404 IIKEZEN AND EWING [CHAr. 16 



to the older data, because drifting stations have not crossed this area and only 

 a few aircraft landiiitrs have been made here. Since workers on From ^nd Serlov 

 were not able to takc^ soundings on a daily schedule (the practice of the post-war 

 drifting stations), soundings are widely spaced and hence only adequate for a 

 speculative description of this rifted ridge. 



Soundings west of S])itsbergen (Boyd, 1948) show^ a strong suggestion of a 

 median-rifted ridge (Fig. 11). To the north, the recently discovered north-south 

 cleft in Nansen's Sill (Hope, 1959) is probably a continuation of the rift. From 

 80°N to 85°N the rifted ridge appears to run north along the Greenwich 

 meridian. The ridge is demanded by the available soundings which, however, 

 are insufficient to confirm or deny its probable rifted character. From 85°N, 0°W 

 the ridge turns east; between 30° and 45° W the soundings of both Fram and 

 Sedov show a strong suggestion of the characteristic rifted ridge of the mid- 

 oceanic belt (Fig. 10, profiles I and II). 



Between 90°W and 120°W scattered soundings suggest a ridge but are in- 

 sufficient to shed any light on the probable rift. As the seismic l)elt ajjproaches 

 the Siberian continental shelf, shallow soundings indicate an extension of 

 shallow de])ths out along the epicenter belt. The Skado Trough, mentioned by 

 Hakkel (Hope, 1959), may indeed actually be the end of the mid-oceanic rift as 

 it cuts into the continental slo])e. As Ho])e ])oints out, the Skado Trough 

 seems too large to be described as a conventional erosional submarine canyon. 



The Arctic seismic belt continues from the mid-oceanic ridge across the 

 Laptev Shelf to the vicinity of the Lena delta where it crosses the shorehne 

 and follows the Verkhoyansk Trough southward into the interior of Siberia. 

 There is a suggestion that this seismic belt joins the Baikal-Rift-Valley seismic 

 belt. The Verkhoyansk Trough, bounded by normal faults for 1000 km and 

 filled with over 3.5 km of Jurassic, Cretaceous and Tertiary sediments, resembles 

 the African and Lower California extensions of the mid-oceanic rift (Nalivkin, 

 1960). 



At present the evidence for the extension of the mid-oceanic ridge through the 

 Arctic Basin is strongly suggestive but not conclusive. 



8. Crustal Structure 



Thus, starting in the North Atlantic, we have followed a morphotectonic belt 

 for over 40,000 miles along the axis of the Atlantic, Indian, South Pacific and 

 Arctic Oceans. Extensions of the belt have been found continuing into the rift 

 valleys of Africa, into the great strike-slip faults of New Zealand and southern 

 California, Chilean canals. Gulf of Aden and Red Sea. The continuity of the 

 epicenter belt is not open to question; the continuity of the rifted ridge is not 

 ])roven beyond question due to S])ar8ity of soundings in some areas, and to 

 offsets at fracture zones. It is not certain whether the rift valley is a single 

 valley or a belt of similar but en echelon features. The en echelon pattern of the 

 Fast African rift valleys is ])robably a better generalization of the average 

 situation than a single grand trough like the Red Sea. 



Typical topographic ]jrofiles of the mid-oceanic ridge in the various oceans 



