Blaikie, Teagan1, McFarlane, Helen1,
1CSIRO Mineral Resources, Perth, Australia
The Tanami Region, located 600 km to the northwest of Alice Springs, preserves an important record of basin development, deformation, magmatism, and the assembly of the North Australian Craton during the Paleoproterozoic. The region comprises extensive polydeformed metasedimentary and volcanic rocks, preserved as the ca. 1885-1840 Ma Tanami Group and the ca. 1824–1816 Ma Ware Group. The Lander Rock Formation of the adjoining Aileron Province represents a comparably aged metasedimentary package that is considered to be laterally equivalent to the Killi Killi formation in the upper part of the Tanami Group. These metasedimentary packages were extensively intruded by 1825–1790 Ma granites and dolerite dykes, and deformed during the ca. 1840 Tanami Event, and the 1825–1790 Ma Stafford Event.
Extensive cover makes geological studies in this region challenging, but newly acquired 200 m line spaced aeromagnetic data and previously acquired gravity and seismic data offers valuable information on the underlying geology. This data were interpreted to produce a solid geological map, and develop a new cohesive structural framework. This aimed to test the different stratigraphic, structural and tectonic models that presently exist for the region. The interpretation initially focussed on mapping the fault architecture and lithological units under cover, and was constrained by the petrophysical characteristics of each unit and correlation of outcropping geology with distinct geophysical features.
Results of the interpretation led to revision of the extent of previously mapped or interpreted units, and recognition of potential correlative units across the two terranes. In the northwest Aileron Province, the extent of the Archean inlier known as the Billabong Complex was revised based on correlation of outcrop with a distinct geophysical response characterised by a variable moderate to high amplitude magnetic intensity and featuring strong magnetic lineaments. The complex is now defined as a fault bounded arcuate belt flanked by granitic units. A continuous geophysical signal, defined by a moderate to low gravity response, and low magnetic intensity with a smooth texture was also recognised between the Killi Killi and Lander Rock formations. Magnetic units with a moderate magnetic intensity and strong linear fabric, which are very similar in character to the Dead Bullock Formation were also noted within the north-western Aileron province, and may represent a previously unrecognised lateral equivalent of the Dead Bullock Formation in this area. These observations support previous interpretations of the deep crustal seismic data which suggest stratigraphy is continuous and drapes the crustal boundary between Tanami Region and Aileron Province. This implies the two terrains were joined together prior to deposition of the Tanami Group and Lander Rock Formation and the onset of deformation and magmatism related to the Stafford Event.
Dr Teagan Blaikie is a research scientist in geophysics based at the CSIRO in Perth. Her work focuses on regional scale interpretation and modelling of geophysical data to understand the architecture and tectonic evolution of sedimentary basins and polydeformed terranes