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Penrose Conference Announcement: Origin and Uplift of the Sierra Nevada, California, USA, p. 11 VOL. 20, No. 2 A PUBLICATION OF THE GEOLOGICAL SOCIETY OF AMERICA FEBRUARY 2010 Rock to regolith conversion: Producing hospitable substrates for terrestrial ecosystems Inside: ▲ Final Announcement and Call for Papers: GSA Cordilleran Section, Joint with Pacific Section, AAPG, p. 12 ▲ New GSA Members, p. 16 ▲ Report: Inaugural Young Earth-Scientists Congress, Beijing, China, p. 21 ▲ Penrose Conference Report: Low d18O Rhyolites and Crustal Melting: Growth and Redistribution of the Continental Crust, p. 24 Not Just Software. RockWare. For Over 27 Years. New ® Version ! 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All of these tools (and more!) are now available in an annual license for academic use: unlimited installations within a department for the same price as a single, standard license. $2,499 303.278.3534 • 800.775.6745 RockWare.com GSA Today - Feb10.indd 1 12/29/09 2:05:50 PM VOLUME 20, NUMBER 2 ▲ FEBRUARY 2010 SCIENCE ARTICLE GSA TODAY publishes news and information for more than 22,000 GSA members and subscribing libraries. GSA TODAY (ISSN 1052-5173 USPS 0456-530) is published 11 times per 4 Rock to regolith conversion: year, monthly, with a combined April/May issue, by The Geological Society of America®, Inc., with offices at 3300 Producing hospitable substrates Penrose Place, Boulder, Colorado. Mailing address: P.O. Box for terrestrial ecosystems 9140, Boulder, CO 80301-9140, USA. Periodicals postage paid Robert C. Graham, Ann M. Rossi, at Boulder, Colorado, and at additional mailing offices. Postmaster: Send address changes to GSA Today, GSA and Kenneth R. Hubbert Sales and Service, P.O. Box 9140, Boulder, CO 80301-9140, USA. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, Cover: Hard, virtually unweathered bedrock in the Sierra Nevada, California, USA, supports a regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect sparse ecosystem in which plants only grow in joint fractures (photo credit: Malcolm M. Clark). official positions of the Society. Porosity produced by weathering converts such biologically inert rock into regolith that holds water and supports more productive ecosystems. See “Rock to regolith conversion: Produc- Copyright © 2010, The Geological Society of America (GSA). ing hospitable substrates for terrestrial ecosystems,” by R.C. Graham et al., p. 4–9. All rights reserved. Copyright not claimed on content prepared wholly by U.S. government employees within the scope of their 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 11 Penrose Conference Announcement: Origin and Uplift of the Sierra Permissions, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA; Nevada, California, USA fax +1-303-357-1073, [email protected]. SUBSCRIPTIONS: GSA members: Contact GSA Sales and 12 Final Announcement and Call for Papers: GSA Cordilleran Section, Service at +1-888-443-4472, +1-303-357-1000, option 3, or [email protected] for information. Nonmembers Joint with Pacific Section, AAPG & Institutions: Free with paid subscription to GSA Bulletin, Geology, Lithosphere, and Geosphere (all four); otherwise US$70. Contact AIP Customer Service, [email protected]. Claims: 14 2009–2010 GSA-USGS Congressional Science Fellow Report: For nonreceipt or for damaged copies, GSA members should Notes from the Staff Bench contact GSA Sales and Service; all others contact AIP Customer Service, [email protected]. Claims are honored for one year; please allow sufficient delivery time for overseas copies, 15 GSA Elections—2010 Officer and Councilor Nominees up to six months. GSA TODAY STAFF: 16 New GSA Members Executive Director and Publisher: John W. Hess Science Editors: Stephen T. Johnston, University of Victoria, School of Earth & Ocean Sciences, Victoria, British 21 Report: Inaugural Young Earth-Scientists Congress, Beijing, China Columbia V8W 3P6, Canada, [email protected]; and David E. Fastovsky, University of Rhode Island, Department of Geosciences, Woodward Hall, Rm. 317, 22 GSA Foundation Update Kingston, Rhode Island 02881, USA, [email protected]. Managing Editor: Kristen E. Asmus, [email protected]; [email protected] 23 In Memoriam Graphics Production: Margo Y. Sajban ADVERTISING: 23 GSA Section Meeting Mentor Program Schedule Classifieds & Display: Ann Crawford, +1-800-472-1988, ext. 1053, +1-303-357-1053, Fax +1-303-357-1070; [email protected] 24 Penrose Conference Report: Low d18O Rhyolites and Crustal GSA ONLINE: www.geosociety.org Melting: Growth and Redistribution of the Continental Crust Printed in the USA using pure soy inks. 26 2010 Calendar of GSA Deadlines & Events 28 Classified Advertising 30 Coming Soon to GSA Today 30 Journal Highlights Rock to regolith conversion: Producing hospitable substrates for terrestrial ecosystems Robert C. Graham, Ann M. Rossi, Soil & Water Sciences POROSITY FORMATION AND GRANITIC ROCK Program, Dept. of Environmental Sciences, University of WEATHERING California, Riverside, California 92521-0424, USA, and Kenneth Unweathered granitic plutons are commonly jointed. The R. Hubbert, USDA Forest Service, Pacific Southwest Research joints are the result of stresses on the rock mass, including Station, 3644 Avtech Parkway, Redding, California 96002, USA those associated with thermal, tectonic, and erosional unload- ing processes. Joint spacings range from several decimeters to ABSTRACT several meters, can be orthogonally oriented, and depend on Weathering processes transform hard fresh rock into fri- the geologic history of the rock. In unweathered bedrock, the able weathered rock, which is then physically disrupted to joint fractures are empty planar voids that range in width from become soil. These regolith materials mantle the land masses a fraction of a millimeter to more than a centimeter (Bergbauer and support terrestrial life but their formation involves some of and Martel, 1999). Fractures are the main source of hydraulic the least understood of Earth’s surficial processes. The conver- connectivity in unweathered bedrock (Paillet, 1993). The rock sion of biologically inert hard rock to a hospitable substrate for mass between the joints contains minor porosity, usually 1% or organisms begins with the production of porosity by weather- less (Twidale and Vidal Romaní, 2005), in the form of micro- ing. Porosity allows water to flow through weathered rock, but fractures <1 µm wide and microporosity within mineral grains it also imparts a water-holding capacity so that water can be (Sardini et al., 2006). The microfractures are generated by stored for prolonged use by organisms. Organisms themselves, stresses incurred during cooling, hydrothermal activity, or tec- in the form of microbes and plant roots, invade the rock as tonism (Schild et al., 2001). Micropores within mineral grains porosity forms. Production of porosity is the fundamental pro- form during crystallization and cooling. Meteoric water flowing cess responsible for converting rock into a medium capable down joint fractures initially enters the bedrock mass through of supporting terrestrial ecosystems. Consequently, the rate inherent microfractures, thereby beginning the chemical weath- of porosity formation during rock weathering is the ultimate ering process (Meunier et al., 2007). measure of the production and sustainability of ecosystem- In biotite-bearing granites, ion exchange weathering is an functional substrates. important first step in generating bulk rock porosity. The re- placement of interlayer K by hydrated Mg cations results in INTRODUCTION expansion of the biotite structure as the mineral is transformed Fresh bedrock exposed at the land surface is an inhospi- to vermiculite (Wahrhaftig, 1965; Nettleton et al., 1970; Isher- table substrate for most life. Exposed bedrock has very low wood and Street, 1976). This expansion, which involves a porosity and hydraulic conductivity (Zhao, 1998; Schild et al., 30%–40% increase in volume, exploits the weakness imparted 2001); consequently, rain and snowmelt run off from it imme- by the lithogenic microfractures and shatters the rock. A small- diately. Water is not stored, so plants do not have a reservoir er expansion of biotite has been noted to occur upon oxidation from