1. Department of Geology & Geophysics, University of Wyoming, 1000 E. University Avenue, Laramie, Wyoming 82071, USA
2. Scripps Institution of Oceanography–Earth Division, University of California–San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
3. Department of Geological Sciences, University of Texas, 1 University Station C9000, Austin, Texas 78712, USA