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首页> 外文期刊>Aquatic geochemistry >Geochemistry of Suspended Particulate Matter (SPM) in the Murray-Darling River System: A Conceptual Isotopic/Geochemical Model for the Fractionation of Major, Trace and Rare Earth Elements
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Geochemistry of Suspended Particulate Matter (SPM) in the Murray-Darling River System: A Conceptual Isotopic/Geochemical Model for the Fractionation of Major, Trace and Rare Earth Elements

机译：墨累-达令河系统中悬浮颗粒物（SPM）的地球化学：主要，微量和稀土元素分级分离的概念同位素/地球化学模型

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A conceptual isotopic/geochemical model is presented to explain the variation of major, trace and rare earth element (REE) geochemistry and Sr isotope systematics in suspended particulate matter (SPM) as a function of particle/collold size. This conceptual model is an extension of a previous investigation of the origin of SPM in the Murray-Darling River system (MDRS) that utilised Sr isotope systematics to examine aspects of SPM (particle/colloid) origin, structure and mineralogy.The geochemical processes that give rise to the often coherent trends in major, trace and REE geochemistry and Sr isotopic signature as a function of particulate (>1 #mu#m) and colloidal (<1 #mu#m) size in the MDRS have been identified using an enhanced SPM Size fractionation technique as a basis to not only obtain a broad range of particle/colloid size ranges, but also to provide sufficient material for subsequent geochemical and isotopic analysis. The conceptual isotopic/geochemical model proposed here contains three major components: (i) the differential weathering of micas and alkali (K-) feldspars to form the majority of the particulate (>1 #mu#m) fractions (high ~(87) Sr/~(86)Sr ratio), which have a geochemical and Sr isotopic signature that closely resembles precursor mineralogies, (ii) the differential weathering of Na, Ca-feldspars (plagioclase) which decompose to form clay minerals in the colloidal (<1 #mu#m) fractions(low ~(87) Sr/~(86)Sr ratio), with a range of geochemical signatures related to the relative proportions of inorganic of inorganic and organic constituents, and (iii) the presence of natural organic matter as coatings on the particulate (>1 #mu#m) and colloidal (<1 #mu#m) matter and possibly as organo-colloids which exert an increasing influence in particular on bulk colloid geochemistry with decreasing colloid size. This conceptual isotopic/geochemical model also accounts for the distinct variation in major, trace and REE geochemistry and Sr isotopic systematics between the particulate (>1 #mu#m) and colloidal (<1 #mu#m) fractions, the variation being primarily a function of the distinctly different precursor mineralogies of the SPM fractions and geochemical fractionation during the weathering and transport. Additionally, this model explains a systematic fractionation of REE apparent within colloidal (<1 #mu#m) fractions. Statisitcal (hierachical cluster) analysis of two particulate and three colloidal fractions from 23 samples from the MDRS is used as a basis to investigate geochemical and mineralogical associations within the particulate and colloidal size fractions and to provide additional supporting evidence for the concenptual isotopic/geochemical model.
机译：提出了一个概念性的同位素/地球化学模型来解释悬浮颗粒物（SPM）中主要，痕量和稀土元素（REE）地球化学和Sr同位素系统随颗粒/胶体尺寸的变化。该概念模型是对Murray-Darling River系统（MDRS）中SPM起源的先前研究的扩展，该研究利用Sr同位素系统学研究了SPM（颗粒/胶体）的起源，结构和矿物学方面。引起了主要，痕迹和REE地球化学和Sr同位素特征的经常一致的趋势，该趋势已通过使用增强的SPM尺寸分级技术不仅作为获得大范围颗粒/胶体尺寸范围的基础，而且还为后续的地球化学和同位素分析提供了足够的材料。本文提出的概念性同位素/地球化学模型包含三个主要成分：（i）云母和碱金属（K-）长石的差异风化作用，形成了大部分颗粒（> 1＃mu＃m）组分（高〜（87）） Sr /〜（86）Sr比），其地球化学和Sr同位素特征与前体矿物学特征非常相似，（ii）Na，Ca长石（斜长石）的不同风化作用，在胶体中分解形成粘土矿物（< 1＃mu＃m）馏分（低〜（87）Sr /〜（86）Sr比），具有与无机无机成分和有机成分的相对比例有关的一系列地球化学特征，以及（iii）存在天然有机物作为颗粒（> 1＃μ＃m）和胶体（<1＃μ＃m）上的涂层，并可能作为有机胶体，对胶体尺寸减小的整体胶体地球化学产生越来越大的影响。这种概念上的同位素/地球化学模型还解释了主要（微量）和REE地球化学以及Sr同位素系统在颗粒部分（> 1＃mu＃m）和胶体部分（<1＃mu＃m）之间的明显差异，主要是在风化和运输过程中，SPM馏分和地球化学分馏的明显不同的前体矿物学的作用。另外，该模型解释了胶体（<1＃mu＃m）馏分中明显的REE的系统分馏。对来自MDRS的23个样品中的两个颗粒物和三个胶体部分进行的统计（多级聚类）分析，是研究颗粒物和胶体尺寸部分中地球化学和矿物学联系的基础，并为概念性同位素/地球化学模型提供了额外的支持证据。

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