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SUMMARY The relatively short duration of the early stages of subduction results in a poor geological record, limiting our understanding of this critical stage. Here, we utilize a 2-D numerical model of incipient subduction, that is the stage after a plate margin has formed with a slab tip that extends to a shallow depth and address the conditions under which subduction continues or fails. We assess energy budgets during the evolution from incipient subduction to either a failed or successful state, showing how the growth of potential energy and slab pull, is resisted by the viscous dissipation within the lithosphere and the mantle. The role of rheology is also investigated, as deformation mechanisms operating in the crust and mantle facilitate subduction. In all models, the onset of subduction is characterized by high lithospheric viscous dissipation and low convergence velocities, whilst successful subduction sees the mantle become the main area of viscous dissipation. In contrast, failed subduction is defined by the lithospheric viscous dissipation exceeding the lithospheric potential energy release rate and velocities tend towards zero. We show that development of a subduction zone depends on the convergence rate, required to overcome thermal diffusion and to localize deformation along the margin. The results propose a minimum convergence rate of ∼0.5 cm yr−1 is required to reach a successful state, with 100 km of convergence over 20 Myr, emphasizing the critical role of the incipient stage.

Earth's mantle is known to harbor water in the form of hydrous and nominally anhydrous minerals. How much water the mantle holds and whether it has remained constant through time are open questions. Previous numerical studies of the deep‐water cycle have been limited to box models or 2‐D calculations. Here we present for the first time results from 3‐D mantle convection models. We address the evolution of the mantle's total water content by adapting a well benchmarked mantle convection code to track water, including its feedbacks on dynamics. While Earth's surface is presently covered by one ocean mass of water, our results suggest that the mantle holds approximately two ocean masses of water based on the best estimates from mineral physics. This value varies only weakly for a wide parameter space of additional complex dynamics such as viscosity laws, density controls, and phase change considerations. Our result of a mantle holding two ocean masses conforms with estimates from other branches of Earth science, suggesting that these models could be an excellent tool in understanding the spatial heterogeneity of the water found in the mantle.

A novel approach to the construction of three-dimensional grids in spherical geometries is described. The grids are based on a range of underlying regular polyhedra. The faces of the polyhedra are arranged into a number of diamonds in the latitudinal and longitudinal directions to facilitate the creation of a structured mesh. Each polyhedron is completely characterized in terms of the arrangement of diamonds. The approach is shown to be very flexible in terms of the meshes that can be generated. It also aids comparisons between the grids used in many mantle convection studies. A spectral element discretization of Poisson's equation is performed to demonstrate the efficacy of the grid generation technique. Rapidly convergent approximations are obtained that demonstrate that fewer degrees of freedom are required to obtain a desired level of accuracy compared with low-order finite element approximations.

Knowledge of Earth’s past mantle structure is inherently unknown. This lack of knowledge presents problems in many areas of Earth science, including in mantle circulation modelling (MCM). As a mathematical model of mantle convection, MCM’s require boundary and initial conditions. While boundary conditions are readily available from sources such as plate reconstructions for the upper surface, and as free slip at the core-mantle boundary (CMB), the initial condition is not known. MCM’s have historically ‘created’ an initial condition using long ‘spin up’ processes using the oldest available plate reconstruction period available. Whilst these do yield good results when models are run to present day, it is difficult to infer with confidence results from early in a model’s history. Techniques to overcome this problem are now being studied in geodynamics, such as by assimilating the known internal structure (e.g. from seismic tomography) of Earth at present day backwards in time. One such method is to use an iterative process known as the forward-adjoint method, which, while an efficient means of solving this inverse problem still strains all but the most cutting edge computational systems. In this study we endeavour to profile the effectiveness of this method using synthetic test cases as our known data source. We conclude that savings in terms of computational expense for forward-adjoint models can be achieved by streamlining the time-stepping of the calculation, as well as determining the most efficient method of updating initial conditions in the iterative scheme. Furthermore we observe that in the models presented, there exists an upper limit on the time interval over which solutions will practically converge, although this limit is likely to be linked to Rayleigh number.

The evolution of the planetary interior during plate tectonics is controlled by slow convection within the mantle. Global-scale geochemical differences across the upper mantle are known, but how they are preserved during convection has not been adequately explained. We demonstrate that the geographic patterns of chemical variations around the Earth’s mantle endure as a direct result of whole-mantle convection within largely isolated cells defined by subducting plates. New 3D spherical numerical models embedded with the latest geological paleo-tectonic reconstructions and ground-truthed with new Hf-Nd isotope data, suggest that uppermost mantle at one location (e.g. under Indian Ocean) circulates down to the core-mantle boundary (CMB), but returns within ≥100 Myrs via large-scale convection to its approximate starting location. Modelled tracers pool at the CMB but do not disperse ubiquitously around it. Similarly, mantle beneath the Pacific does not spread to surrounding regions of the planet. The models fit global patterns of isotope data and may explain features such as the DUPAL anomaly and long-standing differences between Indian and Pacific Ocean crust. Indeed, the geochemical data suggests this mode of convection could have influenced the evolution of mantle composition since 550 Ma and potentially since the onset of plate tectonics.

This, the first John Barron Memorial Lecture, sketches his activity in the 1980s for the UGC in reshaping institutional provision in Classics and in Archaeology, in order to explore its best routes of healthy survival. It reviews developments in Britain within the study of antiquity in the last twenty years, but also reviews current and likely future transformations of the wider environment, both fiscal-financial and technological – all of which threaten marginalization, if not extinction. It then notes that the erosion of the Humboldtian vision of the discipline makes it appear derivative, inward-looking, and lacking an externally recognised raison d'être. That view is best controverted by identifying the most promising future markets in terms of age, world geography, delivery systems, and basic curiosity and interest, and above all by identifying the attitudes which the study of pre-Islamic antiquity can and should instil.

An investigation of the power law relationship between Nusselt number (Nu) and Rayleigh number (Ra) for Earth’s convecting mantle is presented. The Nu(Ra) relationship was calculated from the results of a model with three dimensional spherical geometry and free slip boundary conditions. Both basally and internally heated convection has been examined. For Nu(Ra)=aRaβ, β was found to be 0.294±0.004 for basally heated systems, which is lower than the value of 1/3 suggested by conventional boundary layer theory. The exponent β=0.337±0.009 for internally heated systems, when the internally heated Ra is converted to a basally heated equivalent for comparison. The influence of the method used to calculate β was also considered, with particular attention paid to high Ra. As an example of the significance of β=0.29 rather than 1/3, a Ra of 109 results in a surface heat flux which is ≈32% lower. Within the range of Ra used in this study, there is no evidence that β changes at high Ra. Therefore, that mechanism cannot be used to moderate mantle temperature when projecting back to early Earth conditions. The differing planform of basally and internally heated models was shown to result in different scaling relationships between root mean square surface velocity and Ra for the two modes of heating, in particular, a much lower surface velocity for internally heated cases relative to equivalent Ra basally heated cases.

BackgroundIn reattribution, general practitioners (GPs) request psychosocial information directly and explain medically unexplained symptoms (MUS) using psychosocial information in the consultation. We explored whether reattribution training (RT) increased the communication of psychosocial information and decreased communication about somatic intervention between GPs and their MUS patients.MethodA cluster randomized controlled trial (RCT) of RT versus usual treatment in GPs from 16 practices and 141 patients with MUS on audio-recorded and transcribed doctor–patient communication in an index consultation. In a secondary data analysis, the Liverpool Clinical Interaction Analysis Scheme (LCIAS) was applied by an experienced rater to each turn of speech in the transcript from the index consultation blind to treatment allocation.ResultsAfter RT, patients were more likely to disclose and discuss psychosocial problems, and propose psychosocial explanations for symptoms; around 25% of patients discussed psychosocial information extensively. In the RT group, GPs did not seek new psychosocial disclosure but they reduced advocacy for somatic intervention. After RT, GPs suggested, on average, two utterances of psychosocial explanation and six utterances of somatic intervention.ConclusionsAfter RT, some patients discussed psychosocial issues extensively but GPs did not probe underlying psychosocial issues. They gave mixed psychosocial and somatic messages about MUS, which may have increased patients' concerns about their health. GPs should actively seek the disclosure of underlying psychosocial problems and give clear, unambiguous messages to MUS patients when they are willing to discuss psychosocial issues.

Hot-spots are anomalous regions of magmatism that cannot be directly associated with plate tectonic processes. They are widely-regarded as the surface expression of upwelling mantle plumes. Hot-spots exhibit variable life-spans, magmatic productivity and fixity. This suggests that a wide-range of upwelling structures coexist within Earth's mantle, a view supported by geochemical and seismic evidence, but, thus far, not fully-reproduced by numerical models. Here, results from a new, global, 3-D spherical, mantle convection model are presented, which better reconcile hot-spot observations, the key modification from previous models being increased convective vigor. Model upwellings show broad-ranging dynamics; some drift slowly, while others are more mobile, displaying variable life-spans, intensities and migration velocities. Such behavior is consistent with hot-spot observations, indicating that the mantle must be simulated at the correct vigor and in the appropriate geometry to reproduce Earth-like dynamics. Thermally-driven mantle plumes can explain the principal features of hot-spot volcanism on Earth.

PurposeThe 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.Design/methodology/approachThe 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.FindingsThe proposed methodology works remarkably well at improving solution accuracy for both MOR and SZ simulations. Furthermore, the method is computationally highly efficient.Originality/valueTo 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.

Many outstanding problems in solid Earth science relate to the geodynamical explanation of geochemical observations. Currently, extensive geochemical databases of surface observations exist, but satisfying explanations of underlying mantle processes are lacking. One way to address these problems is through numerical modelling of mantle convection while tracking chemical information throughout the convective mantle. We have implemented a new way to track both bulk compositions and concentrations of trace elements in a finite element mantle convection code. Our approach is to track bulk compositions and trace element abundances via particles. One value on each particle represents bulk composition, and can be interpreted as the basalt component. In our model, chemical fractionation of bulk composition and trace elements happens at self-consistent, evolving melting zones. Melting is defined via a composition-dependent solidus, such that the amount of melt generated depends on pressure, temperature and bulk composition of each particle. A novel aspect is that we do not move particles that undergo melting; instead we transfer the chemical information carried by the particle to other particles. Molten material is instantaneously transported to the surface layer, thereby increasing the basalt component carried by the particles close to the surface, and decreasing the basalt component in the residue. The model is set to explore a number of radiogenic isotopic systems but as an example here the trace elements we choose to follow are the Pb isotopes and their radioactive parents. For these calculations we will show: (1) The evolution of the distribution of bulk compositions over time, showing the build up of oceanic crust (via melting-induced chemical separation in bulk composition); i.e. a basalt-rich layer at the surface, and the transportation of these chemical heterogeneities through the deep mantle. (2) The amount of melt generated over time. (3) The evolution of the concentrations and abundances of different isotopes of the trace elements (U, Th, K and Pb), throughout the mantle. (4) A comparison to a semi-analytical theory relating observed arrays of correlated Pb isotope compositions to melting age distributions (Rudge, 2006).

Patients with symptoms that doctors cannot explain by physical disease are common in primary care. That they receive disproportionate amounts of physical intervention, which is largely ineffective and sometimes iatrogenic, is usually attributed to patients' belief that they are physically diseased, their denial of psychological difficulties, and their demand for physical intervention. The evidence for this view has mainly been doctors' subjective reports. By observing what patients and doctors say in consultation, we tested hypotheses arising from recent qualitative evidence. In particular, that physical intervention is proposed more often by general practitioners (GPs) than by patients, that most patients indicate psychosocial needs, and that GPs offer little effective explanation or empathy. Consultations of 420 consecutive patients identified by British GPs as presenting medically unexplained symptoms (MUS) were audio-recorded, transcribed and coded, utterance-by-utterance, using a specially developed coding scheme based on the previous qualitative analyses of these kinds of consultation. Physical intervention was, as predicted, proposed more often by GPs than patients. Also as predicted, almost all patients provided cues concerning psychosocial difficulties or their need for explanation. Although, contrary to prediction, most GPs did provide explanations other than physical disease, most also suggested physical disease. Few GPs empathised. The findings suggest that the explanation for the high level of physical intervention for MUS lies in GPs' responses rather than patients' demands, and we propose that explanations for 'somatisation' should be sought in doctor-patient interaction rather than in patients' psychopathology.

The presence of magmatism and intermediate-depth (70–300 km deep) seismicity at subduction zones is at first sight surprising. Magmatism is unexpected because the subduction of cool oceanic lithosphere makes these regions the coldest in the mantle. The current model for subduction-zone magmatism is that water released from the subducting slab enters the relatively warm mantle wedge, leading to a reduction in melting temperature and magmatism1, 2, 3, 4. But there is a problem with this scheme because it is thought that water cannot leave the slab by porous flow to enter the wedge. The occurrence of intermediate-depth earthquakes is surprising because of the inhibitory effect of the very high frictional stress on faults expected from the high pressure at these depths. One proposal put forward to explain intermediate-depth seismicity is that high pore-pressure might facilitate faulting by decreasing the friction5, 6, 7. The hypothesis presented here is that non-percolating water provides the high pore-pressure, that the consequent faulting temporarily interconnects the water pores and, when a sufficient vertical height of water is interconnected, a hydrofracture is produced which transports the water out into the mantle wedge, thereby generating subduction-zone magmatism.

International audience; Transition zone slab deformation influences Earth's thermal, chemical, and tectonic evolution. However, the mechanisms responsible for the wide range of imaged slab morphologies remain debated. Here we use 2-D thermo-mechanical models with a mobile trench, an overriding plate, a temperature and stress-dependent rheology, and a 10, 30, or 100-fold increase in lower mantle viscosity, to investigate the effect of initial subducting and overriding-plate ages on slab-transition zone interaction. Four subduction styles emerge: (i) a ''vertical folding'' mode, with a quasi-stationary trench, near-vertical subduction, and buckling/folding at depth (VF); (ii) slabs that induce mild trench retreat, which are flattened/''horizontally deflected'' and stagnate at the upper-lower mantle interface (HD); (iii) inclined slabs, which result from rapid sinking and strong trench retreat (ISR); (iv) a two-stage mode, displaying backward-bent and subsequently inclined slabs, with late trench retreat (BIR). Transitions from regime (i) to (iii) occur with increasing subduct-ing plate age (i.e., buoyancy and strength). Regime (iv) develops for old (strong) subducting and overriding plates. We find that the interplay between trench motion and slab deformation at depth dictates the subduction style, both being controlled by slab strength, which is consistent with predictions from previous compositional subduction models. However, due to feedbacks between deformation, sinking rate, temperature , and slab strength, the subducting plate buoyancy, overriding plate strength, and upper-lower mantle viscosity jump are also important controls in thermo-mechanical subduction. For intermediate upper-lower mantle viscosity jumps (330), our regimes reproduce the diverse range of seismically imaged slab morphologies.

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.

Two large regions of low shear wave velocity in the deep mantle beneath Africa and the Pacific are generally interpreted as hot but chemically dense `piles'. These `piles' are thought to have remained isolated from mantle circulation for several hundred million years, influencing heat transfer within Earth's interior and the mantle's geochemical evolution. The interpretation that these regions are chemically distinct largely hinges on three seismic observations: (i) their shear wave velocity anomalies are considered too large for a purely thermal explanation; (ii) shear wave velocity gradients at their edges are considered too sharp for an isochemical feature; and (iii) their shear and bulk-sound velocity anomalies appear to be anti-correlated, which is not expected for purely thermal structures. However, using compressible global spherical mantle circulation models driven by 300 million years of plate motion history and thermodynamic methods for converting from physical to seismic structure, we show that observed lower mantle shear wave velocity anomalies do not require, and are most likely incompatible with, large-scale compositional heterogeneity. A prescribed core-mantle-boundary temperature of 4000 K, which is consistent with current estimates, combined with anelastic seismic sensitivity to temperature, ensures that purely thermal LLSVPs, strongly focussed beneath Africa and the Pacific by subduction history, can reconcile observed shear wave velocity anomalies and gradients. By contrast, models that include dense chemical `piles' at the base of Earth's mantle, in which `piles' correspond to only 3% of the mantle's volume, produce shear wave velocity anomalies that are too strong to be compatible with tomographic observations, even after filtering results to account for limited tomographic resolution. Our results also suggest that in the presence of post-perovskite, the ratio between shear and compressional wave-speed anomalies cannot be used to discriminate between thermal and compositional heterogeneity at depth. This is also true for the correlation between shear and bulk-sound velocity anomalies: in all models examined, an anti-correlation only occurs within the post-perovskite stability field. Taken together, this implies that compositional heterogeneity, an unavoidable consequence of plate tectonics, must be widely-distributed, occurring on length-scales that do not strongly influence lower mantle dynamics and the lower mantle's long-wavelength seismic structure.

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-sampled 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.

Thermal models of subduction zones, restrict the melt source region to a domain at sufficiently high temperature with water present (either as a free phase or in hydrous minerals). Water, released into the mantle by slab dehydration, traverses the wedge horizontally by a combination of (i) vertical movement as a fluid phase and (ii) fixed in amphiboles carried by the induced mantle flow; only in mantle hotter than amphibole stability can melts escape upwards. We develop a one-dimensional model for the source region fluxed with water. The induced mantle flow advects heat laterally to balance the latent heat of melting, in a column where the liquidus of the melt is depressed by its water content. Melt flux, fraction, temperature and water content are calculated assuming steady state. Melt compositions are predicted from the melt fraction distribution as a function of depth, constrained by the experimental data of Green. On investigating a range of plausible models, we find that the average degrees of melting predicted vary from ca . 2 to 8% . The predicted primary magmas are mafic high magnesium basalts with water contents ranging from 1.6 to 6 wt% , and temperatures from 1160 to 1290 °C. Models with shallower depths of segregation have higher degrees of melting and lower water contents. The volumes predicted by the physical model are a strong function of the water flux assumed to enter the source region. Previous estimates of are growth would suggest either low water fluxes or that not all the melt reaches the arc crust.

Incubation of human bloodstream neutrophils with 50 u/ml recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) “primed” the respiratory burst (as assessed by fMet-Leu-Phe stimulated luminol-dependent chemiluminescence) and resulted in a rapid (within 15 min) upregulation of expression of CD11b and CD18 (as measured by FACS analysis). This rapid “priming” and modulation of receptor expression was not inhibited by cycloheximide and hence appeared to be independent of de novo protein biosynthesis. When neutrophils were incubated for up to 5 h in culture, the fluorescence distributions of CD11b and CD18 declined indicating the loss of expression of these receptors as the neutrophils aged, but in rGM-CSF treated suspensions receptor expression was maintained. When neutrophils were incubated in the presence of cycloheximide, they progressively lost their ability to generate reactive oxidants in response to fMet-Leu-Phe so that by 5 h incubation with this inhibitor they could only generate about 25% of the oxidative response stimulated in untreated cells, and the expression of CD16 and CD18 was grossly impaired. Similar effects were observed in rGM-CSF treated suspensions except that cycloheximide required longer incubation times (typically 4–5 h) before impairment of function or receptor expression occurred. These data show that de novo protein biosynthesis is required for both the maintenance of neutrophil function and also for the continued expression of some plasma membrane receptors.

Analysis of global traveltime data has been formulated in terms of the stochastic properties of the Earth's heterogeneity pattern and random errors in the data. The formalism relates the coherency of traveltime residuals within bundles of rays (summary rays) of varying size to the spherical harmonic power spectrum of the slowness field of the medium. It has been applied to mantle P-wave data from the ISC catalogue. The measure of coherency is the variance within summary rays. It is estimated within bins in source depth, epicentral distance and the scale size of the area defining a summary ray. The variance at infinitesimal scale length represents the incoherent component of the data (random errors). The variation of the variance with scale length contains information about the autocorrelation function or power spectrum of slowness perturbations within the Earth. The variation with epicentral distance reflects the depth variation of the spectrum. The formalism accounts for the uneven distribution (clustering) of stations and events. We find that estimates of random errors correlate well with complexities on the traveltime curve of P-waves. The variance peaks at 1.0–2.0 s^2 at Δ ≈ 20°, where triplications occur on the traveltime curve, drops to 0.15–0.8s^2 at teleseismic distances, and rises to 0.4–1.3 s^2 approaching the core shadow, where the traveltime curves of P-waves and PcP-waves merge. These estimates should be considered upper bounds for the random error variance of the data. The signal to random noise ratio in the teleseismic ISC P-wave data is about S/N ≈ 2. Inversion of the scale-dependent structural signal in the data yields models that concentrate heterogeneity strongly in the upper mantle. The product of correlation length and power drops by about two orders of magnitude from the surface of the Earth to the lower mantle. About half of this quantity in the upper mantle is due to small-scale features (

An adaptive finite element procedure is presented for improving the quality of solutions to convection-dominated problems in geodynamics. The method adapts the mesh automatically around regions of high solution gradient, yielding enhanced resolution of the associated flow features. The approach requires the coupling of an automatic mesh generator, a finite element flow solver, and an error estimator. In this study, the procedure is implemented in conjunction with the well-known geodynamical finite element code ConMan. An unstructured quadrilateral mesh generator is utilized, with mesh adaptation accomplished through regeneration. This regeneration employs information provided by an interpolation-based local error estimator, obtained from the computed solution on an existing mesh. The technique is validated by solving thermal and thermochemical problems with well-established benchmark solutions. In a purely thermal context, results illustrate that the method is highly successful, improving solution accuracy while increasing computational efficiency. For thermochemical simulations the same conclusions can be drawn. However, results also demonstrate that the grid-based methods employed for simulating the compositional field are not competitive with the other methods (tracer particle and marker chain) currently employed in this field, even at the higher spatial resolutions allowed by the adaptive grid strategies.

A feasibility study of a peer-to-peer distributed storage system for the archiving of large datasets produced by the Earth mantle modelling code TERRA is presented. The manner in which the nature of such data affects the indexing, duplication and performance requirements of such a system is analysed and a data-oriented overlay network to improve efficiency is proposed. Duplication methods are analysed and test bed performance measured.

Publisher Summary This chapter presents a model for subduction zone magmatism wherein the mantle wedge melts by hydrous fluxing from the subducting slab. The subducting slab induces secondary flow in the overriding mantle wedge. This induced flow leads to high temperatures attained near but not at the subducting slab. Water is released from amphibole in the oceanic crust at a depth of around 80 km. On entering the mantle, it reacts to form amphibole, which is carried down by the induced flow as part of the solid matrix. At a depth of around 100 km, it breaks down and releases its water. The water ultimately rises vertically through the mantle, passing through the amphibole-saturated mantle until it reaches dry mantle. There it reacts to form amphibole, which is again carried down by the induced flow. This process repeats, with the net effect being the lateral transport of water from the oceanic crust out into the mantle wedge. Finally, the water reaches the high temperatures near the slab where amphibole is unstable. At this point, the hydrous melt leads to ever greater degrees of melting as it rises vertically. The process ultimately leads to such substantial degrees of melting that some of the melts can segregate in sufficiently large cracks to emplace magma in the lithosphere. These processes describe the proposed source region for subduction zone magmatism.

THE INTACT AND SLICED BRAIN By Mircea Steriade 2001. London: MIT Press Price £37.95. pp. 382. ISBN 0262194562 The Intact and Sliced Brain is a monograph of Mircea Steriade’s work as a leader in the field of thalamocortical function over the last 50 years. Although this book is predominantly a record of Steriade’s considerable volume of work, it also reviews the place of this research in the wider context. The book comprises four substantial chapters covering localization of brain function, the methodology underlying brain research, a comparison of in vitro and in vivo results, a chapter on synaptic networks underlying normal and paroxysmal states, as well as a very short fifth chapter on consciousness. The volume is very well produced with an excellent layout, one unusual feature being that work referred to in the text is referenced alongside in the generous margins and many of these references are annotated with the salient points of the particular paper being discussed. Another enjoyable aspect of the annotated margins is the inclusion of, in some cases extended, vignettes of eminent neurophysiologists and neuroanatomists who have historically contributed to our understanding of the functioning of the brain. The book is particularly well referenced and up to date; all the references are …

Seismic images suggest that oceanic plates in the northwest Pacific broke apart as they descended into Earth’s mantle. That might explain the high magma output of some volcanoes in the region, and why others are extinct.

It has been claimed that focused hot cylindrical upwelling plumes cause many of the surface volcanic hotspots on Earth. It has also been argued that they must originate from thermal boundary layers. In this paper, we present spherical simulations of mantle circulation at close to Earth-like vigor with significant internal heating. These show, in addition to thermal boundary layer plumes, a new class of plumes that are not rooted in thermal boundary layers. These plumes develop as instabilities from the edge of bowls of hot mantle, which are produced by cold downwelling material deforming hot sheets of mantle. The resulting bowl and plume structure can look a bit like the “splash� of a water droplet. These splash plumes might provide an explanation for some hotspots that are not underlain by thermal boundary layer–sourced plumes and not initiated by large igneous provinces. We suggest that in Earth's mantle, lithospheric instabilities or small pieces of subducting slab could play the role of the model downwelling material in initiating splash plumes. Splash plumes would have implications for interpreting ocean-island basalt geochemistry, plume fixity, excess plume temperature, and estimating core heat flux. Improved seismic imaging will ultimately test this hypothesis.

ALVING et al.1 have shown that primaquine-sensitive erythrocytes are deficient in glucose-6-phosphate dehydrogenase (G-6-PD) activity and a similar abnormality has also been found in fava-sensitive erythrocytes2. Consequent on their diminished G-6-PD activity, such cells have an unstable reduced glutathione-level (GSH) when exposed to various oxidizing agents3,4. Estimations of GSH stability are defined more clearly when glucose is added to the test system5. Under these conditions, little reduction in the GSH-level occurs when either fava-sensitive or normal erythrocytes are incubated at 37° C for 24 h, whereas a significant decrease, limited to the fava-sensitive cells, is found after incubation for a further 2 h at 37° C with acetylphenylhydrazine (APH). This final post-incubation GSH-level has been used to distinguish fava-sensitive from normal erythrocytes5.

The nature of the mantle underlying prospective hydrocarbon basins during their critical history is poorly known. This mantle can affect the basin dynamically and thermally. Knowing these effects through Earth history would be invaluable for assessing basin prospectivity. Mantle geodynamic modelling has advanced dramatically over the past decade such that the outputs are starting to become of interest in assessing the palaeo-environments of frontier regions. We focus on outlining the elements of the basic mantle circulation modelling (MCM) method, including the input plate motion histories, the equations solved, and the boundary and initial conditions. The method can predict dynamic topography and mantle flow back to the Jurassic. We introduce an extension of the method to allow tracing of the flow of magmatic source regions. This could be realised in the data from geochemical signatures of magmatic outputs over time. We also introduce how MCM can be used to test plate motion histories by comparing present day predictions with seismic tomography.