The Tectonic Evolution of the Tjornes Fracture Zone, Offshore Northern Iceland-ridge Jumps and Rift Propagation

Abstract

The Tjornes Fracture Zone (TFZ) links the rift zones in northern Iceland with the Kolbeinsey Ridge north of Iceland. The TFZ was initiated during the Miocene (7-9 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 which includes both right-lateral, strike-slip faults and three N-S trending extensional grabens (from west to east the Eyjafj\"{o}rdur, Skj\'{a}lfandi and \"{O}xarfj"{o}rdur basins) which are filled with a 0.5-4 km thick sedimentary sequence. There are two WNW-striking bands of seismicity in the TFZ, a northern band known as the Gr\'{\i}msey lineament and a southern band associated with the WNW-trending H\'{u}sav\'{\i}k-Flatey fault (HFF). Over the past three field seasons we have mapped a large portion of TFZ utilizing multibeam echo sounders (both EM300 and a Reson 8101 shallow water system), collected high-resolution multichannel seismics and Chirp sonar, and obtained bottom photographs. The HFF can be traced offshore from H\'{u}sav\'{\i}k village across Skj\'{a}lfandi Bay as two WNW-trending, south-facing fault scarps and northwest of Flatey Island into the southern Eyjafj\"{o}rdur basin as a WNW-trending, north-facing scarp. In Skj\'{a}lfandi Bay several smaller WNW-trending faults are located sub-parallel of the main HFF. Offshore Flateyjarskagi, west of Flatey Island, a zone of intense deformation has been mapped, including clear evidence of right-lateral strike-slip faulting. The sediment-filled basins north of the HFF are bounded by numerous NS-trending faults, some of which extend to the seafloor, suggesting they are actively extending. The very subtle expression of the HFF in eastern Skj\'{a}lfandi Bay, and the more prominent but simple expression of recent (post-glacial) faulting along the western HFF near Flatey Island are consistent with historical and recent seismicity which is concentrated on the H\'{u}sav\'{\i}k fault system on the Tj\"{o}rnes peninsula, along the western HFF and in the southern Eyjafj\"{o}rdur, basin. A GPS geodetic station on the Tj\"{o}rnes peninsula, northeast of the HFF, maintained by the Iceland Meteorological Service shows that over the past 2 years the southern TFZ has been moving with the North American plate suggesting that little strain accommodation is currently occurring along the main HFF. These observations are consistent with a model for the tectonic evolution of the TFZ in which the continued northward propagation of the northern rift zone in Iceland has progressively shifted relative motion between the North American and Eurasian plates northward to the series of NNE-SSW trending rift zones along the Gr\'{\i}msey seismic lineation.

Department

Center for Coastal and Ocean Mapping

Publication Date

12-2003

Volume

84, Issue 46

Journal Title

Fall Meeting, American Geophysical Union (AGU)

Conference Date

Dec 8 - Dec 12, 2003

Publisher Place

San Francisco, CA, USA

Publisher

American Geophysical Union Publications

Document Type

Conference Proceeding

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