Structure, Metamorphism and Stratigraphy of Allochthonous Units of the Southern Exmouth Antiform, Wopmay Orogen, Northwest Territories

Abstract

<p> The area of study is a small area of allochthonous rocks structurally located immediately above an Archean antiform in the Wopmay Orogen of the Northwest Territories. The rocks of the study area represent various units of the Akaitcho Group epicontinental rift fill deposits. All rocks are allochthonous, lying structurally above basement and autochthonous cover. </p> <p> Within the allochthonous rocks, three phases of deformation and a metamorphic culimnation are evident. The first episode (Dl) involved thrusting and folding of the allochthon over the Slave Craton, coinciding with peak metamorphic conditions. This phase of deformation was followed by an episode of coaxial, thick-skinned folding (D2), producing the large scale folds of basement and cover witnessed in the area. A late cross-folding event (D3), has provided up to 6 km of structural relief in the study area. The deformational history thus recorded in the Wopmay Orogen is similar to that documented in other orogenic belts such as the eastern Alps and Gape Smith Belt in Quebec. </p> <p> Metamorphism in the study area is hot side up Buchan type. A progression is observed in pelitic assemblages from muscovite-sillimanite grade to sillimanite-K feldspar grade, from east to west across the study area. A retrogression has produced sillimanite quartz pods (faserkiesel), its occurrence has permitted a relocation of the pre-existing prograde isograd. </p> <p> These finds are consistent with the current tectonic model for the area. </p>