Ingrid Smet

From volcanic rock powder to Sr and Pb isotope ratios: a fit-for-purpose procedure for multi-collector ICP–mass spectrometric analysis

Geochemical research into volcanic rocks often involves isotopic analysis of whole rock powders. The method of Deniel and Pin (Anal. Chim. Acta, 2001, 426, 95–103) for simultaneous isolation of strontium and lead using extraction chromatography via Sr spec™ resin was therefore adapted into a straightforward procedure for Sr and Pb isotope ratio determination by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The main focus was to reduce their rather extensive and costly cleaning procedures for resin and columns without negatively affecting data quality. It was furthermore demonstrated that non-quantitative Sr and Pb recoveries do not compromise the quality of the isotope data obtained and that no Pb isotopic fractionation occurs on the Sr spec™ resin. The accuracy of the analyses was assessed by monitoring rock reference materials. GSJ basalt JB-2, commonly regarded as the most homogeneous Pb isotopic rock reference material, hereby produced one anomalous Pb isotopic composition out of eight analyses, suggesting that JB-2 might also be affected by nugget contamination.

Influence of source materials and fractionating assemblage on magmatism along the Aegean Arc, and implications for crustal growth

Abstract Volcanic products from Methana, Santorini and Nisyros show mineralogical and geochemical characteristics that can be linked to their differentiation at different crustal levels, and varying sources of subducted sediments. The products from Methana, in the western part of the arc, where the overriding plate is thicker, are affected by amphibole fractionation and crustal contamination. Santorini volcano, in the central part of the arc, is located on an extensively thinned section of the overriding plate; it shows high Y-contents, a-typical for average continental crust. Crustal contamination is minor, similar to Nisyros volcano. Products of the latter, easternmost volcanic centre have been variably affected by amphibole fractionation. Its sub-arc magma source is different from the central and western part of the arc, reflecting sedimentary input from the Nile. Amphibole fractionation, caused by crystallization at greater depths, seems necessary to lower Y-contents and yield volcanic products that resemble average continental crust in this respect. In detail, however, none of the magmatic products of the Aegean Arc displays MREE–HREE patterns or levels of compatible elements that are an exact match for average continental crust. Garnet stability and mixing processes appear crucial to obtain the REE and compatible element characteristics of continental crust.

A distinct source and differentiation history for Kolumbo submarine volcano, Santorini volcanic field, Aegean arc

Abstract This study reports the first detailed geochemical characterization of Kolumbo submarine volcano in order to investigate the role of source heterogeneity in controlling geochemical variability within the Santorini volcanic field in the central Aegean arc. Kolumbo, situated 15 km to the northeast of Santorini, last erupted in 1650 AD and is thus closely associated with the Santorini volcanic system in space and time. Samples taken by remotely‐operated vehicle that were analyzed for major element, trace element and Sr‐Nd‐Hf‐Pb isotope composition include the 1650 AD and underlying K2 rhyolitic, enclave‐bearing pumices that are nearly identical in composition (73 wt.% SiO2, 4.2 wt.% K2O). Lava bodies exposed in the crater and enclaves are basalts to andesites (52–60 wt.% SiO2). Biotite and amphibole are common phenocryst phases, in contrast with the typically anhydrous mineral assemblages of Santorini. The strong geochemical signature of amphibole fractionation and the assimilation of lower crustal basement in the petrogenesis of the Kolumbo magmas indicates that Kolumbo and Santorini underwent different crustal differentiation histories and that their crustal magmatic systems are unrelated. Moreover, the Kolumbo samples are derived from a distinct, more enriched mantle source that is characterized by high Nb/Yb (>3) and low 206Pb/204Pb (<18.82) that has not been recognized in the Santorini volcanic products. The strong dissimilarity in both petrogenesis and inferred mantle sources between Kolumbo and Santorini suggests that pronounced source variations can be manifested in arc magmas that are closely associated in space and time within a single volcanic field.