MAGMATIC ACCOMMODATION OF PLATE MOTION ALONG THE MID-ATLANTIC RIDGE IN ICELAND

The Mid-Atlantic Ridge, the slow spreading (~20 mm/yr) mid-ocean ridge boundary between the North America and Eurasia plates, is exposed in Iceland as the result of ridge-hotspot interaction. Plate spreading in Iceland is accommodated along overlapping to en echelon neovolcanic zones comprised of central volcanoes and their fissure swarms. This unique locality allows for investigation of magma-tectonic interactions at spatial scales from the individual central volcano, to the fissure swarm, and to the entire plate boundary, and temporal scales from sub-annual to millions of years. In south Iceland plate motion is thought to be partitioned between the 7-9 Ma Western Volcanic Zone (WVZ) and 2-3 Ma Eastern Volcanic Zone (EVZ). Plate motion across both systems has been accommodated by repeated rifting events and fissure eruptions; however, the number of eruptions, rifting events and volume of erupted material since the end of the last glaciation are different, resulting in dramatically different tectonic morphology. In this study we investigate the current pattern of strain accumulation between the WVZ and EVZ, and how this strain is accommodated in the upper plate at the plate boundary to individual central volcano scale. We model the horizontal velocities estimated from GPS measurements from 2000-2010 to investigate the pattern of strain accumulation in south Iceland. We then give examples of how magmatic accommodation takes place in two active volcanic systems in the EVZ; the Hekla and Torfajokull central volcanoes, and evidence for magmatic accommodation within the Holocene Thrihnukigar volcanic system, Reykjanes Peninsula.