[BCG06-P13] Pb-Pb chronology of Fe-Ti oxides
Keywords:Pb-Pb chronology, Fe-Ti oxides, Acasta Gneiss Complex, mafic rocks
We analyzed Fe- Ti oxides from the anorthosite FC1 in the Duluth complex, which yields the widely used zircon U-Pb standard (1,099 ± 0.6 Ma : Paces & Miller. (1993)). We evaluated the resistance of Fe-Ti oxides to acid leaching using SEM observation. In addition, we analyzed acid washed Fe-Ti oxides for Pb isotopes by MC-ICPMS. The results show that Fe-Ti oxides have high U/Pb ratio (> 189) compared with the whole rock fraction (3.29) and yield a reliable Pb–Pb age (1107 ± 102 Ma: MSWD = 15).
Recently, we have applied Fe-Ti oxide Pb-Pb chronology to an amphibolite in the Acasta Gneiss Complex, Canada. The Acasta Gneiss Complex is an Archean terrane containing the oldest known rocks (Bowring & Williams. (1999)) and is composed of felsic orthogneisses and amphibolites. Although the formation and metamorphic ages of the felsic gneisses have been extensively investigated, no reliable chronological data have been obtained from the amphibolites. We are in the process of determining Pb–Pb ages of Fe-Ti oxides from the amphibolites in an attempt to get the reliable chronological information.