HR: 13:40h
AN: G13C-01    [Abstracts]
TI: Strain Partitioning and Accumulation across Overlapping Spreading Centers: Geodetic GPS Measurements in South Iceland
AU: * La Femina, P C
EM: plafemina@rsmas.miami.edu
AF: University of Miami, RSMAS-MGG 4600 Rickenbacker Cswy, Miami, FL 33149 United States
AU: Dixon, T H
EM: tdixon@rsmas.miami.edu
AF: University of Miami, RSMAS-MGG 4600 Rickenbacker Cswy, Miami, FL 33149 United States
AU: Malservisi, R
EM: rmalservisi@rsmas.miami.edu
AF: University of Miami, RSMAS-MGG 4600 Rickenbacker Cswy, Miami, FL 33149 United States
AU: \'{A}rnad\'{o}ttir, T
EM: thora1@hi.is
AF: Nordic Volcanological Institute, University of Iceland Sturlagata 7, Reykjavik, 101 Iceland
AU: Sigmundsson, F
EM: fs@hi.is
AF: Nordic Volcanological Institute, University of Iceland Sturlagata 7, Reykjavik, 101 Iceland
AU: Sturkell, E
EM: erik@vedur.is
AF: The Icelandic Meteorological Office, Bustadavegur 9, Reykjavik, 150 Iceland
AB: Overlapping spreading centers (OSCs) and propagating ridges are important classes of mid-ocean ridges. Kinematic models of OSCs predict along strike variability in spreading rate associated with the propagation of one center and deactivation of the other. Iceland offers a unique opportunity to investigate strain accumulation and partitioning across slow, overlapping spreading centers, and the influence of a ridge centered hotspot on ridge kinematics and morphology. We present results of detailed GPS observations across the Eastern and Western Volcanic Zones, south Iceland, spanning a seven to nine year inter-rifting period, and compare our observations with two-dimensional elastic half-space models that simulate the long-term spreading process. We then compare the elastic half-space models with simple viscoelastic coupling models. We model three velocity profiles across the EVZ-WVZ system, solving for the spreading rate, locking depth and horizontal location of each spreading center. Our spreading rate estimates indicate along strike variations as expected in an OSC system and total spreading rates consistent with geodetic and geologic plate motion models. Spreading rates in the WVZ increase from northeast (3 $\pm$1 mm/yr) to southwest (7 $\pm$1 mm/yr). Spreading rates in the southwest propagating EVZ decrease from northeast (17 $\pm$1 mm/yr) to southwest (12 $\pm$1 mm/yr). These results are consistent with a model whereby the WVZ is deactivating in the direction of EVZ propagation. The morphology of the two spreading centers reflects the spreading rate differences and their location relative to the Iceland hotspot. The predicted locations of the spreading axis for each zone are consistent with mapped Holocene fissure swarms. The neovolcanic zone of the slower WVZ consists of a narrow (10-20 km wide) axial graben and has had few Holocene eruptions. The faster EVZ consists of two parallel neovolcanic zones separated by a 20 km gap of inactivity, little normal faulting, higher topography and five historical fissure eruptions, reflecting its proximity to the hotspot. The maximum velocity gradient in the EVZ is located on the Veidivotn fissure swarm, which had a small volume eruption in 1864. The last major fissure eruption in the EVZ was the 1783 Lakagigar, located 20 km to the east. This pattern of current and past strain accumulation and release suggests intra-ridge jumping of activity and crustal accretion across a 60 km wide area.
DE: 8109 Continental tectonics--extensional (0905)
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 1206 Crustal movements--interplate (8155)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting