Basalts isotopic ratios

Volpe AM, Olivares JA, Murrell MT (1991) Determination of Radium isotope ratios and abundances in geologica samples by thermal ionization mass spectrometry. Anal Chem 63 916-919 Volpe AM, Goldstein SJ (1993) Ra- °Th disequilibrium in axial and off-axis mid-ocean ridge basalts. Geochim Cosmochim Acta 57 1233-1241... 

T1 isotope ratios might be also used as a tracer in mantle geochemistry (Nielsen et al. 2006 2007). Since most geochemical reservoirs except Fe-Mn marine sediments and low temperature seawater altered basalts are more or less invariant in T1 isotope composition, admixing af small amounts of either of these two components into the mantle should induce small T1 isotope fractionations in mantle derived rocks. And indeed, evidence for the presence of Fe-Mn sediments in the mantle underneath Hawaii was presented by Nielsen et al. (2006). 

Sakai H, Casadevall TJ, Moore JG (1982) Chemistry and isotope ratios of sulfur in basalts and volcanic gases at Kilauea volcano, Hawaii. Geochim Cosmochim Acta 46 729-738 Sakai H, DesMarais DJ, Ueda A, Moore JG (1984) Concentrations and isotope ratios of carbon, nitrogen and sulfur in ocean-floor basalts. Geochim Cosmochim Acta 48 2433-2441 Sano Y, Marty B (1995) Origin of carbon in fumaroUc gas from island arcs. Chem Geol 119 265-274... 

If both chemical concentration gradients and isotopic ratio gradients are present (e.g., basaltic melt with Sr/ Sr ratio of 0.705 and andesitic melt with Sr/ Sr ratio of 0.720), the homogenization of isotopic ratio is referred to as isotopic diffusion (Lesher, 1990 Van Der Laan et al., 1994), although some prefer to call it isotopic homogenization. If there are concentration gradients in both major and trace elements, the diffusion of the trace elements is referred to as trace element diffusion (Baker, 1989). Isotopic diffusion and trace element diffusion are really part of multicomponent diffusion, which is complicated to handle. Isotopic diffusion should not be confused with self-diffusion, and trace element diffusion should not be confused with tracer diffusion. 

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... 

The Island of Ustica and the nearby Prometeo lava field have been less extensively studied than Etna. However, the available data have shown close compositional similarities among these volcanoes. Cinque et al. 1988) found that the Ustica basalts have incompatible element and Sr-isotope ratios that are intermediate between the intraplate basalts from the African plate (e.g. Pantelleria) and the calc-alkaline mafic rocks from Alicudi (Aeolian arc). This has led to the conclusion that the source of Ustica magmas is an intraplate-type mantle contaminated by subduction fluids or melts. A similar conclusion has been reached by Trua et al. (2003). 

Mafic rocks from the Sicily Province display variable abundances of incompatible elements, which increase from tholeiites to alkali basalts and nephelinites. However, all the rocks show low LILE/HFSE ratios, typical of intraplate basalts, in contrast with the high LILE/HFSE compositions of volcanism from the Aeolian arc and the Italian peninsula. They have a relatively restricted range of Sr-Nd isotopic compositions, but variable Pb isotopic ratios, which fall along a trend connecting HIMU and intermediate compositions between DMM and EMI mantle. 

Sr is retained mostly in the mantle, while Rb preferentially accumulates in the crust. The ratio 87Sr/86Sr is continuously and very slowly rising in the mantle but may be strongly increased in the crust. Sr isotope ratios of 0.701—0.703, being indicative of mantle or deep-crust material, have clarified many petro-genetic problems. Investigations in this field, especially on the basalt problem, were carried out by Cast (cf. 1967). 

High precision determination of Rb/ Rb isotope ratios by MC-ICP-MS (Isoprobe, Micromass) is advantageous in comparison to MC-TIMS (VG Sector 54, Micromass) due to an unproved precision, and fraction capability problems can be easily considered using admixed Zr for mass bias correction via the Zr/ °Zr isotope ratio. Rb isotopic composition in geological materials (basalt, granite and greywacke) and synthetic samples (in house mica standard, NBS 607 K-fsp standard) have been examined with a reproducibility of Rb/ Rb measurements of 0.02-0.05 % (2 O ). No anomalous isotope fractionation was observed for the samples investigated. 

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