Magnetotelluric data were acquired for Geoscience Australia by contract along the north-south 08GA-C1-Curnamona seismic traverse to the east of Lake Frome from November 2008 to January 2009 as part of the Australian Government's energy security initiative. 25 sites were spaced an average of 10 km apart, and five-component broadband data were recorded with a frequency bandwidth of 0.001 Hz to 250 Hz and dipole lengths of 100 m. Apparent resistivity and phase plots are presented, along with dimensional analyses of the data based on rotational invariants, the representation of the data by the phase tensor, and Parkinson arrows. These analyses provide insight into the complexity of the Earth conductivity giving rise to the MT responses and are a useful precursor to modelling.

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.

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.

In 2007, three seismic lines were collected by Geoscience Australia and the Geological Survey of Queensland from Cloncurry to south of Charters Towers via Croydon and Georgetown, and a fourth line by AuScope to the northeast of Mt Surprise. Signals were recorded to ~20 seconds two-way travel time (TWT), which equates to about 60 kilometres in depth. The recent lines are among the latest in a series of deep seismic profiles conducted across Queensland since 1980.

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

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.

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>

Description of the Youanmi MT acquisition and processing along the 10GA-YU1, 10GA-YU2, 10GA-YU3 seismic lines. A collaborative project with the Geological Survey of WA.

Magnetotelluric (MT) data were acquired in September 2009 in a collaborative project by Primary Industry and Resources, South Australia (PIRSA), Geoscience Australia and the University of Adelaide (UA) along the east-west southern Flinders ranges seismic traverse in South Australia. The seismic and MT data acquisition are part of the Australian Government's energy security program, with main funding being provided by PIRSA under the Plan for Accelerating Exploration (PACE) initiative. The MT data form a valuable complimentary addition to the seismic data for the investigation of energy potential and crustal architecture of this region. National facility Auscope MT instruments based at UA were used (through ANSIR agreement) to record both broadband data with a frequency range 200 Hz to 0.008 Hz and long period data with a frequency range of 10 Hz to 0.0001 Hz. This enables sensing of Earth electrical conductivity from near-surface in the crust to depths well below the Moho. Two orthogonal components of the magnetic field were measured with induction coils for the broadband acquisition, and three components of the magnetic field were recorded with fluxgate sensors for the long-period data. Two horizontal components of the electric field were measured at each site with orthogonal NS and EW dipoles ~50 m long. Data were recorded at fifteen sites with a nominal spacing of 10 km covering a profile ~150 km in length. Data are processed to industry standard EDI files prior to the generation of apparent resistivity and phase plots. A suite of plots are created to investigate dimensionality including, skew angle, phase tensor ellipses and Parkinson arrows. Parkinson arrows point to regions of high conductance and away from more resistive blocks. Preliminary analysis of the long period data has revealed that the Parkinson arrows generally point to the east at higher frequencies. At lower frequencies these arrows swing southerly pointing to the south east.

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.