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 Northwest Territories, 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.

A New P‐Wave Tomographic Model (CAP22) for North America: Implications for the Subduction and Cratonic Metasomatic Modification History of Western Canada and Alaska

“…The northern CCD is wide, bounded by an arcuate CDF, while the southern CCD is relatively narrow, bounded by a linear CDF, approximately parallel to the coastline. The geomorphological change in the CCD is often linked to the Liard Line Transfer Zone (LLTZ) north of the Macdonald Hay‐River fault, which is the surface expression of the Great Slave Lake shear zone (GSLsz; Cecile et al., 1997; Hayward, 2015; Hayward & Paradis, 2021; Lund, 2008; see Figure 1). Geologically, the LLTZ is interpreted as the boundary between two asymmetric rifting modes along the western margin of Laurentia (e.g., Cecile et al., 1997; Lister et al., 1986; Lund, 2008).…”

Zinc on the edge—isotopic and geophysical evidence that cratonic edges control world-class shale-hosted zinc-lead deposits

“…Major shale-hosted deposits in the Northern Cordillera of western North America are also associated with a (smaller amplitude) gradient in the 30-km upward-continued gravity image (Fig. 3d) as well as with gradients in the 15-, 50-, and 100-km upward-continued images (not shown), as also noted by Hayward and Paradis (2021). The relationship in this province differs from that in the Northern Australian Zinc Belt in two important ways.…”

“…In this contribution, we build on previous work by Hobbs et al (2000), Southgate et al (2013), Gibson et al (2017), Hoggard et al (2020), Huston et al (2020), and Hayward and Paradis (2021). Hobbs et al (2000) presented evidence that the major zinc-lead deposits of the North Australian Zinc Belt are associated with a prominent gravity "worm," which marks a horizontal gradient in upward-continued gravity data.…”

“…Figure 3c shows that there is a broad correlation of basin-hosted zinc-lead deposits in the Northern Cordillera with the 170-km LAB contour, although in detail some of these deposits are located outboard of this contour (e.g., Macmillan Pass and Howards Pass districts). Hayward and Paradis (2021) suggested that the host basin may have been displaced 100 km to the northeast relative to basement.…”

Geodynamic controls on clastic-dominated base metal deposits

“…There are not many ancient margins where upper or lower plate sections have been identified, reflecting a need for additional geophysical data to characterize ancient margin structure. In the ancient western Laurentian margin (North America), however, both plate types have been recognised, and both types host CD-type deposits (Lund, 2008;Hayward and Paradis, 2021). This occurrence of mineralization on both margin types could reflect a combination of all three ore formation mechanisms occurring, with mechanism 3 dominant on the lower plate side.…”