Eruption transition recorded in groundmass nanolites

Abstract

We present detailed petrography of
nanometer scale crystals (nanolites) in the quenched products of the
sub-plinian and vulcanian eruptions from the Shinmoedake, Kirishma volcanic
group in 2011. The nanolites were distinguished from microlites by a steeper
slope of the CSD plots. The vulcanian eruption products (pumice and juvenile
lithic fragments) contain both plagioclase and pyroxene nanolites, while sub-plinian
pumices contain only pyroxene nanolites. The nanolite crystallization
condition may reflect magma dehydration and residence time in a very shallow
conduit, which are not recorded by microlites.