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VVOL.OL. 115,5, NNO.O. 2 A PPUBLICATIONUBLICATION OFOF TTHEHE GGEOLOGICALEOLOGICAL SSOCIETYOCIETY OOFF AAMERICAMERICA FFEBRUARYEBRUARY 22005005 Subduction zone backarcs, mobile belts, and orogenic heat Inside: Subduction zone backarcs, mobile belts, and orogenic heat, ROY D. HYNDMAN, CLAIRE A. CURRIE, AND STEPHANE P. M AZZOTTI, p. 4 2004–2005 Division Officers and Past Chairs, p. 11 GeoVentures™ 2005, p. 29 An Earth Scientist’s Periodic Table of the Elements and Their Ions by L. Bruce Railsback An Earth Scientist’s Periodic Table of the Elements and form as ions rather than in elemental form. The immediate Their Ions is a new periodic table designed to contextualize result is a completely rearranged table in which many trends in geochemistry, mineralogy, aqueous chemistry, elements appear multiple times, because many elements and other natural sciences. First published as an insert assume different charge under different natural conditions. in the September 2003 issue of Geology, this version is The practical result is that many trends in mineralogy, updated and supersized—36" by 76"! seawater chemistry, soil chemistry, the chemistry of This new periodic table of the elements is more useful Earth’s crust and mantle, the chemistry of sediments, and to earth scientists than the conventional periodic table nutrient chemistry become apparent in ways that are not used by chemists. The periodic table presented here recognizable on conventional, elementally constructed, acknowledges that most natural matter occurs in charged periodic tables. MCH092F, 1 folded sheet (36" × 76"), 7 p. text $25.00, member price $20.00—folded MCH092R, 1 rolled sheet (36" × 76"), 7 p. text $30.00, member price $24.00—rolled Order online at: GSA Sales and Service P.O. Box 9140, Boulder, CO 80301-9140 (303) 357-1000, option 3 www.geosociety.org/bookstore 1-888-443-4472 • fax 303-357-1071 Volume 15, Number 2 FEBRUARY 2005 Cover: The North America Cordillera GSA TODAY publishes news and information for more than mobile belt illustrating the high elevation 18,000 GSA members and subscribing libraries. GSA Today and complex tectonics characteristic of hot, lead science articles should present the results of exciting new thin backarc lithospheres. Backarcs remain research or summarize and synthesize important problems weak enough to be deformed by plate or issues, and they must be understandable to all in the earth margin forces for long geological periods. science community. Submit manuscripts to science editors Keith A. Howard, [email protected], or Gerald M. Ross, Right: Heat flow and thermal-tectonic cross [email protected]. section for N. Cascadia backarc illustrating uniform high heat flow and inferred GSA TODAY (ISSN 1052-5173 USPS 0456-530) is published 11 shallow asthenosphere convection. See times per year, monthly, with a combined April/May issue, by The “Subduction zone backarcs, mobile belts, Geological Society of America, Inc., with offices at 3300 Penrose Place, Boulder, Colorado. Mailing address: P.O. Box 9140, and orogenic heat,” by R.D. Hyndman et Boulder, CO 80301-9140, USA. Periodicals postage paid at al., p. 4–10. Boulder, Colorado, and at additional mailing offices. Postmaster: Send address changes to GSA Today, GSA Sales and Service, P.O. Box 9140, Boulder, CO 80301-9140. Copyright © 2005, The Geological Society of America, Inc. (GSA). All rights reserved. Copyright not claimed on content prepared SCIENCE ARTICLE wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, 4 Subduction zone backarcs, mobile belts, and orogenic heat, 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 ROY D. HYNDMAN, CLAIRE A. CURRIE, AND STEPHANE P. MAZZOTTI 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 303- 11 Meeting Wrap-up—Denver 2004: Geoscience in a Changing World 357-1073, [email protected]; reference GSA Today, ISSN 1052-5173. 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Sajban Golden, Colorado, USA ADVERTISING: Classifieds & Display: Ann Crawford, 1-800-472-1988, ext. 1053, 32 GSA Foundation Update (303) 357-1053, Fax 303-357-1070; [email protected] GSA ONLINE: www.geosociety.org 33 Announcements Printed in the USA using pure soy inks. 35 Classified Advertising 37 Journal Highlights 50% Total Recovered Fiber 38 GeoMart Geoscience Directory 10% Postconsumer Subduction zone backarcs, mobile belts, and orogenic heat Roy D. Hyndman, Pacific Geoscience Centre, Geological Survey of Canada, P.O. Box 6000, Sidney, British Columbia V8L4B2, Canada, and School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia V8W3P6, Canada, [email protected]; Claire A. Currie, School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia V8W3P6, Canada; and Stephane P. Mazzotti, Pacific Geoscience Centre, Geological Survey of Canada, P.O. Box 6000, Sidney, British Columbia V8L4B2, Canada ABSTRACT hot backarc lithosphere, not from the Two important problems of continental orogenic deformation process itself. tectonics may be resolved by recogniz- INTRODUCTION ing that most subduction zone backarcs The model of plate tectonics with have hot, thin, and weak lithospheres narrow plate boundaries provides an Figure 1. The North America Cordillera mobile over considerable widths. These are (1) excellent first-order description of global the origin of long-lived active “mobile belt. The high elevation and complex current tectonics. Plate tectonics also provides tectonics illustrate the hot, weak, backarc belts” contrasted to the stability of cra- an elegant explanation for orogenic lithosphere deformed by variable margin forces. tons and platforms, and (2) the origin crustal shortening and thickening in of the heat of continental collision orog- terms of continental or terrane colli- eny. At many continental margin plate sion. However, a number of large-scale deformation over long geological peri- boundaries, there are broad belts with tectonic problems are not explained by ods. They have some characteristic that a long history of distributed deforma- the simple rigid plate and continental allows them to maintain an especially tion. These regions are mobile because collision models. In this article, we pre- thick, strong lithosphere, such as a more the lithosphere is sufficiently weak to sent explanations for two such tectonic refractory mantle composition (Jordan, be deformed by the forces developed problems: the origin of long-lived active 1978; Forte and Perry, 2000). The rea- at plate boundaries. We conclude that “mobile belts” that lie along a number son for the long histories of tectonic mobile belts are weak because they are of continental
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