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