PETROLOGY OF THE TOPFER FORMATION - FIRST TRIASSIC GONDWANA SEQUENCE FROM NEW-ZEALAND

The 2 km(2) outcrop of Topfer Formation is the only known sedimentary formation of Triassic age in New Zealand's Western Province. It consis ts mainly of uniform medium-grained massive, well sorted felsic volcan iclastic sandstone with minor mudstone, conglomerate and coal. Two dis tinct petrofacies (litharenite and feldspathic litharenite) are distin guishable on both detrital and diagenetic composition. On the basis of common framework modes, heavy-mineral assemblages, depositional envir onment, intrusion by Jurassic dolerite and association with Palaeozoic quartzose sandstone, we relate the Topfer Formation to the Middle to Late Triassic Gondwana sequences of the Sydney Basin, Tasmania and Ant arctica. Some similarities in composition of sandstones and igneous co nglomerate clasts of the Topfer Formation and those of the coeval Muri hiku Terrane of New Zealand's Eastern Province suggest a common contin ental magmatic-are source area (possibly the intervening Median Tecton ic Zone). The tiny area of Topfer Formation thus provides a key strati graphic and palaeogeographic link between Gondwana and the Eastern Pro vince terranes of New Zealand.