Behaviors of trace elements in Neoarchean and Paleoproterozoic paleosols: Implications for atmospheric oxygen evolution and continental oxidative weathering
Behaviors of trace elements in Neoarchean and Paleoproterozoic paleosols: Implications for atmospheric oxygen evolution and continental oxidative weathering
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DOI：
10.1016/j.gca.2016.07.008
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发表时间：
2016-11
影响因子：
5
通讯作者：
T. Murakami;K. Matsuura;Y. Kanzaki
中科院分区：
文献类型：
--
作者：
T. Murakami;K. Matsuura;Y. Kanzaki
研究了新太古代和古元古代古土壤（古代风化剖面）中氧化还原敏感和/或生物必需微量元素的行为，以更好地了解大气中氧气的演化。古土壤中单个微量元素的损失或保留可以表明大陆氧化风化以及大气氧的演化是如何随着年龄的增长而发生的，这主要是由于它们不同的氧化还原电位。采用电感耦合等离子体发射光谱和质谱法测定了2个古元古代古土壤的V、Cr、Ni、Cu、Zn和Mo浓度，并从文献中获得了9个新太古代和古元古代古土壤的V、Cr、Ni、Cu、Zn和Mo浓度，以及Co、W和U浓度。微量元素的行为受到其在古土壤中的损失或保留程度的限制。我们采用两种方法进行估计：（i）元素 M 的保留分数（使用 Ti 等固定元素计算古土壤中元素 M 与母岩的质量比）和（ii）古土壤不同剖面深度的元素-元素（特别是 Si 元素）相关性。新太古代和古元古代古土壤中的微量元素行为有两个不同的组：Co、Ni、Zn 和 W 直到古元古代早期才从风化剖面中消失。但在古元古代中晚期保留下来，而V、Cr、Cu、Mo、U则保留在古元古代早期或稍晚的剖面中，但在古元古代中晚期从剖面中消失。更准确地说，古元古代微量元素的这种损失和保留的时间是不同的。这些从保留到丢失或从丢失到保留的变化特征表明这些变化发生并持续了整个古元古代。因此，微量元素行为表明，几乎在整个古元古代，大陆风化作用随着年龄的增长而逐渐氧化，因此，在同一时期内，大气中的氧气随着年龄的增长而类似地增加，但在相对较短的时间内并不是突然增加的。微量元素的损失和保留可以推断它们是如何随着新太古代和古元古代的年龄从大陆释放到海洋的。
The behaviors of redox-sensitive and/or bio-essential trace elements in Neoarchean and Paleoproterozoic paleosols (ancient weathering profiles) were investigated to better understand atmospheric oxygen evolution. The loss or retention of individual trace elements in the paleosols can show how continental oxidative weathering, and thus atmospheric oxygen evolution, took place against age mainly due to their various redox potentials. The V, Cr, Ni, Cu, Zn and Mo concentrations of two Paleoproterozoic paleosols were measured by inductively coupled plasma optical emission spectrometry and mass spectrometry, and those, as well as Co, W and U concentrations, of nine Neoarchean and Paleoproterozoic paleosols were obtained from the literature. The trace element behaviors were constrained by their degrees of loss or retention in the paleosols. We applied two methods to the estimation: (i) retention fraction of element M (a mass ratio of element M of paleosol to parent rock using immobile elements such as Ti) and (ii) element-element (in particular, Si-element) correlations at different profile depths of a paleosol.There are two distinct groups in trace element behavior in the Neoarchean and Paleoproterozoic paleosols: Co, Ni, Zn and W were lost from weathering profiles until the early Paleoproterozoic but retained in the middle and late Paleoproterozoic, while V, Cr, Cu, Mo and U were retained in the profiles until the early Paleoproterozoic or slightly later but lost from the profiles in the middle and late Paleoproterozoic. More precisely, the timings of such loss and retention were different between trace elements during the Paleoproterozoic. The characteristics of these changes from retention to loss or from loss to retention indicate that the changes occurred and lasted throughout the Paleoproterozoic. The trace element behaviors, accordingly, suggest that continental weathering became oxidative progressively with age during almost the whole Paleoproterozoic, and thus, atmospheric oxygen increased similarly with age in the same time period but not suddenly in a relatively short term. The loss and retention of the trace elements may infer how they were released from the continent to the ocean against age in the Neoarchean and Paleoproterozoic.