Smectite formation in metalliferous sediments near the East Pacific Rise at 13°N   总被引：1，自引：0，他引：1  

荣坤波  曾志刚  殷学博  陈帅  王晓媛  齐海燕  马瑶 《海洋学报(英文版)》2018,37(9):67-81

A 43 cm long E271 sediment core collected near the East Pacific Rise(EPR) at 13°N were studied to investigate the origin of smectite for understanding better the geochemical behavior of hydrothermal material after deposition.E271 sediments are typical metalliferous sediments. After removal of organic matter, carbonate, biogenic opal,and Fe-Mn oxide by a series of chemical procedures, clay minerals(2 μm) were investigated by X-ray diffraction,chemical analysis and Si isotope analysis. Due to the influence of seafloor hydrothermal activity and close to continent, the sources of clay minerals are complex. Illite, chlorite and kaolinite are suggested to be transported from either North or Central America by rivers or winds, but smectite is authigenic. It is enriched in iron, and its contents are highest in clay minerals. Data show that smectite is most likely formed by the reaction of hydrothermal Fe-oxyhydroxide with silica and seawater in metalliferous sediments. The Si that participates in this reaction may be derived from siliceous microfossils(diatoms or radiolarians), hydrothermal fluids, or detrital mineral phases. And their δ30 Si values are higher than those of authigenic smectites, which implies that a Si isotope fractionation occurs during the formation because of the selective absorption of light Si isotopes onto Feoxyhydroxides. Sm/Fe mass ratios(a proxy for overall REE/Fe ratio) in E271 clay minerals are lower than those in metalliferous sediments, as well as distal hydrothermal plume particles and terrigenous clay minerals. This result suggests that some REE are lost during the smectite formation, perhaps because their large ionic radii of REE scavenged by Fe-oxyhydroxides preclude substitution in either tetrahedral or octahedral lattice sites of this mineral structure, which decreases the value of metalliferous sediments as a potential resource for REE.  相似文献   

豫西南泥湖地区辉长岩地球化学特征及其与成矿关系          下载免费PDF全文

刘辉 《山东国土资源》2018,34(3)

豫西南泥湖钼矿集区是以花岗斑岩体为中心的钼多金属矿床系列,区内出露大面积加里东期变辉长岩和燕山期辉长岩。通过分析区内辉长岩的岩石学、年代学、地球化学和成矿元素等方面特征,研究其在成岩成矿过程中的作用。区内加里东期变辉长岩和燕山期辉长岩成矿元素总稀土含量低,稀土元素球粒陨石标准化曲线右倾平缓,具有明显的Eu,Tm元素的异常;同比世界基性岩,自晚元古代上地幔主要成矿元素(除钨元素以外)基本没有明显的富集,主成矿元素钼含量呈明显的亏损,预示燕山期成矿花岗质岩浆没有从上地幔获得主要成矿物质。初步认为大规模的钼多金属成矿带的形成与基性岩浆的底垫作用相关,基性岩浆的底垫作用为下地壳部分熔融形成岩浆房提供了热源。  相似文献   

Towards Regional Synergy: Reconciling Rangeland Ecological Functioning with Forage Production of Cultivated Pasture     

SHI Peili  ZHANG Xianzhou 《资源与生态学报(英文版)》2020,11(3):247-252

Animal husbandry and crop farming are specialized for development in separate areas on the Tibetan Plateau. Such a pattern of isolation has led to current concerns of rangeland and farming system degradation due to intensive land use. The crop-livestock integration, however, has been proven to increase food and feed productivity thorough niche complementarity, and is thereby especially effective for promoting ecosystem resilience. Regional synergy has emerged as an integrated approach to reconcile rangeland livestock with forage crop production. It moves beyond the specialized sectors of animal husbandry and intensive agriculture to coordinate them through regional coupling. Therefore, crop-livestock integration (CLI) has been suggested as one of the effective solutions to forage deficit and livestock production in grazing systems. But it is imperative that CLI moves forward from the farm level to the regional scale, in order to secure regional synergism during agro-pastoral development. The national key R & D program, Technology and Demonstration of Recovery and Restoration of Degraded Alpine Ecosystems on the Tibetan Plateau, aims to solve the problems of alpine grassland degradation by building up a grass-based animal husbandry technology system that includes synergizing forage production and ecological functioning, reconciling the relationship between ecology, forage production and animal husbandry, and achieving the win-win goals of curbing grassland degradation and changing the development mode of animal husbandry. It is imperative to call for regional synergy through integrating ecological functioning with ecosystem services, given the alarming threat of rangeland degradation on the Tibetan Plateau. The series of papers in this issue, together with those published previously, provide a collection of rangeland ecology and management studies in an effort to ensure the sustainable use and management of the alpine ecosystems.  相似文献   

不同厚度饱和砂土中群桩结构动力响应试验研究   总被引：2，自引：2，他引：0       下载免费PDF全文

李雨润  强东峰  邹泽  刘荟达  王海 《地震工程学报》2018,40(4):625-630

液化土中桩基础动力响应规律一直是工程抗震领域关注的热点问题。本文基于非液化砂土和不同厚度饱和砂土中的2×2群桩结构模型振动台试验,通过输入一定峰值加速度和频率的正弦波,对群桩在非液化土层和两种不同厚度饱和砂土层中的横向动力响应特性进行振动台试验研究。研究结果表明:在正弦波输入情况下,非液化砂土中群桩承台加速度和位移时程与台面输入时程相比,波形变化规律与峰值大小均相差不大;而对两种不同厚度饱和砂土中承台加速度和位移峰值放大较多,在相对较薄的饱和砂土中群桩承台加速度峰值较台面输入放大了1.83倍,较台面输出位移峰值放大了1.58倍;在相对较厚的饱和砂土中承台加速度和位移峰值则分别放大了2.18倍和1.91倍,说明在相同输入条件下,较厚的饱和砂土在发生液化后群桩承台的动力响应更加显著。  相似文献   

Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation          下载免费PDF全文

Jennifer Von Voigtlander  Marin K. Clark  Dimitrios Zekkos  William W. Greenwood  Suzanne P. Anderson  Robert S. Anderson  Jonathan W. Godt 《地球表面变化过程与地形》2018,43(6):1183-1194

The evolution of volcanic landscapes and their landslide potential are both dependent upon the weathering of layered volcanic rock sequences. We characterize critical zone structure using shallow seismic V_p and V_s profiles and vertical exposures of rock across a basaltic climosequence on Kohala peninsula, Hawai’i, and exploit the dramatic gradient in mean annual precipitation (MAP) across the peninsula as a proxy for weathering intensity. Seismic velocity increases rapidly with depth and the velocity–depth gradient is uniform across three sites with 500–600 mm/yr MAP, where the transition to unaltered bedrock occurs at a depth of 4 to 10 m. In contrast, velocity increases with depth less rapidly at wetter sites, but this gradient remains constant across increasing MAP from 1000 to 3000 mm/yr and the transition to unaltered bedrock is near the maximum depth of investigation (15–25 m). In detail, the profiles of seismic velocity and of weathering at wet sites are nowhere monotonic functions of depth. The uniform average velocity gradient and the greater depths of low velocities may be explained by the averaging of velocities over intercalated highly weathered sites with less weathered layers at sites where MAP > 1000 mm/yr. Hence, the main effect of climate is not the progressive deepening of a near‐surface altered layer, but rather the rapid weathering of high permeability zones within rock subjected to precipitation greater than ~1000 mm/yr. Although weathering suggests mechanical weakening, the nearly horizontal orientation of alternating weathered and unweathered horizons with respect to topography also plays a role in the slope stability of these heterogeneous rock masses. We speculate that where steep, rapidly evolving hillslopes exist, the sub‐horizontal orientation of weak/strong horizons allows such sites to remain nearly as strong as their less weathered counterparts at drier sites, as is exemplified by the 50°–60° slopes maintained in the amphitheater canyons on the northwest flank of the island. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Hydrological trends and the evolution of catchment research in the Alptal valley,central Switzerland     

Manfred Stähli  Jan Seibert  James W. Kirchner  Jana von Freyberg  Ilja van Meerveld 《水文研究》2021,35(4):e14113

When the observation of small headwater catchments in the pre-Alpine Alptal valley (central Switzerland) started in the late 1960s, the researchers were mainly interested in questions related to floods and forest management. Investigations of geomorphological processes in the steep torrent channels followed in the 1980s, along with detailed observations of biogeochemical and ecohydrological processes in individual forest stands. More recently, research in the Alptal has addressed the impacts of climate change on water supply and runoff generation. In this article, we describe, for the first time, the evolution of catchment research at Alptal, and present new analyses of long-term trends and short-term hydrologic behaviour. Hydrometeorological time series from the past 50 years show substantial interannual variability, but only minimal long-term trends, except for the ~2°C increase in mean annual air temperature over the 50-year period, and a corresponding shift towards earlier snowmelt. Similar to previous studies in larger Alpine catchments, the decadal variations in mean annual runoff in Alptal's small research catchments reflect the long-term variability in annual precipitation. In the Alptal valley, the most evident hydrological trends were observed in late spring and are related to the substantial change in the duration of the snow cover. Streamflow and water quality are highly variable within and between hydrological events, suggesting rapid shifts in flow pathways and mixing, as well as changing connectivity of runoff-generating areas. This overview illustrates how catchment research in the Alptal has evolved in response to changing societal concerns and emerging scientific questions.  相似文献   

古元古代大氧化事件(GOE)前后海洋环境的变化: 来自华北条带状铁建造(BIF)岩相学和地球化学的证据^*          下载免费PDF全文

张连昌  兰彩云  王长乐  彭自栋  佟小雪  李文君  董志国 《古地理学报》2020,22(5):827-840

条带状铁建造(BIF)是形成于前寒武纪海洋中的化学沉积岩,记录了古海洋氧化还原状态的重要信息。华北克拉通广泛分布的新太古代和古元古代BIF,是了解古元古代大氧化事件(GOE)前后古海洋氧化还原环境变化的理想对象。初步研究表明,华北克拉通新太古代BIF主要为磁铁矿型氧化物相和硅酸盐相,极少数出现碳酸盐相;古元古代BIF包括赤铁矿型和磁铁矿型氧化物相、硅酸盐相和碳酸盐相,其中赤铁矿相是古元古代BIF独有的。以上矿物学特征表明,新太古代和古元古代水体的氧化还原条件是不同的。华北克拉通新太古代BIF的稀土元素组成缺乏强烈的负Ce异常,反映同期海水氧含量非常低,为缺氧状态; 但少量BIF也包含有负Ce异常,同时具有较大变化范围的Th/U值,指示新太古代海洋的局部水体氧含量相对较高,呈弱氧化状态。与新太古代BIF相比,古元古代BIF的Ce异常变化较大,包括无异常、正异常和负异常,尤其是赤铁矿相BIF具明显的负Ce异常,表明古元古代水体的氧含量和氧化还原结构已发生了明显变化; 结合华北克拉通BIF的Ni/Co、V/(V+Ni)和Th/U等比值特征,认为古元古代海洋呈次氧化—氧化环境。新太古代BIF 强烈富集重铁同位素,S同位素非质量分馏效应较为明显;而古元古代BIF相对富集轻铁同位素,S同位素非质量分馏效应不明显。综上,新太古代海洋环境整体缺氧,但局部可能存在氧气“绿洲”,暗示光合产氧作用在太古代晚期已经存在;大氧化事件期间及之后的古海洋总体具上部氧化、下部还原的分层特征。  相似文献   

Theropod assemblages and a new ichnotaxon Gigandipus chiappei ichnosp. nov. from the Jiaguan Formation,Lower Cretaceous of Guizhou Province,China     

《地学前缘(英文版)》2018,9(6):1745-1754

A newly discovered Jiaguan Formation(Lower Cretaceous) tracksite from the Linjiang region of Guizhou Province, China, reveals the first example of a Cretaceous track morphotype attributable to the non-avian theropod ichnogenus Gigandipus, here named Gigandipus chiappei ichnosp nov. The theropod dominated locality also reveals the second report of the avian theropod ichnogenus Wupus, one of the largest avian traces currently known from the Lower Cretaceous. The Linjiang site provides evidence to support previous interpretations of a distinctive Lower Cretaceous theropod-dominated ichnofauna that was widespread in China and East Asia and highlights the similarity between Lower Cretaceous theropod ichnotaxa in East Asia and those found in the Lower Jurassic both in East Asia and elsewhere. These similarities in turn create various ichnotaxonomic challenges familiar to researchers working on theropod tracks, and we recommend caution in the naming of new theropod ichnotaxa at the ichnogenus level.  相似文献   

The geothermal formation mechanism in the Gonghe Basin: Discussion and analysis from the geological background     

《China Geology》2018,1(3):331-345

The Gonghe Basin, a Cenozoic down-warped basin, is located in the northeastern part of the Qinghai-Xizang (Tibetan) Plateau, and spread over important nodes of the transfer of multiple blocks in the central orogenic belt in the NWW direction. It is also called “Qin Kun Fork” and “Gonghe Gap”. The basin has a high heat flow value and obvious thermal anomaly. The geothermal resources are mainly hot dry rock and underground hot water. In recent years, the mechanism of geothermal formation within the basin has been controversial. On the basis of understanding the knowledge of predecessors, this paper proposes the geothermal formation mechanism of the “heat source–heat transfer–heat reservoir and caprock–thermal system” of the Gonghe Basin from the perspective of a geological background through data integration-integrated research-expert, discussion-graph, compilation-field verification and other processes: (1) Heat source: geophysical exploration and radioisotope calculations show that the heat source of heat in the basin has both the contribution of mantle and the participation of the earth’s crust, but mainly the contribution of the deep mantle. (2) Heat transfer: The petrological properties of the basin and the exposed structure position of the surface hot springs show that one transfer mode is the material of the mantle source upwells and invades from the bottom, directly injecting heat; the other is that the deep fault conducts the deep heat of the basin to the middle and lower parts of the earth’s crust, then the secondary fracture transfers the heat to the shallow part. (3) Heat reservoir and caprock: First, the convective strip-shaped heat reservoir exposed by the hot springs on the peripheral fault zone of the basin; second, the underlying hot dry rock layered heat reservoir and the upper new generation heat reservoir and caprock in the basin revealed by drilling data. (4) Thermal system: Based on the characteristics of the “heat source-heat transfer-heat reservoir and caprock”, it is preliminarily believed that the Gonghe Basin belongs to the non-magmatic heat source hydrothermal geothermal system (type II2₁) and the dry heat geothermal system (type II2₂). Its favorable structural position and special geological evolutionary history have given birth to a unique environment for the formation of the geothermal system. There may be a cumulative effect of heat accumulation in the eastern part of the basin, which is expected to become a favorable exploration area for hot dry rocks.  相似文献   

A Numerical Investigation on Microphysical Properties of Clouds and Precipitation over the Tibetan Plateau in Summer 2014     

Jie TANG  Xueliang GUO  Yi CHANG 《Journal of Meteorological Research》2019,(3):463-477

In order to improve our understanding of microphysical properties of clouds and precipitation over the Tibetan Plateau (TP), six cloud and precipitation processes with different intensities during the Third Tibetan Plateau Atmospheric Science Experiment (TIPEX-Ⅲ) from 3 July to 25 July 2014 in Naqu region of the TP are investigated by using the high-resolution mesoscale Weather Research and Forecasting (WRF) model. The results show unique properties of summertime clouds and precipitation processes over the TP. The initiation process of clouds is closely associated with strong solar radiative heating in the daytime, and summertime clouds and precipitation show an obvious diurnal variation. Generally, convective clouds would transform into stratiform clouds with an obvious bright band and often produce strong rainfall in midnight. The maximum cloud top can reach more than 15 km above sea level and the velocity of updraft ranges from 10 to 40 m s-1. The simulations show high amount of supercooled water content primarily located between 0 and -20℃ layer in all the six cases. Ice crystals mainly form above the level of -20℃ and even appear above the level of -40℃ within strong convective clouds. Rainwater mostly appears below the melting layer, indicating that its formation mainly depends on the melting process of precipitable ice particles. Snow and graupel particles have the characteristics of high content and deep vertical distribution, showing that the ice phase process is very active in the development of clouds and precipitation. The conversion and formation of hydrometeors and precipitation over the plateau exhibit obvious characteristics. Surface precipitation is mainly formed by the melting of graupel particles. Although the warm cloud microphysical process has less direct contribution to the formation of surface precipitation, it is important for the formation of supercooled raindrops, which are essential for the formation of graupel embryos through heterogeneous freezing process. The growth of graupel particles mainly relies on the riming process with supercooled cloud water and aggregation of snow particles.  相似文献