Developing thermochemical models of Australia’s lithosphere

Lithospheric structure and melting processes in southeast Australia: new constraints from joint probabilistic inversions of 3D magnetotelluric and seismic data

“…The electrical conductivity of each individual phase is turned into bulk conductivity through the Generalised Archie's Law (Glover, 2010) The LAB model is in good agreement with the mean LAB obtained using LitMod1D (Afonso et al, 2013a(Afonso et al, , 2013bHaynes et al, 2020), even though the data sets used in each inversion are completely different. The first-order LAB structure is also in agreement with the LAB depths derived from seismic velocity models (Davies et al, 2015;Rawlinson et al, 2017).…”

“…Using prior information from previous inversions in eastern Australia, the initial 3D model (i.e., starting point) of our MCMC simulation is constructed by assembling the LAB depths for each 1D column from the model of Rawlinson et al (2017) The crustal layers' RHP are obtained with a previous 1D joint probabilistic inversion (Haynes et al, 2020;Afonso et al, 2013aAfonso et al, , 2013b. The initial V P for the crustal layers and Moho depths (Figure 1.e) are taken from the regional AusREM model (Australian Seismological Reference Earth Model, Kennett & Salmon, 2012) and the initial value for each thermal node is derived from an adiabat between the initial LAB and the node at 410 km depth (T 410 = 1500 o C).…”

“…The main cementation components used here, however, provide similar values to the Hashin-Shtrikman lower-bound for a lherzolitic matrix ( Özaydın & Selway, structure of Southeast Australia The depth to the thermal LAB (1250 o C, Afonso, Rawlinson, et al, 2016) obtained from the joint probabilistic inversion of seismic velocities and MT data is shown in Figure 4, while the complete 3D temperature structure is shown via depth slices in Figure 5 (first three columns). Figure 4 also includes a recent LAB model obtained from a 1Djoint probabilistic inversion of elevation, surface heat flow, Rayleigh wave dispersion curves, and geoid anomalies using LitMod1D(Haynes et al, 2020;Afonso et al, 2013b); and the estimated LAB depths from two recent seismic tomography models in eastern Australia(Davies et al, 2015;Rawlinson et al, 2017). These results reveal a highly heterogeneous lithospheric structure beneath the Tasmanides: while shallow LAB depths (< 100 km) are imaged on the eastern and south edges of the model, deeper LAB depths (> 250 km) are found beneath the Curnamona Province (CP) and the northern part of the Delamerian Orogen.…”

Lithospheric structure and melting processes in southeast Australia: new constraints from joint probabilistic inversions of 3D magnetotelluric and seismic data

“…The crustal RHP is obtained using the mean crustal RHP from a previous 1D joint probabilistic inversion (Figure 1.e Haynes et al, 2020) while the Moho depths are taken from the regional AusREM model (Kennett & Salmon, 2012). We also incorporate one conductivity cell below each MT station as extra parameters to account for the galvanic distortion effect produced by near-surface inhomogeneities beyond the resolution of our model (Jones, 2011;Chave & Jones, 2012;Avdeeva et al, 2015).…”

“…Figure 3 also includes a recent LAB model obtained from a low-resolution 1D joint probabilistic inversion of elevation, surface heat flow, Rayleigh wave dispersion curves, and geoid anomalies(Haynes et al, 2020;Afonso et al, 2013b) and the estimated LAB depths from two recent seismic tomography models in eastern Australia(Davies et al, 2015;Rawlinson et al, 2017). The maximum absolute difference in lithosphere thickness inside the region is ∼ 200 km, with shallow LAB depths (< 100 km) in the eastern and southern ends of the continental block and deep LAB depths (> 250 km) beneath the Curnamona Province (CP) and the northern part of the Delamerian Orogen.…”