Lithium isotope evidence for subduction-enriched mantle in the source of mid-ocean-ridge basalts

Elliott, Tim; Thomas, Alexander L.; Jeffcoate, Alistair; Niu, Yaoling

doi:10.1038/nature05144

Cited by 196 publications

(108 citation statements)

References 26 publications

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“…In addition, it is well known that weathered products of the crust exhibit negative δ 7 Li values when compared to those obtained from mantle-derived magmas. Fresh peridotites and normal mid-ocean ridge basalts (N-MORB) typically fall in a relatively restricted range (δ 7 Li 3.8 ± 1.5 %), relative to the international Li standard, NIST SRM-8545 (Chan et al 1992;Elliott et al 2006;Jeffcoate et al 2007;Magna et al 2006;Seitz et al 2004;Tomascak et al 2008). Highly fractionated δ 7 Li values (−20 to +15 ‰) were measured in Jack Hills zircons by Ushikubo et al (2008); negative values are consistent with extensive weathering during the Hadean and Archean.…”

Section: Introductionmentioning

confidence: 92%

Li zoning in zircon as a potential geospeedometer and peak temperature indicator

Trail

Cherniak

Watson

et al. 2016

Contrib Mineral Petrol

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920 to 650 °C, calculated diffusivities are in agreement with a previously established Arrhenius relationship calibrated on trace-element-poor Mud Tank zircon. Our revised Arrhenius relationship that includes both datasets is:We also observed that synthetic sector-zoned zircon exhibits near-step-function Li concentration profiles across sectors that correlate with changes in the rare earth element (REE) and P concentrations. This allowed us to examine how Li diffusion might couple with REE diffusion in a manner different than that described above. In particular, re-heating these grains revealed significant Li migration, but no detectable migration of the rare earth elements. Thus, unlike most elements in zircon which are not mobile at the micrometer scale under most timetemperature paths in the crust, Li zoning, relaxation of zoning, or lack of zoning altogether could be used to reveal time-temperature information. Discrete ~10 μm concentration zones of Li within zircon may be partially preserved at 700 °C for tens to hundreds of years, and at 450 °C for millions of years. In this regard, Li zoning in zircon holds significant potential as a geospeedometer, and in some instances as a qualitative indicator of the maximum temperature experienced by the zircon.

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Section: Introductionmentioning

confidence: 92%

Li zoning in zircon as a potential geospeedometer and peak temperature indicator

Trail

Cherniak

Watson

et al. 2016

Contrib Mineral Petrol

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“…The isotopic ratio of Li in modern oceans is ~31‰ (Tomascak et al, 1999). The continental crust has an average lithium-isotope composition of 0 ± 3‰ (Teng et al, 2004), whereas mid-ocean-ridge basalts usually have isotopic values of 3-5‰ (Elliott et al, 2006;Tomascak et al, 2008Tomascak et al, , 1999. The difference of the isotopic ratio between the ocean water and continental and marine silicates is a function of high-and low-temperature alteration of these minerals.…”

Section: Weathering and The Li-isotope Composition Of The Oceansmentioning

confidence: 99%

Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Lechler

Strandmann

Jenkyns

et al. 2015

Earth and Planetary Science Letters

104

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An abrupt rise in temperature, forced by a massive input of CO 2 into the atmosphere, is commonly invoked as the main trigger for Oceanic Anoxic Events (OAEs). Global warming initiated a cascade of palaeoenvironmental perturbations starting with increased continental weathering and an accelerated hydrological cycle that delivered higher loads of nutrients to coastal areas, stimulating biological productivity.The end-result was widespread anoxia and deposition of black shales: the hallmarks of OAEs. In order to assess the role of weathering as both an OAE initiator and terminator (via CO 2 sequestration) during the Early Aptian OAE 1a (Selli Event, ~120 Ma) the isotopic ratio of lithium isotopes was analysed in three sections of shallowmarine carbonates from the Pacific and Tethyan realm and one basinal pelagic section from the Tethyan domain. Because the isotopic composition of lithium in seawater is largely controlled by continental silicate weathering and high-and lowtemperature alteration of basaltic material, a shift to lighter  7 Li values is expected to characterize OAEs. The studied sections illustrate this phenomenon:  7 Li values decrease to a minimum coincident with the negative carbon-isotope excursion that effectively records the onset of OAE 1a. A second negative  7 Li excursion occurs coeval with the minimum in strontium isotopes after the event. The striking similarity to the strontium-isotope record argues for a common driver. The formation and destruction (weathering) of an oceanic LIP could account for the parallel trend in both isotope systems. The double-spike in lithium isotopes is probably related to a change in weathering congruencies. Such a chemostratigraphy is consistent with the hypothesis that an increase in silicate weathering, in conjunction with organic-carbon burial, led to drawdown of atmospheric CO 2 during the early Aptian OAE 1a.

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“…Similar mantle wedge enrichment by slab-derived radiogenic Sr has been hypothesised for the Cascades lavas in the northwestern USA (Borg et al, 1997). Recent lithium isotope work by Elliott et al (2006) suggests that, globally, the mantle is enriched directly by slab-derived fluids rather than by mechanical mixing with subducted crust in subduction erosion.…”

Section: Origin Of the Crustal Component In The Mafic To Intermediatementioning

confidence: 99%

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

Clemens

Darbyshire

Flinders

2009

Lithos

108

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The 425 Ma Arrochar and Garabal Hill-Glen Fyne complexes of highland Scotland are examples of post-orogenic magmatism accompanying extensional collapse of an orogen, in this case the Caledonian. The rocks are dominantly high-K series, but range from medium-K to shoshonitic. Mantle upwelling, melting and the intrusion of large volumes of mafic magma into the crust are inferred to have accompanied lithospheric thinning, and to have provided the heat source for melting of young arc crust accreted during the preceding subduction epoch.Fluids evolved from the subducting slab are inferred to have caused high degrees of enrichment in the overlying mantle wedge. Deep in the crust, the mantle-derived, K-rich mafic to intermediate magmas mixed with felsic crustal melts to form the spectrum of magmas intruded in the two complexes. Microgranular enclaves in the granitic rocks represent mafic magmas derived from the enriched mantle and hybridised by reaction, diffusion and mechanical mixing with their host felsic magmas, but they do not form part of the evolutionary series that produced the host magmas. Rather than inheriting its LILEenriched character directly from crustal melts, or from crustal assimilation by mafic magmas, the high-K series may commonly owe at least part of its potassic character to the involvement of mantle (highly metasomatised by slab-derived fluids) as a major magma source. Enclave suites, though prominent in some granitic rocks should not be assumed to represent magmas that played a significant role in the production of the chemical variations in their host magmas.

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Lithium isotope evidence for subduction-enriched mantle in the source of mid-ocean-ridge basalts

Cited by 196 publications

References 26 publications

Li zoning in zircon as a potential geospeedometer and peak temperature indicator

Li zoning in zircon as a potential geospeedometer and peak temperature indicator

Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

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