Deformation coupling between the Archean Pukaskwa intrusive complex and the Hemlo shear zone, Superior Province, Canada

Abstract

Archean greenstone belts typically form narrow sheared basins separating bulbous tonalo-trondjhemogranodioritic (TTG) intrusive complexes. The role played by gravity in the development of such dome-and-keel structures constitutes a key question in Archean tectonics. The Pukaskwa intrusive complex (PIC)-Hemlo greenstone belt system stands as a remarkable example of the dome-and-keel architecture that commonly occurs in Archean terrains. Abundant strain markers in the greenstone belt and in the Hemlo shear zone (HSZ) attest of late sinistral strike-slip kinematics (D 2 ) whereas, in general, the quartzofeldspathic coarse-grained rocks of the Pukaskwa intrusive complex bear little macroscopically visible kinematic indicators, most likely due to pervasive recrystallization. The PIC consists dominantly of a heterogeneous assemblage of TTG plutonic rocks and gneisses, which overall are less dense than the greenstone rocks. The study of anisotropy of magnetic susceptibility (AMS), based on 120 stations and 1947 specimens from the PIC, reveals east-west trending prolate and plano-linear fabrics across the northern margin of the complex, i.e., along the HSZ. Since geotherms were higher in the Archean than in the present, the effective viscosity of the TTG units would have been sufficiently low to allow their diapiric ascent through denser greenstone rocks. Here we propose an alternative model where thrust tectonics is responsible for the early structuration of the PIC. Later transpressive tectonics causes strain localization along internal strike-slip shear zones and along lithological boundaries.

Emplacement and Deformation of Mesozoic Gabbros of the High Atlas (Morocco): Paleomagnetism and Magnetic Fabrics

“…When the magma reaches the ductile level during its ascent, expansion and replacing of the ductile level occurs, forming laccolith‐shaped bodies, as shown in analogue models of sand‐silicone systems (Román‐Berdiel, ; Roman‐Berdiel et al, , ). The magnetic fabric acquired during magma solidification, blocked around 800°C when the plastic flow ceases (Tarling & Hrouda, ), can respond to (i) external tectonic control, determining the strain field in the region during magma emplacement and the kinematic framework controlled by its structural setting (Antolín‐Tomás et al, ; Aranguren et al, ; Bouchez & Gleizes, ; Bouchez et al, ; Izquierdo‐Llavall et al, ; Liodas et al, ; Román‐Berdiel et al, ) and (ii) internal flow mechanisms not directly related to the strain conditions but rather to the behavior of magma within the magmatic chamber (Archanjo et al , ; Ferré et al, ; Maes et al, ).…”

Configuration of Late Archaean Chilimanzi and Razi Suites of Granites, South-Central Zimbabwe Craton, From Gravity Modelling: Geotectonic Implications

“…The intrusion of volumetrically large Late Archaean granites (Sylvester 1994;Moyen et al 2003) is important for a number of reasons; for example, Archaean tectonics (e.g., Zegers 2004;Lopez et al 2006;Liodas et al 2013;Laurent et al 2014;Halla et al 2017), crust-mantle coupling (e.g., Berger and Rollinson 1997;Zeh et al 2009), local and regional seismicity (Singh et al, 2004), and mineralisation control (e.g., Cassidy et al 1998;Duuring et al 2007;Lin and Beakhouse 2013;Yang 2014). In the Zimbabwe craton (ZC), the intrusion of the ~2.6 Ga Chilimanzi and Razi suites represent the stabilisation of the Zimbabwe craton (e.g., Jelsma et al 1996;Horstwood et al 1999;Jelsma and Dirks 2002;Oberthur et al 2002;Siegesmund et al 2002).…”