The effect of changing regional tectonics on an arc volcano: Methana, Greece

The peninsula of Methana has the longest recorded volcanic history of any volcanic centre in the South Aegean Arc. Regional fault patterns in the arc changed during the Pliocene–Quaternary, with E–W-striking listric faulting increasingly important through the Quaternary, as recorded in well-dated sedimentary basins. This study investigates how the geochemistry and eruptive style of volcanic products is influenced by regional tectonics. The volcanic stratigraphy of Methana was refined using radiometric dating, lithogeochemistry and field observations that included recording deformational structures and enclave abundance. Small N–S-striking Pliocene domes and a central volcano of uncertain type (phase A) were eroded to produce a widespread volcaniclastic apron (phase B). In the early Quaternary, an explosive central volcano with flank eruptions of andesite developed (phase C). Dacite domes and small andesitic stratovolcanoes formed throughout the mid and late Quaternary (phases D–H). ic andesite and andesite of phase C are the least evolved rocks, characterised by high TiO2. Rocks that have experienced important assimilation and fractional crystallisation in the crust have a high abundance of enclaves, Th, U and alkalies (Na, K). Ni and Cr are abundant in phase A andesites, due to crystallisation and entrainment of olivine and pyroxene, whereas phase H andesites have the highest relative abundance of Ba, Rb and Sr from crystallisation and entrainment of hornblende and biotite. ne domes of phase A were emplaced on N–S-striking listric faults during regional E–W extension. Onset of NE–SW faulting, arguably crustal scale and strike slip in character, led to the eruption of the least evolved rocks of phase C. Thereafter, E–W-striking faults controlled the location of volcanism. Volcanism in phases F and G was particularly voluminous and was synchronous with the onset of steep normal faulting in the Gulf of Corinth, 150 km west of Methana. These steep faults cross-cut older, lower angle, listric faults. It is times of changes in regional fault patterns, as in phases C, F and G, that have the greatest influence on the eruptive style and abundance of volcanic products.