Dual Explosive Activity Revealed by Tephra Studies: Peculiar Roman-Age Eruptions at Stromboli

When magmas do not interact: paired Roman-age activity

revealed by tephra studies at Stromboli volcano

by

Francalanci, Braschi, Di Salvo, Lucchi, Petrone

ESM-6 – Analytical methods

A complete set of major and trace element analyses was carried out at the Actlabs laboratories of Ancaster, Ontario, Canada (“WRA+Trace-4Lithoresearch” method) by ICP and ICP/MS. The LOI was corrected for the Fe oxidation using the FeO content determined by titration (Shapiro and Brannock, 1962) in Florence.

Sr and Nd isotope ratios were determined on selected whole-rock samples; measurements were performed at the Department of Earth Sciences of the University of Florence, using standard chemical separation techniques and a Thermal Ionization Mass Spectrometer Triton-Ti® by Thermo-Finnigan, equipped with 9 movable collectors. 87Sr/86Sr and 143Nd/144Nd values were measured dynamically and corrected using an exponential mass fractionation law to 86Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219, respectively, as described by Avanzinelli et al. (2005). Replicate measurements of NBS 987 and La Jolla standards (0.710249 and 0.511856, respectively; Thirlwall 1991) gave mean values of 87Sr/86Sr = 0.710248 ± 0.000016 (2s, n = 57) and 143Nd/144Nd = 0.511846 ± 0.000007 (2s; n = 67). The within run Sr analytical blank was 278 pg, which is in the blank range of our lab (Avanzinelli et al. 2005).

Mineral and matrix glass chemistry was performed on a selected number of samples (STR311a, STR312, STR314b, STR317). Mineral chemistry analyses were performed at the Department of Earth Sciences, University of Cambridge (UK) using a Cameca SX100 electron microprobe (EMPA) equipped with 5 wavelength dispersive spectrometers (WDS) and one energy dispersive spectrometer (EDS). The EMPA has been operated at 15keV and 10nA for major elements, and 100nA for minor and trace elements, using a 10μm de-focussed beam for feldspar and a focussed beam for pyroxene and olivine. Peak counting times were set at 20 sec for major elements and 30 sec for minor and trace elements. Mg acquisition time has been increase to 60 sec for feldspar. In order to increase accuracy and analytical precision and to decrease the Na-migration effect the following analytical conditions have been used for analysing matrix glasses: 15keV and 2nA for major elements, 15keV and 10nA for minor and trace elements. In matrix glasses all elements have been acquired for 30 sec, Cl and S were counted for 60 sec and F for 180 sec. Matrix effects were corrected using the X-PHI Cameca protocol. Accuracy and analytical precision are reported in the electronic supplementary materials (Table ESM-5).

References

Avanzinelli R, Boari E, Conticelli S, Francalanci L, Gualtieri L, Perini G, Petrone CM, Tommasini S, Ulivi M (2005) High precision Sr, Nd, and Pb isotopic analyses using new generation Thermal Ionisation Mass Spectrometer ThermoFinnigan Triton-Ti®. Period Miner 74:3:147-166.

Shapiro L, Brannock WW (1962) Rapid analysis of silicate, carbonate and phosphate rocks. Geol. Survey. Bull., Spec. Pub. n. 1144, 55 p.

Thirlwall MF (1991) Long-term reproducibility of multicollector Sr and Nd ratio analyses. Chem Geol 94:85-104.

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