Multidisciplinary Modeling of Mantle Lithosphere Structure Within the Superior Craton, North America

Abstract

New 3D multi‐azimuthal receiver function analysis identified four regional seismic discontinuities dipping at 7–13° within the mantle of the Superior craton of North America; most are discordant to known major upper crustal structures. Widely observed crustal‐scale structures with near‐vertical axial planes striking east‐west indicate that the most recent and dominant phase of folding and horizontal shortening strain occurred during the Kenoran (D2) crustal deformation concurrent with Au‐mineralization and peak metamorphism at 2.72–2.66 Ga. Two mantle discontinuities strike 065° and 249°, dipping to the southeast and northwest, respectively. These strikes roughly parallel the northern margin of the Superior craton and some intra‐cratonic features such as the axis of the Quetico Basin. Two discontinuities strike 355° and 187°, dipping to the east and west, respectively, and parallel to the western margin of the craton. Our new observations reveal neither moderately dipping, east‐west striking discontinuities nor coherent eclogitic layers characteristic of modern plate tectonic subduction zones. Prominent east‐ and west‐dipping mantle structures relate best to a Paleoproterozoic (Trans‐Hudson) deformation, which is rarely observed in the crust. A new analysis of mantle xenoliths and xenocrysts indicates that carbonatitic metasomatism predominates above some discontinuities where strongly localized conductivity occurs whereas kimberlitic metasomatism predominates below the discontinuities in the broadly conductive mantle.

Active and Passive Seismic Imaging of the Central Abitibi Greenstone Belt, Larder Lake, Ontario

“…We hypothesize four possible explanations for the formation of S1 feature observed in the KSZ12 seismic and P ‐ S convertibility transects. We first note that analysis of three‐component broadband teleseismic data from the permanent station KILO at Kirkland Lake also shows a discontinuity (uninterpreted) at the same depth as S1, that dips toward 150 azimuth (Snyder et al., 2021). (a) It is likely that the S1 feature is caused by the delamination and sinking of the lower crust into the mantle and the middle crust dimmed reflection zones, M1 and M2, were caused by intrusions from the partial melting of the S1 feature.…”

“…The Moho discontinuity is clearly imaged at ∼40 km in all P ‐ S convertibility plots. Based on the identified Moho depth from the seismic reflection transects and previous Moho depth studies (Darbyshire et al., 2007; Snyder et al., 2021), the optimal location of the Moho boundary is determined to be on the trough value (negative convertibility) which is immediately followed by a peak value (positive convertibility). We adopt this notion (trough followed by peak) as an indication of shear‐wave velocity increase from the upper layer to the layer beneath, which will be used to interpret the convertibility profiles in other parts of the profile.…”