Zealandia and Australia at Ordovician continental margins: reconciling their similar and differing detrital zircon provenances within Rodinia

ABSTRACT New detrital zircon ages from biostratigraphically well-controlled Ordovician sandstones in southeast Australia are compared with published counterparts in southern Zealandia. During Rodinia supercontinent assembly (RA), Australia and Zealandia age patterns are similar, everywhere with ubiquitous late Mesoproterozoic magmatic zircon sources. However, during earliest Gondwana supercontinent assembly (GA), the age patterns have different sediment sources: (1) those of late Neoproterozoic age are more strongly represented in Zealandia but of uncertain location, but (2) those of late Cambrian-Ordovician age are more prominent in eastern Australia, having probable origins in the Ross-Delamerian Orogen. In particular, a distinctive zircon component, ca. 600–650 Ma, is ubiquitous in Zealandia but rare in Australia. Early Paleoproterozoic and Archean (Nuna, NU) zircon sources (2000–3200 Ma) become important (and locally up to 25% total) in Zealandia but not in Australia. It is difficult to reconcile all these sediment source requirements within disparate and distant Australian-Antarctic Precambrian complexes. Instead, it is proposed that, through the early Palaeozoic, Zealandia had only local sediment sources in a discrete Rodinia basement continental block outcropping in South Zealandia that was formerly adjacent to South China.