The Australian Lithospheric Architecture Magnetotelluric Project - uncovering the deep earth with magnetotellurics
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The Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) aims to provide a 3D image of the electrical resistivity distribution of the crust and mantle beneath the Australian continent. Zones of low resistivity are now widely established to be areas of mechanically weak lithosphere, which have undergone extensive shearing and faulting and have provided pathways for fluid and magmatic flux. This insight has wide-ranging implications for our understanding of the evolution of the Australian continent and helps to map out fertile zones in the crust that have witnessed large fluid movement at some stage in the tectonic history. As a result, it will inform about the prospectivity of the state.
Black dots show the locations of AusLAMP sites
AusLAMP is a collaborative national magnetotelluric (MT) project focused on acquiring long-period MT data at approximately 2800 sites across Australia, over half degree grid spacing (approximately 55 km). The Geological Survey of South Australia (GSSA) has been an early supporter of this national initiative and has been aggressively pushing its roll-out in South Australia since 2014. This large-scale deployment of long-period MT stations collected every ~55 km has acquired 400 new sites.
Data acquisition was largely funded by PACE initiatives with additional funding by Geoscience Australia, the National Collaborative Research Infrastructure Strategy and the University of Adelaide. The core acquisition team at the University of Adelaide, Philippa Mawby, Bruce Goleby and Geoff Axford, have established lasting relationships with native title holders, pastoralists and national park agencies to roll out the environmentally low impact AusLAMP program across the state. Processing and modelling is done within the GSSA and at the University of Adelaide. Highlights of the 3D resistivity models have been:
- The unveiling of a remarkable connection between deep-crustal low resistivity zones beneath the prospective eastern Gawler Craton Olympic Domain and the abundance of mineral occurrences in this iron oxide – copper–gold (IOCG) belt. See figure below or Thiel et al., 2016
- The 3D MT model across the Ikara-Flinders Ranges and the Curnamona Province which has established compelling conductivity anomalies along the Nackara Arc and Curnamona Province (Robertson et al, 2016; 2017), strongly renewing interest in the Broken Hill Domain.
- Delineation of the western margin of the Gawler Craton and, in joint analysis with closer-spaced profile MT data, identification of large-scale lithospheric boundaries
This new ground-breaking statewide dataset will add another geoscientific layer of information for stakeholders. Together with other statewide geophysical and widespread geochemical isotope data, this vital dataset will assist the GSSA’s new Lithospheric Architecture team to enhance our understanding of the tectonic history of the state and reduce risk in mineral exploration.
Electrical resistivity at a depth of 30 km, performed using ModEM3DMT (Egbert & Kelbert, 2012, Kelbert et al., 2014). Red is conductive, blue is resistive. Green circles are copper occurrences. Three individual models are stitched together for this figure.
The revelation that conductive crustal anomalies act as possible fertility corridors across the state has led to new follow-up initiatives using closer spaced and higher frequency MT surveys. Examples are the PACE Copper funded Olympic Domain MT survey across the Stuart Shelf including numerous IOCG prospects; and the deployment of two broadband MT profiles in 2017 and 2018 led by the University of Adelaide with collaboration and funding from the GSSA. In 2017, an east-west 120 km transect across the Curnamona Province, and in 2018 an northwest-southeast ~90 km transect across Tumby Bay. The aim of both surveys is to focus in on the conductivity corridors and how they are resolved into the upper crust. This work also follows on from previous highly informative insights from the Olympic Dam MT profile (University of Adelaide, Heinson et al 2018), and high-density MT profile across the Beverley uranium mine (Thiel et al. 2016).
For updates of the continent wide progress of AusLAMP see the Geoscience Australia AusLAMP webpage.
AusLAMP in SA is a collaborative project between the GSSA, the University of Adelaide and Geoscience Australia with funding from the GSSA’s PACE Copper initiative, Geoscience Australia and NCRIS. Thank you to the core field team Philippa Mawby, Bruce Goleby and Geoff Axford and all other field crew for collecting the data, and to Goran Boren for instrument maintenance. The instruments were provided by the AuScope instrument pool at the University of Adelaide. Thanks to landholders and traditional owners for allowing access to the lands and to Naser Meqbel for providing 3D grid software. Figures were generated using GMT 5 (Wessel et al., 2013). This project was undertaken with the assistance of resources and services from the National Computational Infrastructure (NCI), which is supported by the Australian Government. This work was also supported with supercomputing resources provided by the Phoenix HPC service at the University of Adelaide. 3D models were visualised and analysed using Emerson SKUA-GOCAD.
For more information, contact:
Program Coordinator - Lithospheric Architecture