Marine geophysical investigations in the Norwegian-Greenland Sea between the latitudes of 62ºN and 74ºN
The Durham University 1977 marine geophysical cruise (R.R.S.Shackleton 977) in the southern Norwegian-Greenland Sea included a survey of the Jan Mayen block between the latitudes of 67ºN and 69.5ºN and a traverse of the Norway Basin. Reduced bathymetric, gravity and magnetic data are presented. The gravity and magnetic data are interpreted using direct inversion techniques. Most of the multichannel seismic data is not yet processed, but drawings of the monitor records and a short processed section are included, together with a description of the processing system. In addition, a detailed review is given of published geophysical data from the southern Norwegian-Greenland Sea and a compilation of marine magnetic anomalies is presented. The principal results are as follows. The Jan Mayen raicrocontinental fragment is about 90 km wide and extends from about 65ºN to 70ºN. Contrary to previous inferences, there is little evidence of pre-Tertiary sediment beneath the block. The crust thickens (to about 16-20 km) passing from the Norway Basin to the Jan Mayen block. A revision of anomaly correlations and identifications in the Norway Basin is presented and the nature of the magnetic source layer is analysed. The central fan shaped anomaly pattern was formed from the end of anomaly 20 time (-43 Ma) to about anomaly 7 time (-27 Ma) as the Jan Mayen block rotated 27.4º anticlockwise relative to Norway about a near pole (64.9ºN, 12.3ºW). Complementary spreading took place about the newly formed Kolbeinsey axis, such that Jan Mayen rotated 29º anticlockwise relative to Greenland (about a pole at 71.1ºN, 16.4ºW). Bathymetric and structural evidence is adduced in favour of this scheme and the implications with respect to the structure and the evolution of the Jan Mayen block are discussed. It is suggested that the anticlockwise reorientation of spreading between Greenland and Norway, which occurred when spreading ceased in the Labrador Sea, caused compressional stresses across a major transform fault at the southern end of the Norway Basin and led to the fission of Jan Mayen from Greenland.