Peralkaline silicic extrusive rocks: magma genesis, evolution, plumbing systems and eruption

Abstract

Peralkaline silicic extrusive rocks are an important component of the volcanological record. Here we review several aspects of their formation and evolution, including the tectonic settings in which they occur, their main petrological and geochemical features, the magmatic lineages along which they evolve, and the parameters ($T$, $P$, fO2, melt water contents) that control the lineages. Particular attention is paid to the composition of the extraordinary melts formed at the lowest temperatures. Various lines of evidence are presented to explain the silica gaps in some lineages. The partial melting of continental crust and the role of crustal contamination are considered to be of relatively minor importance in their genesis. High $P$–$T$ experiments aimed at quantifying the lineages are assessed. Geophysical and petrological evidence for the depth and nature of the plumbing systems are presented. Differentiation mechanisms within reservoirs and the ubiquity of the formation of compositional zonation are discussed, as are the timescales involved. Volcanic hazards and the environmental impact of eruptions are described and a brief assessment of the ore potential of the extrusives is given.

Keywords

• Ore potential
• Peralkaline silicic rocks
• Tectonic settings
• Plumbing systems
• Hazards
• Ore potential