Abstract

Keele Arch is a zone of anomalous structural, erosional, and depositional features along a corridor east of the Colville Hills and the northern Franklin Mountains, Northwest Territories, a region with significant economic potential. First described in 1975, it has since been found to have had a long history of uplift-to-sag reversals. This report presents a series of maps and sections, based largely on flattened reflection seismic lines that illustrate key stages of the arch’s development through time and space. In doing so it lays the foundation for future assessments of the arch’s influence on the surrounding stratigraphy.

Preceded by a late Proterozoic syncline, it evolved through five major stages: 1) subsidence into a chain of Cambrian to mid-Ordovician grabens; 2) uplift of its central and southern zones to form a Late Silurian (pre-Devonian) arch; 3) renewed uplift into a pre-Cretaceous arch between the region east the Colville Hills and the Mackenzie River valley near Johnson River; 4) mid-Cretaceous reactivation of the pre-Cretaceous and southern pre-Devonian arches; and 5) subsidence of its central zone into Brackett Basin during the late-Campanian to Paleocene and inversion of the Cambrian McConnell Graben into the McConnell Range during late-Campanian to Paleocene time.

The feature can be divided into four parts: 1) A northern segment between the Northern Franklin Mountains and the region east of the Colville Hills; 2) The north half of its central zone, where Cambro-Ordovician strata are exposed east of the northern Franklin Mountains; 3) The southern portion of the central zone between Brackett Lake and Keele River, where Tertiary rocks lie at the surface. This is the best documented and most tectonically active segment; and 4) a poorly understood segment under Mackenzie Valley, south of Keele River.

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