Talk and Poster for AESC 2023
Mantle density, temperature, composition, and water content beneath Greater McArthur Basin in North Australian Craton
Lu Li1 Alan Aitken1, Sinan Özaydin2, Weronika Gorczyk1 and Mark Jessell1
- Centre for Exploration Targeting, School of earth science, The University of Western Australia
- School of Geosciences, The University of Sydney
A high-resolution model of mantle rheology is desired to understand the geodynamic process that drives sediment accumulation and preservation in the Greater McArthur Basin. Constraining upper mantle rheology requires a robust estimation of mantle temperature and composition, as well as the influence of water and melt. Seismic tomography is sensitive to changes in both temperature and composition, but it cannot readily distinguish between the two. However, the density change associated with temperature or compositional change are divergent from the effect on seismic velocity, which provides an opportunity to use density to separate temperature and composition. Moreover, a robust estimation of temperature and composition is a prerequisite to constrain the water content from the electrical resistivity model using magnetotellurics.
Here, we use gravity inversion to resolve the density distribution in the mantle. We build an initial density model by converting the seismic tomography model AuSREM with a uniform mantle composition using a mineral physics approach. We then use 3D gravity inversion to resolve the density distribution in the mantle. Based on the resolved mantle density, along with the AuSREM model, we update the compositional model and temperature field. In addition, we use the mantle temperature field, as well as the resistivity model obtained from AusLAMP data, to calculate the water content in the lithospheric mantle.
Our results indicate compositional heterogeneity in the mantle underlying Greater McArthur Basin, with depleted mantle in the south and re-fertilized mantle in the north. We estimate a new lithosphere and asthenosphere boundary based on the 1200°C isotherm. A thinner lithosphere feature trending NE-SW separates two deep lithosphere domains with thickness exceeding 200 km. The southeast domain exhibits thick sediment accumulation, thick lithosphere, and highly-conductive features in the upper mantle, whereas the central domain shows thick sediment preservation, thin lithosphere, and highly-resistive features in the upper mantle. The northwest domain has relatively thin sediment cover and thick lithosphere. These new obtained lithosphere structures allow us to estimate the rheological heterogeneity and understand the evolution of Proterozoic basins.
Refined crustal structure and radiogenic heat production in Greater McArthur Basin region by joint inversion of gravity, pseudo-gravity, and magnetic data
Lu Li1 Alan Aitken1, Weronika Gorczyk1 and Mark Jessell1
- Centre for Exploration Targeting, School of earth science, The University of Western Australia
Understanding the tectonic history and geodynamic processes of continents requires knowledge of crustal properties, including heat and compositional heterogeneity. Geothermal heat flow originates from the mantle, with additional contributions from radiogenic materials in the crust. Estimating the crust's heat contribution requires a robust understanding of the distribution of radiogenic materials, which are highly linked with crustal composition.
In this study, we use a joint inversion of gravity, magnetic, and pseudo-gravity data to resolve the density and magnetic susceptibility distribution in the upper crust, where these properties are coupled based on structural similarity through cross-gradient. Using the resolved density and magnetic susceptibility distributions, we generate a basement lithology classification map that distinguishes between felsic and mafic rocks beneath sedimentary basins. We then use whole-rock geochemical datasets to link lithology with radiogenic heat production.
Our results show that felsic-type crust dominates the northeast portion of the Greater McArthur Basin, with additional felsic crust present in the central Pine Creek region. Based on global whole-rock geochemical datasets, the estimated felsic crust has a heat production value of over 3 μW/m³. The southwest portion of the Greater McArthur Basin is dominated by mafic crust with a heat production value of less than 1.5 μW/m³. We further calculate the radiogenic heat flow using the lithology thickness from the joint inversion. Areas including Pine Creek and Bauhinia show high radiogenic heat flow, exceeding 60 mW/m², which matches the anomalous high measured geothermal heat flow in these regions.