The escoumins supracrustal belt: a record of Mesoproterozoic (Pinwarian) evolution of the Laurentian margin and Grenvillian magmatism, central Grenville Province, Quebec, Canada

Groulier, Pierre-Arthur (2019) The escoumins supracrustal belt: a record of Mesoproterozoic (Pinwarian) evolution of the Laurentian margin and Grenvillian magmatism, central Grenville Province, Quebec, Canada. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The Mesoproterozoic, Pinwarian-age (1.52 – 1.46 Ga) Escoumins supracrustal belt (southern central Grenville Province, Quebec) consists of a volcano-sedimentary sequence (Saint-Siméon Group) and its structural basement (Tadoussac Intrusive Suite), both deformed and metamorphosed to the amphibolite-facies during the Grenvillian orogeny (1.09 – 0.98 Ga). It represents preserved parts of an island arc built on crustal slivers rifted away from the southeastern Laurentian margin during a major Geon 15 extensional event. Change in arc dynamics led to the closure of the previously opened seaway and back-arc basins and to the final accretion of the island arc at about 1.39 Ga, as marked by the emplacement of a major 1.43 – 1.37 Ga arc-related plutonic belt. The Saint-Siméon Group is an oceanic island arc, rifted-arc and back-arc volcano-sedimentary succession that despite deformation and metamorphism, preserves well original characteristics of the rocks. Its middle member (Moulin-à-Baude Formation) consists of highly evolved alkaline felsic to intermediate volcanic rocks and ferrobasalt together with island arc tholeiite, back-arc basalt and arc basaltic andesite interpreted to reflect the rifting of the arc. Some rocks were extensively altered by synvolcanic hydrothermal fluids and show mineral assemblages typical of metamorphosed VMS-type deposits. The supracrustal belt represents higher crustal levels of the orogenic infrastructure in the Grenville and was intruded by diverse types of syn-to late-orogenic plutons: (1) ca. 1.08 Ga crust-derived magnesian felsic magmatism at the onset of the continental collision, (2) ca. 1.06 – 1.04 Ga ferroan and Ba – Sr enriched intermediate to felsic plutons fractionated from a mafic magma derived from partial melting of a Geon 14 subduction-modified subcontinental lithospheric mantle coeval with amphibolite-facies metamorphism in the supracrustal rocks, and (3) ca. 0.99 – 0.98 Ga crust-derived peraluminous two-mica leucogranite bodies and pegmatite coeval with titanite growth and deformation. Despite the deformation and the metamorphic overprint, primary features are still preserved providing key information about the evolution of the southeastern Laurentian margin before the final continental collision. This study represents one of the first complete investigations of a polydeformed and metamorphosed volcano-sedimentary sequence and of its hydrothermal alteration assemblages within the Grenville Province.

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