Nd isotope study of granites from the Arunta Inlier, central Australia: constraints on geological models and limitation of the method

• Published in: Precambrian research 1995-02, Vol.71 (1), p.301-314
• Main Authors: Sun, Shen-su, Warren, R.G., Shaw, R.D.
• Format: Article
• Language: English
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/0301-9268(94)00066-Z

Three chemically distinct types of granite (“high Sr/low Y” calc-alkaline, Palaeoproterozoic “normal” and “enriched”) are present in the Palaeoproterozoic Arunta Inlier of central Australia. Twenty-one representative samples were selected for Nd isotopic analysis to complement geological and geochemical data. Most samples analysed have depleted-mantle Nd isotope model ages (T DM, following McCulloch, 1987) of 2.3 to 2.1 Ga, similar to most of Palaeoproterozoic granites of northern Australia (McCulloch, 1987). These ages do not show a younging trend from the Northern to Southern provinces, although some post ∼ 1750 Ma granites from the Central and Southern provinces, with typical felsic crust 147Sm 144 Nd ratios (0.09–0.11), have younger model ages (less than 2.0 Ga). Post 1700 Ma, “normal-type” granites from the Southern Province have chemical compositions similar to older granites (1880-1760 Ma) of the same suite, even though they have younger model ages (1960-1930 Ma). This implies an increase in a younger component within southern source regions through melting of new underplate and/or additional mantle input. The syn- or post-tectonic granites (1720-1140 Ma) of the “enriched-type” (high heat producing granites rich in Th, U and K) have similar T DM model ages to older granites of the “normal-type” from the same areas. The “enriched-type” granite from the Teapot Granite Complex of the Southern Province are characterised by low Cs, Sr and high Rb Cs (30–50), Th U (7–20) ratios and high Y contents. These chemical characteristics are consistent with magma being formed through anatexis of “normal-type” granite sources. In contrast, an 1820 Ma, S-type granite from the Harverson suite in the Northern Province has an older T DM model age (2.32 Ga) than the T DM 2.18 Ga age of the nearby Aileron Metamorphics, suggesting that the source rock of the granite may contain a significant Archaean component. The Nd isotope data, when integrated with geological and chemical information, are compatible with the recycling of Archaean crustal material. Such a process might have taken place very early in the history of the Arunta Inlier through subduction along a continental margin made up of a stretched, dismembered, thin Archaean basement. Magmatic underplating may have taken place shortly before 1850 Ma and continued episodically during subsequent tectono-thermal events. Crustal melts of mixed source rocks, formed during these events, could contain different amounts of a