Li isotope fractionation in peridotites and mafic melts

Jeffcoate, and Alistair B.; Elliott, Tim; Kasemann, S.; Ionov, Dmitri A.; Cooper, Kari M.; Brooker, Richard A.

doi:10.1016/j.gca.2006.06.1611

Cited by 247 publications

(229 citation statements)

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“…5), an observation that is consistent with diffusion driven Li isotope fractionation (e.g., Richter et al, 2003;Teng et al, 2006;Jeffcoate et al, 2007). However, the rim of zircon C88-29-7-6 presents a counterintuitive observation, where the δ 7 Li value decreases with increasing Li concentration.…”

Section: Isotope Profiles Measured By Nanosimsmentioning

confidence: 52%

“…Rather, such large δ 7 Li variations are similar to those seen in minerals from mantle xenoliths and phenocrysts in lavas, which reflect Li diffusion processes during melt-rock/mineral interaction (Jeffcoate et al, 2007;Parkinson et al, 2007;Rudnick and Ionov, 2007). We thus posit that the large Li isotopic fractionation in zircons results from diffusion.…”

Section: Discussionmentioning

confidence: 65%

“…Following this, a series of studies reported Li diffusion within the country rocks adjacent to Li-rich intrusions (Teng et al, 2006;Marks et al, 2007;Liu et al, 2013), finding large and systematic Li isotopic variation over tens of meters and extremely low δ 7 Li (down to −20❤) values, which they interpreted to be the result of diffusion-driven fractionation of Li isotopes. Jeffcoate et al (2007) and Parkinson et al (2007) observed diffusive fractionation of Li isotopes on a grain scale in peridotites and phenocrysts in basalt. Many additional studies of natural rocks have uncovered evidence of Li diffusion and associated isotopic fractionation, as summarized in Penniston-Dorland et al (2017).…”

Section: Diffusive Fractionation Of LI Isotopesmentioning

confidence: 99%

“…1), and the discrepancy mainly results from the extremely negative δ 7 Li values in the zircons. Such extreme δ 7 Li values have only been observed in highly weathered regoliths (Rudnick et al, 2004) and in rocks and minerals that experienced kinetic fractionation associated with Li diffusion (e.g., Teng et al, 2006;Jeffcoate et al, 2007).…”

Section: Isotopes In Zirconsmentioning

confidence: 99%

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Multi-mode Li diffusion in natural zircons: Evidence for diffusion in the presence of step-function concentration boundaries

Tang

Rudnick

McDonough

et al. 2017

Earth and Planetary Science Letters

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Available online xxxx Editor: A. Yin Keywords:Li diffusion zircon charge coupling geospeedometer ToF-SIMS NanoSIMS Micron-to submicron-scale observations of Li distribution and Li isotope composition profiles can be used to infer the mechanisms of Li diffusion in natural zircon. Extreme fractionation (20-30❤) within each single crystal studied here confirms that Li diffusion commonly occurs in zircon. Sharp Li concentration gradients frequently seen in zircons suggest that the effective diffusivity of Li is significantly slower than experimentally determined (Cherniak and Watson, 2010;Trail et al., 2016), otherwise the crystallization/metamorphic heating of these zircons would have to be unrealistically fast (years to tens of years). Charge coupling with REE and Y has been suggested as a mechanism that may considerably reduce Li diffusivity in zircon (Ushikubo et al., 2008;Bouvier et al., 2012). We show that Li diffused in the direction of decreasing Li/Y ratio and increasing Li concentration (uphill diffusion) in one of the zircons, demonstrating charge coupling with REE and Y. Quantitative modeling reveals that Li may diffuse in at least two modes in natural zircons: one being slow and possibly coupled with REE+Y, and the other one being fast and not coupled with REE+Y. The partitioning of Li between these two modes during its diffusion may depend on the pre-diffusion substitution mechanism of REE and Y in the zircon lattice. Based on our results, sharp Li concentration gradients are not indicative of limited diffusion, and can be preserved at temperatures >700 • C on geologic timescales. Finally, large δ 7 Li variations observed in the Hadean Jack Hills zircons may record kinetic fractionation, rather than a record of ancient intense weathering in the granite source materials.

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Section: Isotope Profiles Measured By Nanosimsmentioning

confidence: 52%

Section: Discussionmentioning

confidence: 65%

Section: Diffusive Fractionation Of LI Isotopesmentioning

confidence: 99%

Section: Isotopes In Zirconsmentioning

confidence: 99%

See 2 more Smart Citations

Multi-mode Li diffusion in natural zircons: Evidence for diffusion in the presence of step-function concentration boundaries

Tang

Rudnick

McDonough

et al. 2017

Earth and Planetary Science Letters

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“…The large isotopic effects observed among co-genetic mineral phases warn against oversimplified interpretations of N isotopic variations as source signatures, and demonstrate the need to take into account isotopic fractionation of light elements during magmatic processes such as partial melting (Burnard, 2004), crystallization (Teng et al, 2008) and kinetic isotope exchanges during entrainment (Deloule et al, 1991;Peslier and Luhr, 2006;Jeffcoate et al, 2006). Furthermore, different metasomatic pulses could involve different batches of a single melt having evolved through crystal fractionation and/or interaction with other minerals in the mantle (Navon and Stolper, 1987), potentially involving the diffusive exchange.…”

Section: Nitrogen Isotope Fractionation During Other Geological Procementioning

confidence: 99%

Nitrogen in peridotite xenoliths: Lithophile behavior and magmatic isotope fractionation

Yokochi

Marty

Chazot

et al. 2009

Geochimica et Cosmochimica Acta

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International audienceIn order to document the origin and speciation of nitrogen in mantle-derived rocks and minerals, the N and Ar contents and isotopic compositions were investigated for hydrous and anhydrous peridotite xenoliths from Ataq, Yemen, from Eifel, Germany, and from Massif Central, France. Nitrogen and Ar were extracted by stepwise combustion with a fine temperature resolution, followed by fusion in a platinum crucible. A large isotopic disequilibrium of up to 25.4‰ is observed within single peridotite xenoliths, with δ15N values as low as −17.3‰ in phlogopite whereas clinopyroxene and olivine show positive δ15N values. Identical Sr isotopic ratios of phlogopite, clinopyroxene and whole rock in this wehrlite sample are consistent with crystallization from a common reservoir, suggesting that the light N signature of phlogopite might be the result of isotopic fractionation during N uptake from the host magma. The nitrogen concentration is systematically high in phlogopite, (7.6–25.7 ppm), whereas that of bulk peridotite xenoliths is between 0.1 and 0.8 ppm. The high N content of phlogopite is at least partly due to host magma–mineral interaction, and may also suggest the occurrence of N as View the MathML source that substituted for K+ during mineral growth in mafic magmas. Such speciation is consistent with the fact that N and Rb contents correlate well for a set of samples from mantle regions that were affected by subduction-related metasomatism and magmatism. The N/Rb ratios of these samples are comparable with values estimated for subduction zone magmas, but are one order of magnitude lower than the N/Rb ratios characterizing subducting slabs. This difference suggests preferential release of N relative to alkalis in the forearc region. N/40Ar* ratios of minerals from analyzed mantle xenoliths are much higher than those of vesicles in MORBs and OIBs, requiring either the occurrence of nitrogen speciation in the mantle more compatible than Ar, significant loss of fluid phase during entrainment, or long residence time of volatile elements in the mantle source(s) of fluids to increase drastically the 40Ar* budget of the latter

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Lithium isotopic systematics of submarine vent fluids from arc and back‐arc hydrothermal systems in the western Pacific

Araoka

Nishio

Gamo

et al. 2016

Geochem Geophys Geosyst

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The Li concentration and isotopic composition (d 7 Li) in submarine vent fluids are important for oceanic Li budget and potentially useful for investigating hydrothermal systems deep under the seafloor because hydrothermal vent fluids are highly enriched in Li relative to seawater. Although Li isotopic geochemistry has been studied at mid-ocean-ridge (MOR) hydrothermal sites, in arc and back-arc settings Li isotopic composition has not been systematically investigated. Here we determined the d 7 Li and 87 Sr/ 86 Sr values of 11 end-member fluids from 5 arc and back-arc hydrothermal systems in the western Pacific and examined Li behavior during high-temperature water-rock interactions in different geological settings. In sediment-starved hydrothermal systems (Manus Basin, Izu-Bonin Arc, Mariana Trough, and North Fiji Basin), the Li concentrations (0.23-1.30 mmol/kg) and d 7 Li values (14.3& to 17.2&) of the end-member fluids are explained mainly by dissolution-precipitation model during high-temperature seawater-rock interactions at steady state. Low Li concentrations are attributable to temperature-related apportioning of Li in rock into the fluid phase and phase separation process. Small variation in Li among MOR sites is probably caused by low-temperature alteration process by diffusive hydrothermal fluids under the seafloor. In contrast, the highest Li concentrations (3.40-5.98 mmol/kg) and lowest d 7 Li values (11.6& to 12.4&) of end-member fluids from the Okinawa Trough demonstrate that the Li is predominantly derived from marine sediments. The variation of Li in sediment-hosted sites can be explained by the differences in degree of hydrothermal fluid-sediment interactions associated with the thickness of the marine sediment overlying these hydrothermal sites. Key Points:First Li isotopic report on submarine vent fluids from arc and back-arc hydrothermal systems Li in vent fluids can be explained mainly by dissolution-precipitation model during seawater-rock and seawater-sediment interactions Variation in Li due to diffusive hydrothermal fluid and the degree of hydrothermal fluid-sediment interaction

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Li isotope fractionation in peridotites and mafic melts

Cited by 247 publications

References 58 publications

Multi-mode Li diffusion in natural zircons: Evidence for diffusion in the presence of step-function concentration boundaries

Multi-mode Li diffusion in natural zircons: Evidence for diffusion in the presence of step-function concentration boundaries

Nitrogen in peridotite xenoliths: Lithophile behavior and magmatic isotope fractionation

Lithium isotopic systematics of submarine vent fluids from arc and back‐arc hydrothermal systems in the western Pacific

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