Geochronological data evaluation: Implications for the Proterozoic tectonics of East Gondwana

Geochronologic data and arguments proposing the division of the pre-Pan-African terranes of East Antarctica (Grenvillian Circum-East Antarctic Orogen) into three genetically different provinces, and the recognition of the Pan-African orogens as sutures are discussed. Problems of zircon U–Pb dating for identifying the absence of precursor Grenvillian events, which are superimposed and concealed by the dominant Pan-African event, are specifically highlighted. Major problems are (i) the lowering of closure temperatures under deformational and/or fluid-rich conditions, (ii) the weighted mean U–Pb concordant ages, (iii) the disappearance of an earlier discordia in the polymetamorphism, (iv) diversity in the interpretation of zonal structure of zircons, (v) general lack of discussion on the formative process of the dated zircons and (vi) the practical difficulty in zircon geochronology for providing evidence of the absence of earlier events superposed by a later high-grade event. It is stressed that it is difficult for zircon geochronology to provide robust evidence for eliminating the possibility of the existence of earlier tectonothermal events superimposed by later high-grade events. The presence of Grenvillian-age basement within the Pan-African terranes and the former linkage of now-separated Grenvillian age belts in East Antarctica cannot therefore be excluded from U–Pb zircon evidence alone.