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Different stages of chemical alteration on metabasaltic rocks in the subduction channel: Evidence from the Western Tianshan metamorphic belt, NW China
Xiao, Yuanyuan1,2,3; Niu, Yaoling1,2,4; Wang, Kuo-Lung3; Iizuka, Yoshiyuki3; Lin, Jinyan5; Wang, Dong1,2; Tan, Yulong5; Wang, Guodong1,2
2017-09-01
Source PublicationJOURNAL OF ASIAN EARTH SCIENCES
Volume145Pages:111-122
SubtypeArticle
AbstractTo understand the geochemistry of subduction zone metamorphism, especially the large-scale mass transfer at forearc to subarc depths, we carried out a detailed study of a similar to 1.5 m size metabasaltic block with well-preserved pillow structures from the Chinese Western Tianshan high- to ultrahigh-pressure metamorphic belt. This metabasaltic block is characterized by omphacite-rich interiors gradually surrounded by abundant channelized (veins) glaucophane-rich patches toward the rims. The glaucophane-rich rims share the same peak metamorphic conditions with omphacite-rich interiors, but have experienced stronger blueschist-facies overprinting during exhumation. Representative samples from the glaucophane-rich rims and omphacite-rich interiors yield a well-defined Rb-Sr isochron age of 307 +/- 23 Ma, likely representing this overprinting event. Both glaucophane-rich rims and omphacite-rich interiors show elevated K-Rb-Cs-Ba-Pb-Sr contents relative to their protolith, reflecting a large-scale enrichment of these elements and formation of abundant phengite during subduction. Compared with the omphacite-rich interiors, the glaucophane-rich rims have gained rare earth elements (REEs, > 25%), U-Th (similar to 75%), Pb-Sr ( > 100%) and some transition metals like Co and Ni (25-50%), but lost P (similar to 75%), Na ( > 25%), Li and Be (similar to 50%); K-Rb-Cs-Ba show only 10% loss. These chemical changes would be caused by serpentinite-derived fluids during the exhumation in the subduction channel. Therefore, there are two stages of fluid action in the subduction channel. As the formation of phengite stabilizes K-Rb-Cs-Ba at the first stage, the residual fluids released from the phengite-rich metabasaltic rocks would be depleted in these elements, which are unlikely to contribute to elevated contents of these elements in arc magmas if phengite remains stable at subarc depths. In addition, the decrease of U/Pb ratios as the preferred enrichment of Pb over U in the eclogitic rocks during the first stage chemical alteration may further lead to the lower radiogenic Pb isotope component of the deeply subducted ocean crust with time, which is inconsistent with the high radiogenic Pb isotope component of high mu (=U-238/Pb-204) basalts.
KeywordSubduction Channelized Glaucophane-rich Rims Surrounding Omphacite-rich Interiors Mass Transfer Subduction Zone Magmatism Mantle Heterogeneity
DOI10.1016/j.jseaes.2017.06.001
Indexed BySCI
Language英语
WOS IDWOS:000410012200008
Citation statistics
Document Type期刊论文
Version出版稿
Identifierhttp://ir.qdio.ac.cn/handle/337002/143144
Collection海洋地质与环境重点实验室
Affiliation1.Chinese Acad Sci, Inst Oceanol, Qingdao 266071, Peoples R China
2.Qingdao Natl Lab Marine Sci & Technol, Lab Marine Geol, Qingdao 266061, Peoples R China
3.Acad Sinica, Inst Earth Sci, Taipei 11529, Taiwan
4.Univ Durham, Dept Earth Sci, Durham DH1 3LE, England
5.Northwest Univ, Dept Geol, Xian 710069, Shaanxi, Peoples R China
First Author Affilication中国科学院海洋研究所
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Xiao, Yuanyuan,Niu, Yaoling,Wang, Kuo-Lung,et al. Different stages of chemical alteration on metabasaltic rocks in the subduction channel: Evidence from the Western Tianshan metamorphic belt, NW China[J]. JOURNAL OF ASIAN EARTH SCIENCES,2017,145:111-122.
APA Xiao, Yuanyuan.,Niu, Yaoling.,Wang, Kuo-Lung.,Iizuka, Yoshiyuki.,Lin, Jinyan.,...&Wang, Guodong.(2017).Different stages of chemical alteration on metabasaltic rocks in the subduction channel: Evidence from the Western Tianshan metamorphic belt, NW China.JOURNAL OF ASIAN EARTH SCIENCES,145,111-122.
MLA Xiao, Yuanyuan,et al."Different stages of chemical alteration on metabasaltic rocks in the subduction channel: Evidence from the Western Tianshan metamorphic belt, NW China".JOURNAL OF ASIAN EARTH SCIENCES 145(2017):111-122.
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