Sr-Nd-Hf Isotopic Analysis of <10 mg Dust Samples: Implications for Ice Core Dust Source Fingerprinting

Újvári, Gábor and Wegner, Wencke and Klötzli, Urs and Horschinegg, Monika and Hippler, Dorothee (2018) Sr-Nd-Hf Isotopic Analysis of <10 mg Dust Samples: Implications for Ice Core Dust Source Fingerprinting. Geochemistry, Geophysics, Geosystems, 19. pp. 60-72. ISSN 1525-2027

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Abstract

Combined Sr-Nd-Hf isotopic data of two reference materials (AGV-1/BCR2) and 50, 10, and 5 mg aliquots of carbonate-free fine grain (<10 lm) separates of three loess samples (Central Europe/NUS, China/BEI, USA/JUD) are presented. Good agreement between measured and reference Sr-Nd-Hf isotopic compositions (ICs) demonstrate that robust isotopic ratios can be obtained from 5 to 10 mg size rock samples using the ion exchange/mass spectrometry techniques applied. While 87Sr/86Sr ratios of dust aluminosilicate fractions are affected by even small changes in pretreatments, Nd isotopic ratios are found to be insensitive to acid leaching, grain-size or weathering effects. However, the Nd isotopic tracer is sometimes inconclusive in dust source fingerprinting (BEI and NUS both close to ENd(0) –10). Hafnium isotopic values (<10 lm fractions) are homogenous for NUS, while highly variable for BEI. This heterogeneity and vertical arrays of Hf isotopic data suggest zircon depletion effects toward the clay fractions (<2 lm). Monte Carlo simulations demonstrate that the Hf IC of the dust <10 lm fraction is influenced by both the abundance of zircons present and maturity of crustal rocks supplying this heavy mineral, while the <2 lm fraction is almost unaffected. Thus, EHf(0) variations in the clay fraction are largely controlled by the Hf IC of clays/ heavy minerals having high Lu/Hf and radiogenic 176Hf/177Hf IC. Future work should be focused on Hf IC of both the <10 and <2 lm fractions of dust from potential source areas to gain more insight into the origin of last glacial dust in Greenland ice cores.

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