Trace-element geochemistry and sedimentary provinces: A study from the Tasman Geosyncline, Australia
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The abundances of La, Th, U and Hf have been determined in flysch sequences of the Tasman Geosyncline, Australia. The arc-derived graywackes differ from those of rifted continental margins and marginal basins, in containing low abundances of La, Th, U and Hf (La = 9.2 ± 1.7 ppm; Th = 1.4 ± 0.6 ppm; U = 0.52 ± 0.2 ppm; Hf = 2.1 ± 0.6 ppm), reflecting similar low abundances in the andesitic source-rocks. Graywackes of rifted continental margins and marginal basins, in contrast, are "mature" and characterised by high abundances of La, Th, U and Hf (La = 39 ± 9.9 ppm; Th = 16 ± 0.6 ppm; U = 3.40 ± 0.5 ppm; Hf = 7.9 ppm), mirroring increased abundances in the granitic and sedimentary source-rocks. Sedimentary rocks deposited in inter-arc basins show wide dispersion but have characteristics intermediate between these two types. The Th/U ratio for magmatic arc sediments is 2.7. For most other sedimentary rocks it remains uniform at 4.5 ± 0.3. For sediments having andesitic and dacitic rocks as provenance the La/Th ratios are 6.7 and 4.5, respectively. This ratio remains constant at 2.6 for most quartzose sedimentary rocks. © 1981.
author list (cited authors)
Bhatia, M. R., & Taylor, S. R.