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The North Australian Zinc Belt is the largest zinc-lead province in the world, containing three of the ten largest known individual deposits (HYC, Hilton-George Fisher, and Mount Isa). The Northern Cordillera in North America is the second largest zinc-lead province, containing a further two of the world’s top ten deposits (Red Dog and Howards Pass). Despite this world-class endowment, exploration in both mineral provinces during the past 2 decades has not been particularly successful, yielding only two significant discoveries (Teena, Australia, and Boundary, Canada). One of the most important aspects of exploration is to choose mineral provinces and districts within geological belts that have the greatest potential for discovery. Here, we present results from these two zinc belts that highlight previously unused datasets for area selection and targeting. Lead isotope mapping using analyses of mineralized material has identified gradients in μ (238U/204Pb) that coincide closely with many major deposits. Locations of these deposits also coincide with a gradient in the depth of the lithosphere-asthenosphere boundary determined from calibrated surface wave tomography models converted to temperature. Furthermore, gradients in upward-continued gravity anomalies and a step in Moho depth correspond to a pre-existing major crustal boundary in both zinc belts. A spatial association of deposits with a linear mid- to lower-crustal resistivity anomaly from magnetotelluric data is also observed in the North Australian Zinc Belt. The change from thicker to thinner lithosphere is interpreted to localize prospective basins for zinc-lead mineralization and to control the gradient in lead isotope and geophysical data. These data, when combined with data indicative of paleoenvironment and changes in plate motion at the time of mineralization, provide new exploration criteria that can be used to identify prospective mineralized basins and define the most favorable parts of these basins.

Dataset provided as supplement to Rovere et al. (2023).The influence of reef isostasy, dynamic topography, and glacial isostatic adjustment on the Last Interglacial sea-level record of Northeastern Australia,CommunicationsEarth & Environment, in press. delta_DT_grids --- grids of predicted change in elevation of Last Interglacial (125 ka) sea-level markers since deposition due to dynamic topography. ASPECT_parameter_files --- ASPECT parameter files for global mantle convection simulations. ASPECT_initial_temperature_files --- input temperature files for driving ASPECT mantle convection simulations, read in to ASPECT using 'ascii data' initial temperature plugin. ASPECT_parameter_files ---input compositionfiles for driving ASPECT mantle convection simulations, read in to ASPECT using 'ascii data' initial composition plugin. 1 represents points within LLVP dense basal layer; 0 represents 'ambient' mantle.

A global understanding of the evolution of oceanic lithosphere yields key insights about lithosphere-asthenosphere interaction. An important starting point is that age-depth and heatflow measurements provide the fundamental constraints for progressive cooling of oceanic lithosphere. When jointly inverting these measurements to identify an optimal plate model, the robustness of the result is predicated upon their quality, number and global distribution. Here, we exploit a revised and extensively augmented database of accurate age-depth measurements (n = 10,874) and a published database of heatflow measurements (n = 3,753). These databases are jointly modelled using both analytical and numerical methodologies to obtain a plate model, which has an average asthenospheric temperature of 1325±50oC and a lithospheric thickness of 105±10 km. These recovered values agree with independent geochemical and seismic constraints of mantle potential temperature and lithospheric thickness. This revised plate cooling model is used to improve our understanding of lithosphere-asthenosphere interaction. First, we use plate cooling to measure residual depth anomalies, which are a reliable proxy for mantle dynamic topography. Our results demonstrate that dynamic topography varies on wavelengths as short as 1000 km with amplitudes of ±1 km. Secondly, we combine plate cooling with the depth distribution of oceanic intraplate earthquakes to identify the isothermal surface above which brittle elastic behaviour occurs. Finally, we demonstrate that age-depth and heatflow measurements exhibit a sustained flattening from ~60 Ma, suggesting that resupply of heat from the asthenosphere is an essential component of the lithosphere-asthenosphere system. Our database of accurate residual depth measurements is used to explore links between mantle dynamics, asthenospheric temperature anomalies extracted from earthquake tomographic models, and basaltic melting.

Geothermal Heat Flow (GHF) is a crucial boundary condition governing ice sheet stability, due to the positive relationship between thermal input into the ice sheet and basal sliding rates. Tectonic history biases the crustal distribution of heat-producing elements, and the pattern of mantle convection influences regional thermal structure, leading to significant intracontinental variations in Antarctic GHF of order 100 mW/m2. However, extensive ice cover across Antarctica severely limits the ability to directly measure GHF or crustal composition. Geophysical proxies are therefore required to access information pertaining to the lateral structure of GHF and its potential impact on ice sheet dynamics.Previous studies have used geomagnetic data to infer the depth above which ferromagnetic structure is locked in, corresponding to the ~850 K isotherm. Others have relied on the sensitivity of seismic velocity to thermal structure to model local variations in surface temperature gradient. Both approaches require assumptions on crustal properties, which are typically chosen ad-hoc, and may affect GHF estimates in a significant and non-systematic manner. Other studies have used the observed covariation between lithospheric seismic velocity and GHF in regions with high measurement densities (e.g., continental USA) to map Antarctic seismic structure into GHF. This introduces a dependency of inferred Antarctic GHF on the range of tectonic environments sampled by the continental region used to derive the empirical relationship.Here, we adopt a distinct approach, in which Monte Carlo sampling is used to include crustal conductivity and heat production as free parameters in a numerical modelling procedure that fits theoretical geotherms to new probabilistic seismic inferences of upper mantle temperature structure beneath Antarctica. By integrating empirical constraints on crustal conductivity derived from P-wave velocity data, we are able to build distributions of covarying crustal conductivity, heat production, and GHF. This allows us to generate a model of Antarctic GHF which is complementary to that of other studies, and includes an estimate of lateral uncertainty structure based on the sensitivity of thermal gradients to crustal composition and anelastic deformation at seismic frequencies.

Uncertainty in present-day glacial isostatic adjustment (GIA) rates represents at least 44% of the total gravity-based ice mass balance signal over Antarctica. Meanwhile, physical couplings between solid Earth, sea level and ice dynamics enhance the dependency of the spatiotemporally varying GIA signal on three-dimensional variations in mantle rheology. Improved knowledge of thermomechanical mantle structure is therefore required to refine estimates of current and projected ice mass balance. Here, we present a Bayesian inverse method for self-consistently mapping shear-wave velocities from high-resolution adjoint tomography into thermomechanical structure using calibrated parameterisations of anelasticity at seismic frequency. We constrain the model using regional geophysical data sets containing information on upper mantle temperature, attenuation and viscosity structure. Our treatment allows formal quantification of parameter covariances, and naturally permits propagation of material parameter uncertainties into thermomechanical structure estimates. We find that uncertainty in steady-state viscosity structure at 150 km depth can be reduced by 4-5 orders of magnitude compared with a forward-modelling approach neglecting covariance between viscoelastic parameters. By accounting for the dependence of viscosity on loading timescale, we find good agreement between our estimates of mantle viscosity beneath West Antarctica, and those derived from satellite GPS. Direct access to temperature structure allows us to estimate lateral variations in lithosphere-asthenosphere boundary (LAB) depth, geothermal heat flow (GHF), and associated uncertainties. We find evidence for shallow LAB depths (63 ± 13 km), and high GHF (76 ± 7 mW m^-2) beneath West Antarctica, suggesting a highly dynamic response to ice mass loss.

Understanding sea level during the warmest peak of the Last Interglacial (125,000 yrs ago; Marine Isotope Stage 5e) is important for assessing future ice-sheet dynamics in response to climate change, and relies on the measurement and interpretation of paleo sea-level indicators, corrected for post-depositional vertical land motions. The coasts and continental shelves of northeastern Australia (Queensland) preserve an extensive Last Interglacial record in the facies of coastal strandplains onland and fossil reefs offshore. However, there is a discrepancy (amounting to tens of meters) in the elevation of sea-level indicators between offshore and onshore sites. Here, we assess the influence of geophysical processes that may have changed the elevation of these sea-level indicators since the Last Interglacial. We modeled sea-level change due to: i) dynamic topography; ii) glacial isostatic adjustment, and iii) isostatic adjustment due to coral reef loading, which we term "reef isostasy". These processes caused relative sea-level changes on the order of, respectively, 10 m, 5 m, and 0.3 m since the Last Interglacial. Of these geophysical processes, the dynamic topography predictions most closely match the tilting observed between onshore and offshore sea-level markers. However, we found that these combined geophysical processes cannot explain the full amplitude of the observed discrepancy between onshore and offshore sea-level indicators.

Estimates of global mean sea level during past warm periods provide an important constraint on ice sheet stability under prolonged warming and have been used to inform projections of future sea-level change. The Mid-Pliocene Warm Period (MPWP), ~3 million years ago, has been a particular focus since it represents the most recent interval in Earth history with inferred temperatures and atmospheric CO2 concentrations similar to those expected in the near future. Although several sea-level estimates for this period have been obtained from palaeoshoreline records, they differ by many metres due to spatially variable Pliocene-to-recent vertical motions of the crust, caused by geodynamic processes including sedimentary loading, tectonic activity, glacial isostatic adjustment, and mantle convection. To address this issue and place more robust bounds on the amplitude of MPWP sea level, we combine a continent-wide suite of Australian sea-level markers with geodynamic simulations to quantify and remove post-Pliocene vertical motions at the continental scale. We find that dynamic topography related to mantle convection is the dominant process responsible for deflecting Australian MPWP sea-level markers and that correcting for it and glacial isostatic adjustment yields a global mean sea-level estimate of +16.0^{+5.5}_{-5.6} m (50th/16th/84th percentiles). Although this range is consistent with other estimates from geomorphic sea-level indicators, the upper bound is lower than assumed in recent ice sheet modelling studies, suggesting a significantly more stable Antarctic Ice Sheet under future warming scenarios.

Following a survey on the impact of the pandemic on early-career researchers, Megan Maunder, Áine O'Brien, Jack Reid, Dominic M. Bowman, Fred Richards and Steven Gough-Kelly sift the data from Generation Covid.

The slow creeping motion of Earth’s mantle drives transient changes in surface topography across a variety of spatial and temporal scales. Recent decades have seen substantial progress in understanding this so-called `dynamic topography’, with a growing number of studies highlighting its fundamental role in shaping the surface of our planet. In this review, we outline the current frontiers of geodynamical research into dynamic topography. It begins with a summary of ongoing observational, theoretical and computational efforts that aim to quantify the present-day expression of dynamic topography, including its geographical distribution and sensitivity to different components of the mantle's flow regime. Next, observational constraints that shed light on how dynamic topography has changed over time are summarised, and compared with predictions from a range of geodynamical modelling studies, to highlight our current understanding of its evolution through the geological past. Although many model predictions can be reconciled with the available observational constraints, these comparisons demonstrate that there remain inconsistencies, particularly at shorter spatial and temporal scales. These discrepancies allow us to isolate the shortcomings of existing modelling approaches and identify pathways towards improving future reconstructions of dynamic topography through space and time. Such reconstructions are vital if we are to robustly connect the evolution of Earth's surface environments to the processes that are occurring deep within its interior.

Uncertainty in present-day glacial isostatic adjustment (GIA) rates represent at least 44% of the total gravity-based ice mass balance signal over Antarctica. Meanwhile, physical couplings between solid Earth, sea level and ice dynamics enhance the dependency of the spatiotemporally varying GIA signal on 3D rheology. For example, the presence of low-viscosity mantle beneath melting marine-based ice sheet sectors such as the Amundsen Sea Embayment may delay or even prevent unstable grounding line retreat. Improved knowledge of upper mantle thermomechanical structure is therefore required to refine estimates of current and projected ice mass balance.Here, we present a Bayesian inverse method for mapping shear wave velocities from high-resolution adjoint tomography into thermomechanical structure using a calibrated parameterisation of anelasticity at seismic frequency. We constrain the model using regional geophysical data sets containing information on upper mantle temperature, attenuation and viscosity structure. The Globally Adaptive Scaling Within Adaptive Metropolis (GASWAM) modification of the Metropolis-Hastings algorithm is utilised to allow efficient exploration of the multi-dimensional parameter space. Our treatment allows formal quantification of parameter covariances, and naturally permits us to propagate uncertainties in material parameters into uncertainty in thermomechanical structure.We find that it is possible to improve agreement on steady state viscosity structure between tomographic models by approximately 30%, and reduce its uncertainty by an order of magnitude as compared to a forward-modelling approach. Direct access to temperature structure allows us to estimate lateral variations in lithospheric thickness, geothermal heat flow, and their associated uncertainties.

Sustainable development and the transition to a clean-energy economy drives ever-increasing demand for base metals, substantially outstripping the discovery rate of new deposits and necessitating dramatic improvements in exploration success. Rifting of the continents has formed widespread sedimentary basins, some of which contain large quantities of copper, lead and zinc. Despite over a century of research, the geological structure responsible for the spatial distribution of such fertile regions remains enigmatic. Here, we use statistical tests to compare deposit locations with new maps of lithospheric thickness, which outline the base of tectonic plates. We find that 85% of sediment-hosted base metals, including all giant deposits (>10 megatonnes of metal), occur within 200 kilometres of the transition between thick and thin lithosphere. Rifting in this setting produces greater subsidence and lower basal heat flow, enlarging the depth extent of hydrothermal circulation available for forming giant deposits. Given that mineralization ages span the past two billion years, this observation implies long-term lithospheric edge stability and a genetic link between deep Earth processes and near-surface hydrothermal mineral systems. This discovery provides an unprecedented global framework for identifying fertile regions for targeted mineral exploration, reducing the search space for new deposits by two-thirds on this lithospheric thickness criterion alone. Major sediment-hosted base metal deposits are located within 200 km of the border between thick and thin lithosphere, according to statistical comparisons between global lithospheric thickness and known deposit locations.

It is generally agreed that the Last Interglacial (LIG; 130 – 115 ka)was a time when global average temperatures and global mean sea level were higher than they are today. However, the exact timing, magnitude, and spatial pattern of ice melt is much debated. One difficulty in extracting past global mean sea level from local observations is that their elevations need to be corrected for glacial isostatic adjustment (GIA), which requires knowledge of Earth’s internal viscoelastic structure. While this structure is generally assumed to be radially symmetric, evidence from seismology, geodynamics, and mineral physics indicates that large lateral variations in viscosity exist within the mantle. In this study, we construct a new model of Earth’s internal structure by converting shear wave speed into viscosity using parameterisations from mineral physics experiments and geodynamical constraints on Earth’s thermal structure. We use this 3D Earth structure, which includes both variations in lithospheric thickness and lateral variations in viscosity, to calculate the first 3D GIA prediction for LIG sea level. We find that the difference between predictions with and without lateral Earth structure can be meters to 10s of meters in the near field of former ice sheets, and up to a few meters in their far field. We demonstrate how forebulge dynamics and continental levering are affected by laterally varying Earth structure, with a particular focus on those sites with prominent LIG sea level records. Results from four 3D GIA calculations show that accounting for lateral structure can act to increase local sea level by up to 1.5mat the Seychelles and minimally decrease it in Western Australia. We acknowledge that this result is only based on a few simulations, but if robust, this shift brings estimates of global mean sea level from these two sites into closer agreement with each other. We further demonstrate that simulations with a suitable radial viscosity profile can be used to locally approximate the 3D GIA result, but that these radial profiles cannot be found by simply averaging viscosity below the sea level indicator site.

The dynamical flattening of the Earth, H, related to the precession constant, is a fundamental astro-geodetic parameter that appears in studies of the Earth's rotation and orbital evolution. We present numerical predictions and observations of the variation in H over time scales ranging from tens of millions of years to decades. The geophysical processes controlling this variation include solid-state convection in the rocky mantle of the Earth that drives plate tectonics, isostatic adjustments due to ice age loading, and ice-ocean mass transfer linked to modern global climate change. The time dependence of H is complex and non-linear, and thus, in contrast to previous suggestions, cannot be captured by a constant rate parameter.

SUMMARY It is generally agreed that the Last Interglacial (LIG; ∼130–115 ka) was a time when global average temperatures and global mean sea level were higher than they are today. However, the exact timing, magnitude and spatial pattern of ice melt is much debated. One difficulty in extracting past global mean sea level from local observations is that their elevations need to be corrected for glacial isostatic adjustment (GIA), which requires knowledge of Earth’s internal viscoelastic structure. While this structure is generally assumed to be radially symmetric, evidence from seismology, geodynamics and mineral physics indicates that large lateral variations in viscosity exist within the mantle. In this study, we construct a new model of Earth’s internal structure by converting shear wave speed into viscosity using parametrizations from mineral physics experiments and geodynamic constraints on Earth’s thermal structure. We use this 3-D Earth structure, which includes both variations in lithospheric thickness and lateral variations in viscosity, to calculate the first 3-D GIA prediction for LIG sea level. We find that the difference between predictions with and without lateral Earth structure can be metres to 10s of metres in the near field of former ice sheets, and up to a few metres in their far field. We demonstrate how forebulge dynamics and continental levering are affected by laterally varying Earth structure, with a particular focus on those sites with prominent LIG sea level records. Results from four 3-D GIA calculations show that accounting for lateral structure can act to increase local sea level by up to ∼1.5 m at the Seychelles and minimally decrease it in Western Australia. We acknowledge that this result is only based on a few simulations, but if robust, this shift brings estimates of global mean sea level from these two sites into closer agreement with each other. We further demonstrate that simulations with a suitable radial viscosity profile can be used to locally approximate the 3-D GIA result, but that these radial profiles cannot be found by simply averaging viscosity below the sea level indicator site.

Much of our understanding of ice sheet sensitivity to climatic forcing is derived from palaeoshoreline records of past sea-level. However, the present-day elevations of these sea-level markers reflect the integrated effect of both ice volume change and solid Earth processes. Accurately quantifying the latter contribution is therefore essential for making reliable inferences of past ice volume. While uncertainties associated with glacial isostatic adjustment (GIA) can be mitigated by focusing on sites far from ice sheets, the same is not true for mantle flow-driven dynamic topography, which is ubiquitous and can generate vertical motions of ~±100 m on million-year timescales. As a result, improved knowledge of the spatio-temporal evolution of this transient topography is required to refine constraints on ice sheet stability and to guide modelling of future trajectories.Since the shortest wavelength and fastest evolving contributions to dynamic topography originate in the shallow mantle, reconstructing dynamic topography over 1–10 Myr timescales requires accurate models of Earth’s lithosphere and asthenosphere. Here, we construct these models by mapping upper mantle shear wave velocities from high-resolution surface wave tomographic models into thermomechanical structure using calibrated parameterisations of anelasticity at seismic frequency. Resulting numerical predictions of present-day dynamic topography are in good agreement with residual depth measurements, with particularly good fits obtained around Australia. In this region, predicted temperatures are also compatible with palaeogeotherms extracted from xenolith suites, indicating that present-day upper mantle structure is well characterised and that numerical “retrodictions” of vertical motions are more likely to be reliable. In addition, Australia is sufficiently distant from major ice sheets that uncertainty in GIA contributions to sea-level change are relatively small. These considerations, combined with new compilations of continent-wide sea-level indicators, make Australia a particularly promising location for separating out ice volume-driven global mean sea-level changes from local sea-level variations related to vertical land motions and gravitational effects.By back-advecting density perturbations from an ensemble of Earth models, we demonstrate that ~±200 m relative sea-level changes across Australia since the Mid-Pliocene Warm Period (MPWP; ∼3 Ma) can be tied directly to changes in dynamic topography. Significantly, after removing this signal from observed relative sea-level changes, a consistent global mean sea-level during the MPWP of 12±8 m above present is obtained, towards the lower end of previous estimates.

The oceanic crust and lithosphere are commonly treated as geologically simple, their fundamental properties encapsulated by the 1D model of layered oceanic crust and the plate-cooling model of lithospheric thickness we learnt as undergraduates. The question of directionality or anisotropy in the behaviour and deeper structure of oceanic plates is relatively rarely considered, despite formation processes, such as rifting and seafloor spreading, and surface topography, such as abyssal hills, that are clearly highly anisotropic. In this presentation, we bring together evidence from a variety of sources from regional studies of rifting and volcanism to numerical modelling and global analyses of bathymetry and gravity data. We show how anisotropy is imprinted into the oceanic lithosphere at formation, both in the early rifting phases and at mature spreading centres, and how that anisotropic signature persists for many millions of years, potentially strengthened by preferential alignment of mineral phases as the moving plates cool and thicken. We then consider how this directionality impacts later deformation, volcanism, and eventually subduction.

Combating global climate change remains one of the greatest challenges facing humanity in the coming decades. Whilst oceanographers, ice sheet dynamicists, and atmospheric modellers all have an obvious role to play in leading efforts to tackle this problem, there remain many aspects that require careful consideration and cross-disciplinary interaction in other areas of the geosciences. In this talk, I will use selected examples to illustrate important links between geodynamics and climate change, including improving our understanding of its potential impacts and mitigation. The first concerns the role of mantle convection in influencing palaeo sea-level records and ice sheet dynamics. For example, Pliocene interglacial periods are commonly invoked as potential climatic analogues for the near-future conditions expected in our warming world, but there is considerable uncertainty over the extent to which important sea-level indicator sites have been perturbed, post-deposition, by convection-induced dynamic topography. The second link involves the growing shortage of metals that are key to the manufacture of technologies for low-carbon energy generation and storage. Tackling this shortfall requires an improvement in our ability to locate new, high-grade metal deposits, particularly those buried beneath shallow sedimentary cover. Novel geodynamical insights into the geological processes responsible for ore genesis will form a core component of narrowing the exploration search-space, and we have recently demonstrated this approach for sediment-hosted metal deposits. Through these case studies, I will show that it is primarily through developing an environment of cross-disciplinary discussion and financial support that our community is most likely to progress in understanding the potential impacts of climate change and how we may mitigate against them. Although one of the least well-studied components, the solid Earth is increasingly being recognised as a critical part of the climate system. Researchers working in topics as diverse as rock mechanics, seismology, convection modelling, and geochemistry all have a crucial role to play.

Bivalve and gastropod shell beds deposited during the Early Pliocene (4.69-5.23 Ma) occur in uplifted outcrops (36 – 180 m above sea level) along the east coast of Patagonian Argentina. These rock units provide a record of sea level during a geologic period when atmospheric CO2 and temperatures were higher than today. As such, reconstructing the elevation of global mean sea level (GMSL) during this time allows us to better understand how sensitive ice sheets are to increased past and future warming. However, reconstructing GMSL from local sea level indicators is hindered by effects such as mantle dynamic topography and glacial isostatic adjustment (GIA) that cause local sea level to deviate from the global mean. Here we use geodynamic modeling to better understand this complex dynamic setting and quantify the amount of uplift along this coastline. Despite being located on a relatively stable passive margin, significant variations in the elevation of the paleo shoreline indicators imply that the underlying convecting mantle is deforming the coastline. In particular, the subduction of the Chile Rise beginning ~18 Ma beneath Patagonia has generated a slab window underneath this region through which hot asthenosphere ascends. However, the former slab is still present deeper in the mantle, which causes a complex interplay between the downwelling slab and the upwelling asthenosphere. To quantify the effects of dynamic topography change since the Pliocene, we run 3D mantle convection simulations using the code ASPECT. We initialize our global model with a composite temperature structure derived from recent tomographic studies and a calibrated parameterization of upper mantle anelasticity. Independent estimates of pressure and temperature from thermobarometric calculations of proximal Pali-Aike xenoliths agree with the thermal structure of the tomography-based Earth model. We back-advect temperature perturbations and extract the resulting change in dynamic topography. Pairing GIA models and a suite of convection simulations in which we vary the viscosity and buoyancy structure with the observed differential paleo shoreline elevations allows us to forward model the most likely scenario for uplift along this coast.

The dynamical flattening of the Earth, H, related to the precession constant, is a fundamental astro-geodetic parameter that appears in studies of the Earth's rotation and orbital evolution. We present numerical predictions and observations of the variation in H over time scales ranging from tens of millions of years to decades. The geophysical processes controlling this variation include solid-state convection in the rocky mantle of the Earth that drives plate tectonics, isostatic adjustments due to ice age loading, and ice-ocean mass transfer linked to modern global climate change. The time dependence of H is complex and non-linear, and thus, in contrast to previous suggestions, cannot be captured by a constant rate parameter.

Oceanic residual depth varies on urn:x-wiley:jgrb:media:jgrb54314:jgrb54314-math-0001 5,000 km wavelengths with amplitudes of ±1 km. A component of this short‐wavelength signal is dynamic topography caused by convective flow in the upper ∼300 km of the mantle. It exerts a significant influence on landscape evolution and sea level change, but its contribution is often excluded in geodynamic models of whole‐mantle flow. Using seismic tomography to resolve buoyancy anomalies in the oceanic upper mantle is complicated by the dominant influence of lithospheric cooling on velocity structure. Here, we remove this cooling signal from global surface wave tomographic models, revealing a correlation between positive residual depth and slow residual velocity anomalies at depths

The thermochemical evolution of oceanic lithosphere and its interaction with the underlying asthenosphere exerts a fundamental control on the dynamics of the Earth system. Since the 1960s, the range, accuracy and spatial coverage of geophysical and geochemical datasets collected in the oceanic realm have substantially increased. These additional constraints have helped to elucidate many aspects of the lithosphere-asthenosphere system, but some apparently contradictory observations have presented additional interpretational challenges. Here, we summarise the merits, limitations and ambiguities of available observational constraints on the thermomechanical evolution of oceanic upper mantle. Newly developed cooling models are generally compatible with these constraints, although there is evidence for systematic differences in behaviour between different oceanic basins. Subsidence, magnetotelluric and seismological observations from the Pacific Ocean are consistent with plate rather than half-space cooling models, whereas results from the Atlantic and Indian Oceans are more equivocal. We provide an overview of proposed mechanisms for seafloor flattening and we show that regional deviations from globally averaged trends can be attributed to asthenospheric temperature variation and to local changes in lithospheric thickness. Although the plate cooling model generally provides a good description of available observations, it is probably a crude approximation of the dynamic processes operating within the thermal boundary layer that underlies oceanic basins. By incorporating mantle density structure inferred from surface wave tomography into more sophisticated convection simulations, we show that the plate model provides a good approximation of the predicted age-dependent behaviour of bathymetric and gravity fields. While the results presented here suggest a unified understanding of the lithosphere-asthenosphere system is within reach, unambiguous evidence for small-scale convection at the base of the lithosphere remains elusive. As a result, the precise mechanism responsible for sea-floor flattening has yet to be identified. It is also unclear why models that incorporate the effect of phase changes such as the garnet-spinel transition tend to fit observations less well than simpler counterparts. These outstanding controversies suggest further research is needed to develop a complete description of the structure and dynamics of the oceanic upper mantle but, encouragingly, the tools at our disposal have never been more powerful.

The connection between the geological record and dynamic topography driven by mantle convective flow has been established over widely varying temporal and spatial scales. As observations of the process have increased and numerical modeling of thermochemical convection has improved, a burgeoning direction of research targeting outstanding issues in ice age paleoclimate has emerged. This review focuses on studies of the Plio-Pleistocene ice age, including investigations of the stability of ice sheets during ice age warm periods and the inception of Northern Hemisphere glaciation. However, studies that have revealed nuanced connections of dynamic topography to biodiversity, ecology, ocean chemistry, and circulation since the start of the current ice-house world are also considered. In some cases, a recognition of the importance of dynamic topography resolves enigmatic events and in others it confounds already complex, unanswered questions. All such studies highlight the role of solid Earth geophysics in paleoclimate research and undermine a common assumption, beyond the field of glacial isostatic adjustment, that the solid Earth remains a rigid, passive substrate during the evolution of the ice age climate system. ▪ Dynamic topography is the large-scale, vertical deflection of Earth's crust driven by mantle convective flow. ▪ This review highlights recent research exploring the implications of the process on key issues in ice age paleoclimate. ▪ This research includes studies of ice sheet stability and inception as well as inferences of peak sea levels during periods of relative ice age warmth. ▪ This review also includes studies on longer timescales, continental-scale ecology and biodiversity, the long-term carbon cycle, and water flux across oceanic gateways.

Sustainable development and transition to a clean-energy economy is placing ever-increasing demand on global supplies of base metals (copper, lead, zinc and nickel). Consumption over the next ~25 years is set to exceed the total produced in human history to date, and it is a growing concern that the rate of exploitation of existing reserves is outstripping discovery of new deposits. Therefore, improvements in the effectiveness of exploration are required to reverse this worrying trend and maintain growth in global living standards.Approximately 70% of known lead, 55% of zinc and 20% of copper has been deposited between 2 Ga and recent by low temperature hydrothermal circulation in shallow sedimentary basins. These basins are formed by extension and rifting, which are key manifestations of the plate-mode of tectonics. Despite 150 years of research, the relationship between deposit locations and local geological structure is enigmatic and there remains no accurate technique for predicting their distribution at continental scales.Here, we show that modern surface wave tomography and recent parameterisations for anelasticity at seismic frequencies can be used to map lithospheric structure, and that sediment-hosted base metal deposits occur exclusively along the edges of thick lithosphere. Approximately 90% of the world's sediment-hosted copper, lead and zinc resources lie within 200 km of these boundaries, including all giant deposits (>10 megatonnes of metal). Incorporation of higher resolution regional seismic studies into global lithospheric thickness models further enhances the robustness of this relationship. This observation implies that lithospheric architecture imparted by the plate-mode of tectonics is stable over billion-year timescales, and that there is a genetic link between lithospheric scale processes and near-surface hydrothermal mineral systems. Our new maps provide an unprecedented global means to identify fertile regions for targeted mineral exploration, and provide a clear economic justification for funding targeted seismic arrays, theoretical advances in imaging techniques, and geodynamic studies that improve our understanding of deep-time plate tectonics.

To meet the rising global demand for base metals – driven primarily by the transition to cleaner-energy sources – declining rates of discovery of new deposits need to be countered by advances in exploration undercover. Here, we report that 85% of the world’s sediment-hosted base metals, including all giant deposits (>10 Mt of metal), occur within 200 km of the edge of thick lithosphere, irrespective of the age of mineralisation. This implies long-term craton edge stability, forcing a reconsideration of basin dynamics and the sediment-hosted mineral system. We find that the thermochemical structure of thick lithosphere results in increased basin subsidence rates during rifting, coupled with low geothermal gradients, which ensure favourable metal solubility and precipitation. Sediments in such basins generally contain all necessary lithofacies of the mineral system. These considerations allow establishment of the first-ever national prospectus for sediment-hosted base metal discovery. Conservative estimates place the undiscovered resource of sediment-hosted base metals in Australia to be ~50–200 Mt of metal. Importantly, this work suggests that ~15% of Australia is prospective for giant sediment-hosted deposits; we suggest that exploration efforts should be focused in this area.

Dominic M Bowman and the ECN Committee share their perspective of the RAS Early Career Network's first career event: postdoctoral career advice from the community

Peninsular India is a cratonic region with asymmetric relief manifest by eastward tilting from the 1.5 km high Western Ghats escarpment toward the floodplains of eastward-draining rivers. Oceanic residual depth measurements on either side of India show that this west-east asymmetry is broader scale, occurring over distances of >2,000 km. Admittance analysis of free-air gravity and topography shows that the elastic thickness is 10 ±3 km, suggesting that regional uplift is not solely caused by flexural loading. To investigate how Indian physiography is generated, we have jointly inverted 530 river profiles to determine rock uplift rate as a function of space and time. Key erosional parameters are calibrated using independent geologic constraints (e.g. emergent marine deposits, elevated paleosurfaces, uplifted lignite deposits). Our results suggest that regional tilt grew at rates of up to 0.1 mm a– 1 between 25 Ma and the present day. Neogene uplift initiated in the south and propagated northward along the western margin. This calculated history is corroborated by low-temperature thermochronologic observations, by sedimentary flux of clastic deposits into the Krishna-Godavari delta, and by sequence stratigraphic architecture along adjacent rifted margins. Onset of regional uplift predates intensification of the Indian monsoon at 8 Ma, suggesting that rock uplift rather than climatic change is responsible for modern-day relief. A positive correlation between residual depth measurements and shear wave velocities beneath the lithosphere suggests that regional uplift is generated and maintained by temperature anomalies of ±100°C within a 200 ±25 km thick asthenospheric channel. This article is protected by copyright. All rights reserved.

Basement structure is known to exert strong magmatic and morphological control on continental volcanoes, but relatively little is known about the structural control of submarine volcanoes. Here we investigate the morphology of the Tasmantid Seamounts, a >2400 km long chain of age‐progressive intraplate volcanoes, ranging from 56 to 7 Ma. The seamounts are emplaced over the extinct Tasman Sea spreading centre, which was active between 84 and 52 Ma. While thick sediment (∼1 km) obscures much of the basement, detailed morphological and geophysical analyses of the seamounts reveal a strong correlation between tectonic setting, seamount orientation, and volcanic structure, despite the ≥20 Ma interval between spreading cessation and seamount emplacement. Seamounts emplaced on fracture zones or spreading segment‐transform fault inside corners are typically large and elongate. Where original morphology is preserved, they often appear rugged and predominantly fissure‐fed. By contrast, comparatively smooth, conical seamounts with isolated dyke‐fed flank cones are often found mid‐segment and at outside corners. Volcanic fabrics also align closely with the expected principal stress directions for strong mechanical coupling across transform faults. This behaviour suggests the lithosphere is dissected by numerous deep faults, channelling magma along pre‐existing structural trends. Generally low effective elastic thicknesses (

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This chapter addresses topics on the dynamic behavior of neural networks as they oscillate and produce specific timing patterns in their activity. A network of simple processing units is capable of producing prolonged self-sustained oscillations and even chaotic behavior. Modulation of a controlled parameter causes the temporal dynamics to increase in complexity until chaos is reached. An external stimulus—a pattern—can be applied to a chaotic network, resulting in a simpler, limit cycle attractor, which can be recognized in a pattern-to-oscillation map. Since random networks tend to have only one observed dynamic attractor, we have designed a weight perturbation schedule to develop multiple dynamic attractors from different initial states of the network. The result is to create different basins of attraction for different patterns or pattern groups. We can observe a tremendous flexibility not only in evoked attractors (usually oscillations) but in their basins of attraction—the collections of states that lead to the same attractor. Attractor training has been done in networks with time-delay mechanisms, where an a priori chosen dynamic attractor can be trained into the network. A comparison to temporal processing in biological systems is discussed.

Topographic domes that are located far from active plate boundaries are often characterised by rapid, youthful\ud uplift, contemporaneous mafic volcanism, radial drainage patterns, and positive long-wavelength gravity anomalies. There is increasing evidence that they are underlain by anomalously low sub-plate seismic velocities. Despite their\ud well-known geomorphological expression, the origin of these epeirogenic features remains enigmatic and is much debated. Here, we investigate potential mechanisms of uplift by combining disparate observations from the Borborema\ud and Angolan plateaux that straddle the Brazilian and southwest African margins, respectively. Oceanic residual depth\ud measurements, drainage analysis, stratigraphic architecture, emergent marine terraces and basement denudation are\ud used to constrain their regional uplift histories. In both cases, the bulk of topographic growth occurred within the\ud last 30 Ma in the absence of significant tectonic deformation. We derive present-day mantle temperature and lithospheric thickness from Neogene to recent volcanic trace element compositions and upper mantle shear wave velocities. Volcanic geochemistry in northeast Brazil is compatible with decompression melting of warm asthenosphere and potentially a minor contribution from metasomatised lithospheric mantle. In Angola, melting of metasomatised lithosphere is most likely triggered by injection of small-degree asthenospheric-derived melts. We find no evidence for an\ud asthenospheric thermal anomaly > 50 ◦ C above ambient beneath either region. Present-day lithospheric thickness is ∼ 100 km beneath Angola and could be as thin as 60 km in the Borborema Province. For Angola, thermobarometry on\ud mantle xenocrysts from Cretaceous kimberlites is used to estimate palaeogeothermal gradients. Results indicate a pre-\ud existing gradient in lithospheric thickness between the edge of the Congo craton and the centre of the Angolan dome\ud at ∼ 120 Ma. This gradient likely steepened as a result of additional Neogene thinning by ∼ 30 ± 10 km beneath the\ud centre of the dome. We conclude that the mechanism for Neogene epeirogenic uplift of the Borborema and Angolan\ud domes is introduction of a small positive temperature anomaly into the asthenosphere that causes thermomechanical\ud thinning of the overlying lithospheric mantle.