1988 Annual Technical Meeting: Geological Association of Canada Newfoundland Section

Document generated on 09/27/2021 11 a.m. Atlantic Geology 1988 Annual Technical Meeting Geological Association of Canada Newfoundland Section Volume 24, Number 2, August 1988 URI: https://id.erudit.org/iderudit/ageo24_2abs02 See table of contents Publisher(s) Atlantic Geoscience Society ISSN 0843-5561 (print) 1718-7885 (digital) Explore this journal Cite this document (1988). 1988 Annual Technical Meeting: Geological Association of Canada Newfoundland Section. Atlantic Geology, 24(2), 219–223. All rights reserved © Atlantic Geology, 1988 This document is protected by copyright law. Use of the services of Érudit (including reproduction) is subject to its terms and conditions, which can be viewed online. https://apropos.erudit.org/en/users/policy-on-use/ This article is disseminated and preserved by Érudit. Érudit is a non-profit inter-university consortium of the Université de Montréal, Université Laval, and the Université du Québec à Montréal. Its mission is to promote and disseminate research. https://www.erudit.org/en/ MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 219 GEOLOGICAL ASSOCIATION OF CANADA NEWFOUNDLAND SECTION ABSTRACTS 1988 ANNUAL TECHNICAL MEETING FEBRUARY 12-13,1988 MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 24,219-223 (1988) 0711-1150/88/020219-5$! .75/0 220 ABSTRACTS Sediment-hosted Manganese in Newfoundland: settings and significance John W. Botsford Centre for Earth Resources Research, Memorial University of Newfoundland St. John’s, Newfoundland A1B 3X5 Sediment-hosted manganese occurs in three principal set The sedimentary concentration of manganese is a redox- tings in Newfoundland: (1) an earliest Midle Cambrian shallow driven process which requires an Eh gradient to facilitate mobi marine sequence within the Avalon zone, (2) allochthonous lization and subsequent precipitation. In the Cambrian, levels of Lower Ordovician slope sequences within the Humber zone, and dissolved oxygen sufficient to facilitate Mn precipitation were (3) Ordovician oceanic sequences within the Dunnage zone in only widespread in the shallow marine environment. The later, central Newfoundland. The Avalon occurrences appear at the deep water occurrences are consistent with an episode of “oce disconformable base of the Middle Cambrian, and consist of anic ventilation” in the Early Ordovician. This resulted in an Eh nodules and thin beds of Mn-carbonate within shale. In the deep gradient at the seafloor which promoted precipitation during water slope sequences of western Newfoundland, Mn precipita early diagenesis. Metamorphosed manganiferous beds (cotic- tion was localized in a late Tremadoc to Arenig interval along ules) within the Appalachian-Caledonian orogen have been portions of the margin. Here Mn-carbonate was precipitated as correlated with the enrichment of other metals and are commonly discrete horizons within shale during shallow-burial diagenesis. of inferred Early and Middle Ordovician age. While these may Central Newfoundland examples also appear in the Lower Ordo relate, in part, to an overall increase in hydrothermal activity they vician, but are most common in deep-ocean chert/shale se may also reflect early, redox-related redistribution of metals in quences of Caradocian age, where Mn-carbonate and silicate oceanic sedimentary sequences. occurs in intervals up to 50 m thick. Thin-skinned Thrust Tectonics along the Grenville Front, Western Labrador Dennis L. Brown Department of Earth Sciences, Memorial University of Newfoundland St. John's, Newfoundland A1B 3X5 The Emma Lake area lies within the Grenville Front Zone in ness is less than 400 m. Thrusts developed as ductile shear zones the parautochthon of the Grenville Province in western Labrador. with southeast-dipping, southeast-plunging penetrative C-S-L In the Emma Lake area Archean crystalline basement rocks of the fabrics. Northwest-verging, northeast- plunging mesoscopic F, Ashuanipi Metamorphic Complex and Lower Proterozoic su- folds above hangingwall ramps have a fold nappe geometry. pracrustal sequences of the Knob Lake Group were folded and Locally, mesoscopic F2 folds refold earlier F, folds about a thrusted northwestward during the Grenville Orogeny. The map shallow, northeast-plunging fold axis. pattern represents an oblique section through the thrust stack, Grenvillian metamorphic grade in the Emma Lake duplex is allowing for the construction of true profiles of the stack using upper-greenschist facies. Kenoran granulite facies basement down-plunge view projection. The geometry of the thrust stack rocks were retrogressed along shear zones to biotite-rich mylo- is that of a northeast-plunging duplex with extensive basement nites and phyllonites, whereas the Lower Proterozoic cover involvement This is the first time a duplex has been recognized sequence underwent prograde metamorphism. Exchange geoth- in the Grenville Front Zone. ermobarometry was conducted on the Menihek Formation, a Horses in the duplex are thickest, typically 50 to 100 m, biotite - chlorite - garnet semipelitic schist of the Knob Lake where they contain basement rocks; the combined duplex thick Group. Extensional Tectonics in Compressional Orogens: Late-stage Gravity Sliding of Ophiolite Thrust Sheets in Oman and W estern Newfoundland Peter A. Cawood and Harold Williams Department of Earth Sciences, Memorial University of Newfoundland St. John's, Newfoundland A1B 3X5 Ophiolite complexes in Oman and western Newfoundland continental margin rocks. The transported rocks overlie contem- are the highest slices in transported stacks of ocean basin and porary passive margin carbonates and their continental base- MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 221 ment. Overall lithologic and structural relations indicate assem the ophiolite sheets. Remobilization of the Oman and west bly and emplacement of the transported rocks by foreland propa Newfoundland ophiolites coincides, or immediately post-dates, gating thrusts. Ophiolite slivers show additional evidence for basement thrusting and culmination formation. The ophiolites further transport after initial emplacement. Basal fault surfaces are interpreted to have moved from the crest of these culmina are sub-horizontal and show an overall extensional geometry, tions to the adjacent depressions on gravity-drive slide surfaces. cutting down through underlying rock units and imbricate fault In Oman, culmination formation and gravity sliding took place surfaces. Locally, the entire underlying imbricate stack has been during the Late Cretaceous Alpine Orogeny and immediately structurally removed and the ophiolites rest directly on shelf post-date ophiolite obduction (arc/continent collision). In carbonates. The ophiolite sheets are broken into a series of plates Newfoundland, ophiolite obduction and allochthon emplace or blocks which occupy depressions adjacent to major structural ment coincide with the Ordovician Taconian Orogeny but culmi culminations. The culminations were generated by late-stage nation formation and gravity sliding did not take place until the thrusting along a sole thrust lying in continental basement. Devonian Acadian Orogeny. Structures generated during basement thrusting are truncated by Melt generation and evolution in Ophiolite Mantle and the development of mantle heterogeneities Stephen J. Edwards Department of Earth Sciences, Memorial University of Newfoundland St. John’s, Newfoundland AIB 3X5 Mantle-derived melts are processed through a highly com during on-going mantle flow, with the result that the segregations plex system prior to their consolidation in the crust and conse were transported within high strain domains away from their quently, primary magmas are unlikely to be preserved. Prelimi original regime of formation. Within the mantle sequence, four nary studies of the segregations found in the tectonized mantle types of lherzolite are distinguishable: (i) primary lherzolite, (ii) harzburgites of the Lewis Hills and Table Mountain massifs, Bay melt-infiltrated harzburgite or dunite, (iii) deformed and recrys of Islands Ophiolite, indicate that they occur as bodies of dunite, tallized olivine-, orthopyroxene- and clinopyroxene-bearing orthopyroxenite, clinopyroxenite (containing native Cu and Fe- segregations, and (iv) harzburgite metasomatized during ophio Ni sulphides), websterite, lherzolite, harzburgite, wehrlite and lite Obduction and emplacement. Only types (i), (ii) and (iii) can gabbro. These bodies exhibit cumulate textures with a tectonite be considered as source rocks for basalt production in the ocean overprint and are assumed to represent totally or partially crystal basins, and although initial primary magmas might be generated lized melts of fairly primitive composition; some dunites are, from mantle which may be homogeneous, later generations of however, residues left after partial melting. Primary magmas primary magma will be produced from heterogeneous mantle. should exist as totally crystallized in situ partial melts, but will Banding and layering are both present in this heterogeneous only be preserved if they acted as closed systems contained mantle which is charged with pockets of trapped melt within low strain domains of ascending diapirs. Low strain domains are rarely preserved and segregations are frequently This abstract was recently presented in Cyprus as part of a poster boudinaged and enveloped by mylonitic harzburgite. Conse display at the symposium; Troodos 87, Ophiolites and Oceanic quently, the melts must have solidified to relatively rigid bodies Lithosphere.

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