Evaluating the provenance of Archean sedimentary rocks of the Diemals Formation (central Yilgarn Craton) using whole-rock chemistry and precise U – Pb zircon chronology

Abstract

Whole-rock chemistry and precise U – Pb zircon chronology have been used to determine the provenance of Archean greenschist-facies siliciclastic sedimentary rocks of the Diemals Formation in the Marda – Diemals area of the central Yilgarn Craton, Western Australia. Field evidence shows that these siliciclastic rocks are, at least in part, derived from uplift and erosion of underlying greenstones, and this is borne out by the similar La/Sc, Cr/Th and REE chemistry of Diemals Formation siltstones and some sandstones to mafic volcanic rocks of the underlying greenstones. The higher Cr/V and lower Y/Ni of some siltstones is consistent with input from ultramafic and mafic rocks. Diemals Formation sandstones and siltstones cannot be separated in terms of ratios such as Zr/La, and siliciclastic rock chemistry reflects provenance rather than the effects of transport and depositional processes, such as sorting. Chemistry does not support input to Diemals Formation sedimentary rocks from the Marda volcanic complex despite both units being close to each other, and having overlapping maximum depositional and crystallisation ages, respectively. Instead, it is likely that detritus for the two units was deposited in adjacent, physically discrete basins. Some Diemals Formation sandstones are geochemically similar to felsic rocks intruding the underlying greenstone succession, with higher La/Sc and lower Cr/Th, and LREE-enriched patterns with negative Eu anomalies. Support for a genetic relationship is shown by the overlap in the maximum depositional age of these sandstones with the crystallisation age of the geochemically identical Pigeon Rocks Monzogranite. Combined whole-rock chemistry and precise U – Pb zircon chronology indicates that Diemals Formation sedimentary rocks were in large part derived from the underlying mafic volcanic rocks, with progressive unroofing of this succession leading to erosion of felsic intrusive rocks, now represented by sandstones found at various levels in the Diemals Formation.

Key Words:

• Archean
• chemistry
• Diemals Formation
• Marda – Diemals greenstone belt
• provenance
• Western Australia
• Yilgarn Craton

Acknowledgements

We thank Stephen Wyche for helpful suggestions on an earlier draft. A detailed review by Rick Squire, and comments by an anonymous reviewer greatly improved the manuscript. Published with permission of the Executive Director of the Geological Survey of Western Australia.

Notes

*Table 2 [indicated by an asterisk (*) in the text and listed at the end of the paper] is a Supplementary Paper; copies may be obtained from the Geological Society of Australia's website (http://www.gsa.org.au) or from the National Library of Australia's Pandora archive (http://nla.gov.au/nla.arc-25194).

Six-figure numbers preceded by GSWA refer to samples curated by the Geological Survey of Western Australia. Grid references (in Table 2*) refer to the Geocentric Datum of Australia 1994 (GDA94), and coordinates are in MGA.