Lower crust and upper mantle electrical anisotropy in southeastern Australia

Abstract

The dominant north-south strike of the Palaeozoic outcrop of central Victoria has been well documented, but to the north, these rocks are covered by the Cainozoic sedimentary deposits of the Murray Basin. Two magnetotelluric surveys were completed to assist in extrapolation of the known structure and to identify possible new targets for mineral discovery. Supporting the results from previous seismic interpretations for the region, the 2D MT inversion models substantiate an intrazone thrust fault system of listric geometries in the Bendigo Zone connected in the mid-crust. With the zone boundary clearly defined the electrical resistivity structure is distinct between the major subdivisions, indicating a different tectonic evolution for the Bendigo and Melbourne Zones. However, the conductive overburden in the region poses complications for the generation of the 2D resistivity models. Static shifts and electrical anisotropy were identified as distortions in the dataset, with further processing needed to attain a complete picture of the underlying geology. The difficulties caused by galvanic distortion were allayed by using the phase tensor response in place of the distorted amplitude response. Phase tensor analysis of MT data has been completed subsequently, the results of which we present here, along with the original 2D inversion models, confirming that electrical anisotropy persists into the mantle.

Electrical conductors in Archean mantle—Result of plume interaction?

“…A deep mantle conductor is situated underneath the central Gawler Craton and appears to be temporally related to the 1590Ma Hiltaba event and Gawler Range Volcanics, which are the result of a plume‐modified orogenesis as an analogue to present day Yellowstone‐type magmatism [ Kelbert et al , ]. Further studies will need to address the depth extent of the conductor to depths beyond 100km and possible anisotropy of the mantle given the strong electrical polarization state derived from phase tensor analysis in this study and from recent findings in other areas of the Australian continent [ Simpson , ; Dennis et al , ] (Figure ). The mantle is resistive underneath the St. Peter Suite, Fowler Domain and the 2550 Ma Mulgathing Complex suggesting a more depleted mantle in those parts.…”

Magnetotelluric evidence for serpentinisation in a Cambrian subduction zone beneath the Delamerian Orogen, southeast Australia

“…This conductor extends beyond the edge of the profile, and an extension of the profile to the west of the transect, and longer period data would be required to have any confidence in interpretations of the anomaly. The Mt Gambier volcanoes are 100- Dennis et al (2012). This feature was thought to be connected to a central Victorian thermal anomaly and mantle-derived CO 2 -rich fluids related to the Quaternary Newer Volcanics, but required further thermal modelling.…”

Inferring geological structural features from geophysical and geological mapping data using machine learning algorithms

“…The Geological Structure data map for the study area is shown in Figure 2d. A preliminary interpretation report on the area was produced by the Korean Institute of Geological & Mineral Resources (KIGAM) as part of a collaborative project among GSV, Monash University and KIGAM (Dennis et al., 2012). The Geological Structure Map provided by GSV originally included 34 geological categories (e.g.…”

“…The data is gridded with a grid size of 50 m, using a minimum curvature gridding method. The final merged grid is presented as two zonally projected grids (Cull et al, 2008;Dennis et al, 2008Dennis et al, , 2012.…”