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Links between forearc decarbonation and generation of high δ26Mg fluids at subarc depths: constraints from carbonate-bearing forearc serpentinites

文献类型：期刊论文

作者Wu, Kai5; Li, Kan2; Zhang, Chang3; Chen, Yuxiao1; Chen, Kaiyun5; Sun, Weidong4; Yuan, Honglin5
刊名GEOCHIMICA ET COSMOCHIMICA ACTA
出版日期2025-08-15
卷号403页码:202-217
关键词Serpentinite Magnesium isotopes Forearc decarbonation Subduction zones
ISSN号0016-7037
DOI10.1016/j.gca.2025.06.024
通讯作者Wu, Kai(wukai@nwu.edu.cn)
英文摘要Subduction zones play a critical role in carbon exchange between Earth's surface and interior. While devolatilization of forearc serpentinites has been proposed as a contributor to arc magma genesis, its role in subductionzone carbon (C) and magnesium (Mg) cycling, as well as its influence on the Mg isotopic variability in global arc lavas, remains poorly constrained. This study investigates Mg isotope fractionation during interactions between forearc peridotites and CO2-rich fluids in the Mianlue tectonic melange, focusing on carbonate-bearing serpentinites from the Jianchaling and Liangyazi regions. Five Jianchaling lizardite-only serpentinites exhibit a narrow range of S26Mg values (-0.28 f 0.02 %o to -0.13 f 0.02 %o), similar to those of four Jianchaling antigoritelizardite serpentinites (-0.27 f 0.03 %o to -0.17 f 0.01 %o). In contrast, seven Liangyazi antigorite-only serpentinites display a broader S26Mg range (-0.27 f 0.03 %o to -0.01 f 0.02 %o). Magnesium isotope compositions of mineral separates reveal temperature-dependent inter-mineral Mg isotope fractionations between carbonate and co-precipitated serpentine minerals. Thermodynamic modeling and mass balance calculations indicate minimal Mg loss from peridotites to fluids during their interaction with CO2-rich fluids. Instead, subsequent fluid infiltration and carbonate dissolution are responsible for the observed Mg isotopic variations. The concurrent precipitation of isotopically heavy silicate minerals and light carbonates in the forearc provides a plausible explanation for the elevated S26Mg values observed in some arc lavas. In subduction zones where the forearc slab-top temperatures can exceed the stability limit of antigorite (600 - 700 degrees C), significant forearc decarbonation produces CO2-rich fluids that interact with forearc peridotites at the bottom of the mantle wedge, forming abundant isotopically heavy silicate minerals. The subsequent breakdown of these silicates and limited release of slab-derived carbonates at subarc depths may be responsible for the high S26Mg values and low CO2 outfluxes characteristic of these subduction zones. In contrast, subduction zones with cooler forearc slab-top temperatures, where subarc slab-top temperatures approach the stability limit of antigorite, experience less significant forearc decarbonation. In such settings, limited formation of isotopically heavy silicate phases and enhanced release of slab carbonates at subarc depths due to infiltrations of slab-derived fluids can potentially result in arc magmas with S26Mg values close to or slightly below the normal mantle. These findings underscore the critical role of fluid-rock interactions in the forearc region in regulating deep carbon cycling and shaping the Mg isotopic signatures of arc magmas.
WOS关键词MG ISOTOPE FRACTIONATION ; LUE SUTURE ZONE ; SUBDUCTION ZONES ; THERMODYNAMIC CONSTRAINTS ; DIELECTRIC-CONSTANT ; MINERAL CARBONATION ; CO2-RICH FLUIDS ; OCEANIC-CRUST ; MANTLE ; TRACE
资助项目National Natural Science Foundation of China[42373022] ; National Natural Science Foundation of China[42130102] ; National Natural Science Foundation of China[41903009] ; Key Research Program of the Institute of Geology and Geophysics, CAS[IGGCAS-202202]
WOS研究方向Geochemistry & Geophysics
语种英语
WOS记录号WOS:001543461100007
出版者PERGAMON-ELSEVIER SCIENCE LTD
源URL[http://ir.qdio.ac.cn/handle/337002/202800]  
专题海洋研究所_深海极端环境与生命过程研究中心
通讯作者Wu, Kai
作者单位1.Guangzhou Univ, Sch Environm Sci & Engn, Key Lab Water Qual & Conservat Pearl River Delta, Minist Educ, Guangzhou 510006, Peoples R China
2.Woods Hole Oceanog Inst, Marine Chem & Geochem Dept, Woods Hole, MA 02543 USA
3.Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher & Environm Coevolut, Beijing 100029, Peoples R China
4.Chinese Acad Sci, Ctr Deep Sea Res, Inst Oceanol, Qingdao 266071, Peoples R China
5.Northwest Univ, Dept Geol, State Key Lab Continental Evolut & Early Life, Xian 710069, Peoples R China
推荐引用方式
GB/T 7714		 Wu, Kai,Li, Kan,Zhang, Chang,et al. Links between forearc decarbonation and generation of high δ26Mg fluids at subarc depths: constraints from carbonate-bearing forearc serpentinites[J]. GEOCHIMICA ET COSMOCHIMICA ACTA,2025,403:202-217.
APA Wu, Kai.,Li, Kan.,Zhang, Chang.,Chen, Yuxiao.,Chen, Kaiyun.,...&Yuan, Honglin.(2025).Links between forearc decarbonation and generation of high δ26Mg fluids at subarc depths: constraints from carbonate-bearing forearc serpentinites.GEOCHIMICA ET COSMOCHIMICA ACTA,403,202-217.
MLA Wu, Kai,et al."Links between forearc decarbonation and generation of high δ26Mg fluids at subarc depths: constraints from carbonate-bearing forearc serpentinites".GEOCHIMICA ET COSMOCHIMICA ACTA 403(2025):202-217.

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来源：海洋研究所

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