Arnhem Province

The poorly understood Palaeoproterozoic Arnhem Province exposed in eastern Arnhem Land, is the focus of new Northern Territory Geological Survey (NTGS) 1:100 000 scale geological mapping.

Field investigations commenced in June 2014 in Gove, Caledon and BL 1:100k map areas, and will continue in 2015. 

Aims of project

This project aims to investigate the timing, nature and geodynamic setting of sedimentation, deformation, metamorphism and magmatism in the Arnhem Province in order to develop an understanding of the geological evolution and resource potential of this terrane. 

This project will investigate potential correlations polymetalic Pine Creek Orogen (PCO) in western Arnhem Land. 

Findings

Findings to date include:

  • field observations coupled with new geochronology and geochemistry indicate the following geological evolution for the Arnhem Province:
    • deposition of siliciclastic sediments, protoliths to the Grindall Formation and the Melville Bay Metamorphics in a deep-water, marine setting at ca 1885 Ma
    • granite magmatism and emplacement of the igneous protolith to garnet-biotite orthogneiss at ca 1880 Ma 
    • deformation and regional high-T, low-P metamorphic event at ca 1871–1856 Ma resulting in in situ partial melting, migmatite formation and subsequent S-type, garnet-cordierite-biotite granite magmatism
    • intrusion of voluminous A-type fayalite-biotite granites of the Giddy Suite at ca 1830–1824 Ma.
  • maximum deposition ages and zircon provenance studies indicate that the Grindall Formation and Melville Bay Metamorphics are not age correlatives with the Cosmo Supergroup of the Pine Creek Orogen as previously thought, but represent older sedimentary successions which have similar provenance to the Cahill Formation and Nourlangie Schist of the Nimbuwah Domain of the PCOm
  • whole rock geochemistry of ca 1871–1862 Ma S-type granites and similar-aged intrusions of the Nimbuwah Complex in the PCO reveals a distinct difference in composition suggesting that they are derived from different source regions
  • preliminary average pressure-temperature constraints on the Melville Bay Metamorphics indicate rocks were metamorphosed under granulite-facies conditions ≥ 840 ± 80°C and 8.3 ± 1.3 kbar at ca 1860 Ma. 

Outputs

The Arnhem Province project will result in a series of new 1:100 000-scale geological maps and GIS products with accompanying explanatory notes, regular abstracts and presentations at AGES and revised Arnhem Province chapter in the Geology and Mineral Resources of the Northern Territory.

Release Date

2016–2017

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Last updated: 29 October 2016