Abstract

Metamorphosed basic volcanic rocks of Permo-Triassic age occur in several distinct geological formations on Timor. Some are found in para-autochthonous units, which have been correlated with similar sequences on the Australian continental shelf; and some occur in apparently allochthonous units, which have been correlated with similar sequences in Malaya and Sumatra. Analyses of the relatively immobile elements, particularly Ti, Zr, Y, Nb, P and the rare earths, from both units revealed that the basalts vary from tholeiitic to mildly alkaline but are all consistent with emplacement in a rift-valley or ocean-floor setting. No difference was detected between the units based on basalt geochemistry, no calc-alkaline basalts similar to those reported in Malaya and Sumatra were found. and the basaltic suites are regionally distributed so as to cross-cut boundaries between the para-autochthonous and allochthonous units. The geochemistry is consistent with the evolution of all the Permo-Triassic units now on Timor as a part of the Australian continental margin but requires revision of detailed interpretations in order to be compatible with an exotic origin for the ‘allochthonous’ units.

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