Abstract
A new three-dimensional (3D) inversion strategy is applied to new compilations of gravity and magnetic data to reassess the role of crustal lineaments in the development of the western Laurentian margin, Selwyn Basin, and associated sediment-hosted zinc–lead (Zn–Pb) deposits. The region’s history is obscured by multiple tectonic overprints, including terrane accretion, plutonism, and thrust faulting. Regionally continuous, broadly northeast-trending crustal lineaments, including the Liard line, Fort Norman structure, and Leith Ridge fault, were interpreted as having had long-standing influence on craton, margin, and sedimentary basin development. An east–northeast-trending lineament, Mackenzie River, traced from the Misty Creek Embayment to Great Bear Lake, is interpreted as the southern edge of a cratonic promontory. The location of the Liard line, associated with a transfer fault that bounds the Macdonald Platform promontory, is refined. New geophysical results support the continuity of the Fort Norman structure below the Selwyn Basin, but limited evidence exists for the Leith Ridge fault in this area. A northwest-trending lineament that bounds the craton is interpreted as a crustal manifestation of lithospheric thinning of the Laurentian margin, as echoed by a change in the depth of the lithosphere–asthenosphere boundary. The structure delimits the eastern extent of mid- to Late Cretaceous granitic intrusions and is straddled by Mississippi Valley-type Zn–Pb occurrences, following their palinspastic restoration. Clastic-dominated Zn–Pb occurrences are aligned along another northwest-trending lineament interpreted to be associated with a shallowing of lower crustal rocks.
Highlights
Page 4 of 63 4Details of the tectonic history of the western margin of the North American craton (Laurentia) in northwestern Canada, formed from the progressive accretion of 2.3-1.8 Ga magmatic arcs and microcontinents
The structure of the Laurentian craton and its relationship to the tectonic development of the northern Cordilleran orogen are obscured by a lack of exposure, and burial beneath the Neoproterozoic to early Paleozoic continental margin sedimentary rocks, including Selwyn basin
Implications for the tectonic evolution of the western Laurentian margin The MRL is interpreted as the southern edge of a cratonic promontory, buried beneath the MRA and Yukon block, defined by tomographic modeling as the Mackenzie craton (Schaeffer and Lebedev 2014; Estève et al 2020)
Summary
Page 4 of 63 4Details of the tectonic history of the western margin of the North American craton (Laurentia) in northwestern Canada, formed from the progressive accretion of 2.3-1.8 Ga magmatic arcs and microcontinents (summarised by Nelson et al 2013). The tectonic processes that formed the Cordilleran orogen of western Canada include terrane accretion, regional plutonism and metamorphism, development of the Selwyn basin and Mackenzie Mountains fold and thrust belt (MMFTB), and large offset strike-slip faults (e.g., Gabrielse et al 2006; Nelson et al 2013 and the references therein; Hayward 2019). The character of regional lineaments, interpreted to have played an important role in the development of Selwyn basin and its mineralisation, yet remaining enigmatic despite prior investigation (e.g., Aitken and Pugh 1984; Gabrielse and Campbell 1992; Cecile et al 1997; Morrow and Miles 2000; Hayward 2015), are explored
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