Petrology and geochemistry of lavas and pyroclastics

Abstract

This chapter offers a comprehensive overview of the main petrologic of geochemical characteristics of the Nisyros volcanic products, integrating published data and some new observations. The mineralogy and petrography of the magmatic rocks are described, including a brief presentation of enclaves, xenoliths and xenocrysts. The disequilibrium textures of amphibole are also presented, in light of the thermodynamic changes recorded by their breakdown structures and reaction rims. The chapter contains a holistic overview of the whole-rock major and trace element geochemistry of the rocks, obtained by compiling the available published data. Calc-alkaline and arc tholeiite trends are inferred, and the silica-gap is observable just before amphibole fractionation starts. A brief description of the main petrographic and geochemical features of each lithostratigraphic unit, according to the map, is offered. The chapter concludes with a discussion on the petrogenetic evolution of the island, including crustal assimilation, fractional crystallisation, magma mixing and mingling, crystal-retention-liquid-segregation, the probable depth of the magma chamber and models for generating the highly silicic magmas characteristic for the younger eruptive events, from the parental basaltic andesite melts that were erupted in the earlier stages.