Source and tectono-metamorphic evolution of mafic and pelitic metasedimentary rocks from the central Quetico metasedimentary belt, Archean Superior Province of Canada

Abstract

To cite this version:Franck Valli, Stéphane Guillot, Kéiko Hattori. Source and tectono-metamorphic evolution of mafic and pelitic metasedimentary rocks from the central Quetico metasedimentary belt, Archean Superior Province of Canada.. Precambrian Research, Elsevier, 2004, 132, pp.155-177. <hal AbstractA study of the Jean Lake area of the Quetico metasedimentary belt, Superior Province, Canada, was conducted in order to evaluate the origin, source and evolution of sedimentary rocks, including mafic rocks previously mapped as ultramafics rocks. Bulk chemical compositions of these rocks show a mixing with two end members: quartzo-feldspathic sediments and komatiitic basalts. High CaO and MgO contents of the rocks suggest a proximal source of komatiitic basalts, probably from the southern Wabigoon subprovince.The rocks in the Jean Lake area record a pressure-temperature (P-T) path with three tectonometamorphic stages. The first stage formed staurolite (500-700°C) under medium P-T (MP-MT) metamorphic conditions shortly after the sedimentation. The second stage yielded the biotitesillimanite-garnet assemblage under the peak condition of 0.6  0.1 GPa and 700  70°C during transpressional deformation. The third stage, low P-medium T (0.25  0.11 GPa, 540  80°C) metamorphism, was associated with regional south-southeast compression and its timing is constrained by a new U-Th-Pb monazite age of 2667  20 Ma. Combining the regional deformation events, we suggest that the sediments in the Jean Lake area were buried up to MP-MT conditions during the D1 deformation at 2698-2689 Ma. They attained the peak metamorphic condition during the regional transpressive D2-D3 deformation (2689-2671 Ma), and retrograded to LP-MT condition during the south-southeast compression of the regional D4 at 2671-2667 Ma.The tectono-metamorphic history of the study area is consistent with the sedimentation in an accretionary prism followed by its docking to the Wabigoon subprovince to the north and Wawa greenstone belt to the south. The P-T-time path of this Archean accretionary prism is similar to that in modern arc accretion systems, except for a higher temperature gradient, ~ 30°C/km, recorded in the Quetico belt compared to ~10°C/km in modern counterparts. The high temperature gradients in the Quetico belt explain the lack of high-pressure metamorphic rocks, such as blueschist, that are common in modern accretionary prisms.

Rapid evolution from sediment to anatectic granulite in an Archean continental collision zone: the example of the Bandelierkop Formation metapelites, South Marginal Zone, Limpopo Belt, South Africa

“…The metamorphic record represents a powerful tool for understanding both present‐day and ancient geodynamic processes and has considerable potential to contribute to our understanding of Archean geodynamic processes. Well‐constrained P–T–t paths exist for specific metamorphic events within major Archean provinces such as the Superior Province, Canada (Easton, ; Valli et al ., ; Benn, ; Percival & Helmstaedt, ) and Yilgarn craton, Australia (Goleby et al ., ; Goscombe et al ., ). The addition of seismic profiles through the crust in these areas (Drummond et al ., ; Ludden & Hynes, ) provides strong evidence supporting the idea that horizontal tectonic processes resulted in the successive lateral accretion of individual blocks or volcanic arcs at c .…”

Subduction Zone Geodynamics

“…The absence of older blueschists may be ascribed to overprinting by subsequent metamorphism or probably to hotter Earth during Archean and early Proterozoic time. Valli et al (2004) estimated a geothermal gradient of 30°C/km for a Late Archean subduction zone and Moyen et al (2006) reported a 3.2 Ga garnetbearing amphibolite (1.2-1.5 GPa) from an arguably 15°/km subduction zone, similar to those observed during the Late Proterozoic (Maruyama et al, 1996). Valli et al (2004) estimated a geothermal gradient of 30°C/km for a Late Archean subduction zone and Moyen et al (2006) reported a 3.2 Ga garnetbearing amphibolite (1.2-1.5 GPa) from an arguably 15°/km subduction zone, similar to those observed during the Late Proterozoic (Maruyama et al, 1996).…”