Relationship among rock groups within and beneath the Humber Arm Allochthon at Fox Island River, western Newfoundland

• Main Author: Schillereff, Herbert Scott
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1980
• Subjects: Newfoundland
• Online Access: https://research.library.mun.ca/6883/; https://research.library.mun.ca/6883/1/HerbertScottSchillereff_2.pdf; https://research.library.mun.ca/6883/3/HerbertScottSchillereff_2.pdf

Middle Cambrian to Middle Ordovician sedimentary and igneous rocks comprise three separate structural slices and two distinct melange zones within the southern part of the Humber Arm Allochthon at Fox Island River, western Newfoundland. These overlie a Cambro-Ordovician platformal carbonate sequence in a stratigraphic-structural succession as follows: -- a) autochthonous Lower Cambrian to Middle Ordovician carbonate sequence, with a prominent Middle Ordovician carbonate breccia and shale unit at its top; -- b) autochthonous Middle Ordovician clastic flysch unit; -- c) Basal Melange, consisting of sedimentary blocks in a shaly matrix; -- d) allochthonous Middle Cambrian to Middle Ordovician sediments and structurally associated mafic volcanics which collectively comprise the lowermost slices of the Humber Arm Allochthon; -- e) Medial Melange, consisting of sedimentary, volcanic and gabbroic blocks in a shaly and tuffaceous matrix; -- f) allochthonous Lower Ordovician and older mafic volcanics which form a small medial slice; -- g) allochthonous Upper Cambrian ophiolitic rocks which form the uppermost slice of the allochthon. -- These rocks are covered by Carboniferous sediments and Pleistocene glacial deposits. -- The structural succession is interpreted according to the model of a stable Atlantic-type continental margin destroyed by ophiolite obduction and westerly transport of rock units during the Taconic Orogeny. A three-part history of obduction, uplift and final gravity-sliding is recognized. The components and age of easterly-derived flysch units and the melange zones suggests that during emplacement, the uppermost volcanic and ophiolitic slices began final westward gravity-sliding first, but that the lowermost sedimentary slice assemblage was detached soon thereafter and was first to arrive in the map-area. -- Pre-emplacement deformation consists of metamorphic tectonism within and fragmentation at the base of the ophiolitic slice. Emplacement-related deformation consists of phacoidal melange cleavages ...