PALEOMAGNETISME

A preliminary palaeomagnetic study has been carried out in Vesterålen, Senja and Kvaløya (Troms) in order to furnish temporal constraints on near offshore fault-activity in the Lofoten area. At Senja, two phases of faulting and brecciation have been identified. A young phase, attendant of the formation of fault-gouges, is Rcent/Tertiary in origin, whereas an older phase has a Permian age. A Permian age (c. 260-270 Ma) is also indicated from heamatite cemented fault-breccias from Kvaløya, and the Permian fault-activity probably witnesses an early rift-phase on the continental margin. Permian fault-rocks (c. 260-270 Ma) are also widespread within the Møre-Trøndelag Fault Zone (Central Norway) and Western Norway.

A palaeomagnetic investigation of the Early-Ordovician (middle to late Arenig) sheeted dyke complexes of Meldal has revealed a complex multicomponent magneti- zation history. Three components of remanent magnetization were identified on their differing dysbilities, 'L' (low stability), 'I' (intermediate) and 'H' (high stability). The 'L' component is condidered to be a recent overprint. The 'I' component corresponds to an in-situ palaeomagnetic pole at 91.9°E, 58.6°N, Dy=12.1,DX=14.3. By comparison with a reference apparent polar wander (APW) path for Baltica, 'I' is considered to be an overprint of Jurassic age. The 'H' component (with the highest magnetic stability) was identified in two block samples from Resfjell. In in-situ form it corresponds to a palaeo-pole at 99°E, 16.4°N and in tilt-corrected form (palaeo-horizontal simply rotated into present horizontal) to a palaeo-pole at 281°E, 13.4°N. Both in-situ and tilt-corrected versions of the data fall far away from reference APW paths for Baltica and Laurentia. We suggest that a series of (Silurian) tectonic rotations, more complicated than the rotation accounted for in our simple tilt- correction procedure, are responsible for this deviation. If the remanence component does indeed pre-date complicated Silurian tectonic rotations, as its deviation from the APW paths suggests, one must consider the possibility of the remanence dating-back to when the sykes were still part of the Iapetus Ocean floor. The palaeolatitude for the dykes implied by the remanence is 12.6°S (tilt-corrected) assuming that 'H' is of reversed polarity. This choice of polarity minimises the net vertical-axis rotation (in this case anticlockwise through 100 degrees or so) necessary to restore the pole to reference data sets. The palaeolatitude 12.6°S would place them near the Laurentian margin of the Iapetus Ocean (if the remanence is presumed t

This report compiles results from six separate studies linked by the common fact that they address absolute dating of initiation and reactivation of brittle faults, dike emplacement and regional unroofing around the Rift region, clearly demonstrate mutual and specific tectonic associations for the Late Paleozoic and Mesozoic that were only previously inferred from available data. Precise age data show very connected and correlatable histories for these marginal proto-North Atlantic zones for early Carboni- ferous, Permian, early Triassic and middle Jurassic times. These regions have been cited in the literature for their import in constraining offshore tectonic and basin development, but the new data provide, for the first time, very quantitative results to pinpoint and interpret these events.

GMAP is a state of the art computer which performs all processing and plotting tasks usually associated with the storage and presentation of palaeomagnetic pole positions, and generation of palaeographic reconstructions. One of GMAP's special features, which places is ahead of other software of its type, is a built-in, statistically robust, method for fitting smooth curves to weighted palaeomagnetic pole position. GMAP is menu-driven and very easy to use; the user is never far removed from the basic data from which palaeogeographic reconstructions are derived, and therefore has a sense of total control over the program's performance. GMAP can generate reconstructions based on individual palaeomagnetic poles, averages palaeomagnetic poles and digitally derived smooth (APW) curves. The user is also free to simply move continents around on the screen, according to less tangible constraints. Palaeogeographic reconstructions can be saved to disk files, and later viewed in chronological order as 'animations'. GMAP is supplied with a full range of continental outlines. These continents may be edited, split or combined to suit the user's personal requirements. It is also possible to import new continents with simple ASCII files or to import continents from the Palaeomap project. An ATLAS of reconstructions (Torsvik & Eide 1998) id included in the system. GMAP can also calculate plate-speeds (minimum), angular rotations and rates of APW based on APW parths. It also contains routines to estimate magnetic polarity bias and the most recent compilations of magnetic polarity data are included with the system. GMAP is in use at leading institutions world-wide, and has been the 'work horse' of EGT and EUROPROBE projects. GMAP also interfaces with the Global Palaeomagnetic Data Base.

Prof. Dr. Trond Helge Torsvik was born on October 12, 1957. He attended the Norwegian Naval Academy before taking degrees from the University of Bergen in 1982 and 1985. In 1991, after a post-doctoral position at Oxford, Trond joined the Geological Survey of Norway in Trondheim, where he continues working today. Since then, he has also held appointments at the University of Bergen, the Norwegian University of Science and Technology, the University of Witwatersrand, and the University of Oslo. Trond is an Elected Fellow of the Royal Society of Norway, the Norwegian Academy of Science, the Academia Europea, and the American Geophysical Union.
Trond has made significant contributions in (among other sciences) paleomagnetism, paleogeography, plate tectonics, and mantle dynamics. His field areas have spanned the world's continents, and probed the Core Mantle Boundary. His list of collaborators is impressively international. Although his published contributions are legion, Trond is also well known for his paleomagnetic and plate reconstruction software, which he has consistently made available to the scientific community.
This seminar, Geodynamics, Geomagnetism and Paleogeography: A 50 Year Celebration, has been organized to honour Trond following the successful completion of his first half century. Statoil ASA, Physics of Geological Processes at the University of Oslo, and the Geological Survey of Norway are proud to sponsor these proceedings as a fitting recognition of the scientific contributions of THT.

The Geological Survey of Norway and the Norwegian Petroleum Directorate established the TWIN Project (Tropical Weathering In Norway) in 2009 to improve the understanding of deep weathering on mainland Norway as well as offshore. All known reports of deep weathering in Norway have been reviewed and registered in a GIS database. We have selected four representative locations for more detailed studies in southern Norway (Kjose, Lista, Vågsøy-Stad and Inderøy) and another four locations in northern Norway (Vestvågøy, Hadseløya, Andøya and Hamarøy).