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TitleMultidisciplinary modeling of mantle lithosphere structure within the Superior Craton, North America
AuthorSnyder, D BORCID logo; Savard, G; Kjarsgaard, B AORCID logo; Vaillancourt, A; Thurston, P; Ayer, J A; Roots, E
SourceGeochemistry, Geophysics, Geosystems (G3) vol. 22, issue 4, e2020GC009566, 2021 p. 1-20, Open Access
logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20210145
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf; html
ProvinceOntario; Quebec; Manitoba
NTS31C; 31D; 31E; 31F; 31K; 31L; 31M; 31N; 32C; 32D; 32E; 32F; 32K; 32L; 32M; 32N; 33C; 33D; 41; 42; 43A; 43B; 43C; 43D; 52; 53A; 53B; 53C; 53D
AreaGreat Lakes; Canada; United States of America
Lat/Long WENS -96.0000 -76.0000 53.0000 44.0000
Subjectsstructural geology; tectonics; stratigraphy; geophysics; geochemistry; economic geology; Science and Technology; Nature and Environment; crustal structure; mantle; lithosphere; modelling; geophysical interpretations; seismic interpretations; magnetotelluric interpretations; resistivity logging; discontinuities; bedding planes; trend surface analyses; tectonic history; metamorphism; deformation; folding; crustal shortening; strain; metasomatism; carbonatites; mineralization; xenoliths; eclogites; kimberlites; isotopic studies; lithology; fluid dynamics; mineral potential; gold; Archean; Superior Craton; Canadian Shield; Kenoran Orogeny; Quetico Basin; Trans-Hudson Orogeny; Paleoproterozoic; Attawapiskat Kimberlite Cluster; Kirkland Lake Kimberlite Cluster; Kapuskasing Structural Zone; Precambrian; Proterozoic
Illustrationslocation maps; geoscientific sketch maps; cross-sections; seismic profiles; tables; profiles; geophysical logs; lithologic sections; 3-D images
ProgramGEM2: Geo-mapping for Energy and Minerals GEM Synthesis
Released2021 03 24
AbstractNew 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.
Summary(Plain Language Summary, not published)
Structure within the Earth is best studied in three dimensions and using several coincident overlays of diverse information with which one can best see where unusual properties match up. Here we use regional surfaces causing discontinuities in seismic waves a few hundred kilometers deep in the Earth, intersected and thus calibrated by rebuilt rock columns using rare rock samples erupted to the surface in two locations. Electrically conductive regions can be mapped using natural (magnetotelluric) currents. East- and west-dipping seismic discontinuity surfaces match surface structures that developed about 1.8 billion years ago marginal to the Superior crustal block. Surfaces dipping to the southeast and northwest match some boundaries between crustal blocks that are over 2.5 billion years old, but many such crustal boundaries trend more east-west. Conductive rocks appear more commonly above these discontinuity surfaces where gas-rich fluids apparently flowed and that the discontinuities somehow filtered these fluids. The mismatch in orientation and dip between the most ancient deep and exposed structures suggests that plate tectonic processes operating today differed earlier than 2.5 billion years ago.

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