HR: 0800h
AN: T41A-1172    [Abstracts]
TI: Tectonic Details of the Tjornes Fracture Zone, an Onshore-Offshore Ridge-Transform in N-Iceland.
AU: Brandsdottir, B
EM: bryndis@raunvis.hi.is
AF: Institute of Earth Science, University of Iceland, Sturlugata 7, Reykjavik, 101 Iceland
AU: Richter, B
EM: br@isor.is
AF: Iceland GeoSuvey, Grensasvegur 9, 108, Reykjavik Iceland
AU: Riedel, C
EM: riedel@dkrz.de
AF: Institut fur Geophysik, University of Hamburg, Edmund-Siemers-Allee 1, Hamburg, D-20146 Germany
AU: Dahm, T
AF: Institut fur Geophysik, University of Hamburg, Edmund-Siemers-Allee 1, Hamburg, D-20146 Germany
AU: Helgadottir, G
EM: gudrun@hafro.is
AF: Marine Research Institute, Skulagata 4, Reykjavik, 121 Iceland
AU: Kjartansson, E
EM: eik@klaki.net
AF: Marine Research Institute, Skulagata 4, Reykjavik, 121 Iceland
AU: * Detrick, R
EM: rdetrick@whoi.edu
AF: Woods Hole Oceanographic Institution, Co-op Building, MS #16, Woods Hole, MA 02543 United States
AU: Magnusson, A
EM: agust@lhg.is
AF: The Icelandic Coast Guard Hydrographic Survey, Seljavegi 32, Reykjavik, 101 Iceland
AU: Asgrimsson, A L
EM: asgrimur@lhg.is
AF: The Icelandic Coast Guard Hydrographic Survey, Seljavegi 32, Reykjavik, 101 Iceland
AU: Palsson, B H
EM: bjornh@lhg.is
AF: The Icelandic Coast Guard Hydrographic Survey, Seljavegi 32, Reykjavik, 101 Iceland
AU: Karson, J
EM: jkarson@duke.edu
AF: Division of Earth and Ocean Sciences, Duke University, Durham, Durham, NC 27708 Canada
AU: S‘mundsson, K
EM: ks@isor.is
AF: Iceland GeoSuvey, Grensasvegur 9, 108, Reykjavik Iceland
AU: Mayer, L A
EM: larry.mayer@unh.edu
AF: CCOM, University of New Hampshire, New Hampshire, Durham, NH 03824 Canada
AU: Calder, B
AF: CCOM, University of New Hampshire, New Hampshire, Durham, NH 03824 Canada
AU: Dricoll, N
EM: ndriscoll@ucsd.edu
AF: Scripps Institution of Oceanography, Univ. of California, San Diego, San Diego, CA 92037 United States
AB: The Tjornes Fracture Zone (TFZ) links the northern rift zone (NVZ) in Iceland with the Kolbeinsey Ridge north of Iceland. The TFZ was initiated during the Miocene (about 7 Ma), following an eastward jump of the spreading axis in northern Iceland. A roughly 150 km long (EW) and 50 km wide (NS) deformation zone has since developed incorporating both right-lateral movement along WNW-trending strike-slip faults and oblique extension (105ø) within three major N-S trending grabens (from west to east the Eyjafjardar ll, Skj lfandi and Oxarfjordur basins). Recently collected EM300 and RESON8101 multibeam bathymetric data, and CHIRP subbottom data combined with onshore mapping have enhanced our understanding of the rift-transform interactions within the TFZ. The transform motion is incorporated within two seismically active WNW trending zones, the Gr¡msey Seismic Zone (GSZ) and the H£sav¡k-Flatey fault (HFF), spaced ~40 km apart along the margins of the extensional basins. Being the propagating continuation of the NVZ offshore the GSZ has both the characteristics of an oblique rift zone and a transform whereas the HFF is more akin to oceanic transform faults. Four left-stepping, en-echelon, NS-striking rift segments (volcanic systems) exist along the GSZ. Large GSZ earthquakes, however, seem to be mainly associated with lateral strike-slip faulting along WNW-striking fault planes. Fissure swarms transecting the offshore volcanic systems also indicate right-lateral strike-slip motion parallel to the spreading direction. The HFF has an overall strike of N65øW and can be traced continuously onshore and offshore along its 75-80 km length, between the NVZ, across Skj lfandi and into Eyjafjardar ll. Four pull-apart basins occur along the fault, the largest at the intersection with Eyjafjardar ll, the southward but magma-starved, continuation of the KR. Tertiary dikes, parallel to the HFF indicate it has been a leaky transtensional feature. The southwestern margin of the fault is characterized by NE-striking lavas which dip steeply (30-50ø) towards Eyjafjardar ll. The lavas are dissected by en echelon arrays of conjugate strike-slip faults intersecting the HFF fault at angles of N20ø-30øW and N20øE. Some can be traced onto land where they exhibit complicated flower patterns. Destructive earthquakes occurred on the HFF in 1755, 1867 and 1872. The 1867 events were most likely associated with rift-transform interaction within the M n reyjar volcanic system, similar to the 1975-1989 Krafla rifting episode, when a lateral intrusion event triggered a M6.5 strike-slip earthquake at the junction of the Krafla fissure swarm and the GSZ. Although transform motion within the TFZ is currently taken up by two parallel fault systems the Tjornes microplate will merge with the North American plate as continued northward propagation of the divergent plate boundary gradually deactivates the extensional basins and HFF.
DE: 8010 Fractures and faults
DE: 8158 Plate motions--present and recent (3040)
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting