Controls over the strontium isotope composition of river water
Controls over the strontium isotope composition of river water
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DOI：
10.1016/0016-7037(92)90332-d
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发表时间：
1992-05
影响因子：
5
通讯作者：
M. Palmer;J. Edmond
中科院分区：
文献类型：
--
作者：
M. Palmer;J. Edmond
锶的浓度和同位素比已被测量的河流和地下沃茨从恒河，奥里诺科河，亚马逊河流域。与主要元素浓度相比，数据集允许在以下环境中对河流输入海洋的锶同位素系统学进行详细检查：1。(1)“典型”流域盆地，含有石灰岩、碳酸盐岩、页岩和铝硅酸盐变质岩和火成岩; 2. (2)不含化学或生物沉积物的屏蔽地形;以及3. (3)构成许多大河最大面积的洪泛平原。河水沃茨的浓度和同位素组成主要由石灰岩和碳酸盐岩中的锶与硅酸盐岩中的锶混合而确定。石灰岩端元的锶同位素组成一般位于中生代海水的范围内，缓冲的87 Sr-86 Sr比值的主要河流。一个主要的例外是喜马拉雅山脉的河流，在那里，火山灰区域变质作用似乎导致了来自共存硅酸盐岩石的放射性锶的石灰岩富集。河流排水屏蔽区的锶同位素系统控制的激烈，transportlimited，风化反应的性质，从而限制了这些地形的锶通量的变化。洪泛区只是溶解锶进入河流沃茨的一个次要来源，一些洪泛区土壤盐分的沉淀会减少溶解锶进入海洋的河流通量。最有效的机制，改变同位素比值和流量的河流锶到海洋是增加冰川作用和大规模的区域变质作用的类型在大陆碰撞。这两种机制提供了一种手段，增加87 Sr-86 Sr的全球河流通量的比例。
Strontium concentrations and isotope ratios have been measured in river and ground waters from the Ganges, Orinoco, and Amazon river basins. When compared with major element concentrations, the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments: 1.(1)“typical” drainage basins containing limestones, evaporites, shales, and alumino-silicate metamorphic and igneous rocks; 2.(2) shield terrains containing no chemical or biogenic sediments; and 3.(3) the floodplains that constitute the largest areas of many large rivers. The strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks. The strontium isotope composition of the limestone endmember generally lies within the Phanerozoic seawater range, which buffers the 87 Sr 86 Sr ratios of major rivers. A major exception is provided by the rivers draining the Himalayas, where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks. The strontium isotope systematics of rivers draining shield areas are controlled by the intense, transportlimited, nature of the weathering reactions, and thereby limits variations in the strontium flux from these terrains. Floodplains are only a minor source of dissolved strontium to river waters, and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans. The most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large-scale regional metamorphism of the type produced during continental collision. Both mechanisms provide a means for increasing the 87 Sr 86 Sr ratio of the global riverine flux.