The influence of silica on reaction rates and molecular hydrogen(H2)generation during olivine hydrothermal alteration

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外文摘要：Hydrothermal alteration of olivine greatly influences geodynamics and the recycling of volatiles(such as water and carbon)in subduction zones.Silica is an important component of geological fluids,and its influence on the hydrothermal alteration of olivine remains poorly constrained.In this study,we performed experiments at 300-515℃ and 3.0 kbar(1 bar=105 Pa)by reacting well homogenized mixtures of olivine and silica powders with saline solutions(0.5 mol L-1 NaCl).Silica greatly influences the reaction pathways,reaction rates,and molecular hydrogen(H2)formation during olivine hydrothermal alteration.In experiments at 300℃ and 3.0 kbar with mixtures of olivine and 10 wt％silica,olivine was replaced by serpentine and talc.The proportions of serpentine and talc were determined according to standard curves based on infrared spectroscopy analyses.Around 6.5％serpentine and 12％talc were produced after an experimental duration of 7 days,which had no change after a longer period(14 days).Compared to the kinetics in silica-free systems,the rates of olivine hydrothermal alteration in ex-periments with 10 wt％silica are much lower.The overall reaction is:4.5Forsterite+5.5SiO2,aq +4H2O=Serpentine+2Talc.With the addition of more silica(20 wt％and 40 wt％),olivine was transformed into talc.The rates of reaction were much faster,e.g.,for experiments with olivine and 20 wt％silica,43％of talc was produced after 14 days,which increased to 77％for experiments with 40 wt％silica over the same period.The overall reaction is:3Forsterite+5SiO2,aq +2H2O=2Talc.In experiments at 400-505℃ and 3.0 kbar,the promoting effect of silica on olivine hydrothermal alteration was also observed,which is closely associated with a decrease in Gibbs free energies of olivine hydrothermal alteration.At 300℃ and 3.0 kbar,silica decreased H2 formed during olivine hydrothermal alteration by around an order of magnitude,resulting in an increase in oxygen fugacity.Based on measured H2,we calibrated oxygen fugacities,ranging from 0.96 to 3.41 log units below FMQ(fayalite-magnetite-quartz buffer assemblage).This study suggests that the infiltration of SiO2-bearing fluids into peridotites greatly influences redox conditions and the rates of olivine hydrothermal alteration.

外文关键词：

Olivine hydrothermal alterationSilicaSerpentinizationHydrogenSerpentine

作者：

Ruifang HUANG、Weidong SUN、Xing DING、Yusheng ZHAO、Yibing LI、Xiuqi SHANG

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作者单位：

CAS Key Laboratory of Ocean and Marginal Sea Geology,South China Sea Institute of Oceanology Chinese Academy of Sciences,Guangzhou 510301,China

SUSTech Academy for Advanced Interdisciplinary Studies,Southern University of Science and Technology,Shenzhen 518055,China

Center of Deep Sea Research,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China

State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China

Institue of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China

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基金：

National Natural Science Foundation of ChinaStrategic Priority Research Program of the Chinese Academy cfSciencesStrategic Priority Research Program of the Chinese Academy cfSciencesShenzhen Municipal Natural science Foundation

项目编号：

41873069XDA22050103XDB42000000JCYJ20220530113016038

出版年：

2024

DOI：

10.1007/s11430-023-1172-9

中国科学:地球科学(英文版)

中国科学院

中国科学:地球科学(英文版)

影响因子：1.002

ISSN：1674-7313

年,卷(期)：2024.67(1)

参考文献量63