Geologic history of the Saguenay region, Quebec (Central Granulite Terrain of the Grenville Province): a working hypothesis

Abstract

The Saguenay region is divided into three lithostructural units, namely (1) a gneiss complex; (2) batholithic anorthosite and mangerite complexes; and (3) late- to post-kinematic plutons. Three age groups of rocks in the gneiss complex are defined by increasing complexity of structure and mobilizates. Rocks of age group I (paragneiss, granite I) show extremely complex structure and contain three generations of mobilizates. Structures in rocks of age group II (granite II, amphibolite II dykes) are less complex and two generations of mobilizates are present. Rocks of age group III (granite III, amphibolite III dykes) contain one foliation and one generation of mobilizates. Metamorphosed mafic dykes are stratigraphic markers permitting correlation of age groups over vast tracts of terrain.Well-preserved igneous structures (cumulate layering) and textures (cumulate textures, ophitic textures) prove that anorthosite and mangerite crystallized from magmas. Anorthosite has been granulated and foliated, metamorphosed at high pressure with formation of orthopyroxene–spinel coronas by reaction of olivine and plagioclase, and intruded by three successive generations of mafic dykes (diorite, leucotroctolite, amphibolite IIIa).Mineral associations in the gneiss complex suggest metamorphism during slow cooling at about 5 kbar (500 MPa) pressure. Successive mineral associations in anorthosite and its cross-cutting dykes suggest a history of decreasing pressure (from >7–9 kbar (700–900 MPa)) and temperature (from 1200–1400 °C). Thus the anorthosite was emplaced at its present level by diapirism. Structures in the gneiss complex and anorthosite are consistent with the model of diapiric rise of anorthosite and mangerite plutons, but suggest presence of a generation of orogenic structures prior to diapirism.

Structural hydrogeology in the Kenogami uplands, Quebec, Canada /

“…The oldest geologic events identified in the Saguenay area occurred between 1900 and 1000Ma (Stockwell 1962;Dimroth et al 1981;Hébert 2004;Roy et al 2006). This period corresponds approximately to the formation of the oldest worldwide orogenic belts and of the amalgamation and dispersion of the supercontinent Columbia 3 (Santosh et al 2009).…”

“…The formation of Rodinia is related to the consuming plate boundaries that dominated the site of Grenvillian Orogeny, especially at collisional belts. The Grenville Orogeny ended with the emplacement of the last igneous masses and their crystallization at their present level, with the development of ductile shear zones (oriented NNE, ESE and ENE to E-W; Du Berger et al 1991) cutting all Precambrian rocks (phase 3' in Table 3.1; Dimroth et al 1981).…”

Caracterisation hydrogeologique du massif rocheux a la Mine Niobec St-Honore Quebec

“…Ces intrusions calco-alcalines forment la troisième unité et sont caractérisées par des relations de recoupement avec les roches encaissantes et par une minéralogie du faciès amphibolite supérieur (Dimroth et al, 1981).…”

Les relations structurales autour du lobe anorthositique de St-Fulgence region du Saguenay

“…(Owen 1980(Owen , 1981 Woussen et al (1981) (Kehlenbeck 1972;Laurin et Sharma, 1975;Hocq, 1977;Woussen et al, 1981;Martin, 1983). Woussen et al (1981) et Dimroth et al (1981) reconnaissent à l'intérieur du massif trois générations différentes de dykes mafiques indiquant des conditions P et T de cristallisation décroissante, en allant vers les plus jeunes. Ceci témoigne que l'anorthosite est remontée dans la croûte terrestre à l'état solide ou suffisamment consolidée pour se faire injecter de dykes.…”

“…La carte géologique simplifiée de la figure 4 montre l'attitude gé-nérale des foliations qui ont tendance à épouser la forme du lobe, à ê-tre parallèles à celui-ci (pour plus de détails voir la carte géologique -Deuxième volet: Le rubanement ainsi que la majorité des structures présentes dans le gneiss tonalitique définissent la schistosité ré-gionale 2a (Owen 1980(Owen , 1981Dimroth et al 1981) 3-Le tout monte à l'état solide dans la croûte terrestre (Woussen et al 1981;Dimroth et al 1981). …”