Magnetotelluric (MT) data have been acquired in 2008 and 2009 at 40 broadband (0:01 s to 500 s) and 12 long-period (10 s to 10 000 s) sites along the east-west deep seismic reflection transect of northern Eyre Peninsula, South Australia. The MT survey is a joint project between the University of Adelaide and Geoscience Australia and is funded by the Australian Government as part of the Onshore Energy Security Program. Long-period sites are spaced 20 km apart and broadband sites infill this spacing to 10 km with also some 5 km spacing. This ensures sufficient coverage to map the upper crustal to upper mantle structures beneath northern Eyre Peninsula.

To investigate the standard electrical conductivity profile beneath a continent, we conducted a magnetotelluric (MT) observation with long dipole span near Alice Springs, central Australia. We utilized geomagnetic data acquired at the Alice Springs geomagnetic observatory operated by Geoscience Australia. Using the BIRRP processing code (Chave and Thomson, 2004), we estimated the MT and GDS (geomagnetic depth sounding) transfer functions for periods from 100 to 10 to 6 sec. The MT-compatible response functions converted from GDS response functions are resistive compared to the Canadian Shield (Chave et al., 1993) for periods around 10 to 5 sec. The calculated MT responses also have generally high apparent resistivity values over the entire period range. We inverted the average MT responses into a one-dimensional conductivity profile using Occam inversion (Constable et al., 1987). The resultant conductivity profile is extremely resistive (0.001 to 0.0001 S/m) down to the mantle transition zone. We compared this one-dimensional structure with electrical conductivity profiles predicted from compositional models of the earth's upper mantle by calculating phase diagrams in the CFMAS (CaO-FeO-MgO-Al2O3-SiO2) system. The on-craton and off-craton chemical composition models (Rudnick et al., 1998) were adopted for the tectosphere. The Perple_X (e.g. Connolly, 2005) programs were used to obtain mineral proportions and compositions with depth. The calculated conductivity profiles with on- and off-craton models show significantly larger magnitude than the observed. The result suggests the continental lithosphere (tectosphere) beneath Australia is extremely dry and its temperature profile is cooler than that used in the calculation.

These presentations from Geosciece Australia staff form part of the 2011 AGES (Annual Geoscience Exploration Seminar) meeting. Extended abstracts associated with these presentations can be found in the Northern Terriorty Geological Survey Record 2011-003.

2009 Georgina-Arunta Seismic and MT Surveys - Acquisition and Processing

Geoscience Australia, along with its partners, have used seismic reflection and magnetotelluric data, acquired under the Onshore Energy Security Program, and pre-existing geological and geophysical data, to provide new insights into the 3D architecture, geodynamics, mineral and the energy potential of the North Queensland region. The 3D architecture was constrained using all available data leading to an improved understanding of the North Queensland region. Innovative 3D geophysical techniques have been adopted to provide new understandings of the 3D alteration patterns associated with potential mineralisation and energy potential of the region. <p>Related material<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&amp;catno=69862">3D Map and Supporting Geophysical Studies in the North Queensland Region - 3D data package</a></p>

As part of the Australian Government's Onshore Energy Security Program and the Queensland Government's Smart Mining and Smart Exploration initiatives, deep seismic reflection surveys (~2300 line km) were conducted in North Queensland to establish the architecture and geodynamic framework of this area in 2006 (Mt Isa Survey; also involving OZ Minerals and pmd*CRC) and 2007 (Cloncurry-Georgetown-Charters Towers Survey; also involving AuScope). The purpose here is to use new geodynamic insights inferred from the seismic and other data to provide comments on the large-scale geodynamic controls on energy and other mineral potential in North Queensland.

This article presents the results of studies in North Queensland associated with the 2007 Mt Isa-Georgetown-Charters Towers seismic survey. Results include seismic interpretation, geophysical studies and 3D maps, tectonic and metallogenic syntheses and energy potential assessment.

Geoscience Australia (GA) has been acquiring both broadband and long-period magnetotelluric (MT) data over the last few years along deep seismic reflection survey lines across Australia, often in collaboration with the States/Territory geological surveys and the University of Adelaide. Recently, new three-dimensional (3D) inversion code has become available from Oregon State University. This code is parallelised and has been compiled on the NCI supercomputer at the Australian National University. Much of the structure of the Earth in the regions of the seismic surveys is complex and 3D, and MT data acquired along profiles in such regions are better imaged by using 3D code rather than 1D or 2D code. Preliminary conductivity models produced from the Youanmi MT survey in Western Australia correlate well with interpreted seismic structures and contain more geological information than previous 2D models. GA has commenced a program to re-model with the new code MT data previously acquired to provide more robust information on the conductivity structure of the shallow to deep Earth in the vicinity of the seismic transects.

The Record contains extended abstracts to accompany presentations at the GOMA (Gawler Craton-Officer Basin-Musgrave Province-Amadeus Basin) seismic and MT workshop, Adelaide 25 November 2010.

PowerPoint presentations presented at the NORTH QUEENSLAND SEISMIC AND MT WORKSHOP in Townsville, June 2009.