Zinc isotope fractionation during mantle melting and constraints on the Zn isotope composition of Earth’s upper mantle

Wang, Zezhou; Liu, Sheng‐Ao; Liu, Jingao; Huang, Junhua; Xiao, Yan; Chu, Zhu‐Yin; Zhao, Xin-Fu; Tang, Leiwen

doi:10.1016/j.gca.2016.11.014

Cited by 144 publications

(247 citation statements)

References 68 publications

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“…All δ 66 Zn values are reported compared to JMC Lyon Zn standard, based on the published difference between IRMM3702 Zn and JMC Lyon Zn (Δ 66 Zn IRMM3702‐JMC Lyon Zn = +0.30‰, Vance et al, ; Moynier et al, ). δ 66 Zn values of BHVO‐2 (0.30 ± 0.03‰), COQ‐1 (0.28 ± 0.06‰), and NIST 683 (0.16 ± 0.05‰) are consistent with previous publications (Moynier et al, ; Wang et al, , and reference therein).…”

Section: Methodssupporting

confidence: 91%

Zinc Geochemical Cycling in a Phosphorus‐Rich Ocean During the Early Ediacaran

et al. 2018

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During the early Ediacaran, there was a large influx of phosphorus into the oceans and a resultant high phosphorus concentration in seawater, where multicellular eukaryotes may have been the primary type of marine productivity. The eukaryotes could play a critical role in regulating Zn cycling and isotopes. To establish Zn geochemical cycling patterns in the phosphorus‐rich ocean, this study investigates Zn isotopic signatures of shallow water phosphorite that contains phosphatized microfossils (Weng'an biota) and deep‐water shale from the Doushantuo Formation. Our results indicate that phosphorite commonly preserves heavier Zn isotope composition, with an average of 0.80‰. The positive δ66Zn values in phosphorites may be ascribed to Zn isotope fractionation associated with the complexation of Zn with phosphate and the adsorption of isotopically heavy Zn onto Fe‐Mn oxides and organism's surfaces. We argue that phosphorite may represent an important sink of isotopically heavy Zn in a phosphorus‐rich ocean during Earth history. Meanwhile, deep‐water organic‐rich shale shows an enrichment of isotopically light Zn with an average of 0.23‰, which may be attributed to sulfide precipitation in mid‐depth environment. The organic‐rich shale may represent an isotopically light Zn sink. In addition, the highest δ66Zn value (0.45‰) in a euxinic black shale may indicate that Zn isotope signal of anoxic deep water is similar to that of modern deep seawater. If that is the case, it suggests that Zn geochemical cycling in the early Ediacaran oceans was similar to that of modern oceans.

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Section: Methodssupporting

confidence: 91%

Zinc Geochemical Cycling in a Phosphorus‐Rich Ocean During the Early Ediacaran

et al. 2018

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“…They attributed such discrepancy to equilibrium Zn isotope fractionation during mantle melting. In contrast, Wang et al () recently showed that the unmetasomatic peridotites have a homogeneous δ 66 Zn (0.18 ± 0.06‰, 2SD) regardless of their variable fertility (Al 2 O 3 = 0.10–3.6 wt %), clearly indicating insignificant Zn isotope fractionation during mantle melting. However, in order to explain the slightly higher δ 66 Zn of midocean ridge basalts (MORBs, 0.28 ± 0.03‰, 2SD), Wang et al () proposed that Zn isotopes can be fractionated by up to 0.10‰ during mantle melting.…”

Section: Introductionmentioning

confidence: 92%

“…In contrast, Wang et al () recently showed that the unmetasomatic peridotites have a homogeneous δ 66 Zn (0.18 ± 0.06‰, 2SD) regardless of their variable fertility (Al 2 O 3 = 0.10–3.6 wt %), clearly indicating insignificant Zn isotope fractionation during mantle melting. However, in order to explain the slightly higher δ 66 Zn of midocean ridge basalts (MORBs, 0.28 ± 0.03‰, 2SD), Wang et al () proposed that Zn isotopes can be fractionated by up to 0.10‰ during mantle melting. This is, however, inconsistent with the undistinguishable δ 66 Zn (0.15–0.20‰) of komatiites and massif peridotites from the Southern Alps orogenic belt (Moynier et al, ).…”

Section: Introductionmentioning

confidence: 92%

“…Crustal recycling and melt percolation are crucial for the chemical evolution of the mantle (e.g., Bodinier & Godard, ). Previous studies have shown that recycling of isotopically heavy subducted slab‐derived components (e.g., carbonate melts and/or fluids) can dramatically modify the Zn isotopic composition of the upper mantle (Liu et al, ; Pons et al, ; Wang et al, ). However, the behavior of Zn isotopes during melt percolation has been not yet known, which significantly hampers the application of Zn isotopes to understand mantle geochemistry.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Melt Percolation on Zn Isotope Heterogeneity in the Mantle: Constraints From Peridotite Massifs in Ivrea‐Verbano Zone, Italian Alps

et al. 2018

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We determined Zn isotopic compositions of 21 orogenic peridotites from the Baldissero and Balmuccia peridotite massifs in Ivrea‐Verbano Zone, Italian Alps, to investigate Zn isotope behaviors during partial melting and melt percolation in the mantle. The samples include lherzolites, harzburgites, and dunites. Lherzolites are strongly depleted in light rare earth element relative to middle and heavy rare earth element with (La/Sm)PM from 0.009 to 0.265 and (La/Yb)PM from 0.003 to 0.125, which can be explained by 5–15% fractional melting of a primitive mantle source. Harzburgites and dunites with nearly identical Mg# (molar 100 * Mg/(Mg + Fe) = 90.2–91.0) have (La/Sm)PM and (La/Yb)PM higher than but Zn contents similar to or lower than those of the parental lherzolites, suggesting that they were influenced by Zn‐depleted silicate melt percolation. Lherzolites have δ66Zn from 0.13 to 0.27‰ showing no correlations with indicators of melt extraction (e.g., Al2O3, Mg#, and La/Yb) and Zn contents. Three sulfide melt‐affected lherzolites show similar δ66Zn to the other normal ones. These observations indicate that 5–15% partial melting and sulfide melt percolation cause limited Zn isotope variations in the mantle. The metasomatic harzburgites and dunites display high δ66Zn (up to 0.46‰) negatively correlated with Zn contents. Such correlations are attributed to kinetic effect during silicate melt percolation, whereby 64Zn preferentially diffuses out from mantle minerals (e.g., olivine) to the percolating silicate melts. A diffusion model suggests that the negative correlation between δ66Zn and Zn contents in dunites can be explained by an empirical βZn (i.e., βZn‐exponent in D66Zn/D64Zn = (m64Zn/m66Zn)βZn) of 0.05–0.06 in olivine.

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“…Terrestrial igneous rocks display an average δ 66 Zn value of 0.28 ± 0.05 (Chen et al, 2013). Wang et al (2016) suggested a possible Zn isotope fractionation during peridotites melting as they measured δ 66 Zn value of 0.17 ± 0.06 in nonmetasomatised peridotites, which is ∼ 0.1 lighter than primitive basalts. In peridotites, spinels are isotopically heavier than olivines and pyroxenes by ∼ 0.1 .…”

Section: Geochemical Implications For Natural Samplesmentioning

confidence: 99%

Equilibrium zinc isotope fractionation in Zn-bearing minerals from first-principles calculations

2016

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Isotopic composition analysis contributes significantly to the investigation of the biogeochemical cycle of zinc with its economical, environmental and health implications. Interpretation of isotopic measurements is however hindered by the lack of a set of equilibrium isotopic fractionation factors between Zn-bearing minerals. In this study, equilibrium mass-dependent Zn isotope fractionation factors in Zn-bearing minerals are determined from first-principles calculations within the density functional theory (DFT) scheme. A wide range of minerals belonging to sulfide, carbonate, oxide, silicate, sulfate and arsenate mineral groups are modelled to account for the natural diversity of Zn crystal-chemical environment. Calculated reduced partition function ratios (β-factors) span a range smaller than 2 at 22 • C. All studied secondary minerals (adamite, gahnite, gunningite, hemimorphite, hydrozincite, zincite) but zinc carbonate (smithsonite) are isotopically heavier than zinc sulfide minerals (sphalerite and wurtzite) from which they could form through supergene processes. Zinc-aluminium spinel and zinc silicate are the isotopically heaviest minerals. The investigation of the crystalchemical parameters at the origin of differences in isotopic properties shows an excellent linear correlation between ln β and Zn interatomic force constants. β-factors are also observed to increase when the Zn-first neighbour bond lengths decrease and charges on atoms involved in the bonding increase and vice versa. These findings are in line with the observation of heavy isotope enrichment in systems having the largest bond strength.

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Zinc isotope fractionation during mantle melting and constraints on the Zn isotope composition of Earth’s upper mantle

Cited by 144 publications

References 68 publications

Zinc Geochemical Cycling in a Phosphorus‐Rich Ocean During the Early Ediacaran

Zinc Geochemical Cycling in a Phosphorus‐Rich Ocean During the Early Ediacaran

Effects of Melt Percolation on Zn Isotope Heterogeneity in the Mantle: Constraints From Peridotite Massifs in Ivrea‐Verbano Zone, Italian Alps

Equilibrium zinc isotope fractionation in Zn-bearing minerals from first-principles calculations

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