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dc.contributor.authorLiu, Ping-Ping  Concept link
dc.contributor.authorTeng, Fang-Zhen  Concept link
dc.contributor.authorDick, Henry J. B.  Concept link
dc.contributor.authorZhou, Mei-Fu  Concept link
dc.contributor.authorChung, Sun-Lin  Concept link
dc.date.accessioned2017-07-07T15:35:59Z
dc.date.issued2017-02
dc.identifier.urihttps://hdl.handle.net/1912/9088
dc.description© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 206 (2017): 151-165, doi:10.1016/j.gca.2017.02.016.en_US
dc.description.abstractTo constrain the Mg isotopic composition of the oceanic mantle, investigate Mg isotope fractionation of abyssal peridotites during seafloor alteration, and assess Mg budget in the oceans, a suite of 32 abyssal peridotite samples from the Gakkel Ridge and Southwest Indian Ridge (SWIR) was, for the first time, selected for high-precision Mg isotope analyses. Although most of these samples are extensively altered, largely by serpentinization and weathering, primary olivine, diopside and enstatite grains are preserved in some samples. Olivine grains from the least altered samples have δ26Mg varying from −0.30 to −0.12‰ (n = 7), whereas enstatite and diopside have δ26Mg varying from −0.27 to −0.16‰ (n = 7), and from −0.23 to −0.09‰ (n = 6), respectively. Whole-rock δ26Mg values range from −0.24 to 0.03‰ with an average of −0.12 ± 0.13‰ (2SD, n = 32). Strongly serpentinized peridotites have lower average δ26Mg values (δ26Mg = −0.19 ± 0.07‰, 2SD, n = 7) than weathering-dominated ones (δ26Mg = −0.10 ± 0.12‰, 2SD, n = 25). Calculated Mg isotopic compositions of fresh mantle peridotites vary from −0.29 to −0.13‰, beyond the previously reported range of the subcontinental lithospheric mantle (−0.25 ± 0.04‰) and the analytical uncertainty (±0.07‰, 2SD). Our study therefore indicates that the oceanic mantle may have similar but slightly heterogeneous Mg isotopic compositions to that of subcontinental lithospheric mantle. Secondary serpentinization does not fractionate Mg isotopes of abyssal peridotites, whereas low-T weathering and formation of clay can result in the enrichment of heavy Mg isotopes in abyssal peridotites. This study also demonstrates that fluid-rock interaction does not necessarily produce rocks with intermediate Mg isotopic compositions. Magnesium isotopes of the rocks thereafter are dependent on the secondary minerals formed. We also conclude that the release of light Mg isotopes into the ocean during alteration of abyssal peridotites can be an important influx of Mg for the seawater Mg budget. Abyssal peridotites with a heavy Mg isotopic signature can be recycled into the mantle in subduction zones and may thus result in heterogeneous Mg isotopic compositions of the oceanic mantle and heavy Mg isotopic compositions of arc magmas.en_US
dc.description.sponsorshipThis study was supported by grants from the National Science Foundation of China (grants 41473038 and 41503010), China Postdoctoral Science Foundation (2015M570145), National Science Foundation (EAR-1056713 and EAR-1340160) and project MOST104 -2745-M-002-001-ASP granted to SLC. Partial support for HJBD was provided by the US National Science Foundation (OCE-1434452).en_US
dc.language.isoenen_US
dc.relation.urihttps://doi.org/10.1016/j.gca.2017.02.016
dc.subjectAbyssal peridotiteen_US
dc.subjectMagnesium isotopeen_US
dc.subjectMantle heterogeneityen_US
dc.subjectMagnesium cyclingen_US
dc.subjectSeafloor alterationen_US
dc.titleMagnesium isotopic composition of the oceanic mantle and oceanic Mg cyclingen_US
dc.typePreprinten_US


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