Paleoproterozoic orogenesis in the southeastern Gawler Craton, South Australia∗

Abstract

Integrated structural, metamorphic and geochronological data demonstrate the existence of a contractional orogen preserved in the ca 1850 Ma Donington Suite batholith along the eastern margin of the Gawler Craton, South Australia. The earliest structures are a pervasive gneissic foliation developed in the Donington Suite and interleaved metasedimentary rocks. This has been overprinted by isoclinal and non-cylindrical folding, and zones of pervasive non-coaxial shear with north-directed transport, suggesting that deformation was the result of orogenic contraction. SHRIMP U -Pb zircon data indicate that a syn-contractional granitic dyke was emplaced at 1846 + 4 Ma. Overprinting the contractional structures are a series of discrete, migmatitic high-strain zones that show a normal geometry with a component of oblique dextral shear. U -Pb zircon data from a weakly foliated microgranite in one such shear zone give an emplacement age of 1843 + 5 Ma. Rare aluminous metasedimentary rocks in the belt preserve a granulite-grade assemblage of garnet þ biotite þ plagioclase þ K-feldspar þ silicate melt that formed at *600 MPa and *7508C. Peak metamorphic garnets are partially replaced by biotite þ sillimaniteþ cordierite assemblages suggesting post-thermal peak cooling and decompression, and are indicative of a clockwise P -T evolution. Chemical U -Th -Pb electron microprobe ages from monazites in retrograde biotite yield a minimum estimate for the timing of retrogression of ca 1830 Ma, indicating that decompression may be linked to the development of the broadly extensional shear zones and that the clockwise P -T path occurred during a single tectonothermal cycle. We define this ca 1850 Ma phase of crustal evolution in the eastern Gawler Craton as the Cornian Orogeny.

Glacial dispersion of hydrothermal monazite in the Prominent Hill deposit: An exploration tool

“…Comparative data for metamorphic monazite is taken from the Mount Woods Domain (Forbes et al, 2011;this study), Corny Point (Reid et al, 2008), and the Fowler Domain (Thomas et al, 2008) (Fig. 1).…”

Australia and Nuna

“…Furthermore, the Cornian Orogeny, preserved in the southeastern Gawler Craton (Reid et al 2008) may also form part of the orogenic system responsible for the amalgamation of the Diamantina Craton. The Western Australian Craton remains the same as initially defined (Myers et al 1996) and was formed during the c. 1960 Ma Glenburgh Orogeny (Johnson et al 2013) before it was amalgamated with the rest of the Australian continent.…”

“…These rocks correlate with the Kalkadoon Batholith in the Mount Isa Terrane, and in the reconstruction of Giles et al (2004) form a continuous magmatic belt. The Donington Suite has an elevated incompatible element signature, 1Nd (1850Ma) values between -2 and -4, and 1Hf (1850Ma) values between 24 and +5.3, suggesting derivation from fractionated mafic crust, with contamination from Archaean crust (Hand et al 2007;Reid et al 2008). Reid et al (2008) suggested that the Donington Suite formed in a continental back-arc region based on the absence of subduction-related geochemical characteristics.…”

“…The Donington Suite has an elevated incompatible element signature, 1Nd (1850Ma) values between -2 and -4, and 1Hf (1850Ma) values between 24 and +5.3, suggesting derivation from fractionated mafic crust, with contamination from Archaean crust (Hand et al 2007;Reid et al 2008). Reid et al (2008) suggested that the Donington Suite formed in a continental back-arc region based on the absence of subduction-related geochemical characteristics. An alternative interpretation is that the wide range of radiogenic isotope values reflects the mixing of Archaean and juvenile magma sources.…”

“…Immediately following the emplacement of the Donington Suite, the eastern Gawler Craton underwent an episode of compressional orogenesis during the c. 1850-1845 Ma Cornian Orogeny (Reid et al 2008). This event is characterized by north-directed transport and the development of non-coaxial folds.…”