CONCH: A Visual Basic program for interactive processing of ion-microprobe analytical data

摘要

A Visual Basic program for flexible, interactive processing of ion-microprobe data acquired for quantitative trace element, Al-26-Mg-26, Mn-53-Cr-53, Fe-60-Ni-60 and U-Th-Pb geochronology applications is described. Default but editable run-tables enable software identification of secondary ion species analyzed and for characterization of the standard used. Counts obtained for each species may be displayed in plots against analysis time and edited interactively. Count outliers can be automatically identified via a set of editable count-rejection criteria and displayed for assessment. Standard analyses are distinguished from Unknowns by matching of the analysis label with a string specified in the Set-up dialog, and processed separately. A generalized routine writes background-corrected count rates, ratios and uncertainties, plus weighted means and uncertainties for Standards and Unknowns, to a spreadsheet that may be saved as a text-delimited file. Specialized routines process trace-element concentration, Al-26-Mg-26, Mn-53-Cr-53, Fe-60-Ni-60, and Th-U disequilibrium analysis types, and U-Th-Pb isotopic data obtained for zircon, titanite, perovskite, monazite, xenotime and baddeleyite. Correction to measured Pb-isotopic, Pb/U and Pb/Th ratios for the presence of common Pb may be made using measured Pb-204 counts, or the Pb-201 or Pb-208 counts following subtraction from these of the radiogenic component. Common-Pb corrections may be made automatically, using a (user-specified) common-Pb isotopic composition appropriate for that on the sample surface, or for that incorporated within the mineral at the time of its crystallization, depending on whether the 204 Pb count rate determined for the Unknown is substantially higher than the average 204 Pb count rate for all session standards. Pb/U inter-element fractionation corrections are determined using an interactive log(e)-log(e) plot of common-Pb corrected Pb-206/U-238 ratios against any nominated fractionation-sensitive species pair (commonly (UO+)-U-238-O-16/U-238(+)) for session standards. Also displayed with this plot are calculated Pb/U and Pb/Th calibration line regression slopes, y-intercepts, calibration uncertainties, standard Pb-204- and Pb-208-corrected Pb-207/Pb-206 dates and other parameters useful for assessment of the calibration-line data. Calibrated data for Unknowns may be automatically grouped according to calculated date and displayed in color on interactive Wetherill Concordia, Tera-Wasserburg Concordia, Linearized Gaussian ("Probability Paper") and Gaussian-summation probability density diagrams. (c) 2006 Elsevier Ltd. All rights reserved.