Abstract
Extensive isotopic resetting occurred in Precambrian basement rocks of Enderby Land, Antarctica. Three examples are highlighted to show the folly of reliance on a single isotopic system and the dangers of isotopic dating without adequate geological constraints. In the first example the Rb-Sr whole-rock age of a Proterozoic granite is 200 Ma younger than its emplacement age derived from U-Pb zircon analyses. The opposite relationship is observed in an Archaean granite whose Rb-Sr age from structural considerations appears to date emplacement but is some 500 Ma older than its U-Pb zircon age, which is inconsistent with the deduced time of emplacement. The third example documents isotopic resetting of the Sm-Nd whole-rock system during transitional amphibolite to granulite facies tectonism. However, in both the Rb-Sr and Sm-Nd whole-rock systems it is the development of penetrative fabric rather than intensity of metamorphic grade which facilitates isotopic resetting. The scale of lithological homogeneity is probably a contributing factor.
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