DEVELOPMENT OF INVERTED METAMORPHIC GRADIENT IN THE INTERNAL DOMAIN OF THE TACONIAN BELT, GASPE PENINSULA

The Mont Logan Nappe is part of the Taconian internal domain of the Qu ebec Appalachians, and is entirely made up of synrift to passive margi n clastics and volcanics of the Shickshock Group. Rocks of the Mont Lo gan Nappe were affected by both Taconian and Acadian deformations but regional prograde metamorphism is Taconian and limited to the D1 defor mational event. Thermobarometry and mineral assemblages indicate that the metasedimentary and metavolcanic rocks of the Mont Logan Nappe hav e recorded peak temperatures in the range 610-700-degrees-C under pres sures of approximately 600-700 MPa, and that prograde metamorphism was accompanied by the development of an inverted metamorphic gradient of -40 to -75-degrees-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.