Abstract
Pantelleritic magmas are low-viscosity peralkaline rhyolites which exhibit large differences in eruptive style (explosive to effusive). The processes that promote fragmentation and explosive eruptions of pantelleritic magma remain subject to debate, but undoubtedly variations of magma viscosity during magma ascent and degassing contribute to differences in eruptive style. Because crystallization can significantly influence magma rheology, we present a review of equilibrium and disequilibrium crystallization experiments of pantellerites, focusing on the crystallization of the main phases, alkali feldspar, and (lesser) clinopyroxene. Our analysis of data for several explosive pantelleritic eruptions on Pantelleria suggests pre-eruptive pressures of 50–100 MPa, temperatures of 700–800 °C for water-saturated conditions. Given these conditions, we show that the low pre-eruptive crystal fractions (0.08 to 0.15), temperatures between 700 and 800 °C, and the decrease of melt H2O content during magma ascent/decompression can promote a significant change in viscosity (up to 106–107 Pa·s), leading to magma brittle fragmentation and explosive eruptions. Because of their typical range of viscosity, pantelleritic magmas may show greater variations in eruptive style due to differences in ascent (decompression) rate when compared with metaluminous rhyolites.
Highlights
Pantellerites are typically identified as silicaoversaturated rhyolites with an alkali/alumina molar ratio [(Na2O + K2O)/Al2O3]
We provide a comprehensive evaluation of the pre-eruptive conditions of volcanic activities at Pantelleria, which have implications for rheological and numerical eruption models that investigate magma ascent and fragmentation of peralkaline rhyolitic magmas
The aim of this contribution is to understand the eruptive dynamics of pantelleritic magmas by studying the phase abundances and chemical compositions of the main mineralogical phases (i.e., alkali feldspar (Afs) and clinopyroxene (Cpx)) present in natural products of the Pantelleria volcanic system
Summary
We provide a comprehensive evaluation of the pre-eruptive conditions of volcanic activities at Pantelleria, which have implications for rheological and numerical eruption models that investigate magma ascent and fragmentation of peralkaline rhyolitic magmas. The aim of this contribution is to understand the eruptive dynamics of pantelleritic magmas by studying the phase abundances and chemical compositions of the main mineralogical phases (i.e., alkali feldspar (Afs) and clinopyroxene (Cpx)) present in natural products of the Pantelleria volcanic system. We investigate how different parameters, such as pre-eruptive temperature and crystal fraction of the main mineralogical phases and (H2O)melt (= concentration of H2O dissolved in melt) influence the eruptive style of pantelleritic magma, contributing to reach magma fragmentation and promoting explosive eruptive behaviour
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