Magmatic inclusions in the search for natural silicate-salt melt immiscibility: methodology and examples

Immiscible phase separation during the cooling and crystallisation of magmas is an inherently fugitive phenomenon and melt inclusions may provide the only remaining evidence of this process. We detail those features of such inclusions that can both prove the existence of immiscible phase separation, and constrain the compositional signature of the process. To do so requires the combination of traditional methods (petrographic examination, microthermometry, etc.) with state of the art microbeam analytical techniques (laser Raman spectroscopy and proton-induced X-ray emission). Examples of inclusions in phenocrysts from barren and mineralised rocks are provided to illustrate the approach and validate the interpretations

Hydrogen isotope behavior during rhyolite glass hydration under hydrothermal conditions

The diffusion of molecular water (H2Om) from the environment into volcanic glass can hydrate the glass up to several wt% at low temperature over long timescales. During this process, the water imprints its hydrogen isotope composition (δDH2O) to the glass (δDgl) offset by a glass-H2O fractionation factor (ΔDgl-H2O = δDgl – δDH2O) which is approximately -33‰ at Earth surface temperatures. Glasses hydrate much more rapidly at higher, sub-magmatic temperatures as they interact with H2O during eruption, transport, and emplacement. To aid in the interpretation of δDgl in natural samples, we present hydrogen isotope results from vapor hydration experiments conducted at 175–375 oC for durations of hours to months using natural volcanic glasses. The results can be divided into two thermal regimes: above 250 oC and below 250 oC. Lower temperature experiments yield raw ΔDgl-H2O values in the range of -33 ± 11‰. Experiments at 225 oC using both positive and negative initial ΔDgl-H2O values converge on this range of values, suggesting this range represents the approximate equilibrium fractionation for H isotopes between glass and H2O vapor (103lnαgl-H2O) below 250 oC. Variation in ΔDgl-H2O (-33 ± 11‰) between different experiments and glasses may arise from incomplete hydration, analytical uncertainty, differences in glass chemistry, and/or subordinate kinetic isotope effects. Experiments above 250 oC yield unexpectedly low δDgl values with ΔDgl-H2O values of ≤–85‰. While alteration alone is incapable of explaining the data, these run products have more extensive surface alteration and are not interpreted to reflect equilibrium fractionation between glass and H2O vapor. Fourier transform infrared spectroscopy (FTIR) shows that glass can hydrate with as much as 5.9 wt% H2Om and 1.0 wt% hydroxl (OH-) in the highest P-T experiment at 375 oC and 21.1 MPa. Therefore, we employ a 1D isotope diffusion– reaction model of glass hydration to evaluate the roles of equilibrium fractionation, isotope diffusion, water speciation reactions internal to the glass, and changing boundary conditions (e.g. alteration and dissolution). At lower temperatures, the best fitting model results to experimental data for low silica rhyolite (LSR) glasses require only an equilibrium fractionation factor and yield 103lnαgl-H2O values of -33‰± 5‰and -25‰± 5‰at 175 oC and 225 oC, respectively. At higher temperatures, ΔDgl-H2O is dominated by boundary layer effects during glass hydration and glass surface alteration. The modeled bulk δDgl value is highly responsive to changes in the δDgl boundary condition regardless of the magnitude of other kinetic effects. Observed glass dissolution and surficial secondary mineral formation are likely to impose a disequilibrium boundary layer that drives extreme δDgl fractionation with progressive glass hydration. These results indicate that the observed ΔDgl-H2O of ~-33 ± 11‰ can be cautiously applied as an equilibrium 103lnαgl-H2O value to natural silicic glasses hydrated below 250 oC to identify hydration sources. This approximate ΔDgl-H2O may be applicable to even higher temperature glasses hydrated on short timescales (of seconds to minutes) in phreatomagmatic or submarine eruptions before H2O in the glass is primarily affected by boundary layer effects associated with alteration on the glass surface

Measurement of low‐density lipoprotein cholesterol levels in primary and secondary prevention patients: Insights from the PALM registry

Background The 2013 American College of Cardiology/American Heart Association Guideline on the Treatment of Blood Cholesterol to Reduce Atherosclerotic Cardiovascular Risk in Adults recommended testing low-density lipoprotein cholesterol ( LDL -C) to identify untreated patients with LDL -C ≥190 mg/dL, assess lipid-lowering therapy adherence, and consider nonstatin therapy. We sought to determine whether clinician lipid testing practices were consistent with these guidelines. Methods and Results The PALM (Patient and Provider Assessment of Lipid Management) registry enrolled primary and secondary prevention patients from 140 US cardiology, endocrinology, and primary care offices in 2015 and captured demographic data, lipid treatment history, and the highest LDL -C level in the past 2 years. Core laboratory lipid levels were drawn at enrollment. Among 7627 patients, 2787 (36.5%) had no LDL -C levels measured in the 2 years before enrollment. Patients without chart-documented LDL -C levels were more often women, nonwhite, uninsured, and non-college graduates (all P\u3c0.01). Patients without prior lipid testing were less likely to receive statin treatment (72.6% versus 76.0%; P=0.0034), a high-intensity statin (21.5% versus 24.3%; P=0.016), nonstatin lipid-lowering therapy (24.8% versus 27.3%; P=0.037), and had higher core laboratory LDL -C levels at enrollment (median 97 versus 92 mg/dL; P\u3c0.0001) than patients with prior LDL -C testing. Of 166 individuals with core laboratory LDL -C levels ≥190 mg/dL, 36.1% had no LDL -C measurement in the prior 2 years, and 57.2% were not on a statin at the time of enrollment. Conclusions In routine clinical practice, LDL -C testing is associated with higher-intensity lipid-lowering treatment and lower achieved LDL -C level

Mantle to surface degassing of alkalic magmas at Erebus volcano, Antarctica

International audienceContinental intraplate volcanoes, such as Erebus volcano, Antarctica, are associated with extensional tectonics, mantle upwelling and high heat flow. Typically, erupted magmas are alkaline and rich in volatiles (especially CO2), inherited from low degrees of partial melting of mantle sources. We examine the degassing of the magmatic system at Erebus volcano using melt inclusion data and high temporal resolution open-path Fourier transform infrared (FTIR) spectroscopic measurements of gas emissions from the active lava lake. Remarkably different gas signatures are associated with passive and explosive gas emissions, representative of volatile contents and redox conditions that reveal contrasting shallow and deep degassing sources. We show that this unexpected degassing signature provides a unique probe for magma differentiation and transfer of CO2-rich oxidised fluids from the mantle to the surface, and evaluate how these processes operate in time and space. Extensive crystallisation driven by CO2 fluxing is responsible for isobaric fractionation of parental basanite magmas close to their source depth. Magma deeper than 4 kbar equilibrates under vapour-buffered conditions. At shallower depths, CO2-rich fluids accumulate and are then released either via convection-driven, open-system gas loss or as closed-system slugs that ascend and result in Strombolian eruptions in the lava lake. The open-system gases have a reduced state (below the QFM buffer) whereas the closed-system gases preserve their deep oxidised signatures (close to the NNO buffer)

Quantifying gas emissions from the "Millennium Eruption" of Paektu volcano, Democratic Peoples Republic of Korea/China

Paektu volcano (Changbaishan) is a rhyolitic caldera that straddles the border between the Democratic People’s Republic of Korea and China. Its most recent large eruption was the Millennium Eruption (ME; 23 km$^{3}$ dense rock equivalent) circa 946 CE, which resulted in the release of copious magmatic volatiles (H$_{2}$O, CO$_{2}$, sulfur, and halogens). Accurate quantification of volatile yield and composition is critical in assessing volcanogenic climate impacts but is challenging, particularly for events before the satellite era. We use a geochemical technique to quantify volatile composition and upper bounds to yields for the ME by examining trends in incompatible trace and volatile element concentrations in crystal-hosted melt inclusions. We estimate that the ME could have emitted as much as 45 Tg of S to the atmosphere. This is greater than the quantity of S released by the 1815 eruption of Tambora, which contributed to the “year without a summer.” Our maximum gas yield estimates place the ME among the strongest emitters of climate-forcing gases in the Common Era. However, ice cores from Greenland record only a relatively weak sulfate signal attributed to the ME. We suggest that other factors came into play in minimizing the glaciochemical signature. This paradoxical case in which high S emissions do not result in a strong glacial sulfate signal may present a way forward in building more https://symplectic.admin.cam.ac.uk/objectedit.html?cid=1&oid=876954generalized models for interpreting which volcanic eruptions have produced large climate impacts.K.I. was supported by the NSF under award no. 1349486 and by AAAS. Fieldwork was supported by the Richard Lounsbery Foundation

Performance of au transmission photocathode on a microchannel plate detector

X-ray framing cameras, employing microchannel plates ͑MCPs͒ for detection and signal amplification, play a key role in research in high-energy-density physics. These instruments convert radiographic x-rays into electrons produced by plasma during such experiments into electrons that are amplified in the channels and then detected by a phosphor material. The separation of detection from signal amplification offers potential improvements in sensitivity and noise properties. We have implemented a suspended Au transmission photocathode ͑160 Å thick͒ on a MCP and are evaluating it using a 1.5 keV Al K␣ x-ray source. We find an approximately twofold increase in the ratio of detected events to incident photons when the photocathode-to-MCP voltage difference is sufficiently large. Our calculations indicate that this increase is probably caused by a combination of signal produced by the photocathode and an increase in the efficiency of detection of x-rays that reach the MCP surface through modification of the local electric field

Earthquakes, volcanoes, and rectified diffusion

Rectified diffusion is a mechanism by which a strain wave can rapidly pump volatiles into a bubble and therefore increase the pressure in a closed system. The dynamic strain of either distant regional tectonic earthquakes or local volcanic tremor can be translated to static strain inside a magma chamber via this process. We formulate a theory appropriate to the conditions of a magma chamber and calculate the increased pressure using realistic physical parameters. For a basaltic system initially at 130 MPa pressure, the excess pressure from rectified diffusion is between 0.4 and 4 MPa for a regional M≥8 earthquake. The pressure from rectified diffusion is often significantly above the static stress caused by deformation for documented cases of triggered eruptions and thus presents a more viable mechanism for triggering. Prolonged tremor can have a similar effect since the total pressure added increases linearly with the duration of the excitation