Geochemistry of Precambrian metapelites from East Antarctica: secular and metamorphic variations

Early Archaean ( >3 b.y. old) metapelites from the Napier Complex of East Antarctica are enriched in MgO and depleted in K2O and Rb compared with late Archaean and Proterozoic metapelites, probably reflecting a higher proportion of mafic to ultramafic material and sodic (tonalitic to granodioritic) felsic igneous rocks in the source. A number of the more magnesian are strongly depleted in Cr, Ni, Cu, and V, and may have been formed by metamorphism of sediments derived from hydrothermally altered mafic or ultramafic igneous rocks. There is evidence for metamorphic depletion of Rb relative to K in these high-temperature granulite facies metapelites, many of which have high K/Rb ratios, and for depletion of U relative to Th in granulite-facies metapelites compared with those of amphibolite facies. The unique occurrence, on a regional scale, of assemblages containing sapphirine + quartz, and osumilite in metapelites of the Napier Complex may be due to their unusual chemical compositions, as well as to exceptionally high temperatures of metamorphism (900-950°C). Such assemblages are found only in the more magnesian rocks (mostly with mg > 0.6) in the Napier Complex, whereas younger metapelites are, with few exceptions, relatively iron-rich. Nevertheless, regional high-grade metamorphism with geothermal gradients sufficiently steep to allow formation of these rare assemblages is likely to have been confined to the Archaean.

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1980-01-01T00:00:00
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Geoscience Australia Persistent Identifier/https://pid.geoscience.gov.au/dataset/ga/81051

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Bureau of Mineral Resources, Geology and Geophysics

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Sheraton, J.W.

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BMR Journal of Australian Geology and Geophysics

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2018-11-01T00:00:00
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2018-04-20T06:10:11
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