The evidence from inclusions in pumices for the direct degassing of volatiles from the magma to the hydrothermal fluids in the Okinawa Trough

This article presents the evidence in support of the direct magma degassing as the principal mechanism of volatiles releasing into the hydrothermal fluids in the Okinawa Trough, as contrasted to the argument for the hydrothermal stripping of volatiles from the volcanic rocks. Laser Raman microprobe and stepped-heating techniques are employed to determine the compositions and contents of the volatiles in pumices in the middle Okinawa Trough. The results show that the volatiles are similar to the gases in the hydrothermal fluids and hydrothermal minerals in composition, the mean percent content of each component and variation trend. This indicates the direct influence of magma degassing on the hydrothermal fluid. In addition, the contents of volatiles in pumices are rather low and do not support the hydrothermal stripping as the main mechanism to enrich the fluids with gases. The results are consistent with the idea that the direct magma degassing is more important than hydrothermal stripping in supplying gases to the hydrothermal fluids in the Okinawa Trough.     

东太平洋海隆热液活动区沉积岩心的地球化学研究

东太平洋隆是现代海底热液活动及热液沉积分布最为广泛的构造环境之一。本文对采自 EPR13°N 现代海底热液活动区附近的两个沉积物岩心分别进行了元素地球化学分析，并结合沉积物中有孔虫壳体对岩心进行关键层位 14C 年代学研究。目的在于通过对比距现代海底热液喷口不同距离的两岩心的地球化学特征，研究热液活动在岩心沉积物中所何存的地球化学记录，探讨海底热液活动对洋中脊附近沉积作用的贡献，以及热液活动在一定地质历史时期内的变化规律。显示，距热液喷口区相对较近的 B13－26 岩心沉积物含有丰富的热液特征组分，绝大多数微量元素和 REE 都与 Fe和Mn 成较强的正相关关系，而与 Al、Na、Ca、Mg、Ti 等元素相关性较弱或呈负相关，说明这些元素的富集机制主要是热液成因非晶质 Fe－Mn 化合物对热液及海水中元素的吸附作用。距热液喷口区相对较远的 B13－62岩心上部沉积物中元素的富集特征与 B13－26 岩心相似，但中下部沉积物中 Fe 与 Mn 无明显的相关关系，说明这些元素的富集主要受深海粘土沉积的影响，而受热液活动的影响减弱或消失。由于与海隆扩张轴距离的不同，两岩心受热液活动影响的强度不同。由海隆扩张轴向外，沉积作用受热活动的影响逐渐减弱，正常深海沉积作用逐渐加强。两个岩心沉积物地球化学上的共性是 Ca 和 Sr 都与其他元素呈现负相关关系或极微弱的正相关关系，表明生物碳酸盐沉积作用的独特性。有孔虫 14C 年龄测定结果表明，B13－26 岩心 35～250cm 段年龄十分接近，前后相差仅在几百年内。根据年龄测量中的误差范围，可以断定这段沉积物岩心是短时间内快速沉积的产物。结合热液活动特征性元素在岩心中的分布特征，判断该岩心段记录一次强烈的热液活动事件，从而形成了典型的事件沉积。在 B13－62 岩心的45～50cm 处测得有孔虫的 14C 年龄为距今 32900±530 yr。由于 14C 测年方法上的局限性，在岩心 135～140cm 处 14C 测年只能给出大于40000 yr 的结果。显然，B13－62 岩心处早期并没有受到热液活动明显的影响，沉积速率非常缓慢，只是在近期受到了热液活动的影响，形成了上部富含 Fe、Mn、Zn、Cr、Co、Ni、V 等热液活动特征元素的沉积。     

上新世以来南海海水表层温度（SST）的变化

The reconstruction of sea surface temperature(SST) is a key issue in research on paleoceanography. The recently related studies are mainly concentrated on the Quaternary. The skeletons of a typical species of benthonic foraminifer(Amphistegina radiata) in the top 0–375.30 m interval of Well "Xike-1" reef core, Shidao Island, the Xisha Islands, are uniformly selected. The ratios of magnesium to calcium concentrations and other indicators are analyzed by an electron microprobe analysis(EMPA) with the purpose of estimating the paleo-SSTs since the Pliocene and further investigating the periodic change law of paleoclimate in the South China Sea(SCS).Meanwhile, the geologic significance of paleoclimatic events in the SCS is discussed with global perspectives. The results indicate that the paleo-SSTs reconstructed by the ratios of magnesium to calcium concentrations in the SCS show a general periodic trend of "high–low–high–low" in values changes since the Pliocene. By comparison,the fluctuations of reconstructed paleo-SSTs are much stronger in the Quaternary. Moreover, the variations of the ratios of magnesium to calcium concentrations in the A. radiata skeletons have recorded a series of major paleoclimatic events since the Pliocene, of which the Quaternary glaciation events and the Arctic ice cap forming events during the late Pliocene are more significant. Thus, using the changes of the ratios of magnesium to calcium concentrations in the A. radiata skeletons from Well "Xike-1" reef core to reflect the relative changes of paleo-SSTs is a relatively feasible and reliable way in the SCS, which is also proved by the correlation of drilling cores characteristics in this area.     

洋中脊和弧后盆地热液区热液流体B同位素组成的系统性差异

硼(B)是流体迁移元素,趋向于在热液流体中富集而成为常量元素。不同来源的B其同位素组成有着明显的区别。因此,B的含量及其同位素组成可标识热液流体(元素)的物质来源、水–岩反应程度及沉积物(元素)混入等重要过程,对海底热液活动及其成矿作用过程具有重要的示踪意义。迄今,对全球主要热液活动区热液流体中B的含量及同位素组成特征已做了大量的测试分析及研究工作,积累了丰富的资料和重要研究成果。但是,对不同地质背景(构造环境)条件下热液流体中B的含量及同位素组成特征尚缺乏系统性的对比分析,进而对造成不同环境热液流体中元素及其同位素组成的系统性差异的原因或机制尚缺乏深入的认识。本文在获取了洋中脊和弧后盆地主要热液活动区热液端元流体中B的含量及其同位素组成数据的基础上,定量估算了热液流体中B的主要来源,并对洋中脊和弧后盆地热液端元流体中B同位素组成的系统性差异进行了分析及成因探讨。结果表明,不同热液活动区热液端元流体的δ11B值都具有较大的变化范围,水–岩反应过程中不同来源B的混合是热液流体B同位素组成变化的主要原因。无沉积物覆盖的洋中脊和弧后盆地热液区热液流体中的B主要为海水与基底岩石来源B的混合,弧后盆地岩浆挥发性组分对热液系统的直接贡献及两种不同地质背景下基底岩石地球化学组成与水–岩反应程度的差异是其热液端元流体B同位素组成差异的主要原因。在有沉积物覆盖的弧后盆地热液区,热液流体中B的同位素组成与前两者之间存在显著差异,具有异常低的δ11B值,水–岩反应过程中沉积物来源B的加入是导致热液流体中δ11B值系统性降低的主要原因,沉积物的吸附作用也在一定程度上影响了热液流体的B同位素组成。有沉积物覆盖的洋中脊热液区热液流体同样受到了沉积物来源B加入的影响,具有较低的δ11B值,且相对于冲绳海槽受到了更强烈的沉积物吸附作用的影响。基于以上分析,并结合热液流体的Sr同位素组成特征,本文提出了洋中脊和弧后盆地这两大构造环境中热液流体B同位素组成系统性差异的成因模式。     

利用GIS和多维数据库技术实现长江口海域环境时空数据分析

基于GIS和多维数据库技术,依据海洋环境数据的特征,建立了长江口及邻近海域海洋环境的时空多维数据模型,研究了海洋环境数据的时空分析方法。依据2003、2004和2006年多航次的现场调查和分析数据,完善了海洋环境时空多维数据模型,对长江口海域环境时空多维海量数据进行了加工处理与可视化分析,并利用ArcGIS软件平台实现了数据的共享与发布,为岸滩蚀退的遏制和河口三角洲环境的综合治理提供了科学的数据基础。     

基于逐月标准化降水蒸散指数的多尺度方法分析气候变化对澜沧江流域归一化植被指数的影响

基于澜沧江流域10个气象站点1951~2012年的日降水资料的逐月标准化降水蒸散指数(SPEI)值、各站1998~2012年流域的归一化植被指数(NDVI)值,利用SPEI以及趋势分析法,多尺度分析了澜沧江流域干旱发生的时间和强度演变特征以及上中下游NDVI时间变化特征,探讨了气候变化对植被变化的影响,并对NDVI与SPEI的变化进行了相关性分析。结果表明,不同站点和不同时间尺度的SPEI值均呈现出干旱化逐年加强的线性趋势,上游相对于中下游干旱态势较轻,且时间尺度越大,干旱波动趋势越明显;在季节尺度上,夏、秋、冬的SPEI值均呈下降趋势,其中冬季干旱最为严重;15年来澜沧江流域各区域年平均NDVI总体表现为先降低后增加,总体植被状况得到改善,其中下游较明显。从年际变化看,对于流域的不同区域,NDVI与不同尺度的SPEI的相关性和滞后性有较大差异,年代际之间的响应规律也不同,中下游的SPEI对同年NDVI的响应比较敏感,而上游则表现出明显的滞后性。说明NDVI对SPEI的响应比较敏感,干旱程度的变化在一定程度上影响着流域的植被状况,SPEI是影响NDVI的因素之一。     

Spatio-temporal analysis of different levels of road expansion on soil erosion distribution: a case study of Fengqing county, Southwest China

The construction of roads has direct and indirect impacts on soil erosion, with spatio-temporal variations existing among different levels of road zones. Aiming to quantitatively analyze the soil loss, this paper explored the relationship between the erosion of soil and its distance from the road in Fengqing county, Southwest China in 1987 and 2004, respectively. The average soil erosion was calculated and expressed with grid map using universal soil loss equation (USLE) model based on GIS and RS. Along the different levels of roads classified as trunk, county, town, village and unpaved road, the buffer zones were subdivided into five stripes, each of which was 200 meters wide. The average soil erosion modulus of each buffer zone was also counted. Results show that the soil loss decreases with increasing distance to the road except rare trunk roads in the region. In addition, the declined intensity varies with the different levels of roads. Soil erosion was more serious along the lower level road than the higher ones. And soil erosion was more severe for all levels of roads in 1987 than those in 2004 because much more rainfalls affected the situation of soil erosion in 1987.     

He, Ne and Ar isotope compositions of fluid inclusions in hydrothermal sulfides from the TAG hydrothermal field Mid-Atlantic Ridge

Helium, neon and argon isotope compositions of fluid inclusions have been measured in hydrothermal sulfide samples from the TAG hydrothermal field at the Mid-Atlantic Ridge. Fluid-inclusion³He/⁴He ratios are 2.2—13.3 times the air value (Ra), and with a mean of 7.2 Ra. Comparison with the local vent fluids (³He/⁴He=7.5—8.2 Ra) and mid-ocean ridge basalt values (³He/⁴He=6—11 Ra) shows that the variation range of³He/⁴He ratios from sulfide-hosted fluid inclusions is significantly large. Values for²⁰Ne/²²Ne are from 10.2 to 11.4, which are significantly higher than the atmospheric ratio (9.8). And fluid-inclusion⁴⁰Ar/³⁶Ar ratios range from 287 to 359, which are close to the atmospheric values (295.5). These results indicate that the noble gases of fluid inclusions in hydrothermal sulfides are a mixture of mantle- and seawater-derived noble gases; the partial mantle-derived components of trapped hydrothermal fluids may be from the lower mantle; the helium of fluid inclusions is mainly from upper mantle; and the Ne and Ar components are mainly from seawater.     

琼东南盆地物源和沉积环境变化的重矿物证据

基于11口钻井岩心样品的重矿物数据,结合古生物学、元素地球化学和地震资料,对琼东南盆地的物源及沉积环境演变进行了分析.结果表明,盆地基底沉积以陆相沉积为主,自渐新世起,盆地逐渐接受海侵,大致经历了海陆过渡→滨浅海→浅海→半深海的沉积环境演变过程,水深总体呈逐渐增大的趋势且在同一时期南部区域水深整体上大于北部.随着沉积环境的变化,各地层(崖城组至莺歌海组)物源呈现出多源性特征,经历了原地→近源→远源的演变过程.在渐新世早期,物源以近源玄武质火山碎屑和邻区陆源碎屑为主,之后演变为远源的陆壳碎屑,物源区包括北部海南岛、南部永乐隆起、东北部神狐隆起、西部红河、西南部中南半岛乃至更广的区域.海南岛物源自早渐新世便开始发育,至中中新世成为盆地最主要的物源,并持续至现今;永乐隆起和神狐隆起物源在晚渐新世至早中新世期间最为发育,于中中新世逐渐消退;红河物源于晚中新世大规模加入,为中央峡谷的主要沉积物源,影响至上新世结束;中南半岛莺西物源自上新世发育,影响至更新世时期.此外,自生组分对盆地(尤其是南部区域)的沉积贡献也不容忽视.     

Depositional features and sedimentary model of Buqu Stage in Mid-Jurassic in Qangtang Basin, Xizang （Tibet）, China

The largest Mesozoic northward transgression in Qangtang Basin of Qinghai-Xizang (Tibet) Plateau occurred during the Buqu Stage, Middle Jurassic. Mainly filled with carbonate rocks, the whole basin is composed of transgression-regression sedimentary cycle. Field outcrops and indoor analysis revealed 8 types of sedimentary facies markers in this region. 4 types of sedimentary facies have been recognized: platform facies,platform marginal facies, foreslope facies and basin facies. Influenced by the northern Lazhuglung-Jinshajiang suture zone, central uplift region and southern Bangongco-Nujiang suture zone, these facies belts extended east-west. The sedimentary model was established based on observed depositional features. From their biological features and sedimentary characteristics, it is suggested that the paleoclimate was warm and humid at that time.The Buqu Formation is a promising target for oil and gas exploration in Shuanghu-Duoyong area in future.