HR: 14:00h
AN: G23C-03    [Abstracts]
TI: Modeling the Secular Velocity Field Across a Divergent Plate Boundary: Geodetic GPS and Geology, South Iceland
AU: * La Femina, P C
EM: plafemina@rsmas.miami.edu
AF: University of Miami - RSMAS, 4600 Rickenbacker Cswy, Miami, FL 33149 United States
AU: Dixon, T H
EM: tdixon@rsmas.miami.edu
AF: University of Miami - RSMAS, 4600 Rickenbacker Cswy, Miami, FL 33149 United States
AU: Malservisi, R
EM: rmalservisi@rsmas.miami.edu
AF: University of Miami - RSMAS, 4600 Rickenbacker Cswy, Miami, FL 33149 United States
AU: Arnadottir, T
EM: thora1@hi.is
AF: Nordic Volcanological Center, Institute of Earth Sciences University of Iceland, Reykjavik, Iceland
AU: Sigmundsson, F
EM: fs@hi.is
AF: Nordic Volcanological Center, Institute of Earth Sciences University of Iceland, Reykjavik, Iceland
AU: Sturkell, E
EM: sturkell@hi.is
AF: Nordic Volcanological Center, Institute of Earth Sciences University of Iceland, Reykjavik, Iceland
AU: Einarsson, P
EM: palli@raunvis.hi.is
AF: Science Institute, University of Iceland, Reykjavik, Iceland
AB: Detailed GPS observations in south Iceland combined with two-dimensional elastic half-space models and numerical viscoelastic coupling models indicate that spreading rates in the Western Volcanic Zone (WVZ) increase from 2.8±0.9 mm/yr in the northeast to 7.0±0.4 mm/yr in the southwest. Conversely, spreading rates in the Eastern Volcanic Zone (EVZ) decrease from 19.0±2.0 mm/yr in the northeast to 11.0±0.8 mm/yr in the southwest, the direction of ridge propagation. Summed extension rates across the two rift zones are approximately constant and equivalent to the total plate rate (~18-20 mm/yr), consistent with a simple propagating ridge model whereby the WVZ is deactivating in the direction of EVZ propagation. We interpret the locations of maximum surface velocity gradient to indicate the sub-surface locus of magma accumulation and presumably the locations of future major rifting events; these are generally consistent with Holocene patterns. The neovolcanic zone of the slower WVZ, with fewer Holocene eruptions, consists of a narrow (10-20 km wide) axial graben. The faster EVZ has little normal faulting, higher topography and five historical fissure eruptions, reflecting its proximity to the hotspot and its nature as an active propagating ridge. The last major rifting event in the EVZ was the 1783-84 Lakagˇgar fissure eruption. However, the maximum surface velocity gradient is located 20 km to the east, on the B rdabunga-Veidiv”tn fissure swarm, which had a small volume eruption in 1862-64. The pattern of current strain accumulation suggests that the historical pattern of intra-ridge jumping of magmatic activity in the EVZ and crustal accretion across a 60 km wide zone is continuing.
DE: 1206 Crustal movements--interplate (8155)
DE: 1243 Space geodetic surveys
DE: 3035 Midocean ridge processes
DE: 8150 Plate boundary--general (3040)
DE: 8158 Plate motions--present and recent (3040)
SC: Geodesy [G]
MN: 2005 Joint Assembly