LEAD ISOTOPES AS A PROVENANCE TOOL FOR QUARTZ - EXAMPLES FROM PLUTONSAND QUARTZITE, NORTHEASTERN MINNESOTA, USA

The U-Pb isotope system in plutonic quartz samples approximates the cr ystallization age of the host granitoid, and thus provides a useful pr ovenance tool for detrital quartz grains. We present lead isotopic dat a and U and Pb concentrations of quartz from three Late Archean granit oids and from the Early Proterozoic Pokegama Quartzite, all in northea stern Minnesota. Lead in granitic quartz is considerably more radiogen ic than in its associated whole rock host, but it is similar or only s lightly more thorogenic than its host. Pb-Pb ages obtained from quartz whole-rock-leached feldspar from the Late Archean granitic plutons ar e consistent with existing geochronology, suggesting that the U-Pb sys tem in quartz remained closed since crystallization. U-Pb isotopic dat a for detrital clear quartz populations in the Pokegama Quartzite reco rd Late Archean ages (2550-2650), consistent with a source from the Su perior Province. Lead isotopic compositions of detrital K-feldspar pop ulations and lead and neodymium isotopic compositions of whole rocks s amples from the Pokegama Quartzite also support a Superior Province so urce. This study highlights the potential of the lead isotope system i n detrital quartz, K-feldspar, and whole rocks in provenance studies o f sandstones.