Archean Ultramafic Flows in Munro Township, Ontario

Research Article| March 01, 1973 Archean Ultramafic Flows in Munro Township, Ontario D. R. PYKE; D. R. PYKE 1Ontario Division of Mines, Geological Branch, Whitney Block, Queen's Park, Toronto, Ontario, Canada Search for other works by this author on: GSW Google Scholar A. J. NALDRETT; A. J. NALDRETT 2Department of Geology, University of Toronto, Toronto, Ontario, Canada Search for other works by this author on: GSW Google Scholar O. R. ECKSTRAND O. R. ECKSTRAND 3Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada Search for other works by this author on: GSW Google Scholar GSA Bulletin (1973) 84 (3): 955–978. https://doi.org/10.1130/0016-7606(1973)842.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation D. R. PYKE, A. J. NALDRETT, O. R. ECKSTRAND; Archean Ultramafic Flows in Munro Township, Ontario. GSA Bulletin 1973;; 84 (3): 955–978. doi: https://doi.org/10.1130/0016-7606(1973)842.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A unique exposure within the Abitibi orogenic belt of northeastern Ontario provides an exceptionally clear view of early Precambrian (Archean) ultramafic volcanic rocks. Approximately 60 ultramafic flow units are exposed over a stratigraphic thickness of 125 m. Individual flow units range in thickness from 0.5 to 15 m, average about 3 m, and display remarkable strike lengths and internal structure, which suggest extreme fluidity.The upper margin of the flow units (0.1 to 1.0 m) is thicker than the lower margin (about 1 cm), and the upper margin is highly fractured, thereby providing an easily recognizable top determinator. Many flow units contain a zone of spinifex, ranging in width from zero to 5 m, which underlies and is gradational with the flow top. Spinifex is a textural term to describe an array of criss-crossing sheafs or booklets characterized by numerous closely spaced and parallel blade- or plate-like crystals of olivine. The texture is generally accepted as having formed by rapid cooling of a crystal-free ultramafic liquid in situ. The variation in size of bladed olivine crystals within a spinifex zone is always from coarse (up to 1 m long) at the bottom to fine at the top, thereby providing a primary top determination. In flow units not containing a spinifex zone the chilled and fractured flow top grades downward into a zone of moderately foliated peridotite which generally constitutes the remaining part of a flow unit.Chemically, the flow units resemble similar ultramafic rocks described from northeastern Ontario, western Australia, and the Barberton area of South Africa; one unique feature is the exceptionally high alumina content of the clinopyroxene This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.