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

Abstract

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.

Keywords

• Garnet geochemistry
• kimberlitic metasomatism
• lithosphere
• mantle seismic discontinuities
• Superior craton