A discussion concerning the floor of the northwest Indian Ocean - The Owen fracture zone and the northern end of the Carlsberg Ridge

Abstract

Examination of the shape of the earthquake epicentre belt near Socotra led to the suggestion that a major fracture displaces the axis of the mid-ocean ridge in that area (Matthews 1963). Subsequent surveys have confirmed the existence of a fracture zone which extends 1500 miles from the coast near Karachi southwestwards to the middle of the Somali Basin. Linear ridges and troughs in the zone are associated with negative gravity anomalies but not with magnetic anomalies. Where the fracture zone crosses the line of the Carlsberg Ridge a sinuous trough is developed: south of this feature a characteristic pattern of magnetic anomalies is associated with the volcanic structures of the mid-ocean ridge, north of it a line of large non-magnetic seamounts has been found. It is concluded that the structure underlying the Owen fracture zone is a system of parallel transcurrent faults affecting the ocean floor only, at which the axis of the mid-ocean ridge suffers a net right lateral displacement of 170 mi.