D. Rhodri Davies

Australian National University | ANU · Research School of Earth Sciences

Reconstructing the thermo-chemical evolution of Earth's mantle and its diverse surface manifestations is a widely recognised grand challenge for the geosciences. It requires the creation of a digital twin: a digital representation of Earth's mantle across space and time that is compatible with available observational constraints on the mantle's str...

Ocean island basalts (OIBs) are generated by mantle plumes, with their geochemistry controlled by a combination of source composition, temperature, and thickness of overlying lithosphere. For example, OIBs erupting onto thicker, older oceanic lithosphere are expected to exhibit signatures indicative of higher average melting pressures. Here, we qua...

Mantle plumes are hot, buoyant upwellings that rise from Earth’s core-mantle-boundary (CMB) at ~2891 km depth to its surface1. As they ascend towards the lithosphere – our planet’s rigid outermost shell – the decreasing pressure facilitates decompression melting, resulting in surface volcanism that shows no obvious association with plate boundaries...

Ocean Island Basalts (OIBs) are generated by mantle plumes, with their geochemistry controlled by a combination of source composition, temperature, and thickness of overlying lithosphere. For example, OIBs erupting onto thicker, older oceanic lithosphere are expected to exhibit signatures indicative of higher average melting pressures. Here, we qua...

Seismic tomography of Earth's mantle images abundant slab remnants, often located in close proximity to active subduction systems. The impact of such remnants on the dynamics of subduction remains underexplored. Here, we use simulations of multi‐material free subduction in a 3‐D spherical shell geometry to examine the interaction between visco‐plas...

Owing to their abundance and relative availability on Earth's seafloor, mid‐ocean ridge basalts (MORBs) have a well‐defined chemical element budget, reflected by the low standard deviation associated with typical normal MORB (N‐MORB) composition. However, the exact mechanisms leading to magma differentiation and MORB generation remain debated, whic...

Ocean Island Basalts (OIBs) are generated by mantle plumes, with their geochemistry controlled by a combination of source composition, temperature, and thickness of overlying lithosphere. For example, OIBs erupting onto thicker, older oceanic lithosphere are expected to exhibit signatures indicative of higher average melting pressures. Here, we qua...

Reconstructing the thermo-chemical evolution of Earth's mantle and its diverse surface manifestations is a widely-recognised grand challenge for the geosciences. It requires the creation of a digital twin: a digital representation of Earth's mantle across space and time that is compatible with available observational constraints on the mantle's str...

Rapid plate motion, alongside pronounced variations in age and thickness of the Australian continental lithosphere, makes it an excellent location to assess the relationship between seismic anisotropy and lithosphere‐asthenosphere dynamics. In this study, SKS and PKS shear‐wave splitting is conducted for 176 stations covering the transition from th...

Seismic tomography of Earth’s mantle images abundant slab remnants, often located in close proximity to active subduction systems. The impact of such remnants on the dynamics of subduction remains under explored. Here, we use simulations of multi-material free subduction in a 3-D spherical shell geometry to examine the interaction between visco-pla...

Subduction termination leads to complex tectonic and geological activity, with the observational record often including clear evidence for exhumation, anomalous magmatism and topographic subsidence, followed by rapid uplift. However, the mechanism(s) driving these responses remain enigmatic and cannot be reconciled with our current understanding of...

The iron spin crossover in ferropericlase, the second most abundant mineral in Earth’s lower mantle, causes changes in a range of physical properties, including seismic wave velocities. Understanding the effect of temperature on the spin crossover is essential to detect its signature in seismic observations and constrain its occurrence in the mantl...

Dynamics of Plate Tectonics and Mantle Convection, written by specialists in the field, gathers state-of-the-art perspectives on the dynamics of plate tectonics and mantle convection. Plate tectonics is a unifying theory of solid Earth sciences. In its initial form, it was a kinematic theory that described how the planet’s surface is fragmented int...

The effects of sphericity are regularly neglected in numerical and laboratory studies that examine the factors controlling subduction dynamics. Most existing studies have been executed in a Cartesian domain, with the small number of simulations undertaken in a spherical shell incorporating plates with an oversimplified rheology, limiting their appl...

Many of the factors expected to control the dynamics and evolution of Earth's subduction zones are under‐explored in an Earth‐like spherical geometry. Here, we simulate multi‐material free‐subduction of a complex rheology slab in a 3‐D spherical shell domain, to investigate the effect of plate age (simulated by covarying plate thickness and density...

On Earth, the velocity at which subducting plates are consumed at their trenches (termed “subduction rate” herein) is typically 3 times higher than trench migration velocities. The subduction rate is also 5 times higher than estimated lower mantle slab sinking rates. Using simple kinematic analyses, we show that if this present‐day “kinematic state...

Several of Earth’s intra-plate volcanic provinces lie on or adjacent to continental lithosphere. Although many are believed to mark the surface expression of mantle plumes, our limited understanding of how buoyant plumes interact with heterogeneous continental lithosphere prevents further progress in identifying mechanisms at the root of continenta...

Firedrake is an automated system for solving partial differential equations using the finite-element method. By applying sophisticated performance optimisations through automatic code-generation techniques, it provides a means of creating accurate, efficient, flexible, easily extensible, scalable, transparent and reproducible research software that...

The subduction of positively buoyant features has been implicated in the development of flat and shallow dipping slabs, the formation of cusps in trench geometry, and the cessation of associated arc magmatism. However, how such buoyant anomalies influence subduction dynamics to produce these different tectonic expressions remains debated. In this p...

Geodynamic simulations underpin our understanding of upper-mantle processes, but their predictions require validation against observational data. Widely used geophysical datasets provide limited constraints on dynamic processes into the geological past, whereas under-exploited geochemical observations from volcanic lavas at Earth's surface constitu...

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 thi...

Firedrake is an automated system for solving partial differential equations using the finite element method. By applying sophisticated performance optimisations through automatic code-generation techniques, it provides a means to create accurate, efficient, flexible, easily extensible, scalable, transparent and reproducible research software, that...

Subduction is a key driver of plate tectonics on Earth1. A range of observations indicate that the termination of subduction leads to diverse and unexplained tectonic and geological activity, including anomalous magmatism, exhumation and topographic subsidence, followed by rapid uplift. However, the mechanism driving this complex surface response r...

Spatio-temporal changes of upper mantle structure play a significant role in generating and maintaining surface topography. Although geophysical models of upper mantle structure have become increasingly refined, there is a paucity of geologic constraints with respect to its present-day state and temporal evolution. Cenozoic intraplate volcanic rock...

Several of Earth's intraplate volcanic provinces are hard to reconcile with the mantle plume hypothesis. Instead, they exhibit characteristics that are more compatible with shallower processes that involve the interplay between uppermost mantle flow and the base of Earth's heterogeneous lithosphere. The mechanisms most commonly invoked are edge-dri...

Computational models of mantle convection must accurately represent curved boundaries and the associated boundary conditions of a 3-D spherical shell, bounded by Earth's surface and the core–mantle boundary. This is also true for comparable models in a simplified 2-D cylindrical geometry. It is of fundamental importance that the codes underlying th...

Subducting slabs are an important driver of plate motions, yet the relative importance of different forces in governing subduction motions and styles remains incompletely understood. Basal drag has been proposed to be a minor contributor to subduction forcing because of the lack of correlation between plate size and velocity in observed and reconst...

Whether tectonic convergence at subduction zones is accommodated predominantly through seismic or aseismic deformation, the former potentially generating large earthquakes, varies considerably between subduction margins. This margin‐scale variability has previously been linked to overriding plate deformation, trench migration, and their influence o...

Computational models of mantle convection must accurately represent curved boundaries and the associated boundary conditions within a 3-D spherical shell, bounded by Earth's surface and the core-mantle boundary. This is also true for comparable models in a simplified 2-D cylindrical geometry. It is of fundamental importance that the codes underlyin...

A significant component of Earth's surface topography is maintained by stresses induced by underlying mantle flow. This “dynamic” topography cannot be directly observed, but it can be approximated—particularly at longer wavelengths—from measurements of residual topography, which are obtained by removing isostatic effects from the observed topograph...

Subducting slabs are an important driver of plate motions, yet the force balance governing subduction dynamics remains incompletely understood. Basal drag has been proposed to be a minor contributor to subduction forcing, because of the lack of correlation between plate size and velocity in observed and reconstructed plate motions. Furthermore, in...

Cratonic margins host many of the natural resources upon which our society depends. Despite this, little is known about the dynamic evolution of these regions and the stability of substantial steps in plate thickness that delineate their boundaries with adjacent mantle. Here, we investigate the spatio-temporal evolution of Australian cratonic litho...

Mantle convection and plate dynamics transfer and deform solid material on scales of hundreds to thousands of km. However, viscoplastic deformation of rocks arises from motions of defects at sub-crystal scale, such as vacancies or dislocations. In this study, results from numerical experiments of dislocation dynamics in olivine for temperatures and...

Upper plate deformation within a subduction zone depends on the complex relationship between surface plate motions, trench motion, slab pull and asthenospheric flow. Previous modelling studies suggest that trench motion rates should be related to slab buoyancy, but this relationship is neither clear nor verified by observations of natural subductio...

Intra-plate volcanism in NE Australia, the eastern Highlands of New Guinea and along the Papuan Peninsula has been reasonably continuous over the Pliocene and Quaternary, without age progression, despite rapid movement of the Australian plate towards the north (∼7 cm/yr). Global seismic tomography indicates a strong zone of reduced seismic wavespee...

Earth’s surface topography is a direct physical expression of our planet’s dynamics. Most is isostatic, controlled by thickness and density variations within the crust and lithosphere, but a substantial proportion arises from forces exerted by underlying mantle convection. This dynamic topography directly connects the evolution of surface environme...

The lowermost mantle is driven to Earth's surface by mantle plumes, providing a volcanic record of its structure and composition. Plumes comprise a head and tail, which melt to form large igneous provinces (LIPs) and ocean island basalts (OIBs), respectively. Recent analyses have shown that LIPs and OIBs exhibit tungsten (W) isotope heterogeneity t...

Mantle plumes are hot buoyant upwellings that rise from Earth's core–mantle-boundary to its surface where they can produce large igneous provinces (LIPs) and volcanic tracks, such as the Siberian Traps and the Hawaiian Emperor chain, respectively. We show that flattened mantle plume heads, which can have radii of >1200 km in the uppermost mantle, c...

The mechanisms underpinning the formation of a focused volcanic arc above subduction zones are debated. Suggestions include controls by: (i) where the subducting plate releases water, lowering the solidus in the overlying mantle wedge; (ii) the location where the mantle wedge melts to the highest degree; and (iii) a limit on melt formation and migr...

The central Indian Ocean is considered the archetypal diffuse oceanic plate boundary. Data from seismic stratigraphy and deep-sea drilling indicate that the contractional deformation of the Indian Ocean lithosphere commenced at 15.4–13.9 Ma, but experienced a sharp increase at 8–7.5 Ma. This has been maintained through to the present day, with over...

Lower mantle tomography models consistently feature an increase in the ratio of shear-wave velocity (V S) to compressional-wave velocity (V P) variations and a negative correlation between shear-wave and bulk-sound velocity (V C) variations. These seismic characteristics, also observed in the recent SP12RTS model, have been interpreted to be indica...

The Pacific plate is thought to be driven mainly by slab pull, associated with subduction along the Aleutians–Japan, Marianas–Izu–Bonin and Tonga–Kermadec trenches. This implies that viscous flow within the sub–Pacific asthenosphere is mainly generated by overlying plate motion (i.e. Couette flow), and that the associated shear–stresses at the lith...

We evaluate the spatial and temporal evolution of Earth's long-wavelength surface dynamic topography since the Jurassic using a series of high-resolution global mantle convection models. These models are Earth-like in terms of convective vigour, thermal structure, surface heat-flux and the geographic distribution of heterogeneity. The models genera...

Cenozoic intraplate volcanism is widespread throughout much of eastern Australia, and manifests as both age-progressive volcanic tracks and non-age progressive lava-fields. Various mechanisms have been invoked to explain the origin and distribution of the volcanism, but a broad consensus remains elusive. We use results from seismic tomography to de...

The timing and magnitude of a Pacific plate motion change within the past 10 Ma remains enigmatic, due to the noise associated with finite–rotation data. Nonetheless, it has been hypothesized that this change was driven by the arrival of the Ontong Java Plateau (OJP) at the Melanesian arc and the consequent subduction polarity reversal. The uncerta...

Mantle plumes are buoyant upwellings of hot rock that transport heat from Earth's core to its surface, generating anomalous regions of volcanism that are not directly associated with plate tectonic processes. The best-studied example is the Hawaiian-Emperor chain, but the emergence of two sub-parallel volcanic tracks along this chain, Loa and Kea,...

The changes that occur at the boundary between the Archean and Proterozoic eons are arguably the most fundamental to affect the evolution of Earth's continental crust. The principal component of Archean continental crust is Granite–Greenstone Terranes (GGTs), with granites always dominant. The greenstones consist of a lower sequence of submarine ko...

The depth of the oceanic lithosphere–asthenosphere boundary (LAB), as inferred from shear wave velocities, increases with lithospheric age, in agreement with models of cooling oceanic lithosphere. On the other hand, the distribution of radial anisotropy under oceanic plates is almost age-independent. In particular, radial anisotropy shows a maximum...

Subduction zone mantle wedge temperatures impact plate interaction, melt generation, and chemical recycling. However, it has been challenging to reconcile geophysical and geochemical constraints on wedge thermal structure. Here we chemically determine the equilibration pressures and temperatures of primitive arc lavas from worldwide intra-oceanic s...

Komatiites are products of decompression melting of mantle so hot that they are almost exclusively restricted to the Archean. The high degree of partial melting (F) and pressure (P) required for their generation facilitates comparison between the magma composition and its mantle source. To investigate compositional variations in Archean komatiites,...

Arc volcanism, volatile cycling, mineralization, and continental crust formation are likely regulated by the mantle wedge's flow regime and thermal structure. Wedge flow is often assumed to follow a regular corner-flow pattern. However, studies that incorporate a hydrated rheology and thermal buoyancy predict internal small-scale-convection (SSC)....

The core mantle boundary (CMB) separates Earth's liquid iron outer core from the solid but slowly convecting mantle. The detailed structure and dynamics of the mantle within ~300 km of this interface remain enigmatic: it is a complex region, which exhibits thermal, compositional and phase-related heterogeneity, isolated pockets of partial melt and...

Hotspots are anomalous regions of volcanism at Earth's surface that show no obvious association with tectonic plate boundaries. Classic examples include the Hawaiian-Emperor chain and the Yellowstone-Snake River Plain province. The majority are believed to form as Earth's tectonic plates move over long-lived mantle plumes: buoyant upwellings that b...

Numerical simulations of thermal convection in the Earth's mantle often employ a pseudoplas-tic rheology in order to mimic the plate-like behavior of the lithosphere. Yet the benchmark tests available in the literature are largely based on simple linear rheologies in which the viscosity is either assumed to be constant or weakly dependent on temper...

The two large low shear-wave velocity provinces (LLSVPs) that dominate lower-mantle structure may hold key information on Earth’s thermal and chemical evolution. It is generally accepted that these provinces are hotter than background mantle and are likely the main source of mantle plumes. Increasingly, it is also proposed that they hold a dense (p...