Magmatic fissures and their systems in Iceland: A tectonomagmatic model

Abstract

Volcanic systems in Iceland comprise a central volcano linked to magmatic fissures, whose subsurface architecture remains enigmatic. The surface dimensions and trends of active fissures show their spatial relation with fault systems. Structure of the Fremri-Namur and Hengill volcanic systems was analyzed. The linear vent arrays marking recent fissures are tightly bound by vertical segmented faults, while normal faults accommodating extension are common on the flanks of the fissure swarm. Evidence of normal frictional slip on the fissure-bounded faults suggests that failure occurred in response to subsidence with subsequent dilation. This is supported by inward tilting of strata adjacent to faults compatible with a downsag phase. We propose that magmatic fissures have vertical feeders with lateral offshoots extending along the rift zone. Their inflation/deflation during an eruptive cycle causes subsidence. Such magmatically generated faults can be subsequently modified by tectonic extension. Copyright 2007 by the American Geophysical Union.