Redefining the Basement Architecture of the Southern Mount Isa Inlier

Brown. D.D. 1 , Bultitude,R.J1., Simpson,J.M, Purdy,D.P1., Connors, K.A.2, Sanislav,I.V. 3.

1Geological Survey Of Queensland, 2University of Queensland, 3James Cook University

The Paleoproterozoic Kalkadoon-Leichhardt belt (KLB) forms the major basement block to a series of Paleoproterozoic Superbasin sequences of the Mount Isa Inlier. The basement sequences of the Mount Isa Inlier have a broad two-fold division comprising: 1) the Leichhardt Volcanics and the Kalkadoon Granodiorite (~1865Ma) formed during the Barramundi Orogeny and 2) a series of pre-1870Ma units which are restricted in distribution to the KLB and margins of the Western Succession (Kurbayia Metamorphic Complex, Yaringa Metamorphics, and Saint Ronans Metamorphics).

The eastern portion of the KLB is overlain by and complexly faulted with the Mary Kathleen Domain (MKD). The MKD is dominantly comprised of calcareous and siliciclastic metasedimentary units belonging to the Paleoproterozoic Leichhardt Superbasin (~1790 – 1740 Ma) and igneous rocks of the Wonga and Burstall suites (~1740 Ma). At the southern outcropping extent, several intrusive units had previously been included in either the Burstall Suite (Saint Mungo Granite), Wonga Suite (Birds Well Granite, Bushy Park Gneiss) or correlated with ~1740 Ma magmatism (Tick Hill Complex) and thus included in the Mary Kathleen Domain.

New SHRIMP and LA-ICP-MS U-Pb geochronology shows that some units in the southern MKD are much older and form part of the basement (KLB). The Bushy Park Gneiss and Birds Well Granite form part of the KLB with crystallisation ages consistent with the Barramundi portion of the KLB. Hafnium isotope studies indicate these units to have εHf which closer to CHUR whereas the previously analysed Barramundi portion of the KLB has uniform εHf values of ~ -4 which indicates some heterogeneity in the southern portion of the inlier.

This is confirmed by interpretation and reinterpretation deep seismic lines CF3 and M6, which reveal an extensive basement package in the subsurface of the Southern Mount Isa inlier and throughout the Eastern Sub province. This package appears to be a controlling factor for deformation and basin development from 1865 Ma.


Dominic Brown has worked on the geology, geochemistry, geochronology and geophysics of Queensland for 15 years at the Geeological Survey of Queensland across a diverse suite of projects.

About the GSA

The Geological Society of Australia was established as a non-profit organisation in 1952 to promote, advance and support Earth sciences in Australia.

As a broadly based professional society that aims to represent all Earth Science disciplines, the GSA attracts a wide diversity of members working in a similarly broad range of industries.