Major terrestrial reservoirs have Pb isotopes more radiogenic than the bulk silicate Earth. This requires a missing unradiogenic Pb reservoir, which has been argued to reside in the lower continental crust or dissolved in the core. Chalcophile element studies indicate that continent formation requires the formation of sulfide-bearing mafic cumulates in arcs. Because Pb, but not U, partitions in...

Neodymium model ages for fine-grained formations of the Paleoproterozoic Huronian Supergroup (McKim, Pecors, Gowganda, Gordon Lake) range from 3.00 to 2.55 Ga and indicate a provenance dominated by the Late Archean Superior Province to the north and west. The stratigraphically highest unit (Gordon Lake Formation) has a distinctive Nd-isotopic composition, with TDM being 100-400 Ma younger than ...

A method for in situ U–Pb isotopic analyses by secondary ion mass spectrometry (SIMS) has been developed for uranium minerals with a range of chemical compositions. This method combines the advantages of conventional U–Pb dating (i.e., use of concordia) and in situ analysis, and therefore is ideally suited for the study of chemically complex and fine-grained uranium oxides associated with urani...

A recurring challenge to ion microprobe U^Pb zircon geochronology has been to discriminate between preservation of original igneous zircon populations and inherited grains. This has proved particularly problematic in studying the polyphase metamorphic rocks that dominate Early Archean gneissic terranes. For example, differing interpretations exist for the origin of complex zircon populations in...

A long-standing goal in high-precision and high-accuracy U–Pb zircon geochronology is the total elimination of discordance caused by Pb loss. In theory, this is fairly straightforward, but in reality it has proven extremely difficult to attain (or even demonstrate attainment of) this goal. However, a new method, bCA (Chemical Abrasion)-TIMSQ, is capable of completely removing zircon domains tha...