ORCID Profile
0000-0002-7662-9468
Current Organisation
Australian National University
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Geodynamics | Geophysics | Seismology and Seismic Exploration | Ore Deposit Petrology | Geology | Oceanography | Exploration Geochemistry | Geomorphology and Regolith and Landscape Evolution | Physical Oceanography | Glaciology | Volcanology | Electrical and Electromagnetic Methods in Geophysics | Isotope Geochemistry | Climate Change Processes
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Earth Sciences | Expanding Knowledge in the Information and Computing Sciences | Effects of Climate Change and Variability on Antarctic and Sub-Antarctic Environments (excl. Social Impacts) | Oil and Gas Exploration | Natural Hazards not elsewhere classified | Expanding Knowledge in the Environmental Sciences | Precious (Noble) Metal Ore Exploration | Titanium Minerals, Zircon, and Rare Earth Metal Ore (e.g. Monazite) Exploration | Mineral Exploration not elsewhere classified |
Related Links
Publications
Lithospheric controls on magma composition along Earth’s longest continental hotspot track
Publisher: Springer Science and Business Media LLC
Date: 09-2015
DOI: 10.1038/NATURE14903
Abstract: Hotspots are anomalous regions of volcanism at Earth's surface that show no obvious association with tectonic plate boundaries. Classic ex les 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 bring hot material from Earth's deep mantle to its surface. It has long been recognized that lithospheric thickness limits the rise height of plumes and, thereby, their minimum melting pressure. It should, therefore, have a controlling influence on the geochemistry of plume-related magmas, although unambiguous evidence of this has, so far, been lacking. Here we integrate observational constraints from surface geology, geochronology, plate-motion reconstructions, geochemistry and seismology to ascertain plume melting depths beneath Earth's longest continental hotspot track, a 2,000-kilometre-long track in eastern Australia that displays a record of volcanic activity between 33 and 9 million years ago, which we call the Cosgrove track. Our analyses highlight a strong correlation between lithospheric thickness and magma composition along this track, with: (1) standard basaltic compositions in regions where lithospheric thickness is less than 110 kilometres (2) volcanic gaps in regions where lithospheric thickness exceeds 150 kilometres and (3) low-volume, leucitite-bearing volcanism in regions of intermediate lithospheric thickness. Trace-element concentrations from s les along this track support the notion that these compositional variations result from different degrees of partial melting, which is controlled by the thickness of overlying lithosphere. Our results place the first observational constraints on the sub-continental melting depth of mantle plumes and provide direct evidence that lithospheric thickness has a dominant influence on the volume and chemical composition of plume-derived magmas.
Reconciling dynamic and seismic models of Earth's lower mantle: The dominant role of thermal heterogeneity
Publisher: Elsevier BV
Date: 11-2012
How Slab Age and Width Combine to Dictate the Dynamics and Evolution of Subduction Systems: A 3‐D Spherical Study
Publisher: American Geophysical Union (AGU)
Date: 28-10-2022
DOI: 10.1029/2022GC010597
Abstract: 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) and width on the evolution of subduction systems. We find that the first‐order predictions of our spherical cases are generally consistent with existing Cartesian studies: (a) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased bending resistance and sinking rates and (b) wider slabs can develop along‐strike variations in trench curvature due to toroidal flow at slab edges, trending toward a “W”‐shaped trench with increasing slab width. We find, however, that these along‐strike variations are restricted to older, stronger, retreating slabs: Younger slabs that drive minimal trench motion remain relatively straight along the length of the subduction zone. We summarize our results into a regime diagram, which highlights how slab age modulates the effect of slab width, and present ex les of the evolutionary history of subduction zones that are consistent with our model predictions.
Comparing the Dynamics of Free Subduction in Cartesian and Spherical Domains
Publisher: American Geophysical Union (AGU)
Date: 12-2022
DOI: 10.1029/2022GC010757
Abstract: 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 applicability. Here, we simulate free‐subduction of composite visco‐plastic plates in 3‐D Cartesian and spherical shell domains, to examine the role of sphericity in dictating the dynamics of subduction, and highlight the limitations of Cartesian models. We identify two irreconcilable differences between Cartesian and spherical models, which limit the suitability of Cartesian‐based studies: (a) the presence of sidewall boundaries in Cartesian models, which modify the flow regime and (b) the reduction of space with depth in spherical shells, alongside the radial gravity direction, which cannot be captured in Cartesian domains. Although Cartesian models generally predict comparable subduction regimes and slab morphologies to their spherical counterparts, there are significant quantitative discrepancies. We find that simulations in Cartesian domains that exceed Earth's dimensions overestimate trench retreat. Conversely, due to boundary effects, simulations in smaller Cartesian domains overestimate the variation of trench curvature driven by plate width. Importantly, spherical models consistently predict higher sinking velocities and a reduction in slab width with depth, particularly for wider subduction systems, enhancing along‐strike slab buckling and trench curvature. Results imply that sphericity must be considered for understanding the dynamics of Earth's wider subduction systems, and is already a significant factor for slabs of width 2,400 km.
Coupled Geodynamical-Geochemical Perspectives on the Generation and Composition of Mid-Ocean Ridge Basalts
Publisher: Authorea, Inc.
Date: 12-10-2023
The concurrent emergence and causes of double volcanic hotspot tracks on the Pacific plate
Publisher: Springer Science and Business Media LLC
Date: 05-2017
DOI: 10.1038/NATURE22054
Abstract: 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 ex le is the Hawaiian-Emperor chain, but the emergence of two sub-parallel volcanic tracks along this chain, Loa and Kea, and the systematic geochemical differences between them have remained unexplained. Here we argue that the emergence of these tracks coincides with the appearance of other double volcanic tracks on the Pacific plate and a recent azimuthal change in the motion of the plate. We propose a three-part model that explains the evolution of Hawaiian double-track volcanism: first, mantle flow beneath the rapidly moving Pacific plate strongly tilts the Hawaiian plume and leads to lateral separation between high- and low-pressure melt source regions second, the recent azimuthal change in Pacific plate motion exposes high- and low-pressure melt products as geographically distinct volcanoes, explaining the simultaneous emergence of double-track volcanism across the Pacific and finally, secondary pyroxenite, which is formed as eclogite melt reacts with peridotite, dominates the low-pressure melt region beneath Loa-track volcanism, yielding the systematic geochemical differences observed between Loa- and Kea-type lavas. Our results imply that the formation of double-track volcanism is transitory and can be used to identify and place temporal bounds on plate-motion changes.
Strong, Multi-Scale Heterogeneity in Earth’s Lowermost Mantle
Publisher: Springer Science and Business Media LLC
Date: 17-12-2015
DOI: 10.1038/SREP18416
Abstract: 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 strong variations in seismic velocity and anisotropy. Nonetheless, characterising the structure of this region is crucial to a better understanding of the mantle’s thermo-chemical evolution and the nature of core-mantle interactions. In this study, we examine the heterogeneity spectrum from a recent P-wave tomographic model, which is based upon trans-dimensional and hierarchical Bayesian imaging. Our tomographic technique avoids explicit model parameterization, smoothing and d ing. Spectral analyses reveal a multi-scale wavelength content and a power of heterogeneity that is three times larger than previous estimates. Inter alia , the resulting heterogeneity spectrum gives a more complete picture of the lowermost mantle and provides a bridge between the long-wavelength features obtained in global S-wave models and the short-scale dimensions of seismic scatterers. The evidence that we present for strong, multi-scale lowermost mantle heterogeneity has important implications for the nature of lower mantle dynamics and prescribes complex boundary conditions for Earth’s geodynamo.
Mapping spherical seismic into physical structure: biases from 3-D phase-transition and thermal boundary-layer heterogeneity
Publisher: Oxford University Press (OUP)
Date: 20-01-2011
How sphericity combines with the age and width of slabs to dictate the dynamics and evolution of subduction systems on Earth
Publisher: Wiley
Date: 04-11-2021
Global Models From Sparse Data: A Robust Estimate of Earth's Residual Topography Spectrum
Publisher: American Geophysical Union (AGU)
Date: 08-2020
DOI: 10.1029/2020GC009240
Network over‐connectivity differentiates autism spectrum disorder from other developmental disorders in toddlers: A diffusion MRI study
Publisher: Wiley
Date: 17-01-2017
DOI: 10.1002/HBM.23520
When do mantle plumes destroy diamonds?
Publisher: Elsevier BV
Date: 11-2018
Indian Ocean floor deformation induced by the Reunion plume rather than the Tibetan Plateau
Publisher: Springer Science and Business Media LLC
Date: 23-04-2018
Reconciling mantle wedge thermal structure with arc lava thermobarometric determinations in oceanic subduction zones
Publisher: American Geophysical Union (AGU)
Date: 10-2016
DOI: 10.1002/2016GC006527
Fluidity: A fully unstructured anisotropic adaptive mesh computational modeling framework for geodynamics
Publisher: American Geophysical Union (AGU)
Date: 06-2011
DOI: 10.1029/2011GC003551
Mantle wedge temperatures and their potential relation to volcanic arc location
Publisher: Elsevier BV
Date: 11-2018
A systematic 2‐D investigation into the mantle wedge's transient flow regime and thermal structure: Complexities arising from a hydrated rheology and thermal buoyancy
Publisher: American Geophysical Union (AGU)
Date: 2014
DOI: 10.1002/2013GC005022
Earth's surface heat flux
Publisher: Copernicus GmbH
Date: 22-02-2010
DOI: 10.5194/SE-1-5-2010
Abstract: Abstract. We present a revised estimate of Earth's surface heat flux that is based upon a heat flow data-set with 38 347 measurements, which is 55% more than used in previous estimates. Our methodology, like others, accounts for hydrothermal circulation in young oceanic crust by utilising a half-space cooling approximation. For the rest of Earth's surface, we estimate the average heat flow for different geologic domains as defined by global digital geology maps and then produce the global estimate by multiplying it by the total global area of that geologic domain. The averaging is done on a polygon set which results from an intersection of a 1 degree equal area grid with the original geology polygons this minimises the adverse influence of clustering. These operations and estimates are derived accurately using methodologies from Geographical Information Science. We consider the virtually un-s led Antarctica separately and also make a small correction for hot-spots in young oceanic lithosphere. A range of analyses is presented. These, combined with statistical estimates of the error, provide a measure of robustness. Our final preferred estimate is 47±2 TW, which is greater than previous estimates.
Petrogenesis and geochemistry of Archean Komatiites
Publisher: Oxford University Press (OUP)
Date: 2016
Effects of basal drag on subduction dynamics from 2D numerical models
Publisher: Copernicus GmbH
Date: 20-01-2021
Abstract: Abstract. 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 reconstructed plate motions. Furthermore, in single subduction system models, low basal drag leads to subduction behaviour most consistent with the observation that trench migration velocities are generally low compared to convergence velocities. By contrast, analytical calculations and global mantle flow models indicate basal drag can be substantial. In this study, we revisit this problem by examining the drag at the base of the lithosphere, for a single subduction system, in 2D models with a free trench and composite non-linear rheology. We compare the behaviour of short and long plates for a range of asthenospheric and lithospheric rheologies. We reproduce results from previous modelling studies, including low ratios of trench over plate motions. However, we also find that any combination of asthenosphere and lithosphere viscosity that produces Earth-like subduction behaviour leads to a correlation of velocities with plate size, due to the role of basal drag. By examining Cenozoic plate motion reconstructions, we find that slab age and plate size are positively correlated: higher slab pull for older plates tends to be offset by higher basal drag below these larger plates. This, in part, explains the lack of plate velocity–size correlation in observations, despite the important role of basal drag in the subduction force balance.
Intra-plate volcanism in North Queensland and eastern new Guinea: A cryptic mantle plume?
Publisher: Elsevier BV
Date: 03-2020
Diffusion Tractography Biomarkers of Pediatric Cerebellar Hypoplasia/Atrophy: Preliminary Results Using Constrained Spherical Deconvolution
Publisher: American Society of Neuroradiology (ASNR)
Date: 10-12-2015
DOI: 10.3174/AJNR.A4607
A 3-D numerical investigation of the impact of buoyant features on subduction dynamics and stress
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-14049
Abstract: The subduction of positively buoyant features has been suggested to cause flat or shallow dipping slabs, the formation of cusps in trench geometry and periods of reduction or full cessation of arc magmatism. Additionally, recent earthquake data indicates that the subduction of the Hikurangi plateau near New Zealand causes a rotation of intraplate stresses. In this study, we present a series of multi-material 3-D simulations of free subduction to investigate how subduction of buoyant elongated features, or ridges, impact downgoing plate velocities, trench motions, slab morphology and intraplate stress regime. We examine how these parameters are affected by the age of the subducting plate and the relative buoyancy and position of the buoyant ridge. We find that buoyant ridges change slab sinking and trench retreat rates and locally rotate intraplate stresses. These, in turn, modify the evolution of slab morphology at depth and trench shape at the surface, as trench retreat is reduced, or switches to trench advance, where the ridge subducts. These effects depend strongly on downgoing plate age: on young and weak plates, the change in trench shape is more localised than on old and strong plates. We observe slab shallowing around the ridge only in young plates, while the stronger pull by the more negatively buoyant old plates causes slab steepening near the buoyant ridge. Buoyant ridges on old plates which are located near stagnating or advancing regions, typical in wide slabs, modify trench behaviour more strongly than ridges in other regions of the trench. Bending-related intraplate earthquakes are more likely in older plates where higher stress is accumulated and the rotation due to the buoyant ridge is more widespread than for younger plates. The combined effects of buoyant feature location, subducting plate age and overriding plate properties can result in a range of responses: from mainly trench deformation, through local slab shallowing, to the formation of a flat slab, a variation in expressions also observed on Earth.
Constraints on the presence of post-perovskite in Earth's lowermost mantle from tomographic-geodynamic model comparisons
Publisher: Elsevier BV
Date: 07-2018
A review of transparent-reflective switchable glass technologies for building facades
Publisher: Elsevier BV
Date: 12-2021
A Coupled Geochemical‐Geodynamic Approach for Predicting Mantle Melting in Space and Time
Publisher: American Geophysical Union (AGU)
Date: 04-2022
DOI: 10.1029/2022GC010421
Abstract: 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 constitute a valuable record of mantle processes back in time. Here, we describe a new peridotite‐melting parameterization, BDD21, that can predict the incompatible‐element concentrations of melts within geodynamic simulations, thereby providing a means to validate these simulations against geochemical datasets. Here, BDD21's functionality is illustrated using the Fluidity computational modeling framework, although it is designed so that it can be integrated with other geodynamic software. To validate our melting parameterization and coupled geochemical‐geodynamic approach, we develop 2‐D single‐phase flow simulations of melting associated with passive upwelling beneath mid‐oceanic ridges and edge‐driven convection adjacent to lithospheric steps. We find that melt volumes and compositions calculated for mid‐oceanic ridges at a range of mantle temperatures and plate spreading rates closely match those observed at present‐day ridges with the same conditions. Our lithospheric step simulations predict spatial and temporal melting trends that are consistent with those recorded at intraplate volcanic provinces in similar geologic settings. Taken together, these results suggest that our coupled geochemical‐geodynamic approach can accurately predict a suite of present‐day geochemical observations. Since our results are sensitive to small changes in upper‐mantle thermal and compositional structure, this novel approach provides a means to improve our understanding of the mantle's thermo‐chemical structure and flow regime into the geological past.
Tungsten isotopes in mantle plumes: Heads it's positive, tails it's negative
Publisher: Elsevier BV
Date: 2019
The influence of lithospheric thickness variations beneath Australia on seismic anisotropy and mantle flow
Publisher: Authorea, Inc.
Date: 08-07-2023
DOI: 10.22541/ESSOAR.168881742.29827772/V1
Abstract: Rapid plate motion, alongside pronounced variations in age and thickness of the Australian continental lithosphere, make 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 the South Australian Craton to eastern Phanerozoic Australia. Comparisons are made with models of lithospheric thickness as well as numerical simulations of mantle flow. Splitting results show uniform ENE-WSW aligned fast directions over the Gawler Craton and broader South Australian Craton, similar to the orientation of crustal structures generated during an episode of NW-SE directed compression and volcanism ~1.6 billion years ago. We propose that heat from volcanism weakened the lithosphere, aiding widespread lithospheric deformation, which has since been preserved in the form of frozen-in anisotropy. Conversely, over eastern Phanerozoic Australia, fast directions show strong alignment with the NNE absolute plate motion. Overall, our results suggest that when the lithosphere is thin ( km), lithospheric contributions are minimal and contributions from asthenospheric anisotropy dominate, reflecting shear of the underlying mantle by Australia’s rapid plate motion above. Further insights from geodynamical simulations of the regional mantle flow-field, which incorporate Australian and adjacent upper mantle structure, predict that asthenospheric material would be drawn in from the south and east towards the fast-moving continental keel. Such a mechanism, alongside interactions between the flow field and lithospheric structure, provides a plausible explanation for smaller-scale anomalous splitting patterns beneath eastern Australia that do not align with plate motion.
Controls on the Dynamics of Subducting Slabs in a 3-D Spherical Shell Domain
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-4710
Abstract: It has long been recognised that the shape of subduction zones is influenced by Earth& #8217 s sphericity, but 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 applicability. There are therefore many outstanding questions relating to the key controls on the dynamics of subduction. For ex le, do predictions from Cartesian subduction models hold true in a spherical geometry? When combined, how do subducting plate age and width influence the dynamics of subducting slabs, and associated trench shape? How do relic slabs in the mantle feedback on the dynamics of subduction? These questions are of great importance to understanding the evolution of Earth's subduction systems but remain under explored.In this presentation, we will target these questions through a systematic geodynamic modelling effort, by examining simulations of multi-material free-subduction of a visco-plastic slab in a 3-D spherical shell domain. We will first highlight the limitation(s) of Cartesian models, due to two irreconcilable differences with the spherical domain: (i) the presence of sidewall boundaries in Cartesian models, which modify the flow regime and (ii) the reduction of space with depth in spherical shells, alongside the radial gravity direction, the impact of which cannot be captured in Cartesian domains, especially for subduction zones exceeding 2400 km in width. We will then demonstrate how slab age (approximated by co-varying thickness and density) and slab width affect the evolution of subducting slabs, using spherical subduction simulations, showing that: (i) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased bending resistance and sinking rates (ii) wider slabs can develop along-strike variations in trench curvature due to toroidal flow at slab edges, trending toward a `W'-shaped trench with increasing slab width, and (iii) the width effect is strongly modulated by slab age, as age controls the slab's tendency to retreat. Finally, we will show the erse range of ways in which remnant slabs in the mantle impact on subduction dynamics and the evolution of subduction systems.
Linking Lithospheric Structure, Mantle Flow and Intra-Plate Volcanism
Publisher: Wiley
Date: 17-09-2020
Comparing the Dynamics of Free Subduction in Cartesian and Spherical Domains
Publisher: Wiley
Date: 25-10-2022
Validation of an MRI Brain Injury and Growth Scoring System in Very Preterm Infants Scanned at 29- to 35-Week Postmenstrual Age
Publisher: American Society of Neuroradiology (ASNR)
Date: 18-05-2017
DOI: 10.3174/AJNR.A5191
A community benchmark for viscoplastic thermal convection in a 2-D square box
Publisher: American Geophysical Union (AGU)
Date: 07-2015
DOI: 10.1002/2015GC005807
Effects of subduction termination processes on continental lithosphere
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5344
Abstract: & & Subduction is the main driver of tectonic activity on Earth. Termination of subduction is followed by erse and unexpected tectonic activity, such as anomalous magmatism, exhumation, subsidence and subsequent rapid uplift. What fundamentally drives these processes remain enigmatic. A prime ex le of subduction termination can be found in northern Borneo (Malaysia), where subduction ceased in the late Miocene and was followed by puzzling tectonic activity, as reconstructed from geological and petrological evidence. Our current understanding of the subduction cycle cannot be reconciled with evidence of post-subduction tectonics in both the near-surface geology and mantle of northern Borneo.& & & & We use new passive-seismic data to image at unprecedent detail a sub-vertical lithospheric drip that developed as a Rayleigh-Taylor gravitational instability from the root of a volcanic arc, which formed above a subducting plate. We use thermo-mechanical simulations to reconcile these images with time-dependent dynamical processes within the crust and underlying mantle, following subduction termination. Our model predictions illustrate how significant extension from a downwelling lithospheric drip can thin the crust in an adjacent orogenic belt, causing lower crustal melting and possible exhumation of subcontinental material, which can explain core-complex formations seen in other areas of recent subduction termination.& &
Thermally-driven mantle plumes reconcile multiple hot-spot observations
Publisher: Elsevier BV
Date: 15-02-2009
3-D Modelling of the Dynamical Mechanisms Driving Continental Intra-Plate Volcanism
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-10559
Abstract: Volcanic provinces within Earth's continents exhibit a wide range of characteristics that reflect the intricate nature of the dynamic interactions at their origin. To improve our understanding of the driving mechanisms at play, we address the generation of intra-plate continental volcanism by modelling the 3-D interaction between an upwelling mantle plume and a thick lithospheric block. We examine scenarios with and without plate motion and assess the spatio-temporal distribution and intensity of produced melts. Our findings demonstrate the critical role of lithospheric thickness in determining the location and volume of plume-driven magmatic provinces. Building on these results obtained using simplified lithospheric structures, we further apply our numerical methodology to simulate the inferred interaction between the Cosgrove plume and eastern Australia during the past 35 Myr. We design the Australian continent using available 3-D lithospheric architecture determined through seismic tomography and impose the inferred plate motion associated with this region. Our models incorporate updated peridotite melting parameterisations to provide quantitative estimates of generated melt volume and composition. We find that plume-driven and shallow edge-driven melting processes, modulated by the lithospheric thickness of the Australian continent, combine to explain the observed volcanic record. Our preliminary results agree well with surface observations and provide further insight into the geodynamics of eastern Australia.
Age-independent seismic anisotropy under oceanic plates explained by strain history in the asthenosphere
Publisher: Elsevier BV
Date: 02-2017
PREDICT-CP: study protocol of implementation of comprehensive surveillance to predict outcomes for school-aged children with cerebral palsy
Publisher: BMJ
Date: 07-2017
Development, and construct validity and internal consistency of the Grasp and Reach Assessment of Brisbane (GRAB) for infants with asymmetric brain injury
Publisher: Elsevier BV
Date: 11-2016
DOI: 10.1016/J.INFBEH.2016.10.004
Abstract: Infants with asymmetric brain injury (asymBI) are at high risk of Unilateral Cerebral Palsy (UCP). The Grasp and Reach Assessment of Brisbane (GRAB) was developed to detect asymmetries in unimanual/bimanual upper limb (UL) reach and grasp behaviours in infants with asymBI. This study reports the development of the GRAB and evaluates its construct validity and internal consistency. Prospective study of twenty four infants with asymBI and twenty typically developing (TD) infants at 18 weeks corrected age (C.A.) in a structured play session. Three different coloured toys were presented at the midline in a block design of six 30-s trials of toy presentation, separated by five 30-s trials of no toy presentation. The number and duration of: (i) unimanual contacts (ii) unimanual grasps (iii) bimanual midline grasps and (iv) duration of other unimanual behaviours (e.g. prehensile movements and transport phase) were measured. An Asymmetry Index (AI) was calculated to determine asymmetries between ULs. Possible AI values ranged from 0 to 100%, indicating proportion of toy presentation time that unimanual behaviours were asymmetric between ULs. Internal consistency of both the Time Phase (TP) and Toy Colour Phase (TCP) test items were determined by calculating Cronbach's alpha coefficients. Each assessment occasion was split into six TPs and two TCPs whereby one TP comprised one 30-s trial of one toy presentation and one TCP comprised two 30-s trials of the same toy presentation. For TP, seven out of nine unimanual behaviours and two out of three bimanual behaviours demonstrated strong internal consistency (Cronbach's alpha coefficients 0.72-0.89). No unimanual activity demonstrated the strongest IC (0.89). For TCP, six out of nine unimanual behaviours demonstrated strong IC (0.73-0.82). Number of unimanual contacts and duration of unimanual prehensile movements demonstrated the strongest IC (0.82). Duration of unimanual contribution to hands at midline and duration of bimanual midline behaviour demonstrated the weakest IC for both TP and TCP (0.46-0.50). For unimanual contacts, the asymBI group were more asymmetric between ULs (mean AI=50%) compared to the TD group (mean AI=30%). For unimanual grasps, both groups were similarly asymmetric (both mean AI=40%). The TD group were almost twice as likely to demonstrate bimanual grasps as the asymBI group (incidence rate ratio IRR 1.9, 95% CI 1.4 to 2.5, p<0.001). Infants with asymBI were less likely to use the impaired UL compared to the unimpaired UL for grasping (IRR 0.6, 95% CI 0.5 to 0.8, p<0.001) and used the impaired UL for a shorter proportion of time compared to the unimpaired UL for grasping (mean difference -9.1%, 95% CI -16.6 to -1.7, p=0.02). The GRAB is a criterion-referenced research measure that detects and quantifies the presence or absence of unimanual and bimanual reach and grasp behaviours at 18 weeks C.A. in infants at risk of UCP. The GRAB demonstrated moderate to strong construct validity and strong IC within an assessment occasion. There was no toy preference or warm-up effect for TP or TCP for either group confirming that the GRAB is a consistent measure across toy presentations within an assessment occasion. In this study, the GRAB identified that infants with asymBI demonstrated a paucity of bimanual grasping compared to TD infants and demonstrated asymmetric unimanual grasping between ULs at 18 weeks C.A.
A coupled geochemical-geodynamical approach for predicting mantle melting in space and time
Publisher: Wiley
Date: 29-08-2021
REACH: study protocol of a randomised trial of rehabilitation very early in congenital hemiplegia.
Publisher: BMJ
Date: 09-2017
DOI: 10.1136/BMJOPEN-2017-017204
Abstract: Congenital hemiplegia is the most common form of cerebral palsy (CP). Children with unilateral CP show signs of upper limb asymmetry by 8 months corrected age (ca) but are frequently not referred to therapy until after 12 months ca. This study compares the efficacy of infant-friendly modified constraint-induced movement therapy (Baby mCIMT) to infant friendly bimanual therapy (Baby BIM) on upper limb, cognitive and neuroplasticity outcomes in a multisite randomised comparison trial. 150 infants (75 in each group), aged between 3 and 6 months ca, with asymmetric brain injury and clinical signs of upper extremity asymmetry will be recruited. Children will be randomised centrally to receive equal doses of either Baby mCIMT or Baby BIM. Baby mCIMT comprises restraint of the unimpaired hand using a simple restraint (eg, glove, sock), combined with intensive parent implemented practice focusing on active use of the impaired hand in a play-based context. In contrast, Baby BIM promotes active play requiring both hands in a play-based context. Both interventions will be delivered by parents at home with monthly home visits and interim telecommunication support by study therapists. Assessments will be conducted at study entry at 6, 12 months ca immediately postintervention (primary outcome) and 24 months ca (retention). The primary outcome will be the Mini-Assisting Hand Assessment. Secondary outcomes include the Bayley Scale for Infant and Toddler Development (cognitive and motor domains) and the Hand Assessment of Infants. A subset of children will undertake MRI scans at 24 months ca to evaluate brain lesion severity and brain (re)organisation after intervention. Full ethical approvals for this study have been obtained from the relevant sites. The findings will be disseminated in peer-reviewed publications. Australian and New Zealand Clinical Trials Registry: ACTRN12615000180516, Pre results.
Continental Magmatism: The Surface Manifestation of Dynamic Interactions Between Cratonic Lithosphere, Mantle Plumes and Edge-Driven Convection
Publisher: Wiley
Date: 27-01-2022
Observations and Models of Dynamic Topography: Current Status and Future Directions
Publisher: Elsevier
Date: 2023
Self-consistent Reconstructions of the Earth's Mantle in Space and Time using Nonlinear Rheologies
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-12057
Abstract: Reconstructing the spatial and temporal evolution of Earth& #8217 s mantle through the recent geological past stands as one of the grand challenges in Geodynamics. One method to invert for the mantle& #8217 s evolution is to reformulate mantle flow as an optimisation problem using the adjoint method, where uncertain properties, such as the mantle& #8217 s previous thermo-chemical states, are found by minimising a misfit functional that represents the difference between model predictions and geodynamic inferences from various disciplines, including seismology, geodesy, and geochemistry. While the rapid growth in high-performance computing capacities has underpinned an ever-growing number of such reconstruction models, they often make several simplifying physical assumptions, or are limited in the number of assimilated datasets, thus limiting their applicability.Here we present our latest attempts at reconstructing the evolution of Earth& #8217 s mantle using complex non-linear rheologies. Our approach builds upon a novel algorithmic differentiation method as implemented in dolfin-adjoint, together with state-of-the-art optimisation methods, developed using the Rapid Optimisation Library. Using analytical and synthetic ex les, we show that the self-consistent derivation of the adjoint equations in our approach provides a pathway for accurate inversions for past-mantle flow.
Reconciling petrological and isotopic mixing mechanisms in the Pitcairn mantle plume using stable Fe isotopes
Publisher: Elsevier BV
Date: 09-2019
Earth’s multi-scale topographic response to global mantle flow
Publisher: Springer Science and Business Media LLC
Date: 16-09-2019
Late Miocene Pacific plate kinematic change explained with coupled global models of mantle and lithosphere dynamics
Publisher: American Geophysical Union (AGU)
Date: 22-07-2017
DOI: 10.1002/2017GL073920
On the origin of recent intraplate volcanism in Australia
Publisher: Geological Society of America
Date: 12-2014
DOI: 10.1130/G36093.1
Pressure‐Driven Poiseuille Flow: A Major Component of the Torque‐Balance Governing Pacific Plate Motion
Publisher: American Geophysical Union (AGU)
Date: 08-01-2018
DOI: 10.1002/2017GL075697
Do mantle plumes preserve the heterogeneous structure of their deep-mantle source?
Publisher: Elsevier BV
Date: 2016
Influence of Subduction Zone Dynamics on Interface Shear Stress and Potential Relationship With Seismogenic Behavior
Publisher: American Geophysical Union (AGU)
Date: 02-2021
DOI: 10.1029/2020GC009267
Abstract: 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 on the plate interface stress state. While these processes are linked to mantle‐scale dynamics, it is unclear how such dynamics influence interface stress. We systematically analyze the interface stress state in a suite of 2‐D thermo‐mechanical subduction models, where slabs display a range of morphologies that arise from erse multiscale interactions with adjacent mantle and the overriding plate. We demonstrate that the thickness of the interface layer varies dynamically, in response to Poiseuille flow induced by slab bending or unbending, leading to associated effects on interface shear stress at typical seismogenic depth. Lower shear stress occurs when slab unbending is significant, which is commonly associated with trench retreat and draping of the slab as it impinges on the higher‐viscosity lower‐mantle. Conversely, higher shear stress is associated with limited slab unbending, which is promoted by negligible trench migration and vertically subducting slabs. We conclude that the ersity of slab dynamics may cause large variations in interface stress state between and maybe within margins. This is an additional variable that potentially controls seismogenic behavior, and we compare broad stress estimates for Circum‐Pacific margins to previous studies. Although predicted shear stress varies with observed seismogenic behavior, more detailed constraints on stress state are needed to test for correlation.
The Effect of a Weak Asthenospheric Layer on Surface Kinematics, Subduction Dynamics and Slab Morphology in the Lower Mantle
Publisher: American Geophysical Union (AGU)
Date: 08-2022
DOI: 10.1029/2022JB024494
Abstract: 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” operated into the past, the subducting lithosphere should have accumulated and folded beneath near‐stationary trenches. These predictions are consistent with seismic tomography, which images localized and widened lower‐mantle slab piles. They are, however, at odds with most dynamic‐subduction models, which predict rapid trench retreat and inclined slabs in the mantle transition zone. We test the hypothesis that a weak asthenospheric layer (WAL), between the lithosphere‐asthenosphere boundary and 220 km depth, compatible with geophysical constraints, can remedy the discrepancies between numerical models and observations. The WAL lubricates the base of the lithosphere, increases the subduction rate while reducing trench retreat. As a consequence, simulations featuring a WAL predict slab accumulation at the mantle transition zone, and thicker, folded slabs in the lower mantle. A WAL viscosity only 2–5 times lower than that of the adjacent mantle is sufficient to shift subduction regimes toward a mode of vertical slab sinking and folding beneath near‐stationary trenches, across a wide range of model parameters, producing surface and slab velocities close to those observed at the present‐day. These findings provide support for the existence of a weak asthenosphere beneath Earth's lithosphere, complementing independent evidence from various geophysical data.
A hierarchical mesh refinement technique for global 3-D spherical mantle convection modelling
Publisher: Copernicus GmbH
Date: 31-07-2013
Abstract: Abstract. A method for incorporating multi-resolution capabilities within pre-existing global 3-D spherical mantle convection codes is presented. The method, which we term "geometric multigrid refinement", is based upon the application of a multigrid solver on non-uniform, structured grids and allows for the incorporation of local high-resolution grids within global models. Validation tests demonstrate that the method is accurate and robust, with highly efficient solutions to large-scale non-uniform problems obtained. Significantly, the scheme is conceptually simple and straightforward to implement, negating the need to reformulate and restructure large sections of code. Consequently, although more advanced techniques are under development at the frontiers of mesh refinement and solver technology research, the technique presented is capable of extending the lifetime and applicability of pre-existing global mantle convection codes.
On the relationship between volcanic hotspot locations, the reconstructed eruption sites of large igneous provinces and deep mantle seismic structure
Publisher: Elsevier BV
Date: 02-2015
Analytical solutions for mantle flow in cylindrical and spherical shells
Publisher: Copernicus GmbH
Date: 09-04-2021
Abstract: Abstract. 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 these models are carefully verified prior to their application in a geodynamical context, for which comparisons against analytical solutions are an indispensable tool. However, analytical solutions for the Stokes equations in these geometries, based upon simple source terms that adhere to physically realistic boundary conditions, are often complex and difficult to derive. In this paper, we present the analytical solutions for a smooth polynomial source and a delta-function forcing, in combination with free-slip and zero-slip boundary conditions, for both 2-D cylindrical- and 3-D spherical-shell domains. We study the convergence of the Taylor–Hood (P2–P1) discretisation with respect to these solutions, within the finite element computational modelling framework Fluidity, and discuss an issue of suboptimal convergence in the presence of discontinuities. To facilitate the verification of numerical codes across the wider community, we provide a Python package, Assess, that evaluates the analytical solutions at arbitrary points of the domain.
Towards automatic finite-element methods for geodynamics via Firedrake
Publisher: Copernicus GmbH
Date: 05-07-2022
Abstract: Abstract. 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 is ideally suited to simulating a wide range of problems in geophysical fluid dynamics. Here, we demonstrate the applicability of Firedrake for geodynamical simulation, with a focus on mantle dynamics. The accuracy and efficiency of the approach are confirmed via comparisons against a suite of analytical and benchmark cases of systematically increasing complexity, whilst parallel scalability is demonstrated up to 12 288 compute cores, where the problem size and the number of processing cores are simultaneously increased. In addition, Firedrake's flexibility is highlighted via straightforward application to different physical (e.g. complex non-linear rheologies, compressibility) and geometrical (2-D and 3-D Cartesian and spherical domains) scenarios. Finally, a representative simulation of global mantle convection is examined, which incorporates 230 Myr of plate motion history as a kinematic surface boundary condition, confirming Firedrake's suitability for addressing research problems at the frontiers of global mantle dynamics research.
How slab age and width combine to dictate the dynamics and evolution of subduction systems: a 3-D spherical study
Publisher: Wiley
Date: 06-07-2022
Global patterns in Earth's dynamic topography since the Jurassic: the role of subducted slabs
Publisher: Copernicus GmbH
Date: 11-09-2017
Abstract: Abstract. 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 generate a degree-2-dominated spectrum of dynamic topography with negative litudes above subducted slabs (i.e. circum-Pacific regions and southern Eurasia) and positive litudes elsewhere (i.e. Africa, north-western Eurasia and the central Pacific). Model predictions are compared with published observations and subsidence patterns from well data, both globally and for the Australian and southern African regions. We find that our models reproduce the long-wavelength component of these observations, although observed smaller-scale variations are not reproduced. We subsequently define geodynamic rules for how different surface tectonic settings are affected by mantle processes: (i) locations in the vicinity of a subduction zone show large negative dynamic topography litudes (ii) regions far away from convergent margins feature long-term positive dynamic topography and (iii) rapid variations in dynamic support occur along the margins of overriding plates (e.g. the western US) and at points located on a plate that rapidly approaches a subduction zone (e.g. India and the Arabia Peninsula). Our models provide a predictive quantitative framework linking mantle convection with plate tectonics and sedimentary basin evolution, thus improving our understanding of how subduction and mantle convection affect the spatio-temporal evolution of basin architecture.
The Role of Slab Remnants in Modulating Free Subduction Dynamics: a 3-D Spherical Numerical Study
Publisher: Authorea, Inc.
Date: 21-08-2023
DOI: 10.22541/ESSOAR.169264792.23974600/V1
Abstract: 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-plastic slabs and remnants that are positioned above, within and below the mantle transition zone. Depending on their size, negatively buoyant remnants can set up mantle flow of similar strength and length scales as that due to active subduction. As such, we find that remnants located within a few hundred km from a slab tip can locally enhance sinking by up to a factor 2. Remnant location influences trench motion: the trench advances towards a remnant positioned in the mantle wedge region, whereas remnants in the sub-slab region enhance trench retreat. These motions aid in rotating the subducting slab and remnant towards each other, reducing the distance between them, and further enhancing the positive interaction of their mantle flow fields. In this process, the trench develops along-strike variations in shape that are dependent on the remnant’s location. Slab-remnant interactions may explain the poor correlation between subducting plate velocities and subducting plate age found in recent plate tectonic reconstructions. Our results imply that slab-remnant interactions affect the evolution of subducting slabs and trench geometry. Remnant-induced downwelling may also anchor and sustain subduction systems, facilitate subduction initiation, and contribute to plate reorganisation events.
Raising the continental crust
Publisher: Elsevier BV
Date: 02-2017
Thermally Dominated Deep Mantle LLSVPs: A Review
Publisher: Springer International Publishing
Date: 2015
Global models from sparse data: A robust estimate of Earth's residual topography spectrum
Publisher: Wiley
Date: 17-06-2020
On the increase in thermal diffusivity caused by the perovskite to post-perovskite phase transition and its implications for mantle dynamics
Publisher: Elsevier BV
Date: 02-2012
Global models from sparse data: A robust estimate of Earth's residual topography spectrum
Publisher: Wiley
Date: 23-07-2020
Single blind randomised controlled trial of GAME (Goals ⿿ Activity ⿿ Motor Enrichment) in infants at high risk of cerebral palsy
Publisher: Elsevier BV
Date: 08-2016
DOI: 10.1016/J.RIDD.2016.04.005
Abstract: Cerebral palsy (CP) is caused by a lesion in the developing infant brain. Recent neuroplasticity literature suggests that intensive, task-specific intervention ought to commence early, during the critical period of neural development. To determine whether "GAME" (Goals - Activity - Motor Enrichment), a motor learning, environmental enrichment intervention, is effective for improving motor skills in infants at high risk of CP. Single blind randomised controlled trial of GAME versus standard care. Primary outcome was motor skills on the Peabody Developmental Motor Scales-2 (PDMS-2). Secondary outcomes included Canadian Occupational Performance Measure (COPM), Bayley Scales of Infant and Toddler Development (BSID-III) and Gross Motor Function Measure-66 (GMFM-66). Outcome assessors were masked to group allocation and data analyzed with multiple regression. All n=30 infants enrolled received the assigned intervention until 16 weeks post enrolment. At 12 months of age, n=26 completed assessments. Significant between group differences were found in raw scores on the PDMS-2 in favour of GAME (B=20.71, 95%CI 1.66-39.76, p=0. 03) and at 12 months on the total motor quotient (B=8.29, 95%CI 0.13-16.45,p =0.05). Significant between group differences favored GAME participants at 12 months on the cognitive scale of the BSID-III and satisfaction scores on the COPM. GAME intervention resulted in advanced motor and cognitive outcomes when compared with standard care.
Effects of post-subduction processes on continental lithosphere
Publisher: Research Square Platform LLC
Date: 08-09-2021
DOI: 10.21203/RS.3.RS-861968/V1
Abstract: Subduction is a key driver of plate tectonics on Earth1. A range of observations indicate that the termination of subduction leads to erse 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 remains enigmatic. A prime ex le of recent subduction termination can be found in northern Borneo (Malaysia), where subduction ceased in the late Miocene2 and was followed by a puzzling tectonic response3,4,5,6,7,8 that cannot be reconciled with our current understanding of post-subduction tectonics. Here, we use new passive-seismic data to image, in unprecedented detail, a sub-vertical lithospheric drip that developed as a Rayleigh-Taylor gravitational instability9 from the root of a volcanic arc. We use thermo-mechanical simulations to reconcile these images with time-dependent dynamical processes within the crust and underlying mantle following subduction termination. Our model predictions illustrate how significant extension from a downwelling lithospheric drip can thin the crust in an adjacent orogenic belt, facilitating lower crustal melting and possible exhumation of subcontinental material. Our study provides a new paradigm for core-complex formation in other areas of recent subduction termination.
Upper plate deformation and trench retreat modulated by subduction-driven shallow asthenospheric flows
Publisher: Elsevier BV
Date: 02-2020
Continental Magmatism: The Surface Manifestation of Dynamic Interactions Between Cratonic Lithosphere, Mantle Plumes and Edge‐Driven Convection
Publisher: American Geophysical Union (AGU)
Date: 07-2022
DOI: 10.1029/2022GC010363
Abstract: 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 continental volcanism. In this study, using a suite of 3‐D geodynamical models, we demonstrate that the magmatic expression of plumes in continental settings is complex and strongly sensitive to the location of plume impingement, differing substantially from that expected beneath more homogeneous oceanic lithosphere. Within Earth's continents, thick cratonic roots locally limit decompression melting. However, they deflect plume conduits during their ascent, with plume material channeled along gradients in lithospheric thickness, activating magmatism away from the plume conduit, sometimes simultaneously at locations more than a thousand kilometres apart. This magmatism regularly concentrates at lithospheric steps, where it may be difficult to distinguish from that arising through edge‐driven convection. At times, the flow field associated with the plume enhances melting at these steps long before plume material enters the melting zone, implying that differentiating geochemical signatures will be absent. Beneath regions of thinner lithosphere, plume‐related flow can force material downwards at lithospheric steps, shutting off pre‐existing edge‐related magmatism. Additionally, variations in lithospheric structure can induce internal destabilization of ponding plume material, driving intricate magmatic patterns at the surface. Our analysis highlights the challenges associated with linking continental magmatism to underlying mantle dynamics, motivating an inter‐disciplinary approach in future studies.
Using thermo-mechanical models of subduction to constrain effective mantle viscosity
Publisher: Elsevier BV
Date: 06-2020
Compressibility of ferropericlase at high-temperature: Evidence for the iron spin crossover in seismic tomography
Publisher: Elsevier BV
Date: 09-2023
Spatio-temporal evolution of Australian lithosphere-asthenosphere boundary from mafic volcanism
Publisher: Geoscience Australia
Date: 2020
DOI: 10.11636/135075
How Aseismic Ridges Modify the Dynamics of Free Subduction: A 3-D Numerical Investigation
Publisher: Frontiers Media SA
Date: 05-05-2022
DOI: 10.3389/FEART.2022.852742
Abstract: 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 paper, using a series of multi-material 3-D simulations of free subduction, we investigate how linear buoyant ridges modify subduction dynamics, in particular downgoing plate velocities, trench motions and slab morphology. We examine the sensitivity of results to downgoing plate age (affecting buoyancy and strength), ridge buoyancy and ridge location along the trench, finding that buoyant ridges can locally change slab sinking and trench retreat rates, in turn modifying the evolution of slab morphology at depth and trench shape at the surface. In all cases examined, trench retreat is reduced, or switches to trench advance, where the ridge subducts. These effects depend strongly on downgoing plate age: on young, weak plates, the change in trench shape is more localised than on old, strong plates. Slab shallowing at the ridge only occurs for young plates, while the stronger and more negatively buoyant older plates pull down the ridge at a steeper angle than the rest of the slab. On old plates, ridges located near regions of trench stagnation or advance, which typically develop in wide slabs, have a stronger effect on trench and slab shape. The combined effects of buoyant feature location, subducting plate age and overriding plate properties can result in a range of responses: from mainly trench deformation, through local slab shallowing, to the formation of a flat slab, a variation in expressions also observed on Earth.
An implicit free surface algorithm for geodynamical simulations
Publisher: Elsevier BV
Date: 03-2012
Proxies for the presence of post-perovskite in the lowermost mantle based on seismic tomography and geodynamic modelling 
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-9966
Abstract: & & The post-perovskite (pPv) phase is often invoked as an explanation for seismic observations of discontinuities, anisotropy and anti-correlation between velocities in the lower mantle. Accurate interpretations of these features in terms of pPv are important, as the phase transition provides a much-needed temperature probe in the lowermost mantle. Robust observations of this phase transition have the potential to constrain the temperature of and heat flow across the core-mantle boundary and thus provide estimates of the heat budget and thermal evolution of the Earth.& & & & Traditionally, the presence of post-perovskite (pPv) has been inferred from observations of seismic discontinuities in the lowermost mantle. However, these only give a very patchy image of lateral variations in the presence of pPv due to the heterogeneous coverage of seismic data. In addition, interpretations are complicated by the fact that the properties and stability field of pPv remain uncertain from a mineral physics point of view.& & & & Here, we describe different proxies for the presence of post-perovskite, proposed based on global seismic tomography. To investigate their accuracy, we utilize synthetic tomography models derived from geodynamic modelling in combination with mineral physics and we compare the predicted presence to the true occurrence of pPv in the model. By using both high-resolution geodynamic models as well as filtered models that have been corrected for the limited resolution of seismic tomography, we can investigate whether a proxy works in theory (on the high-resolution versions) and also in practice (on the filtered models). We will discuss how we may be able to constrain the stability field of pPv based on comparisons with published tomographic models and make recommendations as to what has to improve in seismic tomography to make different proxies work.& &
Subduction dynamics through the mantle transition zone in the presence of a weak asthenospheric layer
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-3822
Abstract: & & Plate kinematics in the vicinity of subduction zones, as well as seismic tomography provide insights into the deep dynamics of subducting slabs. Velocities at which subducting plates are consumed at the trench (the subduction velocities) typically exceed 3& #8211 cm/yr at present-day. Absolute trench velocities (relative to a lower-mantle reference frame) are lower, between -2 and 2 cm/yr [Heuret and Lallemand, 2005]. This implies that the & #8220 accommodation space& #8221 created by the slab rollback associated with lateral trench migration is not nearly sufficient for accommodating the length of incoming slab in the horizontal dimension. In the vertical dimension, even the fastest estimates for slab sinking rates over long time scales amount to only a fraction of 3& #8211 cm/yr [Butterworth et al. 2014, van der Meer et al. 2010, Sigloch & Mihalynuk 2013]. Hence the rates at which the lithosphere typically subducts cannot be accommodated by fast vertical sinking either. Seismic tomography confirms the & #8220 traffic jam& #8221 conditions for slabs in the mantle that are implied by these numbers, with slab thickening imaged in and beneath the mantle transition zone (MTZ). These highly visible, thickened, slabs have been interpreted as the result of folding [Ribe et al., 2007], and their relative localization (massive,& near-vertical & #8220 slab walls& #8221 ) supports the notion of near-stationary trenches over long time scales [Sigloch and Mihalynuk, 2013].& & & & & Buoyancy-driven analog and numerical models of subduction have commonly produced subduction and trench velocities that differ from the first-order observations above. Their subduction velocities typically drop below 1-2 cm/yr once the modelled slab enters the high-viscosity lower mantle, and their trench migration velocities remain almost equal to subduction velocities, thus accommodating the slab mainly in the horizontal direction. In addition, these models tend to produce trench retreat and slab & #8220 rollback& #8221 , unless the latter is very weak and/or the overriding plate is very strong [Goes et al., 2017]. These modelling results have led to the conclusion that near-vertical slab sinking and folding at the MTZ is an end-member regime restricted to very specific subduction set-ups.& & & & & We have added a weak asthenospheric layer to typical 2-D thermo-mechanical models of subduction zones with a complex rheology [e. g., Garel et al., 2014], which partly reconciles the models and the observations. A weak asthenosphere appears as an intuitive candidate for increasing subduction velocity because a reduced mantle drag at the base of the subducting plate lowers the mantle& #8217 s resistance to the plate& #8217 s trench-ward motion. We further found that the models with a weak asthenospheric layer lessens the trench motion and thus tend to produce prominent vertical folding of slabs at the MTZ. Subduction velocities remain higher than trench velocities long after the slab reaches the MTZ, so that 300-to-400-km wide & #8220 slab walls& #8221 are continuously produced in the lower mantle over a relatively wide range of model parameters. The presence of a weak asthenosphere has often been speculated to explain seismic properties beneath oceanic plates, but seldom modelled. This study contributes to a quantification of its potential effects on subduction dynamics.& & &
The Influence of Lithospheric Thickness Variations Beneath Australia on Seismic Anisotropy and Mantle Flow
Publisher: American Geophysical Union (AGU)
Date: 09-2023
DOI: 10.1029/2023GC011066
Linking Intra-Plate Volcanism to Lithospheric Structure and Asthenospheric Flow
Publisher: Wiley
Date: 21-06-2021
The mantle wedge's transient 3‐D flow regime and thermal structure
Publisher: American Geophysical Union (AGU)
Date: 2016
DOI: 10.1002/2015GC006125
Adaptive finite element methods in geodynamics
Publisher: Emerald
Date: 19-09-2008
DOI: 10.1108/09615530810899079
Abstract: The purpose of this paper is to present an adaptive finite element procedure that improves the quality of convection dominated mid‐ocean ridge (MOR) and subduction zone (SZ) simulations in geodynamics. The method adapts the mesh automatically around regions of high‐solution gradient, yielding enhanced resolution of the associated flow features. The approach utilizes an automatic, unstructured mesh generator and a finite element flow solver. Mesh adaptation is accomplished through mesh regeneration, employing information provided by an interpolation‐based local error indicator, obtained from the computed solution on an existing mesh. The proposed methodology works remarkably well at improving solution accuracy for both MOR and SZ simulations. Furthermore, the method is computationally highly efficient. To date, successful goal‐orientated/error‐guided grid adaptation techniques have, to the knowledge, not been utilized within the field of geodynamics. This paper presents the first true geodynamical application of such methods.
Investigations into the applicability of adaptive finite element methods to two-dimensional infinite Prandtl number thermal and thermochemical convection
Publisher: American Geophysical Union (AGU)
Date: 05-2007
DOI: 10.1029/2006GC001470
Post-subduction tectonics induced by extension from a lithospheric drip
Publisher: Springer Science and Business Media LLC
Date: 19-06-2023
Thermal Structure of Eastern Australia's Upper Mantle and Its Relationship to Cenozoic Volcanic Activity and Dynamic Topography
Publisher: American Geophysical Union (AGU)
Date: 08-2021
DOI: 10.1029/2021GC009717
Abstract: 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 rocks that crop out across eastern Australia provide a significant opportunity to quantify mantle conditions at the time of emplacement and to independently validate geophysical estimates. This volcanic activity is ided into two categories: age‐progressive provinces that are generated by the sub‐plate passage of mantle plumes and age‐independent provinces that could be generated by convective upwelling at lithospheric steps. In this study, we acquired and analyzed 78 s les from both types of provinces across Queensland. These s les were incorporated into a comprehensive database of Australian Cenozoic volcanism assembled from legacy analyses. We use geochemical modeling techniques to estimate mantle temperature and lithospheric thickness beneath each province. Our results suggest that melting occurred at depths ≤80 km across eastern Australia. Prior to, or coincident with, onset of volcanism, lithospheric thinning as well as dynamic support from shallow convective processes could have triggered uplift of the Eastern Highlands. Mantle temperatures are inferred to be ∼50–100°C hotter beneath age‐progressive provinces that demarcate passage of the Cosgrove mantle plume than beneath age‐independent provinces. Even though this plume initiated as one of the hottest recorded during Cenozoic times, it appears to have thermally waned with time. These results are consistent with xenolith thermobarometric and geophysical studies.
The mechanisms underpinning Cenozoic intraplate volcanism in eastern Australia: Insights from seismic tomography and geodynamic modeling
Publisher: American Geophysical Union (AGU)
Date: 13-10-2017
DOI: 10.1002/2017GL074911
Automating Finite Element Methods for Geodynamics via Firedrake
Publisher: Copernicus GmbH
Date: 13-01-2022
DOI: 10.5194/GMD-2021-367
Abstract: Abstract. 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 is ideally suited to simulating a wide-range of problems in geophysical fluid dynamics. Here, we demonstrate the applicability of Firedrake for geodynamical simulation, with a focus on mantle dynamics. The accuracy and efficiency of the approach is confirmed via comparisons against a suite of analytical and benchmark cases of systematically increasing complexity, whilst parallel scalability is demonstrated up to 12288 compute cores, where the problem size and the number of processing cores are simultaneously increased. In addition, Firedrake's flexibility is highlighted via straightforward application to different physical (e.g. complex nonlinear rheologies, compressibility) and geometrical (2-D and 3-D Cartesian and spherical domains) scenarios. Finally, a representative simulation of global mantle convection is examined, which incorporates 230 Myr of plate motion history as a kinematic surface boundary condition, confirming its suitability for addressing research problems at the frontiers of global mantle dynamics research.
Interaction of subducted slabs with the mantle transition‐zone: A regime diagram from 2‐D thermo‐mechanical models with a mobile trench and an overriding plate
Publisher: American Geophysical Union (AGU)
Date: 05-2014
DOI: 10.1002/2014GC005257
Linking Intraplate Volcanism to Lithospheric Structure and Asthenospheric Flow
Publisher: American Geophysical Union (AGU)
Date: 08-2021
DOI: 10.1029/2021GC009953
Abstract: 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‐driven convection (EDC) and shear‐driven upwelling (SDU), both of which act to focus upwelling flow and the associated decompression melting adjacent to steps in lithospheric thickness. In this study, we undertake a systematic numerical investigation, in both 2‐D and 3‐D, to quantify the sensitivity of EDC, SDU, and the associated melting to key controlling parameters. Our simulations demonstrate that the spatio‐temporal characteristics of EDC are sensitive to the geometry and material properties of the lithospheric step, in addition to the magnitude and depth‐dependence of upper‐mantle viscosity. These simulations also indicate that asthenospheric shear can either enhance or reduce upwelling velocities and the associated melting, depending upon the magnitude and orientation of flow relative to the lithospheric step. When combined, such sensitivities explain why step changes in lithospheric thickness, which are common along cratonic edges and passive margins, only produce volcanism at isolated points in space and time. Our predicted trends of melt production suggest that, in the absence of potential interactions with mantle plumes, EDC and SDU are viable mechanisms only for Earth's shorter‐lived, lower‐volume intraplate volcanic provinces.
Related Organisations
Imperial College London
Location: United Kingdom of Great Britain and Northern Ireland
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Location: United Kingdom of Great Britain and Northern Ireland
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Earth's Dynamic Topography Through Space And Time
Start Date: 2022
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View Funded ActivitySeeing The Unseeable: A New Generation Of Geophysical Imaging
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View Funded ActivityDynamic Earth Models
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View Funded ActivityG-ADOPT: Geodynamic Adjoint Optimization Platform
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View Funded ActivityDiscovery Projects - Grant ID: DP200100053
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Amount: $573,068.00
Funder: Australian Research Council
View Funded ActivityARC Future Fellowships - Grant ID: FT140101262
Start Date: 10-2014
End Date: 09-2018
Amount: $683,700.00
Funder: Australian Research Council
View Funded ActivitySpecial Research Initiatives - Grant ID: SR200100008
Start Date: 08-2021
End Date: 12-2027
Amount: $20,000,000.00
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP170100058
Start Date: 06-2017
End Date: 06-2020
Amount: $286,000.00
Funder: Australian Research Council
View Funded Activity