An experimental study of carbonated eclogite at 3.5-5.5 GPa – Implications for silicate and carbonate metasomatism in the cratonic mantle

We have experimentally investigated a K-bearing altered mid-ocean ridge basalt (MORB) composition to which 10% CaCO3 was added (GA1+10%cc), at temperatures of 1050-1400oC and pressures of 3•5-5•5 GPa. Experiments were conducted in piston-cylinder apparatus in Pt-Gr (Pt with inner graphite) and Au-Pd capsules. Sub-solidus assemblages for both sets of experiments contain clinopyroxene, garnet, carbonate, rutile, coesite and K-feldspar. Apatite was observed only in the Pt-Gr experiments. Melting behaviour in experiments using different capsule materials contrasted markedly. Experiments in Pt-Gr capsules showed the silicate solidus to be at temperatures less than 1100oC at 3•5GPa and less than 1050oC at 4•5-5•0 GPa.These are similar (3•5GPa) or lower (4•5-5•0 GPa) temperatures compared with the carbonate solidus (1075-1125oC at 3•5-5•0 GPa). Melts in the Pt-Gr runs evolve with increasing degree of melting from K-rich silicate melts at the lowest degree of melting to carbonate-silicate immiscible liquids and silicate-carbonate melts at intermediate degrees of melting, and finally to silicate melts at the highest degrees of melting. Experiments in Au-Pd capsules were performed only at 5•0GPa. The carbonate solidus is between 1200 and 1225oC (at least 100oC higher than in the experiments in Pt-Gr capsules at the same pressure-temperature conditions).The first melts to be produced are carbonatitic and exhibit increasing SiO2 content with increasing temperature.This contrast in melting behaviour is explained by the relatively rapid diffusion of H through the Pt-Gr capsules, resulting in formation of H2O, and thus dramatically depressing both the silicate and the carbonate solidi in the Pt-Gr experiments compared with those in the Au-Pd experiments. This presumably reflects the lower permeability of Au-Pd to H, resulting in a much lower H2O/CO2 ratio in the Au-Pd encapsulated experiments. The presence of water in the melt was demonstrated by Fourier transform infrared (FTIR) spectroscopic analysis of one Pt-Gr experiment, indicating ~0•5wt % H2O in the bulk composition. Further confirmation that H2O plays such a role in the Pt-Gr experiments was provided by an additional experiment performed in a Au-Pd capsule with ~10 wt % H2Ospecifically added. In this experiment immiscible carbonate and silicate melts were observed. Carbonate- silicate liquid immiscibility is considered to occur as a result of the H2O present in the system. These results can be applied to natural systems in several ways. First, the presence of a small amount of either silicate melt or H2O-fluid in the system will act as a ‘flux’, depressing the carbonate solidus to much lower temperatures than inanhydrous systems. Second, the full trend in melt evolution from silicate-rich to carbonate-rich melts, which is also observed in inclusions in diamonds, can be explained by melting of K- and CO2-bearing, water-undersaturated MORB compositions. In cratonic environments low-degree silicate and immiscible silicate and carbonate melts will metasomatize the overlying mantle in different ways, producing, in the first instance, Si enrichment and crystallization of additional orthopyroxene, phlogopite, pyrope-rich garnet and consuming olivine, and, in the second case, carbonate metasomatism, with additional magnesite-dolomite, clinopyroxene and apatite. Both metasomatic styles have been described in natural peridotite xenoliths from the cratonic lithosphere

Recycled gabbro signature in hotspot magmas unveiled by plume–ridge interactions

Lavas erupted within plate interiors above upwelling mantle plumes have chemical signatures that are distinct from midocean ridge lavas. When a plume interacts with a mid-ocean ridge, the compositions of both their lavas changes, but there is no consensus as to how this interaction occurs1–3. For the past 15 Myr, the Pacific–Antarctic mid-ocean ridge has been approaching the Foundation hotspot4 and erupted lavas have formed seamounts. Here we analyse the noble gas isotope and trace element signature of lava samples collected from the seamounts. We find that both intraplate and on-axis lavas have noble gas isotope signatures consistent with the contribution from a primitive plume source. In contrast, nearaxis lavas show no primitive noble gas isotope signatures, but are enriched in strontium and lead, indicative of subducted former oceanic lower crust melting within the plume source5–7. We propose that, in a near-ridge setting, primitive, plumesourced magmas formed deep in the plume are preferentially channelled to and erupted at the ridge-axis. The remaining residue continues to rise and melt, forming the near-axis seamounts. With the deep melts removed, the geochemical signature of subduction contained within the residue becomes apparent. Lavas with strontium and lead enrichments are found worldwide where plumes meet mid-ocean ridges6–8, suggesting that subducted lower crust is an important but previously unrecognised plume component

Reliability of clinical tests to evaluate nerve function and mechanosensitivity of the upper limb peripheral nervous system

BACKGROUND: Clinical tests to assess peripheral nerve disorders can be classified into two categories: tests for afferent/efferent nerve function such as nerve conduction (bedside neurological examination) and tests for increased mechanosensitivity (e.g. upper limb neurodynamic tests (ULNTs) and nerve palpation). Reliability reports of nerve palpation and the interpretation of neurodynamic tests are scarce. This study therefore investigated the intertester reliability of nerve palpation and ULNTs. ULNTs were interpreted based on symptom reproduction and structural differentiation. To put the reliability of these tests in perspective, a comparison with the reliability of clinical tests for nerve function was made. METHODS: Two experienced clinicians examined 31 patients with unilateral arm and/or neck pain. The examination included clinical tests for nerve function (sensory testing, reflexes and manual muscle testing (MMT)) and mechanosensitivity (ULNTs and palpation of the median, radial and ulnar nerve). Kappa statistics were calculated to evaluate intertester reliability. A meta-analysis determined an overall kappa for the domains with multiple kappa values (MMT, ULNT, palpation). We then compared the difference in reliability between the tests of mechanosensitivity and nerve function using a one-sample t-test. RESULTS: We observed moderate to substantial reliability for the tests for afferent/efferent nerve function (sensory testing: kappa = 0.53; MMT: kappa = 0.68; no kappa was calculated for reflexes due to a lack of variation). Tests to investigate mechanosensitivity demonstrated moderate reliability (ULNT: kappa = 0.45; palpation: kappa = 0.59). When compared statistically, there was no difference in reliability for tests for nerve function and mechanosensitivity (p = 0.06). CONCLUSION: This study demonstrates that clinical tests which evaluate increased nerve mechanosensitivity and afferent/efferent nerve function have comparable moderate to substantial reliability. To further investigate the clinometric properties of these tests, more studies are needed to evaluate their validity

Slab melting as a barrier to deep carbon subduction

Interactions between crustal and mantle reservoirs dominate the surface inventory of volatile elements over geological time, moderating atmospheric composition and maintaining a lifesupporting planet1. While volcanoes expel volatile components into surface reservoirs, subduction of oceanic crust is responsible for replenishment of mantle reservoirs2,3. Many natural, ‘superdeep’ diamonds originating in the deep upper mantle and transition zone host mineral inclusions, indicating an affinity to subducted oceanic crust4–7. Here we show that the majority of slab geotherms will intersect a deep depression along the melting curve of carbonated oceanic crust at depths of approximately 300 to 700 kilometres, creating a barrier to direct carbonate recycling into the deep mantle. Low-degree partial melts are alkaline carbonatites that are highly reactive with reduced ambient mantle, producing diamond. Many inclusions in superdeep diamonds are best explained by carbonate melt–peridotite reaction. A deep carbon barrier may dominate the recycling of carbon in the mantle and contribute to chemical and isotopic heterogeneity of the mantle reservoir

A trial assessing N-3 as treatment for injury-induced cachexia (ATLANTIC trial): does a moderate dose fish oil intervention improve outcomes in older adults recovering from hip fracture?

<p>Abstract</p> <p>Background</p> <p>Proximal femoral fractures are associated with increased morbidity and mortality. Pre-existing malnutrition and weight loss amongst this patient group is of primary concern, with conventional nutrition support being largely ineffective. The inflammatory response post proximal femoral fracture surgery and the subsequent risk of cachexia may explain the inability of conventional high energy high protein management to produce an anabolic response amongst these patients. Omega-3 fatty acids derived from fish oils have been extensively studied for their anti-inflammatory benefits. Due to their anti-inflammatory properties, the benefit of fish oil combined with individualized nutrition support amongst proximal femoral fracture patients post surgery is an attractive potential therapeutic strategy. The aim of the ATLANTIC trial is to assess the potential benefits of an anti-inflammatory dose of fish oil within the context of a 12 week individualised nutrition program, commencing seven days post proximal femoral fracture surgery.</p> <p>Methods/Design</p> <p>This randomized controlled, double blinded trial, will recruit 150 community dwelling elderly patients aged ≥65 years, within seven days of surgery for proximal femoral fracture. Participants will be randomly allocated to receive either a 12 week individualized nutrition support program complemented with 20 ml/day anti-inflammatory dose fish oil (~3.6 g eicosapentaenoic acid, ~2.4 g docosahexanoic acid; intervention), or, a 12 week individualized nutrition support program complemented with 20 ml/day low dose fish oil (~0.36 g eicosapentaenoic acid, ~0.24 g docosahexanoic acid; control).</p> <p>Discussion</p> <p>The ATLANTIC trial is the first of its kind to provide fish oil combined with individualized nutrition therapy as an intervention to address the inflammatory response experienced post proximal femoral fracture surgery amongst elderly patients. The final outcomes of this trial will assist clinicians in the development of effective and alternative treatment methods post proximal femoral fracture surgery which may ultimately result in a reduction in systemic inflammation, loss of weight and lean muscle and improvements in nutritional status, mobility, independence and quality of life among elderly patients.</p> <p>Trial Registration</p> <p>ACTRN12609000241235</p

Carbonate–silicate liquid immiscibility in the mantle propels kimberlite magma ascent

Kimberlite is a rare volcanic rock renowned as the major host of diamonds and originated at the base of the subcontinental lithospheric mantle. Although kimberlite magmas are dense in crystals and deeply-derived rock fragments, they ascend to the surface extremely rapidly, enabling diamonds to survive. The unique physical properties of kimberlite magmas depend on the specific compositions of their parental melts that, in absence of historical eruptions and due to pervasive alteration of kimberlite rocks, remain highly debatable. We explain exceptionally rapid ascent of kimberlite magma from mantle depths by combining empirical data on the essentially carbonatite composition of the kimberlite primary melts and experimental evidence on interaction of the carbonate liquids with mantle minerals. Our experimental study shows that orthopyroxene is completely dissolved in a Na2CO3 melt at 2.0–5.0 GPa and 1000–1200 °C. The dissolution of orthopyroxene results in homogeneous silicate–carbonate melt at 5.0 GPa and 1200 °C, and is followed by unmixing of carbonate and carbonated silicate melts and formation of stable magmatic emulsion at lower pressures and temperatures. The dispersed silicate melt has a significant capacity for storing a carbonate component in the deep mantle (13 wt% CO2 at 2.0 GPa). We envisage that this component reaches saturation and is gradually released as CO2 bubbles, as the silicate melt globules are transported upwards through the lithosphere by the carbonatite magma. The globules of unmixed, CO2-rich silicate melt are continuously produced upon further reaction between the natrocarbonatite melt and mantle peridotite. On decompression the dispersed silicate melt phase ensures a continuous supply of CO2 bubbles that decrease density and increase buoyancy and promote rapid ascent of the magmatic emulsion