气候变化领域集成服务门户(CCPortal): Mg and Zn Isotope Evidence for Two Types of Mantle Metasomatism and Deep Recycling of Magnesium Carbonates

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DOI	10.1029/2020JB020684
	Mg and Zn Isotope Evidence for Two Types of Mantle Metasomatism and Deep Recycling of Magnesium Carbonates
	Liu S.-A.; Wang Z.-Z.; Yang C.; Li S.-G.; Ke S.
发表日期	2020
ISSN	21699313
卷号	125 期号:11
英文摘要	To test the ability of Mg and Zn isotopes in discriminating between different types of mantle metasomatism and identifying deep carbon cycling, here we present a comparative study on two types of Cenozoic lavas in SE Tibet, that is, K-rich (potassic-ultrapotassic) lavas and Na-rich alkali basalts. The contrasting bulk rock chemical compositions, Sr-Nd isotopic ratios, and olivine chemistry between them suggest distinct sources in the lithospheric mantle and asthenosphere, respectively. The K-rich lavas have mantle-like δ26Mg, slightly lighter δ66Zn relative to global oceanic basalts, high 87Sr/86Sr, and low 143Nd/144Nd, indicating source metasomatism by recycled siliciclastic sediments. By contrast, the alkali basalts possess remarkably lighter δ26Mg and heavier δ66Zn values relative to the mantle that are typically characterized by carbonates. The coupling of high δ66Zn with high-Zn contents and Zn/Fe ratios further suggests a pyroxenite source containing recycled Zn-rich magnesium carbonates. This is strongly corroborated by the similarity in major elements between the alkali basalts and experimental partial melts of pyroxenite + CO2. Thus, mantle silicate and carbonate metasomatism contributed to the origin of K-rich and Na-rich lavas in SE Tibet, respectively. Notably, the occurrence of the alkali basalts is spatially consistent with a stagnant slab in the mantle transition zone (410–660 km), the latter of which is interpreted to represent the deeply subducted oceanic slab. These observations provide evidence for recycling of carbonates into the deep mantle, which represents a long-term circulation of subducted carbon compared with that of arc-trench systems and has crucial significance for global deep carbon cycling. ©2020. American Geophysical Union. All Rights Reserved.
英文关键词	basaltic lavas; deep carbon cycle; magnesium isotopes; mantle metasomatism; zinc isotopes
语种	英语
来源期刊	Journal of Geophysical Research: Solid Earth
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/187500
作者单位	State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing, China; Isotope Laboratory, Department of Earth and Space Sciences, University of Washington, Seattle, WA, United States
推荐引用方式 GB/T 7714	Liu S.-A.,Wang Z.-Z.,Yang C.,et al. Mg and Zn Isotope Evidence for Two Types of Mantle Metasomatism and Deep Recycling of Magnesium Carbonates[J],2020,125(11).
APA	Liu S.-A.,Wang Z.-Z.,Yang C.,Li S.-G.,&Ke S..(2020).Mg and Zn Isotope Evidence for Two Types of Mantle Metasomatism and Deep Recycling of Magnesium Carbonates.Journal of Geophysical Research: Solid Earth,125(11).
MLA	Liu S.-A.,et al."Mg and Zn Isotope Evidence for Two Types of Mantle Metasomatism and Deep Recycling of Magnesium Carbonates".Journal of Geophysical Research: Solid Earth 125.11(2020).