Basin analysis in polymetamorphic terranes: An example from east Antarctica

摘要

U-Pb and Lu-Hf isotopic signatures of detrital and metamorphic zircon in granulite facies paragneiss from Kemp and MacRobertson lands, east Antarctica, distinguish two extensive Precambrian basins: (1) an Archaean basin deposited between c. 2570. Ma and c. 2500-2430. Ma, which extended across Kemp Land contiguous with equivalent paragneiss in the adjacent Napier Complex in Enderby Land; and (2) a late Mesoproterozoic basin deposited after c. 1110-1080. Ma in MacRobertson Land that extends into eastern Kemp Land, which also incorporates rocks currently exposed in the Eastern Ghats Province of India and the Prydz Bay region of east Antarctica. An unconformity that separates the Archaean and Mesoproterozoic sedimentary packages is near the Stillwell Hills. An eastward increase in the proportion of fragmentary detrital zircon in the younger package reflects proximity to late Mesoproterozoic volcanic sources. The Mesoproterozoic basin likely developed along an Andean-type margin to the Indo-Antarctic craton, possibly in a back-arc setting during the assembly of Rodinia. The widespread dissolution of zircon at c. 990-940. Ma during Rayner orogenesis in Kemp and MacRobertson lands largely precludes a traditional basin analysis via detrital geochronology, but the Hf isotopic ratio of metamorphic zircon precipitated following anatexis provides a homogenised signature, equivalent to a bulk-rock model age, which can be used as a stratigraphic proxy. This approach captures "hidden" provenance information to enable lithostratigraphic correlation in complex high-grade terranes.