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Indian Ocean-MORB-type isotopic signature of Yushigou ophiolite in North Qilian Mountains and its implications

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Science china Earth Sciences 2006年第6期49卷 561-572页

作者： HOU Qingye1,2. ZHAO Zhidan1,2. ZHANG Hongfei3, ZHANG Benren3 & CHEN Yuelong2.1. State key {2. of geological processes and mineral resources, china University of geosciences, Beijing 100083, china 2. School of Earth Science and mineral resources, china University of geosciences, Beijing 100083, china 3. Faculty of Earth Sciences, china University of geosciences, wuhan 430074, china State key {2. of geological processes and mineral resources China University of Geosciences Beijing China School of Earth Science and mineral resources China University of Geosciences Beijing China Faculty of Earth Sciences China University of Geosciences Wuhan China

In order to explore the disputed issue concerning the tectonic affinity ofthe ancient ocean mantle of North Qilian Mountains (NQM), geochemical and Sr, Nd, Pb isotopiccompositions of pillow basalts of the Yushigou Ophiolite (YSGO) suite from NQM have been analyzedsystematically. The pillow basalts exhibit tholeiitic characteristics, with flatchondrite-normalized REE patterns ((La/Yb)_N = 0.98—1.2.). They display no Nb, Ta, Zr, Hf negativeanomalies, and show MORB features in 2.b-Zr/4-Y and Ti/100-Zr-YX3 tectonic discrimination *** results indicate that the Yushigou ophiolite is most likely to be formed in a mid-ocean ridgeor mature back-arc basin. Their isotopic data show a relatively broad and enriched ^(87)Sr/^(86)Sr(0.70509 — 0.70700), restricted ^(143)Nd/^(144)Nd (0.512.55-0.512.78). Pb isotopes are in the rangeof ^(2.6)Pb/^(2.4)Pb (18.054-2..562., ^(2.7)Pb/^(2.4)Pb (15.537-15.743) and ^(2.8)Pb/^(2.4)Pb(38.068-38.530). These isotopic data imply that the basalts originated from the depleted mantle(DMM), with the involvement of enriched mantle components (mainly EMII). Geochemical comparisonsbetween the basalts in YSGO and the MORB-type basalts of ophiolite suites occurring in the knownancient Tethyan tectonic domain indicate that the ancient oceanic mantle represented by YSGO suiteforming in early Paleozoic in the North Qilian Moutains is very similar to the Tethyan mantle inboth trace elements and isotopic compositions. The North Qilian Mountains should be a part of theTethyan tectonic domain in early Paleozoic. This further implies that the Tethyan tectonic domaincan be deduced to early Paleozoic in the study area, which will be helpful to discussing thetectonic affinity and evolution of the North Qilian Mountains.

关键词： geochemistry, Indian Ocean-MORB-type isotopic signatures, Tethyan tectonic domain, Yushigou ophiolite, North Qilian Mountains.

Nb/Ta variations of mafic volcanics on the Archean- Proterozoic boundary: Implications for the Nb/Ta imbalance

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Science china Earth Sciences 2005年第8期48卷 1106-1119页

作者： LIU Yongsheng1,2. GAO Shan1,2. WANG Xuance1, HU Shenghong1 & WANG Jianqi2.1. State key {2. of geological processes and mineral resources, china University of geosciences, wuhan 430074, china 2. key {2. of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, china State key {2. of geological processes and mineral resources China University of Geosciences Wuhan China key laboratory of Continental Dynamics Department of Geology Northwest University Xi’an China

The HFSE and REE of the Precambrian mafic volcanics from the North china craton demonstrate obvious A(Archean)-P(Proterozoic) boundary. The Neoarchean mafic vol- canics show weak correlation between HFSE and TiO2. Their superchondritic Nb/Ta ratio (18.8±1.2. could be attributed to partial melting of mantle peridotite in the presence of garnet. Compared with Neoarchean mafic volcanics, the Paleoproterozoic ones have higher HFSE contents and lower Nb/Ta ratio (15.6±2.9). The significantly elevated HFSE and REE contents of Paleoproterozoic mafic volcanics imply metasomatic enrichment of mantle source, in which Ti-rich silicates could be present as suggested by significant positive correlations between TiO2.and HFSE. The global database of Precambrian mafic volcanics shows a similar A-P boundary. 2. Archean mafic volcanic suites yield an average Nb/Ta ratio of 17.8±1.9 higher than or close to the PM value; Proterozoic mafic volcanics from 2. suites yield an average Nb/Ta ratio of 14.7±4.1 close to the bulk continental crust (BCC) value (11―17.5). Thus, we suggest that the Nb/Ta deficit could be mainly formed in post-Archean time. Archean mafic volcanics could be one of the geochemical reservoirs complementing the low Nb/Ta of the post-Archean continental crust and DM.

关键词： Precambrian mafic volcanics, Nb/Ta deficit, Archean-Proterozoic boundary.

Multistage evolution of continental collision orogen:A case study for western Dabie orogen

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Chinese Science Bulletin 2009年第15期54卷 2568-2579页

作者： WU YuanBao State key {2. of geological processes and mineral resources, Faculty of Earth Sciences, china University of geosciences, wuhan 430074, china State key {2. of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, china State key {2. of geological processes and mineral resources Faculty of Earth Sciences China University of Geosciences Wuhan China State key {2. of Continental Dynamics Department of Geology Northwest University Xi’an China

The foramtion and evolution of collisional orogen is a prominent feature along convergent plate margins, and is generally a complex process. This article presents an integrated study of zircon genesis, U-Pb age and Lu-Hf isotope composition as well as geological characteristics for the western Dabie orogen to constrain its multi-stage evolution history. The results suggest that the formation of oceanic crust in the Huwan area was constrained at ca. 400―430 Ma, which was slightly later than the collision of the northern Qinling with the North china Block. It formed in a marginal basin in the northern margin of the Yangtze Block. The peak metamorphism of eclogite in the Huwan area occurred at ca. 310 Ma, and the timing of the initial exhumation of oceanic eclogite was about 2.0 Ma. The high to ultrahigh pressure (HP-UHP) metamorphic rocks in the Xinxian and the Hong'an metamorphic zones have the same ages and natures as those of the HP-UHP metamorphic rocks in the other Dabie-Sulu terrains, and also have experienced multi-stage exhumation, and thus can be taken as a coherent part of the Dabie-Sulu orogen. Therefore, the Qinling-Dabie-Sulu orogen is a typical multi-stage continental collision orogen, with an amalgamation process extending more than 2.0 Ma.

关键词：大别造山带大陆碰撞西部演变超高压变质岩碰撞造山带苏鲁造山带变质岩区

Geochemistry of the high-Mg andesites at Zhangwu, western Liaoning: Implication for delamination of newly formed lower crust

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Science china Earth Sciences 2007年第12期50卷 1773-1786页

作者： HUANG Hua1,GAO Shan1,2.HU ZhaoChu1,LIU XiaoMing2.& YUAN HongLing2.1 State key {2. of geological processes and mineral resources,china University of geosciences,wuhan 430074,china 2.State key {2. of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,china State key {2. of geological processes and mineral resources China University of Geosciences Wuhan China State key {2. of Continental Dynamics Department of Geology Northwest University Xi’an China

Ten volcanic samples at Zhangwu,western Liaoning Province,North china were selected for a sys-tematic geochemical,mineralogical and geochronological study,which provides an opportunity to ex-plore the interaction between the continental crust and mantle beneath the north margin of the North china *** one basalt sample(SiO2. 50.2.%),the other nine samples are andesitic with SiO2.contents ranging from 53% to 59%.They have relatively high MgO(3.4%―6.1%,Mg#=50―64) and Ni and Cr contents(Ni 2.×10?6―197×10?6,Cr 51×10?6―478×10?6).Other geochemical characteristics of Zhangwu high-Mg andesites(HMAs) include strong fractionation of light rare earth elements(LREE) from heavy rare earth elements(HREE),and Sr from Y,with La/Yb greater than 15,and high Sr/Y(34― 115).Zircons of andesite YX2.0 yield three age groups with no Precambrian age,which precludes ori-gin of the Zhangwu HMAs from the partial melting of the Precambrian *** oldest age group peaking at 2.3 Ma is interpreted to represent the collision of the Siberia block and the North china block,resulting in formation of the Central Asian orogenic belt by closure of the Mongol-Okhotsk *** intermediate age group corresponds to the basalt underplating which caused the wide-spread coeval granitoids in the North china craton with a peak 2.6Pb/2.8U age of 172.*** youngest age group gives a 2.6Pb/2.8U age of 12.±2.Ma,which is interpreted as the eruption age of the Zhangwu *** high 87Sr/86Sri(12. Ma)>0.706 and low εNd(t)= ?6.36―?13.99 of the Zhangwu HMAs are distinct from slab *** common presence of reversely zoned clinopyroxene phenocrysts in the Zhangwu HMAs argues against the origin of the Zhangwu HMAs either from melting of the water saturated mantle or melting of the lower *** light of the evidence mentioned above,the envisaged scenario for the formation of the Zhangwu HMAs is related to the basaltic underplating at the base of the crust,which led to the thickening of the lower crust and

关键词： Zhangwu HMAs, basalt underplating, newly formed lower crust, delamination, North china craton

Spatio-temporal carbon isotope variation during the Ediacaran period in South china and its impact on bio-evolution

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Science china Earth Sciences 2009年第10期52卷 1520-1528页

作者： WANG XinQiang1 & SHI XiaoYing1,2.1 School of Earth Science and mineral resources, {2. University of geosciences, Beijing 100083, {2. 2.State key laboratory of geological processes and mineral resources, Beijing 100083, {2. School of Earth Science and mineral resources China University of Geosciences Beijing China State key {2. of geological processes and mineral resources Beijing China

The Ediacaran period is characterized by the extremely negative carbon isotope anomalies and great biotic evolution in Earth history. At least four negative carbon isotope anomalies have been reported from this interval in South china so far. It is traditionally argued that the isotope variations can be used as a useful tool for global correlation of Ediacaran succession; however, more and more researches argued against this idea. We reviewed the previously published carbon isotope data in South china, and distributed the mean values of a certain time to the paleogeographic maps. The results show that the carbon isotope values (δ13C) vary greatly in different environments, but a clear tendency of becoming lighter from shallow platform to deep basin, with a maximum variation up to 1‰ Moreover, the important changes in Ediacaran biota, marked by the introducing of new taxa or ecologic groups, seemed to always postdate the negative anomalies but coincide with the positive shift. If the negative excursions represented the oxidation of a large dissolved organic carbon (DOC) reservoir in the ocean, the diverse Ediacaran organisms and the carbon isotope anomalies may suggest totally different environments: oxic and anoxic/euxinic. We also suggest that the elimination of euxinic s{2. through precipitation of pyrites is one of the important environment factors in prompting the Ediacaran bio-evolution.

关键词： Ediacaran South china carbon isotope spatio-temporal variations bio-evolution

Petrogenesis of Indosinian volcanic rocks in Songpan-Garze fold belt of the northeastern Tibetan Plateau:New evidence for lithospheric delamination

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Science china Earth Sciences 2010年第9期53卷 1316-1328页

作者： CAI HongMing1,2. ZHANG HongFei1,2. XU WangChun1,2. SHI ZhangLiang1,2.& YUAN HongLin3 1 State key {2. of geological processes and mineral resources, wuhan 430074, china 2.Faculty of Earth Sciences, china University of geosciences, wuhan 430074, china 3 State key {2. of Continental Dynamics, Northwest University, Xi’an 710069, china State key {2. of geological processes and mineral resources Wuhan China Faculty of Earth Sciences China University of Geosciences Wuhan China State key {2. of Continental Dynamics Northwest University Xi’an China

In the Songpan-Garze fold belt of the northeastern Tibetan Plateau, an Indosinian lithospheric delamination model has been proposed, based on previous investigation of widespread granitoids. However, this model lacks comparable information from volcanism in the area. During the Indosinian delamination in the Songpan-Garze fold belt, whether partial melting of litho- spheric mantle taken place is debated. This paper reports U-Pb zircon LA-ICP-MS ages, geochemical and Sr-Nd-Hf isotopic compositions from the Aba and Wasai calc-alkaline volcanic rocks in the central Songpan-Garze fold belt. Obtained magma crystallization ages are 2.0±3 Ma for the Aba andesite and 2.5±1 Ma for the Wasai andesite. These are consistent with magma crystallization ages of the late Indosinian granitoids in the Songpan-Garze fold belt that formed in a post-collisional tectonic setting. The Aba and Wasai andesites have distinct geochemical singnatures. The former has higher Al2.3, K2., Rb but lower Na2., Ba and Sr contents, suggesting differences in their magmatic evolution. The Aba andesites have ISr values of 0.7070-0.7076 and εNd(t) values of -3.9 to -5.3, and the Wasai andesites have ISr values of 0.7075-0.7077 and εNd(t) values of -3.6 to -3.9. Zircons show εHf(t) values of -3.7 to 0.3 for the Aba andesites and -2.7 to 5.5 for the Wasai andesites. Geochemical and Sr-Nd-Hf isotopic compositions indicate that fractional crystallization and crustal assimilation processes are not key roles for their magma evolution, implying that their chemical compositions are those of primary melts. We suggest that the magma of the Aba andesites originated predominantly from a crustal source, with a minor mantle-derived component. The source region of the magma was likely at the crust-mantle boundary. The magma of the Wasai andesites resulted from partial melting of lithospheric mantle, which was probably metasomatized by fluids so that it was amphibole bearing. The petrogenesis of the Aba and Wasai andesite

关键词： volcanism U-Pb dating geochemistry petrogenesis lithospheric delamination Songpan-Garze fold belt

Carbon isotope composition of the Lower Triassic marine carbonates, Lower Yangtze Region, South china

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Science china Earth Sciences 2006年第3期49卷 225-241页

作者： ZUO Jingxun1,2. TONG Jinnan3, QIU Haiou4 & ZHAO Laishi3 1. Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 2.0008, china 2. Henan Institute of geological Survey, Zhengzhou 450007, china 3. State key laboratory of geological processes and mineral resources at china University of geosciences, {12., china 4. Faculty of Material Sciences and Chemical Engineering, china University of geosciences, {12., china Nanjing Institute of Geology and Palaeontology Chinese Academy of Sciences Nanjing China Henan Institute of geological Survey Zhengzhou China State key {2. of geological processes and mineral resources at china University of geosciences Wuhan China Faculty of Material Sciences and Chemical Engineering China University of Geosciences Wuhan China

Studies on three Lower Triassic sections located on the shallow water platform, the deep water slope and in the deep water basin in the Lower Yangtze Region, South china, show the similar trend of carbon isotope evolution. Biostratigraphic correlations among the Lower Triassic sections on the basis of standard conodont zones indicate that three negative shifts occurred in the Griesbachian, the Smithian and the late Spathian stages respectively, and one distinctly positive shift occurred in the early Spathian stage. Trend of carbon isotope evolution of the Lower Triassic reflects some significant changes in the global carbon cycle. Moreover, δ 13C background values are intensively controlled by palaeogeographic environment. In general, δ 13C values from deep-water slope carbonates are lighter than those from carbonate platform and heavier than those from deep-water basin carbonates. The positive carbon isotope excursion may be induced by a significant amount of organic carbon burial in marine sediments and increase in primary productivity. The large negative carbon isotope excursions during the Early Triassic in Lower Yangtze Region are interpreted to relate to volcano eruptions based on tuffaceous claystone interlayers observed near the Permian-Triassic boundary, the Induan- Olenekian boundary and the Lower Triassic-Middle Triassic boundary.

关键词： Lower Triassic, carbon isotope compositions, palaeogeography, volcanic eruptions, Lower Yangtze Region.

Analytical method of Cr stable isotope and its application to water pollution survey

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Chinese Science Bulletin 2010年第7期55卷 664-669页

作者： GAO YongJuan 1,2.3,MA Teng 4,5,LING WenLi 1,2.LIU CunFu 4,5 & LI Li 4,5 1Faculty of Earth Science,china University of geosciences,{2.,china 2.tate key laboratory of geological processes and mineral resources,china University of geosciences,{2.,china 3 Graduate School,china University of geosciences,{2.,china 4 Biogeological and Environmental Geology laboratory of Ministry of Education(china University of geosciences) ,{2.,china 5 Sino-Hungary Joint laboratory of Environmental Sciences and Health,china University of geosciences,{2.,china Faculty of Earth Science China University of Geosciences Wuhan China State key {2. of geological processes and mineral resources China University of Geosciences Wuhan China Graduate School China University of Geosciences Wuhan China Biogeological and Environmental Geology laboratory of Ministry of Education ({2. University of geosciences) Wuhan China Sino-Hungary Joint laboratory of Environmental Sciences and Health China University of Geosciences Wuhan China

High Cr(VI) concentration is a potential serious risk to environment and ecologic ***,it is essential to effectively monitor Cr contamination in water systems and scientifically evaluate its evolution trend.A new method of in-situ tracer technique by Cr isotopic analysis for quantitatively estimating Cr-contamination and its regional evolution in natural waters as well as a case application are reported in this *** on documented literatures,an experimental procedure for chemical separation and purification of Cr in water samples and its analytical method for Cr isotopic measurement by thermal ionization mass spectrometry(TIMS) are *** samples collected around a chemical factory in Hubei Province were analyzed by this *** samples showδ53Cr values ranging from-1.7‰to 7.3‰and an elevating trend with an increasing in distance from the sampling site to pollution source.A functional correlation following Rayleigh fractionation law was established between sample'sδ53Cr value and its extent of Cr *** study suggests that Cr isotopic analysis is an effective method to reveal the spatial distribution and its evolution trend of Cr contamination in the regional water *** is thus helpful to assessing the self-purifying ability of local water system according to Cr isotopic fractionation.

关键词：铬(VI) 水污染调查稳定同位素应用同位素分析供水系统演变趋势示踪技术

Ostracod fauna across the Permian-Triassic boundary at Chongyang, Hubei Province, and its implication for the process of the mass extinction

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Science china Earth Sciences 2010年第6期53卷 810-817页

作者： LIU Hao1, WANG YongBiao1, YUAN AiHua2. YANG Hao1, SONG HaiJun1 & ZHANG SuXin2. key laboratory of Biogeology and Environmental Geology of Ministry of Education, {2., china 2.State key laboratory of geological processes and mineral resources, {2., china key laboratory of Biogeology and Environmental Geology of Ministry of Education Wuhan China State key {2. of geological processes and mineral resources Wuhan China

Thirty species of 10 ostracod genera were identified from 440 fossil specimens isolated through the hot acetolysis of the rock samples collected across the Permian-Triassic boundary at Chongyang section. Twenty species of 6 genera are found to occur in the limestone of Changxing Formation, and 11 species of 7 genera above the main faunal mass extinction horizon. The os-tracod assemblages identified at the Chongyang section are obviously different from those previously reported in the contem-poraneous microbialites in Guangxi and Chongqing regions, not only in the ostracod components but also in the abundance of filter-feeding ostracods relative to the deposit-feeding ostracods, an indicator of the oxygen level of the seawater. This spatial difference in ostracod assemblages might reflect the diversity of oceanic environmental conditions after the end-Permian mass extinction. Ostracods disappear at 2.0 cm below and near the main mass extinction horizon, and on the top of the microbialites, respectively, showing an episodic and gradual collapse process at the Chongyang section. The carbon isotope composition is found to appear at 2.0 cm below the main mass extinction horizon, indicating the initial deterioration of oceanic environment. Fluctuation of the carbon isotope composition is obviously related with the episodic evolution of ostracod species, but not with the abundance of ostracods.

关键词： ostracod microbialite Permian-Triassic mass extinction Chongyang