Pre-eruptive volatile content, melt-inclusion chemistry, and microthermometry of interplinian Vesuvius lavas (pre-A.D. 1631)

• Published in: Journal of volcanology and geothermal research Vol. 82; no. 1; pp. 79 - 95
• Main Authors: Belkin, Harvey E, De Vivo, Benedetto, Török, Kálmán, Webster, James D
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 01.06.1998; Amsterdam Elsevier; New York, NY
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; Igneous and metamorphic rocks petrology, volcanic processes, magmas; microthermometry; Mt. Somma-Vesuvius; pre-eruptive volatiles; secondary-ion mass spectrometry (SIMS); silicate-melt inclusions; Soil and rock geochemistry; volcano de-gassing; Southern Europe; Italy; Campania Italy; Vesuvius; Mt. Somma-Vesuvius; silicate-melt inclusions; microthermometry; volcano de-gassing; pre-eruptive volatiles; secondary-ion mass spectrometry (SIMS); scanning electron microscopy; degassing; Europe; volcanic rocks; strontium; SEM data; igneous rocks; mass spectroscopy; chemical analysis; chlorine; rare earths; lithium; pyroclastics; homogenization; lava; sulfur; boron; volatile elements; inclusions; electron probe data; fluorine
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/S0377-0273(97)00058-9

Silicate-melt inclusions from lavas and pyroclastics from a selected suite of pre-A.D. 1631 interplinian Mt. Somma–Vesuvius lavas and scoria have been experimentally homogenized and studied by microthermometry, electron microprobe (EMPA) and secondary-ion mass spectrometry (SIMS) to examine pre-eruptive volatile content and magma evolution. The melt inclusions have a bubble about 0.06% their volume, uncommonly contain non-condensable gas but do not contain any dense fluid phases. Clinopyroxene-hosted inclusions yield homogenization temperatures ( T h) from 1170 to 1260°C, most between 1220 and 1240°C; plagioclase-hosted inclusions have T h from 1210 to 1230°C; these values are typical for the Vesuvius environment. The dominant factor controlling major element variability in the inclusions is clinopyroxene fractionation; MgO varies from 5 to 3 wt%, SiO 2 varies from 60 to 48 wt%, total alkalis vary from 15 to 4 wt%, and CaO varies from 13 to 5 wt%. H 2O varies from 2.7 to 0.6 wt% and is decoupled from incompatible element evolution suggesting vapor saturation during trapping. Chlorine and F vary from 1.0 wt% to 0 and 0.63 to 0 wt%, respectively. Bulk rock and limited matrix glass analyses show that the lavas lost about half of their F and Cl content except for the A.D. 472–1631 lava which contains similar Cl abundances as the bulk rock. SO 3 varies from 0.5 to 0 wt% and compared with matrix glass and bulk rock demonstrate that the lavas have lost essentially all sulfur. The samples can be classified into three age groups, >25,000 yr B.P., 25,000–17,000 yr B.P., and A.D. 472–1631. There is a systematic increase in some components, e.g., total alkalis, SO 3, Cl, Li, B, and Sr with the youth of the sample and a decrease in others, e.g., Zr and Y. However, on average these samples seem less evolved than later A.D. 1631–1944 lavas.