The Saint‐Daniel Melange: Evolution of an accretionary complex in the Dunnage Terrane of the Quebec Appalachians

Abstract

The Saint‐Daniel Mélange is part of a series of mélanges located along the Baie Verte‐Brompton line in the Northern Appalachians. This line marks the suture between rocks of oceanic affinities and those of the ancient passive margin of North America with which they collided during the Taconian (Middle to Late Ordovician) orogeny. The Saint‐Daniel Mélange contains a wide variety of lithologies including well‐bedded to dismembered sedimentary sequences, pebbly mudstone, olistostromes, and slivers of igneous and metamorphic rocks. Black shales with interbeds of green shale, calcareous siltstone, or sandstone are the dominant units. They exhibit various stages of mélange formation such as those present in shallow parts of an accretionary complex. Units of oceanic origin include sediments derived from the forearc basin and slivers of an ophiolite and of a magmatic arc. Units derived from sediments of the passive margin of North America are also present. The ratio between these various lithologies changes greatly within the mélange on a kilometric scale along strike. The Saint‐Daniel Mélange is a structural complex in which the various units were assigned a sequential order mimicking a stratigraphic order. The Saint‐Daniel Mélange is interpreted as the relict of an accretionary complex because of its actual structural position within the Northern Appalachians and because all its lithologies and their structural fabric can be found in modern accretionary complexes.