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1.
《地学前缘》2017,(5):167-171
锂同位素作为一种示踪工具在地球化学研究中发挥着重要作用。本文首次尝试将锂同位素研究应用于四川甲基卡伟晶岩型锂多金属矿区新三号(X03)矿脉的找矿实践。新三号矿脉ZK1101的系统锂同位素分析结果显示,含矿(锂辉石)伟晶岩中的w(Li)为0.94%~1.80%,δ7 Li值为-1.5‰~-1.0‰,平均值为-1.3‰,相对稳定,变化幅度小;不含矿伟晶岩的w(Li)平均值为0.04%,δ7 Li平均值为+2.0‰,与含矿伟晶岩可区分开;围岩的w(Li)为0.02%~0.12%,δ7 Li值为-13.4‰~-0.4‰,平均值为-7.7‰,变化范围较大。锂同位素在含矿伟晶岩、不含矿伟晶岩和围岩中存在的明显差异,可作为今后找矿的"示踪剂"。锂同位素组成与锂含量之间不存在直接的线性关系,其三者之间的差异可能在于分馏机制的差异:伟晶岩中锂同位素的分馏机制属于"热力学平衡分馏";而围岩中锂同位素的分馏机制属于"动力学非平衡分馏"。新三号矿脉中伟晶岩锂同位素的组成暗示其与矿区二云母花岗岩之间具有成因联系,同时围岩中锂同位素的变化趋势也暗示其深部可能存在隐伏矿体,具有找矿潜力。 相似文献
2.
镁同位素地球化学研究新进展及其应用 总被引:7,自引:3,他引:4
作为一种新兴的地质示踪剂,Mg同位素正受到国际地学界日益广泛的关注。Mg同位素地球化学研究已取得了巨大的进展,近期研究工作主要包括两个方面。首先,调查了地球各主要储库和陨石的Mg同位素组成特征,结果表明陨石和地球地幔具有均一并且相似的Mg同位素组成,平均δ26Mg值分别为-0.28±0.06‰和-0.25±0.07‰;相反,上地壳和水圈的Mg同位素组成很不均一,δ26Mg值变化范围分别为-4.84‰~+0.92‰和-2.93‰~+1.13‰。其次,对一些地质和物理化学过程中Mg同位素的分馏行为进行研究,结果表明:(1)地表风化作用可以造成大的Mg同位素分馏,导致重Mg同位素残留在风化产物中而轻Mg同位素进入水圈;(2)岩浆分异过程中Mg同位素平衡分馏很小;(3)高温化学扩散和热扩散过程中Mg同位素会发生显著的动力学分馏。基于这些研究成果,Mg同位素体系已经被初步应用于示踪早期地球形成和壳内物质再循环等过程,并有望在不久的将来应用于示踪大陆地壳的化学演化和地质温度计等研究领域。 相似文献
3.
贵阳地表水-地下水的硫和氯同位素组成特征及其污染物示踪意义 总被引:5,自引:0,他引:5
喀斯特地表水和地下水的交换活跃,地下水系统容易受到地表污染物的污染。为了解喀斯特城市地表水—地下水系统污染特征和污染物质来源,对贵阳市地表水、地下水、雨水和城市排污污水的硫同位素和氯同位素组成变化进行了研究。贵阳市不同类型水体的δ37Cl值在-4.07‰~+2.03‰之间变化,δ34SSO4值变化为-20.4‰~+20.9‰。大气输入物质和城市排污污水的δ37Cl、δ34S及Cl-/SO42-比值与地表水和地下水的不同,稳定硫和氯同位素的结合研究为示踪地下水污染物来源提供了有效研究手段。贵阳市地下水中的Cl-和SO42-至少有4种来源,人为活动通过城市排污和大气输入向地下水系统大量输入了硫酸盐和氯离子。 相似文献
4.
5.
锂同位素及其地质应用研究进展 总被引:7,自引:0,他引:7
锂同位素示踪是近几年发展起来的一门新兴的稳定同位素地球化学方法,锂有两个稳定同位素:^6Li和^7Li。自在界锂同位素的组成变化很大,其δ^6Li值变化幅度超过60‰,现代大洋水的δ^6Li值为-31.0‰,洋中脊玄武岩(BORB)的δ^6Li值为-4.7‰--3.7‰,由于锂同位素存在大的分馏和不同地质体中在截然不同的δ^6Li值,因此锂同位素地质应用前景十分广泛。目前,锂同位素在研究星云形成过程和宇宙事件,洋壳蚀变和海底热液活动,壳-幔物质循环和板块俯冲作用过程,判断卤水起源和演化等方面的研究中成效显著。 相似文献
6.
文章分析了辽宁太古代红透山铜矿中硫化物的多硫同位素组成和石英的硅氧同位素组成。δ34S在-0.7‰~+3.1‰,极差为3.8‰,平均值为0.21‰,与深部幔源硫相似。δ33S≈0.52δ34S,即δ33S=0(δ33S =δ33S-1000[(1+ δ34S/1000)0.515-1],不具有硫同位素非质量分馏效应,表明该矿床中的硫没有经历大气循环过程。矿石中石英的δ30Si分布在-0.8‰~+0.4‰之间,δ18O分布在+8.5‰~+9.5‰之间,与海底黑烟囱及热水喷气成因硅质岩的硅氧同位素组成相似。提出红透山铜矿为海底热液喷气沉积变质成因。 相似文献
7.
地球演化历史中海水的pH值发生了明显变化,海水pH值可能是控制海相碳酸盐岩能否形成及其成分演化的重要因素,对了解地球早期白云岩的成因和一些矿产的形成等均有重要指示意义.然而,记录海洋pH值变化的替代性指标非常稀少,常用的主要是碳酸盐(岩)的硼同位素.古老碳酸盐的硼同位素往往受到后期地质作用的影响,δ11B-pH转化过程中需要基于多种假设,硼酸和硼酸根之间的分馏系数(αB)、硼酸表观电离常数(pKB*)以及 δ11BSW的不确定性,使硼同位素分析结果具有多解性、不确定性.亟需多个独立指标对海水pH值进行限制,碳酸盐(岩)锂同位素是一个潜在的替代性指标,Roberts et al.(2018)发现有孔虫碳酸盐壳体的δ7Li与海水pH值呈显著负相关关系,认为6Li和7Li水合离子在进入碳酸盐晶格时要脱去溶剂水,这个过程的去溶能与pH值相关,导致锂离子进入有孔虫方解石壳体的过程中存在显著的同位素分馏.在对蓟县剖面中—新元古代海相碳酸盐岩碳酸盐相的硼、锂同位素进行研究时发现,纯净原始碳酸盐岩的锂同位素组成(4.9‰~13.4‰,平均8.03‰)明显低于现代海洋碳酸盐的锂同位素组成,中元古以来碳酸盐(岩)的锂同位素组成总体呈上升趋势.纯净原始碳酸盐岩的锂同位素组成与硼同位素组成及海水的pH值(δ11Bsw=25‰)呈明显反相关关系;硅质条带白云岩的硼、锂同位素组成也呈明显反相关关系,说明碳酸盐(岩)的锂同位素确实有可能成为一种潜在的pH值替代性指标.若碳酸盐(岩)锂同位素可以对海水pH值施加独立约束,那硼、锂同位素联合研究将对重建古海洋的pH值演化具有重大意义. 相似文献
8.
拉萨地块西段中新世赛利普超钾质火山岩富集地幔源区和岩石成因:Li同位素制约 总被引:1,自引:0,他引:1
作为一种“非传统稳定同位素”,锂同位素地球化学研究已经成为近年来国际上研究的热点之一.文章成功应用锂同位素对青藏高原西南部赛利普超钾质火山岩进行了示范研究.研究表明,赛利普超钾质火出岩的w(Li)为11.2×10-6~22.9× 10-6,同位素组成δ7Li为1.2‰~+3.5‰,平均值为0 2‰,与平均上地壳的相当.超钾质火山岩的锂同位素组成与岩浆结晶分异程度参数之间不存在任何相关性,这表明在超钾质火山岩结晶分异过程中没有发生明显的锂同位素分馏,锂同位素组成特征反映了其形成时的源区特征.超钾质火山岩的锂同位素组成变化范围达4.7‰,并且与pb-Sr-Nd同位素和岩浆结晶分异参数之间亦无任何相关性,表明锂同位素异常可能反映了不均匀源区岩石特征.通过计算模拟以及与前人的类似研究成果进行对比,笔者认为俯冲印度地壳而不是特提斯洋壳(包括沉积物)的流体/熔体参与了超钾质火山岩的源区富集,并在此基础上提出了超钾质火山岩成因模式. 相似文献
9.
喀斯特高原湖泊生物地球化学过程中的锌同位素特征 总被引:1,自引:0,他引:1
采用多接收电感耦合等离子体质谱仪(MC-ICP-MS)对喀斯特高原湖泊红枫湖、阿哈湖水体及其主要支流水体悬浮物和一些生物样品中的锌同位素进行了测定,测试精度小于0.11‰(2SD).结果显示,红枫湖水体与其主要支流水体悬浮物中的δ66Zn变化范围分别为-0.29‰~0.26‰和-0.04‰~0.48‰,阿哈湖水体与其主要支流水体悬浮物中的δ66Zn变化范围分别为-0.18‰~0.27‰和-0.179‰~0.46‰,均表现出支流中的锌同位素组成较重的特点.两湖生物样品中的δ66Zn变化范围较大,为-0.35‰~0.57‰,说明湖泊生态系统中各端员的锌同位素组成存在一定差异.根据同位素组成分析,湖泊主要入湖河流及所携带的陆源物质是阿哈湖泊水体中锌的主要来源,锌同位素是一种较好的物源示踪工具.红枫湖夏季δ66zn与Chla(叶绿素)呈显著的正相关(R=0.97),主要是藻类对锌的有机吸附和吸收过程导致锌同位素组成发生变化.此外,湖泊水体悬浮物中的锌同位素组成均在夏季较轻,表明大气的干湿沉降可能是一个较负的锌同位素源.水体悬浮物中的δ66Zn变化范围小于生物样品中的δ66Zn变化范围,说明由于生物作用过程导致的锌同位素分馏大于非生物过程. 相似文献
10.
四川康定甲基卡超大型锂矿是我国最大的硬岩型锂矿床之一,矿区中南部呈岩株状出露的二云母花岗岩常被认为是成矿伟晶岩的"矿源岩",对其开展Li同位素地球化学研究,对探讨矿区稀有金属的来源与演化具有重要意义.研究工作基于详细的野外地质调查,采用MC-ICP-MS方法对岩体锂同位素组成开展了研究.研究结果显示,岩体Li含量介于192×10-6~470×10-6,均值为309×10-6,δ7Li值介于-1.56‰~+0.90‰,均值为-0.24‰,与平均上地壳值基本一致,具有高Li低δ7Li的特征.δ7Li与Li、Rb、Ga、SiO2及εNd(t)不存在明显的相关性,岩体锂同位素组成反映了其形成时的源区特征,未受岩浆结晶分异作用和蚀变作用的影响.岩体岩石地球化学、同位素地球化学资料表明,岩浆来源以三叠系西康群砂泥岩的部分熔融为主,可能有部分深源物质的加入.此外,岩体Li同位素的变化规律表明伟晶岩的成矿流体来源于二云母花岗岩.岩体Li含量与Li同位素组合不仅可用来划分锂矿床类型,而且对稀有金属找矿具有一定的指导意义. 相似文献
11.
Boron isotopes geochemistry of the Changjiang basin rivers 总被引:1,自引:0,他引:1
B. Chetelat C.-Q. Liu J. Gaillardet Z.Q. Zhao Y.K. Xiao 《Geochimica et cosmochimica acta》2009,73(20):6084-6097
We report analyses of B isotopic compositions in water and suspended particulate matter collected in the Changjiang and its main tributaries. We showed that four sources control the dissolved boron budget; namely atmospheric deposition, evaporite dissolution, anthropogenic inputs and silicate weathering. The contribution of silicate weathering to the dissolved B load ranges from 40% to 50% for the Changjiang main channel and from 45% to 88% for the main tributaries. The isotopic composition of dissolved boron derived from silicate weathering range from −3‰ up to +9‰ suggesting that isotopic fractionation occurs during silicate weathering. The boron isotopic composition of suspended particulate matter range from −11.4‰ to −6‰. Boron derived from silicate weathering is preferentially carried out by the dissolved load which accounts for 30-96% of the total boron. We show that the isotopic compositions of both the dissolved load and suspended particulate matter are controlled by the competition between boron leaching and boron uptake into secondary phases. The first process is characterized by a loss of boron relative to the bedrock without apparent isotopic fractionation whereas the last one is associated to a large isotopic fractionation which enriches the dissolved boron in heavy isotope. 相似文献
12.
We report Li isotopic compositions, for river waters and suspended sediments, of about 40 rivers sampled within the Mackenzie River Basin in northwestern Canada. The aim of this study is to characterize the behaviour of Li and its isotopes during weathering at the scale of a large mixed lithology basin. The Mackenzie River waters display systematically heavier Li isotopic compositions relative to source rocks and suspended sediments. The range in δ7Li is larger in dissolved load (from +9.3‰ to +29.0‰) compared to suspended sediments (from −1.7‰ to +3.2‰), which are not significantly different from δ7Li values in bedrocks. Our study shows that dissolved Li is essentially derived from the weathering of silicates and that its isotopic composition in the dissolved load is inversely correlated with its relative mobility when compared to Na. The highest enrichment of 7Li in the dissolved load is reported when Li is not or poorly incorporated in secondary phases after its release into solution by mineral dissolution. This counterintuitive observation is interpreted by the mixing of water types derived from two different weathering regimes producing different Li isotopic compositions within the Mackenzie River Basin. The incipient weathering regime characterizing the Rocky Mountains and the Shield areas produces 7Li enrichment in the fluid phase that is most simply explained by the precipitation of oxyhydroxide phases fractionating Li isotopes. The second weathering regime is found in the lowland area and produces the lower δ7Li waters (but still enriched in 7Li compared to bedrocks) and the most Li-depleted waters (compared to Na). Fractionation factors suggest that the incorporation of Li in clay minerals is the mechanism that explains the isotopic composition of the lowland rivers. The correlation of boron and lithium concentrations found in the dissolved load of the Mackenzie Rivers suggests that precipitation of clay minerals is favoured by the relatively high residence time of water in groundwater. In the Shield and Rocky Mountains, Li isotopes suggest that clay minerals are not forming and that secondary minerals with stronger affinity for 7Li appear.Although the weathering mechanisms operating in the Mackenzie Basin need to be characterized more precisely, the Li isotope data reported here clearly show the control of Li isotopes by the weathering intensity. The spatial diversity of weathering regimes, resulting from a complex combination of factors such as topography, geology, climate and hydrology explains, in fine, the spatial distribution of Li isotopic ratios in the large drainage basin of the Mackenzie River. There is no simple relationship between Li isotopic composition and chemical denudation fluxes in the Mackenzie River Basin. 相似文献
13.
Junyeon Yoon 《Aquatic Geochemistry》2010,16(1):189-206
The lithium concentration of the dissolved load from the Lena River, together with major element chemistry and GIS-based area
and runoff data demonstrate the importance of evaporites in controlling dissolved Li in river waters. Eighty-four percent
of the Li in the dissolved load of upper Lena tributaries comes from evaporites in these drainage basins. Altogether, at least
~20% of the total Li flux of the Lena River originates from this source. This finding has important implications for using
lithium as a proxy for silicate weathering. The Li flux and the 87Sr/86Sr ratio are compared in order to address a difference between the two silicate weathering rate proxies. The proposed controls
on the dissolved δ7Li values in rivers (kinetic vs. equilibrium isotopic fractionation; Rayleigh-type preferential extraction of the heavy isotope)
(Huh et al., Earth Planet Sci Lett 194:189–199, 2001) are evaluated using data from both the Siberian rivers and the Orinoco
River. Neither of the proposed mechanisms satisfactorily explains the comprehensive data set. Instead, a ‘mineralogy-specific
view’ that emphasizes the difference in the secondary mineralogy (i.e., fractionation factor) is presented as a potential
rationalization in the form of the refined Rayleigh-type extraction. 相似文献
14.
Silicon isotope compositions of dissolved silicon and suspended matter in the Yangtze River, China 总被引:5,自引:0,他引:5
Silicon isotope compositions of main channel samples of the Yangtze River were systematically investigated along with their chemical compositions. The concentration of suspended matter in the Yangtze River tends to decrease from the upper reaches to the lower reaches, corresponding to settling of the sediments in the lakes and reservoirs due to reduction of the velocity of water flow. The silica contents of suspended matter vary from 52.1% to 56.9% and their δ30Si values vary from 0 to −0.7‰, both similar to those of shales. From the upper to lower reaches, the silica contents of suspended matter tend to increase, whilst their δ30Si values tend to decrease. Both trends reflect the increase of clay minerals and decrease of carbonates in suspended matter.The concentrations of dissolved silicon vary from 97 to 121 μmol/L and their δ30Si values vary over a wide range from 0.7 to 3.4‰. From the upper to lower reaches, dissolved silica concentrations tend to decrease and their δ30Si values tend to increase. These trends mainly reflect the change of chemical and isotopic characteristics of the tributaries from the upper to lower reaches. The major factors responsible for these changes may be the high meteoric precipitation and significant silicon absorption by grass (in wetlands) and rice (in paddy fields) in drainage areas of the middle and lower reaches.There is no correlation between δ30Si of dissolved silicon and that of suspended matter. The Δ30SiDiss-SPM values vary over a wide range of 1.0-3.7‰, indicating that (1) they are out of isotopic equilibrium, (2) dissolved silicon and the associated suspended matter do not belong to one physico-chemical system, and (3) isotopic exchange rate between them is very slow.The δ30Si value of dissolved silicon output from the Yangtze River to the East Sea is estimated to be 3.0‰, much higher than the values reported for the Amazon and Congo rivers. This increases the δ30Si range of dissolved silicon in the world’s rivers from 0.4-1.2%; to 0.4-3.4%. 相似文献
15.
The Madi rare metal granite is a complex massif, which contains a variety of rare metals, such as Nb, Ta, Li, and Be. In this paper, the geochemical characteristics of the granite were obtained by multi-collector inductively coupled mass spectrometry (MC-ICP-MS). The precise crystalline age of the granite was obtained from monazite U-Pb dating, and the source of the granite was determined using Li-Nd isotopes. The Madi rare metal granite is a high-K (calc-alkaline), peraluminous, S-type granite. The U-Pb monazite age indicates that the crystalline age of the granite is 175.6 Ma, which is Early Jurassic. The granite is characterized by a relatively wide range of δ7Li values (+2.99‰ to +5.83‰) and high lithium concentrations (181 ppm to 1022 ppm). The lithium isotopic composition of the granite does not significantly correlate with the degree of magmatic differentiation. An insignificant amount of lithium isotope fractionation occurred during the granitic differentiation. The lithium isotopic composition of the granite significantly differs from that of the wall rock, but it is very similar to that of a primitive mantle peridotite xenolith (mean δ7Li value +3.5‰). The plot of Li concentration versus δ7Li indicates that the Li isotopic composition of the granite is similar to that of island arc lavas. Based on the above-described evidence, the granite was mainly derived from the crust, but it was contaminated by a deep granitic magma. 相似文献
16.
Lithium and strontium isotopic systematics in playas in Nevada,USA: constraints on the origin of lithium 总被引:1,自引:0,他引:1
Daisuke Araoka Hodaka Kawahata Tetsuichi Takagi Yasushi Watanabe Koshi Nishimura Yoshiro Nishio 《Mineralium Deposita》2014,49(3):371-379
Lithium-rich brine in playas is a major raw material for lithium production. Recently, lithium isotopic ratios (δ7Li) have been identified as a tool for investigating water–rock interactions. Thus, to constrain the origin of lithium in playas by the use of its isotopes, we conducted leaching experiments on various lacustrine sediment and evaporite deposit samples collected from playas in Nevada, USA. We determined lithium and strontium isotopic ratios and contents and trace element contents of the leachate, estimated the initial δ7Li values in the water flowing into the playas, and examined the origin of lithium in playas by comparison with δ7Li values of the possible sources. In samples from the playas, δ7Li values show some variation, reflecting differences both in isotopic fractionation during mineral formation and in initial δ7Li value in water flowing into each playa. However, all δ7Li values in this study are much lower than those in river water and groundwater samples from around the world, but they are close to those of volcanic rocks. Considering the temperature dependence of lithium isotopic fractionation between solid and fluid, these results indicate that the lithium concentrated in playas in Nevada was supplied mainly through high-temperature water–rock interaction associated with local hydrothermal activity and not directly by low-temperature weathering of surface materials. This study, which is the first to report lithium isotopic compositions in playas, demonstrates that δ7Li may be a useful tracer for determining the origin of lithium and evaluating its accumulation processes in playas. 相似文献
17.
应用离子探针技术对山东蓬莱新生代玄武岩中橄榄岩包体的主要组成矿物进行了原位测定,结果显示了强烈偏离正
常地幔矿物组成和平衡的Li 含量和同位素比值。橄榄石、斜方辉石和单斜辉石的Li 含量和δ7Li 分别为(2.0~10.4)×10-6,
(2.8~23.8)×10-6 和(3.3~59.7)×10-6;-28.6‰ ~+0.5‰,-12.7‰ ~+12.8‰和-41.5‰ ~+22.6‰。这种强烈的非平衡体系反
映了最近强烈和复杂的地幔交代作用。辉石的高Li(~ 60×10-6)和δ7Li(~ +20‰)反映了最近富Li地幔熔体/ 流体的特征,
而橄榄石的中等Li 富集(<5×10-6)和强烈的δ7Li 亏损(~ -20‰)则可能记录了更早一期低δ7Li 的地幔交代。同位素剖面
的扩散反演以及Li 强烈富集与LREE 相对亏损之间的解耦显示了两期地幔交代作用的短暂性和近期性。因此,我们认为华
北东部克拉通上地幔中存在与再循环有关的锂同位素异常组分,它们的形成应该与中生代以来太平洋板块向东亚大陆下的
俯冲有关. 这些组分能够在地幔中较长的保存直至最近被热扰动所释放,并被橄榄岩包体所记录。 相似文献
18.
Melesse Alemayehu Hong-Fu Zhang Patrick Asamoah Sakyi Muhammed Haji 《Journal of the Geological Society of India》2018,91(1):99-108
We report Lithium (Li) concentrations and isotopic compositions for co-existing olivine, orthopyroxene (opx), and clinopyroxene (cpx) mineral separates from depleted and metasomatised peridotite xenoliths hosted by basaltic lavas from northwestern Ethiopian plateau (Gundeweyn area). The peridotites contain five lherzolites and one harzburgite and are variably depleted and enriched in LREE relative to HREE. In both depleted and enriched lherzolites, Li is preferentially incorporated into olivine (2.4-3.3 ppm) compared to opx (1.4-2.1 ppm) and cpx (1.4-2.0 ppm) whereas the Li contents of olivines (5.4 ppm) from an enriched harzburgiteare higher than those of lherzolites. Olivines from the samples show higher Li abundances than normal mantle olivines (1.6-1.9 ppm) indicating the occurrence of Li enrichments through melt-preroditite interaction. The average δ7 Li values range from +2.2 to +6.0‰ in olivine, from -0.1 to +2.0‰ in opx and from -4.4 to -0.9‰ in cpx from the lherzolites. The Li isotopic composition (3.5‰) of olivines from harzburgite fall within the range of olivine from lherzolites but the opxs show low in δ7Li (-2.0‰). Overall Li isotopic compositions of olivines from the peridotites fall within the range of normal mantle olivine, δ7Li values of ~+4±2‰ within uncertainty, reflecting metasomatism (enrichment) of the peridotites by isotopically heavy Li-rich asthenospheric melt. Li isotope zonation is also observed in most peridotite minerals. Majority of olivine grains display isotopically heavy cores and light rims and the reverse case is observed for some olivine grains. Orthopyroxene and clinopyroxene grains show irregular distribution in δ7Li. These features of Li isotopic compositions within and between grains in the samples reflect the effect of diffusion-driven isotopic fractionation during meltperidotite interaction and cooling processes. 相似文献
19.
How important is it to integrate riverine suspended sediment chemical composition with depth? Clues from Amazon River depth-profiles 总被引:1,自引:0,他引:1
Julien Bouchez Maarten Lupker Christian France-Lanord 《Geochimica et cosmochimica acta》2011,75(22):6955-6970
The vertical variability in mineralogical, chemical and isotopic compositions observed in large river suspended sediments calls for a depth-integration of this variability to accurately determine riverine geochemical fluxes. In this paper, we present a method to determine depth-integrated chemical particulate fluxes of large rivers, based on river sampling along depth-profiles, and applied to the Amazon Basin lowland tributaries. The suspended particulate matter (SPM) concentration data from depth-profiles is modeled for a number of individual grain size fractions using the Rouse model, which allows to predict the grain size distribution of suspended sediment throughout the whole river cross-section. Then, using (1) the relationship between grain size distribution and the Al/Si ratio (2) relationships between the Al/Si ratio and the chemical concentrations, the chemical composition of river sediment is predicted throughout the river cross-section, and integrated to yield the depth-integrated chemical particulate flux for a number of chemical elements (e.g. Si, Al, Fe, Na, REEs, …). For elements such as Al, Fe, REEs, Th, the depth-integrated flux is around twice as high as the one calculated from river surface sample characteristics. For Na and Si, the depth-integrated flux is three times higher than the “surface” estimate, due to the enrichment of albite and quartz at the bottom of the river. Depth-integrated 87Sr/86Sr composition of suspended sediment, also predictable using this method, differs by more than 10−3 from the surface sample composition.Finally, potential implications of depth-integrated estimates of Amazon sediment chemistry are explored. Depth-integration of particulate 87Sr/86Sr isotopic ratios is necessary for a reliable use of Sr isotopes as a provenance tracer. The concept of steady-state weathering of a large river basin is revisited using depth-integrated sediment composition. This analysis shows that, in the Amazon Basin river, the previously observed discrepancy between (1) weathering intensities of channel surface sediment and (2) silicate-derived dissolved fluxes is only slightly accounted for by the vertical variability of suspended sediment weathering intensities. This observation confirms that most large rivers basins are not eroding at steady-state. 相似文献