Development of inverted metamorphic gradient in the internal domain of the Taconian belt, Gaspé Peninsula

Abstract

The Mont Logan Nappe is part of the Taconian internal domain of the Quebec Appalachians, and is entirely made up of synrift to passive margin elastics and volcanics of the Shickshock Group. Rocks of the Mont Logan Nappe were affected by both Taconian and Acadian deformations but regional prograde metamorphism is Taconian and limited to the D1 deformational event. Thermobarometry and mineral assemblages indicate that the metasedimentary and metavolcanic rocks of the Mont Logan Nappe have recorded peak temperatures in the range 610–700 °C under pressures of approximately 600–700 MPa, and that prograde metamorphism was accompanied by the development of an inverted metamorphic gradient of −40 to −75 °C/km. The preferred interpretation of the cause of the inverted gradient is dissipative heating accompanying deformation along an intracontinental synmetamorphic thrust fault located at the top of the inverted metamorphic sequence.

Inverted metamorphic field gradient towards a Variscan suture zone (Champtoceaux Complex, Armorican Massif, France)

“…, 1984, 1989; North‐western Spain: Arenas et al. , 1995), the Appalachian belt (Camiré, 1995), the Caledonian belt (Andreasson & Lagerblad, 1980; Mason, 1984; Boyle, 1987), the Canadian Cordillera (Gibson et al. , 1999) and the Californian range (Graham & England, 1976; Kidder & Ducea, 2006).…”

“…Bordet, 1961;Gansser, 1964;Le Fort, 1975;Macfarlane, 1995;Vannay & Grasemann, 1998;Guillot, 1999;Hodges, 2000;Dasgupta et al, 2004;Caddick et al, 2007;Kohn, 2008;Searle et al, 2008). Less well-known examples are found, amongst others, in the Variscan belt (Bohemian Massif: Suess, 1926;Sˇtı´pska´& Schulmann, 1995;Central France: Delorme et al, 1949;Rolin & Quenardel, 1980;Burg et al, 1984Burg et al, , 1989North-western Spain: Arenas et al, 1995), the Appalachian belt (Camire´, 1995), the Caledonian belt (Andreasson & Lagerblad, 1980;Mason, 1984;Boyle, 1987), the Canadian Cordillera (Gibson et al, 1999) and the Californian range (Graham & England, 1976;Kidder & Ducea, 2006). The observed inversion of metamorphic zones (the metamorphic grade increasing upward) is explained by either (i) a post-metamorphic deformation of a former normal sequence or (ii) a local transient inversion of the geothermal gradient.…”

Forward potential-field modeling of the Appalachian orogen in the Gaspe Peninsula (Quebec, Canada): Implications for the extent of rift magmatism and the geometry of the taconian orogenic wedge

“…The Mont Logan nappe is made up entirely of the allochthonous Shickshock Group, which is predominantly composed of Neoproterozoic to Cambrian subalkaline tholeiitic metabasalts with minor amounts (ϳ10%) of metasedimentary rocks (Camiré and others, 1995). These polydeformed rocks are metamorphosed to the greenschist facies, except near the Shickshock-Sud fault where they reach the amphibolite facies, the highest metamorphic grade found in the Québec Appalachians (Camiré, 1995).…”

A 40Ar/39Ar study of oceanic and continental deformation processes during an oblique collision: Taconian orogeny in the Quebec reentrant of the Canadian Appalachians

“…The Lac Cascapédia window, located between the Lac Cascapédia and the Shickshock Nord faults, is composed of greenschist facies mudrocks with some intercalated siltstone beds, metamorphic rocks correlative with sedimentary rocks of the external Humber zone (Orignal Formation of the Quebec Supergroup, see below; Figure 4). Regional metamorphism varies from greenschist facies in the north to amphibolite facies in the south, just north of the Shickshock Sud fault [ Mattinson , 1964; St‐Julien et al , 1990; Camiré , 1995].…”