3-D Reconstruction of Pillow Ridge Structure and Stratigraphy, Vatnsskarð Quarry, Reykjanes Peninsula, Iceland

Abstract:

Vatnsskarð quarry is one of two quarries along the northern half of the Krisuvik fissure segment on the Reykjanes Peninsula in southwestern Iceland. The northern half of the segment comprises predominantly glaciovolcanic deposits including pillow lava units, with lesser subaqueous tuff-breccia, lapilli tuff, and hyaloclastite (sensu stricto). High-resolution measurements of individual pillow lavas, intrusions, and lateral stratigraphic variations provide new insight into the emplacement and eruptive processes for glaciovolcanic, pillow-dominated ridges. Field analysis included >50 pillow width/height field measurements, and DGPS tracks from traverses along outcrops, and laser-DGPS points on quarry walls. Our 3-D reconstructions are made using the detailed measurements tied to Gigapan© images, and photo reconstructions using Photoscan© software. The high-resolution Gigapan images facilitate detailed tracings of individual pillows, which are then used for en masse measurements of >500 individual pillow dimensions. The Pillow Size Distributions for individual stratigraphic units are then calculated using ImageJ. Previous work at Undirhliður quarry immediately to the north (Was et al., 2014, EOS, V41D-2839) showed that, using >5000 measurements, different stratigraphic units had distinct characteristic pillow sizes indicating either changes in lava fluxes or in spatial positions with respect to lava supply system. The opportunity to map changes in pillow sizes as well as the spatial relationship between intrusions related to the within-ridge magma supply and pillows provides detailed constraints on the physical mechanisms by which pillow ridges grow exogenously and endogenously.