ocean between the Lhasa terrane and Gondwana had been existed since the Middle Triassic at least.The ages of the two diabases from the ophiolitic complex reveal that mafic magma activities within the Neo-Tethyan ocean could be as a continuing process during 120–130 Ma.Emplacement and preservation of older ophiolitic recorder during evolution of the Neo-Tethyan Ocean may be closely related to the occurrence of the Zhongba micro-terrane within the western YZSZ.展开更多
A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16 32 μm.This was accomplished by introducing N 2 into ICP to increase the sensitivity.The...A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16 32 μm.This was accomplished by introducing N 2 into ICP to increase the sensitivity.The obtained U-Pb ages for zircon standards GJ-1,TEMORA and SK10-2 are consistent with the preferred values within about 1% uncertainty (2σ) by simple external calibration against zircon standard 91500.Different data reduction softwares could yield different uncertainties for calculation of U-Pb ages.The commercially available program GLITTER4.4 could apply an improper uncertainty calculation strategy,but it may yield artificial high precisions for single analyses.Our trace element analyses indicate that Si is not an ideal internal standard for zircon when calibrated against the NIST glasses.Calibration against the NIST glasses using Si as an internal standard,a systematic deviation of 10% 30% was found for most trace elements including Zr.However,the trace element compositions of zircon can be accurately measured by calibration against multiple reference materials with natural compositions (e.g.,BCR-2G,BHVO-2G and BIR-1G),or calibration against NIST SRM 610 and using Zr as an internal standard.Analyses of two pieces of GJ-1 demonstrate that it is relatively homogenous for most trace elements (except for Ti).展开更多
In this study, the Pb/U fractionation between zircon and uraninite during femtosecond Laser Ablation Inductively Coupled Plasma Mass Spectrometry （fs-LA-ICP-MS） analysis was studied in detail. The results show signi...In this study, the Pb/U fractionation between zircon and uraninite during femtosecond Laser Ablation Inductively Coupled Plasma Mass Spectrometry （fs-LA-ICP-MS） analysis was studied in detail. The results show significant Pb/U fractionation between zircon and uraninite during fs-LA-ICP-MS analysis that when calibrated against the zircon standard M257, the obtained U-Pb age of the Chinese national uraninite standard GBW04420 is 17% older than the recommended value. Thus, the accurate in-situ U-Pb dating of uraninite by LA-ICP-MS requires matrix-matched external standards for calibration. Uraninite in thin sections of two U-mineralized leucogranite from the Gaudeanmus in Namibia was analyzed by a fs-LA-ICP-MS equipped with a Signal Smooth Device （SSD）, using laser spot and frequency of 10 μm and 1 Hz, respectively. When calibrated using GBW04420 as the external standard, two samples give weighted mean 2066pb/238U ages of 504±3 Ma （2σ, n=21） and 503±3 Ma （2σ, n=22）, and only one of two samples yields a concordia U-Pb age of 507±1 Ma （2or, n=21）. These results are consistent with ID-TIMS U-Pb ages of 509±1 and 508±12 Ma and are also indistinguishable from zircon U-Pb upper intercept ages of 506±33 Ma （2σ, n=29） and 501±51 Ma （2σ, n=29）. The present study shows that in-situ U-Pb dating of uraninite can deliver more reliable formation ages of the deposit than dating coeval high-U zircon because the latter commonly suffer significant Pb loss after formation. Our results confirm that GBW04420 is an ideal matrix matching standard for in-situ U-Pb dating of uraninite.展开更多
Trace element compositions of garnet, omphacite and apatite in ultrahigh-pressure eclogites from the main hole of the Chinese Continental Scientific Drilling (CCSD) project were in situ analyzed by the LA-ICP-MS metho...Trace element compositions of garnet, omphacite and apatite in ultrahigh-pressure eclogites from the main hole of the Chinese Continental Scientific Drilling (CCSD) project were in situ analyzed by the LA-ICP-MS method. Although both garnet and omphacite have homogeneous major element composi-tions, their trace elements show zonations from core to rim in rare earth elements. In particular, middle rare earth elements in the garnet, heavy rare earth elements in the apatite and all rare earth elements in the omphacite increase from core to rim, respectively. Based on dependence of partition coefficients on temperature and pressure in these minerals, we suggest that the trace elemental zonations in these minerals may record a short-lived heating event during exhumation.展开更多
Deep-water canyon systems can provide important sandstone reservoirs for deep-water oil and gas exploration in the South China Sea;however,the sedimentary provenance of the Central Canyon in the Qiongdongnan Basin rem...Deep-water canyon systems can provide important sandstone reservoirs for deep-water oil and gas exploration in the South China Sea;however,the sedimentary provenance of the Central Canyon in the Qiongdongnan Basin remains controversial.In this work,detrital zircon grains from three drilling sandstones in the Upper Miocene Huangliu Formation in the western part of the Central Canyon were analysed by LA-ICP-MS for U-Pb ages,in order to constrain their provenance.One hundred and ninety-one zircon grains yield concordant U-Pb ages ranging from 28.6 to 3285 Ma.Most of them show oscillatory or linear zoning in CL-images and high Th/U ratios(>0.1),suggesting that they are magmatic zircons.Three major age clusters at about30 Ma(N=6),220–270 Ma(N=29),and 420–440 Ma(N=13),and five minor age clusters at 70–110 Ma(N=7),150–170 Ma(N=4),800–850 Ma(N=11),1800–2000 Ma(N=16),and 2400–2600 Ma(N=7),can be identified in the age spectrum,which are very similar to those of the Upper Miocene sandstones and modern river sands in the Red River area,but different from those of other nearby regions(e.g.,Hainan Island,the Pearl River area,and the Mekong River area)in Southeast Asia.The major age peak at about 30 Ma in our samples is consistent with the timing of tectonothermal events in the Red River Fault Zone.Therefore,we suggest that the provenance of the western part of the Central Canyon,in the Qiongdongnan Basin,was fed dominantly by the Paleo-Red River system during the Late Miocene.展开更多
The Neogene sediments of Gansu Group from northwestern China contain eolian and fluvial deposits.The origins of these sediments are very important for exploring the onset of Asian inland aridification,the pattern of p...The Neogene sediments of Gansu Group from northwestern China contain eolian and fluvial deposits.The origins of these sediments are very important for exploring the onset of Asian inland aridification,the pattern of paleo-atmospheric circulation,and the regional tectonics and geomorphic evolution during the Miocene.Here we present detrital-zircon age spectra of typical eolian and fluvial deposits from highlands and subsidence basin,and compare them with those of surrounding eroded mountain(such as the West Qinling Mountains and Liupan Mountains)materials and Quaternary loess derived from the Asian inlands.The results reveal that(1)the detrital-zircon age spectrum of the Miocene eolian sample is remarkably different from the eroded materials of the West Qinling Mountains and the Miocene fluvial deposits from Tianshui region,but very similar to the Quaternary loess deposits.This indicates that the provenance of Miocene eolian sediments is similar with the Quaternary loess,and thus further confirms the previous conclusions that the distribution of Asian arid lands and the pattern of atmospheric circulation during the Miocene are broadly similar with the Quaternary.(2)The detrital-zircon age spectrum of the fluvial deposits(with age about 11.5 Ma)from Tianshui region is different from the eroded materials of West Qinling Mountains,but similar with that of the Liupan Mountains to the east,which may suggest that the Liupan Mountains have already been exhumed by11.5 Ma.展开更多
基金granted by the National Key Basic Research Program from the Chinese Ministry of Science and Technology(Grant No.2015CB856101)Foundation of Research Center for Tibetan Plateau Geology(21201010000150014-29)the China Geological Survey(No.1212011221066)
文摘Discontinuous ophiolite suites along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet representing remnants of the Neo-Tethyan oceanic lithosphere are considered to be formed between Late Jurassic and Early Cretaceous.Older ophiolite or ophiolitic mélange(e.g.Triassic)to reveal the initial evolution the Neo-Tethyan ocean within the YZSZ have rarely been documented so far.The western YZSZ extending from the Saga to Ladakh area are composed of the northern ophiolitic subbelt,the Zhongba terrane and the southern ophiolitic sub-belt.In this study,we document structural,petrological and geochronological data of mafic intrusions from the Mayoumu massif in the southern ophiolitic sub-belt of the western YZSZ.Two lithos-tectonic sub-units,the southern ophiolitic complex and the northern ophiolitic mélange,are recognized in the Mayoumu massif in terms of structural pattern and petrology.LA-ICP-MS zircon U-Pb dating of gabbro from the ophiolitic mélange yields an age of 243±1 Ma with zirconεHf(t)values of+7.9 to+13.2.Two samples of diabase samples from the ophiolite yield ages of 131±1 Ma and 124±1 Ma with zirconεHf(t)values ranging from+10.8 to+15.0 and+12.3 to+15.4,respectively.Geochemically,rare earth elements(REEs)patterns show that these mafic intrusions are similar to those of the normal mid-ocean-ridge basalt(N-MORB).Enrichment of fluidmobile elements(e.g.Rb and Ba)and depletion of Nb,and Ta suggest that these intrusions were possibly originated from melting of a depleted mantle source influenced by subducted slab.Our data strongly confirms that the Neo-Tethyan ocean between the Lhasa terrane and Gondwana had been existed since the Middle Triassic at least.The ages of the two diabases from the ophiolitic complex reveal that mafic magma activities within the Neo-Tethyan ocean could be as a continuing process during 120–130 Ma.Emplacement and preservation of older ophiolitic recorder during evolution of the Neo-Tethyan Ocean may be closely related to the occurrence of the Zhongba micro-terrane within the western YZSZ.
基金supported by the National Natural Science Foundation of China (GrantNos. 40821061,90914007,40576030 and 90714010)the State Administration of Foreign Expert Affairs of China (Grant No. B07039)the Special Fund for Basic Scientific Research of Central Colleges,China University of Geosciences
文摘A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16 32 μm.This was accomplished by introducing N 2 into ICP to increase the sensitivity.The obtained U-Pb ages for zircon standards GJ-1,TEMORA and SK10-2 are consistent with the preferred values within about 1% uncertainty (2σ) by simple external calibration against zircon standard 91500.Different data reduction softwares could yield different uncertainties for calculation of U-Pb ages.The commercially available program GLITTER4.4 could apply an improper uncertainty calculation strategy,but it may yield artificial high precisions for single analyses.Our trace element analyses indicate that Si is not an ideal internal standard for zircon when calibrated against the NIST glasses.Calibration against the NIST glasses using Si as an internal standard,a systematic deviation of 10% 30% was found for most trace elements including Zr.However,the trace element compositions of zircon can be accurately measured by calibration against multiple reference materials with natural compositions (e.g.,BCR-2G,BHVO-2G and BIR-1G),or calibration against NIST SRM 610 and using Zr as an internal standard.Analyses of two pieces of GJ-1 demonstrate that it is relatively homogenous for most trace elements (except for Ti).
基金supported by the National Natural Science Foundation of China(Grant Nos.41203027 and 41473031)the State Administration of Foreign Expert Affairs of China(Grant No.B07039)the Special Fund for Basic Scientific Research of Central Colleges,China University of Geosciences(Wuhan)(Grant No.CUGL140403)
文摘In this study, the Pb/U fractionation between zircon and uraninite during femtosecond Laser Ablation Inductively Coupled Plasma Mass Spectrometry （fs-LA-ICP-MS） analysis was studied in detail. The results show significant Pb/U fractionation between zircon and uraninite during fs-LA-ICP-MS analysis that when calibrated against the zircon standard M257, the obtained U-Pb age of the Chinese national uraninite standard GBW04420 is 17% older than the recommended value. Thus, the accurate in-situ U-Pb dating of uraninite by LA-ICP-MS requires matrix-matched external standards for calibration. Uraninite in thin sections of two U-mineralized leucogranite from the Gaudeanmus in Namibia was analyzed by a fs-LA-ICP-MS equipped with a Signal Smooth Device （SSD）, using laser spot and frequency of 10 μm and 1 Hz, respectively. When calibrated using GBW04420 as the external standard, two samples give weighted mean 2066pb/238U ages of 504±3 Ma （2σ, n=21） and 503±3 Ma （2σ, n=22）, and only one of two samples yields a concordia U-Pb age of 507±1 Ma （2or, n=21）. These results are consistent with ID-TIMS U-Pb ages of 509±1 and 508±12 Ma and are also indistinguishable from zircon U-Pb upper intercept ages of 506±33 Ma （2σ, n=29） and 501±51 Ma （2σ, n=29）. The present study shows that in-situ U-Pb dating of uraninite can deliver more reliable formation ages of the deposit than dating coeval high-U zircon because the latter commonly suffer significant Pb loss after formation. Our results confirm that GBW04420 is an ideal matrix matching standard for in-situ U-Pb dating of uraninite.
基金Supported by the Ministry of Science and Technology of China (Grant No. 2003CB716501)the National Natural Science Foundation of China (Grant Nos. 40521001 and 40473013)+2 种基金the Program for New Century Excellent Talents in Uni-versity (Grant No. NCET-05-0664)the State Key Laboratory of GPMR, China University of Geosciences (Grant No. GPMR0511)the State Key Laboratory of Continental Dynamics, Northwest University, China
文摘Trace element compositions of garnet, omphacite and apatite in ultrahigh-pressure eclogites from the main hole of the Chinese Continental Scientific Drilling (CCSD) project were in situ analyzed by the LA-ICP-MS method. Although both garnet and omphacite have homogeneous major element composi-tions, their trace elements show zonations from core to rim in rare earth elements. In particular, middle rare earth elements in the garnet, heavy rare earth elements in the apatite and all rare earth elements in the omphacite increase from core to rim, respectively. Based on dependence of partition coefficients on temperature and pressure in these minerals, we suggest that the trace elemental zonations in these minerals may record a short-lived heating event during exhumation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41372112, 91028009)the National Key Projects of Oil and Gas (Grant No. 2011ZX05025-002-02)+1 种基金the Programme of Introducing Talents of Discipline to Universities (Grant No. B14031)the Open Fund of the Key Laboratory of Marine Geology and Environment, China Academy of Sciences (Grant No. MGE2013KG02)
文摘Deep-water canyon systems can provide important sandstone reservoirs for deep-water oil and gas exploration in the South China Sea;however,the sedimentary provenance of the Central Canyon in the Qiongdongnan Basin remains controversial.In this work,detrital zircon grains from three drilling sandstones in the Upper Miocene Huangliu Formation in the western part of the Central Canyon were analysed by LA-ICP-MS for U-Pb ages,in order to constrain their provenance.One hundred and ninety-one zircon grains yield concordant U-Pb ages ranging from 28.6 to 3285 Ma.Most of them show oscillatory or linear zoning in CL-images and high Th/U ratios(>0.1),suggesting that they are magmatic zircons.Three major age clusters at about30 Ma(N=6),220–270 Ma(N=29),and 420–440 Ma(N=13),and five minor age clusters at 70–110 Ma(N=7),150–170 Ma(N=4),800–850 Ma(N=11),1800–2000 Ma(N=16),and 2400–2600 Ma(N=7),can be identified in the age spectrum,which are very similar to those of the Upper Miocene sandstones and modern river sands in the Red River area,but different from those of other nearby regions(e.g.,Hainan Island,the Pearl River area,and the Mekong River area)in Southeast Asia.The major age peak at about 30 Ma in our samples is consistent with the timing of tectonothermal events in the Red River Fault Zone.Therefore,we suggest that the provenance of the western part of the Central Canyon,in the Qiongdongnan Basin,was fed dominantly by the Paleo-Red River system during the Late Miocene.
基金supported by National Natural Science Foundation of China(Grant No.41002051)
文摘The Neogene sediments of Gansu Group from northwestern China contain eolian and fluvial deposits.The origins of these sediments are very important for exploring the onset of Asian inland aridification,the pattern of paleo-atmospheric circulation,and the regional tectonics and geomorphic evolution during the Miocene.Here we present detrital-zircon age spectra of typical eolian and fluvial deposits from highlands and subsidence basin,and compare them with those of surrounding eroded mountain(such as the West Qinling Mountains and Liupan Mountains)materials and Quaternary loess derived from the Asian inlands.The results reveal that(1)the detrital-zircon age spectrum of the Miocene eolian sample is remarkably different from the eroded materials of the West Qinling Mountains and the Miocene fluvial deposits from Tianshui region,but very similar to the Quaternary loess deposits.This indicates that the provenance of Miocene eolian sediments is similar with the Quaternary loess,and thus further confirms the previous conclusions that the distribution of Asian arid lands and the pattern of atmospheric circulation during the Miocene are broadly similar with the Quaternary.(2)The detrital-zircon age spectrum of the fluvial deposits(with age about 11.5 Ma)from Tianshui region is different from the eroded materials of West Qinling Mountains,but similar with that of the Liupan Mountains to the east,which may suggest that the Liupan Mountains have already been exhumed by11.5 Ma.
