P- and S-wave velocity models along two perpendicular profiles 145 and 175 km long on the undrilled continental shelf off Lofoten, northern Norway, have been obtained from the study of nine three-component ocean bottom seismographs.
A high-quality multichannel seismic reflection line was acquired in 1987 along a 175 km long profile across the continental shelf off Lofoten, northern Norway. A seismic wide-angle experiment was performed in 1988 along the same profile, using seven three-component Ocean Bottom Seismographs (OBS) with 20–25 km spacing and shotpoint intervals of 240 m. The study of the data has shown that the combination of the multichannel reflection and the wide-angle (OBS) technique provides information about the crustal structure beneath the Lofoten shelf that could not have been achieved using only one of the techniques. the multichannel reflection data provide a detailed image of the shallow (Cretaceous) structures, which represents an important basis for inversion of the OBS data. the lower crust and the Moho are also well mapped in some parts of the area with the multichannel reflection technique. The OBS data reveal that significant amounts of pre-Cretaceous sediments exist along almost the entire profile, with a maximum thickness of about 5 km in the Vestfjorden Basin. From the OBS data the thickness of the lower crust is inferred to decrease from about 11.5 km under the Røst High to about 2 km below the Lofoten Ridge. the OBS data indicate further that the Moho position under the Vestfjorden Basin is considerably deeper than can be inferred from the reflection data. About 10km below Moho a strong dipping event is observed in the OBS data. This upper mantle reflection might be related to a possible seaward dipping master fault, and/or presence of layers of partially hydrated peridotite.
' The large variation which exists from study to study in the determined apparent surface velocities of energy which travels through the crustal layers of the Scandinavian Shield raises the question of how much of this variation is due to errors in interpretation and how much is due to actual changes in the crustal velocity from area to area. Some insight into this question may be gained from examining two studies of Scandinavian crustal structure employing exactly the same crustal profile, but arriving at different iinal results: the study of Sellevoll & Warrick (1971) and the present study. In the study by Sellevoll8c Warrick (1971), no correction for elevation of the stations was made and the retrograde reflections from the crustal velocity discontinuities do not appear to have been considered. As a result, Sellevoll & Warrick found it necessary to insert a low-velocity channel in their velocity model beneath the higher elevation part of the proflle in order to obtain the observed time delays '. In this quotation two statements are made regarding the paper by Sellevoll & 1. No correction for elevation of the stations was made, and a a result, Sellevoll 2. The retrograde reflections from the crustal velocity discontinuities do not In matter of fact neither of those statements is correct. This misunderstanding by Mass6 & Alexander arises in that they apparently assume the average topographic elevations presented in Fig. 5 (Sellevoll & Warrick 1971) to be identical with the altitude of the stations. This is manifestly not the case. Most stations, in fact, have very small elevations, as they are situated either along the shore-lines of fjords or in valleys which are deeply cut into the surrounding mountains. Thus in the western part of the profile Flora-Asnes, where the topographic elevation exceeds 1500 m, several stations are located at less than 100 m above sea level.
Research Article| July 01, 1988 An intra-oceanic crustal seismic reflecting zone below the dipping reflectors on Lofoten margin M. A. Sellevoll; M. A. Sellevoll 1Seismological Observatory, University of Bergen, Allégaten 41, 5007 Bergen, Norway Search for other works by this author on: GSW Google Scholar M. Mokhtari M. Mokhtari 1Seismological Observatory, University of Bergen, Allégaten 41, 5007 Bergen, Norway Search for other works by this author on: GSW Google Scholar Author and Article Information M. A. Sellevoll 1Seismological Observatory, University of Bergen, Allégaten 41, 5007 Bergen, Norway M. Mokhtari 1Seismological Observatory, University of Bergen, Allégaten 41, 5007 Bergen, Norway Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (7): 666–668. https://doi.org/10.1130/0091-7613(1988)016<0666:AIOCSR>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation M. A. Sellevoll, M. Mokhtari; An intra-oceanic crustal seismic reflecting zone below the dipping reflectors on Lofoten margin. Geology 1988;; 16 (7): 666–668. doi: https://doi.org/10.1130/0091-7613(1988)016<0666:AIOCSR>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Multichannel seismic reflection measurements off Lofoten, Northern Norway," "show an uneven, discontinuous reflector within the crystalline oceanic crust" "at a depth of 7-8 s (two-way traveltime). This intra-oceanic crustal reflector" "is observed seaward as well as beneath sub-basement dipping reflectors, which" "are of disputed (oceanic or continental) origin. Our observations indicate that" "the dipping reflectors are an integrated part of the oceanic crust. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The continental break-up between Norway and Greenland occurred in late Paleocene / early Eocene, and was associated with an intensive volcanisim along the margin. At a passive continental margin the whole process of crustal evolution is generally retained in the crustal structure from the continent to the ocean.
This study presents a 500-km-long crustal transect across the Lofoten volcanic passive continental margin, N. Norway, by compiling the results of two successive Ocean Bottom Seismographic (OBS) experiments performed in 1988. The OBS profiles were acquired from the Norwegian mainland, across the continental shelf, over an area covered with landward flood basalts, to the Lofoten basin. The land side end of the crustal model represents a thinned continental structure. The crust in this part has strong structural complexity, mainly due to faulting during pre-Tertiary continental thinning phases. Between the continental shelf and the seaward dipping reflectors (SDR), the model represents an extremely thinned continental crust and ocean/continent transition zone. This region is interpreted to be dominated by an early Tertiary continental rifting phase that progressed until early Eocene. The observed lower crustal reflectors, which are interpreted as intrusions in the lower crust, as well as the landward flood basalts indicates an extensive magmatic activity during the continental rifting phase. Between the SDR and magnetic anomaly 21, an oceanic crust with thick lower crust and a high velocity layer at the bottom of the crust (7.3km/s) are obtained. This high velocity layer is believed to be created by anomalously hot asthenospheric material rising around a hot spot. The comparison of the crustal structure across the Lofoten margin with the structure of the Voring-More margin shows significant differences in the volume of the lower crustal high velocity layer, which can be interpreted in terms of a NE-ward decrease of the influence of the hot spot.
