Somma-Vesuvius’ activity: a mineral chemistry database

Abstract

Clinopyroxene and olivine are ubiquitous phases in Somma-Vesuvius (SV) volcanics and for the first time they were systematically studied in several products younger than 40 ka. In this manuscript chemical compositions (major, trace and rare earth elements) of a large set of olivine and clinopyroxene crystals from selected rock samples are presented and discussed. Fourteen pumice samples from Plinian pyroclastic deposits as well as three scoriae and eight lava samples from inter-Plinian deposits were collected. A representative number of olivine and clinopyroxene crystals (n ~ 50) were selected for each sample and analysed by electron microprobe and laser ablation inductively coupled plasma mass spectrometer, resulting in a large database, which is now available to the scientific community. All studied eruptive products contain olivine and clinopyroxene crystals spanning a wide range of compositions. Olivines show Fo content varying from 91 to 68, while clinopyroxenes display Mg# ranging from 93 to 71. In samples younger than A.D. 79, the more evolved (Mg#82–72) clinopyroxene crystals show clear Ca enrichment (~23.5–24.5 wt% CaO) with respect to those from older samples (before-A.D.79, ~23–21 wt% CaO). The results corroborate disequilibrium between olivine, clinopyroxene and the hosting melt, and an increasing role of carbonate assimilation in SV magma evolution in the last 2 ka. The database here produced is thought as a share product that makes available mineral data and can be used for further studies by researchers to investigate geochemical evolution of the SV system.