Marine Geology of Atlantic North of Arctic Circle: ABSTRACT

Abstract

End_Page 2488------------------------------As with all oceanic sea floor, the process of axial accretion along the crest of an active mid-oceanic ridge is of paramount tectonic importance to the geologic fabric of the northern Atlantic Ocean floor. The chronologic evolution of the Norwegian-Greenland Sea region has been derived from the analysis of Raff-Mason magnetic anomaly patterns by several investigators. These studies indicate that Norway and Greenland were severed when rifting commenced 60-70 m.y. ago, approximately along what are now the edges of their continental shelves. A half rate of 1.2 cm/year has been measured as the rate for this earliest sea-floor spreading. A second episode of spreading lasted from 40 to 18 m.y. ago, and was accompanied by a westward axial shift of the mid-oceanic ridge in the Norwegian Sea. At present, the axis of activity is along the Iceland-Jan Mayen and Mohns Ridges. Mohns Ridge apparently has been stable throughout the evolution of the region whereas the Iceland-Jan Mayen Ridge appears to be a very recent feature. In the Greenland Sea the Knipovich Ridge is apparently now acting as a trench which connects the mid-oceanic ridge branches in the Arctic and Norwegian Seas. Baffin Bay is enigmatic as to whether it is down-faulted continental or oceanic crust. The writers prefer the hypothesis that Baffin Bay was formed at the same time as the Labrador Sea (prior to 60 m.y. ago) in a proto-North Atlantic by the process of sea-floor spreading. The now-extinct Mid-Labrador Sea ridge would have extended via transform faults through Baffin Bay and perhaps even to the Alpha Ridge in the Arctic. This system then slowed down and became extinct in the Tertiary. End_of_Article - Last_Page 2489------------