A U-PB ZIRCON STUDY OF THE MESOPROTEROZOIC CHARLESTON GRANITE, GAWLERCRATON, SOUTH-AUSTRALIA

The Charleston Granite from the Gawler Craton, South Australia, has be en dated by the ion-microprobe U-Pb zircon method at 1585 +/- 5 Ma (2s igma). This confirms previous interpretations of population-style U-Pb zircon analyses which record a slightly older age due to the presence of inherited zircon. Inherited cores are present in many zircon cryst als, and while the age of some cores can not be accurately determined due to extreme loss of radiogenic Pb, others have ages of approximatel y 1780, approximately 1970, and > 3150 Ma. These cores record a divers e crustal heritage for the Charleston Granite and indicate that ancien t crustal material (> 3150 Ma) is present at depth in the Gawler Crato n. This is also suggested by available Nd isotopic data for both the C harleston Granite and other Gawler Craton Archaean rocks. The Rb-Sr an d K-Ar biotite ages from the Charleston Granite of 1560 to 1570 Ma are close to the U-Pb zircon crystallization age and suggest that the gra nite has not experienced sustained thermal disturbance (> 250-degrees- C) since emplacement and cooling. However, a much younger Rb-Sr total- rock age of 1443 +/- 26 Ma probably reflects low-temperature disturban ce to the Sr isotope system in feldspar.