Appendix a Sample Treatment and Preparation Techniques, and Analytical Methods
Appendix A – Sample preparation techniques, and analytical methods
Juvenile clasts representative of the Molara, Vateliero and Cava Nocelle sequenceswere chosen for petrographic observations in thin section. Prior to crushing and powdering, the clasts of each sample were cleaned with a dental drill equipped with a diamond disk in order to remove altered portions and felsic lithics (see later). Because of the vicinity of sampling localities to the sea, the clasts were washed ultrasonically with de-ionized “milli-Q” water to release possible traces of marine salt. Then, an aliquot of dried clasts of each sample was crushed for mineral and glass separation, whereasanother aliquot was ground in an agate mill for whole-rock chemical and isotopic analyses.
Clinopyroxene, olivine, feldspars (either plagioclase or alkali-feldspar) and biotite crystals, as well as glass shards, were separated after crushing and sieving from cleaned clasts, using a Frantz isodynamic magnetic separator followed by hand-picking under a binocular microscope. In most of the investigated rocks, different types of large single phenocrysts and groups of small phenocrysts of Cpx and Ol (abbreviations following Whitney and Evans 2010) were distinguished on the basis of their color, i.e., green, dark and black for Cpx, light and yellow for Ol, each of them analyzed separately. Large Cpx and Ol phenocrysts, at least 1 mm across and weighing at least 4 mg, were selected for single mineral analysis, by dividing each crystal in two parts: one part was pasted with crystal bond resin on a glass slide, then lowered and polished for mineral chemical analysis; the other part was used for laser fluorination oxygen isotope analysis. Groups of small phenocrysts were also divided in two aliquots: one was treated for oxygen isotope analysis; another was acid attached in toto for Sr-Nd isotope analyses, after leaching with 7% suprapur HF, followed by “milli-Q” water rinse and final check under the microscope, in order to achieve purification of the separates from any adhering glass or matrix.
Whole-rock major oxide and trace element contents were determined at the Dipartimento di Scienze della Terra, University of Perugia (Italy). Major oxides (except MgO, Na2O and LOI, determined by wet chemical analysis) were analyzed, after calcination of the sample powders, by XRF with full matrix correction after Franzini et al (1972; and references therein), according to which the sum of all major oxides is equal to about 100 wt.%. Some trace elements, i.e., V, Cr, Co, Ni, Cu, Zn and Pb, were also analyzed by X-rays fluorescence (XRF) after Kaye (1965). Precision was better than 10 % for V, Cr, Ni, Y, Zr and Ba, and better than 5 % for all the other elements. The accuracy, tested against international rock standards, was better than 10 %. Other trace elements, i.e., Sc, Ga, Rb, Sr, Y, Zr, Nb, Cs, Ba, Rare Earth Elements, Hf, Ta, Th and U, were determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) techniques on lithium tetraborate fusion beads, following Petrelli et al. (2007, 2008). Precision was better than 10 % for elements with concentrations above 2 ppm with the only exception of Pb (~15 %). For elements with concentrations below 2 ppm the precision was about 15 %. Accuracy was better than 10 %.
Mineral and glass chemistry measurements were carried out by electron microprobe analysis (EMPA) techniques on either polished thin sections or single crystals pasted with crystal bond resin on glass slides. Analyses were performed using a CAMECA SX50 (Istituto di Geologia Ambientale e Geoingegneria – Consiglio Nazionale delle Ricerche of Rome, Italy), equipped with five wavelength-dispersive system X-ray spectrometers, and one energy-dispersive system X-ray spectrometer. Operation conditions of the electron beam were an accelerating voltage of 15 kV, a current of 20 nA, and a beam size of either 5 μm (minerals) or 10 μm (glasses). Counting times were set to 20 s for the peak of each element, and 10 s on both sides of the peak for the background. Data were reduced using a ZAF correction procedure for atomic number (Z), X-ray absorption (A) and secondary fluorescence (F) effects. Both natural and synthetic standards were employed to check the precision and accuracy performance of the instrument. Typical analytical uncertainty was 1 % for major oxides and ca. 10 % for minor oxides (i.e., between 1 and 0.1 wt. %).
Strontium and neodymium isotopic compositions were determined by thermal ionization mass spectrometry (TIMS) partly at Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Napoli “Osservatorio Vesuviano” (INGV-OV, Naples), using a ThermoFinnigan Triton TI multicollector mass spectrometer, and partly at Istituto di Geoscienze e Georisorse – Consiglio Nazionale delle Ricerche (IGG-CNR, Pisa), using a Finnigan MAT 262 multicollector mass-spectrometer, after conventional ion-exchange procedures for Sr-Nd separation from the matrix. Measured 87Sr/86Sr ratios were normalized for within-run isotopic fractionation to 86Sr/88Sr = 0.1194, and 143Nd/144Nd ratios to 146Nd/144Nd = 0.7219. Sr and Nd blanks were on the order of 0.3 ng during the period of chemistry processing. The measured Sr and Nd isotope ratios are considered to be free of inter-laboratory bias since, during the collection of isotopic data, replicate analyses of NIST SRM 987 (SrCO3) and La Jolla standards have been performed at both laboratories to check for external reproducibility. 2σmean, i.e. thestandard error with N=180, is better than ±0.000010 forSr and ±0.000005 for Nd measurements. The external reproducibility (2σ, where σ is the standard deviation of the standard results, according to Goldstein et al. 2003), i.e. the meanmeasured value of 87Sr/86Sr for the standard NIST–SRM987,was 0.710230 ± 0.000018 (2σ, N = 77) at the Napoli lab, and 0.710242 ± 0.000012 (2σ, N = 28) at the Pisa lab; that of143Nd/144Nd for the La Jolla standard was 0.511838 ± 0.000012 (2σ, N = 70) at the Napoli lab, and for the JNdi-1 standard was 0.51200 ± 0.000008 (2σ, N = 16) at the Pisa lab.Sr and Nd isotope ratios of the present work, as well as those from literature considered for comparison purposes (Civetta et al. 1991; Piochi et al. 1999), have been normalized to the recommended values of NIST SRM 987 (87Sr/86Sr = 0.71025) and La Jolla (143Nd/144Nd = 0.51185) standards, respectively.
The oxygen isotopic composition of olivine and clinopyroxene single phenocrysts and groups of small phenocrystswas measured at IGG-CNR (Pisa)by conventional laser fluorination following the procedure described by Sharp (1995). Pure F2 desorbed from K3NiF7 salt (Asprey 1976) was used as reagent, and O2 was the analyte measured with a Finnigan Delta XP mass spectrometer. Precision and accuracy of the analyses were monitored by measuring aliquots of laboratory quartz standards (QMS, δ18O = 14.05‰) during each set of analyses, yielding an average reproducibility of ± 0.12‰ (2σ; n = 9). The measured NBS-28 (recommended δ18O = 9.60‰) yielded an average δ18O = 9.54±0.15‰ (2σ, n = 4). No data correction was necessary, and results are reported in the standard per mil delta notation vs. SMOW.
References not listed in the manuscript
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