Controls on trace-element partitioning in cave-analogue calcite
Controls on trace-element partitioning in cave-analogue calcite
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DOI：
10.1016/j.gca.2013.05.044
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发表时间：
2013-11-01
影响因子：
5
通讯作者：
Henderson, Gideon M.
中科院分区：
文献类型：
--
作者：
Day, Christopher C.;Henderson, Gideon M.
我们报告的微量元素数据，从一系列的碳酸盐生长实验在洞穴模拟条件下，在实验室中的目标，更好地了解环境控制的微量元素纳入石笋。实验装置密切模仿自然过程（e。G.通过CO2脱气驱动的沉淀、低离子强度溶液、薄溶液膜），但严格控制生长条件（温度、pCO（2）、滴加速率、方解石饱和指数和初始溶液的组成）。将方解石溶解在20，000 ppmV pCO（2）环境中的去离子水中，并以适当浓度添加微量元素（Li、Na、Mg、Co、Sr、Cd、Ba、U），以模拟天然洞穴滴水。在7、15、25和35 ℃的较低pCO（2）环境中，以每分钟2、6和10滴的滴速将该溶液滴到玻璃板（涂覆有晶种-方解石）上。D（Sr）被证明是统计不变的温度和生长速率的研究在整个范围内。Sr/Ca和增长率之间没有关系，因此，预计在石笋样品可比的增长率。D（Mg）与温度的关系定义为D（Mg）= 0.01e（0.02[+/- 0.006]T），但由于方解石沉淀对Mg/Ca的影响更大，温度预计不是洞穴方解石中Mg/Ca的主要控制因素。在短时间内，在温度缓冲良好的条件下，溶液中剩余的钙分数（f）可能是Mg/Ca和其他微量元素比例的主要控制因素。但是，微量元素对f和T的响应存在差异，这可能允许它们联合使用来评估过去的洞穴条件。高镉/钙石笋是特别指示量低的前方解石沉淀和镉/钙将是一个有用的除了天然石笋的微量元素研究。在实验室实验中，观察到显着的分散的微量元素的比例，这不能用简单的瑞利蒸馏解释。这种分散很好地解释了溶液的混合和混合的方解石与不同馏分的方解石生长。占微量元素浓度或比例的混合的影响，可能有助于实现更强大的解释石笋化学作为一个多代理方法来评估过去的环境的一部分。(C)2013爱思唯尔有限公司保留所有权利。
We report trace-element data from a series of carbonate growth experiments in cave-analogue conditions in the laboratory with the goal of better understanding environmental controls on trace-element incorporation in stalagmites. The experimental setup closely mimics natural processes (e. g. precipitation driven by CO2-degassing, low ionic strength solution, thin solution-film) but with a tight control on growth conditions (temperature, pCO(2), drip rate, calcite saturation index and the composition of the initial solution). Calcite is dissolved in deionized water in a 20,000 ppmV pCO(2) environment, with trace-elements (Li, Na, Mg, Co, Sr, Cd, Ba, U) at appropriate concentrations to mimic natural cave drip-waters. This solution is dripped onto glass plates (coated with seed-calcite) in a lower pCO(2) environment at 7, 15, 25 and 35 degrees C and drip rates of 2, 6 and 10 drips per minute. D(Sr) was shown to be statistically invariant over the full range of temperature and growth rate studied. No relationship between Sr/Ca and growth rate is therefore expected in stalagmite samples over comparable growth rates. D(Mg) has a relationship with temperature defined by D(Mg) = 0.01e(0.02[+/- 0.006]T), but temperature is not expected to be the dominant control on Mg/Ca in cave calcite due to the larger impact of calcite precipitation on Mg/Ca. Over short timescales, in conditions where temperature is well buffered, the fraction of calcium remaining in solution (f) is likely to be the dominant control on Mg/Ca and other trace-element ratios. But differences in the response of trace-elements to f and T may allow their combined use to assess past cave conditions. High Cd/Ca-stalagmite is particularly indicative of low amounts of prior calcite precipitation and Cd/Ca would be a useful addition to trace-element studies of natural stalagmites. Significant scatter is observed in trace-element ratios during the laboratory experiments, which cannot be explained by simple Rayleigh distillation. This scatter is well explained by solution mixing and by the mixing of calcite with different fractions of calcite growth. Accounting for the effects of mixing on trace-element concentrations or ratios may help to achieve more robust interpretations of stalagmite chemistry as part of a multi-proxy approach to assessment of past environments. (C) 2013 Elsevier Ltd. All rights reserved.