钾稳定同位素研究综述     

王昆  李伟强  李石磊 《地学前缘》2020,27(3):104-122

钾稳定同位素是重要的非传统稳定同位素体系,也是近年来迅速发展的热门研究课题。对钾同位素研究历史和现状进行综述,具体包括以下内容:(1)总结了钾元素的地球化学和宇宙化学性质,包括钾在主要地质储库(地幔、地壳、海洋)中的丰度及其分配,钾在岩浆演化中的不相容大离子亲石性,常见含钾火成岩/沉积岩矿物以及钾在表生过程中的循环,也包括主要行星物质(球粒陨石、非球粒陨石、火星和灶神星陨石以及月球样品)中钾的含量、赋存状态、主要矿物,钾在太阳星云冷凝、行星积聚以及岩浆海过程中的中等挥发性质;(2)介绍了钾同位素的研究历史,从1922年Dempster利用最早的质谱仪测量钾同位素在自然界的丰度,到Taylor和Urey在1938发表的经典的钾同位素分馏实验,再到Humayun和Clayton在1995年发表的钾同位素领域的经典研究,最后到近几年的进展;(3)介绍了对钾的前处理(离子交换柱法)以及钾同位素的主要测量方法,包括早期热电离质谱仪法(TIMS),二次离子质谱仪法(SIMS)和近十几年以来高速发展的多接收电感耦合等离子体质谱仪法(MC-ICP-MS)及其不同的技术路线;(4)介绍了高精度钾同位素比值在低温地球化学和生物地球化学中的应用,包括钾同位素在地表的风化过程中、海水洋壳的反向风化作用中的分馏及其在示踪全球钾元素循环和洋壳俯冲等过程中的应用;(5)介绍了高精度钾同位素比值在高温地球化学中的应用,包括钾同位素在岩浆分异和矿物结晶过程中的分馏;(6)介绍了高精度钾同位素比值在宇宙化学中的应用,包括在太阳星云冷凝、行星凝聚、月球形成大碰撞、岩浆海、火山喷发去气过程中的分馏作用。  相似文献   

Ecohydrologic feedbacks controlling sizes of cypress wetlands in a patterned karst landscape     

Xiaoli Dong  A. Brad Murray  James B. Heffernan 《地球表面变化过程与地形》2019,44(5):1178-1191

Many landforms on Earth are profoundly influenced by biota. In particular, biota play a significant role in creating karst biogeomorphology, through biogenic CO₂ accelerating calcite weathering. In this study, we explore the ecohydrologic feedback mechanisms that have created isolated depressional wetlands on exposed limestone bedrock in South Florida – Big Cypress National Preserve –as a case study for karst biogeomorphic processes giving rise to regularly patterned landscapes. Specifically, we are interested in: (1) whether cypress depressions on the landscape have reached (or will reach) equilibrium size; (2) if so, what feedback mechanisms stabilize the size of depressions; and (3) what distal interactions among depressions give rise to the even distribution of depressions in the landscape. We hypothesize three feedback mechanisms controlling the evolution of depressions and build a numerical model to evaluate the relative importance of each mechanism. We show that a soil cover feedback (i.e. a smaller fraction of CO₂ reaches the bedrock surface for weathering as soil cover thickens) is the major feedback stabilizing depressions, followed by a biomass feedback (i.e. inhibited biomass growth with deepening standing water and extended inundation period as depressions expand in volume). Strong local positive feedback between the volume of depressions and rate of volume expansion and distal negative feedback between depressions competing for water likely lead to the regular patterning at the landscape scale. The individual depressions, however, are not yet in steady state but would be in ~0.2–0.4 million years. This represents the first study to demonstrate the decoupling of landscape-scale self-organization and the self-organization of its constituent agents. © 2018 John Wiley & Sons, Ltd.  相似文献   

Spatiotemporal variations of dissolved inorganic carbon and controlling factors in a small karstic catchment,Southwestern China     

Caiqing Qin  Si-Liang Li  Fu-Jun Yue  Sheng Xu  Hu Ding 《地球表面变化过程与地形》2019,44(12):2423-2436

Dissolved inorganic carbon (DIC) is the most important carbon component in karst aquatic system where fluid is highly transmissive, but has rarely been examined in the subtropical karst critical zone (K-CZ). In this study, concentrations of dissolved solutes and isotopic compositions of DIC (δ¹³C_DIC) at 11 sites of a 73.4 km² karstic catchment in Southwestern China were analysed monthly in order to uncover the spatiotemporal variations of both DIC and its dominant sources, and to identify relevant controlling factors. Both DIC concentrations and δ¹³C_DIC were highly variable, ranging from 2.52 to 5.85 mmol l⁻¹ and from −15.7 to −4.5‰, respectively. DIC in underground water (UGW) was higher in concentration and more depleted in ¹³C compared to surface water (SFS). DIC concentrations showed an inconsistent seasonal trend with other solutes, with higher values in the wet season at some sites. δ¹³C_DIC values were lower in the wet season than in the dry season. The results of mixing model IsoSource revealed spatiotemporal patterns of DIC sources. During the dry season, carbonate weathering was the primary contributor to DIC in UGW (excluding in the middle reaches). However, during the wet season, soil CO₂ was the dominant source of DIC in both UGW and SFS, and it was higher than in the dry season. Overall, there are significant spatiotemporal disparities and highly transmissive characteristics of both DIC and its sources in the K-CZ, which are controlled by multiple factors. This study also highlights that rainfall may play a crucial role in accelerating carbon dynamics in the K-CZ. High-frequency sampling campaigns in high-flow periods and deep analyses are needed in future work to elucidate the related processes and mechanisms. © 2019 John Wiley & Sons, Ltd.  相似文献   

Chemical weathering and CO2 consumption in the glaciated Karuxung River catchment,Tibetan Plateau     

Fan Zhang  Xiong Xiao  Lijie Wang  Chen Zeng  Zhengliang Yu  Guanxing Wang  Xiaonan Shi 《水文研究》2021,35(8):e14330

Climate factors play critical roles in controlling chemical weathering, while chemically weathered surface material can regulate climate change. To estimate global chemical weathering fluxes and CO₂ balance, it is important to identify the characteristics and driving factors of chemical weathering and CO₂ consumption on the Tibetan Plateau, especially in glaciated catchments. The analysis of the hydro-geochemical data indicated that silicate weathering in this area was inhibited by low temperatures, while carbonate weathering was promoted by the abundant clastic rocks with fresh surfaces produced by glacial action. Carbonate weathering dominated the riverine solute generation (with a contribution of 58%, 51%, and 43% at the QiangYong Glacier (QYG), the WengGuo Hydrological Station (WGHS), and the lake estuary (LE), respectively). The oxidation of pyrite contributed to 35%, 42%, and 30% of the riverine solutes, while silicate weathering contributed to 5%, 6%, and 26% of the riverine solutes at the QYG, WGHS, and LE, respectively. The alluvial deposit of easily weathering fine silicate minerals, the higher air temperature, plant density, and soil thickness at the downstream LE in comparison to upstream and midstream may lead to longer contact time between pore water and mineral materials, thus enhancing the silicate weathering. Because of the involvement of sulfuric acid produced by the oxidation of pyrite, carbonate weathering in the upstream and midstream did not consume atmospheric CO₂, resulting in the high rate of carbonate weathering (73.9 and 75.6 t km⁻² yr⁻¹, respectively, in maximum) and potential net release of CO₂ (with an upper constraint of 35.6 and 35.2 t km⁻² yr⁻¹, respectively) at the QYG and WGHS. The above results indicate the potential of the glaciated area of the Tibetan Plateau with pyrite deposits being a substantial natural carbon source, which deserves further investigation.  相似文献   

Spheroidal weathering of granite porphyry with well‐developed columnar joints by oxidation,iron precipitation,and rindlet exfoliation          下载免费PDF全文

Yasuto Hirata  Masahiro Chigira  Youqing Chen 《地球表面变化过程与地形》2017,42(4):657-669

Spheroidal weathering, one of the important rock weathering styles, has been attributed to chemical weathering by the water from joint surfaces, and mechanical aspects of the weathering have not been well addressed. We made an investigation on spheroidal weathering of Miocene granite porphyry with well‐developed columnar joints and found that this spheroidal weathering proceeds through chemical processes and accompanying mechanical processes. The investigation of the textures, physical properties, mineralogy, and chemistry of the porphyry revealed the presence of a brown band on the surface margins of corestones, representing the oxidation of pyrite and chlorite, and the precipitation of iron hydroxides, and the consequent generation of micro‐cracks within the band. During weathering, oxidation progresses inwards from joints that surround the rindlets, including both high‐angle columnar and low‐angle planar joints, and causes rounding of the unweathered interior portion of the rock. Microscopic observations of the brown band embedded with fluorescent resin show that pores are first filled with iron hydroxides, and that micro‐cracks then form parallel to the oxidation front in the outer portion of the brown band. Iron hydroxide precipitation increases the P‐wave velocity in the brown band, while micro‐crack formation decreases the tensile strength of the rock. Where the brown band has thickened to ~6 cm, the micro‐cracks are connected to one another to create continuous cracks, which separate the rindlets from the corestone. Micro‐crack formation parallel to the corestone surface may be attributed to compressive stresses generated by small amounts of volumetric expansion due to the precipitation of iron hydroxides in the brown band. Earth surface is under oxidizing environments so that precipitation of iron hydroxides commonly occurs; the spheroidal weathering in this paper is a typical example of the combination of chemical and mechanical processes under such environments. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Controls on deep critical zone architecture: a historical review and four testable hypotheses   总被引：1，自引：0，他引：1       下载免费PDF全文

Clifford S. Riebe  W. Jesse Hahm  Susan L. Brantley 《地球表面变化过程与地形》2017,42(1):128-156

The base of Earth's critical zone (CZ) is commonly shielded from study by many meters of overlying rock and regolith. Though deep CZ processes may seem far removed from the surface, they are vital in shaping it, preparing rock for infusion into the biosphere and breaking Earth materials down for transport across landscapes. This special issue highlights outstanding challenges and recent advances of deep CZ research in a series of articles that we introduce here in the context of relevant literature dating back to the 1500s. Building on several contributions to the special issue, we highlight four exciting new hypotheses about factors that drive deep CZ weathering and thus influence the evolution of life‐sustaining CZ architecture. These hypotheses have emerged from recently developed process‐based models of subsurface phenomena including: fracturing related to subsurface stress fields; weathering related to drainage of bedrock under hydraulic head gradients; rock damage from frost cracking due to subsurface temperature gradients; and mineral reactions with reactive fluids in subsurface chemical potential gradients. The models predict distinct patterns of subsurface weathering and CZ thickness that can be compared with observations from drilling, sampling and geophysical imaging. We synthesize the four hypotheses into an overarching conceptual model of fracturing and weathering that occurs as Earth materials are exhumed to the surface across subsurface gradients in stress, hydraulic head, temperature, and chemical potential. We conclude with a call for a coordinated measurement campaign designed to comprehensively test the four hypotheses across a range of climatic, tectonic and geologic conditions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Engineering characteristics and uses of duricrusts in Australia     

G. H. McNally 《Australian Journal of Earth Sciences》2013,60(6):535-547

The uses and shortcomings of duricrusts (ferricrete, calcrete and silcrete) in engineering construction (as used for road‐base, aggregate, foundation materials and aquifers) are reviewed. Australian production of these materials represents about one‐third of all unprocessed road‐base and they are especially important as pavement courses for lightly trafficked, low‐cost rural and outback roads. However, duricrusts are regarded as marginal materials at best because of their typically poor grading, particle unsoundness, high fines plasticity, and absorption of water and bitumen. These materials are used because they are available locally in areas that are otherwise lacking in hard rock materials, such as deeply weathered and sedimentary rock terrains. The weathering profiles of which they form part are characterized by high permeability (despite being clay‐rich), variable cementation, low compressibility and a tendency to become weaker with depth. Although the more indurated layers are unrippable, they are also difficult to blast. Pedogenic (nodular) duricrusts were formerly sought for natural road‐base, because they occur widely and require only rudimentary processing. However, well‐cemented groundwater (vadose) duricrusts are now the preferred deposits, even though they require crushing and screening. Ferricrete is the most widely exploited of the duricrusts for engineering purposes, especially in northern and southwestern Australia, although calcrete is important in South Australia and in the Murray Basin. Silcrete is only a minor source of aggregate and road‐base, mainly in western Queensland.  相似文献   

南海西南部晚更新世以来元素地球化学特征的古环境意义   总被引：3，自引：0，他引：3  

乔培军  邵磊  杨守业 《海洋地质与第四纪地质》2006,26(4):59-65

对南海西南部近湄公河三角洲中陆坡上的MD01-2392站样品进行的地球化学分析表明,该站的沉积物主要为湄公河带来的陆源碎屑,并且其物源四十万年来没有发生明显变化。分别用元素TiO2、CaO估算出沉积物中陆源碎屑的含量及CaCO3的含量,结果显示CaCO3在间冰期时高,而在冰期时低,表现出“大西洋旋回”的特征。陆源碎屑含量与CaCO3含量相反,显示出南海CaCO3旋回属于稀释旋回。元素的Ti标准化值表明,该站沉积物源区在冰期时化学风化弱,而在间冰期时相对较强,说明间冰期时物源区存在相对温暖湿润的气候环境。  相似文献   

几内亚福雷卡里亚YML铁矿区的富铁矿床地质特征及找矿前景探讨          下载免费PDF全文

江胜国  李宏臣  付方建  王志刚  曹健 《地质找矿论丛》2018,33(1):142-148

YML铁矿区位于几内亚福雷卡里亚省,富铁矿以条带状赤铁矿和铁角砾岩矿为主。矿区内共发育7条矿体,条带状赤铁矿体6条,铁角砾岩矿体1条。条带状赤铁矿体赋存部位多为向形地段,次级紧密褶皱发育,沿走向和倾向有逐渐变薄和尖灭的趋势;铁角砾岩矿体覆盖于地表,以风化壳的形式出现。矿床类型属复合类型,即海底热液喷气沉积叠加后期构造变质型+风化淋滤型。该区具备铁矿形成和保存的地质条件,且已发现具一定储量、品位较高的条带状赤铁矿和大面积的铁角砾岩分布区,区内铁矿找矿远景较好。  相似文献   

准噶尔腹部火山岩风化壳储层特征及其影响因素          下载免费PDF全文

李治  秦启荣  李朋波  顿雅航  付晓燕 《地质找矿论丛》2018,33(4):589-596

文章通过大量岩芯、铸体薄片观察和测井资料分析,对准噶尔腹部石西石炭系火山岩风化壳储层进行了详细地研究。研究结果表明,该火山岩风化壳储层的储集空间主要有基质溶孔、气孔或杏仁体溶孔、角砾间溶孔、微裂缝和裂缝等,其中与裂缝连通的各类溶孔占主导地位;在岩石分布上以集块岩、条带状熔岩、角砾熔岩和致密凝灰岩为主,玄武岩、安山岩和流纹岩则相对较少;储层物性主要表现为高孔低渗,只有裂缝具有较高的渗透率,且裂缝以高角度缝和直立缝为主。研究还发现,岩性岩相、裂缝和风化淋滤作用是影响该风化壳储层的主要因素。区内油层主要聚中在构造高部位、靠近断裂带和有利岩相区域;油层分布在离石炭系风化壳顶面25~150 m的范围内。  相似文献