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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain
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Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain

机译：玄武质地形中伴随风化和河流迁移的钼同位素行为

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The application of the molybdenum (Mo) isotope system as a proxy for determining changes in the redox state of the oceans is predicated on the assumption that the composition of continental input can be characterised from crustal rock types, and remains constant. However, it has recently been shown that the δ~(98/95)Mo composition of global rivers varies between 0.15% and 2.4% and is therefore systematically heavier than the average composition of the continental crust (~0%). In order to understand the processes that control Mo-isotope fractionation during weathering this study presents δ~(98/95)Mo and Mo abundance data for rivers (and estuarine samples) from Iceland that drain predominantly basaltic terrains. Resolvable differences are observed in the isotopic composition of the riverine Mo sources; ice (δ~(98/95)Mo_(ice) >1.8%), basaltic bedrock (δ~(98/95)Mo_(bedrock) ~0.0%) and hydrothermal waters (δ~(98/95)Mohydrothermal ~-3.4%). Systematic changes in the dissolved Mo-isotope composition are also observed within river catchments, with δ~(98/95)Mo values increasing from ~0% in glacial rivers (close to the source) to ~1% downstream, consistent with Mo-isotopes being fractionated during weathering. Analysis of other riverine phases (bedload, colloids and iron-precipitates) demonstrates that these phases preferentially incorporate light Mo-isotopes, and remain coupled to the dissolved load during riverine transportation. A δ~(98/95)Mo profile through the Borgarfj?r{Eth}ur estuary exhibits a predominantly conservative mixing behaviour, but suggests that the release of isotopically light Mo from the particulate and/or colloidal phases may occur in the low salinity part of the estuarine mixing zone.
机译：钼（Mo）同位素系统作为确定海洋氧化还原状态变化的替代方法的应用是基于这样的假设，即大陆输入的成分可以根据地壳岩石类型来表征，并且保持不变。然而，最近发现，全球河流的δ〜（98/95）Mo组成在0.15％和2.4％之间变化，因此系统上比大陆地壳的平均组成（〜0％）重。为了了解在风化过程中控制Mo同位素分馏的过程，本研究提供了主要排放玄武岩地带的冰岛河流（和河口样品）的δ〜（98/95）Mo和Mo丰度数据。在河流钼源的同位素组成中观察到可分辨的差异。冰（δ〜（98/95）Mo_（冰）> 1.8％），玄武岩基岩（δ〜（98/95）Mo_（基岩）〜0.0％）和热液（δ〜（98/95）Mohydrothermal〜- 3.4％）。在流域内还观察到溶解的Mo同位素组成的系统变化，δ〜（98/95）Mo值从冰川河（靠近源头）的〜0％上升到下游的〜1％，与Mo-一致同位素在风化过程中被分离。对其他河流相（床载量，胶体和铁沉淀物）的分析表明，这些相优先掺入轻质的Mo同位素，并在河流运输过程中保持与溶解负荷的耦合。通过Borgarfj？r {Eth} ur河口的δ〜（98/95）Mo曲线显示出主要是保守的混合行为，但表明在低盐度下可能从颗粒相和/或胶体相释放同位素轻的Mo。河口混合区的一部分。

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