Magnetic fabrics of Neogene pyroclastic density currents from eastern Iceland

Resumen

Anisotropy of the Magnetic Susceptibility (AMS, a method to measure rock fabrics) studies have proven useful to characterize volcanic processes. These AMS applications contribute to the advancement of our knowledge on many aspects of volcanic hazards. This study evaluates the magnetic fabric signatures of Neogene pyroclastic density currents from eastern Iceland (Bjólfur and Skessa welded tuffs) related to eruptive transport and depositional processes. AMS ellipsoids are mostly oblate, with anisotropy and bulk susceptibility values dependent of the different lithology. After (slight) tilt correction (dipping westerly only 2º-7º), ellipsoid axes directions, in 5 of a total of 6 sites, show sub-horizontal foliation planes, with flow indicators (lineations and imbrication of the minimum axis) that corroborate with the available structural volcanologic observations. In one site (“SK2” from Skessa welded tuff, where an interchange of maximum and minimum axes has been observed), an inverse fabric interpretation is favoured, due to the presence of single-domain ferromagnetic grains, also indicated by hysteresis data.