Polymetamorphism of marbles in the Morin terrane, Grenville Province, Quebec

Abstract

The Morin terrane (Grenville Province, Quebec) is dominated by the 1.15 Ga Morin Anorthosite Massif and related granitic intrusions, all of which exhibit granulite-facies mineral assemblages. Anorthosite-suite rocks are deformed both in shear zones and in the interior of the terrane and show intrusive contact relations with marble along road cuts near the village of St. Jovite. Intrusive rocks exposed in these road cuts have well-developed skarns, which were deformed with the intrusions after emplacement. Skarn minerals are consumed by garnet-forming reactions (e.g., An + Wo = Gr + Qtz) that preserve granulite-facies temperatures and pressures. Calcite–graphite thermometry of Morin terrane marbles records temperatures of 755 ± 38 °C (n = 21), independent of proximity to anorthosite-suite plutons. Preserved metamorphic conditions and the retrograde pressure–temperature (P–T) path in the Morin terrane are very similar to conditions during the 1.07 Ga Ottawan orogeny in the Adirondack Highlands. Metamorphism and deformation of anorthosite-suite rocks and marbles of the Morin terrane are consistent with anorthosite intrusion followed by a distinct granulite-facies overprint.