Water in coesite: Incorporation mechanism and operation condition, solubility and P-T dependence, and contribution to water transport and coesite preservation

doi:10.1016/j.gsf.2020.05.007

	Water in coesite: Incorporation mechanism and operation condition, solubility and P-T dependence, and contribution to water transport and coesite preservation
	Yan, Wei 1,2; Zhang, Yanyao 3; Ma, Yunlu 1,2; He, Mingyue 4; Zhang, Lifei 1,2; Sun, Weidong5 ; Wang, Christina Yan 6; Liu, Xi 1,2
	2021
发表期刊	GEOSCIENCE FRONTIERS
ISSN	1674-9871
卷号	12 期号:1 页码:313-326
通讯作者	Liu, Xi(xi.liu@pku.edu.cn)
摘要	A series of coesite, coexisting with or without a liquid phase, was synthesized in the nominal system SiO2-H2O at 800-1450 degrees C and 5 GPa. Micro-Raman spectroscopy was used to identify the crystalline phase, electron microprobe and LA-ICP-MS were employed to quantify some major and trace elements, and unpolarized FTIR spectroscopy was applied to probe the different types of hydrogen defects, explore water-incorporation mechanisms and quantify water contents. Trace amounts of Al and B were detected in the coesite. Combining our results with the results in the literatures, we have found no positive correlation between the Al contents and the "Al"-based hydrogen concentrations, suggesting that previously proposed hydrogen-incorporation mechanism H+ Al3+ <-> Si4+ does not function in coesite. In contrast, we have confirmed the positive correlation between the B contents and the B-based hydrogen concentrations. The hydrogen-incorporation mechanism H+ + B3+ <-> Si4+ readily takes place in coesite at different P-T conditions, and significantly increases the water content at both liquid-saturated and liquid-undersaturated conditions. For the SiO2-H2O system, we have found that type-I hydrogarnet substitution plays a dictating role in incorporating water into coesite at liquid-saturated condition, type-II hydrogarnet substitution contributes significantly at nearly dry condition, and both operate at conditions in between. The water solubility of coesite, as dictated by the type-I hydrogarnet substitution, positively correlates with both P and T, c(H)(2O) = -105(30) + 5.2(32) x P + 0.112(26) x T, with c(H)(2O) in wt ppm, P in GPa and T in degrees C. Due to its low water solubility and small fraction in subducted slabs, coesite may contribute insignificantly to the vertical water transport in subduction zones. Furthermore, the water solubility of any coesite in exhuming ultra-high pressure metamorphic rocks should be virtually zero as coesite becomes metastable. With an adequately fast water-diffusion rate, this metastable coesite should be completely dry, which may have been the key factor to the partial preservation of most natural Coe. As a byproduct, a new IR experimental protocol for accurate water determination in optically anisotropic nominally anhydrous minerals has been found. Aided with the empirical method of Paterson (1982) it employs multiple unpolarized IR spectra, collected from randomly-orientated mineral grains, to approximate both total integrated absorbance and total integrated molar absorption coefficient. Its success relies on a high-level orientation randomness in the IR analyses.
关键词	Coesite preservation FTIR New IR experimental Protocol Anhydrous minerals P-T dependence of water solubility Water-incorporation mechanism
DOI	10.1016/j.gsf.2020.05.007
收录类别	SCI
语种	英语
资助项目	DREAM project of MOST, China[2016YFC0600408] ; Chinese Academy of Sciences[XDB18000000] ; Program of the National Mineral Rock and Fossil Specimens Resource Center from MOST, China
WOS研究方向	Geology
WOS类目	Geosciences, Multidisciplinary
WOS记录号	WOS:000597401000021
出版者	CHINA UNIV GEOSCIENCES, BEIJING
引用统计	被引频次：5[WOS] [WOS记录] [WOS相关记录]
文献类型	期刊论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/169400
专题	深海极端环境与生命过程研究中心
通讯作者	Liu, Xi
作者单位	1.Peking Univ, Sch Earth & Space Sci, Beijing 100871, Peoples R China 2.Minist Educ China, Key Lab Orogen Belts & Crustal Evolut, Beijing 100871, Peoples R China 3.Univ Texas Austin, Jackson Sch Geosci, Dept Geol Sci, Austin, TX 78712 USA 4.China Univ Geosci Beijing, Sch Gemmol, Beijing 100083, Peoples R China 5.Chinese Acad Sci, Ctr Deep Sea Res, Inst Oceanog, Qingdao 266071, Peoples R China 6.Chinese Acad Sci, Guangzhou Inst Geochem, Key Lab Mineral & Metallogeny, Guangzhou 510640, Peoples R China
推荐引用方式 GB/T 7714	Yan, Wei,Zhang, Yanyao,Ma, Yunlu,et al. Water in coesite: Incorporation mechanism and operation condition, solubility and P-T dependence, and contribution to water transport and coesite preservation[J]. GEOSCIENCE FRONTIERS,2021,12(1):313-326.
APA	Yan, Wei.,Zhang, Yanyao.,Ma, Yunlu.,He, Mingyue.,Zhang, Lifei.,...&Liu, Xi.(2021).Water in coesite: Incorporation mechanism and operation condition, solubility and P-T dependence, and contribution to water transport and coesite preservation.GEOSCIENCE FRONTIERS,12(1),313-326.
MLA	Yan, Wei,et al."Water in coesite: Incorporation mechanism and operation condition, solubility and P-T dependence, and contribution to water transport and coesite preservation".GEOSCIENCE FRONTIERS 12.1(2021):313-326.

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