Carpentaria Electrical Conductivity Anomaly, Queensland, as a major structure in the Australian Plate

Abstract

The Carpentaria Conductivity Anomaly of western Queensland is a major element in the electrical conductivity structure of the Australian continent. Investigation of it is significant both for its own sake, and as a case history in the general understanding of continental conductivity structure. Following its earlier discovery by reconnaissance magnetometers arrays, detailed magnetotelluric observations were carried out in 1997 along a transect crossing the anomaly between Cloncurry and Julia Creek. The magnetotelluric results define a good conductor within the crust beneath the sediments of the Eromanga Basin. The conductor extends over a depth range of tens of kilometres. This structure, evidently shown also by aeromagnetic and gravity data, is interpreted as the eastern boundary of the Mt Isa Block at a plate suture, which was later covered by the sediments of the Eromanga Basin. Seismic tomographic results show a major gradient in seismic-wave speed in the region. It appears the potential-field, electromagnetic and seismic methods have detected different characteristics of the same geologic structure, with complementary results. The electromagnetic results, new to this paper, define horizontal position well, and give evidence of highly conducting material from the crust to a depth of tens of kilometres. The seismic results extend the depth of the boundary into the upper mantle. The case history supports the hypothesis that the major conductivity anomalies of the geomagnetic deep-sounding method mark continental sutures of fundamental significance in recording the creation of continents.

The Relationship Between the Magnetotelluric Tensor Invariants And The Phase Tensor Of Caldwell, Bibby, And Brown

“…These results compare quite well with the strike angle determined by Groom-Bailey decomposition for short periods on the west of the profile (Lilley et al, 2003).…”

Crustal architecture and geodynamics of North Queensland, Australia: Insights from deep seismic reflection profiling

“…This suture also appears to correspond with the western margin of the Carpentaria Conductivity Anomaly of Lilley et al (2003).…”

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“…Anisotropic conductivity models employ a tensor to describe the Earth's conductivity both vertically and horizontally [Lilley et al, 2001;Caldwell et al, 2004]. The influence of conductivity anisotropy on the effects of geomagnetic activity, such as those due to coastal effects, have been studied by Viljanen and Pirjola [1994b] Fernberg et al [2007].…”