Olivine isotopic ratios

Matrix effects on measured Mg isotope ratios due to the presence of Fe in laser ablation targets require further study. Young et al. (2002a) formd that adding Fe via solution to the plasma to yield FeY Mg+ up to 2.0 resulted in no measurable shifts in Mg/ Mg and Mg/ Mg of laser ablation products. Norman et al. (2004) showed that there is a shift in instrumental fractionation in measured Mg/ Mg on the order of +0.06%o for every 1% decrease in Mg/ (Mg+Fe) of the olivine target. These disparate results might be explained by ionization in different locations in the torch when samples are introduced by aspiration of solutions rather than by gas flow from a laser ablation chamber. Different matrix effects for solutions and laser... 

Hf/177Hf 0.28249 Conticelli et al. 2002 Author s unpublished data). Very high O-isotope ratios have been measured for lavas (S18Osmow +11 to +12 Holm and Munksgaard 1982 Taylor et al. 1984) and for separated olivines (518Osmow + 13 Author s unpublished data). 

Calc-alkaline rocks at Stromboli have lower K20, P2O5 and incompatible trace element contents than the associated shoshonitic and KS rocks. However, REE and the mantle-normalised incompatible element patterns have similar shapes for all rocks, with positive spikes of Ba and negative anomalies of HFSE (Fig. 7.14). Glass inclusions with primitive compositions (MgO 7.8 wt %) contained in olivine (F091-84) from basaltic scoriae of the present-day activity, have the same type of incompatible element patterns as the whole rocks (Bertagnini et al. 2003). Sr-isotope ratios are... 

Other geochemical characteristics of Italian volcanism are also not easily explained by the plume hypotheses. For example, deep mantle plumes are commonly associated with high 3He/4He ratios (e.g. Farley and Neroda 1998). However, measurements carried out on fluid inclusions in olivine phenocrysts from mafic Italian rocks have yielded low He isotopic ratios with R/Ra < 7.5 (e.g. Sano et al. 1989 Graham et al. 1993 Marti et al. 1994 Di Liberto 2003 Martelli et al. 2004), which are much lower than compositions found for plume-related magmas. 

Jones R. H., Leshin L. A., and Guan Y. (2002) Heterogeneity and 0-enrichments in oxygen isotope ratios of olivine from chondrules in the Mokoia CV3 chondrite. Lunar Planet. Sci. XXXIII, 1571. The Lunar and Planetary Institute, Houston (CD-ROM). 

Scarsi P (2000) Fractional extraction of helinm by crashing of olivine and clinopyroxene phenociysts effects on the He/ He measured ratio. Geochim Cosmochim Acta 64 3751-3762 Scarsi P, Craig H (1996) Helium isotope ratios in Ethiopian Rift basalts. Earth Planet Sci Lett 144 505-516... 

Figure 3.7 Mg isotope ratio data for terrestrial mantle-rocks and minerals, whole-rock chondrites, pallasite olivines, Martian meteorites, and lunar basalts and breccia. Error bars represent the external reproducibility in 2SE (= 2a/v/n, where n is the number of measurements per sample). Not considering the dunite DTSl and the harzburgite PCC-1 (with 32% serpentine [15]), which are both likely affected by processes occurring after their emplacement within the Earth s crust, the average (5 Mg of the BSE is —0.54 + 0.04 (2SE), which overlaps with that of average chondrites (—0.52 + 0.04), pallasites (—0.54 + 0.04), Mars (—0.57 + 0.02), and the Moon (—0.51 0.03), showing that the stable Mg isotopic composition of the inner solar system (dotted lines, <5 Mg = —0.54) is homogeneous to within 0.05%o.

Oxygen isotope signatures of Vesuvio rocks show wide variations (S180 —1-7.0 to +10.0) and are negatively correlated with MgO (Ayuso et al. 1998). Helium isotope studies on clinopyroxene and olivine from historical lavas gave values of R/Ra 2.2 to 2.7, close to ratios found in the fumar-oles of Campanian volcanoes (Tedesco et al. 1990 Graham et al. 1993). 

Noble gas isotope compositions are within the range of MORB (Nakai et al. 1997). 3He/4He ratios measured on clinopyroxene and olivine phenociysts show little variation, and compositions normalised to atmospheric values cluster around R/Ra 6.5 (Marty et al. 1994). Similar values have been found in fumarolic gases (Nakai et al. 1997). 

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