1. Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
2. Current address: Department of Earth and Planetary Sciences, University of California at Riverside, 900 University Avenue, Riverside, CA 92521, USA
3. Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78712, USA
4. Current address: School of Teacher Education and School of Earth and Environment, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand