Giant granulite terranes of northeastern Superior Province: the Ashuanipi complex and Minto block

Abstract

The Ashuanipi complex and Minto block of the Superior Province are large regions that have been classified as "high-grade gneiss" terranes on the basis of the presence of orthopyroxene-bearing units. Like the granite-greenstone and metasedimentary subprovinces of the southern Superior Province, the two terranes consist predominantly of intrusive rocks, but are distinguished by their primary magmatic orthopyroxene. Both "high-grade" and "gneiss" are misnomers because granulite-facies gneisses are only sparingly present and the regions consist dominantly of massive, unmetamorphosed plutonic rock.The Ashuanipi complex consists of a deformed, metamorphosed package of metasedimentary rocks and primitive, early tonalite cut by widespread orthopyroxene + garnet granodiorite (diatexite), as well as plutons of tonalite, granite, and syenite.Based on its lithological and chronological similarity and on-strike position, the complex appears to be the continuation of metasedimentary subprovinces such as the Quetico. Its evolution involved deposition of immature greywacke in an accretionary prism, early arc (tonalitic) magmatism and deformation, followed by widespread intracrustal magmatism in the period 2700-2670 Ma. Both metamorphic and igneous rocks record equilibration under granulite-facies conditions (700-835°C; 0.35-0.65 GPa; a,,,, -0.3) and indicate exposure levels of -20 km. The Minto block at the latitude of Leaf River consists of several north-northwest-trending domains of similar scale and diversity to the east-trending subprovinces of the southern Superior Province. The central Goudalie domain is dominantly amphibolite-facies tonalitic rocks including some with ages > 3 Ga, with small belts of volcanic and sedimentary origin. Lake Minto domain contains poorly preserved supracrustal remnants in a plutonic complex comprising hornblende granodiorite, clinopyroxene + orthopyroxene granodiorite, orthopyroxene-biotite diatexite, and granite. The hornblende granodiorite suite constitutes most of the Utsalik and Tikkerutuk domains and is thought to represent continental arc magmatism. On the basis of their distinct aeromagnetic and lithological character, two additional domains are evident north of the Leaf River area, the Inukjuak domain in the west and the Douglas Harbour domain in the east.The northerly grain of the Minto block appears to have been established in situ with respect to the easterly belts of the southern Superior Province (i.e., no large-scale block rotation) during the same interval of time (3.0-2.7 Ga). Modification of the tectonic framework for the Superior Province is required to explain Minto arc magmatism. In the interval -2730-2690 Ma ago, a continental magmatic arc built the Berens River and Bienville subprovinces and Minto block on the southern and eastern edges, respectively, of a northern protocratonic foundation. In the same period, primitive volcanic arcs and accretionary prisms developed outboard on oceanic crust and were accreted to form a southern tectonic regime.Le complexe d'Ashuanipi et...

Age and isotopic geochemical characteristics of Archean carbonatites and alkaline rocks of the Baltic shield

“…According to the first model, the synformal structure of the Minto Block resulted from bilateral subduction beneath the Mesoarchaean crust [Percival et al, 1992Percival, Skulski, 2000]. The second model is based on the data from sapphirine-bearing xenoliths in the enderbite of the Minto granulite complex, which suggests a pressure between 7.5 and 14 kbar (24-46 km) and a very high temperature (755-1260 °C).…”

Neoarchean Mantle-derived Magmatism within the Repulse Bay Block, Melville Peninsula, Nunavut: Implications for Archean Crustal Extraction and Cratonization

“…Giant high grade Neoarchean terranes are commonly exposed within the Superior Province, occurring at the margins of the craton or between granite-greenstone terranes (Percival et al 1992). The Pikwitonei Granulite domain of the northwest Superior Province exposes anhydrous granulite intrusions that formed in the Mesoarchean (3.4-3.0 Ga) and Neoarchean (2.72-2.64 Ga).…”

Formation and evolution of granite magmas from migmatites :

“…1) of Québec is located at the northeastern end of a 2000 km long metasedimentary belt that crosses the entire Archaean Superior province (Card & Ciesielski 1986;Percival et al 1992). It is bounded to the east by early Proterozoic rocks of the Labrador Trough, and to the southeast by Archaean and Proterozoic rocks reworked during the Grenville Orogeny.…”

“…1 (Percival & Sullivan 1988;Davis et al 1990;Fralick & Davies 1999;Zaleski et al 1999). Percival et al (1992) argued for a similar age of sediment deposition in the Ashuanipi subprovince, bracketed by the youngest detrital zircons, 2700 Ma, and the 2690 Ma zircon crystallization age (Percival 1991a;Chevé & BrouiUette 1991) of the Desliens igneous suite that intrudes them. In contrast, the age of sediment deposition in the Opinaca and Nemiscau subprovinces is poorly constrained.…”

“…The major and selected trace element contents of some 61 diatexite migmatites ( The geochemical variation diagrams also contain data from the 18 diatexites given in Percival (1992) and 6 from Lapointe (1996), which were sampled further north in the Ashuanipi (see appendix VII). First of all, general trends that represent the Ashuanipi diatexites will be described, then particular compositional peculiarities will be discussed.…”