Tectonic History of Boothia Uplift and Cornwallis Fold Belt, Arctic Canada

Abstract

The Boothia uplift is an elongate northerly extension of crystalline rocks of the Precambrian shield into the Canadian Arctic Archipelago. The structural grain of the crystalline rocks which comprise the uplift is northerly. This causes the uplift to have an over-all northerly trending elongate outline. Proterozoic to Upper Devonian sediments, which overlie and closely flank the Boothia uplift, form the Cornwallis fold belt. The structure of the Cornwallis fold belt is the result of movements of the underlying Boothia uplift, and for this reason the fold belt also has both a northerly structural grain and outline. Together, the uplift and the fold belt extend at least 600 miles, striking diametrically across the Arctic lowlands and Franklinian miogeosyncline. At various times since the Precambrian, the Boothia uplift has risen, lifting the Cornwallis fold belt with respect to flanking areas. Movements are dated from erosion surfaces and unconformities on the uplift and in the fold belt. In the southern part, the uplift is a simple arch, whereas in the northern, it is predominantly a horst, with a lesser amount of arching. Near-vertical faults bordering the Boothia uplift become high-angle reverse faults toward the surface, presumably the result of lateral spreading of the uplifted area. Such faulting commonly is exposed at the boundary of the uplift in the Arctic lowlands. However, in the much thicker, commonly incompetent succession of the miogeosyncline fold belt, structure is reflected as asymmetrical folding of the Cornwallis fold belt Published model experiments with fine, dry sands, in which a horst-shaped block was uplifted, have steep reverse faults at the boundaries, and strongly resemble the northern part of the Boothia uplift. A mobile belt encompassing the Boothia uplift and Cornwallis fold belt moved periodically, having six documented times of uplift relative to the flanking areas. These uplifts occurred in (1) Precambrian, (2) pre-Middle Cambrian, (3) mid-Early Devonian, (4) late Early to early Middle Devonian, (5) mid-Late Devonian, and (6) Pennsylvanian or Early Permian times. Submergence following the mid-Early Devonian and the late Early to early Middle Devonian uplifts was the result of widespread regional submergence rather than relative depression of the mobile belt alone. The nature of the submergence which followed the other uplifts is unknown. Thus, in the geologic record, the Boothia uplift and Cornwallis fold belt have risen six times with respect to the flanking regions. However, although t ey were covered by sediments at various times and have narrow normal-faulted zones of down-dropped blocks, they do not appear to have sunk as a unit with respect to the flanking regions.