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Canada's Craton Special 2008 Joint Meeting Brochure and Registration Form Inside! VOL. 18, No. 6 A PUBLICATION OF THE GEOLOGICAL SOCIETY OF AMERICA JUNE 2008 CCanada’sanada’s ccraton:raton: A bbottoms-upottoms-up vviewiew Comment: Impacts, mega-tsunami, and other Inside this issue: extraordinary claims, p. 11 Penrose Conference Scheduled, p. 46 It’s Not Just Software. It’s RockWare. For Over 24 Years. New Version! 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GWB Standard $3,499 $295 Commercial/$175 Academic Reaction Path Modeling Workbench The Geochemist’s Since 1983 303.278.3534 • 800.775.6745 AUTHORIZED BUSINESS RockWare.com PARTNER VOLUME 18, NUMBER 6 ▲ JUNE 2008 SCIENCE ARTICLE GSA TODAY publishes news and information for more than 20,000 GSA members and subscribing libraries. GSA Today lead science articles should present the results of exciting new research or summarize and synthesize important problems or issues, and they must be understandable to all in the 4 Canada’s craton: A bottoms-up view earth science community. Submit manuscripts online at Dante Canil www.geosociety.org/pubs/submit_ms.htm. GSA TODAY (ISSN 1052-5173 USPS 0456-530) is published 11 Cover: Polymetamorphic gneiss with an age of ca. times per year, monthly, with a combined April/May issue, by The Geological Society of America®, Inc., with offices at 3300 3.3 Ga from near Mackay Lake, in the central Archean Penrose Place, Boulder, Colorado. Mailing address: P.O. Box Slave Province, Canada. Diamondiferous kimberlites 9140, Boulder, CO 80301-9140, USA. Periodicals postage paid ascended through these basement gneisses and at Boulder, Colorado, and at additional mailing offices. Postmaster: Send address changes to GSA Today, GSA Sales sampled peridotite xenoliths from the underlying and Service, P.O. Box 9140, Boulder, CO 80301-9140. cratonic mantle root en route to the surface. Photo Copyright © 2008, The Geological Society of America (GSA). All courtesy of W. Bleeker, Geological Survey of Canada. rights reserved. Copyright not claimed on content prepared See “Canada’s craton: A bottoms-up view” by wholly by U.S. government employees within scope of their D. Canil, p. 4–10. employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in other subsequent works and to make unlimited photocopies of items in this journal for noncommercial use in classrooms to further education and science. For any other use, contact Copyright Permissions, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA, Fax +1-303-357-1073, [email protected]; 11 Comment: Impacts, mega-tsunami, and other extraordinary claims reference GSA Today, ISSN 1052-5173. Permission is granted to authors to post the abstracts only of their articles on their own or their organization’s Web site providing the posting includes HOUSTON 2008 JOINT ANNUAL MEETING this reference: “The full paper was published in The Geological Society of America’s journal GSA Today, [include year, month, 12 Exhibitors and page numbers if known, where the article will appear].” GSA provides this and other forums for the presentation of 13 Important Dates and Deadlines diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political 14 Field Trips viewpoint. Opinions presented in this publication do not reflect official positions of the Society. 16 Short Courses SUBSCRIPTIONS for 2008 calendar year: Society Members: GSA Today is provided as part of membership dues. Contact 23 K–12 Education Events GSA Sales and Service at +1-888-443-4472, +1-303-357-1000, option 3, or [email protected] for membership information. 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Hess 30 Technical Sessions Science Editors: Stephen T. Johnston, University of Victoria, School of Earth & Ocean Sciences, Victoria, British Columbia V8W 3P6, Canada, [email protected], and David E. Fastovsky, University of Rhode Island, Department of 46 Penrose Conference Scheduled—Plumes and Their Role in Whole Geosciences, Woodward Hall, Rm. 317, Kingston, Rhode Mantle Convection and Recycling Island 02881, USA, [email protected]. Director of Publications: Jon Olsen Managing Editor: Kristen E. Asmus, [email protected] 47 33rd IGC—Redefinition of the Quaternary and Pleistocene Editorial Staff: Kathryn Roche, April Leo Production Coordinator: Margo Y. Sajban 50 GSA Strengthen Its Presence in Washington Graphics Production: Margo Y. Sajban ADVERTISING: Classifieds & Display: Ann Crawford, +1-800-472-1988, ext. 1053, 52 Call for GSA Committee Service +1-303-357-1053, Fax +1-303-357-1070; [email protected] 53 GSA Committees: Progress through Service—Committee GSA ONLINE: www.geosociety.org on Membership Printed in the USA using pure soy inks. 55 GSA Committees: Progress through Service—Professional 50% Total Recovered Fiber Development Committee 10% Postconsumer 61 Classified Advertising 62 Journal Highlights GSA celebrates our three-year association with the International Year of Planet Earth. Canada’s craton: A bottoms-up view Dante Canil, School of Earth and Ocean Sciences, University (giga-annum [Ga]). Thirty-five Archean crustal provinces are of Victoria, 3800 Finnerty Road, Victoria V8W 3P6, British recognized within the cratons of continents today (Bleeker, Columbia, [email protected] 2003). The largest mass of lithosphere beneath these cratons underlies the Moho in the mantle. Thus, the long-term strength and stability of a craton must be engendered in the properties ABSTRACT of its mantle lithosphere, which may ultimately be tied to the The origin of mantle lithosphere underlying Archean crustal origins of continents themselves. provinces is most consistent with depletion at low pressures in The purpose of this review is to summarize some thermal, the spinel facies under degrees of melting higher than observed petrological, and geological constraints on the evolution of in modern ocean basins. Depleted sections of the lithosphere cratonic lithosphere as sampled by kimberlites in Canada. created in convergent margin settings were underthrust and Canada is centered over a large craton and has the larg- stacked to build a thick root with time. Geochronologic and est proportion of Archean crust in the world exposed at its geologic evidence can be interpreted to show that the final surface, making it the focus of diamond exploration in the formation and amalgamation of the bulk of the “mantle root” past 15 years. A significant portion of the Lithoprobe pro- occurs 0.5–1 b.y. later than the age of the lithosphere from gram was devoted to the geophysical imaging of lithosphere which it is comprised. “Silica enrichment” is not ubiquitous in beneath the craton (Fig. 1). The geophysical surveys in this the mantle beneath Archean crustal provinces. Where it does and other such programs (e.g., DeepProbe, Kaapvaal project, occur, it may be a heterogeneous feature possibly imparted by USArray) provide a present-day interpretation of the deep marine weathering of peridotite on the Archean ocean floor lithosphere but by themselves do not explain its origin and before it was stacked to form a mantle root. evolution. Mantle rocks
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