New perspectives on the Li isotopic composition of the upper continental crust and its weathering signature

Lucie Sauzéat (1) , Roberta L Rudnick (1) , Catherine Chauvel (2) , Marion Garçon (3) , Ming Tang (1)

1 University of Maryland [College Park]
2 ISTerre - Institut des Sciences de la Terre
3 Department of Terrestrial Magnetism [Carnegie Institution]

Lithium isotopes are increasingly used to trace both present-day and past weathering processes at the surface of the Earth, and could potentially be used to evaluate the average degree of past weathering recorded by the upper continental crust (UCC). Yet the previous estimate of average δ 7 Li of the UCC has a rather large uncertainty, hindering the use of Li isotopes for this purpose. (2ζ) ppm, and δ 7 Li = +0.6 ± 0.6 (2ζ). The δ 7 Li for desert loess deposits is anti-correlated with the chemical index of alteration (CIA). Using this relationship, along with our average δ 7 Li, we infer that (1) the present-day CIA of the average UCC is (2ζ), higher than the common reference value of 53, and (2) the average proportion of chemically weathered components is as high as (2ζ) % at the surface of the Earth.

Mots clés: Li isotopes; loess; upper continental crust; chemical weathering

Domaines: Géochimie

Lucie Sauzéat, Roberta L Rudnick, Catherine Chauvel, Marion Garçon, Ming Tang. New perspectives on the Li isotopic composition of the upper continental crust and its weathering signature. Earth and Planetary Science Letters, 2015, 428, pp.181-192. ⟨10.1016/j.epsl.2015.07.032⟩. ⟨hal-03758804⟩