Metasomatism-induced mantle magnesium isotopic heterogeneity: Evidence from pyroxenites

doi:10.1016/j.gca.2015.11.001

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	Metasomatism-induced mantle magnesium isotopic heterogeneity: Evidence from pyroxenites
	Hu, Yan 1,2; Teng, Fang-Zhen 1; Zhang, Hong-Fu 2; Xiao, Yan 2; Su, Ben-Xun 2
刊名	GEOCHIMICA ET COSMOCHIMICA ACTA
	2016-07-15
卷号	185 页码:88-111
DOI	10.1016/j.gca.2015.11.001
文献子类	Article
英文摘要	High-precision Mg isotopic measurements on diverse mantle pyroxenite xenoliths collected from Hannuoba, North China Craton, revealed multi-stage interactions between the lithospheric mantle and melts of different origins. The garnet-bearing pyroxenites yield variable delta Mg-26 values from -0.48% to -0.10%, consistent with their origin as reaction products between mantle peridotites and melts from subducted oceanic slab with highly heterogeneous delta Mg-26. Most of their constituent olivine, clinopyroxene, and orthopyroxene have indistinguishable delta Mg-26 ratios around the normal mantle range (-0.25 +/- 0.07%, Teng et al., 2010). The lack of fractionation among these three mineral phases agrees with their similar bonding environments for Mg (6-fold), and hence indicates a general isotopic equilibrium among them. By contrast, garnet has variably lighter delta Mg-26 values (-0.75% to +/- 0.37%, n = 15), consistent with its higher coordination number for Mg (8-fold), and thus weaker Mg-O bonds. The magnitude of fractionation between garnet and olivine/pyroxene, however, is not correlated with equilibrium temperature, and therefore reflects disequilibrium Mg isotope partitioning. Considering the metasomatic origin of these garnets, the disequilibrium isotopic fractionation is most likely the result of rapid and incomplete metasomatic reaction during which garnets were formed at the expense of isotopically heavier co-existing minerals, particularly spinels. The two garnet-free clinopyroxenites, which display highly enriched light rare earth element (LREE) patterns and very low Ti/Eu ratios, are characterized by extremely light delta Mg-26 (as low as -1.51%). Their formation possibly indicates an episode of carbonatite infiltration. In comparison, the three Cr websterites and one Al websterite, as well as an orthopyroxenite, all have mantle-like whole-rock and mineral delta Mg-26 ratios, with equilibrated clinopyroxene-orthopyroxene pairs. Their presence thus implies different episodes of asthenosphere-derived silicate melt injection into the mantle. Collectively, these observations suggest that mantle metasomatism plays an important role in producing inter-mineral Mg isotopic disequilibrium and local Mg isotopic variation in the lithospheric mantle. Therefore, Mg isotopes can be used to trace metasomatic activities in the mantle. (C) 2015 Elsevier Ltd. All rights reserved.
WOS关键词	NORTH CHINA CRATON ; MELT-PERIDOTITE INTERACTIONS ; SINO-KOREAN CRATON ; SALT-LAKE-CRATER ; LITHOSPHERIC MANTLE ; EASTERN CHINA ; ULTRAMAFIC XENOLITHS ; CARBONATITE METASOMATISM ; VOLCANIC-ROCKS ; MAJOR-ELEMENT
WOS研究方向	Geochemistry & Geophysics
语种	英语
WOS记录号	WOS:000377933300007
资助机构	National Science Foundation grants of China(91214293 ; National Science Foundation grants of China(91214293 ; National Science Foundation grants of China(91214293 ; National Science Foundation grants of China(91214293 ; National Science Foundation of America(EAR-0838227 ; National Science Foundation of America(EAR-0838227 ; National Science Foundation of America(EAR-0838227 ; National Science Foundation of America(EAR-0838227 ; Geological Society of America ; Geological Society of America ; Geological Society of America ; Geological Society of America ; 91014007) ; 91014007) ; 91014007) ; 91014007) ; EAR-1056713 ; EAR-1056713 ; EAR-1056713 ; EAR-1056713 ; EAR-1340160) ; EAR-1340160) ; EAR-1340160) ; EAR-1340160) ; National Science Foundation grants of China(91214293 ; National Science Foundation grants of China(91214293 ; National Science Foundation grants of China(91214293 ; National Science Foundation grants of China(91214293 ; National Science Foundation of America(EAR-0838227 ; National Science Foundation of America(EAR-0838227 ; National Science Foundation of America(EAR-0838227 ; National Science Foundation of America(EAR-0838227 ; Geological Society of America ; Geological Society of America ; Geological Society of America ; Geological Society of America ; 91014007) ; 91014007) ; 91014007) ; 91014007) ; EAR-1056713 ; EAR-1056713 ; EAR-1056713 ; EAR-1056713 ; EAR-1340160) ; EAR-1340160) ; EAR-1340160) ; EAR-1340160)
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/53430]
专题	地质与地球物理研究所_岩石圈演化国家重点实验室
作者单位	1.Univ Washington, Dept Earth & Space Sci, Isotope Lab, Seattle, WA 98195 USA 2.Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher Evolut, POB 9825, Beijing 100029, Peoples R China
推荐引用方式 GB/T 7714	Hu, Yan,Teng, Fang-Zhen,Zhang, Hong-Fu,et al. Metasomatism-induced mantle magnesium isotopic heterogeneity: Evidence from pyroxenites[J]. GEOCHIMICA ET COSMOCHIMICA ACTA,2016,185:88-111.
APA	Hu, Yan,Teng, Fang-Zhen,Zhang, Hong-Fu,Xiao, Yan,&Su, Ben-Xun.(2016).Metasomatism-induced mantle magnesium isotopic heterogeneity: Evidence from pyroxenites.GEOCHIMICA ET COSMOCHIMICA ACTA,185,88-111.
MLA	Hu, Yan,et al."Metasomatism-induced mantle magnesium isotopic heterogeneity: Evidence from pyroxenites".GEOCHIMICA ET COSMOCHIMICA ACTA 185(2016):88-111.