The evolution of Keele Arch, a multiphase feature of the northern mainland, Northwest Territories

Abstract

Keele Arch is a zone of structural, erosional, and depositional features along a corridor between the eastern Colville hills and the Franklin Mountains, Northwest Territories. It has a long history of basin-to-arch reversals. Paleomaps and sections illustrate the arch's evolution through six phases: 1) uplift as a very early Cambrian pre-rift high, 2) subsidence into a graben chain during Cambrian to mid-Ordovician time, 3) uplift of its southern half into a pre-Devonian arch extending southward from the present day northern Franklin Mountains to beyond Johnson River, 4) renewed uplift into a pre-Cretaceous arch running from north of Lac des Bois to Johnson River, 5) mid-Cretaceous reactivation of the pre-Cretaceous and southern pre-Devonian arches, 6) subsidence of its central zone into Brackett Basin and inversion of the Cambrian McConnell graben into the McConnell Range during late-Campanian to Paleocene time. Keele Arch consists of four parts: 1) a northern segment extending northeastward from the Northern Franklin Mountains toward Lac des Bois; 2) the north half of Keele Tectonic Zone under the northern Franklin Mountains; 3) between Brackett Lake and Keele River; 4) a fourth and poorly understood segment under Mackenzie Valley, south of Keele River, where the arch axes appear to fall into two sets: an eastern set of Cambrian to mid-Ordovician sag axes and latest Silurian to Eocene uplifts, and a western set of Cambrian to mid-Cretaceous arch axes that tracks across a block of Proterozoic rock directly overlain by Devonian strata. The arch's economic significance is not fully understood.