Extreme lithium isotopic fractionation during continental weathering revealed in saprolites from South Carolina

Rudnick, Roberta L.; Tomascak, Paul B.; Njo, Heather B.; Gardner, Leonard Robert

doi:10.1016/j.chemgeo.2004.08.008

Cited by 263 publications

(186 citation statements)

References 27 publications

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“…Results for both (IRMM-016: δ 7 Li = +0.2 ± 0.4 ‰ (2σ, n=6); UMD-1: δ 7 Li = +54.9 ± 0.8 ‰ (2σ, n=7) agree well with previously published data (e.g. Halama et al, 2007Halama et al, , 2008Rudnick et al 2004). Two international reference materials were analyzed during the course of this study to evaluate the accuracy of the measurements.…”

Section: Lithium Isotopic Analysessupporting

confidence: 86%

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

et al. 2011

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Two distinct types of eclogites from the Raspas Complex (Ecuador), which can be distinguished based on petrography and trace element geochemistry, were analyzed for their stable (Li, O) and radiogenic (Sr, Nd) isotope signature to constrain metasomatic changes due to fluid-overprinting in metabasaltic rocks at high-pressure conditions and to identify fluid sources. MORB-type eclogites are characterized by a relative LREE depletion similar to MORB. High-pressure (HP) minerals from this type of eclogite have highly variable oxygen isotope compositions (garnet: +4.1 to +9.

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Section: Lithium Isotopic Analysessupporting

confidence: 86%

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

et al. 2011

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“…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%

“…On one hand, Li isotopes can be a powerful tracer of chemical weathering (Chan et al, 1992;Pistiner and Henderson, 2003;Rudnick et al, 2004;Liu et al, 2013;Dellinger et al, 2017). On the other hand, the rapid diffusivity of Li and the associated large kinetic isotopic fractionations make Li a promising geospeedometer for determining rates of rapid geologic processes that can be difficult to determine using other perimental studies (Cherniak and Watson, 2010), which showed that Li can diffuse rapidly in zircon under crustal P-T-X conditions.…”

Section: Introductionmentioning

confidence: 99%

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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“…Any fluid/rock interaction at low temperatures is likely to affect both the Li and B isotope systems. The contrasting behavior of Li and B under mantle conditions may be due to that: (i) Li isotope fractionations are smaller than B (James et al 2003;Kisakurek et al 2004;Rudnick et al 2004;Zack et al 2003); (ii) fluids released from UHP eclogites may have much lower eclogite/fluid partition coefficients for B than for Li (Kessel et al 2005); and (iii) the whole-rock budget of Li and B is controlled by different minerals, i.e., B is preferentially hosted in phengite (Domanik et al 1993;Marschall et al 2006;Wunder et al 2005; this study), whereas Li is predominantly hosted in clinopyroxene and olivine (Marschall et al 2006;Seitz et al 2004;Woodland et al 2002;Zack et al 2002). Thus, the small range of d 7 Li values may indicate an exchange at very high temperatures.…”

Section: Element Transport During Prograde Dehydrationmentioning

confidence: 99%

“…Early Li and B isotope analyses have highlighted the behavior of these elements under hydrothermal and low-temperature conditions, with the heavier isotopes ( 7 Li and 11 B) becoming enriched in fluid phases (Chan et al 1992;Hervig et al 2002;Hoefs and Sywall 1997;Palmer and Swihart 1996;Rudnick et al 2004;Seyfried et al 1998). Recently, experimental work documented the partitioning and isotopic fractionation of Li and B between fluids and minerals at higher temperatures (e.g., Wunder et al 2005Wunder et al , 2006Meyer et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Fluid/rock interaction and mass transfer in continental subduction zones: constraints from trace elements and isotopes (Li, B, O, Sr, Nd, Pb) in UHP rocks from the Chinese Continental Scientific Drilling Program, Sulu, East China

Xiao

Hoefs²,

Hou

et al. 2011

Contrib Mineral Petrol

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In order to better understand the role of fluids during subduction and subsequent exhumation, we have investigated whole-rock and mineral chemistry (major and trace elements) and Li, B as well as O, Sr, Nd, Pb isotopes on selected continuous drill-core profiles through contrasting lithological boundaries from the Chinese Continental Scientific Drilling Program (CCSD) in Sulu, China. Four carefully selected sample sets have been chosen to investigate geochemical changes as a result of fluid mobilization during dehydration, peak metamorphism, and exhumation of deeply subducted continental crust. Our data reveal that while O and Sr-Nd-Pb isotopic compositions remain more or less unchanged, significant Li and/or B isotope fractionations occur between different lithologies that are in close contact during various metamorphic stages. Samples that are supposed to represent prograde dehydration as indicated by veins formed at high pressures (HP) are characterized by element patterns of highly fluid-mobile elements in the veins that are complementary to those of the host eclogite. A second sample set represents a UHP metamorphic crustal eclogite that is separated from a garnet peridotite by a thin transitional interface. Garnet peridotite and eclogite are characterized by a [10% difference in MgO, which, together with the presence of abundant hydroxyl-bearing minerals and compositionally different clinopyroxene grains demonstrate that both rocks have been derived from different sources that have been tectonically juxtaposed during subduction, and that hydrous silicate-rich fluids have been added from the subducting slab to the mantle. Two additional sample sets, comprising retrograde amphibolite and relatively fresh eclogite, demonstrate that besides external fluids, internal fluids can be responsible for the formation of amphibolite. Li and B concentrations and isotopic compositions point to losses and isotopic fractionation during progressive dehydration. On the other hand, fluids with isotopically heavier Li and B are added during retrogression. On a small scale, mantle-derived rocks may be significantly metasomatized by fluids derived from the subducted slab. Our study indicates that during high-grade metamorphism, Li and B may show different patterns of enrichment and of isotopic fractionation.

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Extreme lithium isotopic fractionation during continental weathering revealed in saprolites from South Carolina

Cited by 263 publications

References 27 publications

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

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

Fluid/rock interaction and mass transfer in continental subduction zones: constraints from trace elements and isotopes (Li, B, O, Sr, Nd, Pb) in UHP rocks from the Chinese Continental Scientific Drilling Program, Sulu, East China

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