Blackwell Publishing Journal Backfiles 1879-2005
In 1988, an extensive geophysical experiment was performed on the Lofoten passive continental margin, which was formed by the continental break-up between Greenland and northern Norway at 58 Ma. The geological units of the outer Lofoten margin are characterized by seaward-dipping reflectors (SDRs) and landward flood basalt, which extends up to 100 km landwards of SDRs. In this study, we obtain the P-wave velocity structure beneath the Lofoten Basin, the SDRs, and the landward flood basalt by use of ocean-bottom seismograph refraction profiling, and we also discuss the formation of the northern Norwegian passive continental margin.In the Lofoten Basin the crust is of oceanic type, consisting of sedimentary layers, oceanic laver 2 (4.9−5.5 km s−1), layer 3A (6.3−6.8 km s−1) and layer 3B (7.0−7.1 km s−1). Beneath the SDRs the crustal layers are identical to those of the Lofoten Basin, but the thickness of the lower crust, which represents the same velocity as layer 3B, increases to 5 km towards the continent side, and a high-velocity lower crustal layer (7.3 km s−1) is formed at the base of the crust. The ocean-continent transition zone is situated between the landward side of the SDRs and the northward continuation of the Vøring Plateau Escarpment. In this region the velocity of the lower crust gradually decreases and approaches the lower crustal velocity beneath the Lofoten Islands (6.8 km s−1). The model also indicates that the high-velocity layer disappears in this region. Comparing our model with the crustal structure on the Vøring margin, it is clear that the lower crustal body (≥7 km s−1) thickens southwards along the northern Norwegian continental margin. Recent results from petrological and geophysical studies of the generation of the oceanic crust have shown that increasing the temperature of the upwelling asthenospheric material increases the thickness of the oceanic crust. We interpret this as that the oceanic crust in the southern area in the Vøring-Lofoten margin was generated by hotter material than that of the northern area.
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