Deformation-Induced Mechanical Instabilities at the Core-Mantle Boundary

Post-Perovskite: The Last Mantle Phase Transition Our understanding of the core-mantle boundary (CMB) region has improved significantly over the past several years due, in part, to the discovery of the post-perovskite phase. Sesimic data suggest that the CMB region is highly heterogeneous, possibly reflecting chemical and physical interaction between outer core material and the lowermost mantle. In this contribution we present the results of a new mechanism of mass transfer across the CMB and comment on possible repercussions that include the initiation of deep, siderophile-enriched mantle plumes. We view the nature of core-mantle interaction, and the geodynamic and geochemical ramifications, as multiscale processes, both spatially and temporally. Three lengthscales are defined. On the microscale (1-50 km), we describe the effect of loading and subsequent shearing of the CMB region and show how this may drive local flow of outer core fluid upwards into D". We propose that larger scale processes operating on a mesoscale (50-300 km) and macroscale regimes (> 300 km) are linked to the microscale, and suggest ways in which these processes may impact on global mantle dynamics

Sulfur and Metal Fertilization of the Lower Continental Crust

Mantle-derived melts and metasomatic fluids are considered to be important in the transport and distribution of trace elements in the subcontinental lithospheric mantle. However, the mechanisms that facilitate sulfur and metal transfer from the upper mantle into the lower continental crust are poorly constrained. This study addresses this knowledge gap by examining a series of sulfide- and hydrous mineral-rich alkaline mafic-ultramafic pipes that intruded the lower continental crust of the Ivrea-Verbano Zone in the Italian Western Alps. The pipes are relatively small (<300 m diameter) and primarily composed of a matrix of subhedral to anhedral amphibole (pargasite), phlogopite and orthopyroxene that enclose sub-centimeter-sized grains of olivine. The 1 to 5 m wide rim portions of the pipes locally contain significant blebby and disseminated Fe-Ni-Cu-PGE sulfide mineralization.Stratigraphic relationships, mineral chemistry, geochemical modeling and phase equilibria suggest that the pipes represent open-ended conduits within a large magmatic plumbing system. The earliest formed pipe rocks were olivine-rich cumulates that reacted with hydrous melts to produce orthopyroxene, amphibole and phlogopite.Sulfides precipitated as immiscible liquid droplets that were retained within a matrix of silicate crystals and scavenged metals from the percolating hydrous melt. New high-precision chemical abrasion TIMS-UPb dating of zircons from one of the pipes indicates that these pipes were emplaced at 249.1+/-0.2 Ma, following partial melting of lithospheric mantle pods that were metasomatized during the Eo-Variscan oceanic to continental subduction (approx. 420-310 Ma). The thermal energy required to generate partial melting of the metasomatized mantle was most likely derived from crustal extension, lithospheric decompression and subsequent asthenospheric rise during the orogenic collapse of the Variscan belt (<300 Ma). Unlike previous models, outcomes from this study suggest a significant temporal gap between the occurrence of mantle metasomatism, subsequent partial melting and emplacement of the pipes.We argue that this multi-stage process is a very effective mechanism to fertilize the commonly dry and refractory lower continental crust in metals and volatiles. During the four-dimensional evolution of the thermo-tectonic architecture of any given terrain, metals and volatiles stored in the lower continental crust may become available as sources for subsequent ore-forming processes, thus enhancing the prospectivity of continental block margins for a wide range of mineral systems

Channelized melt flow in downwelling mantle: Implications for 226Ra-210Pb disequilibria in arc magmas

We present the results of an analytical model of porous flow of viscous melt into a steadily dilating ‘‘channel’’ (defined as a cluster of smaller veins) in downwelling subarc mantle. The model predicts the pressure drop in the mantle wedge matrix surrounding the channel needed to drive melt flow as a function of position and time. Melt is sucked toward the dilatant region at a near-constant velocity (105 s1) until veins comprising the channel stop opening (t = t). Fluid elements that complete their journey within the time span t < t arrive at a channel. Our results make it possible to calculate the region of influence sampled by melt that surrounds the channel. This region is large compared to the model size of the channelized region driving flow. For a baseline dilation time of 1 year and channel half width of 2 m, melt can be sampled over an 80-m radius and has the opportunity to sample matrix material with potentially contrasting chemistry on geologically short timescales. Our mechanical results are consistent with a downgoing arc mantle wedge source region where melting and melt extraction by porous flow to a channel network are sufficiently rapid to preserve source-derived 238U-230Th-226Ra, and potentially also 226 Ra-210Pb, disequilibria, prior to magma ascent to the surface. Since this is the rate-determining step in the overall process, it allows the possibility that such short-lived disequilibria measured in arc rocks at the surface are derived from deep in the mantle wedge. Stresses due to partial melting do not appear capable of producing the desired sucking effect, while the order of magnitude rate of shear required to drive dilation of 107 s1 is much larger than values resulting from steady state subduction. We conclude that local deformation rates in excess of background plate tectonic rates are needed to ‘‘switch on’’ the dilatant channel network and to initiate the sucking effect

Subjective experiences of compulsory treatment from a qualitative study of early implementation of the Mental Health (Care and Treatment)(Scotland) Act 2003

Compulsory psychiatric treatment is highly contested, and little research has focused specifically on direct experiences. The Mental Health (Care & Treatment) (Scotland) Act, 2003 introduced new roles and provisions including community treatment orders, and was designed to increase participation, ensure treatment was beneficial and was the ‘least restrictive’ alternative. This article draws on findings from semistructured interviews with 49 individuals who had experienced compulsion under this new legislation during 2007-08, that were part of a broader cohort study. Interviews with service users were conducted at two stages with 80% agreeing to be interviewed twice. The sample included people on a variety of compulsory orders from four Health Board areas, some of whom had been detained for the first time, while others reported ‘revolving door’ experiences. Peer researchers who were mental health service users carried out the interviews with professional researchers. The findings suggest that legislation had a limited impact on participation in the process of compulsion. Consensus was that although service users felt there was increased opportunity for their voices to be heard, this was not matched by having increased influence over professional decision-making, especially in relation to drug treatments. According to people's direct experiences, the passing of the legislation in itself had done little to change the dominant psychiatric paradigm. While providing a foundation for improving the process of compulsion, the findings suggest that as well as legislative reform, fundamental shifts in practice are needed both in terms of the nature of therapeutic relationships, and in embracing more holistic and recovery perspectives

Reading newspapers: a theoretical description of a practical activity

A simple observation about the nature of reading initiated this project. The observation was that in reading we are able to use ink on paper as an equivalence of the real world event it details. Attempts to account for this by examining reading as it progresses did not give rise to clarification of this phenomenon, but solely to reading itself. Encounters with the text always resulting in 'ending-up-just-reading'. This is identifiable as a central characteristic of the material and the reader's attitude towards it. As this difficulty with the nature of the undertaking threatened to stop any theoretical progress, various methodologies, including Ethnomethodology, were applied to the material in order to produce a way forward. However, these theoretical approaches did not solve the phenomenon of reading but merely multiplied its problematic features. Their terms displacing the focus of attention away from reading, to the internal expression of the approach itself. Elsewhere within the project a more reflexive approach was adopted. Examining the roles of reader, theorist and author that were variously adopted. The recognition that the author in detailing experiences as a reader of texts succeeds only in creating another text. There is an examination of levels of access available to the project reader and the constraints this places on any reading that can be made. Otherwise expressed, it is the reading of one text through the confines of another, we are always trapped within the medium. From this recognition that 'viewing from within' is an intrinsic, inescapable feature of reading, a solution to 'ending-up-just reading' offers itself. Aspects of reading are made obvious by getting the reader to activate them, as they read of them. The solution is an ethnographical account of the reading of a newspaper story, an interpretive account. Its success may be gauged by the familiarity of its description and its expression of shared reading experiences and common reading practices

Rapid core formation in terrestrial planets by percolative flow: in-situ imaging of metallic melt under high pressure/temperature conditions

Core formation has left a lasting geochemical signature on the Earth. In order to constrain the composition of the Earth we must fully understand the processes by which newly formed Earth, and the bodies which accreted to it, differentiated. Percolation of iron-rich melt through solid silicate has been invoked as a mechanism for differentiation and core formation in terrestrial bodies in the early solar system. However, to date the contribution of percolation to core formation cannot be assessed due to the absence of data on Fe-rich melt migration velocities. Here we use a novel experimental design to investigate textural changes in an analog system, Au melt in polycrystalline h-BN, at 3 GPa, relevant to core formation in the early solar system. Using a combination of high resolution, in-situ X-ray tomography and fast 2-D radiographic imaging, we obtain the first direct data on melt migration velocities at high PT. Melt migration is highly variable and episodic, driven by variations in differential pressure during melt migration and matrix compaction. Smaller scale melt processes, representing migration of melt along pre-existing melt networks, give comparatively fast velocities of 0.6–60 μms−1. Ex-situ experiments are used to compare melt networks in analog systems to Fe-rich melt in silicates. Two competing processes for melt migration are percolation of melt along grain boundaries, and hydraulic fracturing induced by melt injection. Typically, both processes are noted in experimental and natural systems, although the relative importance of each mechanism is variable. Using a simple model for melt flow through a porous media, migration velocities determined here account for full differentiation of Earth-sized bodies within 101–103 Myr, for submicron diameter melt bands, or within a few Myr or micron-sized melt bands. This is consistent with rapid timescales inferred from geochemistry for core formation in planetesimals, implying that percolation may have had an important contribution to core differentiation in the Earth

Investigating local policy drivers for alcohol harm prevention: a comparative case study of two local authorities in England

Background: The considerable challenges associated with implementing national level alcohol policies have encouraged a renewed focus on the prospects for local-level policies in the UK and elsewhere. We adopted a case study approach to identify the major characteristics and drivers of differences in the patterns of local alcohol policies and services in two contrasting local authority (LA) areas in England. Methods: Data were collected via thirteen semi-structured interviews with key informants (including public health, licensing and trading standards) and documentary analysis, including harm reduction strategies and statements of licensing policy. A two-stage thematic analysis was used to categorize all relevant statements into seven over-arching themes, by which document sources were then also analysed. Results: Three of the seven over-arching themes (drink environment, treatment services and barriers and facilitators), provided for the most explanatory detail informing the contrasting policy responses of the two LAs: LA1 pursued a risk-informed strategy via a specialist police team working proactively with problem premises and screening systematically to identify riskier drinking. LA2 adopted a more upstream regulatory approach around restrictions on availability with less emphasis on co-ordinated screening and treatment measures. Conclusion: New powers over alcohol policy for LAs in England can produce markedly different policies for reducing alcohol-related harm. These difference are rooted in economic, opportunistic, organisational and personnel factors particular to the LAs themselves and may lead to closely tailored solutions in some policy areas and poorer co-ordination and attention in others

Organisational barriers to the facilitation of overseas volunteering and training placements in the NHS

Background Undertaking a period of voluntary work or a professional placement overseas has long been a feature of medical training in the UK. There are now a number of high profile National Health Service (NHS) initiatives aimed at increasing access to such opportunities for staff at all levels. We present findings from a qualitative study involving a range of NHS staff and other stakeholders which explored barriers to participation in these activities. Methods A grounded theory methodology was drawn upon to conduct thematic based analysis. Our data included in-depth, semi-structured interviews with a range of returned volunteers, non-volunteers and other stakeholders (n=51) who were, or had been, employed by the NHS. Results There are significant barriers to placement and volunteering activity stemming from structural and organisational shortcomings within the NHS. Difficulties in filling clinical roles has a significant impact on the ability of staff to plan and undertake independent placements. There is currently no clearly defined pathway within the NHS by which the majority of grades can apply for, or organise, a period of overseas voluntary or professional placement activity. There were divergent views on the relevance and usefulness of overseas professional placements. Conclusions We argue that in the context of current UK policy initiatives aimed at facilitating overseas volunteer and professional placement activity, urgent attention needs to be given to the structural and organisational framework within which such initiatives will be required to work

Numerical modelling of liquid metal transport in partially molten H5 ordinary chondrite

An equation-based model of liquid metal segregation in Fe-bearing chondrite meteorites is presented. Textural data from natural samples provide the input conditions. Initial results confirm porous flow of Fe-Ni-S liquid alloy as an important metal segregation mechanism in planetary interiors

Using interactive workshops to prompt knowledge exchange: a realist evaluation of a knowledge to action initiative

Introduction: Interactive workshops are often the default mechanism for sharing knowledge across professional and sector boundaries; yet we understand little about if, and how, they work. Between 2009 and 2011, the Research to Reality programme in North East England ran eight stand-alone facilitated multi-agency workshops focused on priority public health issues. Local authorities, the health service, and academe collaborated on the programme to share latest evidence and best practice. Methods: A realist evaluation asked the overarching question ‘what worked where, for whom, and under what conditions’ regarding the knowledge exchange (KE) mechanisms underpinning any changes. Data were collected from fifty-one interviews, six observations, and analysis of programme documentation. Results: 191 delegates attended (local authority 46%, NHS 24%, academia 22%, third sector 6%, other 2%). The programme theory was that awareness raising and critical discussion would facilitate ownership and evidence uptake. KE activity included: research digests, academic and senior practitioner presentations, and facilitated round-table discussions. Joint action planning was used to prompt informed follow-up action. Participants valued the digests, expert input, opportunities for discussion, networking and ‘space to think’. However, within a few months, sustainability was lost. There was no evidence of direct changes to practice. Multiple barriers to research utilization emerged. Discussion: The findings suggest that in pressured contexts exacerbated by structural reform providing evidence summaries, input from academic and practice experts, conversational spaces and personal action planning are necessary to create enthusiasm on the day, but are insufficient to prompt practice change in the medium term. The findings question makes assumptions about the instrumental, linear use of knowledge and of change focused on individuals as a driver for organizational change. Delegates' views of ‘what would work’ are shared. Mechanisms that would enhance interactive formats are discussed