Cu-Zn isotope systematics in terrestrial basalts
Abstract
High-precision isotopic measurements are now possible for numerous elements thanks to MC-ICPMS (multiple collector inductively coupled mass spectrometry). Transition elements such as Cu and Zn have been shown to have variable isotopic compositions, both on terrestrial (mineralizations, oceanic particulates)(Maréchal 1999) and extra-terrestrial samples (Luck 2003). Isotopic compositions are expressed as relative deviations from standard (i.e. δ65Cu, δ66Zn, in ppm). On Earth, Cu variations on mineralizations span approximately the range -5 ppm to +5 ppm, while Zn variations are more restricted (about -0.5 ppm to +0.5 ppm). We report Cu and Zn isotopic compositions for various terrestrial samples derived from the mantle : MORBs from the 3 major oceans, and OIBs characteristic of the major end-members (EM1, EM2, HIMU and Hawaï). Zn isotopes vary according to mass-dependent fractionation law (this was checked with the three ratios : δ66Zn, δ67Zn and δ68Zn). Zn isotopic values cluster remarkably around positive values of 0.2-0.3 ppm, close to marine particulates, sediments and loess, suggesting that no significant fractionation occurs. On the other hand, Cu isotopic values cluster around 0 ppm, close to CI chondrite value, but lower than loess values. Both elements display roughly constant isotopic values on Mid-Atlantic ridge basalts (glass) collected between 100 to 600 km from Iceland. Maréchal, Telouk, Albarède (1999) Chem. Geol. 156, 251-273 Luck, BenOthman, Barrat, Albarède (2003) Geochim.Cosmochim.Acta 67, 143-151.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....9669B