Australia: The Land Where Time Began

A biography of the Australian continent 

North Australian Craton – Reworking in the Grenvillian of late Palaeoproterozoic Crust of the Southern NAC, Central Australia, Implications for the Assembly of Australia in the Mesoproterozoic

The presence along the central southern margin of the North Australian Craton (NAC) of a deformation system of Grenvillian age (about 1,130Ma) on a regional scale has been revealed by LA-ICP-MS U-Pb monazite and zircon geochronology from metapelites and migmatic (mixture of metamorphic and igneous rock) orthogneiss. From the southern Aileron Province near Alice Springs a deformation of Grenvillian age extends over a strike length of 100 km to the Teapot Granite Complex within the Warumpi Province. Evidence has also been found of migmatisation and resetting of monazite further to the west in the Mt Liebig area, which Wong et al. suggest may extend the foot-print of Grenvillian age to a strike length of at least 250 km. Map-scale folds that are east-west trending and shear zones that are strongly foliated  and dip steeply that define the structural architecture of the interface region between the Aileron Province and the Warumpi Province have been produced by deformation that is associated with the reworking of Grenvillian age. Shallow folds that are westerly plunging associated with the partial melting have evolved into shear zones and mylonites that have recorded movement in which the south side is up. It is suggested by phase equilibria modelling of age-constrained garnet-biotite ± sillimanite ± cordierite-bearing metapelites from the southern Aileron and Warumpi Provinces that metamorphism of Grenvillian age reached temperatures ranging from 770^oC to 820^oC and pressures of 5-5.5 knar, which corresponds to thermal gradients of about 130^oC to 165^oC/kbar. Late Palaeoproterozoic (about 1,650-1,630 Ma) high grade metamorphic rocks were reworked and overprinted by the extensive system of Grenvillian age. The system from the Grenvillian is present above an interface of lithospheric-scale that dips to the south that has been imaged geophysically to depths of at least 200 km. Wong et al. interpreted this feature as representing a fossil subduction zone from the late Palaeoproterozoic. However, the presence in the crust above this feature of a deformation of regional scale from the Grenvillian suggests that it might actually be from the Grenvillian. Wong et al. suggest that if this is the case then suturing of the NAC with the Musgrave Province, which is of Grenvillian age, to the south may be recorded by the deformation along the southern margin of the NAC. This would effectively place the Musgrave Province, from the Mesoproterozoic that is a long-lived ultrahot orogen, in southern central Australia in an upper plate tectonic setting, which was linked to convergence of the NAC with the South Australian Craton (SAC).

Sources & Further reading

1. Wong, B. L., L. J. Morrissey, M. Hand, C. E. Fields and D. E. Kelsey (2015). "Grenvillian-aged reworking of late Paleoproterozoic crust of the southern North Australian Craton, central Australia: Implications for the assembly of Mesoproterozoic Australia." Precambrian Research 270: 100-123.