Magnesium stable isotope composition of Earth's upper mantle

Handler, Monica R.; Baker, Joel A.; Schiller, Martin; Bennett, Vickie C.; Yaxley, Gregory M.

doi:10.1016/j.epsl.2009.03.031

Cited by 156 publications

(151 citation statements)

References 28 publications

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“…Furthermore, the correlations of Mg isotopic compositions with radiogenic isotopic and whole-rock elemental abundances cannot be interpreted by internal isotopic fractionation between minerals and instead requires a source effect, which we will discuss in the next section. Finally, the mantle-like Mg isotopic compositions of the biotites in the more primitive granitoids (granodiorites) are fully consistent with the observation that whole-rock measurements of granodiorites and basalts all have mantle-like Mg isotopic signatures (13,14). This implies that there is little internal fractionation of Mg isotopes between minerals at graniteformation temperatures (600°C).…”

Section: Resultssupporting

confidence: 66%

“…The second scenario requires high-temperature fractionation of Mg isotopes to occur during melting or fractional crystallization. As far as we know, there is no evidence so far of high-temperature stable isotope fractionations large enough to explain the heavy Mg isotope signatures of the granites (13,14). The only exception is that of Fe isotopes (30), but Fe isotope fractionation is likely to be caused by redox reactions, which are absent for Mg.…”

Section: Resultsmentioning

confidence: 97%

“…Mg isotopes are well suited for detecting the effects of chemical weathering on lithology and major element composition because there is no significant isotopic fractionation during hightemperature processes, such as during melting of the mantle to form basalts and during magmatic differentiation (13,14) (Fig. 1A).…”

Section: Mg Isotopes As a Tool For Assessing Chemical Weatheringmentioning

confidence: 99%

“…For example, it can be seen in Fig. 1 A that the Mg isotopic compositions [expressed as ␦ 26 Mg, which is the per-mil deviation of a sample's 26 Mg/ 24 Mg relative to a universal standard, which by convention is Dead Sea Magnesium (DSM-3) standard (15)] of dissolved Mg in global river waters (Ϫ1.1‰) average lighter than seawater (Ϫ0.8‰), the Earth's mantle (Ϫ0.3‰), and juvenile igneous rocks (Ϫ0.3‰) (13,14,(16)(17)(18), indirectly suggesting that leaching of Mg during deep continental weathering of silicates preferentially releases light Mg into rivers and leaves heavy Mg behind in the weathering residues. One caveat of this interpretation of the global Mg isotope data is that the low Mg isotopic composition of river waters may in part be influenced by weathering of carbonates (19), which are extremely light (we will return to this issue later).…”

Section: Mg Isotopes As a Tool For Assessing Chemical Weatheringmentioning

confidence: 99%

See 3 more Smart Citations

The Mg isotopic systematics of granitoids in continental arcs and implications for the role of chemical weathering in crust formation

Shen

Jacobsen

Lee

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

116

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Continental crust is too Si-rich and Mg-poor to derive directly from mantle melting, which generates basaltic rather than felsic magmas. Converting basalt to more felsic compositions requires a second step involving Mg loss, which is thought to be dominated by internal igneous differentiation. However, igneous differentiation alone may not be able to generate granites, the most silicic endmember making up the upper continental crust. Here, we show that granites from the eastern Peninsular Ranges Batholith ( batholith ͉ granite ͉ isotope ͉ magnesium ͉ California

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Section: Resultssupporting

confidence: 66%

Section: Resultsmentioning

confidence: 97%

Section: Mg Isotopes As a Tool For Assessing Chemical Weatheringmentioning

confidence: 99%

Section: Mg Isotopes As a Tool For Assessing Chemical Weatheringmentioning

confidence: 99%

See 2 more Smart Citations

The Mg isotopic systematics of granitoids in continental arcs and implications for the role of chemical weathering in crust formation

Shen

Jacobsen

Lee

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

116

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“…More importantly, our results provide insight into the strongly debated origins of Martinique arc lavas and suggest that contributions of Mg from fluids supplied by the subducted slab may play a significant control in the Mg isotopic systematics of arc lavas. (18,23,28,29). This difference indicates that the source of Martinique lavas is different from that of MORB, which could be related to a diversity of processes that include seawater alteration for submarine lavas, melting of a mantle source with different δ 26 Mg, or crustal contamination during magma ascent.…”

Section: Significancementioning

confidence: 94%

Magnesium isotope geochemistry in arc volcanism

Teng

Chauvel

2016

Proc. Natl. Acad. Sci. U.S.A.

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Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ 26 Mg of the Martinique Island lavas varies from −0.25 to −0.10, in contrast to the narrow range that characterizes the mantle (−0.25 ± 0.04, 2 SD). These high δ 26 Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid−mantle interaction. This, in turn, suggests transfer of a large amount of fluidmobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration. magnesium isotopes | arc magmatism | mantle wedge | Lesser Antilles arc | Martinique Island

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Limited magnesium isotope fractionation during metamorphic dehydration in metapelites from the Onawa contact aureole, Maine

Teng

Wing

et al. 2014

Geochem Geophys Geosyst

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Knowledge on the behavior of Mg isotopes during metamorphic dehydration is the prerequisite for applying Mg isotopes as tracers for crustal recycling. Here we report Mg isotopic compositions of metapelites from the Onawa contact aureole, Maine. Except one sample, all metapelites across the aureole, from the wall-rock regional metamorphic rocks to the partially melted rocks adjacent to the pluton, have similar Mg isotopic compositions (d 26 Mg 5 20.09 to 10.12&). This observation indicates limited Mg isotope fractionation during metamorphic dehydration and fluid-rock interaction, due to the low Mg concentration in fluids relative to rocks. Our results suggest that Mg isotopic compositions of metapelites can record those of their protoliths and, hence, recycled clastic sedimentary materials may preserve their low-temperature Mg isotopic signatures through subduction zones. Therefore, Mg isotopes may serve as new tracers for crustal recycling, for example, tracing components experienced weathering cycles within granite sources.

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Magnesium stable isotope composition of Earth's upper mantle

Cited by 156 publications

References 28 publications

The Mg isotopic systematics of granitoids in continental arcs and implications for the role of chemical weathering in crust formation

The Mg isotopic systematics of granitoids in continental arcs and implications for the role of chemical weathering in crust formation

Magnesium isotope geochemistry in arc volcanism

Limited magnesium isotope fractionation during metamorphic dehydration in metapelites from the Onawa contact aureole, Maine

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