Ben Mather

Antarctic geothermal heat flow (GHF) is one of the least constrained basal boundary conditions affecting subglacial hydrology and ice sheet dynamics. Furthermore, the paucity of knowledge about GHF hampers our understanding of the linkages between geodynamic evolution and tectono-thermal conditions in Antarctica.Here we present the results of enhanced spectral analysis of a new Antarctic aeromagnetic anomaly compilation, conformed at long wavelengths with SWARM satellite magnetic data. We apply manual picking of defractal magnetic power spectra on several different major subglacial lake districts in both West and East Antarctica and compare our results with those obtained using automated workflows implemented in PyCurious. Furthermore, we compare our results with independent GHF estimates from seismology, multivariate-similarity approaches and previous magnetic studies.We show that in the Amundsen Sea Embayment in West Antarctica manual spectral picking resolves the spatial heterogeneity in GHF anomalies better than automated approaches. We newly define a wide coastal region of relatively lower values corresponding to recently inferred mafic intrusions within this sector of the West Antarctic Rift System and higher GHF in the Byrd Subglacial Basin. This is highly significant as it suggests that elevated GHF may contribute to the onset of enhanced ice flow in the interior of the Thwaites Glacier catchment. Additionally, we find localised GHF anomalies in the area of the Thwaites active lakes that may affect subglacial water availability and promote reduced basal shear stress despite the widespread hard bed conditions related to the occurrence of predominantly crystalline rocks.In East Antarctica, the manual approach confirms the existence of elevated GHF beneath the Dome C subglacial lake district. However, the anomaly is more linear than previously recognised and better aligned with the trend of major aeromagnetic anomalies interpreted as reflecting extensive Paleo to Mesoproterozoic basement in the sector of East Antarctica. Notably, remarkably similar magnetic anomalies are imaged in formerly contiguous Australia where highly radiogenic igneous provinces significantly enhance GHF.Overall, we find that the choice of appropriate window sizes and spectral ranges coupled with careful inspection of individual power spectra (including the recognition of outliers) and the choice of defractal parameters is important to better define regional scale heterogeneity in Curie Depth estimates. We also find that incorporating the results of independent seismic, multivariate approaches, and expert knowledge in the geological settings of the different study regions is beneficial to better define the realistic ranges of average Curie Depth and for the conversion from Curie Depth to GHF.The results of our magnetic studies need to be integrated into thermal modelling frameworks together with the evolving knowledge of crustal and lithospheric properties in Antarctica, including intracrustal heat production and sedimentary basin distribution. This approach will yield improved spatial resolution and accuracy of Antarctic GHF and better understanding of the geological origin and significance of major GHF anomalies.

The exchange of carbon between oceanic plates, the deep Earth, and the atmosphere plays a significant role in modulating global climate. Icehouse-greenhouse climate fluctuations have been attributed to changes in palaeogeography and solid Earth degassing, particularly along continental arcs, to arc weathering and to the sequestration of carbon into oceanic carbonate-rich sediments. However, the proportions of these contributions and their effect on modulating global climate are poorly constrained. Here we show that the changing balance between volcanic outgassing and carbon sequestration into oceanic lithosphere is the key driver for major climate shifts. Combined volcanic arc, mid-ocean ridge and continental rift emissions exceed carbon sequestration during greenhouse climates. In contrast, oceanic plate sequestration exceeds emissions during icehouse climates. Our results challenge the long-held view that carbon degassing along volcanic arcs is the main contributor to atmospheric carbon, suggesting instead that mid-ocean ridge and rift degassing surpass arc emissions before 100 Ma.

Anisotropic viscosity is likely prevalent within the upper mantle, but is usually disregarded in geodynamics models. On a crystal scale, olivine’s intrinsic properties are such that dislocation creep occurs over an order of magnitude more easily along olivine’s [100] symmetry axis than along its [001] axis. However, deforming olivine aggregates generate crystallographic preferred orientations (CPO) with their own macroscopically effective anisotropic viscosities that have proven difficult to estimate from the microscopic anisotropies of individual olivine crystals. Here we present a simple method to derive anisotropic viscosity parameters directly from the CPO mean orientation tensors. To calibrate the method, we created a large database of textures likely to occur in geodynamic simulations. We tested our method within numerical simulations of simple shear with both constant and varying shear directions. Finally, we integrated our method into the geodynamic code ASPECT, where it can be used to explore the geodynamic importance of anisotropic viscosity.

Most sediment-hosted mineral deposits occur in marine sedimentary rocks along intracratonic or epicratonic rift basins at the edges of the thick continental lithosphere. Craton thickness, typically 150–200 km, was analysed using the Full-Waveform Seismic Tomography (REVEAL model) to extract horizontal shear wave velocity (Vsh), vertical shear wave velocity (Vsv), and isotropic P-wave velocity (Vp). Principal component analysis and k-means clustering revealed that Vsh effectively defines craton boundaries and similarly thick lithospheric features, aligning well with mineral deposits. IOCG and sediment-hosted deposits are found within ~125 km of these boundaries (based on total metal content) and ~100 km (based on ore tonnage). These deposits form along internal and external craton boundaries, separating Archean nuclei from Proterozoic terranes and along Phanerozoic orogens and accreted passive margins. Thermal and lithospheric models were used to differentiate cratons from other thick lithospheric features, isolating ~85% of all deposits related to the edge of cratons. Additionally, we found that more than ~85% of craton edge deposits are formed within 90 km of craton boundaries. A consistent gradient of increasing metal content with proximity to craton boundaries underscores the significance of these craton boundaries. In fact, more than 85% of known target craton edge deposits are concentrated within just 16% of continental areas, significantly enhancing exploration efficiency and resource discovery by reducing exploration areas.Building on this foundation, we conducted a temporal analysis to explore why some craton boundaries are fertile while others are not, aiming to reduce exploration areas more. By analysing over 20 kinematic features using the latest reconstruction model spanning 1,800 Ma for craton deposits and uniformly generated random points within 180 km of craton boundaries, we reconstructed craton boundaries, deposits, and random points to identify key patterns. Lower craton velocities (

Antarctic geothermal heat flux (GHF) is poorly known restricting our ability to assess its influence on subglacial hydrology and ice sheet dynamics. Within the 4D Antarctica and the 3D Earth ESA projects, a new Antarctic aeromagnetic anomaly compilation, conformed at long wavelengths with SWARM satellite magnetic data was complied. All the datasets were levelled, microlevelled and stitched together. We also differentially continued all survey data to 4 km and re-gridded the compilation onto a 4 km grid mesh.Our new aeromagnetic anomaly compilation enables us to re-assess Antarctic geothermal heat flux (GHF) heterogeneity, a critical basal boundary condition that influences Antarctic ice sheet flow and subglacial melting and hydrology. To estimate GHF we applied Curie Depth Point (CDP) estimation using the centroid, modified centroid and fractal/defractal approaches. We compared our CDP results with independent constraints on crustal and lithosphere thickness derived from seismological, airborne gravity and satellite gravity modelling and effective elastic thickness estimates. We also considered empirical estimates of GHF derived from seismology and recent models of intracrustal heat production from gravity inversion to assess additional uncertainties associated with CDP to GHF conversion. We performed both automated continental scale estimates and nested manual analysis of CDP and GHF with a specific focus on different Antarctic subglacial lake districts.We found elevated GHF in the West Antarctic Rift System (WARS) beneath the rapidly changing Thwaites (THW) and Pine Island sectors of the West Antarctic Ice Sheet (WAIS) and along the edge of the Marie Byrd Land block. Focussed estimates of GHF were performed over the cascading active lakes beneath THW to provide new constraints for hydrological modelling in this critical sector of the WAIS. We image a large degree of heterogeneity in thermal basal boundary conditions beneath the active subglacial lake districts that underlie the ice streams flowing into the Ross Sea Embayment, which we relate to hitherto poorly known tectono-magmatic segmentation of the WARS.In East Antarctica, elevated GHF is associated with some of the active lakes underlying the Byrd glacier catchment, but relatively lower GHF values are typical of both the active and static lakes of the northern Wilkes Subglacial Basin (WSB). This suggests limited upper crustal extension beneath this enigmatic subglacial basin compared to major Mesozoic to Cenozoic extension in the WARS. These findings agree with current seismological evidence for well-preserved fast and cold craton margin lithosphere beneath most of the WSB.We image relatively elevated GHF beneath the Dome C and Dome A subglacial lake districts. This may be caused by cryptic but large-scale provinces of high heat producing Precambrian basement or could reflect major intraplate reactivation of Precambrian fault systems. Elevated GHF is also imaged in Dronning Maud Land and stretching from Enderby Land to Princess Elizabeth Land. We propose that this could reflect Cambrian age lithosphere thinning due to orogenic collapse processes that affected major and yet still cryptic paths of Gondwana-forming orogenic belts fringing East Antarctica. Additionally, Jurassic to Cretaceous thinning was likely superimposed and associated with passive margin formation during Gondwana break-up.

Nickel-Copper (Ni-Cu) sulphide deposits are a diverse class of deposits, formed during the cooling and crystallisation of metal-rich mafic to ultramafic magmas. Despite sharing several key ore-forming processes, many of these deposits form in contrasting geologic environments and periods. The objective of this research project is to investigate the spatial and temporal distribution of Ni-Cu sulphide deposits in a mantle convection and plate tectonic context, and to explore the influence of different mantle and tectonic parameters on their origins and occurrence. We first determine the location of these deposits in relation to relevant geologic and tectonic features through time, including subduction zones, large igneous provinces (LIPs), and mantle plumes. Using a 1 billion year plate model we extract key parameters relating to subduction, as well as the spatio-temporal distribution of LIPs through time. Employing an associated geodynamic model, we identify model mantle plumes and quantify their key properties. Preliminary findings indicate that certain mantle plumes associated with deposits exhibit increased plume flux in the upper mantle preceding deposit formation, and that many deposits are spatially associated with LIPs throughout their formation history. For several deposits located in convergent margin settings, we have identified a notable spike in subduction volume and convergence rate during a 50-100 million year period prior to the onset of mineralisation. While the angle of the subducting slab is highly variable throughout the evolution of these deposits, several deposits are associated with a distinct steepening of the subducting plate in the lead-up to deposit formation. The findings of this study aim to contribute new insights into the dynamic processes governing the genesis of magmatic Ni-Cu sulphide deposits. These insights aid in our understanding of the interplay between mantle dynamics, plate tectonics, and deposit formation, and hold implications for future critical mineral exploration.

The Pacific Ocean, the largest ocean basin, plays a critical role in the global carbon cycle, where a massive quantity of deep-sea sediment is sequestered on the seafloor and ultimately transferred into the mantle through its extensive subduction zones. However, the fluxes of carbonate carbon to the seafloor, and the volume stored and subducted in the Pacific remains relatively unknown over the Cenozoic. Here we estimate the carbonate carbon flux to the Pacific seafloor since the early Cenozoic by modelling the evolution of the carbonate compensation depth (CCD), defined as the water depth where carbonate supply from the surface equals its dissolution at depth. This results in a lack of carbonate sediments below the CCD. Except for the eastern equatorial region, the CCD is poorly constrained or unknown in other regions of the Pacific. Given the regional and latitudinal variations in oceanographic parameters affecting carbonate sedimentation (e.g., water chemistry, surface productivity) across the Pacific basin, the Cenozoic CCD is modelled for six regions of the western and eastern North Pacific, western tropical Pacific, eastern equatorial Pacific, and western and eastern South Pacific. We utilize 110 deep-sea drill sites from DSDP, ODP and IODP expeditions to reconstruct the paleo-water depth through time at each location using pyBacktrack software. We carry out a linear reduced major-axis regression of the carbonate accumulation rate (CAR) versus paleo-water depth to compute the CCD in 0.5 My time intervals, incorporating dynamic topography and eustatic sea-level in our computations. We find that the CCD has fluctuated over the Cenozoic by ~1–1.2 km and shows distinct variabilities within the six regions of the Pacific. For example, a relatively shallow CCD (~2.8–4 km) across the western North and eastern South Pacific versus a deep CCD (~4–4.7 km) in the eastern equatorial region, and highly fluctuating western tropical CCD over the late Cenozoic, suggest substantial latitude-longitude control on the carbonate flux. The results indicate that the total carbonate carbon flux is primarily dominated by the eastern equatorial region between the early Oligocene and the middle Miocene (to maximum 55 Mt C/yr), due to enhanced nutrient concentration and higher primary productivity rate, as reflected by a deeper CCD. This contrasts with minimal carbonate carbon flux in the eastern and western North Pacific ranging between 0 and 5 Mt C/yr over the Cenozoic. Additionally, the Pacific total carbonate carbon mass has experienced a modest rise from the early Eocene (55 Ma) to the early Oligocene at ~34 Ma (from 3000 to 3500 Mt), followed by a gradual increase, reaching 4400 Mt at the present day. This recorded progressive rise since the early Oligocene coincides with the initiation of the Antarctic ice-sheet growth and intensified continental silicate weathering and alkalinity input to the oceans. Our new modelling of the CCD to assess the evolution of the Pacific deep-sea carbonate carbon reservoir during the Cenozoic improves constraints on deep carbon computations in the context of the global carbon cycle.

A new continent-wide aeromagnetic anomaly compilation for Antarctica, conformed at longer wavelengths with SWARM satellite magnetic data includes recent international datasets collected after the ADMAP 2.0 compilation analysed within the 3D Earth project of ESA. This ADMAP 2.0+ product includes: 1) ROSETTA data collected by a US-NZ team over the Ross Ice Shelf; 2) reprocessed US-German and UK data collected over the Amundsen Sea Embayment; 3) German, Danish, UK- Argentina-Norwegian data over the Recovery ice stream catchment; 4) ESA PolarGAP data over South Pole and 5) enhanced vintage datasets for the Gamburtsev Subglacial Mountains and Wilkes and Dome C regions in East Antarctica. A new digital database was assembled using updated line data holdings and all data were levelled. microlevelled and stitched together via grid stitching approaches and subsequently differentially continued to 4 km and re-gridded on a 4 km grid mesh. Here we use this new aeromagnetic anomaly compilation to re-assess Antarctic geothermal heat flux (GHF) heterogeneity, a critical basal boundary condition that influences Antarctic ice sheet flow and subglacial melting patterns and hydrology, and is related to crustal and lithospheric structure, composition, and heat production. Within the 4D Antarctica ESA project we applied Curie Depth Point (CDP) estimation using the centroid, modified centroid and fractal/defractal approaches. Our new CDP map reveals regions of enhanced GHF along the coast of the Amundsen Sea Embayment, in agreement with independent seismological estimates. Potential thermal anomalies within the West Antarctic Rift System (WARS) also underlie the Byrd Subglacial Basin. Linear rift related anomalies are now imaged more clearly beneath the Siple Coast ice streams and active subglacial lake districts. In East Antarctica, the new CDP estimates over the enigmatic WSB are significantly deeper compared even to the coldest sectors of the WARS. This suggests that if Mesozoic to Cenozoic extension affected this region, it mostly occurred at upper crustal levels rather than the whole lithosphere, in general agreement with relatively sparse seismological evidence for a predominantly cratonic lithospheric environment. A particularly intriguing region of enhanced GHF is identified in Dronning Maud Land. We propose that this could arise from lithospheric thinning perhaps associated with delamination processes, which have been independently inferred from petrological signatures in post-orogenic granitoids, emplaced after the pan-African age assembly of Gondwana. Alternatively, this feature could reflect thermal anomalies related to much later passive margin formation during Gondwana rifting and break up. Finally, we discuss intriguing GHF anomalies inferred in the Dome C and Dome A subglacial lake regions in interior East Antarctica. We suggest the hypothesis that these anomalies relate to anomalously high intracrustal heat production, such as observed in Australia in some Proterozoic terranes, or to ill-constrained reactivation of the inherited structural architecture, This includes major Proterozoic and younger Pan-African age orogenic belts that may have been reactivated in response to far field stresses during Mesozoic to Cenozoic Gondwana break up and subsequent sea floor spreading processes.