DETRITAL ZIRCON PROVENANCE OF THE MESOPROTEROZOIC PANDURRA FORMATION, SOUTH AUSTRALIA: GAWLER CRATON ZIRCON POPULATION AND IMPLICATIONS FOR THE BELT SUPERGROUP
The Pandurra Formation is a W to SW derived fluviatile sequence comprising medium to coarse-grained, poorly sorted quartz and lithic sandstones, plus conglomerates and shales. Volcanic horizons have not been recorded and the only radiometric age constraint is a crude syn-Belt whole-rock Rb-Sr isochron suggesting a maximum depositional age of 1424 ± 51 Ma (Fanning et al., 1983).
SHRIMP U-Pb ages of detrital zircons have been determined for 4 drillcore samples of the Pandurra Formation from the Stuart Shelf: a shale and sandstone each from Red Millers Creek 1 and CSR-PY1. In all four samples, the 1580-1620 Ma component forms between 40 to 60% of the detrital zircon population, with older groups between 1640-1780 Ma and a subordinate group >2440 Ma. Clearly the proximal 1585-1595 Ma Gawler Range Volcanics and Hiltaba Granite source dominate the detrital zircon population.
Within the Belt Supergroup of Montana and Idaho, the 1580-1600 Ma population is present in the lower-Belt Prichard Formation and overlying Ravalli Group, but is absent in upper-Belt Missoula Group sandstones (Link and Fanning, 2003). Thus in any supercontinent reconstruction, the Belt basin has to be relatively distal from the Gawler Craton on the Australian margin, as a direct provenance would record a more dominant 1580-1600 Ma component. Likely lower and middle Belt strata contain a mixture of a North American and exotic provenance, with dilution of any direct Gawler signature, if indeed the population in question is uniquely Australian.