High-grade metamorphic equivalents of the Centralian Superbasin in the Harts Range region, central Australia

High-grade metamorphic equivalents of the Centralian Superbasin in the Harts Range region, central Australia.

 

David Maidment, Ian Williams & Martin Hand1

 

1 Department of Geology & Geophysics, The University of Adelaide

 

A SHRIMP study of detrital zircon ages is being undertaken to assess possible correlations between high-grade metasediments from the Harts Range region, east of Alice Springs, and adjacent low-grade sediments of the Amadeus and Georgina Basins. Recent work has suggested that the upper amphibolite to granulite facies Irindina Supracrustal Assemblage (ISA) of the Harts Range is not Palaeoproterozoic, as has previously been assumed, but as young as Cambrian. Neoproterozoic to Early Ordovician stratigraphic units in the Georgina and Amadeus Basins have been sampled to test whether their detrital zircon age patterns are the same as any in the ISA metasediments.

 

Four units from the southern Georgina Basin have been analysed: the Grant Bluff Fm (Late Neoproterozoic); Mt Baldwin Fm (Early Cambrian); Arrinthrunga Fm (Late Cambrian) and the Tomahawk Beds (Cambro-Ordovician). The detrital zircon ages cluster at ~2.5 Ga, 1.9Ð1.7 Ga and 1.2Ð1.0 Ga, consistent with derivation from sources in the Arunta and Musgrave Inliers. These groupings are very similar to those that have been found in ISA metasediments, suggesting that both sequences shared a similar source. A particularly close correlation is evident between the detrital zircon spectra of the Tomahawk Beds and the amphibolite facies Brady Gneiss.

 

The Georgina Basin and ISA sequences also share a common change in provenance over time, further supporting correlation between the two. The late Neoproterozoic to Late Cambrian units of the Georgina Basin contain no zircons younger than ~800 Ma, whilst the Cambro-Ordovician Tomahawk Beds has abundant zircons younger than 800 Ma. Similarly, the structurally lowest units of the ISA are also poor in <800 Ma zircons, whilst the upper units show an increasing abundance of 550-800 Ma zircons.

 

Similar maximum depositional ages, provenance ages and changes in provenance thus indicate that the high-grade metamorphics of the Harts Range region are correlatives of Neoproterozoic to Cambro-Ordovician sediments in the Georgina Basin. Early results from the eastern Amadeus Basin are consistent with this interpretation. The ISA sediments were rapidly buried to about 30-35 km by 480-460 Ma and metamorphosed to granulite-facies. This probably occurred within an intracratonic rift setting, concurrent with the formation of the Larapintine Seaway.