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

作　　者：Wei Yan Yanyao Zhang Yunlu Ma Mingyue He Lifei Zhang Weidong Sun Christina Yan Wang Xi Liu 

机构地区：[1]School of Earth and Space Sciences,Peking University,Beijing,100871,China [2]Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education of China,Beijing,100871,China [3]Department of Geological Sciences,Jackson School of Geosciences,The University of Texas at Austin,Austin,TX,78712,USA [4]School of Gemmology,China University of Geosciences(Beijing),Beijing,100083,China [5]Center of Deep Sea Research,Institute of Oceanography,Chinese Academy of Sciences,Qingdao,266071,China [6]Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou,510640,China

出　　处：《Geoscience Frontiers》2021年第1期313-326,共14页地学前缘（英文版）

基　　金：financially supported by the DREAM project of MOST,China(Grant No.2016YFC0600408);the Strategic Priority Research Program(B)of Chinese Academy of Sciences(Grant No.XDB18000000);the Program of the National Mineral Rock and Fossil Specimens Resource Center from MOST,China。

摘　　要：A series of coesite,coexisting with or without a liquid phase,was synthesized in the nominal system SiO2-H2O at800-1450℃and 5 GPa.Micro-Raman spectroscopy was used to identity the crystalline phase,electron microprobe and LA-ICP-MS were employed to quantity 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 A1 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^++Al^3+■Si^4+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^+■Si^4+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-Ⅰhydrogarnet 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-Ⅰhydrogarnet substitution,positively correlates with both P and T,cH2O=-105(30)+5.2(32)×P+0.112(26)×T,with cH2O in wt ppm,P in GPa and T in℃.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 waterdiffusion rate,this metastable coesite should be completely dry,which may have been the ke

关 键 词：Coesite preservation FTIR New IR experimental Protocol Anhydrous minerals P-T dependence of water solubility Water-incorporation mechanism 

分 类 号：P574[天文地球—矿物学]