Assessment of the relationship between emplacement of the Algoman plutons and regional deformation in the Rainy Lake region, Ontario

Abstract

The Algoman suite of granites and granodiorites, located within the Rainy Lake region of the Superior Province, intruded the Wabigoon–Quetico subprovince boundary about 2686 Ma. Deformation occurred during the late Archean collision between the Wabigoon and Wawa volcanic arcs. The Algoman plutons are the youngest rocks in the region. Their apparent lack of macroscopic deformation fabrics has led previous researchers to use their age as a constraint for the cessation of regional deformation. However, contrasting competence between the relatively rigid granites and surrounding volcanic and metasedimentary rocks suggests that obvious deformation fabrics may not be observed in the plutons even if they were present during deformation. A field, anisotropy of magnetic susceptibility (AMS), gravity inversion model, and microstructural study were undertaken on two neighboring Algoman plutons to determine their emplacement history relative to the regional deformation. There is a steep macroscopic foliation in the adjacent rocks and in parts of the plutons. The magnetic foliation is very strong and roughly coincident with the field foliations. The gravity inversion models indicate that the plutons are relatively shallow (1 km and 4.5 km at their deepest points), and their shapes are consistent with emplacement during dextral transpression. Quartz microstructures, such as undulose extinction and subgrain formation, indicate that there was some solid-state deformation accommodated by dislocation creep mechanisms. The field, AMS, gravity, and microstructural evidence indicate that the plutons were most likely emplaced syntectonically. Thus, the pluton age does not provide a conclusive constraint to the cessation of regional deformation.

Anisotropy of magnetic susceptibility fabrics in syntectonic plutons as tectonic strain markers: the example of the Canso pluton, Meguma Terrane, Nova Scotia

“…The tectonic overprint may begin as the magma in the pluton reaches some threshold of crystallisation, when the solid fraction forms a contiguous framework with increasing strength that transmits anisotropic stresses from the deforming country rocks. Examples like Figure 1D have also been shown to be indicative of syntectonic emplacement (Leblanc et al 1996;Djouadi et al 1997;Gleizes et al 1998;Czeck et al 2006;Gebelin et al 2006).…”

Geologic interpretation of aeromagnetic and chemical data from the Oaks Belt, Wabigoon subprovince, Minnesota: implications for Au-rich VMS deposit exploration

“…Previously interpreted as post-kinematic, their age was used as a marker of the end of regional deformation (Davis et al 1989;Poulsen 2000a). However, field relationships, anisotropy of magnetic susceptibility, microstructural analysis, and gravity inversion techniques suggest these plutons formed syntectonically (Czeck et al 2006).…”