Age constraints on the geological evolution of the Narryer Gneiss Complex, Western Australia

Abstract

Zircon U‐Th‐Pb and mineral K‐Ar and ⁴⁰Ar/³⁹Ar isotopic studies indicate that the maximum deposition age of the Mt Narryer quartzite (which contains detrital zircons up to 4200 Ma old) is 3280 Ma, or by association with other sequences possibly 3100 Ma. This postdates a major episode of high‐grade metamorphism, granite emplacement and deformation at 3300 Ma, which affected adjacent gneiss terranes and which previously had been considered to have affected metasediments and basement gneisses alike. Prograde metamorphism of the Narryer metasediments to amphibolite facies evidently took place during a younger event culminating ca 2700 Ma, prior to injection of granite sheets ca 2650 Ma in age, by which time the present tectonic framework had been assembled.