GEOCHEMICALLY UNRAVELING THE SEDIMENTARY COMPONENTS OF ARCHEAN METASEDIMENTS FROM WESTERN-AUSTRALIA

Major and trace elements of metasediments of the granulite facies Narr yer and the amphibolite facies Jack Hills metasediments have been used to devise plots which enable the original sedimentary components of t hese rocks to be unravelled, despite their metamorphic state. These pl ots overcome the predominant effect of quartz which ranges up to 100% and can be used to study other metasediment suites. Six components con trolled the composition of the elastic metasediments (1) kaolinite, (2 ) illite-muscovite, (3) chlorite-montmorillonite, (4) dolomite, (5) qu artz, (6) resistant heavy minerals such as rutile, zircon, chromite an d monazite. Identifying the first four of these components enables the trace element composition associated with the components to be estima ted. Feldspar was largely destroyed by chemical weathering bur there i s a suggestion that traces of it formed a minor seventh component in t he Narryer rocks. There was little or no mixing of the original kaolin ite-bearing and illite-muscovite-bearing samples, indicating two disti nct sources, although both sets of samples contain >4 Ga zircons, sugg esting a third zircon source. The old zircons may have been derived fr om re-worked sediment or metasediment as they occur in the matrix and in the quartzite clasts of conglomerates. Using Bhatia's criteria, a p assive margin is the likely site of deposition. Gale alkaline tholeiit es in the Narryer succession are intrusive and did not contribute to t he sediments which were derived from extremely heavily weathered grani tes, komatiites, schists and reworked sandstones or quartzites.