Low delta Mg-26 volcanic rocks of Tengchong in Southwestern China: A deep carbon cycle induced by supercritical liquids

doi:10.1016/j.gca.2018.08.032

CORC > 地质与地球物理研究所 > 中国科学院地质与地球物理研究所 > 中国科学院地球与行星物理重点实验室

	Low delta Mg-26 volcanic rocks of Tengchong in Southwestern China: A deep carbon cycle induced by supercritical liquids
	Tian, Heng-Ci 1,2; Yang, Wei 1,2; Li, Shu-Guang 3; Ke, Shan 3; Duan, Xian-Zhe 4
刊名	GEOCHIMICA ET COSMOCHIMICA ACTA
	2018-11-01
卷号	240 页码:191-219
关键词	Magnesium isotopes Supercritical liquids Tengchong volcanic rocks Carbon cycling Residence time
ISSN号	0016-7037
DOI	10.1016/j.gca.2018.08.032
英文摘要	Oceanic subduction zones are important channels for carbon exchange between the Earth's crust and mantle. However, the nature of carbon cycles at depths from 120 to 410 km in the subduction zone remains unknown. To decipher this issue, high-precision stable Mg isotopes of arc-like volcanic rocks from Tengchong, Southwestern China, have been investigated. The Tengchong volcanic rocks comprise basalts and andesites, with Mg0 content varying from 2.41 to 8.48 wt.%. Both the basalts and andesites exhibit homogeneous and light Mg isotopic compositions with delta Mg-26 ranging from -0.51 to -0.45 parts per thousand and -0.49 to -0.33 parts per thousand, respectively. Their delta Mg-26 values are lower than the average mantle (delta Mg-26 = -0.25 +/- 0.07 parts per thousand) and island arc lavas (delta Mg-26 = -0.35 to +0.06%e), but similar to the <110 Ma intra-continental basalts from eastern China (delta Mg-26 = -0.60 to 0.30 parts per thousand). This light Mg isotopic composition could not originate from the accumulation of ilmenite in their mantle source because both the Nb/Ta and delta Mg-26 values of the basalts are invariant with TiO2 content. The recycling of carbonated eclogites is also unlikely because of the lack of any correlation between delta Mg-26 and either (Gd/Yb)(N) or Fe/Mn ratios in the Tengchong basalts. Alternatively, the most probable explanation for the light Mg isotopic composition is the recycling of sedimentary carbonates in the mantle source. This is supported by the high Na2O + K2O/TiO2 ratios (3.3-4.1), low Ti/Ti* and Hf/Hf* values in the basalts, which are consistent with the partial melting trend of carbonated peridotite. Additionally, the high Ba/Th, low Rb/Cs and enriched Sr-Nd isotopes (EMII-like endmember) of the Tengchong basalts indicate the presence of Indian sediments in their mantle source. Furthermore, the extremely high Th/U (6.5-8.3) ratios in basalts suggest the higher mobility of Th than U, which is a unique characteristic of slab-derived supercritical liquids in subduction zones with pressures greater than 6 GPa. Based on the quantitative modeling of Mg-Sr-Nd-Pb isotopes and trace elements, the mantle source of the Tengchong basalts lies along mixing lines of the DMM with 1% supercritical liquids and 15-19% recycled mixture containing 66-72% dolomite, 22-26% calcite and 2-12% Indian sediments. Given that the recycled mixture is mainly dolomite (66-72%), we proposed that the slab-derived supercritical liquids can dissolve dolomite and then metasomatized the overlying mantle to form carbonated peridotite. Partial melting of this mantle source should be located at a depth of similar to 120 to 300 km under which supercritical liquids can occur, which is supported by seismic tomographic observations. The Tengchong andesites display many geochemical features similar to the basalts, such as enrichments in LILEs (Large Ion Lithophile Elements), LREEs (Light Rare Earth Elements) and Sr-Nd-Pb isotopes, as well as low delta Mg-26 values, suggesting a petrogenetic link between these two rock types. Our detailed study suggests that the andesites evolved from the Tengchong basalts via assimilation and fractional crystallization (AFC) processes. This interpretation is also supported by the geophysical tomography, which reveals a low-velocity anomalous zone in the continental crust. This study reveals a new carbon cycle in which Mg-rich carbonate - dolomite - can be dissolved by supercritical liquids and subducted into a deep mantle wedge to depths of 120-300 km in the oceanic subduction zone. This deep metasomatic mantle wedge mixed with the upwelling mantle beneath the Tengchong volcano and partially melted to form the low delta Mg-26 volcanic rocks. (C) 2018 Elsevier Ltd. All rights reserved.
资助项目	National Natural Science Foundation of China[41730214] ; National Natural Science Foundation of China[41322022] ; "Strategic Priority Research Program" of the Chinese Academy of Sciences[XDB18030603] ; Youth Innovation Promotion Association, Chinese Academy of Sciences[2014056] ; National Postdoctoral Program for Innovative Talents[BX201700237] ; Ministry of Science and Technology of People's Republic of China[2016YFE0203000]
WOS关键词	MAGNESIUM ISOTOPE FRACTIONATION ; OCEAN ISLAND BASALTS ; PARTIAL MELTING EXPERIMENTS ; BENEATH EASTERN CHINA ; SR-PB ISOTOPES ; NORTH CHINA ; TRACE-ELEMENT ; CENOZOIC BASALTS ; GEOCHEMICAL EVIDENCE ; YUNNAN PROVINCE
WOS研究方向	Geochemistry & Geophysics
语种	英语
出版者	PERGAMON-ELSEVIER SCIENCE LTD
WOS记录号	WOS:000444915700010
资助机构	National Natural Science Foundation of China ; National Natural Science Foundation of China ; "Strategic Priority Research Program" of the Chinese Academy of Sciences ; "Strategic Priority Research Program" of the Chinese Academy of Sciences ; Youth Innovation Promotion Association, Chinese Academy of Sciences ; Youth Innovation Promotion Association, Chinese Academy of Sciences ; National Postdoctoral Program for Innovative Talents ; National Postdoctoral Program for Innovative Talents ; Ministry of Science and Technology of People's Republic of China ; Ministry of Science and Technology of People's Republic of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; "Strategic Priority Research Program" of the Chinese Academy of Sciences ; "Strategic Priority Research Program" of the Chinese Academy of Sciences ; Youth Innovation Promotion Association, Chinese Academy of Sciences ; Youth Innovation Promotion Association, Chinese Academy of Sciences ; National Postdoctoral Program for Innovative Talents ; National Postdoctoral Program for Innovative Talents ; Ministry of Science and Technology of People's Republic of China ; Ministry of Science and Technology of People's Republic of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; "Strategic Priority Research Program" of the Chinese Academy of Sciences ; "Strategic Priority Research Program" of the Chinese Academy of Sciences ; Youth Innovation Promotion Association, Chinese Academy of Sciences ; Youth Innovation Promotion Association, Chinese Academy of Sciences ; National Postdoctoral Program for Innovative Talents ; National Postdoctoral Program for Innovative Talents ; Ministry of Science and Technology of People's Republic of China ; Ministry of Science and Technology of People's Republic of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; "Strategic Priority Research Program" of the Chinese Academy of Sciences ; "Strategic Priority Research Program" of the Chinese Academy of Sciences ; Youth Innovation Promotion Association, Chinese Academy of Sciences ; Youth Innovation Promotion Association, Chinese Academy of Sciences ; National Postdoctoral Program for Innovative Talents ; National Postdoctoral Program for Innovative Talents ; Ministry of Science and Technology of People's Republic of China ; Ministry of Science and Technology of People's Republic of China
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/89128]
专题	地质与地球物理研究所_中国科学院地球与行星物理重点实验室
通讯作者	Yang, Wei; Li, Shu-Guang
作者单位	1.Chinese Acad Sci, Inst Geol & Geophys, Key Lab Earth & Planetary Phys, Beijing 100029, Peoples R China 2.Chinese Acad Sci, Inst Earth Sci, Beijing 100029, Peoples R China 3.China Univ Geosci, State Key Lab Geol Proc & Mineral Resources, Beijing 100083, Peoples R China 4.Univ South China, Sch Nucl Resource Engn, Hengyang 421001, Peoples R China
推荐引用方式 GB/T 7714	Tian, Heng-Ci,Yang, Wei,Li, Shu-Guang,et al. Low delta Mg-26 volcanic rocks of Tengchong in Southwestern China: A deep carbon cycle induced by supercritical liquids[J]. GEOCHIMICA ET COSMOCHIMICA ACTA,2018,240:191-219.
APA	Tian, Heng-Ci,Yang, Wei,Li, Shu-Guang,Ke, Shan,&Duan, Xian-Zhe.(2018).Low delta Mg-26 volcanic rocks of Tengchong in Southwestern China: A deep carbon cycle induced by supercritical liquids.GEOCHIMICA ET COSMOCHIMICA ACTA,240,191-219.
MLA	Tian, Heng-Ci,et al."Low delta Mg-26 volcanic rocks of Tengchong in Southwestern China: A deep carbon cycle induced by supercritical liquids".GEOCHIMICA ET COSMOCHIMICA ACTA 240(2018):191-219.