Abstract

Recent gravity surveys in eastern and southern Hudson Bay, Canada, have revealed, for the first time, the gravity anomaly pattern over the complete length of the proposed circum-Superior suture. A symmetrical distribution of linear, positive anomalies near the southern and eastern perimeters of Hudson Bay suggests a model in which suturing of Superior and Churchill protoplates was accomplished by subduction of oceanic lithosphere and by progressive double indentation of the rigid-plastic Churchill craton by the Thompson and Ungava salients of the rigid Superior protocontinent. Suturing was initiated at the Thompson salient with extrusion of Churchill material laterally along strike-slip faults into the Hudson Bay embayment. With continued subduction, indentation of the Churchill craton by the Ungava salient commenced, so that Churchill material was now extruded from two directions to fill the embayment of Hudson Bay. Following complete suturing of the Hudson Bay embayment, the motion of the Superior plate relative to the Churchill may have changed by about 90° E to facilitate complete closure of the predecessor of the Labrador Sea. The pattern of faulting and other major structural elements of northern Saskatchewan-Manitoba can be interpreted in terms of the proposed analogue model of plane indentation. The regional faults and their senses of motion correspond generally to that predicted by the theoretical pattern of slip lines associated with a wedge-shaped indenter.

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