Tectonic Details of the Tjornes Fracture Zone, an Onshore-Offshore Ridge-transform in N-Iceland

• Main Authors: Brandsdottir, B, Richter, B, Riedel, C., Dahm, T, Helgadottir, G, Kjartansson, E, Detrick, R S, Magnusson, A, Asgrimmsson, A L, Palsson, B H, Karson, J, S'mundsson, K, Mayer, Larry A., Calder, Brian R., Driscoll, N.
• Format: Text
• Language: unknown
• Published: University of New Hampshire Scholars' Repository 2004
• Subjects: Oceanography and Atmospheric Sciences and Meteorology; Tectonics and Structure; Kolbeinsey; Kolbeinsey Ridge; Sav’; Iceland; Flatey
• Online Access: https://scholars.unh.edu/ccom/569; http://abstractsearch.agu.org/meetings/2004/FM/T41A-1172.html

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 (105�) 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 N65�W 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 ...