CARBONATE PB-PB AGES OF THE WITTENOOM FORMATION AND CARAWINE DOLOMITE, HAMERSLEY BASIN, WESTERN-AUSTRALIA (WITH IMPLICATIONS FOR THEIR CORRELATION WITH THE TRANSVAAL DOLOMITE OF SOUTH-AFRICA)

Pb isotopic analyses of carbonates from the Hamersley Group, Western A ustralia, yield the following results. (1) A late Archean (minimum) ag e of greater than or equal to 2.5 Ga is definitely established for the deposition of both the deeper-water basinal Wittenoom Formation and t he shallow-water Carawine Dolomite. Stratigraphic correlation of the T ransvaal Dolomite (South Africa) with these two formations is supporte d by the present Pb isotope age data, (2) A Pb-Pb isochron age of 2505 +/- 37 Ma for the Paraburdoo Member (lower part) of the Wittenoom For mation is best interpreted as a late diagenetic event, which took plac e similar to 100 Ma after the initial deposition. (3) A Pb-Pb isochron age of 2346 +/- 38 Ma for the Bee Gorge Member most likely represents a still later local event of calcite replacement in fractures and vei ns. (4) A Pb-Pb isochron age of 2541 +/- 32 Ma for Carawine Dolomite c ould represent a regional diagenesis slightly earlier than the Parabur doo carbonates if the Carawine carbonates were deposited contemporaneo usly with the Wittenoom Formation. Alternatively, it may represent the time of early diagenesis which closely followed the initial sedimenta tion. A study of trace element abundances and stable isotope compositi ons has revealed a major difference in Fe and Mn contents and delta(18 )O values between the Wittenoom and Carawine dolomite samples, This su ggests that the two suites of dolomites have undergone separate diagen etic histories with different chemical and oxygen isotopic modificatio ns.