TY - JOUR
T1 - Lithium isotopic composition and concentration of the upper continental crust
AU - Teng, F. Z.
AU - McDonough, W. F.
AU - Rudnick, R. L.
AU - Dalpé, C.
AU - Tomascak, P. B.
AU - Chappell, B. W.
AU - Gao, S.
PY - 2004/10/15
Y1 - 2004/10/15
N2 - The Li isotopic composition of the upper continental crust is estimated from the analyses of well-characterized shales, loess, granites and upper crustal composites (51 samples in total) from North America, China, Europe, Australia and New Zealand. Correlations between Li, δ 7 Li, and chemical weathering (as measured by the Chemical Index of Alteration (CIA)), and δ 7 Li and the clay content of shales (as measured by Al 2O3 SiO 2 ), reflect uptake of heavy Li from the hydrosphere by clays. S-type granites from the Lachlan fold belt (-1.1 to -1.4‰) have δ 7 Li indistinguishable from their associated sedimentary rocks (-0.7 to 1.2‰), and show no variation in δ 7 Li throughout the differentiation sequence, suggesting that isotopic fractionation during crustal anatexis and subsequent differentiation is less than analytical uncertainty (∓1‰,2σ). The isotopically light compositions for both I- and S-type granites from the Lachlan fold belt (-2.5 to + 2.7 ‰) and loess from around the world (-3.1 to + 4.5‰) reflect the influence of weathering in their source regions. Collectively, these lithologies possess a limited range of Li isotopic compositions (δ7 Li of -5‰ to + 5‰), with an average (δ7 Li of 0 ∓ 2‰ at 1σ) that is representative of the average upper continental crust. Thus, the Li isotopic composition of the upper continental crust is lighter than the average upper mantle (δ7 Li of + 4 ∓ 2‰), reflecting the influence of weathering on the upper crustal composition. The concentration of Li in the upper continental crust is estimated to be 35 ∓ 11 ppm (2σ), based on the average loess composition and correlations between insoluble elements (Ti, Nb, Ta, Ga and Al 2 O 3 , Th and HREE) and Li in shales. This value is somewhat higher than previous estimates (∼20 ppm), but is probably indistinguishable when uncertainties in the latter are accounted for.
AB - The Li isotopic composition of the upper continental crust is estimated from the analyses of well-characterized shales, loess, granites and upper crustal composites (51 samples in total) from North America, China, Europe, Australia and New Zealand. Correlations between Li, δ 7 Li, and chemical weathering (as measured by the Chemical Index of Alteration (CIA)), and δ 7 Li and the clay content of shales (as measured by Al 2O3 SiO 2 ), reflect uptake of heavy Li from the hydrosphere by clays. S-type granites from the Lachlan fold belt (-1.1 to -1.4‰) have δ 7 Li indistinguishable from their associated sedimentary rocks (-0.7 to 1.2‰), and show no variation in δ 7 Li throughout the differentiation sequence, suggesting that isotopic fractionation during crustal anatexis and subsequent differentiation is less than analytical uncertainty (∓1‰,2σ). The isotopically light compositions for both I- and S-type granites from the Lachlan fold belt (-2.5 to + 2.7 ‰) and loess from around the world (-3.1 to + 4.5‰) reflect the influence of weathering in their source regions. Collectively, these lithologies possess a limited range of Li isotopic compositions (δ7 Li of -5‰ to + 5‰), with an average (δ7 Li of 0 ∓ 2‰ at 1σ) that is representative of the average upper continental crust. Thus, the Li isotopic composition of the upper continental crust is lighter than the average upper mantle (δ7 Li of + 4 ∓ 2‰), reflecting the influence of weathering on the upper crustal composition. The concentration of Li in the upper continental crust is estimated to be 35 ∓ 11 ppm (2σ), based on the average loess composition and correlations between insoluble elements (Ti, Nb, Ta, Ga and Al 2 O 3 , Th and HREE) and Li in shales. This value is somewhat higher than previous estimates (∼20 ppm), but is probably indistinguishable when uncertainties in the latter are accounted for.
UR - http://www.scopus.com/inward/record.url?scp=5044226795&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2004.03.031
DO - 10.1016/j.gca.2004.03.031
M3 - Review article
AN - SCOPUS:5044226795
SN - 0016-7037
VL - 68
SP - 4167
EP - 4178
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 20
ER -