EPMA, SIMS and FTIR investigations on sodalites and haüynes from Somma-Vesuvius volcano (southern Italy). 14th European workshop EMAS, Modern Developments and Applications in Microbeam Analysis

Sodalite-group minerals (sodalite, tugtupite and danalite subgroups) commonly occur in alkaline igneous rocks, and in some hydrothermal and metamorphic rocks. These minerals present a zeolite-like cubic structure and two structural cavities per unit cell. Cationic and anionic contents of SSG are of interest for the study of magmatic systems; in particular, their volatile components can be useful because they can provide key information on the genetic environment, like degassing dynamics, fluids behaviour during hydrothermal processes and so on [1-4]. Besides, SSG are very promising in different fields of material science, since their (ultra)microporous structures show high flexibility and versatility in hosting tetrahedral cations and variable channels/cavities components. Hence, they can be suitable as advanced materials and behave as models for many technological and commercial applications [5, 6], for instance separation processing (i.e. hydrogen from gaseous macromolecules). The present study is focused on crystal-chemical characterization of cationic and anionic components of SSG occurring in various igneous to metamorphic rocks and ejecta from the alkaline-potassic Somma-Vesuvius volcano (southern Italy), as revealed by using combined microbeam techniques, i.e., EPMA, SIMS and μ-FTIR. Previous studies on sodalite-group minerals by means of EPMA, Raman, and LA-ICP-MS techniques focussed on halogen- (Cl, Br) and S-contents [2, 3, 8]. To the authors’ knowledge no studies on volatiles in SSG have been performed so far by integrated SIMS-FTIR investigations. Compared to bulk analyses, SIMS and μ-FTIR methods are particularly pivotal to probe trace to ultra-trace contents, speciations and orientations of an absorber across the samples [1, 7]. Our investigations show that the studied SSG correspond to sodalite sensu stricto, nosean (sulfatic sodalite) and haüyne. SIMS measurements on H, F and C (quantified as H2O, F and CO2, respectively) show contents: 0.02 - 5.0 wt% H2O, 0.01 - 0.14 wt% F, and 0.69 - 2.95 wt% CO2. Within the single crystals, the F and CO2 concentrations are virtually homogeneous, whereas in terms of H2O, samples can vary from homogenous to strongly heterogeneous. Single-crystal FTIR spectra of SSG can be grouped into sodalites and sulphatic sodalites/haüynes, according to the occurrence of the 12CO2 absorption at 2340 cm-1 [1, 9]. The absorption due to H2O and/or OH groups occurs as a very broad band extending from 3700 cm-1 to 3000 cm-1. In all samples FTIR data show the presence of CO32-. μ-FTIR focal plane array imaging shows a very heterogeneous and antithetical distribution of CO2 and especially of H2O according to the SIMS data. [ 1] Bellatreccia F, Della Ventura G, Piccinini M, Cavallo A and Brilli M 2009 Min. Mag. 73 399-413 [ 2] Hettmann K, Wenzel T, Marks M and Markl G 2012 Am. Mineral. 97 1653-1661 [ 3] Hammerli J, Spandler C, Oliver N H S and Rusk B 2014 Metam. Geol. 32 93-112 [ 4] Wang L X, Marks M A W, Keller J and Markl G 2014 Chem. Geol. 380 133-144 [ 5] Ferraris G and Merlino S 2005 Rew. Min., Geoch. MSA 57 448 pp. [ 6] Riley B J, Pierce D A, Frank S M, Matyáša J and Burns C A 2015 J. Nuclear Mat. 459 313–322 [ 7] Ottolini L and Le Fèvre B 2008 Microchim. Acta 161 329-336 [ 8] Hammerli J, Rusk B, Spandler C, Emsbo P and Oliver N H S 2013 Chem. Geol. 337- 338 75-87 [ 9] Balassone G, Bellatreccia F, Mormone A, Biagioni C, Pasero M, Petti C, Mondillo N and Fameli G 2012 Mineral. Mag. 76 191-212