Geophysical reassessment of the role of ancient lineaments on the development of the western Laurentian margin and its sediment-hosted Zn-Pb deposits, Yukon and NWT, Canada

Abstract

A new 3-D 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 Zn-Pb deposits. The region’s history is obscured by multiple tectonic overprints including terrane accretion, plutonism, and thrust faulting. Regionally continuous, broadly NE-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 ENE-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 NW-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-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 NW-trending lineament interpreted to be associated with a shallowing of lower crustal rocks.