Fracture systems of the Northern Volcanic Rift Zone, Iceland: an onshore part of the Mid-Atlantic plate boundary
Á. R. Hjartardóttir, P. Einarsson, S. Magnúsdóttir, Þ. Björnsdóttir, B. Brandsdóttir, 2016. "Fracture systems of the Northern Volcanic Rift Zone, Iceland: an onshore part of the Mid-Atlantic plate boundary", Magmatic Rifting and Active Volcanism, T. J. Wright, A. Ayele, D. J. Ferguson, T. Kidane, C. Vye-Brown
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Few divergent plate boundaries are subaerial. Active rifts in Iceland provide valuable surface information on divergent spreading processes, rifting and faulting. The 200 km long and 50 km wide Northern Volcanic Rift Zone (NVZ) is composed of 7 volcanic systems, each consisting of a central volcano with a transecting fissure swarm. Fractures and postglacial eruptive fissures in the NVZ were analysed using aerial photographs and satellite images to study their characteristics and behaviour. While non-eruptive fractures characterize the distal (c. 40–100 km) parts of the fissure swarms, eruptive fissures are most common at distances less than c. 20–30 km from the central volcano. Fractures within the fissure swarms are generally subparallel, with a N–NNE strike. Irregular orientations are associated with calderas within the central volcanoes Askja and Krafla, and at the junction of the NVZ and the Tjörnes Fracture Zone, where high fracture densities also occur. WNW-orientated fractures at the southern end of the Krafla Fissure Swarm, and the northern end of the Kverkfjöll Fissure Swarm, exhibit surface expressions of a transform zone. The fissure swarms within the rift zone are mostly seismically and geodetically inactive, becoming highly active during rifting events that occur at time intervals of tens to a few hundred years.
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A major rifting episode began in the Afar region of northern Ethiopia in September 2005. Over a ten-day period, c. 2.5 km3 of magma were intruded along a 60 km-long dyke separating the Arabian and Nubian plates. Over the next five years, a further 13 dyke intrusions caused continued extension, eruptions and seismicity. This activity led to a renewed international focus on the role of magmatism in rifting, with major international collaborative projects working in Afar and Ethiopia to study the ongoing activity and to place it in a broader context. This book brings together articles that explore the role of magmatism in rifting, from the initiation of continental break-up through to full seafloor spreading. We also explore the hazards related to rifting and the associated volcanism. This work has implications for our understanding of how continents break-up and the associated distribution of resources in rift basins and continental margins.