Discussion on detachment faulting and bimodal magmatism in the Palaeoproterozoic Willyama Supergroup, south-central Australia: keys to recognition of a multiply deformed Precambrian metamorphic core complex

Abstract

Gibson & Nutman (2004) postulate that the Willyama Supergroup in the southern Curnamona Province contains a 1690-1670 Ma metamorphic core complex, and imply that this is relevant to the genesis of the Broken Hill Pb-Zn-Ag deposit. We contend that this is a model driven, speculative interpretation predicated upon unsupported assertions that conflict with substantial stratigraphic and geochronological data. Not only does the paper fail to demonstrate an early high-grade event and formation of a metamorphic core complex at 1690-1670 Ma, but it is also factually incorrect in several critical geological and geochronological aspects. The detachment concepts of Gibson & Nutman may appear persuasive, but only by omitting reference to a huge body of published and recent mapping and laboratory research, by companies, universities, and geological surveys, some of which are cited here. Surprisingly, Gibson & Nutman ignore much recent work (e.g. Page et al, 2004) to which one of them has contributed.