DISCRIMINATING VENT SITES ALONG A FORMERLY ICE-CONFINED BASALTIC ERUPTIVE COMPLEX AT SVEIFLUHALS, SW ICELAND

The products of volcano-ice interactions are important because they can be used to constrain the presence and thickness of former ice, for which there may be little or no other evidence. Although, we have a reasonably good understanding of ice-confined, single-vent monogenetic basaltic centers, there are very few published studies of similar multi-vent, multi-fissure complexes despite the fact that there are more than 1000 such complexes in Iceland. These complexes represent an important but largely untapped database on the former terrestrial ice conditions in the North Atlantic since 2Ma. Detailed documentation of the products and processes of such ridge-complexes is necessary in order to infer the evidence former ice conditions. A vital part of such studies is the discrimination of individual vents (both cone and fissure) along the fissure segments. The purpose of this project was to use chemostratigraphy, petrography and structural mapping to discriminate vent sites along the 21km long formerly ice-confined fissure complex of Sveifluháls in SW Iceland. Sveifluháls comprises up to nine sub-parallel fissure segments. Topographic highs in most cases appear to correspond to vents, with an average spacing of 0.7km along the same fissure. However, slumping and collapse and wet volcaniclastic deposits can make identifying vents along the same fissure difficult. To date, I have analyzed 10 samples of pillow basalts from the fissure complex, and undertaken detailed structural mapping. The data have been compiled with GIS tools to map the locations of vent sites. Structural mapping has demonstrated that fissure-fed vents with oversteepened blocks of flank tephra lie between cones that also rarely preserve tephra at original dips in proximal positions. This poster presents the vent locations, orientations of proximal tephra and discusses implications for using such complexes to infer the former ice conditions.