Volcanic stratigraphy, petrology and geochemistry of the Marystown Group; Burin Peninsula, Newfoundland

O'Brien, S. J. (Sean James) (1979) Volcanic stratigraphy, petrology and geochemistry of the Marystown Group; Burin Peninsula, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Marystown Group forms the southern extent of the Late Precambrian volcanic field which underlies much of the western Avalon Zone of Newfoundland. The Marystown Group is faulted against older submarine volcanic and sedimentary rocks of the Burin and Rock Harbour Groups and is disconformably overlain by Eocambrian to Cambrian strata of the Fortune Group. -- The Marystown Group has been divided into seven separate stratigraphic units. In ascending stratigraphic order, these include: (1) Taylor's Bay Formation, (2) Garnish Formation, (3) Calmer Formation, (4, 5 and 6) Barasway Complex and the Hare Hills and Mount Saint Anne Formations (which are interpreted as being correlative), (7) Grand Beach Complex. The evolution of the Marystown Group includes three main volcanologically, petrologically and geochemically separate intervals. The earliest period of volcanism, represented by the Taylor's Bay Formation, produced a sequence of subaqueous and subaerial, basaltic to rhyolitic volcanic rocks of calc-alkaline to mild tholeiitic affinities. The Garnish and Calmer Formations together mark the onset of subaerial sedimentation and extrusion of extensive flood basalt fields of alkaline affinity. A period of felsic, subaerial volcanism represented by the Mount Saint Anne and Hare Hills Formations and the Barasway Complex marks the latest stage of evolution of the Marystown Group. The Grand Beach Complex is stratigraphically similar to the late felsic units of the rest of the Marystown Group but displays unique chemical features. -- The main structural features of the Marystown Group are interpreted to be the result of an orogenic event which post-dates the deposition of Cambrian rocks and pre-dates the intrusion of the lower Carboniferous St. Lawrence Granite. Recent geochronological results suggest that the main deformation is the result of the Acadian Orogeny. Late stage regional flexuring and related north-south and northwest-southeast faulting may represent the latest effects of the Acadian Orogeny or possibly the onset of the Variscan (or Hercynian) orogenic episode. -- The internal stratigraphy of the Marystown Group coincides with late Precambrian volcanic sequences elsewhere in the western Avalon Zone of Newfoundland. Petrological and geochemical variations within the Marystown Group are similar to those documented in the Love Cove Group of the northwestern Avalon Zone. The tectonic significance of these variations is unclear. Similar geochemical trends have been documented in the Cenozoic evolution of the southwestern U.S.A.

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