Zircons were analyzed for U-Th and U-Pb geochronology with the USGS-Stanford SHRIMP RG (http://shrimprg.stanford.edu) in December 2002 (sample 02TSV060) and in a 3-day session in October 2005 (all other samples). Data are presented in Table DR1. Analysis conditions and protocol were similar to those reported by Bacon and Lowenstern (2005) except that a 16�22 nA 16O� primary beam was used and each analysis consisted of 10 scans through the mass range. The empirical U�Th fractionation factor necessary to bring the (230Th/238U) activity ratio to unity for analyzed standards and other pre-Quaternary zircons during the October 2005 session was 1.094. Following Charlier et al. (2005), we assigned this factor a conservative 1sigma uncertainty [...]
Summary
Zircons were analyzed for U-Th and U-Pb geochronology with the USGS-Stanford SHRIMP RG (http://shrimprg.stanford.edu) in December 2002 (sample 02TSV060) and in a 3-day session in October 2005 (all other samples). Data are presented in Table DR1. Analysis conditions and protocol were similar to those reported by Bacon and Lowenstern (2005) except that a 16�22 nA 16O� primary beam was used and each analysis consisted of 10 scans through the mass range. The empirical U�Th fractionation factor necessary to bring the (230Th/238U) activity ratio to unity for analyzed standards and other pre-Quaternary zircons during the October 2005 session was 1.094. Following Charlier et al. (2005), we assigned this factor a conservative 1sigma uncertainty of 0.03 in error calculations. Zircon U concentrations were obtained by comparison of 238U/90Zr2 16O ratios with that of zircon standard CZ3 (Ireland and Williams, 2003), recognizing that this leads to slight overestimation of U and Th concentrations in U- and Th-rich zircons. Most zircons had minimum exposed diameters of ~40�60 ?m, necessitating placement of the ion beam near the center of the crystal. A few zircons were sufficiently large for multiple analysis points. Some grains were analyzed a second time after re-polishing and Au coating the mount. Each analysis was treated independently in the figures. The small zircons commonly are difficult to analyze because overlap of the primary ion beam on the epoxy mounting medium or any epoxy in a cracked zircon produces excess apparent 230Th16O from a molecular interference involving epoxy constituents. Schmitt (2006; GSA Data Repository item 2006112) has identified the isobaric interference as due to 232Th2 12C16O2+ (see also Schmidt et al., 2006, Appendix A). Analyses affected by epoxy contamination are presented in Table DR1 with values for (230Th/232Th) indicated by strikethrough type and are retained because U and Th concentrations and (238U/232Th)
The coordinates are represented in North American Datum of 1927 (NAD27). Location was derived from the following method(s): Location digitized from figure 1 in Bacon, C.R., and others, 2007, Geology, v. 35, no. 6, p. 491