Fault reconstructions using aeromagnetic data in the Great Bear magmatic zone, Northwest Territories, Canada

Abstract

The Great Bear magmatic zone, located in Wopmay orogen, is a 1.875–1.84 Ga belt, 450 km long by 100 km wide of volcanic and allied plutonic rocks interpreted as a Paleoproterozoic magmatic arc. The belt, which contains economically important mineralization, was folded and subsequently cut by a swarm of northeast-striking transcurrent faults, which are part of a regional conjugate fault system interpreted to result from terminal collision of the Nahanni – Fort Simpson terrane. Fault reconstructions based on the interpretation of aeromagnetic data and geological maps provide first-order models of deformation mechanisms associated with, and the configuration of the Great Bear magmatic zone prior to, its dissection by northeast-striking transcurrent faults. The models show that vertical axis block rotation (plane strain) of ∼4.5° can explain fault offsets in the south, but that greater rotation is required to explain many of the displacements in the north. However, offsets on transcurrent faults that border the Camsell River district are greater than can be explained by vertical axis block rotation model alone and may include a component of Mesoproterozoic contractional deformation associated with the Racklan–Forward orogeny. Following reconstruction, iron oxide alkali alteration and associated mineralization, which pre-date transcurrent faulting, form a pair of northerly trending zones on the east and west margins of the belt. We suggest that these zones, whose exposure is related to broad synclinal folding of some of the oldest rocks in the Great Bear magmatic zone, are where iron oxide copper–gold (IOCG)-targeted exploration efforts should be focused on these areas in both outcrop and subcrop.

A Paleoproterozoic Andean-type iron oxide copper-gold environment, the Great Bear magmatic zone, Northwest Canada

“…The latest pulse of Great Bear magmatism consists of ca. 1860 to 1855 Ma coarse-grained granitic plutons with prevalent rapakivi-texture (Gandhi et al, 2001;Bennett and Rivers, 2006a;Jackson and Ootes, 2012), the distribution of which can be traced both from bedrock mapping and from geophysical signatures (e.g., Hildebrand et al, 2010b;Jackson and Ootes, 2012;Hayward and Corriveau, 2014).…”

Chronostratigraphy of the Hottah terrane and Great Bear magmatic zone of Wopmay Orogen, Canada, and exploration of a terrane translation model

“…Northeast-striking brittle faults dextrally offset all units and are transected by the ca. 1740 Ma Cleaver dykes (Irving et al 2004;Hayward and Corriveau 2014).…”

“…Geophysical studies have shown that the Hottah terrane and Great Bear magmatic zone have properties distinct from those of the Slave craton and overlying Coronation margin to the east, and the Fort Simpson magnetic high and enigmatic Nahanni terrane to the west ( Fig. 1; Fraser et al 1972;Hoffman 1988a;Cook et al 1999;Aspler et al 2003;Cook and Erdmer 2005;Wu et al 2005;Spratt et al 2009;Oueity and Clowes 2010;Ootes et al 2013;Hayward and Corriveau 2014). Much of what has been "imaged" in these experiments is covered by the Phanerozoic platform, and directly assessing the underlying bedrock components, especially of the Hottah terrane, is not currently possible.…”

“…Late-stage, northeast-striking, brittle-dextral faulting, such as the dextral McDonald Fault, continued to the Cordilleran thrust front ( Fig. 1A; Pilkington et al 2000;Aspler et al 2003;Hayward and Corriveau 2014), and therefore brittle deformation post-dated arrival of the Nahanni terrane (cf. Hayward and Corriveau 2014).…”

“…1A; Pilkington et al 2000;Aspler et al 2003;Hayward and Corriveau 2014), and therefore brittle deformation post-dated arrival of the Nahanni terrane (cf. Hayward and Corriveau 2014). It is speculated here that these faults were related to some tectonic adjustments even farther west, or perhaps even related to the Trans-Hudson Orogen to the southeast.…”