Effect of oxygen fugacity on OH dissolution in olivine under peridotite-saturated conditions: an experimental study at 1.5-7 GPa and 1100-1300 °C
Effect of oxygen fugacity on OH dissolution in olivine under peridotite-saturated conditions: an experimental study at 1.5-7 GPa and 1100-1300 °C
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橄榄岩饱和条件下氧逸度对橄榄石中OH溶解的影响：1.5-7 GPa、1100-1300 ℃下的实验研究
DOI：
10.1016/j.gca.2015.11.007
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发表时间：
2016-01
影响因子：
5
通讯作者：
Yang Xiaozhi
中科院分区：
文献类型：
--
作者：
Yang Xiaozhi
在过去的三十年里，通过模拟条件下的实验研究来研究OH在橄榄石中的溶解引起了人们越来越大的兴趣，压力、温度和组成的影响受到了相对较好的限制。氧逸度在上地幔的时间和空间尺度上都是高度不均匀的，是表征地幔中许多化学和物理过程的重要参数。然而，对氧逸度对OH在橄榄石中溶解的影响的关注较少，仅有的几个关于这一主题的报道导致了显著的不一致和争论。本文以天然宝石级橄榄石单晶和新鲜橄榄岩包体为原料，以Fe-FeO、Ni-NiO和Fe_2O_3-Fe_3O_4氧缓冲对控制氧逸度，在1.5-7℃和1100-1300℃条件下，在橄榄岩和流体饱和条件下，系统地研究了含铁橄榄石的氧逸度与OH溶解度的关系。用傅里叶变换红外光谱进行偏振分析，确定了水的浓度。结果表明，在所有实验条件下，高频(∼3650-3450 cm−1)和低频(∼3450-3100 cm−1)的OH带都很明显。∼3355和3325 cm−1的氢键强度随氧逸度的增加而增加，表明Fe~(3+)在它们的掺入中起主导作用。在其他相同的条件下，随着压力、温度或氧逸度的增加，水含量逐渐增加。在给定的压力下，氧逸度对提高OH溶解度的影响对温度(1100-1300℃)不敏感，但在给定的温度下，随着压力从1.5 Gpa增加到7 Gpa，氧逸度对OH的增溶作用逐渐增强。相对于氧逸度缓冲液，Fe-FeO和Ni-NiO之间的OH溶解度平均增加了∼50%，与压力和温度无关。在相对氧化条件下，OH的增溶可以用氧逸度在改变橄榄石的点缺陷中的作用来解释。有关橄榄石和上地幔中水的储存量的实验工作必须考虑氧逸度的影响。氧化条件下实验得到的橄榄石在还原深部上地幔中的OH溶解度被高估了。许多天然橄榄石的初始OH信息可能已经被最近的一些次生事件改变了，例如，在它们浅层停留和/或运往地表的过程中，原则上，相对于其共存的矿物，平衡在上地幔中的橄榄石可能是贫化的。文中还对地球和火星上地幔的储水量提出了一些初步的限制条件。
The dissolution of OH in olivine by experimental studies at simulated conditions has attracted increasing interest over the past three decades, and the influence of pressure, temperature and composition has been relatively well constrained. Oxygen fugacity is highly heterogeneous in the upper mantle, on both temporal and spatial scales, and is an important parameter in characterizing many chemical and physical processes in the mantle. However, less attention has been devoted to the effect of oxygen fugacity on OH dissolution in olivine, and the only few available reports on this topic have led to significant inconsistency and debate. In this study, the correlation between oxygen fugacity and OH solubility in Fe-bearing olivine has been systematically investigated by conducting experiments at 1.5–7 GPa and 1100–1300 °C and under peridotite- and fluid-saturated conditions, with natural gem-quality olivine single crystals and fresh peridotite xenoliths as starting materials and with oxygen fugacity controlled by the Fe–FeO, Ni–NiO and Fe2O3–Fe3O4oxygen buffer pairs. The water concentrations were determined by polarized analyses using a Fourier-transform infrared spectroscopy. The results show that, at all the experimental conditions, the OH bands at both high frequency (∼3650–3450 cm−1) and low frequency (∼3450–3100 cm−1) are prominent. The intensity of OH bands at ∼3355 and 3325 cm−1increases positively with oxygen fugacity, suggesting a dominant role of Fe3+in their incorporation. Under otherwise identical conditions, the water content is gradually enhanced with increasing pressure, temperature or oxygen fugacity. The effect of oxygen fugacity on the enhancement of OH solubility appears not sensitive to temperature (1100–1300 °C) at a given pressure, but becomes progressively stronger with increasing pressure from 1.5 to 7 GPa given the temperature. Relative to oxygen fugacity buffers, the OH solubility is on average increased by ∼50% between Fe–FeO and Ni–NiO, independent of pressure and temperature. The enhanced OH solubility at relatively oxidizing conditions could be explained by the role of oxygen fugacity in changing the point defects of olivine. Experimental work concerning the storage capacity of water in olivine and in the upper mantle must consider the effect of oxygen fugacity. The OH solubility of olivine in the reducing deep upper mantle obtained from experiments under oxidizing conditions would be overestimated. The initial OH information of many natural olivines may have been modified by some recent secondary events, e.g., during their shallow residence and/or transport to the surface, and in principle, olivine equilibrated in the upper mantle may be D-depleted relative to its coexisting minerals. Some preliminary constraints on the water storage capacity in the upper mantle of the Earth and the Mars are also provided.
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影响因子：
5.3
作者：
Xiaozhi Yang;D. Liu;Q. Xia
通讯作者：
Xiaozhi Yang;D. Liu;Q. Xia
影响因子：
5
作者：
A. Peslier;M. Bizimis;M. Matney
通讯作者：
A. Peslier;M. Bizimis;M. Matney
影响因子：
56.9
作者：
B. Wood;L. T. Bryndzia;Kathleen E. Johnson
通讯作者：
B. Wood;L. T. Bryndzia;Kathleen E. Johnson
影响因子：
5.8
作者：
Berry, AJ;Hermann, J;Foran, GJ
通讯作者：
Foran, GJ
影响因子：
5
作者：
A. Peslier;A. Woodland;J. Wolff
通讯作者：
A. Peslier;A. Woodland;J. Wolff