Re-Os同位素对峨眉山大火成岩省成因制约的探讨

峨眉山大火成岩省（ELIP）主要由玄武岩、玄武质火山碎屑岩及少量的苦橄岩（包括越南的科马提岩）、长英质岩石以及层状岩体和岩墙组成,其物质来源直接关系到其成因是否与地幔柱活动有关。Re-Os同位素体系是地核、地幔和地壳物质的最佳示踪剂。前人对ELIP内的Re-Os同位素研究表明,低Ti玄武岩的Os含量为0．006×10^-9-0．40010^-9,^187Os／^188Os初始值为0．1371～1．403,并提出其与地幔柱活动有关;而高Ti玄武岩的Os含量为0．00410^-9～0．56010^-9,^187Os／^188Os初始值为0．1271～5．19,认为起源于大陆岩石圈地幔或地幔柱上升过程中受到大量岩石圈地幔“混染”（xu JF et al．,2007）;科马提岩的0s含量为1．2410^-9～7．0010^-9,^187Os／^188Os初始值为0．1251～0．1261,苦橄岩的Os含量为0．3210^-9～2．32910^-9,^187Os／^188Os初始值为0．1233～0．1266,指示苦橄岩和科马提岩均来自亏损地幔源区（Hanski et al．,2004;陈雷等,2007）。本文利用Os含量最低、^187Os／^188Os最高的高Ti玄武岩作为地壳端员,用铁质陨石、原始上地幔（PUM）和亏损地幔（DMM）作为地核和各种地幔端员,分别做二元混合计算,结果显示绝大多数玄武岩和所有苦橄岩及科马提岩均落在地壳和DMM混合曲线附近,并且邻区特提斯洋地幔岩与DMM具有相近的Os含量和^187Os／^188Os组成,据此推测峨眉山火成岩的形成与特提斯洋的活动有关,主要受控于地壳和亏损地幔的相互作用。     

新疆叶尔羌河流域地下水同位素特征及其补给来源分析

笔者以新疆叶尔羌河流域为例,在研究区水文地质调查的基础上,根据不同区域、不同深度D、~(18)O和T值的变化分析地下水补给来源.解决了传统研究方法很难解决的问题.为干旱地区地下水起源及空间分布规律研究提供了新思路。研究结果表明:(1)研究区地下水不是来自大气降水的直接入渗,而是地表水渗漏补给。(2)流域分为两个独立的地下水循环系统,分别接受叶尔羌河与提孜那甫河河水补给。(3)潜水和承压水的起源相同,属统一的地下水系统。(4)地下水径流表现为倾斜平原区径流强烈,地下水以水平运动为主;细土平原区地下水径流迟缓,地下水以垂直蒸发运动为主.径流方向与地表水流向密切相关。     

采用碳氮稳定同位素技术对黄海中南部鳗鱼食性的研究

根据2005年4～5月在黄海和长江口海域进行的春季底拖网调查，应用稳定同位素方法研究了黄海中南部鯷鱼（Engraulis　japonicus）及其可能摄食饵料的碳氮稳定同位素比值，结果表明：（1）黄海中南部鯷鱼的食物组成为不同粒径的浮游动物、太平洋磷虾（Euphausia pacifuca）和仔稚鱼，其中以粒径为500-900μm的浮游动物为主，贡献比例占61％～84％；仔稚鱼贡献比例占16％～21％，较传统胃含物方法分析的结果小；（2）黄海中部海域鯷鱼的碳氮稳定同位素比值平均值较南部海域高，原因可能与各海域的能量来源不同或存在微食物环有关，也可能与不同海域鯷鱼的能量转换途径不一样，即与食物链长短不一有关．     

钙质成岩作用对有孔虫氧同位素的影响

通过对南海北部ODPl84航次1148站井深477m之下深海相渐新世浮游有孔虫Globoquadrina压扁壳、次生方解石和充填壳的氧同位素对比，定量分析了钙质成岩作用对壳体氧同位素的影响，结果发现，受成岩作用影响，1148站浮游有孔虫氧同位素显著变轻，这种变化趋势与低纬度开放性大洋明显不同。其原因可能与南海海盆扩张早期，大量陆源物质从较窄陆架可以直接沉积到海底，由于陆源物质氧同位素相对偏负，当与海洋沉积物混合后，引起本区沉积物孔隙水氧离子浓度变轻。而扩张初始，高的沉积速率可能使钙质壳体被快速封存在一个相对孤立的系统中，造成孔隙水离子成为影响壳体氧同位素变化的主要因素。当氧同位素相对较重的有孔虫壳体溶解和重结晶并与孔隙水离子发生交换时，引起壳体δ^18O负向偏移。     

中太平洋铁锰结壳铅同位素研究

已有研究表明大洋中溶解的铅(Pb)来源于陆源物质，但是，对Pb进入大洋的途径争议很大。为此分析了取自中太平洋两块铁锰结壳样品的Pb同位素组成，获得了整个新生代的中太平洋Pb同位素演化历史。结果表明这两块结壳的Pb同位素随时间的演化曲线与中北太平洋沉积物岩心LL44-GPC3中风成碎屑的Pb同位素演化曲线相似。证实该区深水中的天然溶解铅主要来自风成粉尘，并且50Ma之前中太平洋中溶解Pb同位素组成主要取决于源自美洲的风成粉尘的输入，40Ma之后主要取决于源自亚洲的风成粉尘的输入。     

九龙江河口区水体中的226Ra和228Ra

用ＭｎＯ２－纤维富集大体积水样中的Ｒａ同位素，并用直接射气法测定２２６Ｒａ和２２８Ａｃ的β计数法测定２２８Ｒａ的方法，研究了九龙江河口区２２６Ｒａ，２２８Ｒａ的行为，结果表明：在该河口区２２６Ｒａ，２２８Ｒａ均呈非保守行为，２２６Ｒａ，２２８Ｒａ的最高值分别在盐度为１９和９处测得。２２８Ｒａ／２２６Ｒａ）Ａ．Ｒ．值在盐度小于１９的区域约为３左右。与世界其他河口区相比，九龙江河口区的２２６Ｒａ，２２     

Carbon Isotope Geochemistry of the Orinoco Basin

Stable carbon isotope ratios have been used to study the sources of particulate organic carbon (POC) and total dissolved inorganic carbon in the Orinoco Basin. The isotopic composition of total dissolved inorganic carbon shows a range of from -8·1 to -23·0 ppt, an indication of dominance of biological processes. The isotopic composition of POC exhibits a range of from -24·1 to -34·6 ppt with little seasonal variation. The isotopic evidence indicates that the POC is predominantly of terrestrial origin rather than a result of in situ planktonic production. The similarity of isotopic composition of POC and coastal sediments suggests that riverine organic detritus has been transported 30-50 km offshore in a direction parallel to the Orinoco river channel.     

Upstream dams and downstream clams: growth rates of bivalve mollusks unveil impact of river management on estuarine ecosystems (Colorado River Delta, Mexico)

We studied how the extensive diversion of Colorado River water, induced by dams and agricultural activities of the last 70 years, affected the growth rates of two abundant bivalve mollusk species (Chione cortezi and Chione fluctifraga) in the northern Gulf of California. Shells alive on the delta today (‘Post-dam’ shells) grow 5.8–27.9% faster than shells alive prior to the construction of dams (‘Pre-dam’ shells). This increase in annual shell production is linked to the currently sharply reduced freshwater influx to the Colorado River estuary. Before the upstream river management, lower salinity retarded growth rates in these bivalves. Intra-annual growth rates were 50% lower during spring and early summer, when river flow was at its maximum. Growth rates in Chione today are largely controlled by temperature and nutrients; prior to the construction of dams and the diversion of the Colorado River flow, seasonal changes in salinity played an important role in regulating calcification rates.Our study employs sclerochronological (growth increment analysis) and geochemical techniques to assess the impact of reduced freshwater influx on bivalve growth rates in the Colorado River estuary. A combination of both techniques provides an excellent tool to evaluate the impact of river management in areas where no pre-impact studies were made.     

Deposition Rates of Terrestrial and Marine Organic Carbon in the Osaka Bay, Seto Inland Sea, Japan, Determined Using Carbon and Nitrogen Stable Isotope Ratios in the Sediment

Carbon and nitrogen stable isotope ratios (¹³C and ¹⁵N) of surface sediments were measured within Osaka Bay, in the Seto Inland Sea in Japan, in order to better understand the sedimentation processes operating on both terrestrial and marine organic matter in the Bay. The ¹³C and ¹⁵N of surface sediments in the estuary of the Yodo River were less than –23 and 5 respectively, but increased in the area up to about 10 km from the river mouth. At greater distances they became constant (giving ¹³C of about –20 and ¹⁵N about 6). It can be concluded that large amounts of terrestrial organic matter exist near the mouth of the Yodo River. Stable isotope ratios in the estuary of the Yodo River within 10 km of the river mouth were useful indicators allowing study of the movement of terrestrial organic matter. Deposition rates for total organic carbon (TOC) and total nitrogen (TN) over the whole of the Bay were estimated to be 63,100 ton C/year and 7,590 ton N/year, respectively. The deposition rate of terrestrial organic carbon was estimated to be 13,200 (range 2,000–21,500) ton C/year for the whole of Osaka Bay, and terrestrial organic carbon was estimated to be about 21% (range 3–34) of the TOC deposition rate. The ratio of the deposition rate of terrestrial organic carbon to the rate inflow of riverine TOC and particulate organic carbon (POC) were estimated to be 19% (range 3–31) and 76% (range 12–100), respectively.     

Seasonal and annual variations of marine sinking particulate flux during 1993~1996 in the central South China Sea

A total of 67 samples from the upper and lower sediment traps in the central South China Sea were analyzed, which were collected during 1993~1996. It is indicated that the distribution of stable isotope values, surface primary productivity, fluxes of total particulate matter, carbonate, biogenic opal, organic carbon, planktonic foraminiferal species and their total amount exhibit obviously seasonal and annual fluctuations. High values of the fluxes occurred in the prevailing periods of the northeastern and southwestern monsoons, and the low values occurred during the periods between the two monsoons. The fluxes of some planktonic foraminiferal species (Globigerinoides sacculifer, G. ruber, Globigerinita glutinata, Neogloboquadrina dutertrei) and their percentages also exhibit two prominent peaks during the prevailing periods of the northeastern and southwestern monsoons respectively, while those of Globigerina bulloides, Globorotalia menardii and Pulleniatina obliquiloculata only exhibit one peak in the prevailing periods of the northeastern monsoon. In addition, fluxes and percentages of Globigerinoides sacculifer and Globorotalia menardii as well as the fluxes of carbonate and total amount of planktonic foraminifera decrease gradually from 1993 to 1996, and those of Globigerina bulloides, Globigerinita glutinata and biogenic opal increase gradually from 1993 to 1996. The fluxes of carbonate and organic carbon in the upper trap are higher than those in the lower one. The study indicates that the seasonal and annual variations of the sediment fluxes and planktonic foraminiferal species are mainly controlled by the changes of surface primary productivity and hydrological conditions related to the East Asian monsoon. The lower carbonate and organic carbon fluxes in the lower trap are related to the dissolution.