Petrologic constraints on the activity of the youngest explosive events at Yali volcano (South Aegean Active Volcanic Arc, Greece): plumbing system architecture and implication for hazard assessment.

Abstract

The Yali volcanic centre is a relatively young volcano that was active within the last 40,000 year and is part of the Nisyros-Kos volcanic field, representing the most recent evidence of magmatic activity in the western part of the South Aegean Active Volcanic Arc, together with the post-caldera lava dome activity occurred at the nearby Nisyros volcano.   The Yali volcanic activity (bot explosive and effusive) is still poorly studied, and the plumbing system architecture and magma ascent pathways are barely defined, although it represents an important element to be considered for the evaluation of the volcanic hazard and the potential risk in the area, associated to the accumulation of evolving magma body in the crust.   The aim of our study is thus to detail the nature of juvenile materials and the evaluation of the magmatic processes occurring in the plumbing system. This would provide important information to define the relationships between the different eruptive events that occurred during the Yali volcano evolution.   The present-day edifice is constituted by the remnant of the original volcano after intense tectonic and erosion processes. It is composed by two distinct parts with difficult stratigraphic correlation due to the limited exposure and continuity of the deposits. The SW part is built up by a thick succession of pyroclastic materials, generated by the eruption of a submarine pyroclastic deposit (Lower Pumice -YLP) followed by a subaerial activity leading to the emplacement of a pumice-rich pyroclastic fallout (Upper Pumice-YUP) that is topped by two layers of reworked pumice-rich deposits (YRL), separated by a thin paleosoil. The NE part is formed by the eruption of large perlitic lava flows and obsidian lava domes associated to an explosive episode generating the Kamara tuff cone.    The main volume of the erupted products (pumices and lavas) is composed by evolved juveniles of rhyolitic composition. All the pyroclastic deposits, including the Kamara tuff cone host a variable amount of mafic, crystal-rich clasts (SiO2 from 52.5 to 67.5 wt.%) suggesting the occurrence of mingling processes between different evolved magmas in the feeding reservoir/s, thus implying a mafic, deep, refill of the plumbing system. Our data show that the YLP and YUP pumice have similar homogeneous composition, with the latter having a slightly less evolved character. They also display a quite distinct major, trace elements and Sr-Nd isotopes behavior compared to pumices of the YRL. The lavas are even more evolved than pumices. Moreover, the mafic components reveal a heterogeneous composition and isotopic signatures, suggesting the presence of a complex plumbing system feeding the different explosive and effusive eruptions.