Physical volcanology of the Kvsoir caldera, South-east Iceland

Abstract

The Kvosir caldera is a small, silicic volcanic structure located in the mountains North-East of Höfn, South-East Iceland. It is part of a cluster of silicic centres surrounding the Slaufrudalur pluton, Iceland's largest exposed granitic pluton. This work presents the first detailed description of the caldera based on field mapping, photogrammetry and whole-rock geochemical analysis of 18 samples. The caldera infill is composed of pyroclastic material including multiple ignimbrite units, breccias and lava flows recording repeated explosive and eAusive eruptive phases interspersed with periods of volcanic rest. Composition is overwhelmingly rhyolitic. Pervasive hydrothermal alteration, evidenced by chlorite and epidote mineralisation as well as silicification, is widespread throughout the caldera sequence. Major and trace element geochemistry indicates that Kvosir volcanic products share a broadly similar compositional signature with the Slaufrudalur pluton, supporting a genetic link between the two structures and suggesting they were part of the same magmatic system. The tectonic aAinity of the Kvosir samples most closely resembles that of the Northern Rift Zone though the hydrothermal overprinting of mobile elements introduces significant uncertainty.