Late Neoproterozoic passive margin of East Gondwana: Geochemical constraints from the Anakie Inlier, central Queensland, Australia

Abstract

Development of the East Gondwana passive margin and when it occurred are constrained by the composition of low-grade mafic schists and U–Pb ages of detrital zircons in psammitic schists from the Bathampton Metamorphics in the Anakie Inlier of central Queensland. These rocks show considerable variation in light lithophile elements due to post-magmatic processes. They have flat heavy rare earth element patterns, low-TiO 2 (<2 wt.%) contents and their immobile element Ti, V, Y, La, Nb, Th and Zr values, indicate that they have an N-MORB-like magmatic affinity. However, they differ from N-MORB in that they show light rare earth depleted patterns and lower incompatible trace element contents. Their relative low abundance and association with metasediments suggest they formed in a magma-poor rifted margin setting. They are associated with psammitic rocks with detrital zircon ages indicating probable deposition in the late Neoproterozoic at ca 600 Ma. A magma-poor rifted margin in northeastern Australia differs from the volcanic passive setting that occurred in southeastern Australia at this time. These findings support development of the East Gondwana margin at 600 Ma that may have been related to rifting of a microcontinent off East Gondwana well after the breakup of Rodinia at ca 750 Ma.