Subduction Cycling of U, Th, and Pb Katherine A. Kelley*§, Terry Plank*, John Ludden† & Hubert Staudigel‡ *Department of Earth Sciences, Boston University, 685 Commonwealth Ave., Boston, MA 02215 USA, Ph: (617) 353- 4213; tplank@bu.edu § Now at Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Rd. NW, Washington, DC 20015, USA, Ph: (202) 478-8475 Fax: (202) 478-8821; kelley@dtm.ciw.edu †CRPG/CNRS Vandoeuvre-lès-Nancy, BP 20, France; john.ludden@cnrs-dir.fr ‡ Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0225 USA; Ph: (858) 534-8764; hstaudigel@ucsd.edu Correspondence and requests for materials should be addressed to K. Kelley. Words in main text: 5174 Page Count (estimated printed length): 13 pages [Submitted to Earth and Planetary Science Letters; 2 February, 2004]