New geophysical interpretations of deep crustal and upper mantle structures of the Superior Province provide the 'smoking gun' against Archean plate tectonics Lyal Harris1 & Jean H Bédard2 1 INRS-ETE, Québec, Canada, lyal.harris@ete.inrs.ca 2Geol. Surv. Canada Geophysical data for the Archean Superior Province, Canada, highlight upper mantle (SCLM) and mid- to deep crustal domains and faults oblique to those mapped at the surface that are impossible to reconcile with current plate tectonic accretionary models. SCLM domains, most of which are oblique to sub-province boundaries, represent rifted Mesoarchean blocks and Neoarchean volcanosedimentary sequences were deposited in related rifts in the overlying crust. NNE- to NNW striking rectilinear faults at high angles to overlying mapped broad ductile shear zones and faults are identified in the mid- to deep crust. In the W Superior these deep transverse faults with no to little surface expression intersect concentric circular to elliptical features, ca. 90-185 km across, along the S boundary of the N Superior proto-craton. Their similarity in size and geometry to coronae on Venus, attributed by planetary geologists to form above mantle upwellings, suggests formation above secondary mantle upwellings from a mantle plume or an overturn upwelling zone (OUZO) beneath the N Superior proto-craton. Emplacement of 2.73 Ga mafic-ultramafic intrusions was controlled by these concentric and intersecting transverse structures, showing that they were present (and likely produced) during greenstone belt formation. Magnetotelluric (MT) data for the W Superior portray linear resistivity anomalies trending N-S in the deep crust and SCLM, plus anomalies parallel to E-W subprovinces at shallower crustal depths. MT data, albeit of much lower resolution near the N Superior proto-craton, suggests that the concentric features may also have a SCLM expression. Intra-crustal decoupling during dextral transpression and bulk N-S shortening led to the preservation of these early-formed deep structures in strong anhydrous, melt-depleted felsic and mafic granulite. The cratonic mobilism model (Bédard et al., 2013) is adapted by including ‘plume-push’ against the deep N Superior protocraton SCLM keel imaged with seismic tomography, in addition to regional mantle flow (‘mantle wind’) to explain deformation. Comparisons with Venus confirm the feasibility of this model to produce the required bulk shortening in the absence of plate tectonics.

• published: 28 Apr 2021
• views: 2635