Approaching earth science problems in a “data-driven” philosophy can help glean new insights into our problem and quantify uncertainty.
Stagnant slabs in the transition zone linked to widespread volcanism in Eastern Australia and Zealandia Dr. Ben Mather , Prof. Dietmar Muller, Dr. Maria Seton, Dr. Nick Mortimer, Saskia Ruttor Regional context Interested in the last 100 million years of tectonic evolution when Australia separated from Antarctica. The region now known as “Zealandia” is most likely a fragment of continental crust that was rafted off mainland Australia. Mortimer et al. (2017), GSA today ← Muller et al. (2016), EPSL Volcanic activity 3 major hotspot chains: Tasmantid seamount chain Lord Howe seamount chain Cosgrove track These chains are made up of central volcanoes with leucitite-bearing eruptions. However, there smaller lava field volcanoes that exhibit no time dependence. Lava shield volcanoes outnumber eruptions from central volcanoes. Hotspot chains What drives non-age progressive eruptions in Eastern Australia and Zealandia? Previous geodynamic studies Convective eddy that forms at the trailing edge of sharp discontinuities in lithospheric thickness Davies et al. 2014, Farrington et al 2010, Demidjuk et al. 2007 Shear-driven upwellings in the mantle that induce partial melting at the base of the lithosphere Conrad et al. 2011 Edge-driven convection Asthenopheric shear
The eastern margin of Australia has experienced extensive mafic volcanism since its breakaway from Antarctica (~ 80 Ma). A plume origin has been suggested for intraplate volcanism, however, the timing and location of eruption points does not clearly correlate with Australia’s northward motion of 5-8cm/yr. That Cenozoic volcanism coincides with dynamically supported topography of up to 1km throughout the eastern highlands suggests a complex interaction between a mantle plume and lithospheric geometry as Australia migrated northward. Further complications to dynamic topography arise from boundary forces such as the sinking eastern Gondwana slab and large Pacific mantle upwelling. We present a synthesis of geochemistry, seismic, and geodynamic constraints within an integrated plate reconstruction of Australia over the last 80 million years. This provides a framework within which to test geodynamic models that match geophysical and geochemical observations.
Probabilistic methods for constraining lithospheric thermal structure by jointly inverting geothermal, magnetic, and seismic data using Bayesian inference.
Quagmire is an open source, parallel python module for modelling surface processes and landscape evolution.
Presenting updates on AuScope-supported research in geophysics and geodynamics, including developments in computational tools for surface processes and geothermal modelling.
A 3D temperature model of Ireland has provided a unique insight into the thermochemical structure within Ireland’s subsurface.
Temperature models for assessing geothermal potential are usually concerned with the upper 5 km of the crust. The configuration of deeper crustal lithologies, and the thermo-chemical properties assigned to them, greatly affects temperature variation in the upper crust, but are highly uncertain. We pose an inverse problem that integrates surface heat flow observations, seismic velocities, and Curie depth to constrain upper crustal temperature in Ireland. From our inversions we can retrieve information on boundary conditions, crustal heat production, and thermal conductivity. We quantify the uncertainty of these thermo-chemical properties to produce statistically robust temperature models of the crust. The uncertainty of the temperature field in the upper crust directly controls whether a geothermal resource is viable. In Ireland there is a gradual increase in surface heat flow from SW to NE based on limited heat flow data. However, we determine that the heat production of felsic bodies contribute a more significant amount of heat to the upper crust, despite relatively high uncertainty.
Surface heat flux is highly sensitive to small temperature fluctuations at varying timescales. The magnitude of these variations depend on the duration of climatic fluctuations and add significant uncertainty to present-day surface heat flow estimates. We assimilate heat flow data with multiple geophysical observations that resolve the crust in its present-day state to improve the constraints on subsurface thermal models and quantify the uncertainty in surface heat flux. The Curie depth isotherm is computed from magnetic data to constrain temperatures in the middle-lower crust, while P and S-wave velocities that we extract from tomographic models are sensitive to temperature to varying degrees throughout the lithosphere. We integrate these within an adjoint inversion framework that we apply to Southeastern Australia to invert the structure of thermal conductivity and heat sources within the crust. Based on previous inversions solely constrained by surface heat flow points and seismic velocity, we found that relatively high rates of heat production in Proterozoic crust control the variation of heat flux at the surface. This Proterozoic crust shares tectonic provenance with Antarctica and may have significant implications for its heat flow regime. Here, we will quantify the uncertainty reduction of thermal structure from assimilating Curie depth in addition to seismic velocity and heat flow observations. Our inversion framework can be easily adapted to integrate additional data types available for Antarctica to improve the precision of geothermal heat flux estimates.
Geothermal power is traditionally viable only in volcanically active regions, however direct application of this energy source for industrial heating can exploit low enthalpy sources buried in the crust. Attempts to examine the geothermal potential of Ireland have been impeded by sparse heat flow measurements and a lack of thermal constraints to apply to rocks, such as thermal conductivity and heat production. Our project seeks to increase the density of heat flow measurements in Ireland to provide new constraints on the temperature field. In addition, we revisit historic heat flow measurements to account for a palaeoclimate correction associated with the last glacial maximum some 15,000 years ago. This has the effect of increasing heat flow values by approximately 15%. We assimilate these data within a novel inversion framework to quantify the uncertainty of subsurface temperature. Additional constraints can be obtained from the depth to Curie temperature – the point at which rocks lose their magnetism (approximately 580°C) – which we computed across Ireland using the recently acquired Tellus airborne magnetic data. Our simulations highlight a gradual increase in subsurface temperature SW to NE and localised heat flow anomalies associated with granite bodies enriched in high heat-producing elements. The uncertainty of these anomalies are, however, relatively high, thus we seek to improve the precision of temperature estimates by resolving finer geological detail and assimilating seismic velocities.