Metamorphism and geothermometry near Coniston, Ontario; a clue to the tectonic evolution of the Grenville Front

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doi: 10.1139/e81-085
Authors:La Tour, Timothy E.
Author Affiliations:Primary:
Univ. West. Ont., Geol. Dep., London, ON, Canada
Volume Title:Canadian Journal of Earth Sciences Revue Canadienne des Sciences de la Terre
Source:Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre, 18(5), p.884-898. Publisher: National Research Council of Canada, Ottawa, ON, Canada. ISSN: 0008-4077
Publication Date:1981
Note:In English with French summary. 43 refs.; illus. incl. 4 anals., 3 tables, geol. sketch maps
Summary:The staurolite and sillimanite isograds at the Grenville front near Coniston coincide with two discrete mylonite zones, MZ I and MZ II. MZ I is characterized by mylonitic fabrics and is associated with retrograde metamorphic features; MZ II is characterized by blastomylonitic fabrics and prograde metamorphic features. Garnet-biotite geothermometry yields approx 540oC for staurolite grade rocks and approx 610oC for sillimanite grade. The spatial distribution of outcrops indicates an improbably high thermal gradient of 114oC/m, which can be reconciled by recognizing that the mylonite zones represent structural discontinuities in a terrain of normal gradient. MZ II is probably the older zone, formed at or near the peak of metamorphism during sustained heat flow and crustal thickening. MZ I formed later as T waned. The close proximity of the two zones reflects episodic or continuous deformation confined by the NW boundary of the Grenville mobile belt. [P.Br.]
Subjects:Biotite; Data; Garnet group; Geochemistry; Geologic thermometry; Grade; Isograds; Metamorphic rocks; Metamorphism; Metapelite; Metasedimentary rocks; Mica group; Mineral assemblages; Mylonites; Nesosilicates; Orthosilicates; P-T conditions; Petrology; Phase equilibria; Sheet silicates; Silicates; Tectonics; Temperature; Zoning; Canada; Canadian Shield; Eastern Canada; Grenville Front; North America; Ontario; Coniston
Coordinates:N462500 N463500 W0804500 W0805500
Abstract Numbers:82M/0942
Record ID:1981052659
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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