青藏高原北缘山脉隆升时限的同位素证据

青藏高原北缘江尕勒萨依地区新生代地层中自生矿物的O和C同位素测试结果显示,δ18O和δ13C在渐新世早期和中新世早期都出现急剧的变化。沉积学特征也表明中新世早期新生代沉积物质粒度快速变大,而上新世至早第四纪沉积速率急剧加大。由此推断,青藏高原北缘山脉最早期的隆升开始于渐新世的早期;并在中新世早期出现过山脉的快速隆升;而上新世至第四纪早期山脉的隆升最为强烈。

豫西祁雨沟金矿床成矿流体岩浆来源的流体包裹体和稳定同位素证据(英文)

Gold ores of the Qiyugou deposit in the easternpart of the Xiong’ershan region are hosted in brecciapipes within a Mesozoic granitic porphyry.Threestages of alteration-hydrothermal activity are recog-nized within the Qiyugou breccias.

软流圈的贯入和弧后拉张:来自日本东北部的同位素证据

从日本弧东北部的弧后一侧的第三纪火山岩中测定了 Nd 和 Sr 的同位素组份。在整个时期内 Sr 同位素由富集状态特征^(87)Sr/^(86)Sr=0.705437)到富集贫化状态^(87)Sr/^(86)Sr=0.70270)的线性趋势。Nd 同位素以互相消长的形式,从低值(∈Nd=-0.80)开始然后随年代的减少而渐增。Nd 和 Sr 从富集到贫化的同位素变化与日本海在15百万年前的张开是同时期的。这种相同现象表明:日本海张开是由软流圈贯入引起的。在张开期前,地幔楔是由双层结构组成的:即陆下岩石圈和下伏的软流圈。这一阶段的火山岩的特征是富集同位素的状态,此火山岩系来自具有较大比例陆下岩石圈的物源。弧后一侧的陆下岩石圈因同位素贫化的软流圈贯入而变薄,它加速了在弧后一侧地幔楔内 MORB(大洋中脊玄武岩)物源的长大,并形成了张开后期 Nd 和 Sr 同位素呈贫化状态的岩浆的生成。

吐哈盆地煤成油的同位素地球化学证据

分析了吐哈盆地原油和下侏罗统煤系源岩全烃、族组分和正构烷烃分子碳同位素 ,并与国内外已知煤成油进行了对比研究 ,旨在为吐哈盆地煤成油提供同位素地球化学证据。研究表明 :吐哈盆地原油 δ13C分布于 - 2 5.1‰～ - 2 7.8‰之间 ,平均值 - 2 6.6‰ ( 4 7) ;与中下侏罗统煤系源岩氯仿沥青“A”δ13C分布范围和平均值基本一致 ;与国内外已知煤成油 δ13C可以对比 ;原油 δ13C饱 分布于 - 2 5.2‰～ - 2 8.2‰之间 ,平均值 - 2 6.9‰ ( 2 8) ;δ13C芳 位于 - 2 4 .7‰～ - 2 7.1‰范围 ,平均值在- 2 5.9‰ ( 2 7) ;δ13C非 的分布范围为 - 2 5.1‰～ - 2 7.3‰ ,平均值 - 2 6.3‰ ( 2 6) ;δ13C沥 分布在- 2 5.2‰～ - 2 8.1‰范围 ,平均值 - 2 6.9‰ ( 2 1) ;与氯仿沥青“A”族组分 δ13C的分布范围与平均值基本相似 ;与我国已知煤成油 δ13C饱 和 δ13C芳 的分布范围和平均值也类似 ;原油正构烷烃分子碳同位素具有随碳数增大而变轻的特征 ;C7～ C2 7正构烷烃δ13C大致分布于 - 2 2‰至 - 32‰之间 ;氯仿沥青“A”正构烷烃分子碳同位素基本落在原油正构烷烃分子碳同位素的分布范围内 ;与我国已知煤成油类似 ,因此 。

Genesis of the Nanyangtian scheelite deposit in southeastern Yunnan Province,China: evidence from mineral chemistry,fluid inclusions,and C–O isotopes

The Nanyangtian skarn-type scheelite deposit is an important part of the Laojunshan W-Sn polymetallic metallogenic region in southeastern Yunnan Province, China. The deposit comprises multiple scheelite ore bodies; multilayer skarn-type scheelite ore bodies are dominant, with a small amount of quartz vein-type ore bodies. Skarn minerals include diopside, hedenbergite, grossular, and epidote. Three mineralization stages exist： skarn, quartz- scheelite, and calcite. The homogenization temperatures of fluid inclusions in hydrothermal minerals that formed in different paragenetic phases were measured as follows： 221-423 ℃ （early skarn stage）, 177-260 ℃ （quartz- scheelite stage）, and 173-227 ℃ （late calcite stage）. The measured salinity of fluid inclusions ranged from 0.18% to 16.34% NaCleqv （skarn stage）, 0.35%-7.17% NaCleqv （quartz-scheelite stage）, and 0.35%-2.24% NaCleqv （late calcite vein stage）. Laser Raman spectroscopic studies on fluid inclusions in the three stages showed H2O as the main component, with N2 present in minor amounts. Minor amounts of CH4 were found in the quartz-scheelite stage. It was observed that the homogenization temperature gradu- ally reduced from the early to the late mineralization stages; moreover, δ^13CI, DB values for ore-bearing skarn in the mineralization period ranged from - 5.7%0 to - 6.9‰ and the corresponding δ^18OsMow values ranged from 5.8%0 to 9.1‰, implying that the ore-forming fluid was mainly sourced from magmatic water with a minor amount of meteoric water. Collectively, the evidence indicates thatthe formation of the Nanyangtian deposit is related to Laojunshan granitic magmatism.

Sedimentary Records of Mangrove Evolution During the Past one Hundred Years Based on Stable Carbon Isotope and Pollen Evidences in Maowei, SW China

Mangroves accumulate sedimentary sequences, where cores can provide historical records of mangrove evolution with past climate change and human activity. The study traced the history of mangrove evolution during the past one hundred years in a mangrove swamp of Maowei Sea, SW China. The sedimentation rates(0.38-0.95 cm yr^(-1)) were calculated on the basis of ln(^(210)Pb_(xs)/Al) and mass depth in the core sediments. Chemical tracers, such as δ^(13)C_(org) and C:N values, were utilized to trace the contribution of mangrove-derived organic matter using a ternary mixing model. Because of potential diagenetic alteration and / or overlap in the isotopic signatures of different components, simultaneous use of mangrove pollen diagrams can help to supplement some of these limitations. Combined with mangrove pollen, mangrove evolution was reconstructed and could be divided into three stages: flourishment(1886-1905 AD), slight degradation(1905-1949 AD) and rapid degradation period(1949-2007 AD), which was consistent with previous reports. The reclamation of mangrove swamps to shrimp ponds was the major reason for rapid degradation of mangrove ecosystems in recent years, rather than climate change in the region.

Trophic ecology of small yellow croaker (Larimichthys polyactis Bleeker): stable carbon and nitrogen isotope evidence

The trophic ecology of the small yellow croaker （Larimichthys polyactis） was studied using stable isotope analyses. Samples were collected from July to September 2009 and 34 individuals from eight sites were examined for stable carbon and nitrogen isotopes. Stable carbon isotope ratios （~3C） ranged from -20.67 to -15.43, while stable nitrogen isotope ratios （~SN） ranged 9.18-12.23. The relationship between fi^3C and ~SN suggested high resource partitioning in the sampling area. Significant differences in stable isotope values among the eight sampling sites may be linked to environmental diversities involving various physical processes （such as ocean current, wind and tide） and different carbon sources. Furthermore, the stable isotope ratios may also explain the ontogenetic variability in diet and feeding, because δ13C and δ15N varied significantly with increasing body size. The findings are consistent with other studies on diet analyses in small yellow croaker. It was also demonstrated that stable isotope analysis could be used to estimate the trophic characters of small yellow croaker in feeding patterns and migrating habits.

The Moon

Recent geochemical and geophysical data from the Moon enable a revision of earlier interpretations regarding lunar origin, structure and bulk composition. Earth and Moon show many similarities among their isotopic compositions, but they have evolved in totally dissimilar ways, probably related to the deficiency of water and volatile elements in the Moon as well as the vast differences in size and internal pressure. Some global geochemical differences from the Earth such as volatile depletion based on K/U ratios have been established. However, all current lunar samples come from differentiated regions, making the establishment of a bulk composition more reliant on bulk geophysical properties or isotopic similarities; it remains unclear how the latter arose or relate to whole Moon composition. The lack of fractionation effects among the refractory and super-refractory elements indicates that the proto-lunar material seems unlikely to have been vaporized while the presence of volatile elements may place lower limits on proto-lunar temperatures. The apparent lack of geochemical evidence of an impacting body enables other possible impactors, such as comets, to be considered. Although the origin of the Moon remains currently unknown, it is generally believed that the Moon originated as the result of a giant impact on the Earth.

In situ SIMS oxygen isotope analyses: Evidence for the formation of aluminum-rich chondrules from ordinary chondrites

Aluminum-rich chondrules （ARCs）, which share mineralogic and chemical properties with both Ca, Al-rich inclusions （CAIs） and ferromagnesian chondrules, play an important role in revealing their temporal and petrogenetic relationships. In this work, seven ARCs were found in three ordinary chondrites GRV 022410 （H4）, GRV 052722 （H3.7） and Julesburg （L3.6）. They contain bulk Al2O3 - 17%-33% and exhibit igneous textures composed of olivine, high- and low-Ca pyroxene, plagioclase, spinel and glass. In situ SIMS analyses show that ARCs have oxygen isotopic compositions （δ18O=-6.1‰-7.1‰; δ17O= -4.5‰-5.1‰） close to ferromagnesian chondrules but far more depleted in 160 than CAIs （δ18O=-40‰; δ17O=-40‰）. Most ARCs plot close to the terrestrial mass fractionation （TF） line, and a few between the TF and carbonaceous chondrite anhydrous mixing （CCAM） lines. Plagioclase, nepheline and glass suffered O-isotopic exchanges during the metamorphism processes in the parent body. Spinel, olivine and pyroxene represent the primary O-isotopic compositions of ARCs, and define a fitted line with a slope of- 0.7±0.1. Compared with the results of previous studies, shallower slope as well as more depleted 160 compositions further demonstrates that ARCs in ordinary chondrites are not a simple mixing product of ferromagnesian chondrules and CAIs. Instead, they probably experienced higher-degree oxygen isotope exchange with a δ6O-poor nebular gas reservoir during multiple melting episodes.

Petrogenesis of early Yanshanian highly evolved granites in the Longyuanba area,southern Jiangxi Province:Evidence from zircon U-Pb dating,Hf-O isotope and whole-rock geochemistry

Early Yanshanian(Jurassic) granitoids are widespread in the Nanling Range,South China.Whereas large granitic batholiths commonly crop out in the center of the Nanling Range(corresponding geographically to the central and northern parts of Guangdong Province),many small stocks occur in the southern part of Jiangxi Province.Most of the small stocks are associated closely with economically significant rare-metal deposits(W,Sn,Nb,Ta).Here we report the results for biotite granites and two-mica granites from three Yanshanian stocks of the Longyuanba complex.LA-ICPMS U-Pb dating of zircon yields an age of 156.1±2.1 Ma for Xiaomubei biotite granite,and U-Pb zircon dating using SIMS yields an age of 156.7±1.2 Ma for Longyuanba-Chengjiang biotite granite and 156.4±1.3 Ma for Jiangtoudong two-mica granite.Biotite granites are silica-rich(SiO 2 =70%-79%),potassic(K 2 O/Na 2 O>1.9),and peraluminous(ASI=1.05-1.33).Associated samples are invariably enriched in Rb,Th,Pb and LREE,yet depleted in Ba,Nb,Sr,P and Ti,and their REE pattern shows a large fractionation between LREE and HREE((La/Yb) N =10.7-13.5) and a pronounced Eu negative anomaly(δEu=0.28-0.41).Two-mica granite samples are also silica-rich(SiO 2 =75%-79%),potassic(K 2 O/Na 2 O>1.2),and peraluminous(ASI=1.09-1.17).However,in contrast to the biotite granites,they are more enriched in Rb,Th,Pb and extremely depleted in Ba,Nb,Sr,P and Ti,and exhibit nearly flat((La/Yb) N =0.75-1.08) chondrite-normalized REE patterns characterized by strong Eu depletion(δEu=0.02-0.04) and clear tetrad effect(TE 1.3 =1.10-1.14).Biotite granites and two-mica granties have comparable Nd isotopic signatures,and their εNd(t) are concentrated in the 13.0 to 9.6 and 11.5 to 7.7 respectively.Their zircon Hf-O isotopes of both also show similarity(biotite granites:εHf(t)= 10.8-7.9,δ 18 O=7.98‰-8.89‰ and εHf(t)= 13.8 to 9.1,δ 18 O=8.31‰-10.08‰;two-mica granites:εHf(t)= 11.3 to 8.0,δ 18 O=7.91‰-9.77‰).The results show that both biotite and two-mica granites were derived mainly from sedimentary source rocks with a minor contribution from mantle-derived materials.In spite of some S-type characteristics,the biotite granites were formed by fractional crystallization of I-type magma and assimilation of peraluminous sedimentary rocks during their ascent to the surface.Therefore,they belong to highly fractionated I-type granites.Two-mica granites exhibit a tetrad effect in their REE patterns,but share the same isotopic features with the biotite granites,suggesting that they are highly fractionated I-type granites as well.Their Lanthanide tetrad effects may be attributed to the hydrothermal alteration by magmatic fluids that have suffered degassing at late stages.Granitic magmas undergoing fractional crystallization and wall-rock assilimation can generate highly evolved granites with no REE tetrad effect in the uni-phase system.However,in the late-stage of magmatic evolution in the multi-phase system(i.e.,magmatic-hydrothermal system),these magmas also can lead to the highly evolved granites exhibiting mew-shaped REE pattern characterized by tetrad effect as the consequence of melt-fluid and fluid-vapor fractionation,and the resultant autometasomatism.We thus suggest that the REE pattern exhibiting tetrad effect feature is an important indicator of rare metal mineralization in the early Yanshanian time in southern China,implying the metamorphism of the ore fluid.

Detection and indication of 1,3,4-C27-29 triol in the sediment of northern South China Sea

After the detection of the 1,20,21-C29 long-chain triol in some sediments and freshwater pteridophytes, in this study a new homologous long-chain triol, 1,3,4-C27-29, is detected for the first time in the Site4B core sediment in the northern South China Sea. The hydroxyl location and length of the carbon chain of this newly discovered triol differ from those of 1,20,21-C29 triol. The test results of its molecular distribution and individual carbon isotope reveal that 1,3,4-C29triol has a good correlation with n-C26-30 even carbon-numbered long-chain fatty alcohols, with R2 （n=68） values of 0.905, 0.929 and 0.903, respectively, and its carbon isotope composition, at -32.3%o_1.9%o, is similar to that of rt-C26.30, at -29.13%o^0.87%o, -32.98%o^1.28%o, and -32.98%o^1.28%o. 1,3,4-C29 triol from the Site4B core sediment and terrigenous long-chain fatty alcohol （n-C26.34） show highly consistent distribution trends in the entire section; thus, the former could serve as a proxy indicator of the terrigenous input. Considering that the 1,20,21-C29 triol in previous research belongs to Azolla, which are fresh water pteridophytes, the 1,3,4-C27-29 triol identified in this study might have similar biogenetic derivation. Thus, determination of its biogenic area and growing environment could provide potential organic geochemical evidence supporting the terrigenous input and source in the northern South China Sea.

Paleotemperature variations at Lake Caohai, southwestern China, during the past 500 years:Evidence from combined δ^(18)O analysis of cellulose and carbonates

The oxygen isotopic values of aquatic plant cellulose and carbonates in Lake Caohai sediments were measured using a continuous flow isotopic ratio mass spectrometer(CF-IRMS).Because of predictable oxygen isotopic fractionation between cellulose and its source water,the oxygen isotopic composition of paleo-lake water has been established quantitatively.Combined oxygen isotopic values of cellulose and carbonates were used in the‘Craig’equation to determine paleotemperatures and their variation in the lake during the past 500 years.Results show that the paleotemperature trend correlates well with meteorological records from Weining.There are four notable cold intervals at Lake Caohai over the past 500 years,namely 1540–1570AD,1670–1715AD,1780–1870AD and 1900–1930AD,and the former three cold intervals have been observed in the conventional Little Ice Age(LIA).These cold periods at Lake Caohai correspond well with those recorded from tree ring,peat,and ice core data from adjacent regions,particularly temperature those inferred fromδ18O of peat cellulose from Hongyuan Southwestern China.The trend in paleotemperature variations at Lake Caohai are also consistent with both the change of Indian summer monsoon,derived fromδ18O values of a stalagmite in Dongge,and a recorded shift in solar activity.The findings of this study illustrate that coupled analysis ofδ18O values of cellulose and carbonates from lake sediments may be used as a paleotemperature proxy.These results also provide further evidence of the existence of LIA in southwestern China.