Magma decompression rates during explosive eruptions of Kīlauea volcano, Hawaii, recorded by melt embayments

NASA Astrophysics Data System (ADS)

Ferguson, David J.; Gonnermann, Helge M.; Ruprecht, Philipp; Plank, Terry; Hauri, Erik H.; Houghton, Bruce F.; Swanson, Donald A.

2016-10-01

The decompression rate of magma as it ascends during volcanic eruptions is an important but poorly constrained parameter that controls many of the processes that influence eruptive behavior. In this study, we quantify decompression rates for basaltic magmas using volatile diffusion in olivine-hosted melt tubes (embayments) for three contrasting eruptions of Kīlauea volcano, Hawaii. Incomplete exsolution of H2O, CO2, and S from the embayment melts during eruptive ascent creates diffusion profiles that can be measured using microanalytical techniques, and then modeled to infer the average decompression rate. We obtain average rates of ~0.05-0.45 MPa s-1 for eruptions ranging from Hawaiian style fountains to basaltic subplinian, with the more intense eruptions having higher rates. The ascent timescales for these magmas vary from around ~5 to ~36 min from depths of ~2 to ~4 km, respectively. Decompression-exsolution models based on the embayment data also allow for an estimate of the mass fraction of pre-existing exsolved volatiles within the magma body. In the eruptions studied, this varies from 0.1 to 3.2 wt% but does not appear to be the key control on eruptive intensity. Our results do not support a direct link between the concentration of pre-eruptive volatiles and eruptive intensity; rather, they suggest that for these eruptions, decompression rates are proportional to independent estimates of mass discharge rate. Although the intensity of eruptions is defined by the discharge rate, based on the currently available dataset of embayment analyses, it does not appear to scale linearly with average decompression rate. This study demonstrates the utility of the embayment method for providing quantitative constraints on magma ascent during explosive basaltic eruptions.

Coupled petrological-geodynamical modeling of a compositionally heterogeneous mantle plume

NASA Astrophysics Data System (ADS)

Rummel, Lisa; Kaus, Boris J. P.; White, Richard W.; Mertz, Dieter F.; Yang, Jianfeng; Baumann, Tobias S.

2018-01-01

Self-consistent geodynamic modeling that includes melting is challenging as the chemistry of the source rocks continuously changes as a result of melt extraction. Here, we describe a new method to study the interaction between physical and chemical processes in an uprising heterogeneous mantle plume by combining a geodynamic code with a thermodynamic modeling approach for magma generation and evolution. We pre-computed hundreds of phase diagrams, each of them for a different chemical system. After melt is extracted, the phase diagram with the closest bulk rock chemistry to the depleted source rock is updated locally. The petrological evolution of rocks is tracked via evolving chemical compositions of source rocks and extracted melts using twelve oxide compositional parameters. As a result, a wide variety of newly generated magmatic rocks can in principle be produced from mantle rocks with different degrees of depletion. The results show that a variable geothermal gradient, the amount of extracted melt and plume excess temperature affect the magma production and chemistry by influencing decompression melting and the depletion of rocks. Decompression melting is facilitated by a shallower lithosphere-asthenosphere boundary and an increase in the amount of extracted magma is induced by a lower critical melt fraction for melt extraction and/or higher plume temperatures. Increasing critical melt fractions activates the extraction of melts triggered by decompression at a later stage and slows down the depletion process from the metasomatized mantle. Melt compositional trends are used to determine melting related processes by focusing on K2O/Na2O ratio as indicator for the rock type that has been molten. Thus, a step-like-profile in K2O/Na2O might be explained by a transition between melting metasomatized and pyrolitic mantle components reproducible through numerical modeling of a heterogeneous asthenospheric mantle source. A potential application of the developed method is shown for the West Eifel volcanic field.

Causes and implications of suppressed vesiculation and crystallization in phenocryst embayments

NASA Astrophysics Data System (ADS)

Cashman, K. V.; Rust, A.

2016-12-01

Recent studies of crystal-hosted melt embayments have modeled water diffusion to estimate rates of magma ascent. Uncertainties in these calculations have been linked primarily to the assumed initial pressure. None of these studies, however, have addressed the conditions under which crystal-hosted clear glass channels form in samples dominated by crystal- and bubble-rich groundmass. Embayments are common in phenocrysts from the 1974 basaltic eruption of Fuego volcano. They are hosted by both plagioclase and olivine phenocrysts where rapid and spatially heterogeneous growth creates a local melt channel. Embayment shapes differ in the two phases, however, depending on the characteristic rapid growth morphologies. Embayment channels are typically 20-50 µm wide and may reach 100-200 µm in length. Interestingly, these length scales are similar to those of melt embayments in plagioclase within the dacitic Mount St. Helens. We suggest that these characteristic length scales are key to embayment preservation as clear glass. We explore two hypotheses: (1) that the space constraints of the embayment inhibit bubble nucleation and growth, or (2) that rapid decompression-driven crystal growth on all sides of the melt channel temporarily increases the melt temperature and water content (and therefore element diffusivity) above ambient. Support for the second hypothesis - that diffusion out of the melt channels is energetically more favorable than nucleation of new bubble and crystal phases - is suggested by observed diffusion profiles of melt components within the embayments. Understanding the origin of melt channels has important implications for diffusion-based studies of magma decompression. First, if the embayments are formed by rapid, syn-eruptive crystal growth, then the effective diffusion length scale must increase with time. Second, if local and temporary heating increase elemental diffusion rates, then characteristic diffusion time scales will be overestimated. By extension, we also note that similar conditions may characterize rapid growth of skeletal and hopper crystals.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Chuanlong; Smith, Jesse S.; Sinogeikin, Stanislav V.

A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. It may also exist as a transient state in solid–solid transitions, as demonstrated in recent studies of colloidal particles and glass-forming metallic systems. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. By thermal heating, a crystalline solid will always melt into a liquid above the melting point. Here we report that a high-pressure crystalline phase of bismuth can melt into a metastable liquid below the melting line through a decompression process. Themore » decompression-induced metastable liquid can be maintained for hours in static conditions, and transform to crystalline phases when external perturbations, such as heating and cooling, are applied. It occurs in the pressure–temperature region similar to where the supercooled liquid Bi is observed. Finally, akin to supercooled liquid, the pressure-induced metastable liquid may be more ubiquitous than we thought.« less

Re-appraisal of the Magma-rich versus Magma-poor Paradigm at Rifted Margins: consequences for breakup processes

NASA Astrophysics Data System (ADS)

Tugend, J.; Gillard, M.; Manatschal, G.; Nirrengarten, M.; Harkin, C. J.; Epin, M. E.; Sauter, D.; Autin, J.; Kusznir, N. J.; McDermott, K.

2017-12-01

Rifted margins are often classified based on their magmatic budget only. Magma-rich margins are commonly considered to have excess decompression melting at lithospheric breakup compared with steady state seafloor spreading while magma-poor margins have suppressed melting. New observations derived from high quality geophysical data sets and drill-hole data have revealed the diversity of rifted margin architecture and variable distribution of magmatism. Recent studies suggest, however, that rifted margins have more complex and polyphase tectono-magmatic evolutions than previously assumed and cannot be characterized based on the observed volume of magma alone. We compare the magmatic budget related to lithospheric breakup along two high-resolution long-offset deep reflection seismic profiles across the SE-Indian (magma-poor) and Uruguayan (magma-rich) rifted margins. Resolving the volume of magmatic additions is difficult. Interpretations are non-unique and several of them appear plausible for each case involving variable magmatic volumes and mechanisms to achieve lithospheric breakup. A supposedly 'magma-poor' rifted margin (SE-India) may show a 'magma-rich' lithospheric breakup whereas a 'magma-rich' rifted margin (Uruguay) does not necessarily show excess magmatism at lithospheric breakup compared with steady-state seafloor spreading. This questions the paradigm that rifted margins can be subdivided in either magma-poor or magma-rich margins. The Uruguayan and other magma-rich rifted margins appear characterized by an early onset of decompression melting relative to crustal breakup. For the converse, where the onset of decompression melting is late compared with the timing of crustal breakup, mantle exhumation can occur (e.g. SE-India). Our work highlights the difficulty in determining a magmatic budget at rifted margins based on seismic reflection data alone, showing the limitations of margin classification based solely on magmatic volumes. The timing of decompression melting onset and melting rates (magmatic processes) relative to crustal thinning (tectonic processes) appear equally, if not more important, than the magmatic budget for unravelling the evolution of rifted margins.

Sulfur isotope fractionation between fluid and andesitic melt: An experimental study

USGS Publications Warehouse

Fiege, Adrian; Holtz, François; Shimizu, Nobumichi; Mandeville, Charles W.; Behrens, Harald; Knipping, Jaayke L.

2014-01-01

Glasses produced from decompression experiments conducted by Fiege et al. (2014a) were used to investigate the fractionation of sulfur isotopes between fluid and andesitic melt upon magma degassing. Starting materials were synthetic glasses with a composition close to a Krakatau dacitic andesite. The glasses contained 4.55–7.95 wt% H2O, ∼140 to 2700 ppm sulfur (S), and 0–1000 ppm chlorine (Cl). The experiments were carried out in internally heated pressure vessels (IHPV) at 1030 °C and oxygen fugacities (fO2) ranging from QFM+0.8 log units up to QFM+4.2 log units (QFM: quartz–fayalite–magnetite buffer). The decompression experiments were conducted by releasing pressure (P) continuously from ∼400 MPa to final P of 150, 100, 70 and 30 MPa. The decompression rate (r) ranged from 0.01 to 0.17 MPa/s. The samples were annealed for 0–72 h (annealing time, tA) at the final P and quenched rapidly from 1030 °C to room temperature (T).The decompression led to the formation of a S-bearing aqueous fluid phase due to the relatively large fluid–melt partitioning coefficients of S. Secondary ion mass spectrometry (SIMS) was used to determine the isotopic composition of the glasses before and after decompression. Mass balance calculations were applied to estimate the gas–melt S isotope fractionation factor αg-m.No detectable effect of r and tA on αg-m was observed. However, SIMS data revealed a remarkable increase of αg-m from ∼0.9985 ± 0.0007 at >QFM+3 to ∼1.0042 ± 0.0042 at ∼QFM+1. Noteworthy, the isotopic fractionation at reducing conditions was about an order of magnitude larger than predicted by previous works. Based on our experimental results and on previous findings for S speciation in fluid and silicate melt a new model predicting the effect of fO2 on αg-m (or Δ34Sg–m) in andesitic systems at 1030 °C is proposed. Our experimental results as well as our modeling are of high importance for the interpretation of S isotope signatures in natural samples (e.g., melt inclusions or volcanic gases).

Melting of the precipitated ice IV in LiCl aqueous solution and polyamorphism of water.

PubMed

Mishima, Osamu

2011-12-08

Melting of the precipitated ice IV in supercooled LiCl-H(2)O solution was studied in the range of 0-0.6 MPa and 160-270 K. Emulsified solution was used to detect this metastable transition. Ice IV was precipitated from the aqueous solution of 2.0 mol % LiCl (or 4.8 mol % LiCl) in each emulsion particle at low-temperature and high-pressure conditions, and the emulsion was decompressed at different temperatures. The melting of ice IV was detected from the temperature change of the emulsified sample during the decompression. There was an apparently sudden change in the slope of the ice IV melting curve (liquidus) in the pressure-temperature diagram. At the high-pressure and high-temperature side of the change, the solute-induced freezing point depression was observed. At the low-pressure and low-temperature side, ice IV transformed into ice Ih on the decompression, and the transition was almost unrelated to the concentration of LiCl. These experimental results were roughly explained by the presumed existence of two kinds of liquid water (low-density liquid water and high-density liquid water), or polyamorphism in water, and by the simple assumption that LiCl dissolved maily in high-density liquid water. © 2011 American Chemical Society

Generation of volcanic ash: a textural study of ash produced in various laboratory experiments

NASA Astrophysics Data System (ADS)

Lavallée, Yan; Kueppers, Ulrich; Dingwell, Donald B.

2010-05-01

In volcanology, ash is commonly understood as a fragment of a bubble wall that gets disrupted during explosive eruptions. Most volcanic ashes are indeed the product of explosive eruptions, but the true definition is however that of a particle size being inferior to 2 mm. The term does not hold any information about its genesis. During fragmentation, particles of all sizes in various amounts are generated. In nature, fragmentation is a brittle response of the material (whether a rock or magma) caused by changes in 1) strain rate and 2) temperature, and/or 3) chemical composition. Here we used different experimental techniques to produce ash and study their physical characteristics. The effects of strain rate were investigated by deforming volcanic rocks and magma (pure silicate melt and crystal-bearing magma) at different temperatures and stresses in a uniaxial compression apparatus. Failure of pure silicate melts is spontaneous and generates more ash particles than fragmentation of crystal-bearing melts. In the latter, the abundance of generated ash correlates positively with the strain rate. We complemented this investigation with a study of particles generated during rapid decompression of porous rocks, using a fragmentation apparatus. Products of decompression experiments at different initial applied pore pressure show that the amount of ash generated by bubble burst increase with the initial applied pressure and the open porosity. The effects of temperature were investigated by dropping pure silicate melts and crystal-bearing magma at 900 and 1100°C in water at room temperature. Quenching of the material is accompanied by rapid contraction and near instantaneous fragmentation. Pure silicate melts respond more violently to the interaction with water and completely fragmented into small particles, including a variety of ash morphologies and surface textures. Crystal-bearing magmas however fragmented only very partially when in contact with water and produced a few ash particles (< 0.05 g). The morphology and surface textures of the experimentally generated ash particles were imaged through scanning electron microscopy, and the observations will be discussed in terms of fragmentation processes.

The ascent of kimberlite: Insights from olivine

NASA Astrophysics Data System (ADS)

Brett, R. C.; Russell, J. K.; Andrews, G. D. M.; Jones, T. J.

2015-08-01

Olivine xenocrysts are ubiquitous in kimberlite deposits worldwide and derive from the disaggregation of mantle-derived peridotitic xenoliths. Here, we provide descriptions of textural features in xenocrystic olivine from kimberlite deposits at the Diavik Diamond Mine, Canada and at Igwisi Hills volcano, Tanzania. We establish a relative sequence of textural events recorded by olivine during magma ascent through the cratonic mantle lithosphere, including: xenolith disaggregation, decompression fracturing expressed as mineral- and fluid-inclusion-rich sealed and healed cracks, grain size and shape modification by chemical dissolution and abrasion, late-stage crystallization of overgrowths on olivine xenocrysts, and lastly, mechanical milling and rounding of the olivine cargo prior to emplacement. Ascent through the lithosphere operates as a "kimberlite factory" wherein progressive upward dyke propagation of the initial carbonatitic melt fractures the overlying mantle to entrain and disaggregate mantle xenoliths. Preferential assimilation of orthopyroxene (Opx) xenocrysts by the silica-undersaturated carbonatitic melt leads to deep-seated exsolution of CO2-rich fluid generating buoyancy and supporting rapid ascent. Concomitant dissolution of olivine produces irregular-shaped relict grains preserved as cores to most kimberlitic olivine. Multiple generations of decompression cracks in olivine provide evidence for a progression in ambient fluid compositions (e.g., from carbonatitic to silicic) during ascent. Numerical modelling predicts tensile failure of xenoliths (disaggregation) and olivine (cracks) over ascent distances of 2-7 km and 15-25 km, respectively, at velocities of 0.1 to >4 m s-1. Efficient assimilation of Opx during ascent results in a silica-enriched, olivine-saturated kimberlitic melt (i.e. SiO2 >20 wt.%) that crystallizes overgrowths on partially digested and abraded olivine xenocrysts. Olivine saturation is constrained to occur at pressures <1 GPa; an absence of decompression cracks within olivine overgrowths suggests depths <25 km. Late stage (<25 km) resurfacing and reshaping of olivine by particle-particle milling is indicative of turbulent flow conditions within a fully fluidized, gas-charged, crystal-rich magma.

Amplification of seismic waves beneath active volcanoes

NASA Astrophysics Data System (ADS)

Navon, O.; Lensky, N. G.; Collier, L.; Neuberg, J.; Lyakhovsky, V.

2003-04-01

Long-period (LP) seismic events are typical of many volcanoes and are attributed to energy leaking from waves traveling through the volcanic conduit or along the conduit - country-rock interface. The LP events are triggered locally, at the volcanic edifice, but the source of energy for the formation of tens of events per day is not clear. Energy may be supplied by volatile-release from a supersaturated melt. If bubbles are present in equilibrium with the melt in the conduit, and the melt is suddenly decompressed, transfer of volatiles from the supersaturated melt into the bubbles transforms stored potential energy into expansion work. For example, small dome collapses may decompress the conduit by a few bars and lead to solubility decrease, exsolution of volatiles and, consequently, to work done by the expansion of the bubbles under pressure. This energy is released over a timescale that is similar to that of LP events and may amplify the original weak seismic signals associated with the collapse. Using the formulation of Lensky et al. (2002), following the decompression, when the transfer of volatiles into bubbles is fast enough, expansion accelerates and the bulk viscosity of the bubbly magma is negative. New calculations show that under such conditions a sinusoidal P-wave is amplified. We note that seismic waves created by tectonic earthquakes that are not associated with net decompression, do not lead to net release of volatiles or to net expansion. In this case, the bulk viscosity is positive and waves traveling through the magma should attenuate. The proposed model explains how weak seismic signals may be amplified as they travel through a conduit that contains supersaturated bubbly magma. It provides the general framework for amplifying volcanic seismicity such as the signals associated with long-period events.

Constraints on Mantle Plume Melting Conditions in the Martian Mantle Based on Improved Melting Phase Relationships of Olivine-Phyric Shergottite Yamato 980459

NASA Technical Reports Server (NTRS)

Kiefer, Walter S.; Rapp, Jennifer F.; Usui, Tomohiro; Draper, David S.; Filiberto, Justin

2016-01-01

Martian meteorite Yamato 980459 (hereafter Y98) is an olivine-phyric shergottite that has been interpreted as closely approximating a martian mantle melt [1-4], making it an important constraint on adiabatic decompression melting models. It has long been recognized that low pressure melting of the Y98 composition occurs at extremely high temperatures relative to martian basalts (1430 degC at 1 bar), which caused great difficulties in a previous attempt to explain Y98 magma generation via a mantle plume model [2]. However, previous studies of the phase diagram were limited to pressures of 2 GPa and less [2, 5], whereas decompression melting in the present-day martian mantle occurs at pressures of 3-7 GPa, with the shallow boundary of the melt production zone occurring just below the base of the thermal lithosphere [6]. Recent experimental work has now extended our knowledge of the Y98 melting phase relationships to 8 GPa. In light of this improved petrological knowledge, we are therefore reassessing the constraints that Y98 imposes on melting conditions in martian mantle plumes. Two recently discovered olivine- phyric shergottites, Northwest Africa (NWA) 5789 and NWA 6234, may also be primary melts from the martian mantle [7, 8]. However, these latter meteorites have not been the subject of detailed experimental petrology studies, so we focus here on Y98.

Measuring the speed of magma ascent during explosive eruptions of Kilauea, Hawaii

NASA Astrophysics Data System (ADS)

Ferguson, D. J.; Ruprecht, P.; Plank, T. A.; Hauri, E. H.; Gonnermann, H. M.; Houghton, B. F.; Swanson, D. A.

2014-12-01

The size and intensity of volcanic eruptions is controlled by a combination of the physical properties of magmas and the conditions of magma ascent. At basaltic volcanoes, where relatively fluid magmas are erupted, sustained explosive eruptions vary widely in style, from Hawaiian fountains erupted 10s to 100s of meter high to large Plinian type events, involving >20 km high eruption plumes. Decompression of magmas leads to volatile saturation and bubble growth, however it remains disputed how the dynamics of shallow ascent and degassing might control this disparate eruptive behaviour, or whether factors such as the initial volatile content exert the primary control on eruption style. A key issue is that the physical conditions of magma ascent, which may significantly impact eruptive dynamics, remain largely unconstrained by observational data. Here we quantify two primary variables - decompression rates and volatile contents - for magmas from three contrasting eruptions of Kīlauea volcano, Hawaii, using microanalysis and modelling of volatile diffusion along small melt tubes or embayments found in olivine crystals carried by the ascending magmas. During ascent decreasing solubility causes dissolved volatiles to diffuse along the embayment towards growing bubbles at the crystal edge. By modelling the diffusion of H2O, CO2 and S we obtain decompression rates, and indirectly ascent velocities, for the rising magma. For Hawaiian style fountaining events we obtain ascent rates of 0.05-0.07 MPa s-1 (~1 m s-1), whereas for a more intense subplinian eruption we obtain a notably faster rate of 0.29 MPa s-1 (>10m s-1). The timescales of melt transport from the storage region during these eruptions varied from around 3 to 40 minutes. We find no link between pre-eruptive volatile contents and eruption intensity, rather our results suggest that the eventual size of sustained explosive basaltic eruptions is likely governed by factors affecting the ascent velocity of melts in the volcanic conduit. The observed decompression rates are consistent with measured discharge rates, and with models predicting greater magma chamber overpressure for larger eruptions. Ascent rates may also further modulate dynamic processes in the volcanic conduit, such as the flow regime and bubble expansion, and consequently eruptive intensity.

Decompression experiments identify kinetic controls on explosive silicic eruptions

USGS Publications Warehouse

Mangan, M.T.; Sisson, T.W.; Hankins, W.B.

2004-01-01

Eruption intensity is largely controlled by decompression-induced release of water-rich gas dissolved in magma. It is not simply the amount of gas that dictates how forcefully magma is propelled upwards during an eruption, but also the rate of degassing, which is partly a function of the supersaturation pressure (??Pcritical) triggering gas bubble nucleation. High temperature and pressure decompression experiments using rhyolite and dacite melt reveal compositionally-dependent differences in the ??Pcritical of degassing that may explain why rhyolites have fueled some of the most explosive eruptions on record.

Water-in-Olivine Magma Ascent Chronometry: Every Crystal is a Clock

NASA Astrophysics Data System (ADS)

Newcombe, M. E.; Asimow, P. D.; Ferriss, E.; Barth, A.; Lloyd, A. S.; Hauri, E.; Plank, T. A.

2017-12-01

The syneruptive decompression rate of basaltic magma in volcanic conduits is thought to be a critical control on eruptive vigor. Recent efforts have constrained decompression rates using models of diffusive water loss from melt embayments (Lloyd et al. 2014; Ferguson et al. 2016), olivine-hosted melt inclusions (Chen et al. 2013; Le Voyer et al. 2014), and clinopyroxene phenocrysts (Lloyd et al. 2016). However, these techniques are difficult to apply because of the rarity of melt embayments and clinopyroxene phenocrysts suitable for analysis and the complexities associated with modeling water loss from melt inclusions. We are developing a new magma ascent chronometer based on syneruptive diffusive water loss from olivine phenocrysts. We have found water zonation in every olivine phenocryst we have measured, from explosive eruptions of Pavlof, Seguam, Fuego, Cerro Negro and Kilauea volcanoes. Phenocrysts were polished to expose a central plane normal to the crystallographic `b' axis and volatile concentration profiles were measured along `a' and `c' axes by SIMS or nanoSIMS. Profiles are compared to 1D and 3D finite-element models of diffusive water loss from olivine, with or without melt inclusions, whose boundaries are in equilibrium with a melt undergoing closed-system degassing. In every case, we observe faster water diffusion along the `a' axis, consistent with the diffusion anisotropy observed by Kohlstedt and Mackwell (1998) for the so-called `proton-polaron' mechanism of H-transport. Water concentration gradients along `a' match the 1D diffusion model with a diffusivity of 10-10 m2/s (see Plank et al., this meeting), olivine-melt partition coefficient of 0.0007­-0.002 (based on melt inclusion-olivine pairs), and decompression rates equal to the best-fit values from melt embayment studies (Lloyd et al. 2014; Ferguson et al. 2016). Agreement between the melt embayment and water-in-olivine ascent chronometers at Fuego, Seguam, and Kilauea Iki demonstrates the potential of this new technique, which can be applied to any olivine-bearing mafic-intermediate eruption using common analytical tools (SIMS and FTIR). In theory, each crystal is a clock, with the potential to record variable ascent in the conduit, over the course of an eruption, and between eruptions.

Pressure Induced Liquid-to-Liquid Transition in Zr-based Supercooled Melts and Pressure Quenched Glasses.

PubMed

Dmowski, W; Gierlotka, S; Wang, Z; Yokoyama, Y; Palosz, B; Egami, T

2017-07-26

Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids, but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.

Influence of starting material on the degassing behavior of trachytic and phonolitic melts

NASA Astrophysics Data System (ADS)

Preuss, Oliver; Marxer, Holger; Nowak, Marcus

2015-04-01

The dynamic magmatic processes beneath volcanic systems, occurring during magma ascent, cannot be observed directly in nature. Simulation of magma ascent in the lab realized by continuous decompression (CD) of a volatile containing melt is essential to understand these processes that may lead to potentially catastrophic eruptions threatening millions of people in highly populated areas like Naples located between the Campi Flegrei Volcanic Field and the Monte Somma-Vesuvio strato-volcano. In this project, experimental simulations of Campanian Ignimbrite (CI) magma ascent will give insight to the mechanisms of the CI super eruption, thus providing tools for volcanic hazard assessment at the high risk Campanian Volcanic District and other comparable volcanic systems. Additionally, comparable experiments with the same conditions using the 'white pumice' composition of the catastrophic Vesuvius AD 79 (VAD79) eruption, have been conducted. So far, the experiments were performed in an internally heated argon pressure vessel coupled with a high-pressure low-flow metering valve and a piezoelectric nano-positioning system using a starting pressure of 200 MPa, H2O content of about 5 wt% and two different decompression rates (0.024 and 0.17 MPa/s) at a superliquidus temperature of 1050 ° C to ensure a crystal free melt and a homogeneous bubble nucleation. Experiments were conducted with both, glass powder and cylinders, subsequently decompressed to 75 and 100 MPa and rapidly quenched. Beside the results that e.g. decompression rate, volatile content, fluid solubility and target pressure affect the degassing behavior of the melt, the influence of the starting material on the degassing processes is significant. Analyses of BSE- and transmitted light microscopy images revealed a different degassing behavior of glass cylinder experiments compared to powders. Nitrogen has a very low solubility in hydrous silicate melts, supporting our suggestion that preexisting nitrogen rich bubbles (from trapped air between the single glass grains) in the melt lead to growth of these preexisting bubbles resulting in near equilibrium degassing where no further nucleation is needed. This results in much higher porosities of the degassed samples compared to those where pure dissolved H2O is present. The same effect was observed by repeating these experiments with a phonolitic VAD79 composition. In ongoing experiments using glass cylinders as starting material, approximately 0.4 wt% chlorine (average Campanian Ignimbrite melt inclusion data [1]) will be added as a volatile component to study the influence on the degassing behavior of hydrous CI melt. [1] Marianelli et al. (2006) Geology 34(11), 937

Mantle Flow and Melting Processes Beneath Back-Arc Basins

NASA Astrophysics Data System (ADS)

Hall, P. S.

2007-12-01

The chemical systematics of back-arc basin basalts suggest that multiple mechanisms of melt generation and transport operate simultaneously beneath the back-arc, resulting in a continuum of melts ranging from a relatively dry, MORB-like end-member to a wet, slab-influenced end-member [e.g., Kelley et al., 2006; Langmuir et al., 2006]. Potential melting processes at work include adiabatic decompression melting akin to that at mid-ocean ridges, diapiric upwelling of hydrous and/or partially molten mantle from above the subducting lithospheric slab [e.g., Marsh, 1979; Hall and Kincaid, 2001; Gerya and Yuen, 2003], and melting of back-arc mantle due to a continuous flux of slab-derived hydrous fluid [Kelley et al., 2006]. In this study, we examine the potential for each of these melting mechanisms to contribute to the observed distribution of melts in back-arc basins within the context of upper mantle flow (driven by plate motions) beneath back-arcs, which ultimately controls temperatures within the melting region. Mantle velocities and temperatures are derived from numerical geodynamic models of subduction with back-arc spreading that explicitly include adiabatic decompression melting through a Lagrangian particle scheme and a parameterization of hydrous melting. Dynamical feedback from the melting process occurs through latent heating and viscosity increases related to dehydration. A range of parameters, including subduction rate and trench-back-arc separation distances, is explored. The thermal evolution of individual diapirs is modeled numerically as they traverse the mantle, from nucleation above the subducting slab to melting beneath the back-arc spreading center, and a range of diapir sizes and densities and considered.

Deep thermal disturbances related to the sub-surface groundwater flow (Western Alps, France)

NASA Astrophysics Data System (ADS)

Mommessin, Grégoire; Dzikowski, Marc; Menard, Gilles; Monin, Nathalie

2013-04-01

In mountain area, the bedrock of the valley side is affected by a thickness of decompressed rock in subsurface (decompressed zone). Groundwater flowing in this zone disrupts the depth geothermal gradients. The evolution of thermal gradients under the decompressed zone depends of groundwater temperature changes into the decompressed zone. In this study, the phenomenon is studied from data acquired in exploration drilling prior to the construction of the France - Italy transalpine tunnel (High Speed Line project between Lyon and Turin). The study area is located in the Vanoise siliceous series between Modane and Avrieux (Western Alps, France). Of 31 boreholes, we selected 14 wells showing a natural thermal disturbance (not due to the drilling) linked to the groundwater flow in decompressed zone. The drill holes have a length between 200 and 1380m and well logs were carried out (gamma log, acoustic log, temperature log, flowmeter log). The rocks are constituted mainly by quartzite with high thermal conductivity or by schist and gneiss with low thermal conductivity. The decompressed zone concerns the quartzite with thicknesses ranging from 50m to 750m where groundwater flow imposes a constant temperature throughout the rock thickness. In the very low permeability rocks under the decompressed zone, the thermal gradient shows variations with depth. These variations suggest a water temperature change in the decompressed zone probably due to a paleoclimate event. We used the derived of the equation describing the propagation of a temperature in a 1D semi-infinite, in response to a sudden temperature disturbance at the boundary of the medium, to estimate the age and the amplitude of temperature change in the decompressed zone. The medium under the decompressed zone is supposed to be initially in a steady state and only conductive. Numerical tests assess that the 1D model is applicable in the slope context. The results obtained from 13 wells data show a few warming degrees (1 to 4°K) of the decompressed zone occurring about two to four centuries BP. The latest high altitude drilling shows about two degrees cooling of the decompressed zone two centuries ago. The groundwater temperature warming can be due to a type of recharge change with a reduction of the snowmelt contribution or it can be provided by an increase of atmospheric and rainfall temperature. The observed cooling in the latest drilling can be interpreted as a groundwater flow change caused by the permafrost melting. The temperature change occurs during the end of Little Ice Age.

Isotopic fractionation of volatile species during bubble growth in magmas

NASA Astrophysics Data System (ADS)

Watson, E. B.

2016-12-01

Bubbles grow in decompressing magmas by simple expansion and also by diffusive supply of volatiles to the bubble/melt interface. The latter phenomenon is of significant geochemical interest because diffusion can fractionate isotopes, raising the possibility that the isotopic character of volatile components in bubbles may not reflect that of volatiles dissolved in the host melt over the lifetime of a bubble—even in the complete absence of equilibrium vapor/melt isotopic fractionation. None of the foregoing is conceptually new, but recent experimental studies have established the existence of isotope mass effects on diffusion in silicate melts for several elements (Li, Mg, Ca, Fe), and this finding has now been extended to the volatile (anionic) element chlorine (Fortin et al. 2016; this meeting). Knowledge of isotope mass effects on diffusion of volatile species opens the way for quantitative models of diffusive fractionation during bubble growth. Significantly different effects are anticipated for "passive" volatiles (e.g., noble gases and Cl) that are partitioned into existing bubbles but play little role in nucleation and growth, as opposed to "active" volatiles whose limited solubilities lead to bubble nucleation during magma decompression. Numerical solution of the appropriate diffusion/mass-conservation equations reveals that the isotope effect on passive volatiles partitioned into bubbles growing at a constant rate in a static system depends (predictably) upon R/D, Kd and D1/D2 (R = growth rate; D = diffusivity; Kd = bubble/melt partition coefficient; D1/D2 = diffusivity ratio of the isotopes of interest). Constant R is unrealistic, but other scenarios can be explored by including the solubility and EOS of an "active" volatile (e.g., CO2) in numerical simulations of bubble growth. For plausible decompression paths, R increases exponentially with time—leading, potentially, to larger isotopic fractionation of species partitioned into the growing bubble.

Pressure Induced Liquid-to-Liquid Transition in Zr-based Supercooled Melts and Pressure Quenched Glasses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dmowski, W.; Gierlotka, S.; Wang, Z.

Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids,more » but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.« less

Timescales associated with the opening phase of large caldera forming eruptions

NASA Astrophysics Data System (ADS)

Myers, M.; Wallace, P. J.; Wilson, C. J. N.

2014-12-01

We present a geochemical application for determining the decompression history prior to caldera formation through analysis of the first-erupted fractions of fall deposits for two voluminous eruptions: the 2.1 Ma Huckleberry Ridge Tuff (HRT; 2500 km3) and the 767 ka Bishop Tuff (BT; 650 km3). The BT is an archetypical example of a continuous explosive eruption, with the whole of the eruption inferred to have lasted ~6 days [1]. In contrast, the fall deposits at the base of the HRT contain evidence for intra-eruption reworking, interpreted as representing eruption breaks on the order of weeks to months [2]. We have analyzed volatiles in melt inclusions (MI) from the first stages of the fall deposits to track initial magma movement and conduit development, as diffusive loss of hydrogen species occurs on timescales ranging from hours to weeks [3]. MI from the initial 3 cm of the HRT deposit show considerable variability in H2O concentrations (4.4-1.3 wt.%) which we attribute to diffusive loss during syn-eruptive decompression. Using a diffusion model [4], the timescales for H2O loss by diffusion from the majority of MIs (T~800 °C) are on the order of 1-6 days, with some values approaching several weeks. However, fitting of diffusion profiles to transects of H2O and CO2 measured along reentrants (unsealed inclusions) provide timescales of final ascent between 1 and 3 hours [3]. These timescales suggest a two-stage depressurization history preceding, and in the earliest stages of, the HRT eruption. MI from the first 4 cm of the BT, however, present a narrower spread in H2O concentrations, from 4.3-5.9 wt.%. If the lower values are the result of diffusive loss, then the decompression timescales required (T~720°C) are as much as 1-2 months, suggesting that some parcels of magma experienced extended decompression before the start of the eruption. Current work incorporating BT reentrants and MIs over the full initial BT stratigraphy will show whether a two-phase decompression model is also necessary. [1] Wilson & Hildreth (1997), J Geol 105, 407. [2] Wilson (2009), AGU Fall Meeting, #V23C-2085. [3] Liu et al. (2007), JGR, 112, B06204. [4] Cottrell et al. (2002), G3, 3, 1-26.

High seismic attenuation at a mid-ocean ridge reveals the distribution of deep melt.

PubMed

Eilon, Zachary C; Abers, Geoffrey A

2017-05-01

At most mid-ocean ridges, a wide region of decompression melting must be reconciled with a narrow neovolcanic zone and the establishment of full oceanic crustal thickness close to the rift axis. Two competing paradigms have been proposed to explain melt focusing: narrow mantle upwelling due to dynamic effects related to in situ melt or wide mantle upwelling with lateral melt transport in inclined channels. Measurements of seismic attenuation provide a tool for identifying and characterizing the presence of melt and thermal heterogeneity in the upper mantle. We use a unique data set of teleseismic body waves recorded on the Cascadia Initiative's Amphibious Array to simultaneously measure seismic attenuation and velocity across an entire oceanic microplate. We observe maximal differential attenuation and the largest delays ([Formula: see text] s and δ T S ~ 2 s) in a narrow zone <50 km from the Juan de Fuca and Gorda ridge axes, with values that are not consistent with laboratory estimates of temperature or water effects. The implied seismic quality factor ( Q s ≤ 25) is among the lowest observed worldwide. Models harnessing experimentally derived anelastic scaling relationships require a 150-km-deep subridge region containing up to 2% in situ melt. The low viscosity and low density associated with this deep, narrow melt column provide the conditions for dynamic mantle upwelling, explaining a suite of geophysical observations at ridges, including electrical conductivity and shear velocity anomalies.

Adiabatic temperature changes of magma-gas mixtures during ascent and eruption

USGS Publications Warehouse

Mastin, L.G.; Ghiorso, M.S.

2001-01-01

Most quantitative studies of flow dynamics in eruptive conduits during volcanic eruptions use a simplified energy equation that ignores either temperature changes, or the thermal effects of gas exsolution. In this paper we assess the effects of those simplifications by analyzing the influence of equilibrium gas exsolution and expansion on final temperatures, velocities, and liquid viscosities of magma-gas mixtures during adiabatic decompression. For a given initial pressure (p1), temperature (T1) and melt composition, the final temperature (Tf) and velocity (Umax) will vary depending on the degree to which friction and other irreversible processes reduce mechanical energy within the conduit. The final conditions range between two thermodynamic end members: (1) Constant enthalpy (dh=0), in which Tf is maximal and no energy goes into lifting or acceleration; and (2) constant entropy (ds=0), in which Tf is minimal and maximum energy goes into lifting and acceleration. For ds=0, T1=900 ??C and p1=200 MPa, a water-saturated albitic melt cools by ???200 ??C during decompression, but only about 250 ??C of this temperature decrease can be attributed to the energy of gas exsolution per se: The remainder results from expansion of gas that has already exsolved. For the same T1 and p1, and dh=0, Tf is 10-15 ??C hotter than T1 but is about 10-25 ??C cooler than Tf in similar calculations that ignore the energy of gas exsolution. For ds=0, p1=200 MPa and T1= 9,000 ??C, assuming that all the enthalpy change of decompression goes into kinetic energy, a water-saturated albitic mixture can theoretically accelerate to ???800 m/s. Similar calculations that ignore gas exsolution (but take into account gas expansion) give velocities about 10-15% higher. For the same T1, p1 = 200 MPa, and ds = 0, the cooling associated with gas expansion and exsolution increases final melt viscosity more than 2.5 orders of magnitude. For dh = 0, isenthalpic heating decreases final melt viscosity by about 0.7 orders of magnitude. Thermal effects of gas exsolution are responsible for less than 10% of these viscosity changes. Isenthalpic heating could significantly reduce flow resistance in eruptive conduits if heat generation were concentrated along conduit walls, where shearing is greatest. Isentropic cooling could enhance clast fragmentation in near-surface vents in cases where extremely rapid pressure drops reduce gas temperatures and chill the margins of expanding pyroclasts.

Partially Melted UHP Eclogite in the Sulu Orogenic Belt, China and its rheological significance to deep continental subduction: Micro- to Macro-scale Evidence

NASA Astrophysics Data System (ADS)

Wang, Lu; Kusky, Timothy; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

2015-04-01

Partially Melted UHP Eclogite in the Sulu Orogenic Belt, China and its rheological significance to deep continental subduction: Micro- to Macro-scale Evidence Numerous studies have described partial melting processes in low-high pressure meta-sedimentary rocks, some of which may generate melts that coalesce to form plutons. However, migmatized ultrahigh pressure (UHP) eclogite has never been clearly described from the microscale to macroscale, though experimental studies prove dehydration partial melting of eclogite at high pressure condition1 and low degrees of partially melted eclogite have been reported from the Qaidam UHP orogenic belt in NW China2,3 or inferred from multiphase solid (MS) inclusions within eclogite4 in the Sulu UHP belt. We present field-based documentation of decompression partial melting of UHP eclogite from Yangkou and General's Hill, Sulu Orogen. Migmatized eclogite shows successive stages of anatexis, initially starting from intragranular and grain boundary melt droplets, which grow into a 3D interconnected intergranular network, then segregate and accumulate in pressure shadow areas, and finally merge to form melt channels and dikes that transport melts to upper lithospheric levels. In-situ phengite breakdown-induced partial melting is directly identified by MS inclusions of Kfs+ barium-bearing Kfs + Pl in garnet, connected by 4-10 μm wide veinlets consisting of Bt + Kfs + Pl next to the phengite. Intergranular veinlets of plagioclase + K-feldspar first form isolated beads of melt along grain boundaries and triple junctions of quartz, and with higher degrees of melting, eventually form interconnected 3D networks along grain boundaries in the leucosome, allowing melt to escape from the intergranular realm and collect in low-stress areas. U-Pb (zircon) dating and petrological analyses on residue and leucocratic rocks shows that partial melting occurred at 228-219 Ma, shortly after peak UHP metamorphism (~230 Ma), and at depths of 30-90 km. Whole-rock trace element analyses show that the leucocratic rocks, residue and peak metamorphic stage eclogite (no decompression partial melting) show well matched mass balance relationships. Melts derived from eclogite partial melting lubricated the subducted eclogite slices and facilitated their buoyant rise from mantle depths to crustal levels. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behavior of subducted lithosphere and its rapid exhumation, controlling flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust. Deeply subducted, partially melted eclogite from General's Hill show that eclogites can develop regularly spaced melt channels, a meter or two thick, that would act as significant seismic anomalies5. This may provide direct evidence for the nature of enigmatic 'bright zones' presented in some deep-crustal seismic reflection profiles which have been interpreted to represent areas of melt, high fluid content or unusual rock compositions6. Hermann, J. & Green, D. H. (2001). Earth Planet. Sci. Lett. 188, 149-168. Song, S.G., et al. (2014). Geochim. Cosmochim. Acta 130 42-62. Zhang, G.B., et al. (2014). Lithos, doi: 10.1016/j.lithos.2014.12.009 Gao, X. Y., et al. (2012). J. Metamorph. Geol. 30, 193-212. Wang, L., et al. (2014). Nature Communications. 5:5604 doi: 10.1038/ncomms6604. Brown, L. et al. (1996). Science 274, 1688-1690.

Paradise Lost: Uncertainties in melting and melt extraction processes beneath oceanic spreading ridges

NASA Astrophysics Data System (ADS)

Kelemen, P. B.

2014-12-01

In many ways, decompression melting and focused melt transport beneath oceanic spreading ridges is the best understood igneous process on Earth. However, there are remaining - increasing - uncertainties in interpreting residual mantle peridotites. Indicators of degree of melting in residual peridotite are questionable. Yb concentration and spinel Cr# are affected by (a) small scale variations in reactive melt transport, (b) variable extents of melt extraction, and (c) "impregnation", i.e. partial crystallization of cooling melt in pore space. Roughly 75% of abyssal peridotites have undergone major element refertilization. Many may have undergone several melting events. The following three statements are inconsistent: (1) Peridotite melt productivity beyond cpx exhaustion is > 0.1%/GPa. (2) Crustal thickness is independent of spreading rate at rates > 2 cm/yr full rate (excluding ultra-slow spreading ridges). (3) Thermal models predict, and observations confirm, thick thermal boundary layers beneath slow spreading ridges. If (a) melt productivity is << 0.1%/GPa beyond cpx-out, and (b) cpx-out occurs > 15 km below the seafloor beneath most ridges, then the independence of crustal thickness with spreading rate can be understood. Most sampled peridotites from ridges melted beyond cpx-out. Cpx in these rocks formed via impregnation and/or exsolution during cooling. Most peridotites beneath ridges may undergo cpx exhaustion during decompression melting. This would entail an upward modification of potential temperature estimates. Alternatively, perhaps oceanic crustal thickness does vary with spreading rate but this is masked by complicated tectonics and serpentinization at slow-spreading ridges. Dissolution channels (dunites) are predicted to coalesce downstream, but numerical models of these have not shown why > 95% of oceanic crust forms in a zone < 5 km wide. There may be permeability barriers guiding deeper melt toward the ridge, but field studies have not identified them. Permeable "shear bands" may guide melt to the ridge, but their nature in open systems at natural grain size and strain rates is uncertain. 2D and 3D focused solid upwelling due to melt buoyancy deep in the melting region, where pyroxenes are abundant and permeability is low, may warrant renewed attention.

Near-isothermal conditions in the middle and lower crust induced by melt migration.

PubMed

Depine, Gabriela V; Andronicos, Christopher L; Phipps-Morgan, Jason

2008-03-06

The thermal structure of the crust strongly influences deformation, metamorphism and plutonism. Models for the geothermal gradient in stable crust predict a steady increase of temperature with depth. This thermal structure, however, is incompatible with observations from high-temperature metamorphic terranes exhumed in orogens. Global compilations of peak conditions in high-temperature metamorphic terranes define relatively narrow ranges of peak temperatures over a wide range in pressure, for both isothermal decompression and isobaric cooling paths. Here we develop simple one-dimensional thermal models that include the effects of melt migration. These models show that long-lived plutonism results in a quasi-steady-state geotherm with a rapid temperature increase in the upper crust and nearly isothermal conditions in the middle and lower crust. The models also predict that the upward advection of heat by melt generates granulite facies metamorphism, and widespread andalusite-sillimanite metamorphism in the upper crust. Once the quasi-steady-state thermal profile is reached, the middle and lower crust are greatly weakened due to high temperatures and anatectic conditions, thus setting the stage for gravitational collapse, exhumation and isothermal decompression after the onset of plutonism. Near-isothermal conditions in the middle and lower crust result from the thermal buffering effect of dehydration melting reactions that, in part, control the shape of the geotherm.

Degassing of basaltic magma: decompression experiments and implications for interpreting the textures of volcanic rocks

NASA Astrophysics Data System (ADS)

Le Gall, Nolwenn; Pichavant, Michel; Cai, Biao; Lee, Peter; Burton, Mike

2017-04-01

Decompression experiments were performed to simulate the ascent of basaltic magma, with the idea of approaching the textural features of volcanic rocks to provide insights into degassing processes. The experiments were conducted in an internally heated pressure vessel between NNO-1.4 and +0.9. H2O-only (4.9 wt%) and H2O-CO2-bearing (0.71-2.45 wt% H2O, 818-1094 ppm CO2) melts, prepared from Stromboli pumice, were synthesized at 1200°C and 200 MPa, continuously decompressed between 200 and 25 MPa at a rate of either 39 or 78 kPa/s (or 1.5 and 3 m/s, respectively), and rapidly quenched. Run products were characterized both texturally (by X-ray computed tomography and scanning electron microscopy) and chemically (by IR spectroscopy and electron microprobe analysis), and then compared with products from basaltic Plinian eruptions and Stromboli paroxysms (bubble textures, glass inclusions). The obtained results demonstrate that textures are controlled by the kinetics of nucleation, growth, coalescence and outgassing of the bubbles, as well as by fragmentation, which largely depend on the presence of CO2 in the melt and the achievement in chemical equilibrium. Textures of the H2O-only melts result from two nucleation events, the first at high pressure (200 < P < 150 MPa) and the second at low pressure (50 < P < 25 MPa), preceding fragmentation. Both events, restricted to narrow P intervals, are driven by melt H2O supersaturation. In contrast, textures of the H2O-CO2-bearing basaltic melts result from continuous bubble nucleation, which is driven by the generation of melts supersaturated in CO2. This persistent non-equilibrium degassing causes the bubbles to evolve through power law distributions, as small bubbles continue to form and grow. This is what is observed in Plinian products. From our results, the evolution to mixed power law-exponential distributions, as found in Stromboli products, is indicative of the prevalence of bubble coalescence and an evolution toward chemical equilibrium. In line with this, a strong correlation was found between experimental and natural bubble textures (bubble number densities, shapes, sizes and distributions), having implications for interpreting bubbles in volcanic rocks and quantifying magma ascent rates. Next step will be to perform in situ decompression experiments to simulate both degassing and crystallization of basaltic magma during ascent in the shallow volcanic conduit (P < 50 MPa), using synchrotron X-ray imaging. The obtained 4D (3D + time) data will help us refine our understanding of magma ascent processes. This experimental programme requires first technology adaptation and development, which is in progress.

Magmatism in Lithosphere Delamination process inferred from numerical models

NASA Astrophysics Data System (ADS)

Göǧüş, Oǧuz H.; Ueda, Kosuke; Gerya, Taras

2017-04-01

The peel away of the oceanic/continental slab from the overlying orogenic crust has been suggested as a ubiquitous process in the Alpine-Mediterranean orogenic region (e.g. Carpathians, Apennines, Betics and Anatolia). The process is defined as lithospheric delamination where a slab removal/peel back may allow for the gradual uprising of sub-lithospheric mantle, resulting in high heat flow, transient surface uplift/subsidence and varying types of magma production. Geodynamical modeling studies have adressed the surface response to the delamination in the context of regional tectonic processes and explored wide range of controlling parameters in pre-syn and post collisional stages. However, the amount and styles of melt production in the mantle (e.g. decompression melting, wet melting in the wedge) and the resulting magmatism due to the lithosphere delamination remains uncertain. In this work, by using thermomechanical numerical experiments, designed in the configuration of subduction to collision, we investigated how melting in the mantle develops in the course of delamination. Furthermore, model results are used to decipher the distribution of volumetric melt production, melt extraction and the source of melt and the style of magmatism (e.g. igneous vs. volcanic). The model results suggest that a broad region of decompression melting occurs under the crust, mixing with the melting of the hydrated mantle derived by the delaminating/subducting slab. Depending on the age of the ocean slab, plate convergence velocity and the mantle temperature, the melt production and crust magmatism may concentrate under the mantle wedge or in the far side of the delamination front (where the subduction begins). The slab break-off usually occurs in the terminal stages of the delamination process and it may effectively control the location of the magmatism in the crust. The model results are reconciled with the temporal and spatial distribution of orogenic vs. anorogenic magmatism in the Mediterranean region in which the latter may have developed due to the delamination process.

The oxidation state of the mantle and the extraction of carbon from Earth's interior.

PubMed

Stagno, Vincenzo; Ojwang, Dickson O; McCammon, Catherine A; Frost, Daniel J

2013-01-03

Determining the oxygen fugacity of Earth's silicate mantle is of prime importance because it affects the speciation and mobility of volatile elements in the interior and has controlled the character of degassing species from the Earth since the planet's formation. Oxygen fugacities recorded by garnet-bearing peridotite xenoliths from Archaean lithosphere are of particular interest, because they provide constraints on the nature of volatile-bearing metasomatic fluids and melts active in the oldest mantle samples, including those in which diamonds are found. Here we report the results of experiments to test garnet oxythermobarometry equilibria under high-pressure conditions relevant to the deepest mantle xenoliths. We present a formulation for the most successful equilibrium and use it to determine an accurate picture of the oxygen fugacity through cratonic lithosphere. The oxygen fugacity of the deepest rocks is found to be at least one order of magnitude more oxidized than previously estimated. At depths where diamonds can form, the oxygen fugacity is not compatible with the stability of either carbonate- or methane-rich liquid but is instead compatible with a metasomatic liquid poor in carbonate and dominated by either water or silicate melt. The equilibrium also indicates that the relative oxygen fugacity of garnet-bearing rocks will increase with decreasing depth during adiabatic decompression. This implies that carbon in the asthenospheric mantle will be hosted as graphite or diamond but will be oxidized to produce carbonate melt through the reduction of Fe(3+) in silicate minerals during upwelling. The depth of carbonate melt formation will depend on the ratio of Fe(3+) to total iron in the bulk rock. This 'redox melting' relationship has important implications for the onset of geophysically detectable incipient melting and for the extraction of carbon dioxide from the mantle through decompressive melting.

The controversy over plumes: Who is actually right?

NASA Astrophysics Data System (ADS)

Puchkov, V. N.

2009-01-01

The current state of the theory of mantle plumes and its relation to classic plate tectonics show that the “plume” line of geodynamic research is in a period of serious crisis. The number of publications criticizing this concept is steadily increasing. The initial suggestions of plumes’ advocates are disputed, and not without grounds. Questions have been raised as to whether all plumes are derived from the mantle-core interface; whether they all have a wide head and a narrow tail; whether they are always accompanied by uplifting of the Earth’s surface; and whether they can be reliably identified by geochemical signatures, e.g., by the helium-isotope ratio. Rather convincing evidence indicates that plumes cannot be regarded as a strictly fixed reference frame for moving lithospheric plates. More generally, the very existence of plumes has become the subject of debate. Alternative ideas contend that all plumes, or hot spots, are directly related to plate-tectonic mechanisms and appear as a result of shallow tectonic stress, subsequent decompression, and melting of the mantle enriched in basaltic material. Attempts have been made to explain the regular variation in age of volcanoes in ocean ridges by the crack propagation mechanism or by drift of melted segregations of enriched mantle in a nearly horizontal asthenospheric flow. In the author’s opinion, the crisis may be overcome by returning to the beginnings of the plume concept and by providing an adequate specification of plume attributes. Only mantle flows with sources situated below the asthenosphere should be referred to as plumes. These flows are not directly related to such plate-tectonic mechanisms as passive rifting and decompression melting in the upper asthenosphere and are marked by time-progressive volcanic chains; their subasthenospheric roots are detected in seismic tomographic images. Such plumes are mostly located at the margins of superswells, regions of attenuation of seismic waves at the mantle-core interface.

Some physical aspects of fluid-fluxed melting

NASA Astrophysics Data System (ADS)

Patiño Douce, A.

2012-04-01

Fluid-fluxed melting is thought to play a crucial role in the origin of many terrestrial magmas. We can visualize the fundamental physics of the process as follows. An infinitesimal amount of fluid infiltrates dry rock at the temperature of its dry solidus. In order to restore equilibrium the temperature must drop, so that enthalpy is released and immediately reabsorbed as enthalpy of melting. The amount of melt produced must be such that the energy balance and thermodynamic equilibrium conditions are simultaneously satisfied. We wish to understand how an initially dry rock melts in response to progressive fluid infiltration, under both batch and fractional melting constraints. The simplest physical model for this process is a binary system in which one of the components makes up a pure solid phase and the other component a pure fluid phase, and in which a binary melt phase exists over certain temperature range. Melting point depression is calculated under the assumption of ideal mixing. The equations of energy balance and thermodynamic equilibrium are solved simultaneously for temperature and melt fraction, using an iterative procedure that allows addition of fluid in infinitesimal increments. Batch melting and fractional melting are simulated by allowing successive melt increments to remain in the system (batch) or not (fractional). Despite their simplified nature, these calculations reveal some important aspects of fluid-fluxed melting. The model confirms that, if the solubility of the fluid in the melt is sufficiently high, fluid fluxed melting is an efficient mechanism of magma generation. One might expect that the temperature of the infiltrating fluid would have a significant effect on melt productivity, but the results of the calculations show this not to be the case, because a relatively small mass of low molecular weight fluid has a strong effect on the melting point of minerals with much higher molecular weights. The calculations reveal the somewhat surprising result that fluid infiltration produces more melt during fractional melting than during batch melting. This behavior, which is opposite to that of decompression melting of a dry solid, arises because the melting point depression effect of the added fluid is greater during fractional melting than during batch melting, which results in a greater release of enthalpy and, therefore, greater melt production for fractional melting than for batch melting, for the same total amount of fluid added. The difference may be considerable. As an example, suppose that 0.1 mols of H2O infiltrate 1 mol or silicate rock. Depending on the rock composition this may corresponds to ˜ 1 wt% H2O. For a given choice of model parameters (initial temperature, heat capacity and entropy of fusion), about 28% of the rock melts during fractional melting, versus some 23 % during batch melting. Fluid fluxing is a robust process of melt generation, without which magmatism at Earth's convergent plate margins would be impossible.

An experimental study of the fluid-melt partitioning of volatiles (H2O, CO2, S) during the degassing of ascending basalt

NASA Astrophysics Data System (ADS)

Le Gall, Nolwenn; Pichavant, Michel; Di Carlo, Ida; Scaillet, Bruno

2017-04-01

We performed decompression experiments to constrain the fluid-melt partitioning of volatiles (H2O, CO2, S) in ascending basalt magmas associated with violent eruptions. Experiments were conducted in an internally heated pressure vessel under oxidizing conditions (fO2: NNO+1.1) so that all sulphur occurs as sulfate (S6+) in the melt. Volatile-bearing (2.72 ± 0.02 wt% H2O, 1291 ± 85 ppm CO2, 1535 ± 369 ppm S) melts, prepared from Stromboli pumice, were synthesized at 1200°C and 200 MPa, decompressed between 150 and 25 MPa at constant rates of 39 and 78 kPa/s (or 1.5 and 3 m/s), and rapidly quenched. Run products were characterized both chemically (by IR spectroscopy and electron microprobe analysis) and texturally (by scanning electron microscopy), and then compared with Stromboli pumice products (glass inclusions, volcanic gases). In H2O-CO2-S-bearing basaltic melts, bubbles start to nucleate heterogeneously on Fe sulfides for supersaturation pressures ΔPHeN ≤ 1 MPa and to nucleate homogeneously for ΔPHoN < 50 MPa (ΔPHeN and ΔPHoN are the difference between the saturation pressure and the pressure at which heterogeneous and homogeneous bubble nucleation are observed, respectively). Bubble growth, coalescence and outgassing occur in addition to continuous bubble nucleation, which is sustained by the preservation of CO2 supersaturated melts during decompression. In addition to model the degassing behaviour of sulphur (and also of CO2 and H2O), our experiments aim to assist in the interpretation of geochemical observables. On the one hand, the volatile degassing trend recorded by Stromboli natural glasses (unsealed glass embayments) was closely experimentally simulated, with a coupled decrease of H2O and S whereas CO2 concentrations remain elevated. On the other hand, the experimental H2O/CO2 and CO2/SO2 fluid molar ratios, calculated by mass balance, both reproduced or closely approached the lower ranges of gas ratios measured at Stromboli for quiescent magma degassing and explosive activity. Compared to models that attribute a deep origin to CO2-rich fluxes and high CO2/SO2 gas ratios, our experimental observations support a model of low pressure (Pf << 25 MPa) explosive degassing of CO2-rich melts generated as a result of disequilibrium degassing to generate Strombolian paroxysms.

Increased mantle heat flow with on-going rifting of the West Antarctic rift system inferred from characterisation of plagioclase peridotite in the shallow Antarctic mantle

NASA Astrophysics Data System (ADS)

Martin, A. P.; Cooper, A. F.; Price, R. C.

2014-03-01

The lithospheric, and shallow asthenospheric, mantle in Southern Victoria Land are known to record anomalously high heat flow but the cause remains imperfectly understood. To address this issue plagioclase peridotite xenoliths have been collected from Cenozoic alkalic igneous rocks at three localities along a 150 km transect across the western shoulder of the West Antarctic rift system in Southern Victoria Land, Antarctica. There is a geochemical, thermal and chronological progression across this section of the rift shoulder from relatively hot, young and thick lithosphere in the west to cooler, older and thinner lithosphere in the east. Overprinting this progression are relatively more recent mantle refertilising events. Melt depletion and refertilisation was relatively limited in the lithospheric mantle to the west but has been more extensive in the east. Thermometry obtained from orthopyroxene in these plagioclase peridotites indicates that those samples most recently affected by refertilising melts have attained the highest temperatures, above those predicted from idealised dynamic rift or Northern Victoria Land geotherms and higher than those prevailing in the equivalent East Antarctic mantle. Anomalously high heat flow can thus be attributed to entrapment of syn-rift melts in the lithosphere, probably since regional magmatism commenced at least 24 Myr ago. The chemistry and mineralogy of shallow plagioclase peridotite mantle can be explained by up to 8% melt extraction and a series of refertilisation events. These include: (a) up to 8% refertilisation by a N-MORB melt; (b) metasomatism involving up to 1% addition of a subduction-related component; and (c) addition of ~ 1.5% average calcio-carbonatite. A high MgO group of clinopyroxenes can be modelled by the addition of up to 1% alkalic melt. Melt extraction and refertilisation mainly occurred in the spinel stability field prior to decompression and uplift. In this region mantle plagioclase originates by a combination of subsolidus recrystallisation during decompression within the plagioclase stability field and refertilisation by basaltic melt.

Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

NASA Astrophysics Data System (ADS)

Lang, Helen M.; Gilotti, Jane A.

2015-06-01

Pseudosection modeling constrains the pressure-temperature (P-T) exhumation path of partially melted ultrahigh-pressure (UHP) metapelites exposed in the North-East Greenland UHP terrane. A robust peak P and T estimate of 3.6 GPa and 970 °C based on mineral assemblages in nearby kyanite eclogites is the starting point for the P-T path. Although the peak assemblage for the metapelite is not preserved, the calculated modeled peak assemblage contained substantial clinopyroxene, garnet, phengite, K-feldspar and coesite with minor kyanite and rutile. Combining the pseudosection and observed textures, the decompression path crosses the coesite-quartz transition before reaching the dry phengite dehydration melting reaction where phengite is abruptly consumed. In the range of 2.5 to 2.2 GPa, clinopyroxene is completely consumed and garnet grows to its maximum volume and grossular content, matching the high grossular rims of relict megacrysts. Plagioclase joins the assemblage and the pseudosection predicts up to 12-13 vol.% melt in the supersolidus assemblage, which contained garnet, liquid, K-feldspar, plagioclase, kyanite, quartz and rutile. At this stage, the steep decompression path flattened out and became nearly isobaric. The melt crystallization assemblage that formed when the path crossed the solidus with decreasing temperature contains phengite, garnet, biotite, 2 feldspars, kyanite, quartz and rutile. Therefore, the path must have intersected the solidus at approximately 1.2 GPa, 825 °C. The pseudosection predicts that garnet is consumed on the cooling path, but little evidence of late garnet consumption or other retrograde effects is observed. This may be due to partial melt loss from the rock. Isochemical PT-n and PT-X sections calculated along the P-T path display changes in mineral assemblage and composition that are consistent with preserved assemblages.

Clinical outcomes of radiotherapy as initial local therapy for Graves' ophthalmopathy and predictors of the need for post-radiotherapy decompressive surgery.

PubMed

Prabhu, Roshan S; Liebman, Lang; Wojno, Ted; Hayek, Brent; Hall, William A; Crocker, Ian

2012-06-19

The optimal initial local treatment for patients with Graves' ophthalmopathy (GO) is not fully characterized. The purpose of this retrospective study is to describe the clinical outcomes of RT as initial local therapy for GO and define predictors of the need for post-RT salvage bony decompressive surgery. 91 patients with active GO and without prior surgery were treated with RT as initial local therapy between 01/1999 and 12/2010, with a median follow-up period of 18.3 months (range 3.7 - 142 months). RT dose was 24 Gy in 12 fractions. 44 patients (48.4%) had prior use of steroids, with 31 (34.1%) being on steroids at the initiation of RT. The most common presenting symptoms were diplopia (79%), proptosis (71%) and soft tissue signs (62%). 84 patients (92.3%) experienced stabilization or improvement of GO symptoms. 58 patients (64%) experienced improvement in their symptoms. 19 patients (20.9%) underwent salvage post-RT bony decompressive surgery. Smoking status and total symptom score at 4 months were independent predictors of post-RT bony decompression with odds ratios of 3.23 (95% CI 1.03 - 10.2) and 1.59 (95% CI 1.06 - 2.4), respectively. Persistent objective vision loss at 4 months post-RT was the most important symptom type in predicting salvage decompression. Chronic dry eye occurred in 9 patients (9.9%) and cataracts developed in 4 patients (4.4%). RT is effective and well tolerated as initial local therapy for active GO, with only 21% of patients requiring decompressive surgery post RT. Most patients experience stabilization or improvement of GO symptoms, but moderate to significant response occurs in the minority of patients. Smoking status and total symptom severity at 4 months, primarily persistent objective vision loss, are the primary determinants of the need for post-RT salvage bony decompression. Patients who smoke or present with predominantly vision loss symptoms should be advised as to their lower likelihood of symptomatic response to RT and their increased likelihood of requiring post-RT decompressive surgery.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dmowski, W.; Gierlotka, S.; Wang, Z.

Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids,more » but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.« less

Submarine and subaerial lavas in the West Antarctic Rift System: Temporal record of shifting magma source components from the lithosphere and asthenosphere

NASA Astrophysics Data System (ADS)

Aviado, Kimberly B.; Rilling-Hall, Sarah; Bryce, Julia G.; Mukasa, Samuel B.

2015-12-01

The petrogenesis of Cenozoic alkaline magmas in the West Antarctic Rift System (WARS) remains controversial, with competing models highlighting the roles of decompression melting due to passive rifting, active plume upwelling in the asthenosphere, and flux melting of a lithospheric mantle metasomatized by subduction. In this study, seamounts sampled in the Terror Rift region of the Ross Sea provide the first geochemical information from submarine lavas in the Ross Embayment in order to evaluate melting models. Together with subaerial samples from Franklin Island, Beaufort Island, and Mt. Melbourne in Northern Victoria Land (NVL), these Ross Sea lavas exhibit ocean island basalt (OIB)-like trace element signatures and isotopic affinities for the C or FOZO mantle endmember. Major-oxide compositions are consistent with the presence of multiple recycled lithologies in the mantle source region(s), including pyroxenite and volatile-rich lithologies such as amphibole-bearing, metasomatized peridotite. We interpret these observations as evidence that ongoing tectonomagmatic activity in the WARS is facilitated by melting of subduction-modified mantle generated during 550-100 Ma subduction along the paleo-Pacific margin of Gondwana. Following ingrowth of radiogenic daughter isotopes in high-µ (U/Pb) domains, Cenozoic extension triggered decompression melting of easily fusible, hydrated metasomes. This multistage magma generation model attempts to reconcile geochemical observations with increasing geophysical evidence that the broad seismic low-velocity anomaly imaged beneath West Antarctica and most of the Southern Ocean may be in part a compositional structure inherited from previous active margin tectonics.

Crustal xenoliths in post-collisional Variscan lamprophyres: records of late Variscan collision and orogenic extension

NASA Astrophysics Data System (ADS)

Soder, Christian; Ludwig, Thomas; Schwarz, Winfried; Trieloff, Mario

2017-04-01

Crustal xenoliths entrained in post-collisional shoshonitic lamprophyres from the Variscan Odenwald (Mid-German Crystalline Zone, MGCZ) include felsic granulites (garnet, quartz, plagioclase, K-feldspar, biotite, omphacite, rutile) and basaltic eclogites (omphacite, garnet, quartz, kyanite, phengite, epidote, rutile). Classical thermobarometry, Zr-in-rutile thermometry and equilibrium phase diagrams reveal temperatures of 700-800°C and pressures of 1.7-1.8 GPa. Both lithologies record isothermal decompression resulting in partial melting at still elevated pressures (1.3-1.5 kbar) before entrainment into the magma. The development of diverse fine-grained microstructures is linked to the interaction with the rising melt. The eclogitic garnet preserves compositional sector zonation patterns, which indicate rapid crystal growth, shortly followed by overgrowth/recrystallization during decompression. The preservation of these zonation patterns indicates crystallization immediately before the lamprophyre magmatism. These findings are supported by SIMS U-Pb dating of zircon rims, which gave ages of 330±3 Ma for both lithologies, indistinguishable from the published age of lamprophyre emplacement. Therefore, the xenoliths are a unique document of the late Variscan collisional process with marked crustal thickening to 60 km and a subsequent decompression event. Magmatic protolith ages are 430 Ma for the basaltic eclogite and 2.1 Ga for the felsic granulite. Silurian magmatism is well established within the MGCZ while the Paleoproterozoic age represents a hitherto unknown magmatic event.

Aluminosilicate melts and glasses at 1 to 3 GPa: Temperature and pressure effects on recovered structural and density changes

USGS Publications Warehouse

Bista, S; Stebbins, Jonathan; Hankins, William B.; Sisson, Thomas W.

2015-01-01

In the pressure range in the Earth’s mantle where many basaltic magmas are generated (1 to 3 GPa) (Stolper et al. 1981), increases in the coordination numbers of the network-forming cations in aluminosilicate melts have generally been considered to be minor, although effects on silicon and particularly on aluminum coordination in non-bridging oxygen-rich glasses from the higher, 5 to 12 GPa range, are now well known. Most high-precision measurements of network cation coordination in such samples have been made by spectroscopy (notably 27Al and 29Si NMR) on glasses quenched from high-temperature, high-pressure melts synthesized in solid-media apparatuses and decompressed to room temperature and 1 bar pressure. There are several effects that could lead to the underestimation of the extent of actual structural (and density) changes in high-pressure/temperature melts from such data. For non-bridging oxygen-rich sodium and calcium aluminosilicate compositions in the 1 to 3 GPa range, we show here that glasses annealed near to their glass transition temperatures systematically record higher recovered increases in aluminum coordination and in density than samples quenched from high-temperature melts. In the piston-cylinder apparatus used, rates of cooling through the glass transition are measured as very similar for both higher and lower initial temperatures, indicating that fictive temperature effects are not the likely explanation of these differences. Instead, transient decreases in melt pressure during thermal quenching, which may be especially large for high initial run temperatures, of as much as 0.5 to 1 GPa, may be responsible. As a result, the equilibrium proportion of high-coordinated Al in this pressure range may be 50 to 90% greater than previously estimated, reaching mean coordination numbers (e.g., 4.5) that are probably high enough to significantly affect melt properties. New data on jadeite (NaAlSi2O6) glass confirm that aluminum coordination increase with pressure is inhibited in compositions low in non-bridging O atoms.

Rifting, Volcanism, and the Geochemical Character of the Mantle Beneath the West Antarctic Rift System (Invited)

NASA Astrophysics Data System (ADS)

Mukasa, S. B.; Aviado, K. B.; Rilling-Hall, S.; Bryce, J. G.; Cabato, J.

2013-12-01

The West Antarctic Rift System (WARS) is one of the largest extensional alkali volcanic provinces on Earth, but the mechanisms responsible for generating the massive amounts of its associated magmatism remain controversial. The failure of both passive and active decompression melting models to adequately explain the observed lava volumes has prompted debate about the relative roles of thermal plume-related melting and ancient subduction-related flux melting. 40Ar/39Ar dating and geochemical analyses of the lavas, as well as volatile and trace-element determinations of olivine-hosted melt inclusions shed light on the relationship between rifting and volcanism, and also improve our understanding of the geochemical character of the mantle beneath the WARS. Results show that the magmatism post-dates the main phase of extension along the Terror Rift within the WARS, which supports a decompression-melting model without the benefit of a significant thermal anomaly. However, the observed large magma volumes seem to require a volatile-fluxed mantle, a notion supported by a long history of subduction (>500 Myr) along the paleo-Pacific margin of Gondwana. In fact, the legacy of that subduction may manifest itself in the high H2O concentrations of olivine-hosted melt inclusions (up to 3 wt% in preliminary results from ion probe measurements). The major oxide compositions of lavas in the WARS are best matched to experimental melts of garnet pyroxenite and carbonated peridotite sources. The Pb and Nd isotopic systems are decoupled from each other, suggesting removal of fluid-mobile elements from the mantle source possibly during the long history of subduction along this Gondwana margin. Extremely unradiogenic 187Os/188Os ranging to as low as 0.1081 × 0.0001 hints at the involvement of lithospheric components in generation of magmas in the WARS.

The crustal structure of the Enderby Basin, East Antarctica

NASA Astrophysics Data System (ADS)

Davis, Joshua K.; Lawver, Lawrence A.; Norton, Ian O.; Dalziel, Ian W. D.; Gahagan, Lisa M.

2018-05-01

The passive margin and ocean crust of the Enderby Basin, East Antarctica preserves a record of the breakup of East Gondwana. Using a suite of public domain geophysical data, we have examined and described the crustal morphology of the basin. Based on our geophysical observations, we divide the Enderby Basin into three distinct morphologic domains. The Eastern Domain demonstrates the most volcanic morphology of the basin, with abundant seaward dipping reflector packages and anomalously thick oceanic crust. These features suggest an early influence by the Kerguelen Hotspot on continental breakup within the domain. The Central Domain is characterized by two regions of oceanic crust of varying morphology segregated by a high amplitude magnetic anomaly. Geophysical observations suggest that the basement directly inboard of this magnetic anomaly is composed of thin, rugged, and poorly structured, proto-oceanic crust, similar in morphology to oceanic crust formed at ultraslow/slow mid-ocean ridged. Outboard of this anomaly, oceanic crust appears to be well-structured and of normal thickness. We offer three, non-exclusive, explanations for the observed change in ocean crustal structure: (1) melt production was initially low at the time of continental breakup, and the progressive decompression of the mantle led to a gradual increase in melt production and ocean crust thickness, (2) melt production was initially low to due lower extension rates and that melt production increased following a change in spreading rate, (3) a change in spreading ridge geometry led to more effective seafloor spreading rate and concurrent increase in melt production. The Western Domain of the Enderby Basin is characterized by abundant fracture zones and anomalously thin oceanic crust. We believe these features arose as a geometric consequence of the originally oblique orientation of continental rifting relative to the extension direction within the domain. Together these observations suggest that the breakup of East Gondwana was highly variable, with notable along-strike differences in crustal deformation and seafloor spreading processes.

Source Evolution After Subduction Initiation as Recorded in the Izu-Bonin-Mariana Fore-arc Crust

NASA Astrophysics Data System (ADS)

Shervais, J. W.; Reagan, M. K.; Pearce, J. A.; Shimizu, K.

2015-12-01

Drilling in the Izu-Bonin-Mariana (IBM) fore-arc during IODP Expedition 352 and DSDP Leg 60 recovered consistent stratigraphic sequences of volcanic rocks reminiscent of those found in many ophiolites. The oldest lavas in these sections are "fore-arc basalts" (FAB) with ~51.5 Ma ages. Boninites began eruption approximately 2-3 m.y. later (Ishizuka et al., 2011, EPSL; Reagan et al., 2013, EPSL) and further from the trench. First results from IODP Expedition 352 and preliminary post-cruise data suggest that FAB at Sites U1440 and U1441 were generated by decompression melting during near-trench sea-floor spreading, and that fluids from the subducting slab were not involved in their genesis. Temperatures appear to have been unusually high and pressures of melting appear to have been unusually low compared to mid-ocean ridges. Spreading rates at this time appear to have been robust enough to maintain a stable melt lens. Incompatible trace element abundances are low in FAB compared to even depleted MORB. Nd and Hf Isotopic compositions published before the expedition suggest that FAB were derived from typical MORB source mantle. Thus, their extreme deletion resulted from unusually high degrees of melting immediately after subduction initiation. The oldest boninites from DSDP Site 458 and IODP Sites U1439 and U1442 have relatively high concentrations of fluid-soluble elements, low concentrations of REE, and light depleted REE patterns. Younger boninites, have even lower REE concentrations, but have U-shaped REE patterns. Our first major and trace element compositions for the FAB through boninite sequence suggests that melting pressures and temperatures decreased through time, mantle became more depleted though time, and spreading rates waned during boninite genesis. Subduction zone fluids involved in boninite genesis appear to have been derived from progressively higher temperatures and pressures over time as the subducting slab thermally matured.

Boninite-like intraplate magmas from Manihiki Plateau require ultra-depleted and enriched source components

PubMed Central

Golowin, Roman; Portnyagin, Maxim; Hoernle, Kaj; Hauff, Folkmar; Gurenko, Andrey; Garbe-Schönberg, Dieter; Werner, Reinhard; Turner, Simon

2017-01-01

The Ontong Java and Manihiki oceanic plateaus are believed to have formed through high-degree melting of a mantle plume head. Boninite-like, low-Ti basement rocks at Manihiki, however, imply a more complex magma genesis compared with Ontong Java basement lavas that can be generated by ∼30% melting of a primitive mantle source. Here we show that the trace element and isotope compositions of low-Ti Manihiki rocks can best be explained by re-melting of an ultra-depleted source (possibly a common mantle component in the Ontong Java and Manihiki plume sources) re-enriched by ≤1% of an ocean-island-basalt-like melt component. Unlike boninites formed via hydrous flux melting of refractory mantle at subduction zones, these boninite-like intraplate rocks formed through adiabatic decompression melting of refractory plume material that has been metasomatized by ocean-island-basalt-like melts. Our results suggest that caution is required before assuming all Archaean boninites were formed in association with subduction processes. PMID:28181497

Enhanced East Pacific Rise hydrothermal activity during the last two glacial terminations

NASA Astrophysics Data System (ADS)

Lund, D. C.; Asimow, P. D.; Farley, K. A.; Rooney, T. O.; Seeley, E.; Jackson, E. W.; Durham, Z. M.

2016-01-01

Mid-ocean ridge magmatism is driven by seafloor spreading and decompression melting of the upper mantle. Melt production is apparently modulated by glacial-interglacial changes in sea level, raising the possibility that magmatic flux acts as a negative feedback on ice-sheet size. The timing of melt variability is poorly constrained, however, precluding a clear link between ridge magmatism and Pleistocene climate transitions. Here we present well-dated sedimentary records from the East Pacific Rise that show evidence of enhanced hydrothermal activity during the last two glacial terminations. We suggest that glacial maxima and lowering of sea level caused anomalous melting in the upper mantle and that the subsequent magmatic anomalies promoted deglaciation through the release of mantle heat and carbon at mid-ocean ridges.

Graphite solubility and co-vesiculation in basalt-like melts at one-ATM

NASA Technical Reports Server (NTRS)

Colson, R. O.

1993-01-01

The identity and source of the vapor phase that caused lunar lava-fountaining and vesiculation in lunar basalts continues to be of interest because of its implications for the composition and state of the lunar interior and because of its implications for lunar resources. In light of the apparent near-absence of H2O on the Moon, it has been suggested that the vapor phase may be CO2-CO. This premise is supported by the presence of carbon on the surface of volcanic glass beads. However, although the rapid exsolution of CO2 from a melt during decompression may be consistent with firefountaining, it fails to provide a satisfying explanation for vesiculation in mare basalt where exsolution of the gas phase would more reasonably be related to cooling/crystallization at low pressure rather than decompression from high pressure. Also, geochemical trends in lunar volcanic glasses suggest that their source has an oxygen fugacity more reducing than the iron-wustite buffer, an oxygen fugacity that is inconsistent with presence of dissolved CO2-CO at depth. The results of experiments in which a vesicular 'basalt' is produced from a melt equilibrated with graphite and pure CO gas at one atmosphere pressure are reported. The vesiculation is apparently related to exsolution of CO or a CO species during cooling of the melt or growth of quench crystals. Additionally, particulate carbon dispersed through the quenched sample suggests that elemental carbon is either in solution in the melt prior to quenching or tends to go into suspension perhaps as colloid-like particles. These two observations may provide insight into the nature of fire-fountaining and vesiculation on the Moon.

Constraints from Water on Mantle Melting and Slab Fluid Composition

NASA Astrophysics Data System (ADS)

Plank, T.; Wade, J.

2005-12-01

Water drives mantle melting and fluid migration in subduction zones, but most models for these phenomena have been developed without constraints from water measurements in arc magmas. For example, the Central American volcanic arc (CAVA) records systematic variations in La/Yb, Ba/La and d18O, and these proxies have been used to predict the extent of mantle melting during decompression [1] and water-addition [2]. Here we use water concentrations in olivine-hosted melt inclusions from arc tephra, along with estimates derived from a clinopyroxene hygrometer [3], to test different models for mantle melting and slab fluid composition along the CAVA (from Nicaragua to Costa Rica). We use Ti as a proxy for mantle melt fraction (F) and invert H2O concentrations in CAVA magmas to obtain those in the mantle source (H2Oo), as in [4]. The relationship between F and H2Oo is nominally linear for Costa Rica mantle, with wet melting productivity dF/dH2O = 30 (wt%/wt%), higher than that used in [2], but consistent with experimentally-determined and MELTS-calculated productivity at 50 degrees above the dry solidus. This predicts mantle temperature beneath Costa Rica of at least 1350°C, and allows for a small (1-2% F) decompression-melting contribution, relative to the wet melting contribution (8-20% F). The percent of wet melting correlates locally with Ba/La, but not regionally, and so the use of Ba/La as a wet melting proxy [1] should be limited to single volcanoes or clusters. The water content of the CAVA melting region varies from 2500-9000 ppm H2O but does not decrease monotonically from Nicaragua to Costa Rica as does Ba/La. The relationship between H2Oo and Ba/La is thus complex, and requires a large along-strike decrease in Ba/La and H2O/La in the slab fluids towards the southeast. Such variation appears to be driven largely by La concentration, reflecting more dilute fluids (higher H2O/La) beneath Nicaragua and more solute-rich fluids (e.g., sediment melts with high La/ H2O) beneath Costa Rica. [1] Walker, J.A., M.J. Carr, L.C. Patino, C.M. Johnson, M.D. Feigenson, R.L. Ward Contrib. Mineral. Petrol. [2] Eiler, J.M., M.J. Carr, M. Reagan, E. Stolper, 2005. Geochem. Geophys. Geosyst. [3] Plank, T., Benjamin, E., Wade, J., Grove, T.L. 2004. Fall Mtg, AGU. [4] Kelley, K., Plank, T., Newman, S., Stolper, E.M., Grove, TL, Hauri, E. 2005. JGR.

Timing of anatexis and melt crystallization in the Socorro-Guaxupé Nappe, SE Brazil: Insights from trace element composition of zircon, monazite and garnet coupled to Usbnd Pb geochronology

NASA Astrophysics Data System (ADS)

Rocha, B. C.; Moraes, R.; Möller, A.; Cioffi, C. R.; Jercinovic, M. J.

2017-04-01

The timing of partial melting and melt crystallization in granulite facies rocks of the Socorro-Guaxupé Nappe (SGN), Brazil is constrained using a combination of imaging techniques, LA-ICP-MS and EPMA dating, trace element geochemistry and thermobarometry. (Orthopyroxene)-garnet-bearing migmatite that records extensive biotite dehydration melting shows evidence for a clockwise P-T-t path. UHT peak conditions were attained at 1030 ± 110 °C, 11.7 ± 1.4 kbar, with post-peak cooling to 865 ± 38 °C, 8.9 ± 0.8 kbar. Cryogenian igneous inheritance of ca. 720-640 Ma is identified in oscillatory zoned zircon cores (n = 167) with steep HREE patterns. Resorbed, Y-rich monazite cores preserve a prograde growth stage at 631 ± 4 Ma prior to the partial melting event, providing an upper age limit for the granulite facies metamorphism in the SGN. REE-rich, Th-depleted monazite related to apatite records the initial stages of decompression at 628 ± 4 Ma. Multiple monazite growth episodes record melt crystallization events at 624 ± 3 Ma, 612 ± 5 Ma and 608 ± 6 Ma. Stubby, equant "soccer ball" zircon provide evidence for melt crystallization at 613 ± 2 Ma and 607 ± 4 Ma. The excess scatter in zircon and monazite age populations between 629 ± 4 and 601 ± 3 Ma is interpreted as discontinuous and episodic growth within this age range, characterizing a prolonged metamorphic event in the SGN lasting ca. 30 m.y. The development of Y + HREE-rich monazite rims at ca. 600 Ma documents retrograde garnet breakdown, extensive biotite growth and the final stages of melt crystallization. Th-rich, Y + HREE-poor monazite rims at ca. 590 Ma record monazite recrystallization.

Experimental Observations of Multiscale Dynamics of Viscous Fluid Behavior: Implications in Volcanic Systems

NASA Astrophysics Data System (ADS)

Arciniega-Ceballos, A.; Spina, L.; Scheu, B.; Dingwell, D. B.

2015-12-01

We have investigated the dynamics of Newtonian fluids with viscosities (10-1000 Pa s; corresponding to mafic to intermediate silicate melts) during slow decompression, in a Plexiglas shock tube. As an analogue fluid we used silicon oil saturated with Argon gas for 72 hours. Slow decompression, dropping from 10 MPa to ambient pressure, acts as the excitation mechanism, initiating several processes with their own distinct timescales. The evolution of this multi-timescale phenomenon generates complex non-stationary microseismic signals, which have been recorded with 7 high-dynamic piezoelectric sensors located along the conduit. Correlation analysis of these time series with the associated high-speed imaging enables characterization of distinct phases of the dynamics of these viscous fluids and the extraction of the time and the frequency characteristics of the individual processes. We have identified fluid-solid elastic interaction, degassing, fluid mass expansion and flow, bubble nucleation, growth, coalescence and collapse, foam building and vertical wagging. All these processes (in fine and coarse scales) are sequentially coupled in time, occur within specific pressure intervals, and exhibit a localized distribution in space. Their coexistence and interactions constitute the stress field and driving forces that determine the dynamics of the system. Our observations point to the great potential of this experimental approach in the understanding of volcanic processes and volcanic seismicity.

Laboratory and numerical decompression experiments: an insight into the nucleation and growth of bubbles

NASA Astrophysics Data System (ADS)

Spina, L.; Colucci, S.; De'Michieli Vitturi, M.; Scheu, B.; Dingwell, D. B.

2014-12-01

Numerical modeling, joined with experimental investigations, is fundamental for studying the dynamics of magmatic fluid into the conduit, where direct observations are unattainable. Furthermore, laboratory experiments can provide invaluable data to vunalidate complex multiphase codes. With the aim on unveil the essence of nucleation process, as well as the behavior of the multiphase magmatic fluid, we performed slow decompression experiments in a shock tube system. We choose silicon oil as analogue for the magmatic melt, and saturated it with Argon at 10 MPa for 72h. The slow decompression to atmospheric conditions was monitored through a high speed camera and pressure sensors, located into the experimental conduit. The experimental conditions of the decompression process have then been reproduced numerically with a compressible multiphase solver based on OpenFOAM. Numerical simulations have been performed by the OpenFOAM compressibleInterFoam solver for 2 compressible, non-isothermal immiscible fluids, using a VOF (volume of fluid) phase-fraction based interface capturing approach. The data extracted from 2D images obtained from laboratory analyses were compared to the outcome of numerical investigation, showing the capability of the model to capture the main processes studied.

Overturn of magma ocean ilmenite cumulate layer: Implications for lunar magmatic evolution and formation of a lunar core

NASA Technical Reports Server (NTRS)

Hess, P. C.; Parmentier, E. M.

1993-01-01

We explore a model for the chemical evolution of the lunar interior that explains the origin and evolution of lunar magmatism and possibly the existence of a lunar core. A magma ocean formed during accretion differentiates into the anorthositic crust and chemically stratified cumulate mantle. The cumulative mantle is gravitationally unstable with dense ilmenite cumulate layers overlying olivine-orthopyroxene cumulates with Fe/Mg that decreases with depth. The dense ilmenite layer sinks to the center of the moon forming the core. The remainder of the gravitationally unstable cumulate pile also overturns. Any remaining primitive lunar mantle rises to its level of neutral buoyancy in the cumulate pile. Perhaps melting of primitive lunar mantle due to this decompression results in early lunar Mg-rich magmatism. Because of its high concentration of incompatible heat producing elements, the ilmenite core heats the overlying orthopyroxene-bearing cumulates. As a conductively thickening thermal boundary layer becomes unstable, the resulting mantle plumes rise, decompress, and partially melt to generate the mare basalts. This model explains both the timing and chemical characteristics of lunar magmatism.

Syn-eruptive CO2 Degassing of Submarine Lavas Flows: Constraints on Eruption Dynamics

NASA Astrophysics Data System (ADS)

Soule, S. A.; Boulahanis, B.; Fundis, A.; Clague, D. A.; Chadwick, B.

2013-12-01

At fast- and intermediate-spreading rate mid-ocean ridges, quenched lava samples are commonly supersaturated in CO2 with concentrations similar to the pressure/depth of shallow crustal melt lenses. This supersaturation is attributed to rapid ascent and decompression rates that exceed the kinetic rates of bubble nucleation and growth. During emplacement, CO2 supersaturated lavas experience nearly isothermal and isobaric conditions over a period of hours. A recent study has demonstrated systematic decreases in CO2 with increasing transport distance (i.e. time) along a single flow pathway within the 2005-06 eruption at the East Pacific Rise (~2500 m.b.s.l.). Based on analysis of vesicle population characteristics and complementary noble gas measurements, it is proposed that diffusion of CO2 into bubbles can be used as a basis to model the gas loss from the melt and thus place constraints on the dynamics of the eruption. We suggest that submarine lava flows represent a natural experiment in degassing that isolates conditions of low to moderate supersaturation and highlights timescales of diffusion and vesiculation processes that are relevant to shallow crustal and conduit processes in subaerial basaltic volcanic systems. Here we report a new suite of volatile concentration analyses and vesicle size distributions from the 2011 eruption of Axial Volcano along the Juan de Fuca Ridge (~1500 m.b.s.l.). The lava flows from this eruption are mapped by differencing of repeat high-resolution bathymetric surveys, so that the geologic context of the samples is known. In addition, in-situ instrument records record the onset of the eruption and place constraints on timing that can be used to verify estimates of eruption dynamics derived from degassing. This sample suite provides a comprehensive view of the variability in volatile concentrations within a submarine eruption and new constraints for evaluating models of degassing and vesiculation. Initial results show systematic variability in CO2 supersaturation along eruptive fissures as well as with increasing distance along flows pathways providing constraints on threshold decompression rates required to nucleate and grow bubbles in a basaltic melt, timescales of degassing in natural systems, and the properties of consequent vesicle populations.

Pathway from subducting slab to surface for melt and fluids beneath Mount Rainier.

PubMed

McGary, R Shane; Evans, Rob L; Wannamaker, Philip E; Elsenbeck, Jimmy; Rondenay, Stéphane

2014-07-17

Convergent margin volcanism originates with partial melting, primarily of the upper mantle, into which the subducting slab descends. Melting of this material can occur in one of two ways. The flow induced in the mantle by the slab can result in upwelling and melting through adiabatic decompression. Alternatively, fluids released from the descending slab through dehydration reactions can migrate into the hot mantle wedge, inducing melting by lowering the solidus temperature. The two mechanisms are not mutually exclusive. In either case, the buoyant melts make their way towards the surface to reside in the crust or to be extruded as lava. Here we use magnetotelluric data collected across the central state of Washington, USA, to image the complete pathway for the fluid-melt phase. By incorporating constraints from a collocated seismic study into the magnetotelluric inversion process, we obtain superior constraints on the fluids and melt in a subduction setting. Specifically, we are able to identify and connect fluid release at or near the top of the slab, migration of fluids into the overlying mantle wedge, melting in the wedge, and transport of the melt/fluid phase to a reservoir in the crust beneath Mt Rainier.

Pathway from subducting slab to surface for melt and fluids beneath Mount Rainier

NASA Astrophysics Data System (ADS)

McGary, R. Shane; Evans, Rob L.; Wannamaker, Philip E.; Elsenbeck, Jimmy; Rondenay, Stéphane

2014-07-01

Convergent margin volcanism originates with partial melting, primarily of the upper mantle, into which the subducting slab descends. Melting of this material can occur in one of two ways. The flow induced in the mantle by the slab can result in upwelling and melting through adiabatic decompression. Alternatively, fluids released from the descending slab through dehydration reactions can migrate into the hot mantle wedge, inducing melting by lowering the solidus temperature. The two mechanisms are not mutually exclusive. In either case, the buoyant melts make their way towards the surface to reside in the crust or to be extruded as lava. Here we use magnetotelluric data collected across the central state of Washington, USA, to image the complete pathway for the fluid-melt phase. By incorporating constraints from a collocated seismic study into the magnetotelluric inversion process, we obtain superior constraints on the fluids and melt in a subduction setting. Specifically, we are able to identify and connect fluid release at or near the top of the slab, migration of fluids into the overlying mantle wedge, melting in the wedge, and transport of the melt/fluid phase to a reservoir in the crust beneath Mt Rainier.

210Pb-226Ra disequilibria in young gas-laden magmas

NASA Astrophysics Data System (ADS)

Reagan, Mark; Turner, Simon; Handley, Heather; Turner, Michael; Beier, Christoph; Caulfield, John; Peate, David

2017-03-01

We present new 238U-230Th-226Ra-210Pb and supporting data for young lavas from southwest Pacific island arcs, Eyjafjallajökull, Iceland, and Terceira, Azores. The arc lavas have significant 238U and 226Ra excesses, whereas those from the ocean islands have moderate 230Th and 226Ra excesses, reflecting mantle melting in the presence of a water-rich fluid in the former and mantle melting by decompression in the latter. Differentiation to erupted compositions in both settings appears to have taken no longer than a few millennia. Variations in the (210Pb/226Ra)0 values in all settings largely result from degassing processes rather than mineral-melt partitioning. Like most other ocean island basalts, the Terceira basalt has a 210Pb deficit, which we attribute to ~8.5 years of steady 222Rn loss to a CO2-rich volatile phase while it traversed the crust. Lavas erupted from water-laden magma systems, including those investigated here, commonly have near equilibrium (210Pb/226Ra)0 values. Maintaining these equilibrium values requires minimal persistent loss or accumulation of 222Rn in a gas phase. We infer that degassing during decompression of water-saturated magmas either causes these magmas to crystallize and stall in reservoirs where they reside under conditions of near stasis, or to quickly rise towards the surface and erupt.

Intracontinental Rifts As Glorious Failures

NASA Astrophysics Data System (ADS)

Burke, K.

2012-12-01

Rifts: "Elongate depressions overlying places where the lithosphere has ruptured in extension" develop in many environments because rocks are weak in extension (Sengor 2nd edn. Springer Encycl. Solid Earth Geophys.). I focus on intra-continental rifts in which the Wilson Cycle failed to develop but in which that failure has led to glory because rocks and structures in those rifts throw exceptional light on how Earth's complex continental evolution can operate: The best studied record of human evolution is in the East African Rift; The Ventersdorp rifts (2.7 Ga) have yielded superb crustal-scale rift seismic reflection records; "Upside-down drainage" (Sleep 1997) has guided supra-plume-head partial melt into older continental rifts leading Deccan basalt of ~66Ma to erupt into a Late Paleozoic (~ 300Ma) rift and the CAMP basalts of ~201 Ma into Ladinian, ~230 Ma, rifts. Nepheline syenites and carbonatites, which are abundant in rifts that overlie sutures in the underlying mantle lithosphere, form by decompression melting of deformed nepheline syenites and carbonatites ornamenting those sutures (Burke et al.2003). Folding, faulting and igneous episodes involving decompression melting in old rifts can relate to collision at a remote plate margin (Guiraud and Bosworth 1997, Dewey and Burke 1974) or to passage of the rift over a plume generation zone (PGZ Burke et al.2008) on the Core Mantle Boundary (e.g.Lake Ellen MI kimberlites at ~206 Ma).

Delayed, disequilibrium degassing in rhyolite magma: Decompression experiments and implications for explosive volcanism

USGS Publications Warehouse

Mangan, M.; Sisson, T.

2000-01-01

Recent numerical models and analog shock tube experiments show that disequilibrium degassing during magma ascent may lead to violent vesiculation very near the surface. In this study a series of decompression experiments using crystal-free, rhyolite melt were conducted to examine the development of large supersaturations due to delayed, homogenous (spontaneous) bubble nucleation. Melts were saturated at 900??C and 200 MPa with either 5.2 wt% dissolved H2O, or with 4.2 wt% H2O and 640 ppm CO2, and isothermally decompressed at linear rates of either 0.003, 0.025, or 8.5 MPa/s to final pressures between 25 and 175 MPa. Additional isobaric saturation experiments (900??C, 200-25 MPa) using pure H2O or mixed H2O-CO2 fluids establish reference equilibrium solubility curves/values. Homogenous nucleation is triggered in both H2O-only and H2O-CO2 experiments once the supersaturation pressure (??Pss) reaches ?? 120-150 MPa and the melt contains ?? two times its equilibrium water contents. Bubble number density and nucleation rate depend on the supersaturation pressure, with values on the order of 102/cm3 and < 1/cm3/s for ??Pss~120 MPa; 106/cm3 and 103-105/cm3/s for ??Pss??~130-150 MPa; and 107/cm3 and 106/cm3/s for ??Pss??160-175 MPa. Nucleation rates are consistent with classical nucleation theory, and infer an activation energy for nucleation of 1.5 x 10-18 J/nucleus, a critical bubble radius of 2 x 10-9 m, and an effective surface tension for rhyolite at 5.2 wt% H2O and 900??C of 0.10-0.11 N/m. The long nucleation delay limits the time available for subsequent diffusion such that disequilibrium dissolved H2O and CO2 contents persist to the end of our runs. The disequilibrium degassing paths inferred from our experiments contrast markedly with the equilibrium or quasi-equilibrium paths found in other studies where bubble nucleation occurs heterogenously on crystals or other discontinuities in the melt at low ??Pss. Homogenous and heterogenous nucleation rates are comparable, however, as are bubble number densities, so that at a given decompression rate it appears that nucleation mechanism, rather than nucleation rate, determines degassing efficiency by fixing the pressure (depth) at which vesiculation commences and hence the time available for equilibration prior to eruption. Although real systems are probably never truly crystal-free, our results show that rhyolitic magmas containing up to 104 crystals/cm3, and perhaps as high as 106 crystals/cm3, are controlled by homogenous, rather than heterogenous, nucleation during ascent. ?? 2000 Elsevier Science B.V. All rights reserved.

Crystallisation regimes and kinetics in experimentally decompressed dacitic magma

NASA Astrophysics Data System (ADS)

Blum-Oeste, N.; Schmidt, B. C.; Webb, S. L.

2011-12-01

Kinetic processes during magma ascent may have a strong influence on the eruption style. In water bearing dacitic magmas decompression induced exsolution of water and accompanying crystallisation of plagioclase are the main processes which drive the system towards a new equilibrium state. We present new data on the evolution of residual glass composition and crystal size distributions of plagioclase from decompression experiments. Experiments have been conducted in cold seal pressure vessels at 850°C on a natural dacite composition from Taapaca volcano (N. Chile). After an initial equilibration at 2kbar decompression rates between 6.3 and 450bar/h were applied to final pressures between 50 and 1550bar where samples were rapidly quenched. Complementary equilibrium experiments were done at corresponding pressures. The glass composition evolves from the initial state towards the equilibrium at the final pressure. The completeness of this re-equilibration depends on run duration and reaction rates. We introduce the "re-equilibration index" (REI), a fraction between 0 (initial state) and 1 (final state) which allows comparison of chemical components in terms of re-equilibration at different decompression rates. REI divided by the decompression duration gives the "re-equilibration rate" (RER). The REI varies among oxides and it decreases with increasing decompression rate. The highest REIs of ~0.9 have been found for MgO, K2O and Al2O3 at 6.3bar/h whereas Na2O shows the lowest number with 0.25 at this decompression rate. Towards faster decompression all REIs tend to decrease which shows a decreasing completeness of re-equilibration. At 450bar/h the highest REIs are ~0.25. RERs increase from below ~0.005/h at 6.3bar/h up to almost 0.08/h for Al2O3 at 450bar/h. The variability of RERs of different oxides also increases with decompression rates. At 450bar/h the RERs reach from <0.005/h up to 0.08/h. Although RERs strongly increase from low to high decompression rates, this does not compensate for the decreasing duration available for re-equilibration as REIs clearly show. The volume fraction of plagioclase decreases from ~21% at 6.3bar/h to ~16% at 450bar/h which fits the decrease in REIs. The population density of small crystals decreases whereas the population density of larger crystals increases from slow to fast decompression. This reflects a transition from nucleation controlled crystallisation at slow decompression to a growth dominated regime at fast decompression. As RERs show re-equilibration is faster in the growth dominated regime. Although this transition in nucleation processes might be counter-intuitive it can be explained by the observation of slightly higher water concentrations at fast decompression rates resulting in higher liquidus temperatures and thus lower undercooling.

Silica-enriched mantle sources of subalkaline picrite-boninite-andesite island arc magmas

NASA Astrophysics Data System (ADS)

Bénard, A.; Arculus, R. J.; Nebel, O.; Ionov, D. A.; McAlpine, S. R. B.

2017-02-01

Primary arc melts may form through fluxed or adiabatic decompression melting in the mantle wedge, or via a combination of both processes. Major limitations to our understanding of the formation of primary arc melts stem from the fact that most arc lavas are aggregated blends of individual magma batches, further modified by differentiation processes in the sub-arc mantle lithosphere and overlying crust. Primary melt generation is thus masked by these types of second-stage processes. Magma-hosted peridotites sampled as xenoliths in subduction zone magmas are possible remnants of sub-arc mantle and magma generation processes, but are rarely sampled in active arcs. Published studies have emphasised the predominantly harzburgitic lithologies with particularly high modal orthopyroxene in these xenoliths; the former characteristic reflects the refractory nature of these materials consequent to extensive melt depletion of a lherzolitic protolith whereas the latter feature requires additional explanation. Here we present major and minor element data for pristine, mantle-derived, lava-hosted spinel-bearing harzburgite and dunite xenoliths and associated primitive melts from the active Kamchatka and Bismarck arcs. We show that these peridotite suites, and other mantle xenoliths sampled in circum-Pacific arcs, are a distinctive peridotite type not found in other tectonic settings, and are melting residues from hydrous melting of silica-enriched mantle sources. We explore the ability of experimental studies allied with mantle melting parameterisations (pMELTS, Petrolog3) to reproduce the compositions of these arc peridotites, and present a protolith ('hybrid mantle wedge') composition that satisfies the available constraints. The composition of peridotite xenoliths recovered from erupted arc magmas plausibly requires their formation initially via interaction of slab-derived components with refractory mantle prior to or during the formation of primary arc melts. The liquid compositions extracted from these hybrid sources are higher in normative quartz and hypersthene (i.e., they have a more silica-saturated character) in comparison with basalts derived from prior melt-depleted asthenospheric mantle beneath ridges. These primary arc melts range from silica-rich picrite to boninite and high-Mg basaltic andesite along a residual spinel harzburgite cotectic. Silica enrichment in the mantle sources of arc-related, subalkaline picrite-boninite-andesite suites coupled with the amount of water and depth of melting, are important for the formation of medium-Fe ('calc-alkaline') andesite-dacite-rhyolite suites, key lithologies forming the continental crust.

Kinetic D/H fractionation during hydration and dehydration of silicate glasses, melts and nominally anhydrous minerals

NASA Astrophysics Data System (ADS)

Roskosz, M.; Deloule, E.; Ingrin, J.; Depecker, C.; Laporte, D.; Merkel, S.; Remusat, L.; Leroux, H.

2018-07-01

The distribution of hydrogen isotopes during diffusion-driven aqueous processes in silicate glasses, melts and crystals was investigated. Hydration/dehydration experiments were performed on silica glasses at 1000 °C and 1 bar total pressure. Dehydration triggered by decompression-driven bubble nucleation and growth was performed on rhyolitic melts at 800 °C and a few hundred MPa. Hydrogen extraction from a nominally anhydrous mineral (grossular) single crystal was carried out at 800 °C and ambient pressure. After these three series of experiments, pronounced water (sensu lato) concentration profiles were observed in all recovered samples. In the grossular single-crystal, a large spatial variation in H isotopes (δD variation > 550‰) was measured across the sample. This isotopic distribution correlates with the hydrogen extraction profile. The fit to the data suggests an extreme decoupling between hydrogen and deuterium diffusion coefficients (DH and DD respectively), akin to the decoupling expected in a dilute ideal gas (DH/DD ≈ 1.41). Conversely, no measurable spatially- and time-resolved isotopic variations were measured in silicate glasses and melts. This contrasted behavior of hydrogen isotopes likely stands in the different water speciation and solution mechanisms in the three different materials. Glasses and melts contain essentially hydroxyl and molecular water groups but the mobile species is molecular water in both cases. Protonated defects make up most of the water accommodated in grossular and other nominally anhydrous minerals (NAM). These defects are also the mobile species that diffuse against polarons. These results are crucial to accurately model the degassing behavior of terrestrial and lunar magmas and to derive the initial D/H of water trapped in fluid inclusions commonly analyzed in mantle NAMs, which suffered complex geological histories.

Reduction rate by decompression as a treatment of odontogenic cysts.

PubMed

Oliveros-Lopez, L; Fernandez-Olavarria, A; Torres-Lagares, D; Serrera-Figallo, M-A; Castillo-Oyagüe, R; Segura-Egea, J-J; Gutierrez-Perez, J-L

2017-09-01

Odontogenic cysts are defined as those cysts that arise from odontogenic epithelium and occur in the tooth-bearing regions of the jaws. Cystectomy, marsupialization or decompression of odontogenic cyst are treatment approach to this pathology. The aim of this study was to evaluate the effectiveness of the decompression as the primary treatment of the cystic lesions of the jaws and them reduction rates involving different factors. 23 patients with odontogenic cysts of the jaws, previously diagnosed by anatomical histopathology (follicular cysts (7) and radicular cysts (16)) underwent decompression as an initial treatment. Clinical examination and pre and post panoramic radiograph were measured and analyzed. In addition, data as gender, age, time reduction and location of the lesion were collected. Significant results were obtained in relation to the location of lesions and the reduction rate (p<0.01). In a higher initial lesion, a greater reduction rate was observed (p<0.05). Decompression as an initial treatment of cystic lesions of the jaws was effective; it reduces the size of the lesions avoiding a possible damage to adjacent structures. Cystic lesions in the mandible, regardless of the area where they occur will have a higher reduction rate if it is compared with the maxilla. Similar behavior was identified in large lesions compared to smaller.

Chemistry of Tertiary sediments in the surroundings of the Ries impact structure and moldavite formation revisited

NASA Astrophysics Data System (ADS)

Žák, Karel; Skála, Roman; Řanda, Zdeněk; Mizera, Jiří; Heissig, Kurt; Ackerman, Lukáš; Ďurišová, Jana; Jonášová, Šárka; Kameník, Jan; Magna, Tomáš

2016-04-01

Moldavites, tektites of the Central European strewn field, have been traditionally linked with the Ries impact structure in Germany. They are supposed to be derived mainly from the near-surface sediments of the Upper Freshwater Molasse of Miocene age that probably covered the target area before the impact. Comparison of the chemical composition of moldavites with that of inferred source materials requires recalculation of the composition of sediments to their water-, organic carbon- and carbon dioxide-free residuum. This recalculation reflects the fact that these compounds were lost almost completely from the target materials during their transformation to moldavites. Strong depletions in concentrations of many elements in moldavites relative to the source sediments (e.g., Mo, Cu, Ag, Sb, As, Fe) contrast with enrichments of several elements in moldavites (e.g., Cs, Ba, K, Rb). These discrepancies can be generally solved using two different approaches, either by involvement of a component of specific chemical composition, or by considering elemental fractionation during tektite formation. The proposed conceptual model of moldavite formation combines both approaches and is based on several steps: (i) the parent mixture (Upper Freshwater Molasse sediments as the dominant source) contained also a minor admixture of organic matter and soils; (ii) the most energetic part of the ejected matter was converted to vapor (plasma) and another part produced melt directly upon decompression; (iii) following further adiabatic decompression, the expanding vapor phase disintegrated the melt into small melt droplets and some elements were partially lost from the melt because of their volatility, or because of the volatility of their compounds, such as carbonyls of Fe and other transition metals (e.g., Ni, Co, Mo, Cr, and Cu); (iv) large positively charged ions such as Cs+, Ba2+, K+, Rb+ from the plasma portion were enriched in the late-stage condensation spherules or condensed directly onto negatively charged melt droplets; (v) simultaneously, the melt droplets coalesced into larger tektite bodies. Steps (iii)-(v) may have overlapped in time. The still melted moldavite bodies reaching their final size were reshaped by further melt flow. This melt flow was related to moldavite rotation and escape (bubbling off) of the last portion of gaseous volatiles during their flight in a low-pressure region above the dense layer of the atmosphere.

Mediterranean Magmatism: Bimodal Melting Patterns Inferred By Numerical Models

NASA Astrophysics Data System (ADS)

Gogus, O.; Ueda, K.; Gerya, T.

2017-12-01

Melt production by the decompression melting of the asthenospheric mantle occurs in the course of the lithospheric foundering process. The magmatic imprints of such foundering process are often described as anorogenic magmatism and this is usually followed by the orogenic magmatism, related to the subduction events in the Mediterranean region. Here, by using numerical geodynamic experiments we explore various styles of magmatism, their interaction with each other and the amount of magma production in the ocean subduction to slab peel away/delamination configuration. Model results show that the early stage of the ocean subduction under the continental lithosphere is associated with the short pulse of wet melting-orogenic magmatism and then the melting process is mostly dominated by dry melting-anorogenic magmatism, until the slab break-off occurs. While the melt types mixes/alternates during the evolution of the model, the wet melting facilitates the production of dry melting because of its uprising and emplacement under the crust where dry melting is present. The melt production pattern and the amount does not change significantly with different depths of the slab break-off (160-200 km). Model results can explain the transition from the calc-alkaline to alkaline volcanism in the western Mediterranean (Alboran domain) where ocean subduction to delamination has been interpreted.

The Fate of Sulfur during Decompression Melting of Peridotite and Crystallization of Basalts - Implications for Sulfur Geochemistry of MORB and the Earth's Upper Mantle

NASA Astrophysics Data System (ADS)

Ding, S.; Dasgupta, R.

2014-12-01

Magmatism in mid-ocean ridges is the main pathway of sulfur (S) from the Earth's mantle to the surficial reservoir. MORB is generally considered sulfide saturated due to the positive correlation between S and FeOT concentration (e.g., [1]). However, most MORBs are differentiated, and both S content and sulfur concentration at sulfide saturation (SCSS) change with P, T, and magma composition (e.g., [2]). Therefore, it remains uncertain, from the MORB chemistry alone, whether mantle melts parental to MORB are sulfide saturated. In this study, we modeled the behavior of S during isentropic partial melting of a fertile peridotite using pMELTS [3] and an SCSS parameterization [4]. Our results show that during decompression melting, at a fixed mantle potential temperature, TP (e.g., 1300 °C), SCSS of aggregate melt first slightly increases then decreases at shallower depth with total variation <200 ppm. However, an increase of TP results in a significant increase of SCSS of primitive melts. Our model shows that at 15% melting (F), sulfide in the residue is exhausted for a mantle with <200 ppm S. The resulted sulfide-undersaturated partial melts contain <1000 ppm S and are 4-6 times enriched in Cu compared to the source. In order to compare our modeled results directly to the differentiated basalts, isobaric crystallization calculation was performed on 5, 10, and 15% aggregate melts. SCSS changes along liquid line of descent with a decrease in T and increase in FeOT. Comparison of S contents between the model results and MORB glasses [5] reveals that many MORBs derive from sulfide undersaturated melts. Further, for a TP of 1300-1350 °C and F of 10-15 wt.%, reproduction of self-consistent S, and Cu budget of many MORB glasses requires that S of their mantle source be ~25-200 ppm. We will discuss the interplay of TP, average F, and the conditions of differentiation to bracket the S geochemistry of MORB and MORB source mantle and develop similar systematics for OIBs and OIB source. References: [1] Le Roux et al. (2006) EPSL, 251, 209-231. [2] Baker and Moritti (2011) Rev. in Mineral. Geochem, 73, 167-213. [3] Ghiorso et al. (2002) Geochem. Geophy. Geosy. 3, 5. [4] Li and Ripley (2009) Econ. Geol. 104, 405-412. [5] Jenner and O'Neill (2012) Geochem. Geophy. Geosy. 13, 1.

Melting mode and source lithology inferred from trace element systematic in historical olivine from Lanzarote, Canary Islands

NASA Astrophysics Data System (ADS)

Gómez-Ulla, Alejandra; Sigmarsson, Olgeir; Guðfinnsson, Guðmundur H.

2017-04-01

Trace element concentrations and ratios in olivine phenocrysts, such as fractionation-corrected Ni x (FeO/MgO) and Fe/Mn, have been shown useful as probes of pyroxenite derived component in mixtures of primary mantle melts (e.g. Sobolev et al., 2007). For instance, higher Ni and lower Mn and Ca contents are expected in partial melts of pyroxenite compared to those of lherzolite. We have measured trace element concentrations in olivine from 1730-1736 AD (Timanfaya) and 1824 AD eruptions in Lanzarote (Canary Islands), which erupted mafic and mantle nodule bearing magmas, ranging in composition from highly silica-undersaturated basanite through alkali basalt to tholeiite. The early basanite exhibit the largest olivine trace element variation covering the range of those from MORB and OIB worldwide, whereas later erupted tholeiite have values typical from pyroxenite derived melts. The Fo value decreased systematically with time during the 1730-36 eruption and the proportion of silica-saturated primary melt increased in the parental magma mixture with time. At the end of the eruption, tholeiite magmas crystallized olivine with, increasing concentrations of Mn and Ca and higher Ca/Al at relatively uniform Ni x (FeO/MgO) and Fe/Mn, all of which is readily explained by increased decompression melting at lower temperature. The basanite from the eruption that took place in 1824 AD has olivine with even higher Fo value and trace element variability similar those of the Timanfaya basanite. The fact that the Lanzarote basanite contain olivine with trace element systematic spanning that of MORB and pyroxenite melt can be explained by CO2-flux melting of a lithologically heterogeneous source, generating the diverse compositions. Initial reactive porous flow through depleted oceanic lithosphere and equilibration with dunitic restite of percolating pyroxenite melt may have amplified the observed Ni depletion in olivine of the earliest basanite. The fact that olivine compositions and basanite magma were reproduced approximately a century later may reflect episodic carbonatic fluxing in the slowly uprising Canarian mantle plume.

Vitreous Anorthite (CaAl2Si2O8) at High Pressure: A First-Principles Molecular Dynamics Study

NASA Astrophysics Data System (ADS)

Ghosh, D. B.; Karki, B. B.

2017-12-01

Due to the high abundance of silicates and aluminosilicates inside the earth, their corresponding melts are likely to be one of the key transport agents in the chemical and thermal evolution of our planet and therefore, have long been the subject of investigations. Experimentally, in-situ melt properties of these materials, particularly at high pressure-temperature conditions are extremely difficult to constrain and the corresponding glass phases are considered as analogs. This, however, prohibits one-to-one comparison between the properties of silicate melt and its corresponding glass. With the aim to enable such comparison, we investigate the equation of state and structural properties of CaAl2Si2O8 glass at 300 K as a function of pressure up to 160 GPa from first principles molecular dynamics simulation results. Our results show that at ambient pressure: (i) Si's remain mostly (> 95%) under tetrahedral oxygen surroundings, (ii) unlike anorthite crystal, presence of high coordination (> 4) Al's with 30% abundance, (iii) and significant presence of both non bridging (8%) and triply (17%) coordinated oxygen. In the 0-10 GPa interval, mainly topological changes occur in the Si-O (also Al-O to some extent) surroundings in the cold compressed case in comparison to smooth increase in the average bond distance and coordination in the hot compressed case. Further compression results in gradual increases in: mean coordination, proportion of O-triclusters and increasing appearance of tetrahedral oxgyens, with Si-O (Al-O) reaching 6 (6.5) and O-T > 3 (T=Si and Al) at the highest compression. Due to the absence of kinetic barrier, the hot compressed glasses consistently produce greater densities and higher coordination numbers than the cold compression cases. Decompressed glasses show irreversible compaction along with retention of high coordination species when decompressed from > 10 GPa and degree of irreversibility depends on the peak pressure of decompression. These structural details suggest that the pressure response of the cold compressed glasses are not only inherently different in the 0 - 10 GPa interval, the density and the average coordination are consistently lower than the hot compressed glasses. Hot-compressed glasses may therefore be the better analog in the study of high-pressure silicate melts.

An empirical method for calculating melt compositions produced beneath mid-ocean ridges: for axis and off-axis (seamounts) melting application

NASA Astrophysics Data System (ADS)

Batiza, Rodey

1991-12-01

We present a new method for calculating the major element compositions of primary melts parental to mid-ocean ridge basalt (MORB). This model is based on the experimental data of Jaques and Green (1980), Falloon et al. (1988), and Falloon and Green (1987, 1988) which are ideal for this purpose. Our method is empirical and employs solid-liquid partition coefficients (Di) from the experiments. We empirically determine Di=f(P,F) and use this to calculate melt compositions produced by decompression-induced melting along an adiabat (column melting). Results indicate that most MORBs can be generated by 10-20% partial melting at initial pressures (P0) of 12-21 kbar. Our primary MORB melts have MgO=10-12 wt %. We fractionate these at low pressure to an MgO content of 8.0 wt% in order to interpret natural MORB liquids. This model allows us to calculate Po, Pf, To, Tf, and F for natural MORB melts. We apply the model to interpret MORB compositions and mantle upwelling patterns beneath a fast ridge (East Pacific Rise (EPR) 8°N to 14°N), a slow ridge (mid-Atlantic Ridge (MAR) at 26°S), and seamounts near the EPR (Lamont seamount chain). We find mantle temperature differences of up to 50°-60°C over distances of 30-50 km both across axis and along axis at the EPR. We propose that these are due to upward mantle flow in a weakly conductive (versus adiabatic) temperature gradient. We suggest that the EPR is fed by a wide (~100 km) zone of upwelling due to plate separation but has a central core of faster buoyant flow. An along-axis thermal dome between the Siqueiros transform and the 11°45' Overlapping Spreading Center (OSC) may represent such an upwelling; however, in general there is a poor correlation between mantle temperature, topography, and the segmentation pattern at the EPR. For the Lamont seamounts we find regular across-axis changes in Po and F suggesting that the melt zone pinches out off axis. This observation supports the idea that the EPR is fed by a broad upwelling which diminishes in vigor off axis. In contrast with the EPR axis, mantle temperature correlates well with topography at the MAR, and there is less melting under offsets. The data are consistent with weaker upwelling under offsets and a adiabatic temperature gradient in the subaxial mantle away from offsets. The MAR at 26°S exhibits the so-called local trend of Klein and Langmuir (1989). Our model indicates that the local trend cannot be due solely to intracolumn melting processes. The local trend seems to be genetically associated with slow-spreading ridges, and we suggest it is due to melting of multiple individual domains that differ in initial and final melting pressure within segments fed by buoyant focused mantle flow.

An empirical method for calculating melt compositions produced beneath mid-ocean ridges: Application for axis and off-axis (seamounts) melting

NASA Astrophysics Data System (ADS)

Niu, Yaoling; Batiza, Rodey

1991-12-01

We present a new method for calculating the major element compositions of primary melts parental to mid-ocean ridge basalt (MORB). This model is based on the experimental data of Jaques and Green (1980), Falloon et al. (1988), and Falloon and Green (1987, 1988) which are ideal for this purpose. Our method is empirical and employs solid-liquid partition coefficients (Di) from the experiments. We empirically determine Di = ƒ(P,F) and use this to calculate melt compositions produced by decompression-induced melting along an adiabat (column melting). Results indicate that most MORBs can be generated by 10-20% partial melting at initial pressures (P0) of 12-21 kbar. Our primary MORB melts have MgO = 10-12 wt %. We fractionate these at low pressure to an MgO content of 8.0 wt % in order to interpret natural MORB liquids. This model allows us to calculate Po, Pƒ, To, Tƒ, and F for natural MORB melts. We apply the model to interpret MORB compositions and mantle upwelling patterns beneath a fast ridge (East Pacific Rise (EPR)8°N to 14°N), a slow ridge (mid-Atlantic Ridge (MAR) at 26°S), and seamounts near the EPR (Lament seamount chain). We find mantle temperature differences of up to 50°-60°C over distances of 30-50 km both across axis and along axis at the EPR. We propose that these are due to upward mantle flow in a weakly conductive (versus adiabatic) temperature gradient. We suggest that the EPR is fed by a wide (-100 km) zone of upwelling due to plate separation but has a central core of faster buoyant flow. An along-axis thermal dome between the Siqueiros transform and the 11°45' Overlapping Spreading center (OSC) may represent such an upwelling; however, in general there is a poor correlation between mantle temperature, topography, and the segmentation pattern at the EPR. For the Lament seamounts we find regular across-axis changes in Po and F suggesting that the melt zone pinches out off axis. This observation supports the idea that the EPR is fed by a broad upwelling which diminishes in vigor off axis. In contrast with the EPR axis, mantle temperature correlates well with topography at the MAR, and there is less melting under offsets. The data are consistent with weaker upwelling under offsets and an adiabatic temperature gradient in the sub axial mantle away from offsets. The MAR at 26°S exhibits the so-called local trend of Klein and Langmuir (1989). Our model indicates that the local trend cannot be due solely to intracolumn melting processes. The local trend seems to be genetically associated with slow-spreading ridges, and we suggest it is due to melting of multiple individual domains that differ in initial and final melting pressure within segments fed by buoyant focused mantle flow.

Nature of the Mantle Sources and Bearing on Tectonic Evolution in the West Antarctic Rift System

NASA Astrophysics Data System (ADS)

Mukasa, S. B.; Rilling-Hall, S.; Marcano, M. C.; Wilson, T. J.; Lawver, L. A.; LeMasurier, W. E.

2012-12-01

We collected samples from subaerial lava flows and dredged some Neogene basanitic lavas from seven volcanic edifices in the Ross Sea, Antarctica - a part of the West Antarctic Rift System (WARS) and one of the world's largest alkaline magmatic provinces - for a study aimed at two principal objectives: (1) Geochemical interrogation of the most primitive magmatic rocks to try and understand the nature of the seismically abnormal mantle domain recently identified beneath the shoulder of the Transantarctic Mountains (TAM), the Ross Sea Embayment and Marie Byrd Land; and (2) Using 40Ar/39Ar geochronology to establish a temporal link between magmatism and tectonism, particularly in the Terror Rift. We have attempted to answer the questions of whether magmatism is due to a hot mantle or wet mantle, and whether rifting in the area triggered magmatic activity or vice versa. Results show that the area does not have an age-progressive hotspot track, and the magmatism post-dates the main phase of extension along the Terror Rift within the WARS, which supports a decompression-melting model without the benefit of a significant thermal anomaly. In fact, preliminary volatile measurements on olivine-hosted melt inclusions have yielded water concentrations in excess of 2 wt%, indicating that flux melting was an important complementary process to decompression melting. The major oxide compositions of lavas in the WARS are best matched to experimental melts of carbonated peridotite, though garnet pyroxenite can also be a minor source. The Pb and Nd isotopic systems are decoupled from each other, suggesting removal of fluid-mobile elements from the mantle source possibly during the long history of subduction along the Paleo-Pacific margin of Gondwana. Extremely unradiogenic 187Os/188Os ranging to as low as 0.1081 ± 0.0001 hints at the involvement of lithospheric components in generation of magmas in the WARS.

Decompression-induced melting of ice IV and the liquid-liquid transition in water

NASA Astrophysics Data System (ADS)

Mishima, Osamu; Stanley, H. Eugene

1998-03-01

Although liquid water has been the focus of intensive research for over 100 years, a coherent physical picture that unifies all of the known anomalies of this liquid, is still lacking. Some of these anomalies occur in the supercooled region, and have been rationalized on the grounds of a possible retracing of the liquid-gas spinodal (metastability limit) line into the supercooled liquid region, or alternatively the presence of a line of first-order liquid-liquid phase transitions in this region which ends in a critical point,. But these ideas remain untested experimentally, in part because supercooled water can be probed only above the homogeneous nucleation temperature TH at which water spontaneously crystallizes. Here we report an experimental approach that is not restricted by the barrier imposed by TH, involving measurement of the decompression-induced melting curves of several high-pressure phases of ice in small emulsified droplets. We find that the melting curve for ice IV seems to undergo a discontinuity at precisely the location proposed for the line of liquid-liquid phase transitions. This is consistent with, but does not prove, the coexistence of two different phases of (supercooled) liquid water. From the experimental data we calculate a possible Gibbs potential surface and a corresponding equation of state for water, from the forms of which we estimate the coordinates of the liquid-liquid critical point to be at pressure Pc ~ 0.1GPa and temperature Tc ~ 220K.

Physical Cause of Kimberlite Occurrences Clustering

NASA Astrophysics Data System (ADS)

Khazan, Y.; Aryasova, O.

2011-12-01

High abundances of incompatible elements in kimberlites are indicative of low or even infinitesimal melting degree in a source. This means that initially protokimberlite melts exist as a system of dispersed small inclusions while the kimberlite transportation to the surface assumes formation of macroscopic melt pools. In other words, an inevitable stage of the protokimberlite melt evolution is its segregation from the porous matrix inside a partially molten zone and accumulation to the zone top where the melt fraction greatly exceeds the initial melting degree. Khazan (2010), Khazan, Aryasova (2011) demonstrated that the characteristic segregation time, τ, depends on the ratio L/δ of the molten zone thickness, L, to the compaction length, δ, (McKenzie, 1984), which in its turn is defined by melt and matrix viscosities and matrix permeability. For low-viscosity melts the segregation time decreases with increasing molten zone thickness as τ≈19.5(η/ΔρgL) (η is the matrix viscosity, Δρ is the density contrast) and is independent of poorly known melt viscosity, matrix permeability, and melting degree. Since no system can exist longer than its decay time is, the decreasing segregation time dependence on the molten zone thickness constrains the latter. To illustrate, assume that the melting is due to decompression and accompanies ascent of a mantle diapir with a velocity V. In this case the molten zone thickness increases linearly with time L=Vt where t is measured from the onset of melting and cannot exceed the segregation time, so that t≤τ (Fig. 1) and L≤L*=4.4(Vη/Δρg)^0.5. Under a robust parameter choice (η=10^19 Pa s, Δρ=300 kg/m^3, V=3 cm/year) L* is about 8 km, with the corresponding segregation time τ being of 0.3 Myear (Fig. 1). After the first segregation, a new partially molten zone grows resulting in the next segregation when its thickness reaches the maximum possible value L*. This sequence of events repeats until the whole diapir passes by the melting level. One may estimate a diapir diameter D of 30 to 80 km based upon a size of low-amplitude uplifts associated with the kimberlite fields (e. g., Kaminsky et al., 1995). So the diapir ascent results in a cluster of ~D/L*=3-10 same age and composition eruptions. A total activity accociated with the cluster continues of τD/L*=1 to 3 Myear as it is really observed (Heaman et al.,2004). The described sequence of events is schematic(lly illustrated in Fig. 2. Heaman L et al., Lithos, 2004, 76, 377. Kaminsky F et al., J. Geochem. Explor. 1995, 53, 167. Khazan Y, Geoph. J. Int. 2010, 183, 601. Khazan Y, Aryasona O, Izvestiya, Phys. Solid Earth. 2011, 47, No. 5, 425. McKenzie D, J Petrol. 1984, 25, 713.

Bromine cycle in subduction zones through in situ Br monitoring in diamond anvil cells

NASA Astrophysics Data System (ADS)

Bureau, Hélène; Foy, Eddy; Raepsaet, Caroline; Somogyi, Andrea; Munsch, Pascal; Simon, Guilhem; Kubsky, Stefan

2010-07-01

The geochemical partitioning of bromine between hydrous haplogranitic melts, initially enriched with respect to Br and aqueous fluids, has been continuously monitored in situ during decompression. Experiments were carried out in diamond anvil cells from 890 °C to room temperature and from 1.7 GPa to room pressure, typically from high P, T conditions corresponding to total miscibility (presence of a supercritical fluid). Br contents were measured in aqueous fluids, hydrous melts and supercritical fluids. Partition coefficients of bromine were characterized at pressure and temperature between fluids, hydrous melts and/or glasses, as appropriate: DBrfluid/melt = (Br) fluid/(Br) melt, ranges from 2.18 to 9.2 ± 0.5 for conditions within the ranges 0.66-1.7 GPa, 590-890 °C; and DBrfluid/glass = (Br) fluid/(Br) glass ranges from 60 to 375 at room conditions. The results suggest that because high pressure melts and fluids are capable of accepting high concentrations of bromine, this element may be efficiently removed from the slab to the mantle source of arc magmas. We show that Br may be highly concentrated in subduction zone magmas and strongly enriched in subduction-related volcanic gases, because its mobility is strongly correlated with that of water during magma degassing. Furthermore, our experimental results suggest that a non negligible part of Br present in the subducted slab may remain in the down-going slab, being transported toward the transition zone. This indicates that the Br cycle in subduction zones is in fact divided in two related but independent parts: (1) a shallower one where recycled Br may leave the slab with a water and silica-bearing "fluid" leading to enriched arc magmas that return Br to the atmosphere. (2) A deeper cycle where Br may be recycled back to the mantle maybe to the transition zone, where it may be present in high pressure water-rich metasomatic fluids.

Experimental and textural constraints on mafic enclave formation in volcanic rocks

USGS Publications Warehouse

Coombs, M.L.; Eichelberger, J.C.; Rutherford, M.J.

2002-01-01

We have used experiments and textural analysis to investigate the process of enclave formation during magma mixing at Southwest Trident volcano, Alaska. Andesite enclaves are present throughout the four dacite lava flows produced by the eruption, and resemble mafic enclaves commonly found in other volcanic rocks. Our experiments replicate the pressure-temperature-time path taken by enclave-forming andesite magma as it is engulfed in dacite during magma mixing. Pressure and temperature information for the andesite and dacite are from [Coombs et al., Contrib. Mineral. Petrol. 140 (2000) 99-118]. The andesite was annealed at 1000??C, and then cooled to 890??C at rates of 110??C h1, 10??C h1 and 2??C h1. Once cooled to 890??C, andesite was held at this lower temperature from times ranging from 1 to 40 h. The andesite that was cooled at the slower rates of 2??C h1 and 10??C h1 most resembles enclave groundmass texturally and compositionally. Based on simple thermal calculations, these rates are more consistent with cooling of the andesite groundmass below an andesite-dacite interface than with cooling of enclave-sized spheres. If enclaves do crystallize as spheres, post-crystallization disaggregation must occur. Calculations using the MELTS algorithm [Ghiorso and Sack, Contrib. Mineral. Petrol. 119 (1995) 197-212] show that for incoming andesite to become less dense than the dacite to become less dense ???34 volume % of its groundmass must crystallize to undergo~18 volume % vesiculation; these values are similar to those determined for Southwest Trident enclaves. Thus such crystallization may lead to 'flotation' of enclaves and be a viable mechanism for enclave formation and dispersal. The residual melt in the cooling experiments did not evolve to rhyolitic compositions such as seen in natural enclaves due to a lack of a decompression step in the experiments. Decompression experiments on Southwest Trident dacite suggest an average ascent rate for the eruption of ???2-3 MPa h1. An andesite experiment that was cooled and then decompressed at this rate contains melt that matches that of the natural enclaves. It is apparent that decompression (ascent)-induced crystallization occurs in enclaves, but not in the form of microlites as happens in the dacite host, due either to insufficient residence time at chamber temperatures or to the pre-existing microphenocrysts which act as sites for new growth. ?? 2002 Elsevier Science B.V. All rights reserved.

Assessment of two methods of gastric decompression for the initial management of gastric dilatation-volvulus.

PubMed

Goodrich, Z J; Powell, L L; Hulting, K J

2013-02-01

To assess gastric trocarization and orogastric tubing as a means of gastric decompression for the initial management of gastric dilatation-volvulus. Retrospective review of 116 gastric dilatation-volvulus cases from June 2001 to October 2009. Decompression was performed via orogastric tubing in 31 dogs, gastric trocarization in 39 dogs and a combination of both in 46 dogs. Tubing was successful in 59 (75·5%) dogs and unsuccessful in 18 (23·4%) dogs. Trocarization was successful in 73 (86%) dogs and unsuccessful in 12 (14%) dogs. No evidence of gastric perforation was noted at surgery in dogs undergoing either technique. One dog that underwent trocarization had a splenic laceration identified at surgery that did not require treatment. Oesophageal rupture or aspiration pneumonia was not identified in any dog during hospitalization. No statistical difference was found between the method of gastric decompression and gastric compromise requiring surgical intervention or survival to discharge. Orogastric tubing and gastric trocarization are associated with low complication and high success rates. Either technique is an acceptable method for gastric decompression in dogs with gastric dilatation-volvulus. © 2013 British Small Animal Veterinary Association.

Block Copolymer Adhesion Measured by Contact Mechanics Methods

NASA Astrophysics Data System (ADS)

Falsafi, A.; Bates, S.; Tirrell, M.; Pocius, A. V.

1997-03-01

Adhesion measurements for a series of polyolefin diblocks and triblocks are presented. These materials have poly(ethylene-propylene) or poly(ethyl-ethylene) rubbery block, and semicrystalline polyethylene block as physical crosslinker. The experiments consist of compression and decompression profiles of contact area between the samples as a function of normal load, analyzed by the JKR Theory. The samples are prepared either by formation of caps from the bulk material in melting and subsequent cooling, and/or coating them in thin films on surface modified elastic foundations of polydimethylsiloxane caps. The latter minimizes the viscoelastic losses which are dominant in the bulk of material. The effect of molecular architecture and microstructure on adhesion energy and dynamics of separation, obtained from decompression experiments, is discussed in view of their influence on molecular arrangements at the contacting surfaces.

Thermal vesiculation during volcanic eruptions.

PubMed

Lavallée, Yan; Dingwell, Donald B; Johnson, Jeffrey B; Cimarelli, Corrado; Hornby, Adrian J; Kendrick, Jackie E; von Aulock, Felix W; Kennedy, Ben M; Andrews, Benjamin J; Wadsworth, Fabian B; Rhodes, Emma; Chigna, Gustavo

2015-12-24

Terrestrial volcanic eruptions are the consequence of magmas ascending to the surface of the Earth. This ascent is driven by buoyancy forces, which are enhanced by bubble nucleation and growth (vesiculation) that reduce the density of magma. The development of vesicularity also greatly reduces the 'strength' of magma, a material parameter controlling fragmentation and thus the explosive potential of the liquid rock. The development of vesicularity in magmas has until now been viewed (both thermodynamically and kinetically) in terms of the pressure dependence of the solubility of water in the magma, and its role in driving gas saturation, exsolution and expansion during decompression. In contrast, the possible effects of the well documented negative temperature dependence of solubility of water in magma has largely been ignored. Recently, petrological constraints have demonstrated that considerable heating of magma may indeed be a common result of the latent heat of crystallization as well as viscous and frictional heating in areas of strain localization. Here we present field and experimental observations of magma vesiculation and fragmentation resulting from heating (rather than decompression). Textural analysis of volcanic ash from Santiaguito volcano in Guatemala reveals the presence of chemically heterogeneous filaments hosting micrometre-scale vesicles. The textures mirror those developed by disequilibrium melting induced via rapid heating during fault friction experiments, demonstrating that friction can generate sufficient heat to induce melting and vesiculation of hydrated silicic magma. Consideration of the experimentally determined temperature and pressure dependence of water solubility in magma reveals that, for many ascent paths, exsolution may be more efficiently achieved by heating than by decompression. We conclude that the thermal path experienced by magma during ascent strongly controls degassing, vesiculation, magma strength and the effusive-explosive transition in volcanic eruptions.

Unlocking the Secrets of the Mantle Wedge: New Insights Into Melt Generation Processes in Subduction Zones

NASA Astrophysics Data System (ADS)

Grove, T. L.

2007-05-01

Recent laboratory studies of the melting and crystallization behavior of mantle peridotite and subduction zone lavas have led to new insights into melting processes in island arc settings. Melting of the mantle wedge in the presence of H2O begins at much lower temperatures than previously thought. The solidus of mantle peridotite at 3 GPa is ~ 800 °C, which is 200 °C below previous estimates. At pressures greater than 2.4 GPa chlorite becomes a stable phase on the solidus and it remains stable until ~ 3.5 GPa. Therefore, melting over this pressure range occurs in the presence of chlorite, which contains ~ 12 wt. % H2O. Chlorite stabilized on the peridotite solidus by slab-derived H2O may be the ultimate source of H2O for subduction zone magmatism. Thus, chlorite could transport large amounts of H2O into the descending mantle wedge to depths where it can participate in melting to generate hydrous arc magmas. Our ability to identify primitive mantle melts at subduction zones has led to the following observations. 1) Primitive mantle melts show evidence of final equilibration at shallow depths near the mantle - crust boundary. 2) They contain variable amounts of dissolved H2O (up to 6 wt. %). 3) They record variable extents of melting (up to > 25 wt. %). To produce melts with such variable characteristics requires more than one melting process and requires consideration of a new type of melting called hydrous flux melting. Flux melting occurs when the H2O - rich melt initially produced on the solidus near the base of the mantle wedge ascends and continuously reacts with overlying hotter, shallower mantle. The mantle melts and magmatic H2O content is constantly diluted as the melt ascends and reacts with shallower, hotter mantle. Anhydrous mantle melts are also found in close temporal and spatial proximity to hydrous flux melts. These melts are extracted at similar depths near the top of the mantle wedge when mantle is advected up and into the wedge corner and melted by adiabatic decompression. In light of these new insights into the chemical processes that lead to melt generation in subduction zones, further study of the influence of mantle dynamics and physical processes on melting is crucial. Variations in mantle permeability near the base of the wedge may exercise important controls on the access of fluids and/or melts to the overlying wedge. The presence of chlorite in the wedge may also influence rheological properties and seismicity in the vicinity of the slab - wedge interface. Improved knowledge of rheology and permeability will help us to develop more robust models of mantle flow and temperature distribution in the mantle wedge. These are crucial for refining melting models. By combining evidence from petrology, geochemistry and geophysics the mysteries that attend the generation of melt in the mantle wedge can be resolved.

Empirical models for use in designing decompression procedures for space operations

NASA Technical Reports Server (NTRS)

Conkin, Johnny; Edwards, Benjamin F.; Waligora, James M.; Horrigan, David J., Jr.

1987-01-01

Empirical models for predicting the incidence of Type 1 altitude decompression sickness (DCS) and venous gas emboli (VGE) during space extravehicular activity (EVA), and for use in designing safe denitrogenation decompression procedures are developed. The models are parameterized using DCS and VGE incidence data from NASA and USAF manned altitude chamber decompression tests using 607 male and female subject tests. These models, and procedures for their use, consist of: (1) an exponential relaxation model and procedure for computing tissue nitrogen partial pressure resulting from a specified prebreathing and stepped decompression sequence; (2) a formula for calculating Tissue Ratio (TR), a tissue decompression stress index; (3) linear and Hill equation models for predicting the total incidence of VGE and DCS attendant with a particular TR; (4) graphs of cumulative DCS and VGE incidence (risk) versus EVA exposure time at any specified TR; and (5) two equations for calculating the average delay period for the initial detection of VGE or indication of Type 1 DCS in a group after a specific denitrogenation decompression procedure. Several examples of realistic EVA preparations are provided.

Markov Chain Monte Carlo Inversion of Mantle Temperature and Composition, with Application to Iceland

NASA Astrophysics Data System (ADS)

Brown, Eric; Petersen, Kenni; Lesher, Charles

2017-04-01

Basalts are formed by adiabatic decompression melting of the asthenosphere, and thus provide records of the thermal, chemical and dynamical state of the upper mantle. However, uniquely constraining the importance of these factors through the lens of melting is challenging given the inevitability that primary basalts are the product of variable mixing of melts derived from distinct lithologies having different melting behaviors (e.g. peridotite vs. pyroxenite). Forward mantle melting models, such as REEBOX PRO [1], are useful tools in this regard, because they can account for differences in melting behavior and melt pooling processes, and provide estimates of bulk crust composition and volume that can be compared with geochemical and geophysical constraints, respectively. Nevertheless, these models require critical assumptions regarding mantle temperature, and lithologic abundance(s)/composition(s), all of which are poorly constrained. To provide better constraints on these parameters and their uncertainties, we have coupled a Markov Chain Monte Carlo (MCMC) sampling technique with the REEBOX PRO melting model. The MCMC method systematically samples distributions of key REEBOX PRO input parameters (mantle potential temperature, and initial abundances and compositions of the source lithologies) based on a likelihood function that describes the 'fit' of the model outputs (bulk crust composition and volume and end-member peridotite and pyroxenite melts) relative to geochemical and geophysical constraints and their associated uncertainties. As a case study, we have tested and applied the model to magmatism along Reykjanes Peninsula in Iceland, where pyroxenite has been inferred to be present in the mantle source. This locale is ideal because there exist sufficient geochemical and geophysical data to estimate bulk crust compositions and volumes, as well as the range of near-parental melts derived from the mantle. We find that for the case of passive upwelling, the models that best fit the geochemical and geophysical observables require elevated mantle potential temperatures ( 120 °C above ambient mantle), and 5% pyroxenite. The modeled peridotite source has a trace element composition similar to depleted MORB mantle, whereas the trace element composition of the pyroxenite is similar to enriched mid-ocean ridge basalt. These results highlight the promise of this method for efficiently exploring the range of mantle temperatures, lithologic abundances, and mantle source compositions that are most consistent with available observational constraints in individual volcanic systems. 1 Brown and Lesher (2016), G-cubed, 17, 3929-3968

Trace element behavior and P-T-t evolution during partial melting of exhumed eclogite in the North Qaidam UHPM belt (NW China): Implications for adakite genesis

NASA Astrophysics Data System (ADS)

Zhang, Guibin; Niu, Yaoling; Song, Shuguang; Zhang, Lifei; Tian, Zuolin; Christy, Andrew G.; Han, Lei

2015-06-01

We have studied trace element behavior and timing of decompression melting of UHP rocks during exhumation recorded in the magmatic products, i.e., the melt phase (leucosomes), cumulate (garnetite) and residue (amphibolitized eclogite) from a single outcrop in the south Dulan area, North Qaidam UHPM belt, NW China. Two distinct episodes of partial melting are recognized. First, Grt-free tonalitic-trondhjemitic leucosome melts with higher silica crystallized at 424.0 ± 2.7 Ma. Garnets grew in the leucosome melt but fractionated out to form garnetite cumulates along with Ti-rich phases (rutile and titanite), strengthening the adakitic signature of the leucosome. Later Grt-bearing leucosome melts with an age of 412.4 ± 2.9 Ma cross-cut boudins and layers of amphibolitized eclogite. Geochemical investigation of bulk-rocks and in situ minerals verifies the genetic relationship between the amphibolitized eclogite and the tonalitic-trondhjemitic melts. Zircons from the amphibolitized eclogite have older (> 700 Ma) protolith ages, with subsequent eclogite-facies metamorphism, retrograde granulite-facies overprinting and partial melting. Phase modeling and Zr-in-rutile thermometry calculations in combination with zircon geochronology reveal the evolution P-T-t path for the exhumation and the partial melting of the deeply subducted continental crust at the North Qaidam subduction zone in the Early Paleozoic.

Vesiculation of rhyolite magma in the IDDP-1 borehole at Krafla, Iceland

NASA Astrophysics Data System (ADS)

Trewick, Laura; Tuffen, Hugh; Owen, Jacqueline; Kennedy, Ben; Eichelberger, John; Zierenberg, Robert

2016-04-01

In 2009 the IDDP-1 borehole at Krafla, Iceland unexpectedly intersected rhyolitic magma at 2.1 km depth [1,2], providing unprecedented opportunities to investigate silicic melt formation and storage, and potential for powerful geothermal energy production. A key objective is to constrain the nature of the rhyolitic melt and its response to drilling. As no intact core was extracted, evidence is fragmental - from glassy rhyolitic clasts retrieved from the cuttings. These exhibit a range of glass colours, vesicularities and phenocryst contents [1,2]. Here we use benchtop infra-red spectroscopy and petrological microscopy to characterise the H2O concentrations and bubble number densities within diverse glassy clasts, complemented by 1 Atm bubble growth experiments with a heated stage to investigate vesicle growth. Juvenile glassy clasts were divided into three categories (brown>banded>very dark glass). H2O concentrations within clasts showed some spatial variability, with enrichment towards bubble-rich areas that may be resorption-related but could not be adequately characterised with a benchtop source. However, mean values ranged from 1.41-1.68 wt %, with no statistically significant difference between clast types. This is broadly consistent with previous studies [1,2]. Bubble growth rates in all clast types were determined during isothermal dwells at 600, 650 and 700 °C, for which bubbles grew at 0.03-0.09, 0.11-0.31, and 0.46-0.82 μm s-1 respectively. The highest growth rates were measured for the most water-rich clast analysed - a banded clast with mean H2O of 1.68 wt %, and initially-larger bubbles also grew more rapidly. Measured bubble number densities (BNDs) range from 10[11.7] m-3 in banded clasts to 10[13.1] m-3 in very dark clasts, corresponding to decompression rates of ~0.1-1 MPa/s [3], although experimentation on IDDP-1 magma is needed to properly calibrate BNDs as a decompression rate meter. Nonetheless, such decompression rates suggest nucleation occurred over tens-hundreds of seconds, as pressure dropped from magmastatic towards lower borehole values. The duration of vesicle growth was roughly estimated from measured bubble sizes, which range from ~5 μm in very dark clasts to ~30 μm in banded clasts, and extrapolated bubble growth rates at magmatic temperature (900 °C) and appropriate pressure. Results suggest only brief pre-quenching growth occurred, over ~seconds. We therefore propose that magma adjacent to the drill head experienced decompression prior to interception, leading to a brief period of bubble nucleation and a briefer period of growth prior to fragmentation and quenching. The high bubble strain, low bubble number density and largest bubble sizes in banded clasts all point towards slower decompression and more protracted viscous flow in this part of the rhyolitic magma. However, better temporal constraints are required on the extraction of distinct clast types to determine how magma response evolved through time, and better piece together this enigmatic magmatic jigsaw. 1. Elders WA et al. 2011 Geology 39, 231-234. 2. Zierenberg RA et al. 2013 Cont. Mineral. Petrol. 165:327-347. 3. Hamada M et al 2010 Bull. Volcanol., 72, 735-746.

Trends in Orbital Decompression Techniques of Surveyed American Society of Ophthalmic Plastic and Reconstructive Surgery Members.

PubMed

Reich, Shani S; Null, Robert C; Timoney, Peter J; Sokol, Jason A

To assess current members of the American Society of Ophthalmic Plastic and Reconstructive Surgery (ASOPRS) regarding preference in surgical techniques for orbital decompression in Graves' disease. A 10-question web-based, anonymous survey was distributed to oculoplastic surgeons utilizing the ASOPRS listserv. The questions addressed the number of years of experience performing orbital decompression surgery, preferred surgical techniques, and whether orbital decompression was performed in collaboration with an ENT surgeon. Ninety ASOPRS members participated in the study. Most that completed the survey have performed orbital decompression surgery for >15 years. The majority of responders preferred a combined approach of floor and medial wall decompression or balanced lateral and medial wall decompression; only a minority selected a technique limited to 1 wall. Those surgeons who perform fat decompression were more likely to operate in collaboration with ENT. Most surgeons rarely remove the orbital strut, citing risk of worsening diplopia or orbital dystopia except in cases of optic nerve compression or severe proptosis. The most common reason given for performing orbital decompression was exposure keratopathy. The majority of surgeons perform the surgery without ENT involvement, and number of years of experience did not correlate significantly with collaboration with ENT. The majority of surveyed ASOPRS surgeons prefer a combined wall approach over single wall approach to initial orbital decompression. Despite the technological advances made in the field of modern endoscopic surgery, no single approach has been adopted by the ASOPRS community as the gold standard.

NanoSIMS results from olivine-hosted melt embayments: Modeling ascent rate in explosive basaltic eruptions

NASA Astrophysics Data System (ADS)

Lloyd, A. S.; Plank, T.; Ruprecht, P.; Hauri, E. H.; Gonnermann, H. M.; Rose, W. I.

2012-12-01

A critical parameter governing the explosivity of volcanic eruptions is the rate at which magma ascends and degases, because this affects bubble nucleation, coalescence, and ultimately fragmentation. Although several methods have been used to determine magma ascent rates, it remains a poorly constrained parameter for most eruptions. One promising method employs diffusion modeling of H2O and CO2 concentration gradients in melt embayments/open melt inclusions [1,2]. Here we utilize the fine spatial resolution of the nanoSIMS to obtain concentration gradients for five volatile species, improving upon previous efforts that were more limited in spatial resolution (FTIR, [1]) and in number of volatile analytes (H2O only by BSE, [2]). Focusing on explosive basaltic eruptions, for which very little is known about ascent rates, we chose ash and lapilli samples from the Oct 1974 sub-plinian eruption of Volcán de Fuego. Glassy, olivine-hosted embayments with evidence of outlet bubbles were analyzed by nanoSIMS at a minimum distance between spots of 15 μm. Major element zonation in the embayments was investigated by EMP, and high resolution BSE images were captured to complement the nanoSIMS spot measurements for H2O (as in [2]). We report analyses for 5 embayments that vary in length from 100 to 350 μm. Low-solubility volatiles (CO2, H2O, S) decrease towards the embayment outlet, consistent with diffusive reequilibration with the more-degassed surrounding melt. High-solubility volatiles (Cl, F) increase towards the outlet, apparently behaving as magmaphile elements. Major elements exhibit constant concentrations along the embayment, except for a 20-50 μm wide zone near the embayment outlet, perhaps representing a boundary layer at the outlet bubble, where concentrations vary consistent with olivine and clinopyroxene microlite growth. BSE grayscale values are thus affected by both H2O diffusion and major element zonation at the embayment outlet, and cannot be used to estimate H2O concentration gradients [2]. Forward modeling of CO2 and H2O profiles takes into account temperature- and composition-dependent diffusivities and a closed-system degassing path for the exterior magma (as observed in melt inclusions from the same sample). Assuming a constant decompression rate from 200 MPa and an initial composition of 600 ppm CO2 and 4.3 wt% H2O at 1030°C, models yield preliminary results with very rapid ascent times (100 s, or 2 MPa/s). A two-stage model, however, allows slower decompression during CO2 exsolution (0.1 MPa/s) and faster ascent when H2O begins to exsolve (1.5 MPa/s), for total ascent times on the order of 10 to 20 minutes. This example highlights the additional constraints that come from measuring multiple diffusing species. [1] Liu et al, JGR, 2007 [2] Humphreys et al, EPSL, 2008.

The Neurological Compromised Spine Due to Ewing Sarcoma. What First: Surgery or Chemotherapy? Therapy, Survival, and Neurological Outcome of 15 Cases With Primary Ewing Sarcoma of the Vertebral Column.

PubMed

Mirzaei, Lida; Kaal, Suzanne E J; Schreuder, Hendrik W B; Bartels, Ronald H M A

2015-11-01

The vertebral column is an infrequent site of primary involvement in Ewing sarcoma. Yet when Ewing sarcoma is found in the spine, the urge for decompression is high because of the often symptomatic compression of neural structures. It is unclear in alleviating a neurological deficit whether chemotherapy is preferred over decompressive laminectomy. To underline, in this case series, the efficiency of initial chemotherapy before upfront surgery in the setting of high-grade spinal cord or cauda equina compression of primary Ewing sarcoma. Fifteen patients with Ewing sarcoma primarily located in the spine were treated at our institution between 1983 and 2015. Localization, neurological deficit expressed as Frankel grade, and outcome expressed as Rankin scale before and after initial chemotherapy, the recurrence rate, and overall survival were evaluated. The multidisciplinary approach of 1 case will be discussed in detail. Nine patients (60%) were female. The age at presentation was 15.0 ± 5.5 years (range: 0.9-22.8 years). Ten patients (67%) were initially treated with chemotherapy, and 1 patient (7%) was treated primarily with radiotherapy followed by chemotherapy. The remaining 4 patients (27%) were initially treated with decompressive surgery. All patients treated primarily nonsurgically improved neurologically at follow-up, showing the importance of chemotherapy as an effective initial treatment option. Adequate and quick decompression of neural structures with similar results can be achieved by chemotherapy and radiotherapy, avoiding the local spill of malignant cells.

Elasticity of MgSiO3 glass to pressures of the transition zone

NASA Astrophysics Data System (ADS)

Speziale, S.; Reichmann, H. J.; Marquardt, H.; Shim, S.-H.

2009-04-01

Geophysical observations suggest the presence of liquid silicates in regions at the top of the transition zone and at the core-mantle boundary. In addition, a mainly silicate magma ocean probably played a crucial role in the evolution of the early Earth. For these reasons understanding the physical behavior of silicates melts at high pressures is important. In situ experimental investigation of the physical properties of silicate melts at high pressures poses substantial technical difficulties, and computer simulations are nowadays the most effective method to explore the elasticity and the density of such material at relevant conditions of the deep Earth. Due to these difficulties, glasses are often used as "frozen" proxies of melts for experimental studies of their physical properties. Here we present the pressure dependence of sound velocity of MgSiO3 glass measured by Brillouin spectroscopy in the diamond-anvil cell across the whole pressure range of the upper mantle and transition zone. We measured both compressional and shear velocity at 36 different pressures both on compression and decompression. Fixing the starting density to 2.742 ± 0.003 g/cm3, we determined both bulk modulus KS0 and shear modulus G0, and their pressure derivatives at ambient conditions to be KS0 = 76.2 ± 1.0 GPa, G0 = 40.11 ± 0.32 GPa, (‚KS/‚P)0 = 3.04 ± 0.23, and (‚G/‚P )0 = 0.46 ± 0.06. We observe two discontinuities of the pressure dependence of both compressional and shear velocity at 7 ± 2 GPa and at 21 ± 1 GPa. These two discontinuities take place at pressures at which: (a) changes in the pressure dependence of both Si-O-Si bending and Si-O stretching vibrations of the polymerized SiO4 network were observed in the same glass by laser Raman scattering [1], and (b) new spectral features were observed by X-ray Raman scattering [2].The velocities measured upon decompression are significantly different from those measured during compression. The whole of our velocity measurements in compression and decompression suggest that MgSiO3 glass is subject to a multi-step pressure-induced irreversible densification. We estimate that the overall density increase is of the order of 2 percent after complete decompression. We will discuss issues related to the accuracy of density determination from high-pressure Brillouin scattering measurements of glasses at ambient temperature. References [1] Grocholski B., et al. (2008) Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abs. DI41A-1746. [2] Lee S.K., et al. (2008) Proc. Natl. Acad. Sci. U.S.A., 105(23), 7925-7929.

Kyanite-Bearing Migmatites at Ledge Mountain, Adirondack Highlands

NASA Astrophysics Data System (ADS)

Swanson, B.; Leech, M.; Metzger, E. P.

2017-12-01

Sillimanite-rich felsic migmatites exposed at Ledge Mountain represent the only location in the Adirondack Highlands where kyanite has been found. The texturally young kyanite is overprinted on sillimanite in largely undeformed pegmatitic leucosomes, suggesting a late episode of melting taking place deeper than previously thought, and requiring a counter-clockwise P-T path. A final phase of anatexis ca. 1050 Ma in the Eastern Adirondack Highlands is consistent with an influx of fluid or decompression from extension in sillimanite-bearing migmatites. Temperatures both from this study and previous work are consistent with granulite-facies metamorphism, however the presence of kyanite requires higher pressure conditions corresponding to deeper burial of these central Adirondack rocks. We used Perple_X to model phase equilibria using XRF+ICP-MS whole-rock chemistries for the kyanite-bearing migmatites. Pseudosection models suggest that the peak P-T mineral assemblage kyanite + mesoperthite + garnet + rutile formed at approximately 15-20kb and 1000°C which is higher than previously proposed for granulites in the region. These P-T conditions for peak metamorphism are similar to those reported for the distinctive and relatively rare assemblage that we observe kyanite + hypersolvus feldspar (now mesoperthite) + garnet + rutile. We have evidence of isothermal decompression to <11kb and 880°-1000°C based on Grt + Pl equilibrium in the assemblage Grt + Pl ± Kfs + Qz + Ilm + melt. The leucocratic melt phase comprises 16 vol. % of the rock at these P-T conditions which is sufficient for ductile flow in the deep crust. This melt phase is present syn-exhumation and helped to buoyantly exhume Ledge Moutain rocks beneath bounding normal faults as a granitic gneiss dome. Preliminary U-Pb SHRIMP zircon ages from Ledge Mountain kyanite-bearing migmatites show anatexis continuing well after high-grade metamorphism is believed to have ceased in the range. A counter-clockwise P-T path is consistent with the mechanisms in the current model, and this study indicates anatectic melting persisted into the Rigolet phase. The Ledge Mountain migmatite may represent the Hawkeye granite and/or Lyon Mountain Gneiss that were metamorphosed to sillimanite grade and then overprinted by a higher pressure, lower temperature assemblage.

Deep lateral wall orbital decompression following strabismus surgery in patients with Type II ophthalmic Graves' disease.

PubMed

Ellis, Michael P; Broxterman, Emily C; Hromas, Alan R; Whittaker, Thomas J; Sokol, Jason A

2018-01-10

Surgical management of ophthalmic Graves' disease traditionally involves, in order, orbital decompression, followed by strabismus surgery and eyelid surgery. Nunery et al. previously described two distinct sub-types of patients with ophthalmic Graves' disease; Type I patients exhibit no restrictive myopathy (no diplopia) as opposed to Type II patients who do exhibit restrictive myopathy (diplopia) and are far more likely to develop new-onset worsening diplopia following medial wall and floor decompression. Strabismus surgery involving extra-ocular muscle recession has, in turn, been shown to potentially worsen proptosis. Our experience with Type II patients who have already undergone medial wall and floor decompression and strabismus surgery found, when additional decompression is necessary, deep lateral wall decompression (DLWD) appears to have a low rate of post-operative primary-gaze diplopia. A case series of four Type II ophthalmic Graves' disease patients, all of whom had already undergone decompression and strabismus surgery, and went on to develop worsening proptosis or optic nerve compression necessitating further decompression thereafter. In all cases, patients were treated with DLWD. Institutional Review Board approval was granted by the University of Kansas. None of the four patients treated with this approach developed recurrent primary-gaze diplopia or required strabismus surgery following DLWD. While we still prefer to perform medial wall and floor decompression as the initial treatment for ophthalmic Graves' disease, for proptosis following consecutive strabismus surgery, DLWD appears to be effective with a low rate of recurrent primary-gaze diplopia.

The Roles of Temperature and Composition in High-Pressure Structural Changes in Aluminosilicate Melts

NASA Astrophysics Data System (ADS)

Stebbins, J. F.

2009-12-01

Extensive recent NMR studies show large effects of composition on the extent of structural change in aluminosilicate glasses quenched from melts at high pressure, which correlate with observed, recovered density increases. Although such results will eventually need to be complemented by quantitative, in situ spectroscopic and scattering measurements, they already provide important constraints on the types of models necessary to capture the complexity of structure-property relationships for multicomponent natural magmas. For example, smaller and/or higher charged network modifier/charge compensator cations (e.g. Mg2+ vs. Ca2+, Ca2+ vs. K+) generally promote greater densification as well as increased conversion of four-coordinated to five- and six-coordinated Al (Al-27 NMR), but such effects may be non-linear in mixed-cation systems. At the same time, simple calculations with estimates of changes in partial molar volumes suggest that much of the observed density increases must be due to compression of “soft” sites in the structure and to the accompanying narrowing of inter-tetrahedral network bond angles (e.g. Si-O-Si). These can in turn be detected as reductions in mean Na-O distances (Na-23 NMR) and shifts in Si-29 spectra. As the field strength of the modifier cation increases farther (e.g. from Ca2+ to La3+), this pattern shifts: such “intermediate” cations can react to pressure increases by increasing their own coordinations and M-O distances (La K-edge XAS), reducing effects on network cation coordination. An extreme example of this can be seen as the Al/Si ratio changes: only at low Al contents are increases in Si coordination large enough to be detected by Si-29 NMR. Numerous recent studies of high-pressure glasses by O-17 NMR (e.g. S.K. Lee et al.) have emphasized the role of non-bridging oxygens (NBO) in increases of Si and Al coordination with pressure, as well as the critical importance of this species to melt properties. It is likely that modifier cation field strength has an important effect on this process as well: it is now well-known from borosilicate analog systems that higher field-strength modifiers (e.g. Ca2+ vs. Na+) stabilize local concentrations of negative charge as on NBO. This competing effect may again complicate models of density vs. composition. At best, quenched and decompressed glasses sample the melt structure only at the high P glass transition temperature. Given that the solidus temperatures of greatest interest to geological processes generally increase with pressure, changes in melt structure with temperature become even more important. The still poorly-known effects of ambient T decompression on glass structure also need to be resolved by future studies of the kinetics of this process and key in-situ measurements. Simple estimates of density changes during quench from a high P/T melt and subsequent decompression suggest that there is not a great deal of “room” for inelastic structural relaxation in typical aluminosilicate glasses, unless the high pressure thermal expansivity has a much larger structural contribution (Si coordination shift with T?) than is known from ambient P.

Modulation of magmatic processes by CO2 flushing

NASA Astrophysics Data System (ADS)

Caricchi, Luca; Sheldrake, Tom E.; Blundy, Jon

2018-06-01

Magmatic systems are the engines driving volcanic eruptions and the source of fluids responsible for the formation of porphyry-type ore deposits. Sudden variations of pressure, temperature and volume in magmatic systems can produce unrest, which may culminate in a volcanic eruption and/or the abrupt release of ore-forming fluids. Such variations of the conditions within magmatic systems are commonly ascribed to the injection of new magma from depth. However, as magmas fractionating at depth or rising to the upper crust release CO2-rich fluids, the interaction between carbonic fluids and H2O-rich magmas stored in the upper crust (CO2 flushing), must also be a common process affecting the evolution of subvolcanic magma reservoirs. Here, we investigate the effect of gas injection on the stability and chemical evolution of magmatic systems. We calculate the chemical and physical evolution of magmas subjected to CO2-flushing using rhyolite-MELTS. We compare the calculations with a set of melt inclusion data for Mt. St. Helens, Merapi, Etna, and Stromboli volcanoes. We provide an approach that can be used to distinguish between melt inclusions trapped during CO2 flushing, magma ascent and decompression, or those affected by post-entrapment H2O-loss. Our results show that CO2 flushing is a widespread process in both felsic and mafic magmatic systems. Depending upon initial magma crystallinity and duration of CO2 input, flushing can either lead to volcanic eruption or fluid release. We suggest that CO2 flushing is a fundamental process modulating the behaviour and chemical evolution of crustal magmatic systems.

Ridge Outgassing and Melt Production from 4Ga to Present

NASA Astrophysics Data System (ADS)

Fuentes, J.; Crowley, J.; Dasgupta, R.; Mitrovica, J. X.

2017-12-01

The majority of Earth's volcanism occurs at ocean ridges via decompression melting. This process exerts a strong control on the mantle and surface volatile contents throughout Earth history. In this study, we investigate mantle temperature, ridge melt production, and ridge CO2 outgassing from 4 Ga to present by coupling an analytical mantle convection model (Crowley and O'Connell 2012) with a recent petrologic model of peridotite melting in the presence of CO2 (Dasgupta et al. 2013). By taking advantage of the computational efficiency of the convection model, we simulate time-dependent convection with a large suite of realistic mantle and lithospheric parameters to produce a full range of possible thermal histories. We only accept models which evolve from stagnant-lid convection to mobile-lid convection in order to be consistent with previous geodynamic modeling and geochemical studies (i.e. Condie et al. 2016, Debaille et al. 2013). The presence of volatiles in the mantle leads to deeper, low degree melting. This effect, combined with higher temperatures sustained during the phase of stagnant-lid convection, has a significant effect on the total mass of CO2 outgassed (as well as other volatiles), with major implications for early Earth climate and its continued evolution.

The evolution of continental roots in numerical thermo-chemical mantle convection models including differentiation by partial melting

NASA Astrophysics Data System (ADS)

de Smet, J. H.; van den Berg, A. P.; Vlaar, N. J.

1999-09-01

Incorporating upper mantle differentiation through decompression melting in a numerical mantle convection model, we demonstrate that a compositionally distinct root consisting of depleted peridotite can grow and remain stable during a long period of secular cooling. Our modeling results show that in a hot convecting mantle partial melting will produce a compositional layering in a relatively short time of about 50 Ma. Due to secular cooling mantle differentiation finally stops before 1 Ga. The resulting continental root remains stable on a billion year time scale due to the combined effects of its intrinsically lower density and temperature-dependent rheology. Two different parameterizations of the melting phase-diagram are used in the models. The results indicate that during the Archaean melting occurred on a significant scale in the deep regions of the upper mantle, at pressures in excess of 15 GPa. The compositional depths of continental roots extend to 400 km depending on the potential temperature and the type of phase-diagram parameterization used in the model. The results reveal a strong correlation between lateral variations of temperature and the thickness of the continental root. This shows that cold regions in cratons are stabilized by a thick depleted root.

Pre-1991 sulfur transfer between mafic injections and dacite magma in the Mt. Pinatubo reservoir

USGS Publications Warehouse

Di, Muro A.; Pallister, J.; Villemant, B.; Newhall, C.; Semet, M.; Martinez, M.; Mariet, C.

2008-01-01

Before the 1991-1992 activity, a large andesite lava dome belonging to the penultimate Pinatubo eruptive period (Buag ??? 500??BP) formed the volcano summit. Buag porphyritic andesite contains abundant amphibole-bearing microgranular enclaves of basaltic-andesite composition. Buag enclaves have lower K2O and incompatible trace element (LREE, U, Th) contents than mafic pulses injected in the Pinatubo reservoir during the 1991-1992 eruptive cycle. This study shows that Buag andesite formed by mingling of a hot, water-poor and reduced mafic magma with cold, hydrous and oxidized dacite. Depending on their size, enclaves experienced variable re-equilibration during mixing/mingling. Re-equilibration resulted in hydration, oxidation and transfer of mobile elements (LILE, Cu) from the dacite to the mafic melts and prompted massive amphibole crystallization. In Buag enclaves, S-bearing phases (sulfides, apatite) and melt inclusions in amphibole and plagioclase record the evolution of sulfur partition among melt, crystal and fluid phases during magma cooling and oxidation. At high temperature, sulfur is partitioned between andesitic melt and sulfides (Ni-pyrrhotite). Magma cooling, oxidation and hydration resulted in exsolution of a S-Cl-H2O vapor phase at the S-solubility minimum near the sulfide-sulfate redox boundary. Primary magmatic sulfide (pyrrhotite) and xenocrystic sulfide grains (pyrite), recycled together with olivines and pyroxenes from old mafic intrusives, were replaced by Cu-rich phases (chalcopyrite, cubanite) and, partially, by Ba-Sr sulfate. Sulfides degassed and transformed into residual spongy magnetite in response to fS2 drop during final magma ascent and decompression. Our research suggests that a complete evaluation of the sulfur budget at Pinatubo must take into account the en route S assimilation from the country rocks. Moreover, this study shows that the efficiency of sulfur transfer between mafic recharges and injected magmas is controlled by the extent and rate of mingling, hydrous flushing and melt oxidation. Vigorous mixing/mingling and transformation of the magmatic recharge into a spray of small enclaves is required in order to efficiently strip their primary S-content that otherwise remains locked in the sulfides. Hydrous flushing increases the magma oxidation state of the recharges and modifies their primary volatile concentrations that cannot be recovered by the study of late-formed mineral phases and melt inclusions. Conversely, S stored in both late-formed Cu-rich sulfides and interstitial rhyolitic melt represents the pre-eruptive sulfur budget immediately available for release from mafic enclaves during their decompression. ?? 2008 Elsevier B.V.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McKinstry, Craig A.; Carlson, Thomas J.; Brown, Richard S.

In 2005 the U.S. Army Corps of Engineers (USACE) began a study to investigate the response of hatchery and run-of-the-river (ROR) juvenile Chinook salmon to the effects of rapid decompression during passage through mainstem Federal Columbia River Power System (FCRPS) Kaplan turbines. In laboratory studies conducted by Pacific Northwest National Laboratory (PNNL) for USACE since 2005, juvenile fish have been exposed to rapid decompression in a barometric pressure chamber. An initial study considered the response of juvenile Chinook salmon bearing radio transmitters to rapid decompression resulting from exposure to a pressure time history simulating the worst case condition that mightmore » be experienced during passage through an operating turbine. The study in 2005 found that acclimation depth was a very important treatment factor that greatly influenced the significantly higher incidence of injury and mortality of rapidly decompressed Chinook salmon bearing radio telemetry devices. In 2006 we initiated a statistical investigation using data in hand into derivation of a new end-point measure for assessment of the physiological response of juvenile Chinook salmon to rapid decompression. Our goal was a measure that would more fully utilize both mortality and injury data while providing a better assessment of the most likely survival outcome for juvenile physostomous fish exposed to rapid decompression. The conclusion of the analysis process was to classify fish as mortally injured when any of the 8 injuries are present, regardless of whether the fish was last observed alive or not. The mortally injured classification has replaced mortality as the end point metric for our rapid decompression studies. The process described in this report is an example of how a data set may be analyzed to identify decision criterion for objective classification of test fish to a specific end-point. The resulting list of 8 mortal injuries is applicable to assess injuries from rapid decompression and is currently being applied to ongoing studies. We intend to update this analysis as more data becomes available and to extend it to ROR Chinook salmon smolt. The method itself is applicable to other injury and mortality data for juvenile salmonids from laboratory and field studies related to all dam passage routes and for collision, strike, and shear injuries in addition to decompression.« less

Scuba diving accidents.

PubMed

Dembert, M L

1977-08-01

The principal scuba diving medical problems of barotrauma, air embolism and decompression sickness have as their pathophysiologic basis the Ideal Gas Law and Boyle's Law. Hyperbaric chamber recompression therapy is the only definitive treatment of air embolism and decompression sickness. However, with a basic knowledge of diving medicine, the family physician can provide effective supportive care to the patient prior to initiation of hyperbaric therapy.

The role of superheating in the formation of Glass Mountain obsidians (Long Valley, CA) inferred through crystallization of sanidine

NASA Astrophysics Data System (ADS)

Waters, Laura E.; Andrews, Benjamin J.

2016-10-01

The Glass Mountain obsidians (Long Valley, CA) are crystal poor (<8 vol%) and highly evolved (high SiO2, low Sr), and therefore, their formation required extremely efficient separation of melts from a crystal-rich source. A petrologic and experimental investigation of the mineral phases in Glass Mountain lavas identifies conditions under which phenocrysts grew and the driving mechanism for crystallization, which places constraints on the possible processes that generated the obsidians. The obsidian in this study (GM-11) is saturated in nine phases (sanidine + quartz + plagioclase + titanomagnetite + ilmenite + zircon + apatite + allanite + biotite), and results of high-resolution SEM compositional mapping and electron microprobe analysis reveal that individual sanidine crystals are normally zoned and span a range of compositions (Or40-78). Sanidines have a "granophyric" texture, characterized by intergrowths of quartz and sanidine. Mineral phases in the natural sample are compared to H2O-saturated phase equilibrium experiments conducted in cold-seal pressure vessels, over a range of conditions (700-850 °C; 75-225 MPa), and all are found to be plausible phenocrysts. Comparison of sanidine compositions from the natural sample with those grown in phase equilibrium experiments demonstrates that sanidine in the natural sample occurs in a reduced abundance. Further comparison with phase equilibrium experiments suggests that sanidine compositions track progressive loss of dissolved melt water (±cooling), suggesting that crystallization in the natural obsidian was driven predominantly by degassing resulting from decompression. It is paradoxical that an effusively (slowly) erupted lava should contain multiple phenocryst phases, including sanidine crystals that span a range of compositions with granophyric textures, and yet remain so crystal poor. To resolve this paradox, it is necessary that the solidification mechanism (degassing or cooling) that produced the sanidine crystals (and other mineral phases) must have an associated kinetic effect(s) that efficiently hinders crystal nucleation and growth. Decompression experiments conducted in this study and from the literature collectively demonstrate that the simplest way to inhibit nucleation during degassing-induced crystallization is to initiate degassing ± cooling from superliquidus conditions, and therefore, the Glass Mountain obsidians were superheated prior to crystallization.

ORACLE Stroke Study: Opinion Regarding Acceptable Outcome Following Decompressive Hemicraniectomy for Ischemic Stroke.

PubMed

Honeybul, Stephen; Ho, Kwok M; Blacker, David W

2016-08-01

There continues to be considerable interest in the use of decompressive hemicraniectomy in the management of malignant cerebral artery infarction; however, concerns remain about long-term outcome. To assess opinion on consent and acceptable outcome among a wide range of healthcare workers. Seven hundred seventy-three healthcare workers at the 2 major public neurosurgical centers in Western Australia participated. Participants were asked to record their opinion on consent and acceptable outcome based on the modified Rankin Score (mRS). The evidence for clinical efficacy of the procedure was presented, and participants were then asked to reconsider their initial responses. Of the 773 participants included in the study, 407 (52.7%) initially felt that they would provide consent for a decompressive craniectomy as a lifesaving procedure, but only a minority of them considered an mRS score of 4 or 5 an acceptable outcome (for mRS score ≤4, n = 67, 8.7%; for mRS score = 4, n = 57, 7.4%). After the introduction of the concept of the disability paradox and the evidence for the clinical efficacy of decompressive craniectomy, more participants were unwilling to accept decompressive craniectomy (18.1% vs 37.8%), but at the same time, more were willing to accept an mRS score ≤4 as an acceptable outcome (for mRS score ≤4, n = 92, 11.9%; for mRS score = 4, n = 79, 10.2%). Most participants felt survival with dependency to be unacceptable. However, many would be willing to provide consent for surgery in the hopes that they may survive with some degree of independence. DESTINY, Decompressive Surgery for the Treatment of Malignant Infarction of the Middle Cerebral ArterymRS, modified Rankin Scale.

Vulnerability of larval and juvenile white sturgeon to barotrauma: can they handle the pressure?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Richard S.; Cook, Katrina V.; Pflugrath, Brett D.

2013-07-01

Techniques were developed to determine which life stages of fish are vulnerable to barotrauma from expansion of internal gases during decompression. Eggs, larvae and juvenile hatchery-reared white sturgeon (Acipenser transmontanus; up to 91 days post hatch; dph), were decompressed to assess vulnerability to barotrauma and identify initial swim bladder inflation. Barotrauma related injury and mortality were first observed 9 dph, on the same day as initial exogenous feeding. However, barotrauma related injury did not occur again until swim bladder inflation 75 dph (visible from necropsy and x-ray radiographs). Swim bladder inflation was not consistent among individuals, with only 44% beingmore » inflated 91 dph. Additionally, swim bladder inflation did not appear to be size dependent among fish ranging in total length from 61-153 mm at 91 dph. The use of a combination of decompression tests and x-ray radiography was validated as a method to determine initial swim bladder inflation and vulnerability to barotrauma. Extending these techniques to other species and life history stages would help to determine fish susceptibility to hydroturbine passage and aid in fish conservation.« less

Incorporation of cooling-induced crystallization into a 2-dimensional axisymmetric conduit heat flow model

NASA Astrophysics Data System (ADS)

Heptinstall, David; Bouvet de Maisonneuve, Caroline; Neuberg, Jurgen; Taisne, Benoit; Collinson, Amy

2016-04-01

Heat flow models can bring new insights into the thermal and rheological evolution of volcanic 3 systems. We shall investigate the thermal processes and timescales in a crystallizing, static 4 magma column, with a heat flow model of Soufriere Hills Volcano (SHV), Montserrat. The latent heat of crystallization is initially computed with MELTS, as a function of pressure and temperature for an andesitic melt (SHV groundmass starting composition). Three fractional crystallization simulations are performed; two with initial pressures of 34MPa (runs 1 & 2) and one of 25MPa (run 3). Decompression rate was varied between 0.1MPa/° C (runs 1 & 3) and 0.2MPa/° C (run 2). Natural and experimental matrix glass compositions are accurately reproduced by all MELTS runs. The cumulative latent heat released for runs 1, 2 and 3 differs by less than 9% (8.69E5 J/kg*K, 9.32E5 J/kg*K, and 9.49E5 J/kg*K respectively). The 2D axisymmetric conductive cooling simulations consider a 30m-diameter conduit that extends from the surface to a depth of 1500m (34MPa). The temporal evolution of temperature is closely tracked at depths of 10m, 750m and 1400m in the centre of the conduit, at the conduit walls, and 20m from the walls into the host rock. Following initial cooling by 7-15oC at 10m depth inside the conduit, the magma temperature rebounds through latent heat release by 32-35oC over 85-123 days to a maximum temperature of 1002-1005oC. At 10m depth, it takes 4.1-9.2 years for the magma column to cool by 108-131oC and crystallize to 75wt%, at which point it cannot be easily remobilized. It takes 11-31.5 years to reach the same crystallinity at 750-1400m depth. We find a wide range in cooling timescales, particularly at depths of 750m or greater, attributed to the initial run pressure and the dominant latent heat producing crystallizing phase, Albite-rich Plagioclase Feldspar. Run 1 is shown to cool fastest and run 3 cool the slowest, with surface emissivity having the strongest cooling influence in the upper tens of meters of the conduit in all runs.

Incorporation of cooling-induced crystallisation into a 2-dimensional axisymmetric conduit heat flow model

NASA Astrophysics Data System (ADS)

Heptinstall, D. A.; Neuberg, J. W.; Bouvet de Maisonneuve, C.; Collinson, A.; Taisne, B.; Morgan, D. J.

2015-12-01

Heat flow models can bring new insights into the thermal and rheological evolution of volcanic systems. We shall investigate the thermal processes and timescales in a crystallizing, static magma column, with a heat flow model of Soufriere Hills Volcano (SHV), Montserrat. The latent heat of crystallization is initially computed with MELTS, as a function of pressure and temperature for an andesitic melt (SHV groundmass starting composition). Three fractional crystallization simulations are performed; two with initial pressures of 34MPa (runs 1 & 2) and one of 25MPa (run 3). Decompression rate was varied between 0.1MPa/°C (runs 1 & 3) and 0.2MPa/°C (run 2). Natural and experimental matrix glass compositions are accurately reproduced by all MELTS runs. The cumulative latent heat released for runs 1, 2 and 3 differs by less than 9% (8.69e5 J/kg*K, 9.32e5 J/kg*K, and 9.49e5 J/kg*K respectively). The 2D axisymmetric conductive cooling simulations consider a 30m-diameter conduit that extends from the surface to a depth of 1500m (34MPa). The temporal evolution of temperature is closely tracked at depths of 10m, 750m and 1400m in the center of the conduit, at the conduit walls, and 20m from the walls into the host rock. Following initial cooling by 7-15oC at 10m depth inside the conduit, the magma temperature rebounds through latent heat release by 32-35oC over 85-123 days to a maximum temperature of 1002-1005oC. At 10 m depth, it takes 4.1-9.2 years for the magma column to cool over 108-130oC and crystallize to 75wt%, at which point it cannot be easily remobilized. It takes 11-31.5 years to reach the same crystallinity at 750-1400m depth. We find a wide range in cooling timescales, particularly at depths of 750m or greater, attributed to the initial run pressure and dominant latent heat producing crystallizing phases (Quartz), where run 1 cools fastest and run 3 cools slowest. Surface cooling by comparison has the strongest influence on the upper tens of meters in all runs.

The Magmatic Budget of Rifted Margins: is it Related to Inheritance?

NASA Astrophysics Data System (ADS)

Manatschal, G.; Tugend, J.; Gillard, M.; Sauter, D.

2017-12-01

High quality reflection and refraction seismic surveys show a divergent style of margin architecture often referred to as magma-poor or magma-rich. More detailed studies show, however, that the evolution of these margins can be similar, despite the variable quantity and distribution of magmatism. These observations suggest that simple relations between magmatic and extensional systems are inappropriate to describe the magmatic history of rifted margins. Moreover, the study of magmatic additions indicates that they may occur, prior to, during or after lithospheric breakup. Furthermore, the observation that the magmatic budget may change very abruptly along strike and across the margin is difficult to reconcile with the occurrence of plumes or other deep-seated large-scale mantle phenomena only. These overall observations result in questions on how magmatic and tectonic processes are interacting during rifting and lithospheric breakup and on how far the inherited composition and temperature of the decompressing mantle may control the magmatic budget during rifting. In our presentation we will review examples from present-day and fossil rifted margins to discuss their structural and magmatic evolution and whether they are considered as magma-rich or magma-poor. The key questions that we aim to address are: 1) whether decompression melting is the driving force, or rather the consequence of extension, 2) how far the magmatic budget is controlled by inherited mantle composition and temperature, and 3) how important magma storage is during initial stages of rifting. Eventually, we will discuss to what extent the evolution of margins may reflect the interplay between inheritance (innate/"genetic code") and the actual physical processes (acquired/external factors).

Metamorphic P-T conditions and CO2 influx history of medium-grade metapelites from Karakorum, Trans-Himalaya, India

NASA Astrophysics Data System (ADS)

Sachan, Himanshu K.; Santosh, M.; Prakash, Divya; Kharya, Aditya; Chandra Singh, P.; Rai, Santosh K.

2016-07-01

The medium grade metapelites of Pangong-Tso area in the trans-Himalayan region underwent sillimanite-grade metamorphism initiated during the Cretaceous, associated with the collision of the Kohistan arc and the Indian plate with Asia. This paper present results from a petrological and fluid inclusion study to understand the metamorphic P-T conditions and fluid history of these rocks. The calculated phase equilibria in the Na2O-CaO-K2O-FeO-MgO-MnO-Al2O3-SiO2-H2O-TiO2 (NCKFMMnASHT) system suggest P-T conditions of 8 kbar and 650 °C for the peak metamorphic event. Primary fluid inclusions occur in staurolite and garnet, whereas quartz carries mostly secondary fluid inclusions. The trapped fluids in primary inclusions show initial melting temperatures in the range of -56.9 to -56.6 °C, suggesting nearly pure CO2 composition. The secondary fluids are of mixed carbonic-aqueous nature. The re-equilibrated inclusions show annular morphology as well as necking phenomena. The CO2 isochores for the primary inclusions indicate pressures of 6.1-6.7 kbar, suggesting that the CO2-rich fluids were trapped during post-peak exhumation of the rocks, or that synmetamorphic carbonic fluids underwent density reversal during isothermal decompression. The secondary CO2-H2O fluids must have been trapped during the late exhumation stage, as their isochores define further lower pressures of 4.8 kbar. The morphology of re-equilibrated fluid inclusions and the rapid decrease in pressure are consistent with a near-isothermal decompression trajectory following the peak metamorphism. The carbonic fluids were probably derived locally from decarbonation reactions of the associated carbonate rocks during metamorphism or from a deep-seated reservoir through Karakorum fault.

Paleocene Picrites of Davis Strait: Products of a Plume or Plates?

NASA Astrophysics Data System (ADS)

Beutel, E. K.; Clarke, D. B.

2017-12-01

Voluminous, subaerial, ultra-depleted, 62 Ma, primary picritic lavas occur on both sides of Davis Strait separating Baffin Island and West Greenland. Temporally, the picrites are coeval with the initiation of sea-floor spreading in Labrador Sea and Baffin Bay around 62 Ma. Petrogenetically, the chemical characteristics of these picrites (MgO = 18-21 wt. %; K2O = 0.01-0.20 wt. %; 87Sr/86Sri ≈ 0.7030; ɛNdi ≈ +5.2-8.6; 3He/4He ≤ 49.5RA) demand only derivation by partial melting of highly depleted subcontinental lithospheric mantle (SCLM) at a pressure of 4 GPa, followed by rapid ascent to the surface, but do not necessarily require high temperatures or high degrees of partial melting. Tectonically, these picrites formed in thick Archean and Paleoproterozoic cratonic terranes during Paleogene rifting between Greenland and North America. Structurally, the picrites are related to the major intersection of a NNW suture zone under Baffin Bay and the E-W trending Paleoproterozoic Nagssugtoqidian Fold Belt. During the late Mesozoic, ENE extension created normal faulted basins quasi-parallel with the NNW suture and thinned the mantle lithosphere. Elastic finite element models and present day studies of crustal extension show that the thicker Nagssugtoqidian Fold Belt underwent less thinning and extension than the NNW suture zone in the Archean Rae craton. These extensional disparities occur at the orthogonal intersection of pre-existing E-W trending strike-slip faults in the thicker Nagssugtoqidian Fold Belt with the NNW thinned Archean suture zone, and likely resulted in the formation of one or more pull-apart basins. Because the strike-slip faults are ancient suture zones, trans-tension within these suture zones easily reached 120 km, creating not only decompression melting in the SCLM, but also a pathway for the picritic melts to rapidly reach the surface. Such a purely tectonic model requires no spatially or temporally improbable deep mantle plume for generation of the Paleocene picrites of Davis Strait.

On the time-scales of magmatism at island-arc volcanoes.

PubMed

Turner, S P

2002-12-15

Precise information on time-scales and rates of change is fundamental to an understanding of natural processes and the development of quantitative physical models in the Earth sciences. U-series isotope studies are revolutionizing this field by providing time information in the range 10(2)-10(4) years, which is similar to that of many modern Earth processes. I review how the application of U-series isotopes has been used to constrain the time-scales of magma formation, ascent and storage beneath island-arc volcanoes. Different elements are distilled-off the subducting plate at different times and in different places. Contributions from subducted sediments to island-arc lava sources appear to occur some 350 kyr to 4 Myr prior to eruption. Fluid release from the subducting oceanic crust into the mantle wedge may be a multi-stage process and occurs over a period ranging from a few hundred kyr to less than one kyr prior to eruption. This implies that dehydration commences prior to the initiation of partial melting within the mantle wedge, which is consistent with recent evidence that the onset of melting is controlled by an isotherm and thus the thermal structure within the wedge. U-Pa disequilibria appear to require a component of decompression melting, possibly due to the development of gravitational instabilities. The preservation of large (226)Ra disequilibria permits only a short period of time between fluid addition and eruption. This requires rapid melt segregation, magma ascent by channelled flow and minimal residence time within the lithosphere. The evolution from basalt to basaltic andesite probably occurs rapidly during ascent or in magma reservoirs inferred from some geophysical data to lie within the lithospheric mantle. The flux across the Moho is broadly andesitic, and some magmas subsequently stall in more shallow crustal-level magma chambers, where they evolve to more differentiated compositions on time-scales of a few thousand years or less.

Complicated Pseudomeningocele Repair After Chiari Decompression: Case Report and Review of the Literature.

PubMed

De Tommasi, Claudio; Bond, Aaron E

2016-04-01

Pseudomeningocele is a recognised complication after posterior fossa decompression for Chiari malformation. Its management can be challenging and treatment options vary in literature. A difficult-to-treat case of a pseudomeningocele after posterior fossa decompression for a Chiari I malformation is presented. A 34-year-old woman underwent an initial decompression followed by multiple revision surgeries after the development of a symptomatic pseudomeningocele and a low-grade infection. Complications associated with standard treatment modalities, including lumbar drainage and dural repair, are discussed. A review of the existing literature is presented. The reported case ultimately required complete removal of all dural repair materials to eliminate the patient's low-grade infection, a muscular flap, and placement of a ventricular-peritoneal shunt for definitive treatment after a trial of a lumbar drain led to herniation and development of a syrinx. Copyright © 2016 Elsevier Inc. All rights reserved.

The Extended Oxygen Window Concept for Programming Saturation Decompressions Using Air and Nitrox

PubMed Central

Kot, Jacek; Sicko, Zdzislaw

2015-01-01

Saturation decompression is a physiological process of transition from one steady state, full saturation with inert gas at pressure, to another one: standard conditions at surface. It is defined by the borderline condition for time spent at a particular depth (pressure) and inert gas in the breathing mixture (nitrogen, helium). It is a delicate and long lasting process during which single milliliters of inert gas are eliminated every minute, and any disturbance can lead to the creation of gas bubbles leading to decompression sickness (DCS). Most operational procedures rely on experimentally found parameters describing a continuous slow decompression rate. In Poland, the system for programming of continuous decompression after saturation with compressed air and nitrox has been developed as based on the concept of the Extended Oxygen Window (EOW). EOW mainly depends on the physiology of the metabolic oxygen window—also called inherent unsaturation or partial pressure vacancy—but also on metabolism of carbon dioxide, the existence of water vapor, as well as tissue tension. Initially, ambient pressure can be reduced at a higher rate allowing the elimination of inert gas from faster compartments using the EOW concept, and maximum outflow of nitrogen. Then, keeping a driving force for long decompression not exceeding the EOW allows optimal elimination of nitrogen from the limiting compartment with half-time of 360 min. The model has been theoretically verified through its application for estimation of risk of decompression sickness in published systems of air and nitrox saturation decompressions, where DCS cases were observed. Clear dose-reaction relation exists, and this confirms that any supersaturation over the EOW creates a risk for DCS. Using the concept of the EOW, 76 man-decompressions were conducted after air and nitrox saturations in depth range between 18 and 45 meters with no single case of DCS. In summary, the EOW concept describes physiology of decompression after saturation with nitrogen-based breathing mixtures. PMID:26111113

Geochemistry, petrology and geodynamic setting of the Urumieh plutonic complex, Sanandaj-Sirjan zone, NW Iran: New implication for Arabian and Central Iranian plate collision

NASA Astrophysics Data System (ADS)

Jafari, Amin; Fazlnia, Abdolnaser; Jamei, Susan

2018-03-01

The Urumieh plutonic complex, in the northernmost part of Sanandaj-Sirjan zone (SSZ) of Iran, consists of ten basic-acidic units which formed in response to subduction and continental collision of the SSZ with the Arabian plate to the south during Mid-Late Cretaceous times. Geochemically, the plutonic unit is divided into three distinct groups: I-type, S-type and A-type that mainly belong to calc-alkalic series. The I-type intrusions, especially mafic members, are enriched in LREE and LILE and possibly formed from metasomatized mantle wedge during the subduction of the Neo-Tethys oceanic crust beneath the SSZ. The felsic I-type rocks are depleted in Ba, Sr, Nb, Ta, Ti and Eu, but enriched in Rb, Th, K, Ce, U and La. These data suggest that they formed in deep crustal levels via partial melting of crustal sources by injection of hot mantle magmas. The S-type rocks are characterized by low Na2O (<3.02 wt%), high LILE, relatively high values of molar Al2O3/(MgO+FeO) and K2O/Na2O ratios combined with low CaO/(MgO+FeO*) ratios. These features show that the S-type granites originated from partial melting of a metapelitic to metagreywacke source. The A-type alkali feldspar granites formed through the slab break off after the continental collision in northwestern Iran by decompression melting of crustal protolith. The author's new model implies that collision between Arabian margin and north SSZ initiated in the Late Cretaceous and completed until Late Paleocene. In contrast, in the southeast, subduction was active during this period of time, but collision presumably occurred during the Middle to Late Miocene.

Basement Basalts from IODP Site 1438, Amami-Sankaku Basin: Implications for Sources and Melting Processes during Subduction Initiation in the Izu-Bonin-Mariana System

NASA Astrophysics Data System (ADS)

McCarthy, A. J.; Hickey-Vargas, R.; Yogodzinski, G. M.; Ishizuka, O.; Hocking, B.; Bizimis, M.; Savov, I. P.; Kusano, Y.; Arculus, R. J.

2016-12-01

IODP Expedition 351 Site 1438 is located in the Amami-Sankaku basin, just west of the Kyushu-Palau Ridge (KPR), a remnant of the early Izu-Bonin-Mariana (IBM) volcanic arc. 150 meters of basement basalt were drilled beneath 1460 m of volcaniclastic sediments and sedimentary rock. The age range inferred for these basalts is 51-52 Ma, close to the 48-52 Ma age of basalts associated with subduction initiation in the IBM forearc (forearc basalts or FABs). Site 1438 basement basalts form several distinct subunits, all relatively mafic (MgO = 6-14 %; Mg# = 51-83). Non-fluid-mobile incompatible trace element patterns are profoundly depleted. Sm/Nd (0.34-0.43) and Lu/Hf (0.18-0.37) reach values higher than most normal MORBs while La/Yb (0.31-0.98) and Ti/V (15.8-27.0) are lower. These features are shared with basalts drilled just west of the KPR at ODP Site 1201 and DSDP Site 447, and many FABs. Abundances of fluid-mobile incompatible elements vary together and are correlated with subunits defined by flow margins and rock physical properties, suggesting control by post-eruptive seawater alteration rather than varying inputs of subduction fluids. Hf-Nd isotopes for Site 1438 basement basalts range from (present-day) ɛNd of 7.0 to 9.5 and ɛHf of 14.5 to 19.8 in a well-correlated array. Their more radiogenic Hf-isotope character could indicate an Indian-type MORB source, however, basalts with ɛHf >16.5, are more radiogenic than many Indian MORB. Pb isotope data will help distinguish differing mantle source domains and origins for fluid-mobile elements. Overall, the combined geochemical data indicate that the mantle source of basement basalts in drill sites west of the KPR (1438, 1201, 447) are closely similar to those for FAB, and that as a group, these rocks are more depleted than more than 90% of global MORB. Our interpretation is that both IBM forearc basalts and basalts from drill sites immediately west of the KPR formed by melting of the same uniquely depleted mantle source during subduction initiation. Melting may have been promoted by rapid decompression and by flux melting with a solute-poor hydrous subduction fluid. These basalts were erupted over a broad area in an extensional setting, which later narrowed as subduction and the subduction-related IBM volcanic arc became established.

Magmas with slab fluid and decompression melting signatures coexisting in the Gulf of Fonseca: Evidence from Isla El Tigre volcano (Honduras, Central America)

NASA Astrophysics Data System (ADS)

Mattioli, Michele; Renzulli, Alberto; Agostini, Samuele; Lucidi, Roberto

2016-01-01

Isla El Tigre volcano is located in the Gulf of Fonseca (Honduras) along the Central America volcanic front, where a significant change in the strike of the volcanic chain is observed. The studied samples of this poorly investigated volcano are mainly subalkaline basic to intermediate lavas (basalts and basaltic andesites) and subordinate subalkaline/alkaline transitional basalts, both having the typical mineralogical and geochemical characteristics of arc volcanic rocks. On the basis of petrographic and geochemical features, two groups of rocks have been distinguished. Lavas from the main volcanic edifice are highly porphyritic and hy-qz normative, and have lower MgO contents (< 5 wt.%). They show significant LILE and LREE enrichments and Nb-Ta depletions, and have a strong slab signature as well as incompatible element contents similar to those of the main front of the adjacent volcanoes in El Salvador and Nicaragua (e.g., Ba/La up to 80). In contrast, lavas from the parasitic cones have higher MgO contents (> 5 wt.%), are ol-hy normative and show lower HFSE depletions relative to LILE and LREE, with lower Ba/La, Ba/Nb and Zr/Nb ratios. This suggests that mantle-derived magmas were not produced by the same process throughout the activity of the volcano. The bulk rock geochemistry and 87Sr/86Sr (0.70373-0.70382), 143Nd/144Nd (0.51298-0.51301), 206Pb/204Pb (18.55-18.58), 207Pb/204Pb (15.54-15.56) and 208Pb/204Pb (38.23-38.26) isotopic data of Isla El Tigre compared with the other volcanoes of the Gulf of Fonseca and all available literature data for Central America suggests that this stratovolcano was mainly built by mantle-derived melts driven by slab-derived fluid-flux melting, while magmas erupted through its parasitic cones have a clear signature of decompression melting with minor slab contribution. The coexistence of these two different mantle melting generation processes is likely related to the complex geodynamic setting of the Gulf of Fonseca, where the volcanic front changes direction by ca. 30° and two fundamental tectonic structures of the Chortis continental block, mainly the N-S Honduras Depression and the NE-SW Guayape Fault Zone, cross each other.

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

NASA Astrophysics Data System (ADS)

Kamenetsky, Vadim S.; Yaxley, Gregory M.

2015-06-01

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.

Magma Dynamics at Mid-Ocean Ridges by Noble Gas Kinetic Fractionation: Assessment of Magmatic Ascent Rates and Mantle Composition

NASA Astrophysics Data System (ADS)

Paonita, A.; Martelli, M.

2007-12-01

Topical scientific literature on magma degassing at mid-ocean ridges more and more focuses on exsolution processes occurring under conditions that are far from thermodynamic equilibrium between bubbles and silicate melt. Indeed, the dynamics of magma ascent and decompression can be faster than that of CO2 diffusion into bubbles, in which case the diffusivity ratios among volatiles are the main control of the composition of the exsolving gas phase. We have developed a model of bubble growth in silicate melts that calculates the extent of both CO2 supersaturation and kinetic fractionation among noble gases in vesicles in relation to the decompressive rate of basaltic melts. The model predicts that, due to comparable Ar and CO2 diffusivity, magma degassing at low pressure fractionates both He/Ar and He/CO2 ratios by a similar extent, while the slower CO2 diffusion at high pressure causes early kinetic effects on Ar/CO2 ratio and dramatically changes the degassing paths. By using this tool, we have reviewed the global He-Ar-CO2 dataset of fluid inclusions in mid-ocean-ridge glasses. We display that non-equilibrium fractionations among He, Ar and CO2, driven by their different diffusivities in silicate melts, are common in most of the natural conditions of magma decompression and their signature strongly depends on pressure of degassing. The different geochemical signatures among suites of data coming from different ridge segments mainly depend on the depth of the magma chamber where the melt was stored. Moreover, variations inside a single suite emerge due to the interplay between variable ascent speed of magma and cooling rate of the emplaced lava. As a result, two data groups coming from the Pito Seamount suite (Easter Microplate East ridge), showing different degree of CO2 supersaturation and He/Ar fractionation, provide ascent rates which differ by ten folds or even more. The large variations in both the He/CO2 and Ar/CO2 ratios at almost constant He/Ar, displayed in products coming from the Mid-Atlantic Ridge 24°N segment and the Rodriguez Triple Junction, require magma storage and degassing processes occurring at high-pressure conditions. In contrast, the simultaneous increase in both He/CO2 and He/Ar of the East Pacific Rise and South-East Indian Ridge data sets suggests the dominance of low-pressure fractionation, implying that the shallow magma chambers are at a lower depth than those of the Mid-Atlantic Ridge 24°N and Rodriguez Triple Junction. Our conclusions support the presence of a relationship between spreading rate and depth of high-temperature zones below ridges, and are consistent with the depth of magma chambers as suggested from seismic studies. Finally, the non-equilibrium degassing model provides striking constraints on the compositions of noble gases and carbon in mantle-derived magmas. Our results dispense in fact with the supposed need for He-Ar-CO2 heterogeneities in the upper mantle, because the degassing of a single, popping-rock-like primary magma is able to explain all the available data.

Decompression sickness in a vegetarian diver: are vegetarian divers at risk? A case report.

PubMed

van Hulst, Robert A; van der Kamp, Wim

2010-01-01

We present a case of a diver who suffered decompression sickness (DCS), but who also was a strict vegetarian for more than 10 years. He presented with symptoms of tingling of both feet and left hand, weakness in both legs and sensory deficits for vibration and propriocepsis after two deep dives with decompression. The initial clinical features of this case were most consistent with DCS, possibly because of a vulnerable spinal cord due to cobalamin deficiency neuropathy. This case illustrates the similarities between DCS and a clinically defined vitamin B12 deficiency. The pathophysiology of vitamin B12 deficiency and common pathology and symptoms of DCS are reviewed.

Collision in the Central Alps: 1. Thermal Modelling

NASA Astrophysics Data System (ADS)

Engi, M.; Roselle, G. T.; Brouwer, F. M.; Berger, A.

2003-04-01

Recent tectonic reconstructions for the Central Alps, based in part on seismic profiles across of the orogen, have produced fairly robust kinematic scenarios for the Tertiary evolution. We have used these to set up 2D finite element models [1] to simulate the thermal evolution at orogenic scales. Results are helpful to understand the metamorphic and geochronological record in the Central Alps. Several features recognized as crucial in collisional orogens have been incorporated in our models: Adaptive grids are used to accommodate tectonic mass flow; properties of a tectonic accretion channel (TAC), situated near the footwall of the upper (Apulian) plate, are incorporated (TAC: 5-10 km wide [2]); a mobile fragment (pit: 5-10 km thick, 25-50 km long) at the plate interface is allowed to first be subducted, then to be extruded along the subduction channel to mid-crustal levels during the nappe stacking phase, and finally to be exhumed by backthrusting and erosion; partial melting and its thermal effects are computed. The thermal evolution in crucial parts of the model orogen is depicted in P-T and T-t trajectories, and in time slices showing the evolution of metamorphic facies and degrees of late partial melting. Comparison of simulation results with the regional distribution of (Eocene) high pressure fragments in the Lepontine Alps and of their (Oligo/Miocene) Barrovian overprint indicate that (a) decompression is near-isothermal along a very imited part of the path only; (b) the highest temperatures attained following collision do not reach the observed ˜700^oC unless the TAC is fairly radiogenic (heat production ge˜2 μW/m^3) or there is substantial heat advected by asthenospheric melts migrating up the subduction channel; (c) moderate amounts of partial melting occurred within the the TAC during decompression, following the assembly (at mid-crustal levels) of various crustal and mantle fragments with very diverse P-T-t histories. [1] Roselle et al. (2002) Amer. J. Sci. 302: 381-409 [2] Engi et al. (2001) Geology 29: 1143-1146

Resolving the potential mantle reservoirs that influence volcanism in the West Antarctic Rift System

NASA Astrophysics Data System (ADS)

Maletic, E. L.; Darrah, T.

2017-12-01

Lithospheric extension and magmatism are key characteristics of active continental rift zones and are often associated with long-lasting alkaline magmatic provinces. In these settings, a relationship between lithospheric extension and mantle plumes is often assumed for the forces leading to rift evolution and the existence of a plume is commonly inferred, but typically only extension is supported by geological evidence. A prime example of long-lasting magmatism associated with an extensive area of continental rifting is the West Antarctic Rift System (WARS), a 2000 km long zone of ongoing extension within the Antarctic plate. The WARS consists of high alkaline silica-undersaturated igneous rocks with enrichments in light rare earth elements (LREEs). The majority of previous geochemical work on WARS volcanism has focused on bulk classification, modal mineralogy, major element composition, trace element chemistry, and radiogenic isotopes (e.g., Sr, Nd, and Pb isotopes), but very few studies have evaluated volatile composition of volcanics from this region. Previous explanations for WARS volcanism have hypothesized a plume beneath Marie Byrd Land, decompression melting of a fossilized plume head, decompression melting of a stratified mantle source, and mixing of recycled oceanic crust with one or more enriched mantle sources from the deep mantle, though researchers are yet to reach a consensus. Unlike trace elements and radiogenic isotopes which can be recycled between the crust and mantle and which are commonly controlled by degrees of partial melting and prior melt differentiation, noble gases are present in low concentrations and chemically inert, allowing them to serve as reliable tracers of volatile sources and subsurface processes. Here, we present preliminary noble gas isotope (e.g., 3He/4He, CO2/3He, CH4/3He, 40Ar/36Ar, 40Ar*/4He) data for a suite of lava samples from across the WARS. By coupling major and trace element chemistry with noble gas elemental and isotopic composition and other volatiles from a suite of volcanic rocks in the WARS, we can better constrain a magmatic source and provide geological evidence that could support or oppose the existence of a mantle plume, HIMU plume, or deconvolve mantle-lithosphere interactions.

Vulnerability of larval and juvenile white sturgeon to barotrauma: can they handle the pressure?

PubMed

Brown, Richard S; Cook, Katrina V; Pflugrath, Brett D; Rozeboom, Latricia L; Johnson, Rachelle C; McLellan, Jason G; Linley, Timothy J; Gao, Yong; Baumgartner, Lee J; Dowell, Frederick E; Miller, Erin A; White, Timothy A

2013-01-01

Techniques were developed to determine which life stages of fish are vulnerable to barotrauma from expansion of internal gases during decompression. Eggs, larvae, and juvenile hatchery-reared white sturgeon (Acipenser transmontanus; up to 91 days post hatch; d.p.h.) were decompressed to assess vulnerability to barotrauma and identify initial swim bladder inflation. Barotrauma-related injury and mortality were first observed 9 d.p.h., on the same day as initial exogenous feeding. However, barotrauma-related injury did not occur again until swim bladder inflation 75 d.p.h. (visible at necropsy and on radiographs). Swim bladder inflation was not consistent among individuals, with only 44% being inflated 91 d.p.h. Additionally, swim bladder inflation did not appear to be size dependent among fish ranging in total length from 61 to 153 mm at 91 d.p.h. The use of a combination of decompression tests and radiography was validated as a method to determine initial swim bladder inflation and vulnerability to barotrauma. Extending these techniques to other species and life-history stages would help to determine the susceptibility of fish to hydro turbine passage and aid in fish conservation.

Vulnerability of larval and juvenile white sturgeon to barotrauma: can they handle the pressure?

PubMed Central

Brown, Richard S.; Cook, Katrina V.; Pflugrath, Brett D.; Rozeboom, Latricia L.; Johnson, Rachelle C.; McLellan, Jason G.; Linley, Timothy J.; Gao, Yong; Baumgartner, Lee J.; Dowell, Frederick E.; Miller, Erin A.; White, Timothy A.

2013-01-01

Techniques were developed to determine which life stages of fish are vulnerable to barotrauma from expansion of internal gases during decompression. Eggs, larvae, and juvenile hatchery-reared white sturgeon (Acipenser transmontanus; up to 91 days post hatch; d.p.h.) were decompressed to assess vulnerability to barotrauma and identify initial swim bladder inflation. Barotrauma-related injury and mortality were first observed 9 d.p.h., on the same day as initial exogenous feeding. However, barotrauma-related injury did not occur again until swim bladder inflation 75 d.p.h. (visible at necropsy and on radiographs). Swim bladder inflation was not consistent among individuals, with only 44% being inflated 91 d.p.h. Additionally, swim bladder inflation did not appear to be size dependent among fish ranging in total length from 61 to 153 mm at 91 d.p.h. The use of a combination of decompression tests and radiography was validated as a method to determine initial swim bladder inflation and vulnerability to barotrauma. Extending these techniques to other species and life-history stages would help to determine the susceptibility of fish to hydro turbine passage and aid in fish conservation. PMID:27293603

The Case against Mercury as the Angrite Parent Body (APB)

NASA Technical Reports Server (NTRS)

Hutson, M. L.; Ruzicka, A. M.; Mittlefehldt, D. W.

2007-01-01

Angrites are not plausibly from Mercury based on their high FeO contents and ancient ages (e.g., [1]). Rather, the early crystallization ages of angrites argues for a small asteroidal-sized parent body for these meteorites (e.g., [2]). Despite this, recently it has been proposed that Mercury is the APB [3, 4, 5, 6]. Preserved corona and symplectite textures and the presence of 120 triple junctions in NWA 2999 have been cited as requiring a planetary origin [3, 4], with the symplectites in NWA 2999 resulting from rapid decompression during uplift via thrust faults on Mercury [4], and the coronas during subsequent cooling at low pressure. Glasses along grain boundaries and exsolution lamellae possibly indicative of rapid melting and cooling in NWA 4950 are cited as evidence of rapid decompression [6]. To explain the discrepancy between spectral observations of the Mercurian surface and the high FeO contents in angrites, an early (4.5 Ga), collisionally-stripped FeO-rich basaltic surface has been suggested for Mercury [5, 6].

MRI Evaluation of Post Core Decompression Changes in Avascular Necrosis of Hip.

PubMed

Nori, Madhavi; Marupaka, Sravan Kumar; Alluri, Swathi; Md, Naseeruddin; Irfan, Kazi Amir; Jampala, Venkateshwarlu; Apsingi, Sunil; Eachempati, Krishna Kiran

2015-12-01

Avascular necrosis of hip typically presents in young patients. Core decompression in precollapse stage provides pain relief and preservation of femoral head. The results of core decompression vary considerably despite early diagnosis. The role of MRI in monitoring patients post surgically has not been clearly defined. To study pre and post core decompression MRI changes in avascular necrosis of hip. This is a contiguous observational cohort of 40 hips treated by core decompression for precollapse avascular necrosis of femoral head, who had a baseline MRI performed before surgery. Core decompression of the femoral head was performed within 4 weeks. Follow up radiograph and MRI scans were done at six months. Harris hip score preoperatively, 1 month and 6 months after the surgery was noted. Success in this study was defined as postoperative increase in Harris hip score (HHS) by 20 points and no additional femoral collapse. End point of clinical adverse outcome as defined by fall in Harris hip score was conversion or intention to convert to total hip replacement (THR). MRI parameters in the follow up scan were compared to the preoperative MRI. Effect of core decompression on bone marrow oedema and femoral head collapse was noted. Results were analysed using SPSS software version. Harris hip score improved from 57 to 80 in all patients initially. Six hips had a fall in Harris hip score to mean value of 34.1 during follow up (9 to 12 months) and underwent total hip replacement. MRI predictors of positive outcome are lesions with grade A extent, Grade A & B location. Bone marrow oedema with lesions less than 50% involvement, medial and central location. Careful selection of patients by MR criteria for core decompression provides satisfactory outcome in precollapse stage of avascular necrosis of hip.

Salvage C2 ganglionectomy after C2 nerve root decompression provides similar pain relief as a single surgical procedure for intractable occipital neuralgia.

PubMed

Pisapia, Jared M; Bhowmick, Deb A; Farber, Roger E; Zager, Eric L

2012-02-01

To determine the effectiveness of C2 nerve root decompression and C2 dorsal root ganglionectomy for intractable occipital neuralgia (ON) and C2 ganglionectomy after pain recurrence following initial decompression. A retrospective review was performed of the medical records of patients undergoing surgery for ON. Pain relief at the time of the most recent follow-up was rated as excellent (headache relieved), good (headache improved), or poor (headache unchanged or worse). Telephone contact supplemented chart review, and patients rated their preoperative and postoperative pain on a 10-point numeric scale. Patient satisfaction and disability were also examined. Of 43 patients, 29 were available for follow-up after C2 nerve root decompression (n = 11), C2 dorsal root ganglionectomy (n = 10), or decompression followed by ganglionectomy (n = 8). Overall, 19 of 29 patients (66%) experienced a good or excellent outcome at most recent follow-up. Among the 19 patients who completed the telephone questionnaire (mean follow-up 5.6 years), patients undergoing decompression, ganglionectomy, or decompression followed by ganglionectomy experienced similar outcomes, with mean pain reduction ratings of 5 ± 4.0, 4.5 ± 4.1, and 5.7 ± 3.5. Of 19 telephone responders, 13 (68%) rated overall operative results as very good or satisfactory. In the third largest series of surgical intervention for ON, most patients experienced favorable postoperative pain relief. For patients with pain recurrence after C2 decompression, salvage C2 ganglionectomy is a viable surgical option and should be offered with the potential for complete pain relief and improved quality of life (QOL). Copyright © 2012. Published by Elsevier Inc.

Inner Ear Damage during Decompression from Deep Dives 1975-1982.

DTIC Science & Technology

1984-01-01

was controlled and delivered by a computer-based system (PDP 11/04 computer; Digital Equipment Corp.). During training and testing, the animals were...decompression sickness. Initial trials with control animals had shown that the monkeys could withstand the Table 6 treatment .thout showing visible...observed shortly after the dive (Fig. 3). In this regard, the amount of exudate is similar to that observed in control animals. Moreover, bone and/or

Confort 15 model of conduit dynamics: applications to Pantelleria Green Tuff and Etna 122 BC eruptions

NASA Astrophysics Data System (ADS)

Campagnola, S.; Romano, C.; Mastin, L. G.; Vona, A.

2016-06-01

Numerical simulations are useful tools to illustrate how flow parameters and physical processes may affect eruption dynamics of volcanoes. In this paper, we present an updated version of the Conflow model, an open-source numerical model for flow in eruptive conduits during steady-state pyroclastic eruptions (Mastin and Ghiorso in A numerical program for steady-state flow of magma-gas mixtures through vertical eruptive conduits. U.S. Geological Survey Open File Report 00-209, 2000). In the modified version, called Confort 15, the rheological constraints are improved, incorporating the most recent constitutive equations of both the liquid viscosity and crystal-bearing rheology. This allows all natural magma compositions, including the peralkaline melts excluded in the original version, to be investigated. The crystal-bearing rheology is improved by computing the effect of strain rate and crystal shape on the rheology of natural magmatic suspensions and expanding the crystal content range in which rheology can be modeled compared to the original version ( Conflow is applicable to magmatic mixtures with up to 30 vol% crystal content). Moreover, volcanological studies of the juvenile products (crystal and vesicle size distribution) of the investigated eruption are directly incorporated into the modeling procedure. Vesicle number densities derived from textural analyses are used to calculate, through Toramaru equations, maximum decompression rates experienced during ascent. Finally, both degassing under equilibrium and disequilibrium conditions are considered. This allows considerations on the effect of different fragmentation criteria on the conduit flow analyses, the maximum volume fraction criterion ("porosity criterion"), the brittle fragmentation criterion and the overpressure fragmentation criterion. Simulations of the pantelleritic and trachytic phases of the Green Tuff (Pantelleria) and of the Plinian Etna 122 BC eruptions are performed to test the upgrades in the Confort 15 modeling. Conflow and Confort 15 numerical results are compared analyzing the effect of viscosity, decompression rate, temperature, fragmentation criteria (critical strain rate, porosity and overpressure criteria) and equilibrium versus disequilibrium degassing in the magma flow along volcanic conduits. The equilibrium simulation results indicate that an increase in viscosity, a faster decompression rate, a decrease in temperature or the application of the porosity criterion in place of the strain rate one produces a deepening in fragmentation depth. Initial velocity and mass flux of the mixture are directly correlated with each other, inversely proportional to an increase in viscosity, except for the case in which a faster decompression rate is assumed. Taking into account up-to-date viscosity parameterization or input faster decompression rate, a much larger decrease in the average pressure along the conduit compared to previous studies is recorded, enhancing water exsolution and degassing. Disequilibrium degassing initiates only at very shallow conditions near the surface. Brittle fragmentation (i.e., depending on the strain rate criterion) in the pantelleritic Green Tuff eruption simulations is mainly a function of the initial temperature. In the case of the Etna 122 BC Plinian eruption, the viscosity strongly affects the magma ascent dynamics along the conduit. Using Confort 15, and therefore incorporating the most recent constitutive rheological parameterizations, we could calculate the mixture viscosity increase due to the presence of microlites. Results show that these seemingly low-viscosity magmas can explosively fragment in a brittle manner. Mass fluxes resulting from simulations which better represent the natural case (i.e., microlite-bearing) are consistent with values found in the literature for Plinian eruptions (~106 kg/s). The disequilibrium simulations, both for Green Tuff and Etna 122 BC eruptions, indicate that overpressure sufficient for fragmentation (if present) occurs only at very shallow conditions near the surface.

Rapakivi texture formation via disequilibrium melting in a contact partial melt zone, Antarctica

NASA Astrophysics Data System (ADS)

Currier, R. M.

2017-12-01

In the McMurdo Dry Valleys of Antarctica, a Jurassic aged dolerite sill induced partial melting of granite in the shallow crust. The melt zone can be traced in full, from high degrees of melting (>60%) along the dolerite contact, to no apparent signs of melting, 10s of meters above the contact. Within this melt zone, the well-known rapakivi texture is found, arrested in various stages of development. High above the contact, and at low degrees of melting, K-feldspar crystals are slightly rounded and unmantled. In the lower half of the melt zone, mantles of cellular textured plagioclase appear on K-feldspar, and thicken towards the contact heat source. At the highest degrees of melting, cellular-textured plagioclase completely replaces restitic K-feldspar. Because of the complete exposure and intact context, the leading models of rapakivi texture formation can be tested against this system. The previously proposed mechanisms of subisothermal decompression, magma-mixing, and hydrothermal exsolution all fail to adequately describe rapakivi generation in this melt zone. Preferred here is a closed system model that invokes the production of a heterogeneous, disequilibrium melt through rapid heating, followed by calcium and sodium rich melt reacting in a peritectic fashion with restitic K-feldspar crystals. This peritectic reaction results in the production of plagioclase of andesine-oligoclase composition—which is consistent with not just mantles in the melt zone, but globally as well. The thickness of the mantle is diffusion limited, and thus a measure of the diffusive length scale of sodium and calcium over the time scale of melting. Thermal modeling provides a time scale of melting that is consistent with the thickness of observed mantles. Lastly, the distribution of mantled feldspars is highly ordered in this melt zone, but if it were mobilized and homogenized—mixing together cellular plagioclase, mantled feldspars, and unmantled feldspars—the result would be akin to rapakivi granites observed globally in Proterozoic systems. In essence, the melt zone is an embryonic rapakivi granite; not yet fully developed and displaying clear ties to its parental rock.

Multiscale Behavior of Viscous Fluids Dynamics: Experimental Observations

NASA Astrophysics Data System (ADS)

Arciniega-Ceballos, Alejandra; Spina, Laura; Scheu, Bettina; Dingwell, Donald B.

2016-04-01

The dynamics of Newtonian fluids with viscosities of mafic to intermediate silicate melts (10-1000 Pa s) during slow decompression present multi-time scale processes. To observe these processes we have performed several experiments on silicon oil saturated with Argon gas for 72 hours, in a Plexiglas autoclave. The slow decompression, dropping from 10 MPa to ambient pressure, acting as the excitation mechanism, triggered several processes with their own distinct timescales. These processes generate complex non-stationary microseismic signals, which have been recorded with 7 high-dynamic piezoelectric sensors located along the conduit flanked by high-speed video recordings. The analysis in time and frequency of these time series and their correlation with the associated high-speed imaging enables the characterization of distinct phases and the extraction of the individual processes during the evolution of decompression of these viscous fluids. We have observed fluid-solid elastic interaction, degassing, fluid mass expansion and flow, bubble nucleation, growth, coalescence and collapse, foam building and vertical wagging. All these processes (in fine and coarse scales) are sequentially coupled in time, occur within specific pressure intervals, and exhibit a localized distribution along the conduit. Their coexistence and interactions constitute the stress field and driving forces that determine the dynamics of the conduit system. Our observations point to the great potential of this experimental approach in the understanding of volcanic conduit dynamics and volcanic seismicity.

Arthroscopic-assisted core decompression of the humeral head.

PubMed

Dines, Joshua S; Strauss, Eric J; Fealy, Stephen; Craig, Edward V

2007-01-01

Humeral head osteonecrosis is a progressive disease that requires prompt diagnosis and treatment. Core decompression is a viable treatment option for early-stage cases. Most surgeons perform core decompression by arthroscopically visualizing the necrotic area of bone and using a cannulated drill to take a core. Several attempts are frequently needed to reach the proper location. In the hip multiple passes are associated with complications. We describe the use of an anterior cruciate ligament (ACL) tibial drill guide to precisely localize the area of necrotic bone. Diagnostic arthroscopy is performed to assess the areas of osteonecrosis. Core decompression is performed by use of an ACL tibial guide, brought in through the anterior or posterior portal to precisely localize the necrotic area in preparation for drilling. Under image intensification, Steinmann pins are advanced into the area of osteonecrosis. Once positioned, several 4-mm cores are made. We treated 3 patients with this technique, and all had immediate pain relief. The use of the ACL guide allows precise localization of the area of humeral head involvement and avoids multiple drillings into unaffected areas. Initial indications are that arthroscopic-assisted core decompression with an ACL guide is an effective alternative to previously used methods.

The Role of Garnet Pyroxenite in High-Fe Mantle Melt Generation: High Pressure Melting Experiments

NASA Astrophysics Data System (ADS)

Tuff, J.; Takahashi, E.; Gibson, S.

2004-12-01

Evidence for the existence of heterogeneous or 'marble cake' convecting mantle1 is provided recently by rare, high MgO ( ˜ 15 wt.%) primitive magmas with anomalously high abundances of FeO* ( ˜ 13.5 to 16 wt. %2,3; where FeO* = total Fe as FeO). These high-Fe mantle melts show a limited occurrence in the initial stage of magmatism in large igneous provinces (e.g. Deccan, Ethiopia and Paraná-Etendeka) and some have incompatible trace-element and radiogenic-isotopic ratios (Sr, Nd and Pb) that resemble those of ocean-island basalts. This suggests that they are predominantly derived from the convecting mantle2. The ferropicrites are mildly- to sub-alkaline and have low contents of Al2O3 (< 10 wt.%) and heavy rare-earth elements (e.g. Lu < 0.18ppm) that are consistent with the increased stability of garnet, due to the high FeO* content in the ferropicrite mantle source. It has been proposed that the source of the high FeO* may be garnet-pyroxenite streaks derived from subducted mafic oceanic crust2. We have undertaken melting experiments between 1 atmosphere and 7 GPa in order to determine the anhydrous phase relations of an uncontaminated ferropicrite lava from the base of the Early-Cretaceous Paraná-Etendeka continental flood-basalt province. The sample has high contents of MgO ( ˜ 14.9 wt.%), FeO* (14.9 wt.%) and NiO (0.07 wt.%). Olivine phenocrysts have maximum Fo contents of 85 and are in equilibrium with the host rock, assuming a Kd of 0.32 and we believe that the sample is representative of a primary Fe-rich mantle plume derived melt. In total, 75 experimental runs were carried out. Melting phase relations as well as compositions and modal proportions of all coexisting phases were successfully determined in 60 run products. Phase relations indicate that the ferropicrite melt was generated either at ˜ 2.2 GPa from an olivine-pyroxene residue or ˜ 5 GPa from a garnet-pyroxene residue. A low bulk-rock Al2O3 content (9 wt.%) and high [Gd/Yb]n ratio (3.1) are consistent with residual garnet in the ferropicrite melt source and favour high-pressure melting of garnet-pyroxenite. The garnet pyroxenite may represent subducted oceanic lithosphere entrained by the upwelling Tristan mantle plume starting-head. During adiabatic decompression, intersection of the garnet pyroxenite solidus at ˜ 5 GPa would occur at mantle potential temperatures of ˜ 1550° C. Subsequent melting of peridotite at ˜ 4.5 GPa may be restricted by the thick overlying sub-continental lithosphere such that dilution of the garnet-pyroxenite component would be significantly less than in intra-plate oceanic settings. This model accounts for the limited occurrence of ferropicrite magma in the initial stage of continental large igneous provinces and its absence in ocean-island basalt successions. 1 Allègre et al., Philosophical Transactions of the Royal Society of London A297, 447-477 (1980). 2 Gibson et al., Earth and Planetary Science Letters 174, 355-374 (2000). 3 Gibson, Earth and Planetary Science Letters 195, 59-74 (2002).

Endoscopic transmaxillary transMüller's muscle approach for decompression of superior orbital fissure: a cadaveric study with illustrative case.

PubMed

Wang, Xiang; Li, Yi-Ming; Huang, Cheng-Guang; Liu, Hong-Chao; Li, Qing-Chu; Yu, Ming-Kun; Hou, Li-Jun

2014-03-01

In an effort to avoid the damage and inconvenience associated with transcranial approaches, we developed an endoscopic transmaxillary transMüller's muscle approach for decompression of the superior orbital fissure (SOF). The endoscopic transmaxillary transMüller's muscle route was performed in ten cadaveric heads. We measured important anatomic landmarks, and angles radiographically. This approach was initially attempted in one patient with traumatic superior orbital fissure syndrome (tSOFS). A maxillary antrostomy was carried out with a buccal sulcus incision. The sinus ostium and the course of infraorbital nerve were used as endoscopic anatomic landmarks. Then the inferior orbital fissure was drilled out, followed by separating the Müller's muscle. The periorbita were peeled off from the lateral wall, followed by the endoscope going along the periorbital space, until the lateral aspect of the SOF could be visualized. Decompression was successfully performed in all specimens. The initial clinical application justified this approach. The patient had an uneventful postoperative course and satisfactory recovery. This approach offers sufficient endoscopic visualization and reliable decompression of SOF. It avoids the need for brain retraction, temporalis muscle manipulation, or any external incision, and appears to be able to deliver satisfying aesthetic results as well as favourable functional recovery. Copyright © 2013 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.

Severe capillary leak syndrome after inner ear decompression sickness in a recreational scuba diver.

PubMed

Gempp, Emmanuel; Lacroix, Guillaume; Cournac, Jean-Marie; Louge, Pierre

2013-07-01

Post-decompression shock with plasma volume deficit is a very rare event that has been observed under extreme conditions of hypobaric and hyperbaric exposure in aviators and professional divers. We report a case of severe hypovolemic shock due to extravasation of plasma in a recreational scuba diver presenting with inner ear decompression sickness. Impaired endothelial function can lead to capillary leak with hemoconcentration and hypotension in severe cases. This report suggests that decompression-induced circulating bubbles may have triggered the endothelial damage, activating the classic inflammatory pathway of increased vascular permeability. This observation highlights the need for an accurate diagnosis of this potentially life-threatening condition at the initial presentation in the Emergency Department after a diving-related injury. An elevated hematocrit in a diver should raise the suspicion for the potential development of capillary leak syndrome requiring specific treatment using albumin infusion as primary fluid replacement. Copyright © 2013 Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goriely, S.; Chamel, N.; Pearson, J. M.

The rapid neutron-capture process, or r-process, is known to be of fundamental importance for explaining the origin of approximately half of the A>60 stable nuclei observed in nature. In recent years nuclear astrophysicists have developed more and more sophisticated r-process models, eagerly trying to add new astrophysical or nuclear physics ingredients to explain the solar system composition in a satisfactory way.We show here that the decompression of the neutron star matter may provide suitable conditions for a robust r-processing. After decompression, the inner crust material gives rise to an abundance distribution for A>130 nuclei similar to the one observed inmore » the solar system. Similarly, the outer crust if heated at a temperature of about 8 10{sup 9} K before decompression is made of exotic neutron-rich nuclei with a mass distribution close to the 80{<=}A{<=}130 solar one. During the decompression, the free neutrons (initially liberated by the high temperatures) are re-captured leading to a final pattern similar to the solar system distribution.« less

[Role of the small intestinal decompression tube and Gastrografin in the treatment of early postoperative inflammatory small bowel obstruction].

PubMed

Li, Wei; Li, Zhixia; An, Dali; Liu, Jing; Zhang, Xiaohu

2014-03-01

To evaluate the role of the small intestinal decompression tube (SIDT) and Gastrografin in the treatment of early postoperative inflammatory small bowel obstruction (EPISBO). Twelve patients presented EPISBO after abdominal surgery in our department from April 2011 to July 2012. Initially, nasogastric tube decompression and other conventional conservative treatment were administrated. After 14 days, obstruction symptom improvement was not obvious, then the SIDT was used. At the same time, Gastrografin was injected into the small bowel through the SIDT in order to demonstrate the site of obstruction of small bowel and its efficacy. In 11 patients after this management, obstruction symptoms disappeared, bowel function recovered within 3 weeks, and oral feeding occurred gradually. Another patient did not pass flatus after 4 weeks and was reoperated. After postoperative follow-up of 6 months, no case relapsed with intestinal obstruction. For severe and long course of early postoperative inflammatory intestinal obstruction, intestinal decompression tube plus Gastrografin is safe and effective, and can avoid unnecessary reoperation.

Elective decompression of the left ventricle in pediatric patients may reduce the duration of venoarterial extracorporeal membrane oxygenation.

PubMed

Hacking, Douglas F; Best, Derek; d'Udekem, Yves; Brizard, Christian P; Konstantinov, Igor E; Millar, Johnny; Butt, Warwick

2015-04-01

We aimed to determine the effect of elective left heart decompression at the time of initiation of central venoarterial extracorporeal membrane oxygenation (VA ECMO) on VA ECMO duration and clinical outcomes in children in a single tertiary ECMO referral center with a large pediatric population from a national referral center for pediatric cardiac surgery. We studied 51 episodes of VA ECMO in a historical cohort of 49 pediatric patients treated between the years 1990 and 2013 in the Paediatric Intensive Care Unit (PICU) of the Royal Children's Hospital, Melbourne. The cases had a variety of diagnoses including congenital cardiac abnormalities, sepsis, myocarditis, and cardiomyopathy. Left heart decompression as an elective treatment or an emergency intervention for left heart distension was effectively achieved by a number of methods, including left atrial venting, blade atrial septostomy, and left ventricular cannulation. Elective left heart decompression was associated with a reduction in time on ECMO (128 h) when compared with emergency decompression (236 h) (P = 0.013). Subgroup analysis showed that ECMO duration was greatest in noncardiac patients (elective 138 h, emergency 295 h; P = 0.02) and in patients who died despite both emergency decompression and ECMO (elective 133 h, emergency 354 h; P = 0.002). As the emergency cases had a lower pH, a higher PaCO2 , and a lower oxygenation index and were treated with a higher mean airway pressure, positive end-expiratory pressure, and respiratory rate prior to receiving VA ECMO, we undertook multivariate linear regression modeling to show that only PaCO2 and the timing of left heart decompression were associated with ECMO duration. However, elective left heart decompression was not associated with a reduction in length of PICU stay, duration of mechanical ventilation, or duration of oxygen therapy. Elective left heart decompression was not associated with improved ECMO survival or survival to PICU discharge. Elective left heart decompression may reduce ECMO duration and has therefore the potential to reduce ECMO-related complications. A prospective, randomized controlled trial is indicated to study this intervention further. Copyright © 2014 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Simulating the behavior of volatiles belonging to the C-O-H-S system in silicate melts under magmatic conditions with the software D-Compress

NASA Astrophysics Data System (ADS)

Burgisser, Alain; Alletti, Marina; Scaillet, Bruno

2015-06-01

Modeling magmatic degassing, or how the volatile distribution between gas and melt changes at pressure varies, is a complex task that involves a large number of thermodynamical relationships and that requires dedicated software. This article presents the software D-Compress, which computes the gas and melt volatile composition of five element sets in magmatic systems (O-H, S-O-H, C-S-O-H, C-S-O-H-Fe, and C-O-H). It has been calibrated so as to simulate the volatiles coexisting with three common types of silicate melts (basalt, phonolite, and rhyolite). Operational temperatures depend on melt composition and range from 790 to 1400 °C. A specificity of D-Compress is the calculation of volatile composition as pressure varies along a (de)compression path between atmospheric and 3000 bars. This software was prepared so as to maximize versatility by proposing different sets of input parameters. In particular, whenever new solubility laws on specific melt compositions are available, the model parameters can be easily tuned to run the code on that composition. Parameter gaps were minimized by including sets of chemical species for which calibration data were available over a wide range of pressure, temperature, and melt composition. A brief description of the model rationale is followed by the presentation of the software capabilities. Examples of use are then presented with outputs comparisons between D-Compress and other currently available thermodynamical models. The compiled software and the source code are available as electronic supplementary materials.

Fluid-assisted melting in a collisional orogen

NASA Astrophysics Data System (ADS)

Berger, A.; Burri, T.; Engi, M.; Roselle, G. T.

2003-04-01

The Southern Steep Belt (SSB) of the Central Alps is the location of backthrusting during syn- to post-collisional deformation. From its metamorphic evolution and lithological contents the SSB has been interpreted as a tectonic accretion channel (TAC [1]). The central part of the SSB is additionally characterized by anatexites, leucogranitic aplites and pegmatites. Dehydration melting of muscovite is rare but did occurr locally. Moreover, no evidence of dehydration melting of biotite has been formed in that products of incongruent melting reactions (garnet, opx or cordierite) are missing. The melts are mainly produced by the infiltration of an external aqueous fluid. The fluids must have originated from the breakdown of hydrous minerals at temperatures below the water saturated solidus of the quartz-feldspar-system, such that the liberated fluids could not been trapped in the melt. Using the thermal modeling program MELONPIT [2] and assuming that solid fragments ascended in combination with tectonic accreated radioactive material, a complex thermal evolution inside the TAC has been derived. During subduction of the downgoing plate, isotherms were locally inverted, then subsequently relaxed, when subduction slowed down. At the collisional stage a small region develope, where the isotherms were still bent, and where temperatures increased during decompression. Assuming that dehydration reactions were followed by upward flow of fluids released from this region fluid present partial melting was triggered. The flow direction of the fluid was controlled by the pressure gradient and the steeply oriented foliations in the SSB. According to the model, the area of upward flowing fluids should be limited to the SSB. This is consistent with the observed regional distribution of leucosomes derived from in-situ melts. [1] Engi et al. (2001) Geology 29: 1143-1146 [2] Roselle et al. (2002) Am. J. Sci. 302: 381-409

Episodic kinematics in continental rifts modulated by changes in mantle melt fraction.

PubMed

Lamb, Simon; Moore, James D P; Smith, Euan; Stern, Tim

2017-07-05

Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor 'spreading centres' found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres, but direct observation of this process is difficult beneath the oceans. Continental rifts, however-which are also associated with mantle melt production-are amenable to detailed measurements of their short-term kinematics using geodetic techniques. Here we show that such data can provide evidence for an upwelling mantle flow, as well as information on the dimensions and timescale of mantle melting. For North Island, New Zealand, around ten years of campaign and continuous GPS measurements in the continental rift system known as the Taupo volcanic zone reveal that it is extending at a rate of 6-15 millimetres per year. However, a roughly 70-kilometre-long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence, and is flanked by regions of extension and uplift. These features fit a simple model that involves flexure of an elastic upper crust, which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15 kilometres. We propose that flexure is caused by melt-induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis, triggering a transient lower-crustal flow. A drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence, whereas melt accumulation reduces viscosity and allows uplift-processes that are also likely to occur in oceanic spreading centres.

Long-term results with percutaneous interspinous process devices in the treatment of neurogenic intermittent claudication.

PubMed

Fransen, Patrick

2017-12-01

Neurogenic intermittent claudication (NIC) is the main symptom of degenerative lumbar spinal stenosis. Percutaneous interspinous process decompression devices (IPDs) have been designed as an alternative therapy to conservative treatment and to open decompressive surgery for patients suffering from NIC. Initial short-term results were encouraging. We present the long-term results of a group of patients that we followed to provide insight on long-term outcomes and effectiveness of this technique compared to other decompression methods. Fifteen patients operated for NIC by implantation of percutaneous IPDs have been prospectively monitored for reoperations or complications. Follow-up (FU) was interrupted if the patient was reoperated. Results were considered poor if the patient had to be reoperated at any stage of the FU or if the treatment failed to alleviate the pain after 6 months. Results were considered average if the patient still suffered some pain but did not require reoperation. The patients were followed up to 7 years after the initial surgery. The mean length of the FU was 3.53 years and all patients could be followed. At the end of the FU, the results were good in only 20.0% (3/15), average in 13.3% (2/15) and poor in 66.7% (10/15). Despite initial satisfactory results, long-term FU is disappointing, with 80% poor or average results. The long-term reoperation rate is high (66.6%), increases over time and is higher than after implantation of IPDs for decompression augmentation. Although this technique is simple and safe, its effectiveness seems short-lived. We recommend cautious use and informing patients about the risk of relatively early failure and recurrence.

Superficial Palmar Arch Aneurysm after Carpal Tunnel Decompression, a Rare Complication: A Case Report

PubMed Central

Gull, S.; Spence, R. A. J.; Loan, W.

2011-01-01

False aneurysms of the palmar arteries are rare. They are usually associated with traumatic injuries to the hand vasculature. We present a case of superficial palmar arch aneurysm (SPAA), complicating carpal tunnel decompression which presented as a pulsatile mass at the site of previous surgery. Initial diagnosis was made on clinical examination and confirmed on doppler ultrasound (US) and computed tomographic angiography (CTA). The feeding vessel of the aneurysm was subsequently occluded using coil embolization. PMID:21547251

Behavior of fragmentation front in a porous viscoelastic material

NASA Astrophysics Data System (ADS)

Ichihara, M.; Takayama, K.

2002-12-01

We are developing laboratory experiments to investigate dynamics of magma fragmentation during explosive volcanic eruptions. Fragmentation of such a mixture as magma consisting of viscoelastic melt, bubbles and solid particles, is not known yet, and experiments are necessary to establish a mathematical model. It has been shown that viscoelastic silicone compound (Dow Corning 3179) is a useful analogous material to simulate magma fragmentation. In the previous work, a porous specimen made of the compound was rapidly decompressed and development of brittle fragmentation was observed. However, there were arguments that the experiment was different from actual processes which produce fragments as small as volcanic ash, because in the experiment the specimen was broken into only several pieces. This time, results of the improved experiments are presented. The experimental apparatus is a kind of a vertical shock tube, which mainly consists of a high pressure test section and low pressure chambers. The test section is made of acrylic tube of which inner diameter is 25 mm. The internal phenomenon is recorded by a high-speed video camera. Pressure is measured in the gas above and beneath the specimen by piezoelectric transducers. The specimen is prepared in the following way. First, an acrylic tube filled with the compound is put in a nitrogen tank and kept at 45 bar for more than 8 hours. The compound absorbs the gas and equilibrates with the nitrogen. Next, the tank is decompressed back to the atmospheric pressure slowly. Nitrogen exsolves and bubbles are formed in the compound quite uniformly. Finally, the expanded compound sticking out of both ends of the tube is cut down, and the tube containing the specimen is attached to the shock tube. The specimen is rapidly decompressed by 24, 16, and 8 bars. The high-speed video images demonstrate a sequence of the fragmentation process. We observe propagation of a clear fracture front at 50 m/s for 24 bar of decompression and at smaller speed for smaller decompression. The pressure change associated with development of the fragmentation is analyzed and effects of over pressure in the pores and permeable gas flow on fragmentation behavior are discussed.

Experimental constraints on the damp peridotite solidus and oceanic mantle potential temperature

NASA Astrophysics Data System (ADS)

Sarafian, Emily; Gaetani, Glenn A.; Hauri, Erik H.; Sarafian, Adam R.

2017-03-01

Decompression of hot mantle rock upwelling beneath oceanic spreading centers causes it to exceed the melting point (solidus), producing magmas that ascend to form basaltic crust ~6 to 7 kilometers thick. The oceanic upper mantle contains ~50 to 200 micrograms per gram of water (H2O) dissolved in nominally anhydrous minerals, which—relative to its low concentration—has a disproportionate effect on the solidus that has not been quantified experimentally. Here, we present results from an experimental determination of the peridotite solidus containing known amounts of dissolved hydrogen. Our data reveal that the H2O-undersaturated peridotite solidus is hotter than previously thought. Reconciling geophysical observations of the melting regime beneath the East Pacific Rise with our experimental results requires that existing estimates for the oceanic upper mantle potential temperature be adjusted upward by about 60°C.

[Analysis of decompression safety during extravehicular activity of astronauts in the light of probability theory].

PubMed

Nikolaev, V P; Katuntsev, V P

1998-01-01

Objectives of the study were comparative assessment of the risk of decompression sickness (DCS) in human subjects during shirt-sleeve simulation of extravehicular activity (EVA) following Russian and U.S. protocols, and analysis of causes of the difference between real and simulated EVA decompression safety. To this end, DCS risk during exposure to a sing-step decompression was estimated with an original method. According to the method, DCS incidence is determined by distribution of nucleation efficacy index (z) in the worst body tissues and its critical values (zm) as a function of initial nitrogen tension in these tissues and final ambient pressure post decompression. Gaussian distribution of z values was calculated basing on results of the DCS risk evaluation on the U.S. EVA protocol in an unsuited chamber test with various pre-breath procedures (Conkin et al., 1987). Half-time of nitrogen washout from the worst tissues was presumed to be 480 min. Calculated DCS risk during short-sleeve EVA simulation by the Russian and U.S. protocols with identical physical loading made up 19.2% and 23.4%, respectively. Effects of the working spacesuit pressure, spacesuit rigidity, metabolic rates during operations in EVA space suit, transcutaneous nitrogen exchange in the oxygen atmosphere of space suit, microgravity, analgesics, short compression due to spacesuit leak tests on the eye of EVA are discussed. Data of the study illustrate and advocate for high decompression safety of current Russian and U.S. EVA protocols.

Long-term outcome of severe herpes simplex encephalitis: a population-based observational study.

PubMed

Jouan, Youenn; Grammatico-Guillon, Leslie; Espitalier, Fabien; Cazals, Xavier; François, Patrick; Guillon, Antoine

2015-09-21

Herpes simplex encephalitis (HSE) is a rare disease with a poor prognosis. No recent evaluation of hospital incidence, acute mortality and morbidity is available. In particular, decompressive craniectomy has rarely been proposed in cases of life-threatening HSE with temporal herniation, in the absence of evidence. This study aimed to assess the hospital incidence and mortality of HSE, and to evaluate the characteristics, management, the potential value of decompressive craniectomy and the outcome of patients with HSE admitted to intensive care units (ICUs). Epidemiological study: we used the hospital medical and administrative discharge database to identify hospital stays, deaths and ICU admissions relating to HSE in 39 hospitals, from 2010 to 2013. Retrospective monocentric cohort: all patients with HSE admitted to the ICU of the university hospital during the study were included. The use of decompressive craniectomy and long-term outcome were analyzed. The initial brain images were analyzed blind to outcome. The hospital incidence of HSE was 1.2/100,000 inhabitants per year, 32 % of the patients were admitted to ICUs and 17 % were mechanically ventilated. Hospital mortality was 5.5 % overall, but was as high as 11.9 % in ICUs. In the monocentric cohort, 87 % of the patients were still alive after one year but half of them had moderate to severe disability. Three patients had a high intracranial pressure (ICP) with brain herniation and eventually underwent decompressive hemicraniectomy. The one-year outcome of these patients did not seem to be different from that of the other patients. It was not possible to predict brain herniation reliably from the initial brain images. HSE appears to be more frequent than historically reported. The high incidence we observed probably reflects improvements in diagnostic performance (routine use of PCR). Mortality during the acute phase and long-term disability appear to be stable. High ICP and brain herniation are rare, but must be monitored carefully, as initial brain imaging is not useful for identifying high-risk patients. Decompressive craniectomy may be a useful salvage procedure in cases of intractable high ICP.

Evaluation of the Boussignac Cardiac arrest device (B-card) during cardiopulmonary resuscitation in an animal model.

PubMed

Moore, Johanna C; Lamhaut, Lionel; Hutin, Alice; Dodd, Kenneth W; Robinson, Aaron E; Lick, Michael C; Salverda, Bayert J; Hinke, Mason B; Labarere, José; Debaty, Guillaume; Segal, Nicolas

2017-10-01

The purpose of this study was to examine continuous oxygen insufflation (COI) in a swine model of cardiac arrest. The primary hypothesis was COI during standard CPR (S-CPR) should result in higher intrathoracic pressure (ITP) during chest compression and lower ITP during decompression versus S-CPR alone. These changes with COI were hypothesized to improve hemodynamics. The second hypothesis was that changes in ITP with S-CPR+COI would result in superior hemodynamics compared with active compression decompression (ACD) + impedance threshold device (ITD) CPR, as this method primarily lowers ITP during chest decompression. After 6min of untreated ventricular fibrillation, S-CPR was initiated in 8 female swine for 4min, then 3min of S-CPR+COI, then 3min of ACD+ITD CPR, then 3min of S-CPR+COI. ITP and hemodynamics were continuously monitored. During S-CPR+COI, ITP was always positive during the CPR compression and decompression phases. ITP compression values with S-CPR+COI versus S-CPR alone were 5.5±3 versus 0.2±2 (p<0.001) and decompression values were 2.8±2 versus -1.3±2 (p<0.001), respectively. With S-CPR+COI versus ACD+ITD the ITP compression values were 5.5±3 versus 1.5±2 (p<0.01) and decompression values were 2.8±2 versus -4.7±3 (p<0.001), respectively. COI during S-CPR created a continuous positive pressure in the airway during both the compression and decompression phase of CPR. At no point in time did COI generate a negative intrathoracic pressures during CPR in this swine model of cardiac arrest. Copyright © 2017 Elsevier B.V. All rights reserved.

MRI Evaluation of Post Core Decompression Changes in Avascular Necrosis of Hip

PubMed Central

Marupaka, Sravan Kumar; Alluri, Swathi; MD, Naseeruddin; Irfan, Kazi Amir; Jampala, Venkateshwarlu; Apsingi, Sunil; Eachempati, Krishna Kiran

2015-01-01

Introduction Avascular necrosis of hip typically presents in young patients. Core decompression in precollapse stage provides pain relief and preservation of femoral head. The results of core decompression vary considerably despite early diagnosis. The role of MRI in monitoring patients post surgically has not been clearly defined. Aim To study pre and post core decompression MRI changes in avascular necrosis of hip. Materials and Methods This is a contiguous observational cohort of 40 hips treated by core decompression for precollapse avascular necrosis of femoral head, who had a baseline MRI performed before surgery. Core decompression of the femoral head was performed within 4 weeks. Follow up radiograph and MRI scans were done at six months. Harris hip score preoperatively, 1 month and 6 months after the surgery was noted. Success in this study was defined as postoperative increase in Harris hip score (HHS) by 20 points and no additional femoral collapse. End point of clinical adverse outcome as defined by fall in Harris hip score was conversion or intention to convert to total hip replacement (THR). MRI parameters in the follow up scan were compared to the preoperative MRI. Effect of core decompression on bone marrow oedema and femoral head collapse was noted. Results were analysed using SPSS software version. Results Harris hip score improved from 57 to 80 in all patients initially. Six hips had a fall in Harris hip score to mean value of 34.1 during follow up (9 to 12 months) and underwent total hip replacement. MRI predictors of positive outcome are lesions with grade A extent, Grade A & B location. Bone marrow oedema with lesions less than 50% involvement, medial and central location. Conclusion Careful selection of patients by MR criteria for core decompression provides satisfactory outcome in precollapse stage of avascular necrosis of hip. PMID:26816966

Nanobubbles Form at Active Hydrophobic Spots on the Luminal Aspect of Blood Vessels: Consequences for Decompression Illness in Diving and Possible Implications for Autoimmune Disease-An Overview.

PubMed

Arieli, Ran

2017-01-01

Decompression illness (DCI) occurs following a reduction in ambient pressure. Decompression bubbles can expand and develop only from pre-existing gas micronuclei. The different hypotheses hitherto proposed regarding the nucleation and stabilization of gas micronuclei have never been validated. It is known that nanobubbles form spontaneously when a smooth hydrophobic surface is submerged in water containing dissolved gas. These nanobubbles may be the long sought-after gas micronuclei underlying decompression bubbles and DCI. We exposed hydrophobic and hydrophilic silicon wafers under water to hyperbaric pressure. After decompression, bubbles appeared on the hydrophobic but not the hydrophilic wafers. In a further series of experiments, we placed large ovine blood vessels in a cooled high pressure chamber at 1,000 kPa for about 20 h. Bubbles evolved at definite spots in all the types of blood vessels. These bubble-producing spots stained positive for lipids, and were henceforth termed "active hydrophobic spots" (AHS). The lung surfactant dipalmitoylphosphatidylcholine (DPPC), was found both in the plasma of the sheep and at the AHS. Bubbles detached from the blood vessel in pulsatile flow after reaching a mean diameter of ~1.0 mm. Bubble expansion was bi-phasic-a slow initiation phase which peaked 45 min after decompression, followed by fast diffusion-controlled growth. Many features of decompression from diving correlate with this finding of AHS on the blood vessels. (1) Variability between bubblers and non-bubblers. (2) An age-related effect and adaptation. (3) The increased risk of DCI on a second dive. (4) Symptoms of neurologic decompression sickness. (5) Preconditioning before a dive. (6) A bi-phasic mechanism of bubble expansion. (7) Increased bubble formation with depth. (8) Endothelial injury. (9) The presence of endothelial microparticles. Finally, constant contact between nanobubbles and plasma may result in distortion of proteins and their transformation into autoantigens.

Nanobubbles Form at Active Hydrophobic Spots on the Luminal Aspect of Blood Vessels: Consequences for Decompression Illness in Diving and Possible Implications for Autoimmune Disease—An Overview

PubMed Central

Arieli, Ran

2017-01-01

Decompression illness (DCI) occurs following a reduction in ambient pressure. Decompression bubbles can expand and develop only from pre-existing gas micronuclei. The different hypotheses hitherto proposed regarding the nucleation and stabilization of gas micronuclei have never been validated. It is known that nanobubbles form spontaneously when a smooth hydrophobic surface is submerged in water containing dissolved gas. These nanobubbles may be the long sought-after gas micronuclei underlying decompression bubbles and DCI. We exposed hydrophobic and hydrophilic silicon wafers under water to hyperbaric pressure. After decompression, bubbles appeared on the hydrophobic but not the hydrophilic wafers. In a further series of experiments, we placed large ovine blood vessels in a cooled high pressure chamber at 1,000 kPa for about 20 h. Bubbles evolved at definite spots in all the types of blood vessels. These bubble-producing spots stained positive for lipids, and were henceforth termed “active hydrophobic spots” (AHS). The lung surfactant dipalmitoylphosphatidylcholine (DPPC), was found both in the plasma of the sheep and at the AHS. Bubbles detached from the blood vessel in pulsatile flow after reaching a mean diameter of ~1.0 mm. Bubble expansion was bi-phasic—a slow initiation phase which peaked 45 min after decompression, followed by fast diffusion-controlled growth. Many features of decompression from diving correlate with this finding of AHS on the blood vessels. (1) Variability between bubblers and non-bubblers. (2) An age-related effect and adaptation. (3) The increased risk of DCI on a second dive. (4) Symptoms of neurologic decompression sickness. (5) Preconditioning before a dive. (6) A bi-phasic mechanism of bubble expansion. (7) Increased bubble formation with depth. (8) Endothelial injury. (9) The presence of endothelial microparticles. Finally, constant contact between nanobubbles and plasma may result in distortion of proteins and their transformation into autoantigens. PMID:28861003

Shock-induced deformation of Shergottites: Shock-pressures and perturbations of magmatic ages on Mars

NASA Astrophysics Data System (ADS)

El Goresy, Ahmed; Gillet, Ph.; Miyahara, M.; Ohtani, E.; Ozawa, S.; Beck, P.; Montagnac, G.

2013-01-01

Shergottites and Chassignites practiced major deformation effects whose nature, magnitude and relevance were controversially evaluated and disputatively debated. Our studies of many shocked shergottites present, contrary to numerous previous reports, ample evidence for pervasive shock-induced melting amounting of at least 23 vol.% of the shergottite consisting of maskelynite and pyrrhotite, partial melting of pyroxene, titanomagnetite, ilmenite and finding of several high-pressure polymorphs and pressure-induced dissociation reactions. Our results cast considerable doubt on using the refractive index (RI) or cathodoluminescence (CL) spectra of maskelynite, in estimating the magnitudes of peak-shock pressure in both shergottites and ordinary chondrites. RI of maskelynite was set after quenching of the feldspar liquid before decompression to maskelynite glass followed by glass relaxation after decompression at the closure temperature of relaxation. The RI procedure widely practiced in the past 38 years revealed unrealistic very high-pressure estimates discrepant with the high-pressure mineral inventory in shocked shergottites and ordinary chondrites and with results obtained by robust laboratory static experiments. Shergottites contain the silica high-pressure polymorphs: the scrutinyite-structured polymorph seifertite, a monoclinic ultra dense polymorph of silica with ZrO2-structure, stishovite, a dense liquidus assemblage consisting of stishovite + Na-hexa-aluminosilicate (Na-CAS) and both K-lingunite and Ca-lingunite. Applying individual high-pressure silica polymorphs alone like stishovite, to estimate the equilibrium shock pressure, is inadequate due to the considerable shift of their nominal upper pressure bounds intrinsically induced by spatially variable absorptions of minor oxides like Al2O3, Na2O, FeO, MgO and TiO2. This practice revealed variable pressure estimates even within the same shergottite subjected to the same peak-shock pressure. Occurrence of Na-CAS + stishovite, lack of the NaAlSiO4 Ca-ferrite structured polymorph or jadeite indicates that the peak-shock pressures barely exceeded 22 GPa. We present convincing and ample evidence refuting the claim that the shock-induced high-pressure inventory in shergottites and ordinary chondrites are disequilibrium assemblages resulted from local pressure spikes in excess of 80 GPa and during the decompression stage. Such scenario calls for a series of incomplete and quenched retrograde reactions starting with the crystallization of Mg-silicate perovskite + magnesiowüstite, if the claimed peak-shock pressure was in excess of 80 GPa. This would be followed by replacement of this pair by majorite-pyropess + magnesiowüstite or akimotoite + magnesiowüstite below 23 GPa and 2000 °C, polycrystalline ringwoodite above 16 GPa, respectively and finally replacement by polycrystalline olivine below 16 GPa. Such incomplete retrograde reactions were never encountered in any shergottite, chassignite or shocked ordinary chondrite so far. Olivine-ringwoodite phase transformation in the L6 Y-791384 commences with the coherent mechanism producing ringwoodite lamellae with their (1 1 1) planes parallel to the (1 0 0) of olivine followed by the incoherent mechanism due to build up of strain in the parental olivine. This is in accord with the olivine-ringwoodite settings produced in static laboratory experiments in a multi-anvil device. Olivine-ringwoodite phase transitions were also encountered in comparable settings in the shergottite NWA 1068. Application of experimentally obtained kinetic parameters of the olivine-ringwoodite phase transitions reveals possible duration of the natural dynamic events up to few seconds thus unambiguously refuting the claimed disequilibrium decompression mechanism. The shock-induced pervasive melting of labradorite, pyrrhotite, titanomagnetite, ilmenite and partial melting of clinopyroxene strongly suggests shock-induced partial to complete resetting of the Ar-Ar, Rb-Sr, Sm-Nd, Re-Os, U-Pb and Lu-Hf radiometric systems. This also casts considerable doubt on the radiometric ages shorter than 575 Ma reported in the past 38 years to allegedly be the igneous crystallization ages. These short ages probably resulted from partial or total shock-induced age resetting.

Microstructures and Petrology of Melt Inclusions in the Anatectic Sequence of Jubrique (Betic Cordillera, S Spain): Implications for Crustal Anatexis

NASA Astrophysics Data System (ADS)

Acosta-vigil, A.; Barich, A.; Garrido, C. J.; Cesare, B.; Tajčmanová, L.; Bartoli, O.

2014-12-01

We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence garnet decreases whereas biotite increases in proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ≈5 to 200 micrometers, with a mean size of ≈30-40 micrometers. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ≈850 ºC and 12-14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ≈800-850 ºC and 5-6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous conventional petrologic studies on these strongly deformed rocks have proposed that anatexis started during decompression from peak to post-peak conditions and in the field of sillimanite. The study of melt inclusions shows, however, that melt was already present in the system at peak conditions, and that most garnet grew in the presence of melt.

Outcome after decompressive craniectomy for the treatment of severe traumatic brain injury.

PubMed

Howard, Jerry Lee; Cipolle, Mark D; Anderson, Meredith; Sabella, Victoria; Shollenberger, Daniele; Li, P Mark; Pasquale, Michael D

2008-08-01

Using decompressive craniectomy as part of the treatment regimen for severe traumatic brain injury (STBI) has become more common at our Level I trauma center. This study was designed to examine this practice with particular attention to long-term functional outcome. A retrospective review of prospectively collected data was performed for patients with STBI admitted from January 1, 2003 to December 31, 2005. Our institution manages patients using the Brain Trauma Foundation Guidelines. Data collected from patients undergoing decompressive craniectomy included: age, Injury Severity Score, admission and follow-up Glasgow Coma Score, timing of, and indication for decompressive craniectomy, and procedure-related complications. The Extended Glasgow Outcome Scale (GOSE) was performed by a experienced trauma clinical research coordinator using a structured phone interview to assess long-term outcome in the survivors. Student's t test and chi2 were used to examine differences between groups. Forty STBI patients were treated with decompressive craniectomy; 24 were performed primarily in conjunction with urgent evacuation of extra-axial hemorrhage and 16 were performed primarily in response to increased intracranial pressure with 4 of these after an initial craniotomy. Decompressive craniectomy was very effective at lowering intracranial pressure in these 16 patients (35.0 mm Hg +/- 13.5 mm Hg to 14.6 mm Hg +/- 8.7 mm Hg, p = 0.005). Twenty-two decompressive craniectomy patients did not survive to hospital discharge, whereas admission Glasgow Coma Score and admission pupil size and reactivity correlated with outcome, age, and Injury Severity Score did not. At a mean of 11 months (range, 3-26 months) after decompressive craniectomy, 6 survivors had a poor functional outcome (GOSE 1-4), whereas 12 survivors had a good outcome (GOSE 5-8). Therefore, 70% of these patients had an unfavorable outcome (death or severe disability), and 30% had a favorable long-term functional outcome. Fifteen of 18 survivors went on to cranioplasty, whereas 4 of 18 had cerebrospinal infection. The majority of survivors after decompressive craniectomy have a good functional outcome as analyzed by GOSE. Overall, 30% of patients with STBI who underwent decompressive craniectomy had a favorable long-term outcome. Improving patient selection and optimizing timing of this procedure may further improve outcome in these very severely brain injured patients.

Recent volcanism in the Siqueiros transform fault: Picritic basalts and implications for MORB magma genesis

USGS Publications Warehouse

Perfit, M.R.; Fornari, D.J.; Ridley, W.I.; Kirk, P.D.; Casey, J.; Kastens, K.A.; Reynolds, J.R.; Edwards, M.; Desonie, D.; Shuster, R.; Paradis, S.

1996-01-01

Small constructional volcanic landforms and very fresh-looking lava flows are present along one of the inferred active strike-slip faults that connect two small spreading centers (A and B) in the western portion of the Siqueiros transform domain. The most primitive lavas (picritic and olivine-phyric basalts), exclusively recovered from the young-looking flows within the A-B strike-slip fault, contain millimeter-sized olivine phenocrysts (up to 20 modal%) that have a limited compositional range (Fo91.5-Fo89.5) and complexly zoned Cr-Al spinels. High-MgO (9.5-10.6 wt%) glasses sampled from the young lava flows contain 1-7% olivine phenocrysts (Fo90.5-Fo89) that could have formed by equilibrium crystallization from basaltic melts with Mg# values between 71 and 74. These high MgO (and high Al2O3) glasses may be near-primary melts from incompatible-element depleted oceanic mantle and little modified by crustal mixing and/or fractionation processes. Phase chemistry and major element systematics indicate that the picritic basalts are not primary liquids and formed by the accumulation of olivine and minor spinel from high-MgO melts (10% < MgO < 14%). Compared to typical N-MORB from the East Pacific Rise, the Siqueiros lavas are more primitive and depleted in incompatible elements. Phase equilibria calculations and comparisons with experimental data and trace element modeling support this hypothesis. They indicate such primary mid-ocean ridge basalt magmas formed by 10-18% accumulative decompression melting in the spinel peridotite field (but small amounts of melting in the garnet peridotite field are not precluded). The compositional variations of the primitive magmas may result from the accumulation of different small batch melt fractions from a polybaric melting column.

Tectonic and Magmatic Controls on Extension and Crustalaccretion in Backarc Basins, Insights from the Lau Basin and Southern Mariana Trough

NASA Astrophysics Data System (ADS)

Sleeper, Jonathan D.

This dissertation examines magmatic and tectonic processes in backarc basins, and how they are modulated by plate- and mantle-driven mechanisms. Backarc basins initiate by tectonic rifting near the arc volcanic front and transition to magmatic seafloor spreading. As at mid-ocean ridges (MORs), spreading can be focused in narrow plate boundary zones, but we also describe a diffuse spreading mode particular to backarc basins. At typical MORs away from hot spots and other melting anomalies, spreading rate is the primary control on the rate of mantle upwelling and decompression melting. At backarc spreading centers, water derived from the subducting slab creates an additional mantle-driven source of melt and buoyant upwelling. Furthermore, because basins open primarily in response to trench rollback, which is inherently a non-rigid process, backarc extensional systems often have to respond to a constantly evolving stress regime, generating complex tectonics and unusual plate boundaries not typically found at MORs. The interplay between these plate- and mantle-driven processes gives rise to the variety of tectonic and volcanic morphologies peculiar to backarc basins. Chapter 2 is focused on the Fonualei Rift and Spreading Center in the Lau Basin. The southern portion of the axis is spreading at ultraslow (<20 mm/yr) opening rates in close proximity to the arc volcanic front and axial morphology abruptly changes from a volcanic ridge to spaced volcanic cones resembling arc volcanoes. Spreading rate and arc proximity appear to control transitions between two-dimensional and three-dimensional mantle upwelling and volcanism. In the second study (Chapter 3), I develop a new model for the rollback-driven kinematic and tectonic evolution of the Lau Basin, where microplate tectonics creates rapidly changing plate boundary configurations. The third study (Chapter 4) focuses on the southern Mariana Trough and the transitions between arc rifting, seafloor spreading, and a new mode of "diffuse spreading," where new crust is accreted in broad zones rather than along a narrow spreading axis, apparently controlled by a balance between slab water addition and its extraction due to melting and crustal accretion.

Deglaciation and glacial erosion: a joint control on magma productivity by continental unloading

NASA Astrophysics Data System (ADS)

Sternai, Pietro; Caricchi, Luca; Castelltort, Sebastien

2016-04-01

Glacial-interglacial cycles affect the processes through which water and rocks are redistributed across the Earth's surface, thereby linking solid-Earth and climate dynamics. Regional and global scale studies suggest that continental lithospheric unloading due to ice melting during the transition to interglacials leads to increased continental magmatic, volcanic and degassing activity. Such a climatic forcing on the melting of the Earth's interior, however, has always been evaluated without considering the additional continental unloading associated with erosion. Current datasets relating to the evolution of erosion rates are typically limited by temporal resolutions that are too low or span too short time intervals to allow for direct comparisons between the contributions from ice melting and erosion to continental unloading at the timescale of the late Pleistocene glacial cycles. Yet, they provide a fundamental observational basis on which to calibrate numerical predictions. Here, we present and discuss numerical results involving synthetic but realistic topographies, ice caps and glacial erosion rates suggesting that erosion may be as important as deglaciation in affecting continental unloading, sub-continental decompression melting and magma productivity. Thus, the timing and magnitude of deglaciation and erosion must be characterized if the forcing of climate change on the continental magmatic/volcanic activity is to be extracted from the remnants of eroded volcanic centers. Our study represents an additional step towards a more general understanding of the links between a changing climate, glacial processes and the melting of the solid Earth.

A tale of phenocrysts: trace element contents of boninites and forearc basalts from IODP Expedition 352

NASA Astrophysics Data System (ADS)

Chapman, T.; Clarke, G. L.; Reagan, M. K.; Sakuyama, T.; Godard, M.; Shervais, J. W.; Prytulak, J.; Shimizu, K.; Nelson, W. R.; Heaton, D. E.; Whattam, S. A.; Li, H.; Pearce, J. A.

2016-12-01

The Izu-Bonin Mariana (IBM) forearc represents an ideal location to study the dynamics of subduction initiation and to reveal the volcanic sequences appropriate to assess ophiolite origins. The volcanic stratigraphy recovered on Expedition 352 illustrates an abrupt shift from forearc basalt (FAB) to boninite magmatism, with limited transitional rock types, as observed from submersible and previous drill work in the Izu-Bonin and Mariana sections. The transition represents a change from decompression melting to fluxed melting of the mantle wedge. The volcanic stratigraphy has several distinct boninite chemical evolution trends (basaltic boninite, low- and high-silica boninite). Mineral assemblages and phenocryst trace element compositions vary throughout the volcanic sequence providing an opportunity to explore more completely boninite and FAB transitions and petrogenesis. FABs are characterised by early plagioclase crystallization and HREE enriched clinopyroxene with high Ti contents. Basaltic boninite and some low-silica boninite lavas have overlapping REE concentrations consistent with early plagioclase growth preceded by clinopyroxene. In contrast, textures and HREE depleted concentrations of clinopyroxene in high-silica boninite imply late plagioclase growth relative to olivine and orthopyroxene. Variations in mineral compositions and paragenesis in boninites reflect changes in magma compositions and a progressive depletion of mantle sources over time. This is illustrated via key incompatible and compatible trace element ratios and concentrations (e.g. Zr/Ti & V or Cr). The transition from FAB to low-Si boninite was subtle in terms of mineral modes, but was more evident in terms of the phase and lava compositions.

Recovery of TES-MEPs during surgical decompression of the spine: a case series of eight patients.

PubMed

Visser, Jetze; Verra, Wiebe C; Kuijlen, Jos M; Horsting, Philip P; Journée, Henricus L

2014-12-01

This study aimed to illustrate the recovery of transcranial electrical stimulation motor evoked potentials during surgical decompression of the spinal cord in patients with impaired motor function preoperatively. Specific attention was paid to the duration of neurologic symptoms before surgery and the postoperative clinical recovery. A case series of eight patients was selected from a cohort of 74 patients that underwent spine surgery. The selected patients initially had low or absent transcranial electrical stimulation motor evoked potentials followed by a significant increase after surgical decompression of the spinal cord. A significant intraoperative increase in amplitude of motor evoked potentials was detected after decompression of the spinal cord or cauda equina in patients suffering from spinal canal stenosis (n = 2), extradural meningioma (n = 3), or a herniated nucleus polposus (n = 3). This was related to an enhanced neurologic outcome only if patients (n = 6) had a short onset (less than ½ year) of neurologic impairment before surgery. In patients with a short onset of neurologic impairment because of compression of the spinal cord or caudal fibers, an intraoperative recovery of transcranial electrical stimulation motor evoked potentials can indicate an improvement of motor function postoperatively. Therefore, transcranial electrical stimulation motor evoked potentials can be considered as a useful tool to the surgeon to monitor the quality of decompression of the spinal cord.

Etnean and Hyblean volcanism shifted away from the Malta Escarpment by crustal stresses

NASA Astrophysics Data System (ADS)

Neri, Marco; Rivalta, Eleonora; Maccaferri, Francesco; Acocella, Valerio; Cirrincione, Rosolino

2018-03-01

A fraction of the volcanic activity occurs intraplate, challenging our models of melting and magma transfer to the Earth's surface. A prominent example is Mt. Etna, eastern Sicily, offset from the asthenospheric tear below the Malta Escarpment proposed as its melt source. The nearby Hyblean volcanism, to the south, and the overall northward migration of the eastern Sicilian volcanism are also unexplained. Here we simulate crustal magma pathways beneath eastern Sicily, accounting for regional stresses and decompression due to the increase in the depth of the Malta Escarpment. We find non-vertical magma pathways, with the competition of tectonic and loading stresses controlling the trajectories' curvature and its change in time, causing the observed migration of volcanism. This suggests that the Hyblean and Etnean volcanism have been fed laterally from a melt pooling region below the Malta Escarpment. The case of eastern Sicily shows how the reconstruction of the evolution of magmatic provinces may require not only an assessment of the paleostresses, but also of the contribution of surface loads and their variations; at times, the latter may even prevail. Accounting for these competing stresses may help shed light on the distribution and wandering of intraplate volcanism

A British Ophthalmological Surveillance Unit (BOSU) study into dysthyroid optic neuropathy in the United Kingdom.

PubMed

Wong, Yun; Dickinson, Jane; Perros, Petros; Dayan, Colin; Veeramani, Pratibha; Morris, Daniel; Foot, Barny; Clarke, Lucy

2018-06-18

This prospective British Ophthalmological Surveillance Unit (BOSU) study on dysthyroid optic neuropathy (DON) determines the incidence, presenting features and management throughout the UK. New cases were identified through the BOSU yellow card and an initial questionnaire and a subsequent 9-month follow-up questionnaire were posted out. From August 2015 to August 2016 DON was reported in 49 patients with 71 eyes affected, 22 patients had bilateral DON. The most common presenting symptom was blurred vision (83%) and the most common examination finding was upgaze restriction (85%). 85% of patients were initially treated with 3 days of either 1 g or 500 mg intravenous methyl prednisolone. We received 25 follow-up questionnaires (51% of the initial cohort) with 38 eyes treated for DON and 13 bilateral cases. The average steroid dose over 9 months was 4.5 g and 47% of patients had a surgical orbital decompression. The mean visual acuity gain after 9 months of follow-up for all patients was 0.25 LogMAR. The mean visual acuity gain after just medical therapy was 0.25 LogMAR and after both medical therapy and orbital decompression it was 0.24 LogMAR. In conclusion, the incidence of DON in the UK from this study is 0.75 per million population per annum. The majority of patients are treated with initial medical therapy and almost half of all patients subsequently went on to have an orbital decompression. With either medical therapy or medical and surgical therapy, vision can improve in patients with DON.

Magma ocean formation due to giant impacts

NASA Technical Reports Server (NTRS)

Tonks, W. B.; Melosh, H. J.

1993-01-01

The thermal effects of giant impacts are studied by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths. Additionally, the effects of the planet's initial temperature on the generated melt volume are examined. The shock pressure required to completely melt the material is determined using the Hugoniot curve plotted in pressure-entropy space. Once the melting pressure is known, an impact melting model is used to estimate the radial distance melting occurred from the impact site. The melt region's geometry then determines the associated melt volume. The model is also used to estimate the partial melt volume. Magma ocean depths resulting from both excavated and retained melt are calculated, and the melt fraction not excavated during the formation of the crater is estimated. The fraction of a planet melted by the initial shock wave is also estimated using the model.

Modelling the Composition of Outgassing Bubbles at Basaltic Open Vent Volcanoes

NASA Astrophysics Data System (ADS)

Edmonds, M.; Clements, N.; Houghton, B. F.; Oppenheimer, C.; Jones, R. L.; Burton, M. R.

2015-12-01

Basaltic open vent volcanoes exhibit a wide range in eruption styles, from passive outgassing to Strombolian and Hawaiian explosive activity. Transitions between these styles are linked to contrasting two-phase (melt and gas) flow regimes in the conduit system. A wealth of data now exists characterising the fluxes and compositions of gases emitted from these volcanoes, alongside detailed observations of patterns of outgassing at the magma free surfaces. Complex variations in gas composition are apparent from high temporal resolution measurement techniques such as open path spectroscopy. This variability with time is likely a function of individual bubbles' histories of growth during ascent, with variable degrees of kinetic inhibition. Our previous studies at Kilauea and Stromboli have, for example, linked CO2-rich gases with the bursting of bubbles that last equilibrated at some depth beneath the surface. However, very few studies have attempted to reconcile such observations with quantitative models of diffusion-limited bubble growth in magmas prior to eruption. We present here an analytical model that simulates the growth of populations of bubbles by addition of volatile mass during decompression, with growth limited by diffusion. The model simulates a range of behaviors between the end members of separated two-phase flow and homogeneous bubbly flow in the conduit, tied to thermodynamic models of solubility and partitioning of volatile species (carbon, water, sulfur). We explore the effects of the form of bubble populations at depth, melt viscosity, total volatile content, magma decompression rate and other intrinsic parameters on expected gas compositions at the surface and consider implications for transitions between eruption styles. We compare the the model to data suites from Stromboli and Kilauea.

Phase equilibria modeling in igneous petrology: use of COMAGMAT model for simulating fractionation of ferro-basaltic magmas and the genesis of high-alumina basalt

NASA Astrophysics Data System (ADS)

Ariskin, Alexei A.

1999-05-01

A new version of COMAGMAT-3.5 model designed for computer simulations of equilibrium and fractional crystallization of basaltic magmas at low to high pressures is presented. The most important modifications of COMAGMAT include an ability to calculate more accurately the crystallization of magnetite and ilmenite, allowing the user to study numerically the effect of oxygen fugacity on basalt magma fractionation trends. Methodological principles of the use of COMAGMAT were discussed based on its thermodynamical and empirical basis, including specific details of the model calibration. Using COMAGMAT-3.5 a set of phase equilibria calculations (called Geochemical Thermometry) has been conducted for six cumulative rocks from the Marginal Border Series of the Skaergaard intrusion. As a result, initial magma temperature (1165±10°C) and trapped melt composition proposed to be parental magma to the Skaergaard intrusion were determined. Computer simulations of perfect fractionation of this composition as well as another proposed parent produced petrochemical trends opposite to those followed from natural observations. This is interpreted as evidence for an initial Skaergaard magma containing a large amount of olivine and plagioclase crystals (about 40-45%), so that the proposed and calculated parents are related through the melt trapped in the crystal-liquid mixture. This promotes the conclusion that the Skaergaard magma fractionation process was intermediate between equilibrium and fractional crystallization. In this case the classic Wager's trend should be considered an exception rather than a rule for the differentiation of ferro-basaltic magmas. A polybaric version of COMAGMAT has been applied for the genetic interpretation of a volcanic suite from the Klyuchevskoi volcano, Kamchatka, Russia. To identify petrological processes responsible for the observed suite ranging from high-magnesia to high-alumina basalts, we used the model to simulate the Klyuchevskoi suite assuming isobaric crystallization of a parental HMB magma at a variety of pressures and a separate set of simulations assuming fractionation during continuous magma ascent from a depth of 60 km. These results indicate that the Klyuchevskoi trend can be produced by ˜40% fractionation of Ol-Aug-Sp±Opx assemblages during ascent of the parental HMB magma over the pressure range 19-7 kbar with the rate of decompression being 0.33 kbar/% crystallized (at 1350-1110°C), with ˜2 wt.% of H 2O in the initial melt and ˜3 wt.% of H 2O in the resultant high-Al basalt.

The temperature of the Icelandic mantle from olivine-spinel aluminum exchange thermometry

NASA Astrophysics Data System (ADS)

Matthews, S.; Shorttle, O.; Maclennan, J.

2016-11-01

New crystallization temperatures for four eruptions from the Northern Volcanic Zone of Iceland are determined using olivine-spinel aluminum exchange thermometry. Differences in the olivine crystallization temperatures between these eruptions are consistent with variable extents of cooling during fractional crystallization. However, the crystallization temperatures for Iceland are systematically offset to higher temperatures than equivalent olivine-spinel aluminum exchange crystallization temperatures published for MORB, an effect that cannot be explained by fractional crystallization. The highest observed crystallization temperature in Iceland is 1399 ± 20°C. In order to convert crystallization temperatures to mantle potential temperature, we developed a model of multilithology mantle melting that tracks the thermal evolution of the mantle during isentropic decompression melting. With this model, we explore the controls on the temperature at which primary melts begin to crystallize, as a function of source composition and the depth from which the magmas are derived. Large differences (200°C) in crystallization temperature can be generated by variations in mantle lithology, a magma's inferred depth of origin, and its thermal history. Combining this model with independent constraints on the magma volume flux and the effect of lithological heterogeneity on melt production, restricted regions of potential temperature-lithology space can be identified as consistent with the observed crystallization temperatures. Mantle potential temperature is constrained to be 1480-30+37 °C for Iceland and 1318-32+44 °C for MORB.

Oceanization of the lithospheric mantle: the study case of the spinel peridotites from Monte Maggiore (Corsica, France).

NASA Astrophysics Data System (ADS)

Piccardo, G. B.

2009-04-01

The Monte Maggiore peridotite body, cropping out within the Alpine Corsica metamorphic belt, is an ophiolite massif derived from the more internal setting of the Jurassic Ligurian Tethys basin. It is mostly composed by spinel and plagioclase peridotites that are cut by MORB gabbroic dykes. The spinel peridotites, similarly to other ophiolitic peridotites from the Internal Ligurides, have been considered, on the basis of their low abundance of fusible components, low Si and high Mg contents, as refractory residua after MORB-type partial melting related to the formation of the Jurassic basin (e.g. Rampone et al., 1997). Recent studies (e.g. Müntener & Piccardo 2003; Rampone et al. 2008) have evidenced that these depleted spinel peridotites show diffuse melt-rock interaction micro-textures and contrasting bulk vs. mineral chemistry features which cannot be simply reconciled with partial melting. Accordingly, these peridotites have been recognized as reactive peridotites, formed by interaction of pristine peridotites with melts percolating by porous flow. Geochemical data have evidenced the depleted MORB signature of the percolating melts. Recent field studies at Monte Maggiore (Piccardo, 2007; Piccardo & Guarnieri, 2009), have revealed: 1) the presence and local abundance of pyroxenite-bearing, cpx-rich spinel lherzolites and 2) the replacement relationships of the reactive peridotites on the pyroxenite-bearing lherzolite rock-types. The pyroxenite-veined spinel lherzolites record a composite history of subsolidus evolution under lithospheric P-T conditions, thus indicating their provenance from the sub-continental lithospheric mantle. Accordingly, the pristine sub-continental mantle protoliths were infiltrated by MORB melts and transformed by melt-rock interaction to reactive spinel peridotites and refertilized by melt impregnation to plagioclase-enriched peridotites. Available isotopic data on the Mt. Maggiore spinel and plagioclase peridotites and gabbroic rocks (Rampone, 2004; Rampone et al., 2008; 2009) provide reliable geochronological informations (i.e. Sm-Nd cpx-plg-wr isochron ages and Sm-Nd model ages) and evidence that the whole mafic and ultramafic rocks show an overall Sm/Nd isotopic homogeneity. Cpx-plg-wr data from gabbroic dykes define internal isochrones yielding Jurassic ages (162+/-10 Ma and 159+/-15 Ma, respectively). The plg-cpx(-wr) isochrons for impregnated plagioclase peridotites yields age of 155+/-6 Ma. The initial ɛNd values (8.9-9.7) are indicative of a MORB affinity. Calculated DM model ages for both spinel and plagioclase peridotites point to a Late Jurassic age (150 Ma). Isotope ratios of cpx from spinel and plagioclase peridotites conform to the linear array defined by overall gabbroic rocks. The isotopic evidence from the melt-percolated, reactive and impregnated peridotites indicates that the pristine lithospheric mantle protoliths were isotopically homogenized by the melt-rock interaction during percolation/impregnation processes which erased any pre-existing isotopic signature. Moreover, the overall Sm/Nd isotopic homogeneity indicates that the asthenospheric mantle sources of the infiltrating melts were isotopically homogeneous. Accordingly, it is plausible that percolation and intrusion were operated by similar and coeval Late Jurassic MORB-type melts. In conclusion, petrologic and isotopic data allow to recognize that the extending sub-continental lithospheric mantle was infiltrated by Late Jurassic MORB melts, formed by asthenospheric decompression-induced partial melting during continental extension and rifting. Melt-peridotite interaction modified the compositional features of the lithospheric mantle and caused its isotopic resetting. Accordingly, the sub-continental lithospheric mantle underwent an "oceanization" process (i.e. isotope resetting to "oceanic" MORB signatures) during Late Jurassic times operated by asthenospheric MORB melts. Depending on the melt composition, the lithospheric level and the mode of melt-rock interaction, fertile peridotites from the sub-continental lithospheric mantle were transformed, concomitantly, to depleted spinel peridotites and refertilized plagioclase peridotites.

Experimental approach to form anorthositic melts: phase relations in the system CaAl2Si2O8 - CaMgSi2O6 - Mg2SiO4 at 6 wt.% H2O

NASA Astrophysics Data System (ADS)

Zirner, Aurelia Lucretia Katharina; Ballhaus, Chris; Fonseca, Raúl; Müncker, Carsten

2014-05-01

Massive anorthosite dykes are documented for the first time from the Limassol Forest Complex (LFC) of Cyprus, the LFC being a deformed equivalent of the Troodos ultramafic massif. Both the Troodos and LFC complexes are part of the Tethyan realm consisting of Cretaceous oceanic crust that formed within a backarc basin 90 Ma ago and was obduced during late Miocene. From crosscutting relations with the sheeted dyke complex, it follows that the anorthosites belong to one of the latest magmatic events on Cyprus. In hand specimen, the rocks appear massive and unaltered, although in thin section magmatic plagioclase (An93) is partially replaced by albite and thomsonite (zeolite). Where magmatic textures are preserved, plagioclase forms cm-sized, acicular, radially arranged crystal aggregates that remind of spinifex textures. Six major types of anorthosite occurrences have previously been described, none of them matching with the above described anorthosite dykes [1]. The origin of these anorthosite dykes remains poorly understood. Even though they occur as intrusive dykes, it is evident that they cannot represent liquidus compositions, at least under dry conditions. Whole-sale melting of pure An93 would require temperatures in excess of 1450 °C, which is a quite unrealistic temperature of the modern Earth's crust. The working hypothesis is that boninitic melts with approximately 4 wt.% H2O, as found in the cyprian upper pillow lavas (UPL), could produce such rocks by olivine-pyroxene fractionation. Indeed, experiments indicate that such lithologies can be generated by medium-pressure fractional crystallization of hydrous basaltic melts followed by decompression-degassing. High pH2O stabilizes olivine but tends to suppress plagioclase as the highest polymerized phase. Hence the An component is accumulated in the (late-stage) melt. When such a system experiences sudden decompression, the aqueous phase will exsolve and will trigger massive precipitation of anorthite. Experiments at various temperatures are being performed in the ol-cpx-plag-H2O system, with olivine from a xenolith (Fo95) and anorthite and diopside glasses as starting materials. The materials are ground and mixed in the desired proportions, then equilibrated with 6 wt. % H2O at 0.5 GPa total pressure in a piston-cylinder press. A phase diagram of the Fo-Di-An-H2O system at 0.5 GPa will be constructed to outline the precise phase relations and fractionation paths are high H2O partial pressure. Aim is to delineate the anorthite saturation field in the ol-cpx-plag-H2O system, and to assess to which extent plagioclase can be suppressed as a liquidus phase when a basaltic melt fractionates under hydrous conditions. [1] Ashwal, L. D. (1993). Anorthosites, Springer-Verlag.

New Polish occupational health and safety regulations for underwater works.

PubMed

Kot, Jacek; Sićko, Zdzisław

2007-01-01

In Poland, the new regulation of the Ministry of Health on Occupational Health for Underwater Works (dated 2007) pursuant to the Act on Underwater Works (dated 2003) has just been published. It is dedicated for commercial, non-military purposes. It defines health requirements for commercial divers and candidates for divers, medical assessment guide with a list of specific medical tests done on initial and periodical medical examination in order for a diver or a candidate for diver to be recognised fit for work, health surveillance during diving operations, compression and decompression procedures, list of content for medical equipment to be present at any diving place, formal qualifications for physicians conducting medical assessment of divers, requirements for certifications confirming the medical status of divers and candidates for divers. Decompression tables cover divings up to 120 meters of depth using compressed air, oxygen, nitrox and heliox as breathing mixtures. There are also decompression tables for repetitive diving, altitude diving and diving in the high-density waters (mud diving). It this paper, general description of health requirements for divers, as well as decompression tables that are included in the new Regulation on Occupational Health for Underwater Works are presented.

Incidence of DCS and oxygen toxicity in chamber attendants: a 28-year experience.

PubMed

Witucki, Pete; Duchnick, Jay; Neuman, Tom; Grover, Ian

2013-01-01

Decompression sickness (DCS) and central nervous system oxygen toxicity are inherent risks for "inside" attendants (IAs) of hyperbaric chambers. At the Hyperbaric Medicine Center at the University of California San Diego (UCSD), protocols have been developed for decompressing IAs. Protocol 1: For a total bottom time (TBT) of less than 80 minutes at 2.4 atmospheres absolute (atm abs) or shallower, the U.S. Navy (1955) no-decompression tables were utilized. Protocol 2: For a TBT between 80 and 119 minutes IAs breathed oxygen for 15 minutes prior to initiation of ascent. Protocol 3: For a TBT between 120-139 minutes IAs breathed oxygen for 30 minutes prior to ascent. These protocols have been utilized for approximately 28 years and have produced zero cases of DCS and central nervous system oxygen toxicity. These results, based upon more than 24,000 exposures, have an upper limit of risk of DCS and oxygen toxicity of 0.02806 (95% CI) using UCSD IA decompression Protocol 1, 0.00021 for Protocol 2, and 0.00549 for Protocol 3. We conclude that the utilization of this methodology may be useful at other sea-level multiplace chambers.

A Challenging Case of Acute Mercury Toxicity

PubMed Central

Alghoula, Faysal; Holewinski, Christopher

2018-01-01

Background Mercury exists in multiple forms: elemental, organic, and inorganic. Its toxic manifestations depend on the type and magnitude of exposure. The role of colonoscopic decompression in acute mercury toxicity is still unclear. We present a case of acute elemental mercury toxicity secondary to mercury ingestion, which markedly improved with colonoscopic decompression. Clinical Case A 54-year-old male presented to the ED five days after ingesting five ounces (148 cubic centimeters) of elemental mercury. Examination was only significant for a distended abdomen. Labs showed elevated serum and urine mercury levels. An abdominal radiograph showed radiopaque material throughout the colon. Succimer and laxatives were initiated. The patient had recurrent bowel movements, and serial radiographs showed interval decrease of mercury in the descending colon with interval increase in the cecum and ascending colon. Colonoscopic decompression was done successfully. The colon was evacuated, and a repeat radiograph showed decreased hyperdense material in the colon. Three months later, a repeat radiograph showed no hyperdense material in the colon. Conclusion Ingested elemental mercury can be retained in the colon. Although there are no established guidelines for colonoscopic decompression, our patient showed significant improvement. We believe further studies on this subject are needed to guide management practices. PMID:29559996

Flotation of Magnetite Crystals upon Decompression - A Formation Model for Kiruna-type Iron Oxide-Apatite Deposits

NASA Astrophysics Data System (ADS)

Knipping, J. L.; Simon, A. C.; Fiege, A.; Webster, J. D.; Reich, M.; Barra, F.; Holtz, F.; Oeser-Rabe, M.

2017-12-01

Trace-element characteristics of magnetite from Kiruna-type iron oxide-apatite deposits indicate a magmatic origin. A possible scenario currently considered for the magmatic formation, apart from melt immiscibility, is related to degassing of volatile-rich magmas. Decompression, e.g., induced by magma ascent, results in volatile exsolution and the formation of a magmatic volatile phase. Volatile bubbles are expected to nucleate preferentially on the surface of oxides like magnetite which is due to a relatively low surface tension of oxide-bubble interfaces [1]. The "bulk" density of these magnetite-bubble pairs is typically lower than the surrounding magma and thus, they are expected to migrate upwards. Considering that magnetite is often the liquidus phase in fluid-saturated, oxidized andesitic arc magmas, this process may lead to the formation of a rising magnetite-bubble suspension [2]. To test this hypothesis, complementary geochemical analyses and high pressure experimental studies are in progress. The core to rim Fe isotopic signature of magnetite grains from the Los Colorados deposit in the Chilean Iron Belt was determined by Laser Ablation-MC-ICP-MS. The δ56Fe data reveal a systematic zonation from isotopically heavy Fe (δ56Fe: 0.25 ±0.07 ‰) in the core of magnetite grains to relatively light Fe (δ56Fe: 0.15 ±0.05 ‰) toward grain rims. This variation indicates crystallization of the magnetite cores at early magmatic stages from a silicate melt and subsequent growth of magnetite rims at late magmatic - hydrothermal stages from a free volatile phase. These signatures agree with the core to rim trace-element signatures of the same magnetite grains. The presence of Cl in the exsolved volatile phase and the formation of FeCl2 complexes is expected to enhance the transport of Fe in fluids and the formation of magmatic-hydrothermal magnetite [3]. First experiments (975 °C, 350 to 100 MPa, 0.025 MPa/s) show certain magnetite accumulation only 15 minutes after decompression in the upper part of the experimental products, indicating that magnetite flotation can be an efficient mechanism to separate and accumulate magnetite. [1] Hurwitz and Navon (1994) Earth Planet. Sci. Lett.122, 267-280 [2] Edmonds et al. (2014) Geol. Soc. London, Spec. Pub. 410. [3] Simon et al. (2004) Geochim. Cosmochim. Acta 68, 4905-4914.

Does decompression of odontogenic cysts and cystlike lesions change the histologic diagnosis?

PubMed

Schlieve, Thomas; Miloro, Michael; Kolokythas, Antonia

2014-06-01

The purpose of this study was to report the histopathologic findings after postdecompression definitive treatment of odontogenic cystlike lesions and determine whether the diagnosis was consistent with the pretreatment diagnosis, thereby answering the clinical question: does decompression change the histologic diagnosis? The authors implemented a retrospective cohort study from a sample of patients diagnosed with a benign odontogenic cystlike lesion and who underwent decompression followed by definitive surgery as part of their treatment. The predictor variable was treatment by decompression and the dependent variable was change in histologic diagnosis. Age, gender, and lesion location were included as variables. The χ(2) test was used for statistical analysis of the categorical data and P values less than .05 were considered statistically significant. Twenty-five cysts and cystlike lesions in 25 patients were treated with decompression followed by enucleation and curettage. The mean age was 34 years (range, 13 to 80 yr) and 56% (14) were male patients. Lesions were located in the mandible in 76% (19 of 25) of patients. Postdecompression histologic examination at the time of definitive surgical treatment was consistent with the preoperative biopsy diagnosis in 91% (10 of 11) of keratocystic odontogenic tumors, 67% (2 of 3) of glandular odontogenic cysts, 75% (3 of 4) of dentigerous cysts, and 100% (7 of 7) of cystic ameloblastomas. The histologic diagnosis at time of definitive treatment by enucleation and curettage is consistent with the predecompression diagnosis. Therefore, all lesions should be definitively treated after decompression based on the initial lesion diagnosis, with all patients placed on appropriate follow-up protocols. Copyright © 2014 American Association of Oral and Maxillofacial Surgeons. All rights reserved.

Sulfur Saturation Limits in Silicate Melts and their Implications for Core Formation Scenarios for Terrestrial Planets

NASA Technical Reports Server (NTRS)

Holzheid, Astrid; Grove, Timothy L.

2002-01-01

This study explores the controls of temperature, pressure, and silicate melt composition on S solubility in silicate liquids. The solubility of S in FeO-containing silicate melts in equilibrium with metal sulfide increases significantly with increasing temperature but decreases with increasing pressure. The silicate melt structure also exercises a control on S solubility. Increasing the degree of polymerization of the silicate melt structure lowers the S solubility in the silicate liquid. The new set of experimental data is used to expand the model of Mavrogenes and O'Neill(1999) for S solubility in silicate liquids by incorporating the influence of the silicate melt structure. The expected S solubility in the ascending magma is calculated using the expanded model. Because the negative pressure dependence of S solubility is more influential than the positive temperature dependence, decompression and adiabatic ascent of a formerly S-saturated silicate magma will lead to S undersaturation. A primitive magma that is S-saturated in its source region will, therefore, become S-undersaturated as it ascends to shallower depth. In order to precipitate magmatic sulfides, the magma must first cool and undergo fractional crystallization to reach S saturation. The S content in a metallic liquid that is in equilibrium with a magma ocean that contains approx. 200 ppm S (i.e., Earth's bulk mantle S content) ranges from 5.5 to 12 wt% S. This range of S values encompasses the amount of S (9 to 12 wt%) that would be present in the outer core if S is the light element. Thus, the Earth's proto-mantle could be in equilibrium (in terms of the preserved S abundance) with a core-forming metallic phase.

Pressure-temperature-time-deformation path of kyanite-bearing migmatitic paragneiss in the Kali Gandaki valley (Central Nepal): Investigation of Late Eocene-Early Oligocene melting processes

NASA Astrophysics Data System (ADS)

Iaccarino, Salvatore; Montomoli, Chiara; Carosi, Rodolfo; Massonne, Hans-Joachim; Langone, Antonio; Visonà, Dario

2015-08-01

Kyanite-bearing migmatitic paragneiss of the lower Greater Himalayan Sequence (GHS) in the Kali Gandaki transect (Central Himalaya) was investigated. In spite of the intense shearing, it was still possible to obtain many fundamental information for understanding the processes active during orogenesis. Using a multidisciplinary approach, including careful meso- and microstructural observations, pseudosection modelling (with PERPLE_X), trace element thermobarometry and in situ monazite U-Th-Pb geochronology, we constrained the pressure-temperature-time-deformation path of the studied rock, located in a structural key position. The migmatitic gneiss has experienced protracted prograde metamorphism after the India-Asia collision (50-55 Ma) from ~ 43 Ma to 28 Ma. During the late phase (36-28 Ma) of this metamorphism, the gneiss underwent high-pressure melting at "near peak" conditions (710-720 °C/1.0-1.1 GPa) leading to kyanite-bearing leucosome formation. In the time span of 25-18 Ma, the rock experienced decompression and cooling associated with pervasive shearing reaching P-T conditions of 650-670 °C and 0.7-0.8 GPa, near the sillimanite-kyanite transition. This time span is somewhat older than previously reported for this event in the study area. During this stage, additional, but very little melt was produced. Taking the migmatitic gneiss as representative of the GHS, these data demonstrate that this unit underwent crustal melting at about 1 GPa in the Eocene-Early Oligocene, well before the widely accepted Miocene decompressional melting related to its extrusion. In general, kyanite-bearing migmatite, as reported here, could be linked to the production of the high-Ca granitic melts found along the Himalayan belt.

Spherulites growth in trachytic melts: a textural quantitative study from synchrotron X-ray microtomography and SEM data

NASA Astrophysics Data System (ADS)

Arzilli, Fabio; Mancini, Lucia; Giuli, Gabriele; Cicconi, Maria Rita; Voltolini, Marco; Carroll, Michael R.

2013-04-01

This study shows the first textural data on synthetic alkali-feldspar spherulites grown in trachytic melts during cooling and decompression experiments with water-saturated conditions. Previous textural studies have shown the shape evolution and the growth process of spherulites as a function of undercooling (T) and water content, although just in basaltic and rhyolitic melts [1-3]. Spherulites are spherical clusters of polycrystalline aggregates that occur commonly in rhyolitic melts under highly non-equilibrium conditions [3-4]. Cooling and decompression experiments have been carried out on trachytic melts in order to investigate crystallization kinetics of alkali feldspars and the implications for magma dynamics during the ascent towards the surface. Experiments have been conducted using cold seal pressure vessel apparatus at pressure range of 30 - 200 MPa, temperature of 750 - 850 °C and time of 2 - 16 hours, thereby reproducing pre- and syn-eruptive conditions of the Campi Flegrei volcanoes. This study presents quantitative data on spherulite morphologies obtained both by scanning electron microscopy (SEM) and synchrotron X-ray microtomography. Size, aspect ratio, number and crystallographic misorientation of alkali feldspar crystals will be measured. Furthermore, experiments performed at different durations could allow us to follow the growth and the evolution of spherulites. The shape of spherulites changes as a function of ΔT and experimental durations. Two kind of spherulites occured during experiments: open spherulites and close spherulites. The open spherulites are characterized by an structure with large (generally rectangular prismatic), widely spaced fibers with main axis converging towards a central nucleus, in agreement with previous observations [5-6]. Instead, the close spherulites consist of acicular and tiny fibers radially aggregated around a nucleus and single crystals are hardly distinguishable. First preliminary results show: a) spherulites grow between 70-200 MPa, thus the nucleation process was favored at higher water contents; b) open spherulites seem to be favored at low ΔT, whereas close spherulites were favored in experiments at higher ΔT and long durations; c) estimated growth rates of spherulites were of 10-7 cm/s. References: [1] Lofgren G. (1971); Journal of Geophysical Research, 76, 5635-5648. [2] Gimeno D. (2003); Journal of Non-Crystaline Solids, 323, 84-90. [3] Watkins J., Manga M., Huber C. and Martin M. (2008); Contributions to Mineralogy and Petrology, [4] Grànàsy L., Pusztai T., Tegze G., Warren J. A. and Douglas J. F. (2005); Physical Review, 72, 011605. [5] Keith, H. D. and Padden F. J. (1963); Journal of Applied Physics, 8, 2409-2421. [6] Lofgren G. (1980); Princeton University Press, pp. 487-551.

Keweenaw hot spot: Geophysical evidence for a 1.1 Ga mantle plume beneath the Midcontinent Rift System

USGS Publications Warehouse

Hutchinson, D.R.; White, R.S.; Cannon, W.F.; Schulz, K.J.

1990-01-01

The Proterozoic Midcontinent Rift System of North America is remarkably similar to Phanerozoic rifted continental margins and flood basalt provinces. Like the younger analogues, the volcanism within this older rift can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad, asthenospheric, thermal anomaly which we call the Keweenaw hot spot. Great Lakes International Multidisciplinary Program on Crustal Evolution seismic reflection profiles constrain end-member models of melt thickness and stretching factors, which yield an inferred mantle potential temperature of 1500°–1570°C during rifting. Combined gravity modeling and subsidence calculations are consistent with stretching factors that reached 3 or 4 before rifting ceased, and much of the lower crust beneath the rift consists of relatively high density intruded or underplated synrift igneous material. The isotopic signature of Keweenawan volcanic rocks, presented in a companion paper by Nicholson and Shirey (this issue), is consistent with our model of passive rifting above an asthenospheric mantle plume.

Microstructures and petrology of melt inclusions in the anatectic sequence of Jubrique (Betic Cordillera, S Spain): Implications for crustal anatexis

NASA Astrophysics Data System (ADS)

Barich, Amel; Acosta-Vigil, Antonio; Garrido, Carlos J.; Cesare, Bernardo; Tajčmanová, Lucie; Bartoli, Omar

2014-10-01

We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though strongly thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and in contact with the peridotites, and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence, garnet decreases whereas biotite increases in modal proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ≈ 5 to 200 μm, with a mean size of ≈ 30-40 μm. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ≈ 850 °C and 12-14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ≈ 800-850 °C and 5-6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous conventional petrologic studies on these strongly deformed rocks have proposed that anatexis started during decompression from peak to post-peak conditions and in the field of sillimanite. The study of melt inclusions shows, however, that melt was already present in the system at peak conditions, and that most garnet grew in the presence of melt.

Global variations in abyssal peridotite compositions

NASA Astrophysics Data System (ADS)

Warren, Jessica M.

2016-04-01

Abyssal peridotites are ultramafic rocks collected from mid-ocean ridges that are the residues of adiabatic decompression melting. Their compositions provide information on the degree of melting and melt-rock interaction involved in the formation of oceanic lithosphere, as well as providing constraints on pre-existing mantle heterogeneities. This review presents a compilation of abyssal peridotite geochemical data (modes, mineral major elements, and clinopyroxene trace elements) for > 1200 samples from 53 localities on 6 major ridge systems. On the basis of composition and petrography, peridotites are classified into one of five lithological groups: (1) residual peridotite, (2) dunite, (3) gabbro-veined and/or plagioclase-bearing peridotite, (4) pyroxenite-veined peridotite, and (5) other types of melt-added peridotite. Almost a third of abyssal peridotites are veined, indicating that the oceanic lithospheric mantle is more fertile, on average, than estimates based on residual peridotites alone imply. All veins appear to have formed recently during melt transport beneath the ridge, though some pyroxenites may be derived from melting of recycled oceanic crust. A limited number of samples are available at intermediate and fast spreading rates, with samples from the East Pacific Rise indicating high degrees of melting. At slow and ultra-slow spreading rates, residual abyssal peridotites define a large (0-15% modal clinopyroxene and spinel Cr# = 0.1-0.6) compositional range. These variations do not match the prediction for how degree of melting should vary as a function of spreading rate. Instead, the compositional ranges of residual peridotites are derived from a combination of melting, melt-rock interaction and pre-existing compositional variability, where melt-rock interaction is used here as a general term to refer to the wide range of processes that can occur during melt transport in the mantle. Globally, 10% of abyssal peridotites are refractory (0% clinopyroxene, spinel Cr# > 0.5, bulk Al2O3 < 1 wt.%) and some ridge sections are dominated by harzburgites while lacking a significant basaltic crust. Abyssal ultramafic samples thus indicate that the mantle is multi-component, probably consisting of at least three components (lherzolite, harzburgite, and pyroxenite). Overall, the large compositional range among residual and melt-added peridotites implies that the oceanic lithospheric mantle is heterogeneous, which will lead to the generation of further heterogeneities upon subduction back into the mantle.

Impact of timing of cranioplasty on hydrocephalus after decompressive hemicraniectomy in malignant middle cerebral artery infarction.

PubMed

Finger, Tobias; Prinz, Vincent; Schreck, Evelyn; Pinczolits, Alexandra; Bayerl, Simon; Liman, Thomas; Woitzik, Johannes; Vajkoczy, Peter

2017-02-01

Patients with malignant middle cerebral artery infarction frequently develop hydrocephalus after decompressive hemicraniectomy. Hydrocephalus itself and known shunt related complications after ventriculo-peritoneal shunt implantation may negatively impact patientś outcome. Here, we aimed to identify factors associated with the development of hydrocephalus after decompressive hemicraniectomy in malignant middle cerebral artery infarction. A total of 99 consecutive patients with the diagnosis of large hemispheric infarctions and the indication for decompressive hemicraniectomy were included. We retrospectively evaluated patient characteristics (gender, age and selected preoperative risk factors), stroke characteristics (side, stroke volume and existing mass effect) and surgical characteristics (size of the bone flap, initial complication rate, time to cranioplasty, complication rate following cranioplasty, type of implant, number of revision surgeries and mortality). Frequency of hydrocephalus development was 10% in our cohort. Patients who developed a hydrocephalus had an earlier time point of bone flap reimplantation compared to the control group (no hydrocephalus=164±104days, hydrocephalus=108±52days, p<0.05). Additionally, numbers of revision surgeries after cranioplasty was associated with hydrocephalus with a trend towards significance (p=0.08). Communicating hydrocephalus is frequent in patients with malignant middle cerebral artery infarction after decompressive hemicraniectomy. A later time point of cranioplasty might lead to a lower incidence of required shunting procedures in general as we could show in our patient cohort. Copyright © 2016 Elsevier B.V. All rights reserved.

The effects of magmatic redistribution of heat producing elements on the lunar mantle evolution inferred from numerical models that start from various initial states

NASA Astrophysics Data System (ADS)

Ogawa, Masaki

2018-02-01

To discuss how redistribution of heat producing elements (HPEs) by magmatism affects the lunar mantle evolution depending on the initial condition, I present two-dimensional numerical models of magmatism in convecting mantle internally heated by incompatible HPEs. Mantle convection occurs beneath a stagnant lithosphere that inhibits recycling of the HPE-enriched crustal materials to the mantle. Magmatism is modeled by a permeable flow of magma generated by decompression melting through matrix. Migrating magma transports heat, mass, and HPEs. When the deep mantle is initially hot with the temperature TD around 1800 K at its base, magmatism starts from the beginning of the calculated history to extract HPEs from the mantle. The mantle is monotonously cooled, and magmatism ceases within 2 Gyr, accordingly. When the deep mantle is initially colder with TD around 1100 K, HPEs stay in the deep mantle for a longer time to let the planet be first heated up and then cooled only slightly. If, in addition, there is an HPE-enriched domain in the shallow mantle at the beginning of the calculation, magma continues ascending to the surface through the domain for more than 3 Gyr. The low TD models fit in with the thermal and magmatic history of the Moon inferred from spacecraft observations, although it is not clear if the models are consistent with the current understanding of the origin of the Moon and its magnetic field. Redistribution of HPEs by magmatism is a crucial factor that must be taken into account in future studies of the evolution of the Moon.

Upper mantle structure of the Tonga-Lau-Fiji region from Rayleigh wave tomography

NASA Astrophysics Data System (ADS)

Wei, S. Shawn; Zha, Yang; Shen, Weisen; Wiens, Douglas A.; Conder, James A.; Webb, Spahr C.

2016-11-01

We investigate the upper mantle seismic structure in the Tonga-Lau-Fiji region by jointly fitting the phase velocities of Rayleigh waves from ambient-noise and two-plane-wave tomography. The results suggest a wide low-velocity zone beneath the Lau Basin, with a minimum SV-velocity of about 3.7 ± 0.1 km/s, indicating upwelling hot asthenosphere with extensive partial melting. The variations of velocity anomalies along the Central and Eastern Lau Spreading Centers suggest varying mantle porosity filled with melt. In the north where the spreading centers are distant from the Tonga slab, the inferred melting commences at about 70 km depth, and forms an inclined zone in the mantle, dipping to the west away from the arc. This pattern suggests a passive decompression melting process supplied by the Australian plate mantle from the west. In the south, as the supply from the Australian mantle is impeded by the Lau Ridge lithosphere, flux melting controlled by water from the nearby slab dominates in the back-arc. This source change results in the rapid transition in geochemistry and axial morphology along the spreading centers. The remnant Lau Ridge and the Fiji Plateau are characterized by a 60-80 km thick lithosphere underlain by a low-velocity asthenosphere. Our results suggest the removal of the lithosphere of the northeastern Fiji Plateau-Lau Ridge beneath the active Taveuni Volcano. Azimuthal anisotropy shows that the mantle flow direction rotates from trench-perpendicular beneath Fiji to spreading-perpendicular beneath the Lau Basin, which provides evidence for the southward flow of the mantle wedge and the Samoan plume.

Magma Plumbing System at a Young Back-Arc Spreading Center: The Marsili Volcano, Southern Tyrrhenian Sea

NASA Astrophysics Data System (ADS)

Trua, T.; Marani, M. P.; Gamberi, F.

2018-01-01

Although spreading rate is commonly taken as a proxy for decompression mantle melting at mid-ocean ridges (MORs), magmatism at back-arc spreading centers (BASCs) is further influenced by the subduction-related flux melting of the mantle. These regions consequently show a diversity of crustal structures, lava compositions, and morphologies not typically found in MORs. Here we investigate the crustal plumbing system of the small-scale, Marsili back-arc spreading center of the Southern Tyrrhenian Sea using plagioclase data from a wide spectrum of lavas (basalts to andesites) dredged from its summit and flanks. We employ petrological modeling to identify the plagioclase populations carried in the individual lavas, allocate them to plausible magmatic components present within the plumbing system, and trace the processes occurring during magma ascent to the surface. The properties of the system, such as mush porosity and abundance of the melt bodies, vary from one magma extraction zone to another along the BASC, evidencing the local variability of melt supply conditions. The plagioclase crystals document a range of relationships with the host lavas, indicating magma extraction from a composite, vertically extensive mush and melt-lens system resembling that of MORs. At the same time, however, in small BASCs, such as in the case of the Marsili Basin, crustal accretion and resulting morphology are significantly influenced by the three-dimensional setting of the basin margins. This is an important deviation from the conventional model based on the linear continuity and essentially two-dimensional framework of MORs.

Nature of metastable amorphous-to-crystalline reversible phase transformations in GaSb

NASA Astrophysics Data System (ADS)

Kalkan, B.; Edwards, T. G.; Raoux, S.; Sen, S.

2013-08-01

The structural, thermodynamic, and kinetic aspects of the transformations between the metastable amorphous and crystalline phases of GaSb are investigated as a function of pressure at ambient temperature using synchrotron x-ray diffraction experiments in a diamond anvil cell. The results are consistent with the hypothesis that the pressure induced crystallization of amorphous GaSb into the β-Sn crystal structure near ˜5 GPa is possibly a manifestation of an underlying polyamorphic phase transition between a semiconducting, low density and a metallic, high density amorphous (LDA and HDA, respectively) phases. In this scenario, the large differences in the thermal crystallization kinetics between amorphous GaSb deposited in thin film form by sputtering and that prepared by laser melt quenching may be related to the relative location of the glass transition temperature of the latter in the pressure-temperature (P-T) space with respect to the location of the critical point that terminate the LDA ↔ HDA transition. The amorphous → β-Sn phase transition is found to be hysteretically reversible as the β-Sn phase undergoes decompressive amorphization near ˜2 GPa due to the lattice instabilities that give rise to density fluctuations in the crystal upon decompression.

Low-melting elemental metal or fusible alloy encapsulated polymerization initiator for delayed initiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hermes, Robert E.

2017-08-15

An encapsulated composition for polymerization includes an initiator composition for initiating a polymerization reaction, and a capsule prepared from an elemental metal or fusible alloy having a melting temperature from about 20.degree. C. to about 200.degree. C. A fluid for polymerization includes the encapsulated composition and a monomer. When the capsule melts or breaks open, the initiator is released.

Phase equilibrium constraints on the origin of basalts, picrites, and komatiites

NASA Astrophysics Data System (ADS)

Herzberg, C.; O'Hara, M. J.

1998-07-01

Experimental phase equilibrium studies at pressures ranging from 1 atm to 10 GPa are sufficient to constrain the origin of igneous rocks formed along oceanic ridges and in hotspots. The major element geochemistry of MORB is dominated by partial crystallization at low pressures in the oceanic crust and uppermost mantle, forcing compliance with liquid compositions in low-pressure cotectic equilibrium with olivine, plagioclase and often augite too; parental magmas to MORB formed by partial melting, mixing, and pooling have not survived these effects. Similarly, picrites and komatiites can transform to basalts by partial crystallization in the crust and lithosphere. However, parental picrites and komatiites that were successful in erupting to the surface typically have compositions that can be matched to experimentally-observed anhydrous primary magmas in equilibrium with harzburgite [L+Ol+Opx] at 3.0 to 4.5 GPa. This pressure is likely to represent an average for pooled magmas that collected at the top of a plume head as it flattened below the lithosphere. There is substantial uniformity in the normative olivine content of primary magmas at all depths in a plume melt column, and this results in pooled komatiitic magmas that are equally uniform in normative olivine. However, the imposition of pressure above 3 GPa produces picrites and komatiites with variations in normative enstatite and Al 2O 3 that reveal plume potential temperature and depths of initial melting. Hotter plumes begin to melt deeper than cooler plumes, yielding picrites and komatiites that are enriched in normative enstatite and depleted in Al 2O 3 because of a deeper column within which orthopyroxene can dissolve during decompression. Pressures of initial melting span the 4 to 10 GPa range, increasing in the following order: Iceland, Hawaii, Gorgona, Belingwe, Barberton. Parental komatiites and picrites from a single plume also exhibit internal variability in normative enstatite and Al 2O 3, indicating either a poorly mixed partial melt aggregation process in the plume or the imposition of partial crystallization of olivine-orthopyroxenite on a well-mixed parental magma. Plume shape and thermal structure can also influence the petrology and geochemistry of picrites and komatiites. Liquids extracted from harzburgite residues [L+Ol+Opx] will dominate magmatism in a plume head, and can erupt to form komatiites in oceanic plateaus. Liquids extracted from garnet peridotite residues in a plume axis will gain in importance when the plume head partially solidifies and is removed from the hotspot by a moving lithosphere, as is the case for Hawaii. The paradoxical involvement of garnet indicated by the heavy rare earth elements in picrites that otherwise have a harzburgite signature in Hawaii can be explained by the mixing and collection of magmas from the plume axis. Volcanic rocks from Hawaii and Gorgona and xenoliths from cratonic mantle provide evidence for the importance of partial crystallization of plume magmas when they encounter a cold lithosphere. Harzburgite residua and olivine-orthopyroxene cumulates formed in plumes can yield compositionally distinct lithospheric mantle which is buoyant, and this could have provided an important foundation for the stabilization of the first continents.

Widespread Magmatism as a Result of Impact Related Decompression Melting on Early Mars

NASA Astrophysics Data System (ADS)

Edwards, C. S.; Bandfield, J. L.; Christensen, P. R.; Rogers, D.

2012-12-01

Flat-floored craters on Mars have been observed since early spacecraft viewed the surface. Early work characterized these craters as infilled by sedimentary materials [e.g. Christensen, 1983] but later work using THEMIS thermal inertia determined these craters contain some of the rockiest materials on the planet and not sedimentary materials [Edwards et al., 2009]. Here we investigate the distribution, physical properties (morphology and thermal inertia), and composition of these craters over the entire planet. We find the majority of rocky crater floors identified (~3300) are concentrated in the low albedo (0.1-0.17), cratered southern highlands. These craters are associated with the highest thermal inertia values (e.g. > 500 to 2000 J m-2 K-1 s-1/2), some of the most mafic materials on the planet (enriched in olivine/pyroxene vs. high-Si phases/plagioclase, often with >10-15% olivine areal abundance), and formed ~3.5 billion years ago. Based on the properties of the crater fill materials described, three mechanisms are considered for the formation of flat-floored, high thermal inertia crater floors on Mars including: 1) the lithification/induration of sediments, 2) the ponding of crustal melt material related to the heat generated during the impact process, and 3) infilling by volcanic materials. We find the only likely scenario is volcanic infilling through fractures created in the impact event. Furthermore, we find the generation of the primitive magma would be directly sourced from the decompression melting of the martian mantle due to the removal of several kilometers of overlying crustal material by the impactor. As the ancient martian crust was likely thin and the geothermal gradients were significantly higher than present day [e.g. Zuber, 2001], the decompression melting of the mantle [Bertka and Holloway, 1994] would be more likely to occur on early Mars then under present day conditions. This is borne out by the ancient ages (~3-4Ga) of the crater floors that indicates their formation early in martian history and not after the crustal thickening of the southern highlands and reduction of the geothermal gradient. Based on the distribution of these crater floors, we find that this process occurred over much of the surface of early Mars, during or shortly thereafter the Late Heavy Bombardment when the crust was still relatively thin and heat flow was high. We have shown that this process was widespread and ubiquitous, responsible for the eruption of significant volumes of primitive mantle material, both inside and outside of craters, and is an important planetary process that has gone previously undocumented. However, this process is likely not unique to Mars and while we have not examined other planetary bodies in detail, craters on Earth's moon and Mercury show distinctive morphologic similarities [e.g. Schultz, 1976] that suggest this process occurred throughout the early solar system on many rocky bodies. References: Bertka, C. M., et al. (1994), Contributions to Mineralogy and Petrology, 115(3), 313-322. Christensen, P. R. (1983), Icarus, 56(3), 496-518. Edwards, C. S., et al. (2009), J. Geophys. Res, 114, E11001. Schultz, P. H. (1976), The Moon, 15, 241-273. Zuber, M. T. (2001), Nature, 412, 220-227.

Glaciation control of melting rates in the mantle: U-Th systematics of young basalts from Southern Siberia and Central Mongolia

NASA Astrophysics Data System (ADS)

Rasskazov, S.; Chebykin, E.

2012-04-01

Eastern Sayans, Siberia and Hangay, Central Mongolia are mountainous uplifts effected by Quaternary volcanism, but only the former area was covered by glaciers that were as thick as 500 m. Glaciation time intervals were marked by moraines and sub-glacial hyaloclastite-bearing volcanic edifices, whereas interglacial ones were exhibited by sub-aerial "valley" flows and cinder cones. To estimate temporal variations of maximum rates of melting and mantle upwelling in the glacial and glacial-free areas, we measured radionuclides of the U-Th system for 74 samples of the Middle-Late Pleistocene through Holocene basalts by ICP-MS technique (Chebykin et al. Russian Geol. Geophys. 2004. 45: 539-556) using mass-spectrometer Agilent 7500ce. The obtained U-Th isochron ages for the Pleistocene volcanic units in the age interval of the last 400 Kyr are mostly consistent with results of K-Ar dating. The measured (230Th/238U) ratios for the Holocene basalts from both areas are within the same range of 1.08-1.16 (parentheses denote units of activity), whereas the 50 Kyr lavas yield, respectively, the higher and lower initial (230Th0/238U) ratios (1.18-1.46 and 1.05-1.13). This discrepancy demonstrates contrast maximum rates of melting in conventional garnet peridotite sources. We suggest that this dynamical feature was provided by the abrupt Late Pleistocene deglaciation that caused the mantle decompression expressed by the earlier increasing melting beneath Eastern Sayans than beneath Hangay. In the last 400 Kyr, magmatic liquids from both Eastern Sayans and Hangay showed the overall temporal decreasing (230Th0/238U) (i.e. relative increasing rates of melting and upwelling of the mantle) with the systematically lower isotopic ratios (i.e. increased mantle activity) in the former area than in the latter. The 400 Kyr phonotephrites in Hangay showed elevated concentrations of Th (6-8 ppm) and Th/U (3.7-3.9). The high (230Th0/238U) (4.3-6.0) reflected slow fractional melting, accompanied by rapid removal of melts. In episodes of 50-35 and ~9 Kyr, the ratio decreased from interval 1.23-1.52 to 1.08-1.22, indicating a relative increase of the porosity, maximum rates of melting, and upwelling of the mantle. The 350 Kyr magmatic melts in Eastern Sayans revealed the lower concentrations of Th (~2 ppm) and Th/U (2.7-2.9) due to more depleted composition of the source region, but their high (230Th0/238U) (2.7-2.9) also demonstrated slow fractional melting and upwelling. The defined maxima of melting and upwelling of the mantle beneath this area at 170 and 50 Kyr (Mmax = 1.1 × 10-3 kg/m3/yr, Wmax = 11 cm yr-1) were separated from each other by a minimum at 150 Kyr. These variations are interpreted in terms of temporal control of the mantle dynamic parameters by growing and thawing glaciers. The work was supported by the Russian Federal Aim Program "Scientific and scientific-pedagogical personnel of innovative Russia" for 2009-2013, the state contract number P736.

First-principles molecular dynamics simulations of anorthite (CaAl2Si2O8) glass at high pressure

NASA Astrophysics Data System (ADS)

Ghosh, Dipta B.; Karki, Bijaya B.

2018-06-01

We report first-principles molecular dynamics study of the equation of state, structural, and elastic properties of CaAl2Si2O8 glass at 300 K as a function of pressure up to 155 GPa. Our results for the ambient pressure glass show that: (1) as with other silicates, Si atoms remain mostly (> 95%) under tetrahedral oxygen surroundings; (2) unlike anorthite crystal, presence of high-coordination (> 4) Al atoms with 30% abundance; (3) and significant presence of both non-bridging (8%) and triply (17%) coordinated oxygen. To achieve the glass configurations at various pressures, we use two different simulation schedules: cold and hot compression. Cold compression refers to sequential compression at 300 K. Compression at 3000 K and subsequent isochoric quenching to 300 K is considered as hot compression. At the initial stages of compression (0-10 GPa), smooth increase in bond distance and coordination occurs in the hot-compressed glass. Whereas in cold compression, Si (also Al to some extent) displays mainly topological changes (without significantly affecting the average bond distance or coordination) in this pressure interval. Further increase in pressure results in gradual increases in mean coordination, with Si-O (Al-O) coordination eventually reaching and remaining 6 (6.5) at the highest compression. Similarly, the ambient pressure Ca-O coordination of 5.9 increases to 9.5 at 155 GPa. The continuous pressure-induced increase in the proportion of oxygen triclusters along with the appearance and increasing abundance of tetrahedral oxygens results in mean O-T (T = Si and Al) coordination of > 3 from a value of 2.1 at ambient pressure. Due to the absence of kinetic barrier, the hot-compressed glasses consistently produce greater densities and higher coordination numbers than the cold compression cases. Decompressed glasses show irreversible compaction along with retention of high-coordination species when decompressed from pressure ≥ 10 GPa. The different density retention amounts (12, 17, and 20% when decompressed from 12, 40, and 155 GPa, respectively) signifies that the degree of irreversibility depends on the peak pressure of decompression. The calculated compressional and shear wave velocities (5 and 3 km/s at 0 GPa) for the cold-compressed case display sluggish pressure response in the 0-10 GPa interval as opposed to smooth increase in the hot-compressed one. Shear velocity saturates rather rapidly with a value of 5 km/s, whereas compressional wave velocity displays continuous increase, reaching/exceeding 12.5 km/s at 155 GPa. These structural details suggest that the pressure response of the cold-compressed glasses is not only inherently different at the 0-10 GPa interval, the density, coordination, and wave velocity data are consistently lower than the hot-compressed glasses. Hot-compressed glasses may, therefore, be the better analog in the study of high-pressure silicate melts.

Numerical models of the magmatic processes induced by slab breakoff

NASA Astrophysics Data System (ADS)

Freeburn, Rebecca; Bouilhol, Pierre; Maunder, Ben; Magni, Valentina; van Hunen, Jeroen

2017-11-01

After the onset of continental collision, magmatism often persists for tens of millions of years, albeit with a different composition, in reduced volumes, and with a more episodic nature and more widespread spatial distribution, compared to normal arc magmatism. Kinematic modelling studies have suggested that slab breakoff can account for this post-collisional magmatism through the formation of a slab window and subsequent heating of the overriding plate and decompression melting of upwelling asthenosphere, particularly if breakoff occurs at depths shallower than the overriding plate. To constrain the nature of any melting and the geodynamic conditions required, we numerically model the collision of two continental plates following a period of oceanic subduction. A thermodynamic database is used to determine the (de)hydration reactions and occurrence of melt throughout this process. We investigate melting conditions within a parameter space designed to generate a wide range of breakoff depths, timings and collisional styles. Under most circumstances, slab breakoff occurs deeper than the depth extent of the overriding plate; too deep to generate any decompressional melting of dry upwelling asthenosphere or thermal perturbation within the overriding plate. Even if slab breakoff is very shallow, the hot mantle inflow into the slab window is not sustained long enough to sufficiently heat the hydrated overriding plate to cause significant magmatism. Instead, for relatively fast, shallow breakoff we observe melting of asthenosphere above the detached slab through the release of water from the tip of the heating detached slab. Melting of the subducted continental crust during necking and breakoff is a more common feature and may be a more reliable indicator of the occurrence of breakoff. We suggest that magmatism from slab breakoff alone is unable to explain several of the characteristics of post-collisional magmatism, and that additional geodynamical processes need to be considered when interpreting magmatic observations.

The impact of dissolved fluorine on bubble nucleation in hydrous rhyolite melts

NASA Astrophysics Data System (ADS)

Gardner, James E.; Hajimirza, Sahand; Webster, James D.; Gonnermann, Helge M.

2018-04-01

Surface tension of hydrous rhyolitic melt is high enough that large degrees of supersaturation are needed to homogeneously nucleate H2O bubbles during eruptive magma ascent. This study examines whether dissolved fluorine lowers surface tension of hydrous rhyolite, and thus lowers the supersaturation required for bubble nucleation. Fluorine was targeted because it, like H2O, changes melt properties and is highly soluble, unlike all other common magmatic volatiles. Rhyolite melts were saturated at Ps = 245 MPa with H2O fluid that contained F, generating rhyolite with 6.7 ± 0.4 wt.% H2O and 1.1-1.3 wt.% F. When these melts were decompressed rapidly to Pf = 149-202 MPa and quenched after 60 s, bubbles nucleated at supersaturations of ΔP = Ps - Pf ≥52 MPa, and reached bubble number densities of NB = 1012-13 m-3 at ΔP = 78-101 MPa. In comparison, rhyolite saturated with 6.34 ± 0.09 wt.% H2O, but only 0.25 wt.% F, did not nucleate bubbles until ΔP ≥ 100-116 MPa, and even then, at significantly lower NB (<1010 m-3). Numerical modeling of bubble nucleation and growth was used to estimate the values of surface tension required to generate the observed values of NB. Slight differences in melt compositions (i.e., alkalinity and H2O content), H2O diffusivity, or melt viscosity cannot explain the observed differences in NB. Instead, surface tension of F-rich rhyolite must be lower by approximately 4% than that of F-poor rhyolite. This difference in surface tension is significant and, for example, exceeds that found between hydrous basaltic andesite and hydrous rhyolite. These results suggest that is likely that surface tension for F-rich magmas, such as topaz rhyolite, is significantly lower than for F-poor magmas.

The Temperature of the Icelandic Mantle Plume from Aluminium-in-Olivine Thermometry

NASA Astrophysics Data System (ADS)

Matthews, S.; Shorttle, O.; Maclennan, J.

2015-12-01

Temperature is a key control on the physical properties of the mantle, in particular the extent of melting during upwelling. It is not, however, a unique control on many of the parameters used to estimate mantle temperature. For example igneous crustal thickness which has often been used as a first-order proxy for mantle temperature, is also affected by mantle lithology and plume flux. Alternatives to geophysical indicators of mantle temperature are petrological thermometers. However, these record crystallisation temperatures, therefore a series of assumptions about the coupled melt- solid mantle thermal history must be made when calculating back to mantle potential temperature. In this study we investigate how these assumptions may affect mantle temperature estimates and how crystallisation temperatures may offer insights into the melting and melt transport processes, focussing on a new set of crystallisation temperature estimates we have made on primitive Icelandic basalts.We used the aluminium-in-olivine thermometer of Coogan et al. (2014) to estimate crystallisation temperatures of olivine phenocrysts in a suite of samples from the Northern Volcanic Zone (NVZ) of Iceland. The data suggest that within a single volcanic system crystallisation temperature depends strongly on the olivine forsterite content, thus the history of melt evolution, and how the eruption samples this, must be considered when extrapolating to mantle temperature. To assess the influence of the assumptions required to obtain mantle temperature we constructed a simple thermal model incorporating varying proportions of lherzolite, pyroxenite and harzburgite undergoing decompression melting. A trade off between increasing mantle temperature and decreasing pyroxenite (or increasing harzburgite) in the source is observed. Using this dataset and our model, calculations reveal a potential temperature of 1470±130 °C for Iceland, and a temperature excess of 150±40 °C relative to ambient mantle. These estimates are consistent with temperatures estimated using crustal thickness and melt chemistry.

Giant magmatic water reservoirs at mid-crustal depth inferred from electrical conductivity and the growth of the continental crust

NASA Astrophysics Data System (ADS)

Laumonier, Mickael; Gaillard, Fabrice; Muir, Duncan; Blundy, Jon; Unsworth, Martyn

2017-01-01

The formation of the continental crust at subduction zones involves the differentiation of hydrous mantle-derived magmas through a combination of crystallization and crustal melting. However, understanding the mechanisms by which differentiation occurs at depth is hampered by the inaccessibility of the deep crust in active continental arcs. Here we report new high-pressure electrical conductivity and petrological experiments on hydrated andesitic melt from Uturuncu volcano on the Bolivian Altiplano. By applying our results to regional magnetotelluric data, we show that giant conductive anomalies at mid-crustal levels in several arcs are characterized by relatively low amounts of intergranular andesitic partial melts with unusually high dissolved water contents (≥8 wt.% H2O). Below Uturuncu, the Altiplano-Puna Magma Body (APMB) displays an electrical conductivity that requires high water content (up to 10 wt.%) dissolved in the melt based on crystal-liquid equilibria and melt H2O solubility experiments. Such a super-hydrous andesitic melt must constitute about 10% of the APMB, the remaining 90% being a combination of magmatic cumulates and older crustal rocks. The crustal ponding level of these andesites at around 6 kbar pressure implies that on ascent through the crust hydrous magmas reach their water saturation pressure in the mid-crust, resulting in decompression-induced crystallization that increases magma viscosity and in turn leads to preferential stalling and differentiation. Similar high conductivity features are observed beneath the Cascades volcanic arc and Taupo Volcanic Zone. This suggests that large amounts of water in super-hydrous andesitic magmas could be a common feature of active continental arcs and may illustrate a key step in the structure and growth of the continental crust. One Sentence Summary: Geophysical, laboratory conductivity and petrological experiments reveal that deep electrical conductivity anomalies beneath the Central Andes, Cascades and Taupo Volcanic Zone image the ponding of super-hydrous andesitic melts which contributes to the growth of continental crust.

Emplacement conditions of komatiite magmas from the 3.49 Ga Komati Formation, Barberton Greenstone Belt, South Africa1

NASA Astrophysics Data System (ADS)

Parman, S. W.; Dann, J. C.; Grove, T. L.; de Wit, M. J.

1997-08-01

This paper provides new constraints on the crystallization conditions of the 3.49 Ga Barberton komatiites. The compositional evidence from igneous pyroxene in the olivine spinifex komatiite units indicates that the magma contained significant quantities of dissolved H2O. Estimates are made from comparisons of the compositions of pyroxene preserved in Barberton komatiites with pyroxene produced in laboratory experiments at 0.1 MPa (1 bar) under anhydrous conditions and at 100 and 200 MPa (1 and 2 kbar) under H2O-saturated conditions on an analog Barberton composition. Pyroxene thermobarometry on high-Ca clinopyroxene compositions from ten samples requires a range of minimum magmatic water contents of 6 wt.% or greater at the time of pyroxene crystallization and minimum emplacement pressures of 190 MPa (6 km depth). Since high-Ca pyroxene appears after 30% crystallization of olivine and spinel, the liquidus H2O contents could be 4 to 6 wt.% H2O. The liquidus temperature of the Barberton komatiite composition studied is between 1370 and 1400°C at 200 MPa under H2O-saturated conditions. When compared to the temperature-depth regime of modern melt generation environments, the komatiite mantle source temperatures are 200°C higher than the hydrous mantle melting temperatures inferred in modern subduction zone environments and 100°C higher than mean mantle melting temperatures estimated at mid-ocean ridges. When compared to previous estimates of komatiite liquidus temperatures, melting under hydrous conditions occurs at temperatures that are ˜ 250°C lower than previous estimates for anhydrous komatiite. Mantle melting by near-fractional, adiabatic decompression takes place in a melting column that spans ˜ 38 km depth range under hydrous conditions. This depth interval for melting is only slightly greater than that observed in modern mid-ocean ridge environments. In contrast, anhydrous fractional melting models of komatiite occur over a larger depth range (˜ 130 km) and place the base of the melting column into the transition zone.

Interaction between climate, volcanism, and isostatic rebound in Southeast Alaska during the last deglaciation

USGS Publications Warehouse

Praetorius, Summer; Mix, Alan; Jensen, Britta; Froese, Duane; Milne, Glenn A.; Wolhowe, Matthew; Addison, Jason A.; Prahl, Fred

2016-01-01

Observations of enhanced volcanic frequency during the last deglaciation have led to the hypothesis that ice unloading in glaciated volcanic terrains can promote volcanism through decompression melting in the shallow mantle or a reduction in crustal magma storage time. However, a direct link between regional climate change, isostatic adjustment, and the initiation of volcanism remains to be demonstrated due to the difficulty of obtaining high-resolution well-dated records that capture short-term climate and volcanic variability traced to a particular source region. Here we present an exceptionally resolved record of 19 tephra layers paired with foraminiferal oxygen isotopes and alkenone paleotemperatures from marine sediment cores along the Southeast Alaska margin spanning the last deglacial transition. Major element compositions of the tephras indicate a predominant source from the nearby Mt. Edgecumbe Volcanic Field (MEVF). We constrain the timing of this regional eruptive sequence to 14.6–13.1 ka. The sudden increase in volcanic activity from the MEVF coincides with the onset of Bølling–Allerød interstadial warmth, the disappearance of ice-rafted detritus, and rapid vertical land motion associated with modeled regional isostatic rebound in response to glacier retreat. These data support the hypothesis that regional deglaciation can rapidly trigger volcanic activity. Rapid sea surface temperature fluctuations and an increase in local salinity (i.e., δ18Osw) variability are associated with the interval of intense volcanic activity, consistent with a two-way interaction between climate and volcanism in which rapid volcanic response to ice unloading may in turn enhance short-term melting of the glaciers, plausibly via albedo effects on glacier ablation zones.

Elimination of CT-detected gas bubbles derived from decompression illness with abdominal symptoms after a short hyperbaric oxygen treatment in a monoplace chamber: a case report.

PubMed

Oyaizu, Takuya; Enomoto, Mitsuhiro; Tsujimoto, Toshihide; Kojima, Yasushi; Okawa, Atsushi; Yagishita, Kazuyoshi

2017-01-01

We report the case of a 54-year-old male compressed-air worker with gas bubbles detected by computed tomography (CT). He had complained of strong abdominal pain 30 minutes after decompression after working at a pressure equivalent to 17 meters of sea water for three hours. The initial CT images revealed gas bubbles in the intrahepatic portal vein, pulmonary artery and bilateral femoral vein. After the first hyperbaric oxygen treatment (HBO₂ at 2.5 atmospheres absolute/ATA for 150 minutes), no bubbles were detected on repeat CT examination. The patient still exhibited abdominal distension, mild hypesthesia and slight muscle weakness in the upper extremities. Two sessions of U.S. Navy Treatment Table 6 (TT6) were performed on Days 6 and 7 after onset. The patient recovered completely on Day 7. This report describes the important role of CT imaging in evaluating intravascular gas bubbles as well as eliminating the diagnosis of other conditions when divers or compressed-air workers experience uncommon symptoms of decompression illness. In addition, a short treatment table of HBO₂ using non-TT6 HBO₂ treatment may be useful to reduce gas bubbles and the severity of decompression illness in emergent cases. Copyright© Undersea and Hyperbaric Medical Society.

Modeling Explosive Eruptions at Kīlauea, Hawai'i

NASA Astrophysics Data System (ADS)

Gonnermann, H. M.; Ferguson, D. J.; Blaser, A. P.; Houghton, B. F.; Plank, T. A.; Hauri, E. H.; Swanson, D. A.

2014-12-01

We have modeled eruptive magma ascent during two explosive eruptions of Kīlauea volcano, Hawai'i. They are the Hawaiian style Kīlauea Iki eruption, 1959, and the subplinian Keanakāko'i eruption, 1650 CE. We have modeled combined magma ascent in the volcanic conduit and exsolution of H2O and CO2 from the erupting magma. To better assess the relative roles of conduit processes and magma chamber, we also coupled conduit flow and magma chamber through mass balance and pressure. We predict magma discharge rates, superficial gas velocities, H2O and CO2 concentrations of the melt, magma chamber pressure, surface deformation, and height of the volcanic jet. Models are in part constrained by H2O and CO2 measured in olivine-hosted melt inclusions and by decompression rates recorded in melt embayment diffusion profiles. We present a parametric analysis, indicating that the pressure within the chamber that fed the subplinian Keanakāko'i eruption was significantly higher than lithostatic pressure. In contrast, chamber pressure for the Hawaiian Kīlauea Iki eruption was close to lithostatic. In both cases the superficial gas velocity, which affects the geometrical distribution of gas-liquid mixtures during upward flow in conduits, may have exceeded values at which bubble coalescence did not affect the flow.

Effect of hypobaric air, oxygen, heliox (50:50), or heliox (80:20) breathing on air bubbles in adipose tissue.

PubMed

Hyldegaard, O; Madsen, J

2007-09-01

The fate of bubbles formed in tissues during decompression to altitude after diving or due to accidental loss of cabin pressure during flight has only been indirectly inferred from theoretical modeling and clinical observations with noninvasive bubble-measuring techniques of intravascular bubbles. In this report we visually followed the in vivo resolution of micro-air bubbles injected into adipose tissue of anesthetized rats decompressed from 101.3 kPa to and held at 71 kPa corresponding to approximately 2.750 m above sea level, while the rats breathed air, oxygen, heliox (50:50), or heliox (80:20). During air breathing, bubbles initially grew for 30-80 min, after which they remained stable or began to shrink slowly. Oxygen breathing caused an initial growth of all bubbles for 15-85 min, after which they shrank until they disappeared from view. Bubble growth was significantly greater during breathing of oxygen compared with air and heliox breathing mixtures. During heliox (50:50) breathing, bubbles initially grew for 5-30 min, from which point they shrank until they disappeared from view. After a shift to heliox (80:20) breathing, some bubbles grew slightly for 20-30 min, then shrank until they disappeared from view. Bubble disappearance was significantly faster during breathing of oxygen and heliox mixtures compared with air. In conclusion, the present results show that oxygen breathing at 71 kPa promotes bubble growth in lipid tissue, and it is possible that breathing of heliox may be beneficial in treating decompression sickness during flight.

Clinical Features and Surgical Treatment of Superficial Peroneal Nerve Entrapment Neuropathy.

PubMed

Matsumoto, Juntaro; Isu, Toyohiko; Kim, Kyongsong; Iwamoto, Naotaka; Yamazaki, Kazuyoshi; Isobe, Masanori

2018-06-20

Superficial peroneal nerve (S-PN) entrapment neuropathy (S-PNEN) is comparatively rare and may be an elusive clinical entity. There is yet no established surgical procedure to treat idiopathic S-PNEN. We report our surgical treatment and clinical outcomes. We surgically treated 5 patients (6 sites) with S-PNEN. The 2 men and 3 women ranged in age from 67 to 91 years; one patient presented with bilateral leg involvement. Mean post-operative follow-up was 25.3 months. We recorded their symptoms before- and at the latest follow-up visit after surgery using a Numerical Rating Scale and the Japan Orthopedic Association score to evaluate the affected area. We microsurgically decompressed the affected S-PN under local anesthesia without a proximal tourniquet. We made a linear skin incision along the S-PN and performed wide S-PN decompression from its insertion point at the peroneal tunnel to the peroneus longus muscle (PLM) to the point where the S-PN penetrated the deep fascia. One patient who had undergone decompression in the area of a Tinel-like sign at the initial surgery suffered symptom recurrence and required re-operation 4 months later. We performed additional extensive decompression to address several sites with a Tinel-like sign. All 5 operated patients reported symptom improvement. In patients with idiopathic S-PNEN, neurolysis under local anesthesia may be curative. Decompression involving only the Tinel area may not be sufficient and it may be necessary to include the area from the PLM to the peroneal nerve exit point along the S-PN.

The initiation of segmented buoyancy-driven melting during continental breakup

PubMed Central

Gallacher, Ryan J.; Keir, Derek; Harmon, Nicholas; Stuart, Graham; Leroy, Sylvie; Hammond, James O. S.; Kendall, J-Michael; Ayele, Atalay; Goitom, Berhe; Ogubazghi, Ghebrebrhan; Ahmed, Abdulhakim

2016-01-01

Melting of the mantle during continental breakup leads to magmatic intrusion and volcanism, yet our understanding of the location and dominant mechanisms of melt generation in rifting environments is impeded by a paucity of direct observations of mantle melting. It is unclear when during the rifting process the segmented nature of magma supply typical of seafloor spreading initiates. Here, we use Rayleigh-wave tomography to construct a high-resolution absolute three-dimensional shear-wave velocity model of the upper 250 km beneath the Afar triple junction, imaging the mantle response during progressive continental breakup. Our model suggests melt production is highest and melting depths deepest early during continental breakup. Elevated melt production during continental rifting is likely due to localized thinning and melt focusing when the rift is narrow. In addition, we interpret segmented zones of melt supply beneath the rift, suggesting that buoyancy-driven active upwelling of the mantle initiates early during continental rifting. PMID:27752044

Adiabat_1ph 3.0 and the MAGMA website: educational and research tools for studying the petrology and geochemistry of plate margins

NASA Astrophysics Data System (ADS)

Antoshechkina, P. M.; Asimow, P. D.

2010-12-01

Adiabat_1ph is a menu-driven front-end to the MELTS, pMELTS and pHMELTS models of thermodynamic equilibrium in silicate systems. Its public release in late 2004 was described in a software brief in G3 (doi:10.1029/2004GC000816). The software package is available for Windows, MacOS X, and Linux and includes Perl scripts that, if desired, will allow almost complete automation of the calculation process. Adiabat_1ph 3.0 is scheduled for release in October 2010 and includes, for the first time, an option to double-click the run_adiabat.command script and to drag and drop file names from a browser (e.g. Explorer on Windows, Finder on Mac). This alternative mode of operation is particularly suited for teaching at undergraduate and graduate levels, as well as for quick, ad hoc, calculations for research purposes. The original method of invoking the program from the command line is retained for more intensive applications. Version 3.0 is the first to specifically target the Windows 7 and Snow Leopard platforms. The release also includes new features that are relevant to the study of plate margins. The Marianas Trough forms the southern part of the Izu-Bonin-Marianas (IBM) arc system, one of the chosen areas of focus for the MARGINS Subduction Factory initiative. Attempts to model the complicated hydrous fractionation trends observed in this region were the motivation for adding modified versions of the ‘reverse-fractionation’ and ‘amoeba’ routines (see doi:10.1016/S0012-821X(04)00058-5) into adiabat_1ph. The ‘amoeba’ scheme, which varies a trial parental melt composition until forward fractionation yields a specified target composition, has been extended so the best-fit liquid line of descent of a group of samples can be found. We have tested the adiabat_1ph versions using glass compositions from the 9N area of the East Pacific Rise and melt inclusions from the Siqueiros Fracture Zone (see Antoshechkina et al., this meeting). One of the first user requested features to be incorporated into adiabat_1ph after its release was the ability to simulate flux melting, in which a metasomatic fluid or melt, of fixed composition, was added to the system before each equilibration step. This idea was further developed in the coupled dynamic and petrological subduction zone model GyPSM, so that fluid flux into the wedge was controlled by the location of dehydration reactions in the slab. The adiabat_1ph release candidate includes a similar option so that the user may specify assimilated compositions, which evolve as the calculation proceeds. This added flexibility opens up a number of possibilities, such as more realistic simulations of melt-rock reactions at mid-ocean ridges. Adiabat_1ph files may be downloaded from the MAGMA website at http://magmasource.caltech.edu/ and feedback is welcomed at a dedicated forum, especially ideas for new software features. MAGMA is an online resource for the study of mantle melting and magma evolution, hosted by Caltech. As well as MELTS-related resources, there are tools for visualization of binary and ternary phase diagrams. Flash movies of phase diagrams for adiabatic decompression melting of peridotite and pyroxenite sources can be played in a web browser or downloaded from a server.

Constraining Slab Breakoff Induced Magmatism through Numerical Modelling

NASA Astrophysics Data System (ADS)

Freeburn, R.; Van Hunen, J.; Maunder, B. L.; Magni, V.; Bouilhol, P.

2015-12-01

Post-collisional magmatism is markedly different in nature and composition than pre-collisional magmas. This is widely interpreted to mark a change in the thermal structure of the system due to the loss of the oceanic slab (slab breakoff), allowing a different source to melt. Early modelling studies suggest that when breakoff takes place at depths shallower than the overriding lithosphere, magmatism occurs through both the decompression of upwelling asthenopshere into the slab window and the thermal perturbation of the overriding lithosphere (Davies & von Blanckenburg, 1995; van de Zedde & Wortel, 2001). Interpretations of geochemical data which invoke slab breakoff as a means of generating magmatism mostly assume these shallow depths. However more recent modelling results suggest that slab breakoff is likely to occur deeper (e.g. Andrews & Billen, 2009; Duretz et al., 2011; van Hunen & Allen, 2011). Here we test the extent to which slab breakoff is a viable mechanism for generating melting in post-collisional settings. Using 2-D numerical models we conduct a parametric study, producing models displaying a range of dynamics with breakoff depths ranging from 150 - 300 km. Key models are further analysed to assess the extent of melting. We consider the mantle wedge above the slab to be hydrated, and compute the melt fraction by using a simple parameterised solidus. Our models show that breakoff at shallow depths can generate a short-lived (< 3 Myr) pulse of mantle melting, through the hydration of hotter, undepleted asthenosphere flowing in from behind the detached slab. However, our results do not display the widespread, prolonged style of magmatism, observed in many post-collisional areas, suggesting that this magmatism may be generated via alternative mechanisms. This further implies that using magmatic observations to constrain slab breakoff is not straightforward.

A kinematic model for the late Cenozoic development of southern California crust and upper mantle

NASA Technical Reports Server (NTRS)

Humphreys, Eugene D.; Hager, Bradford H.

1990-01-01

A model is developed for the young and ongoing kinematic deformation of the southern California crust and upper mantle. The kinematic model qualitatively explains both the overall seismic structure of the upper mantle and much of the known geological history of the late Cenozoic as consequences of ongoing convection beneath southern California. In this model, the high-velocity upper-mantle anomaly of the Transverse ranges is created through the convergence and sinking of the entire thickness of subcrustal lihtosphere, and the low-velocity upper-mantle anomaly beneath the Salton Trough region is attributed to high temperatures and 1-4 percent partial melt related to adiabatic decompression during mantle upwelling.

Preservation of Partial Melt Textures in Inclusions in Garnet Megacrysts of Pelitic Paragneiss, UHP Terrane, North-East Greenland Eclogite Province

NASA Astrophysics Data System (ADS)

Lang, H. M.; Gilotti, J. A.

2005-12-01

Although paragneiss is not common in the North-East Greenland Eclogite Province (NEGEP), of the few paragneiss samples collected in the UHP zone, some contain inclusion-rich garnet megacrysts (to 2 cm) in an anatectic matrix. In the matrix, quartz ribbons are segregated from anatectic melt layers and lenses that contain plagioclase, antiperthitic alkali-feldspar, white mica, biotite, small garnets, rutile and minor kyanite. In addition to one-phase and two-phase inclusions of quartz, polycrystalline quartz (no definitive coesite-replacement textures), and phengitic white mica, the garnet megacrysts contain some relatively large polyphase inclusions with all or most of the following phases: kyanite, rutile, phengitic white mica, biotite, quartz, Na-rich plagioclase, K-feldspar and zircon. Textures in these complex, polyphase inclusions suggest that their constituent minerals crystallized from a melt. Crystals are randomly oriented with early crystallizing minerals (kyanite, rutile, micas) forming euhedral grains and later crystallizing minerals (quartz and feldspars) filling the interstitial spaces. The textures and mineral assemblages are consistent with dehydration melting of phengitic white mica + quartz (enclosed in garnet) during decompression of the rocks from UHP metamorphic conditions. Although anatectic minerals in the matrix may have experienced extensive retrograde re-equilibration subsequent to crystallizing from a melt, the minerals trapped in the crystallized melt inclusions in garnet are likely to preserve their original textures and compositions. Microtextures in the melt inclusions and surrounding garnet suggest that partial melting was accompanied by volume expansion and that some melt penetrated garnets. Some radial fractures extend from inclusion margins into surrounding garnet. Individual fractures may have formed by volume expansion on melting or expansion accompanying the coesite-quartz transformation. Small and large polycrystalline quartz inclusions are commonly rimmed by a moat of plagioclase + K-feldspar, which extends into apophyses in garnet. These feldspar rims indicate that the most mobile and volatile-rich portion of the melt was able to penetrate garnets and travel along garnet-inclusion boundaries. Possible melt inclusions have been described in natural garnets from other UHP terranes (Stockert, et al., 2001, Geology; Hwang, et al., 2001, Earth and Planetary Science Letters) and have been produced experimentally (Perchuk, et al., 2005, Terra Nova). In the experiments and at least one of the natural occurrences, patchy microstructures (attributed to high Ca) were observed in BSE images of garnet surrounding the melt inclusions. Although we observe no garnet zoning in BSE images, patchy high-Ca zoning is apparent on X-ray maps of garnet surrounding the melt inclusions in our samples. Small, euhedral, high-Ca garnets are abundant in melt lenses in the matrix, so crystallization or recrystallization of high-Ca garnet surrounding the melt inclusions is not surprising.

Evidence for small-scale convection in the Pacific and Atlantic upper mantle from joint analysis of surface wave phase velocity and seafloor bathymetry

NASA Astrophysics Data System (ADS)

Ma, Z.; Dalton, C. A.

2017-12-01

It has been long observed that the rate of seafloor subsidence in the Pacific Ocean is lower than predicted by half-space cooling at ages older than 70 Myr. The magnitude, geographical distribution, onset time, and physical origin of the flattening are fundamental to our understanding of the evolution of oceanic lithosphere, and give important constraints on the Earth's heat budget and ocean volume throughout its history. However, none of these quantities is well established even after a long history of debates. Here, we present evidence from bathymetry and seismic tomography for the wide-scale operation of small-scale convection in the Pacific and Atlantic upper mantle. We track the temporal evolution of surface wave phase velocity and seafloor topography along age trajectories, which connect each piece of seafloor with the ridge segment that created it. The half-space cooling model (HSCM) and plate cooling model are used to predict the age dependence of phase velocity and bathymetry and to identify, for each age trajectory, the age at which the HSCM fails to explain the observations. The phase velocity and bathymetry are analyzed independently and yet yield identical results for more than 80% of points. We observe a wide range of ages at which the HSCM fails in the Atlantic and a much narrower range in the Pacific. We find that the age at which the HSCM fails is anti-correlated with the present-day depth of the ridge axis, with younger failure ages corresponding to deeper ridge axes and therefore colder mantle beneath the ridge.Such dependence is best explained by the small-scale convection model in which the effective viscosity of the lithosphere is regulated by the dehydration process that happens at the mid-ocean ridges. Decompression melting at a ridge removes water from the mantle and generates a depleted, dehydrated, and viscous layer. Since high mantle potential temperatures cause decompression melting to begin at greater depths, the thickness of the dehydrated layer is expected to scale with potential temperature. Moreover, numerical models have shown that such rheological layering controls the onset time of small-scale convection, with delayed onset for thicker layers. Our results therefore suggest that the stability of oceanic lithosphere is governed by the extent of melting at the ridge that created it.

From the Exoplanetary Bestiary to the Exoplanetary Zoo

NASA Astrophysics Data System (ADS)

Unterborn, C. T.; Panero, W. R.; Stixrude, L. P.; Kellogg, L. H.; Lithgow-Bertelloni, C. R.; Diamond, M. R.

2014-12-01

While much attention has been focused on the exoplanetary "bestiary" of super-Earths, lava worlds, and diamond planets, habitable planets are more likely to be found in a more similar exoplanetary "zoo." Many planet-hosting stars are similar in composition to the Sun, with moderate variations in metal abundances. Even for those stars with O and Fe abundances similar to the Sun, many have 100% variations in the refractory, rock-forming elements such as Si, Mg, Al and Ca. For an Earth sized planet, this variation creates planets with drastically different mantle mineral assemblages and variable melting, elastic, and viscous properties, leading to variable dynamical behavior. This dynamical behavior dictates the dominant mode of heat extraction, be it through a conducting rigid lid or via plate tectonics. Without tectonics, there is no mechanism known with which to create a deep water and carbon cycle, thus creating a long-lived habitable surface. We present the results of integrated modeling in which we consider the effects of variations in bulk mantle composition on Earth-mass planets. To explore the variations expected in this planetary zoo, we present condensation sequence calculations for stars of varying refractory element abundances. These calculations constrain the potential refractory mineral reservoir from which Earth-mass terrestrial planets will form. As planets of this size inevitably will convect, the thermal structure of the mantle is controlled by surface melting temperature and the first crust can be estimated from decompression melting of a convecting mantle. The thermodynamic code HeFESTo determines the mineralogy and resulting thermoelastic properties of both the mantle and potential foundering of crustal material. Finally, with parameterized convection modeling and 2- and 3-D convection modeling, we determine terrestrial mantle's convective regime as a function of bulk composition. We therefore consider a planet's potential for Earth-like plate tectonics by applying compositional perturbations from the Earth. Aspects affecting this potential include the location of the basalt-eclogite transition in the upper mantle and the density contrast, and thus negative buoyancy, between the foundering crust and mantle. Portions of this work were initiated at the CIDER 2014 program.

Equation of state and high-pressure/high-temperature phase diagram of magnesium

NASA Astrophysics Data System (ADS)

Stinton, G. W.; MacLeod, S. G.; Cynn, H.; Errandonea, D.; Evans, W. J.; Proctor, J. E.; Meng, Y.; McMahon, M. I.

2014-10-01

The phase diagram of magnesium has been investigated to 211 GPa at 300 K, and to 105 GPa at 4500 K, by using a combination of x-ray diffraction and resistive and laser heating. The ambient pressure hcp structure is found to start transforming to the bcc structure at ˜45 GPa, with a large region of phase-coexistence that becomes smaller at higher temperatures. The bcc phase is stable to the highest pressures reached. The hcp-bcc phase boundary has been studied on both compression and decompression, and its slope is found to be negative and steeper than calculations have previously predicted. The laser-heating studies extend the melting curve of magnesium to 105 GPa and suggest that, at the highest pressures, the melting temperature increases more rapidly with pressure than previously reported. Finally, we observe some evidence of a new phase in the region of 10 GPa and 1200 K, where previous studies have reported a double-hexagonal-close-packed (dhcp) phase. However, the additional diffraction peaks we observe cannot be accounted for by the dhcp phase alone.

Use of psychological decompression in military operational environments.

PubMed

Hughes, Jamie G H Hacker; Earnshaw, N Mark; Greenberg, Neil; Eldridge, Rod; Fear, Nicola T; French, Claire; Deahl, Martin P; Wessely, Simon

2008-06-01

This article reviews the use of psychological decompression as applied to troops returning from active service in operational theaters. Definitions of the term are considered and a brief history is given. Current policies and practices are described and the question of mandatory decompression is considered. Finally, the evidence base for the efficacy of decompression is examined and some conclusions are drawn. This article highlights variations in the definition and practice of decompression and its use. Although there is, as yet, no evidence that decompression works, there is also no evidence to the contrary. Given the lack of knowledge as to the balance of risks and benefits of decompression and the absence of any definitive evidence that decompression is associated with improved mental health outcomes or that lack of decompression is associated with the reverse, it is argued that the use of decompression should remain a matter for discretion.

Nerve decompression and neuropathy complications in diabetes: Are attitudes discordant with evidence?

PubMed Central

Nickerson, D. Scott

2017-01-01

ABSTRACT External neurolysis of the nerve at fibro-osseous tunnels has been proprosed to treat or prevent signs, symptoms, and complications in the lower extremity of diabetes patients with sensorimotor polyneuropathy. Nerve decompression is justified in the presence of symptomatic compressed nerves in the several fibro-osseous tunnels of the extremities, which are known to be frequent in diabetes. Quite a body of literature has accumulated reporting results after such nerve decompression in the leg, describing pain relief and sensibility improvement, as well as balance recovery, diabetic foot ulcer prevention, curtailed ulcer recurrence risk, and amputation avoidance. Historical academic hesitance to endorse surgical treatments for pain and numbness in diabetes was based primarily on the early retrospective reports’ potential for bias and placebo effects, and that the hypothetical basis for surgery lies outside the traditional etiology paradigm of length-dependent axonopathy. This reticence is here critiqued in view of recent studies using objective, measured outcome protocols which nullify such potential confounders. Pain relief is now confirmed with Level 1 studies, and Level 2 prospective information suggests protection from initial diabetic foot ulceration and most neuropathic ulcer recurrences. In view of the potential for nerve decompression to be useful in addressing some of the more difficult, expensive, and life altering complications of diabetic neuropathy, this secondary compression thesis and operative treatment methodology may deserve reassessment. PMID:28959382

The thermal properties of beeswaxes: unexpected findings.

PubMed

Buchwald, Robert; Breed, Michael D; Greenberg, Alan R

2008-01-01

Standard melting point analyses only partially describe the thermal properties of eusocial beeswaxes. Differential scanning calorimetry (DSC) revealed that thermal phase changes in wax are initiated at substantially lower temperatures than visually observed melting points. Instead of a sharp, single endothermic peak at the published melting point of 64 degrees C, DSC analysis of Apis mellifera Linnaeus wax yielded a broad melting curve that showed the initiation of melting at approximately 40 degrees C. Although Apis beeswax retained a solid appearance at these temperatures, heat absorption and initiation of melting could affect the structural characteristics of the wax. Additionally, a more complete characterization of the thermal properties indicated that the onset of melting, melting range and heat of fusion of beeswaxes varied significantly among tribes of social bees (Bombini, Meliponini, Apini). Compared with other waxes examined, the relatively malleable wax of bumblebees (Bombini) had the lowest onset of melting and lowest heat of fusion but an intermediate melting temperature range. Stingless bee (Meliponini) wax was intermediate between bumblebee and honeybee wax (Apini) in heat of fusion, but had the highest onset of melting and the narrowest melting temperature range. The broad melting temperature range and high heat of fusion in the Apini may be associated with the use of wax comb as a free-hanging structural material, while the Bombini and Meliponini support their wax structures with exogenous materials.

Baastrup's Disease Is Associated with Recurrent of Sciatica after Posterior Lumbar Spinal Decompressions Utilizing Floating Spinous Process Procedures

PubMed Central

Mannoji, Chikato; Murakami, Masazumi; Kinoshita, Tomoaki; Hirayama, Jiro; Miyashita, Tomohiro; Eguchi, Yawara; Yamazaki, Masashi; Suzuki, Takane; Aramomi, Masaaki; Ota, Mitsutoshi; Maki, Satoshi; Takahashi, Kazuhisa; Furuya, Takeo

2016-01-01

Study Design Retrospective case-control study. Purpose To determine whether kissing spine is a risk factor for recurrence of sciatica after lumbar posterior decompression using a spinous process floating approach. Overview of Literature Kissing spine is defined by apposition and sclerotic change of the facing spinous processes as shown in X-ray images, and is often accompanied by marked disc degeneration and decrement of disc height. If kissing spine significantly contributes to weight bearing and the stability of the lumbar spine, trauma to the spinous process might induce a breakdown of lumbar spine stability after posterior decompression surgery in cases of kissing spine. Methods The present study included 161 patients who had undergone posterior decompression surgery for lumbar canal stenosis using a spinous process floating approaches. We defined recurrence of sciatica as that resolved after initial surgery and then recurred. Kissing spine was defined as sclerotic change and the apposition of the spinous process in a plain radiogram. Preoperative foraminal stenosis was determined by the decrease of perineural fat intensity detected by parasagittal T1-weighted magnetic resonance imaging. Preoperative percentage slip, segmental range of motion, and segmental scoliosis were analyzed in preoperative radiographs. Univariate analysis followed by stepwise logistic regression analysis determined factors independently associated with recurrence of sciatica. Results Stepwise logistic regression revealed kissing spine (p=0.024; odds ratio, 3.80) and foraminal stenosis (p<0.01; odds ratio, 17.89) as independent risk factors for the recurrence of sciatica after posterior lumbar spinal decompression with spinous process floating procedures for lumbar spinal canal stenosis. Conclusions When a patient shows kissing spine and concomitant subclinical foraminal stenosis at the affected level, we should sufficiently discuss the selection of an appropriate surgical procedure. PMID:27994785

Baastrup's Disease Is Associated with Recurrent of Sciatica after Posterior Lumbar Spinal Decompressions Utilizing Floating Spinous Process Procedures.

PubMed

Koda, Masao; Mannoji, Chikato; Murakami, Masazumi; Kinoshita, Tomoaki; Hirayama, Jiro; Miyashita, Tomohiro; Eguchi, Yawara; Yamazaki, Masashi; Suzuki, Takane; Aramomi, Masaaki; Ota, Mitsutoshi; Maki, Satoshi; Takahashi, Kazuhisa; Furuya, Takeo

2016-12-01

Retrospective case-control study. To determine whether kissing spine is a risk factor for recurrence of sciatica after lumbar posterior decompression using a spinous process floating approach. Kissing spine is defined by apposition and sclerotic change of the facing spinous processes as shown in X-ray images, and is often accompanied by marked disc degeneration and decrement of disc height. If kissing spine significantly contributes to weight bearing and the stability of the lumbar spine, trauma to the spinous process might induce a breakdown of lumbar spine stability after posterior decompression surgery in cases of kissing spine. The present study included 161 patients who had undergone posterior decompression surgery for lumbar canal stenosis using a spinous process floating approaches. We defined recurrence of sciatica as that resolved after initial surgery and then recurred. Kissing spine was defined as sclerotic change and the apposition of the spinous process in a plain radiogram. Preoperative foraminal stenosis was determined by the decrease of perineural fat intensity detected by parasagittal T1-weighted magnetic resonance imaging. Preoperative percentage slip, segmental range of motion, and segmental scoliosis were analyzed in preoperative radiographs. Univariate analysis followed by stepwise logistic regression analysis determined factors independently associated with recurrence of sciatica. Stepwise logistic regression revealed kissing spine ( p =0.024; odds ratio, 3.80) and foraminal stenosis ( p <0.01; odds ratio, 17.89) as independent risk factors for the recurrence of sciatica after posterior lumbar spinal decompression with spinous process floating procedures for lumbar spinal canal stenosis. When a patient shows kissing spine and concomitant subclinical foraminal stenosis at the affected level, we should sufficiently discuss the selection of an appropriate surgical procedure.

Long-term outcome and prognostic factors after C2 ganglion decompression in 68 consecutive patients with intractable occipital neuralgia.

PubMed

Choi, Kyu-Sun; Ko, Yong; Kim, Young-Soo; Yi, Hyeong-Joong

2015-01-01

Occipital neuralgia is a rare cause of severe headache characterized by paroxysmal shooting or stabbing pain in the distribution of the greater occipital or lesser occipital nerve. In cases of intractable occipital neuralgia, a definite cause has not been uncovered, so various types of treatment have been applied. The aim of this study is to evaluate the prognostic factors, safety, and long-term clinical efficacy of second cervical (C2) ganglion decompression for intractable occipital neuralgia. Retrospective analysis was performed in 68 patients with medically refractory occipital neuralgia who underwent C2 ganglion decompression. Factors based on patients' demography, pre- and postoperative headache severity/characteristics, medication use, and postoperative complications were investigated. Therapeutic success was defined as pain relief by at least 50 % without ongoing medication. The visual analog scale (VAS) score was significantly reduced between the preoperative and most recent follow-up period. One year later, excellent or good results were achieved in 57 patients (83.9 %), but poor in 11 patients (16.1 %). The long-term outcome after 5 years was only slightly less than the 1-year outcome; 47 of the 68 patients (69.1 %) obtained therapeutic success. Longer duration of headache (over 13 years; p = 0.029) and presence of retro-orbital/frontal radiation (p = 0.040) were significantly associated with poor prognosis. In the current study, C2 ganglion decompression provided durable, adequate pain relief with minimal complications in patients suffering from intractable occipital neuralgia. Due to the minimally invasive and nondestructive nature of this surgical procedure, C2 ganglion decompression is recommended as an initial surgical treatment option for intractable occipital neuralgia before attempting occipital nerve stimulation. However, further study is required to manage the pain recurrence associated with longstanding nerve injury.

Surgical Decompression for Chiari Malformation Type I: An Age-Based Outcomes Study Based on the Chicago Chiari Outcome Scale.

PubMed

Gilmer, Holly S; Xi, Mengqiao; Young, Sonja H

2017-11-01

There is currently inadequate evidence on the efficacy of surgical decompression for Chiari malformation type I (CM1) in different age groups of patients. In this study, we compared postoperative outcomes across 3 different age groups using the Chicago Chiari Outcome Scale (CCOS). A total of 144 patients who underwent Chiari decompression at our institution between 2008 and 2014 were divided into 3 groups: group A, children age 0-18 years; group B, younger adults age 19-40 years; and group C, older adults, age 41+ years. Patient outcomes were assigned a numerical value based on the CCOS and subjected to statistical analysis. Direct comparisons were made across the 3 age groups. The mean overall score was 14.0 over a mean follow-up of 27.2 months. All 3 groups demonstrated clinical improvement following Chiari decompression; however, group A demonstrated significantly better postoperative improvements than groups B and C in total CCOS scores (7.8% and 12.2%, respectively; P < 0.001) and all the component scores except complications. Group B was not significantly different from group C in total score or any of the component scores. There was a logarithmic relationship between age and outcome (R 2  = 0.64), in which the outcome scores experienced an initial decline with increasing age but leveled off by early adulthood. A direct comparison among the age groups revealed a negative age effect on surgical decompression outcomes in CM1 patients. Children performed significantly better than younger and older adults. This finding supports early surgical intervention for symptomatic pediatric patients to achieve long-term surgical benefit. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Latent Presentation of Decompression Sickness After Altitude Chamber Training in an Active Duty Flier.

PubMed

Gentry, James; Rango, Juan; Zhang, Jianzhong; Biedermann, Shane

2017-04-01

Decompression sickness (DCS) is a potential danger and risk for both divers and aircrew alike. DCS is also a potential side effect of altitude (hypobaric) chamber training as well and can present long after training occurs. Literature review shows that altitude chamber induced DCS has approximately a 0.25% incidence. A 32-yr-old, active duty military member developed symptoms of DCS 3 h after his hypobaric chamber training. Unfortunately, he did not seek treatment for DCS until 48 h after the exposure. His initial treatment included ground level oxygen therapy for 30 min at 12 L of oxygen per minute using a nonrebreathing mask. He achieved complete symptom resolution and was returned to duty. However, 12 d after his initial Flight Medicine evaluation, the patient returned complaining of a right temporal headache, multijoint pains, and fatigue. He was treated in the hyperbaric chamber and had complete resolution of symptoms. He was returned to flying status and 5 mo later denied any return of symptoms. Hypobaric chamber familiarity training is a requirement for all military aircrew personnel to allow them assess their ability to identify symptoms of hypoxia. This training method is not only costly to maintain, but it also places aircrew and chamber technicians at risk for potential long-term side effects from failed recompression treatment of DCS. We are presenting a case of recurrent DCS symptoms 12 d after initial ground level oxygen therapy.Gentry J, Rango J, Zhang J, Biedermann S. Latent presentation of decompression sickness after altitude chamber training in an active duty flier. Aerosp Med Hum Perform. 2017; 88(4):427-430.

Surgical Missteps in the Management of Venous Thoracic Outlet Syndrome Which Lead to Reoperation.

PubMed

Archie, Meena M; Rollo, Johnathon C; Gelabert, Hugh A

2018-05-01

Surgical management of spontaneous subclavian thrombosis due to venous thoracic outlet syndrome (vTOS) results in durable relief of symptoms. The need to reoperate is rare. We report our experience with reoperation for vTOS. Patients evaluated for vTOS between 1996 and 2016 were identified in a prospective database. Data recorded included demographics, initial presentation, initial surgery, recurrent presentation, reoperation, and final outcomes. In all, 261 patients were evaluated for vTOS, of these, 246 patients underwent first rib resections. Ten (3.8%) patients required evaluation for recurrent vTOS symptoms. Prior management included thrombolysis (4) and anticoagulation alone (6). Prior surgical approaches included infraclavicular (2), supraclavicular (2) and transaxillary (6). One operation was complicated by a hemothorax, and one a brachial plexus injury. Indication for reoperation included congestive symptoms (6) and recurrent thrombosis (4). Evaluation included chest X-rays (10), venogram (8), intra-venous ultrasound (2), and computed tomography venography (3). Significant compression by remaining rib segments were identified in all: inadequate resection of the anterior first rib (7), inadequate resection of posterior rib segment (1), and erroneous resection of second rib (2). Reoperations include 7 transaxillary approaches, 1 medial claviculectomy, and 1 paraclavicular decompression. One phrenic nerve palsy occurred following paraclavicular decompression. All underwent postoperative venography and angioplasty. At final evaluation, 8 veins are patent and congestive symptoms resolved, and 1 crushed stent could not be reopened despite decompression. The incidence of reoperation for first rib resection in cases of vTOS is low and appears largely due to missteps during the initial operation. Awareness of potential errors including inadequacy of resection, intraoperative disorientation, and misunderstanding of the limitations of surgical approaches will result in fewer reoperations. Published by Elsevier Inc.

Tectono-sedimentary evolution of the eastern Gulf of Aden conjugate passive margins: Narrowness and asymmetry in oblique rifting context

NASA Astrophysics Data System (ADS)

Nonn, Chloé; Leroy, Sylvie; Khanbari, Khaled; Ahmed, Abdulhakim

2017-11-01

Here, we focus on the yet unexplored eastern Gulf of Aden, on Socotra Island (Yemen), Southeastern Oman and offshore conjugate passive margins between the Socotra-Hadbeen (SHFZ) and the eastern Gulf of Aden fracture zones. Our interpretation leads to onshore-offshore stratigraphic correlation between the passive margins. We present a new map reflecting the boundaries between the crustal domains (proximal, necking, hyper-extended, exhumed mantle, proto-oceanic and oceanic domains) and structures using bathymetry, magnetic surveys and seismic reflection data. The most striking result is that the magma-poor conjugate margins exhibit asymmetrical architecture since the thinning phase (Upper Rupelian-Burdigalian). Their necking domains are sharp ( 40-10 km wide) and their hyper-extended domains are narrow and asymmetric ( 10-40 km wide on the Socotra margin and 50-80 km wide on the Omani margin). We suggest that this asymmetry is related to the migration of the rift center producing significant lower crustal flow and sequential faulting in the hyper-extended domain. Throughout the Oligo-Miocene rifting, far-field forces dominate and the deformation is accommodated along EW to N110°E northward-dipping low angle normal faults. Convection in the mantle near the SHFZ may be responsible of change in fault dip polarity in the Omani hyper-extended domain. We show the existence of a northward-dipping detachment fault formed at the beginning of the exhumation phase (Burdigalien). It separates the northern upper plate (Oman) from southern lower plate (Socotra Island) and may have generated rift-induced decompression melting and volcanism affecting the upper plate. We highlight multiple generations of detachment faults exhuming serpentinized subcontinental mantle in the ocean-continent transition. Associated to significant decompression melting, final detachment fault may have triggered the formation of a proto-oceanic crust at 17.6 Ma and induced late volcanism up to 10 Ma. Finally, the setting up of a steady-state oceanic spreading center occurs at 17 Ma.

Experimental study of Gas Phase Formation and Evolution in Low fO2 Planetary Basalts.

NASA Astrophysics Data System (ADS)

Rutherford, M. J.; Wetzel, D. T.; Saal, A. E.; Hauri, E. H.

2012-12-01

The existence of a gas phase in planetary basaltic magmas is demonstrated by the ubiquitous presence of vesicles in returned lunar samples and meteorites as well as basalts from Earth and Mars. Additionally, formation of the fine-grained glass bead deposits during eruption of lunar picritic glasses required a large gas-bubble volume (> 90%) at the time of eruption/fragmentation. Up to 100-200 ppm levels of H, S, Cl and F still remain as diffusion-loss profiles in individual lunar glass beads SIMS (1), and higher volatile concentrations occur in olivine melt inclusions (2). The composition and origin of such volcanic gases were investigated by experiments on a volatile (C-O-H-S-Cl-F)-bearing picritic glass composition as a function of fO2 near iron-wustite (IW). The C-O-H species dissolved in gas-saturated basaltic melt above IW-0.5 are carbonate, OH and H2O with 100 to 10,000 ppm H2O in the sample; below IW-0.5, the C-species present (Raman and FTIR) are Fe(CO)5 (iron pentacarbonyl) and lesser CH4 [3]. The change in melt speciation in part reflects a change in calculated speciation in the coexisting gas [4]. The carbon solubility in these experimental melts increases linearly with increasing pressure; the more oxidized glasses contain 32-620 ppm C for pressures of 98 to 980 MPa, the reduced glasses contain 8-240 ppm C for pressures between 36 and 900 MPa. Thus, the C solubility of the more reduced Fe-carbonyl and CH4 is about one-half that of carbonate at the same pressure, and indicates the carrying capacity for C in reduced (i.e., lunar) magmas is much lower than it is in present day terrestrial magmas. Varioles up to 200 um in diameter formed in some experiments with higher dissolved water contents (1%); they have radiating crystalline textures (olivine, glass and poorly crystallized graphite) initiated at a central nucleation site. A sharp peak in the variole Ramen spectra indicates methane as well as CO is released during variole formation and a reaction such as 2CO = C +CO2 formed the graphite. Several series of experiments on chips of low fO2 glass created at high pressure quantify S, Cl and F partitioning into the H2O-CO gas phase with decompression steps from 200 to 40 MPa. A gas formed with the first pressure drop, indicating melt supersaturation with CO and/or CH4; H2O and lesser amounts of S, Cl and F partitioned into the initial gas, and continued to do so with additional drops in pressure. The ubiquitous Fe-metal seen in lunar picritic glasses may form by graphite oxidation, but also may form by breakdown of Fe(CO)5 as the melt continues to saturate during ascent. [1] A. E. Saal et al.(2008) Nature 454, 192-195. [2] E. H. Hauri et al (2011) Science 333, 213 -215. [3] Wetzel, D., Rutherford, M.J. Jacobsen S.D., Hauri, E.H., and Saal, A.E., (submitted); Nature Geoscience Aug. 1, 2012. [4] Zhang, C. and Duan, Z. (2009) GCA, 73, 2089-2102.

Cryovolcanic Conduit Evolution and Eruption on Icy Satellites

NASA Astrophysics Data System (ADS)

Mitchell, K. L.

2014-12-01

In silicate volcanism, such as on Earth or Io, eruptions typically result from fracture formation caused by interaction of tectonic stresses with inflating, pressurized magma sources, leading to transport of melt through an evolving conduit. On icy satellites the paradigm may be similar, resulting from some combination of tidal stresses and expansion of freezing water within, or near the base of, an ice shell. Such a fracture will result in eruption if mass continuity can be established, with buoyancy aided by exsolution and expansion of dissolved volatiles. After onset, conduit shape evolves due to: (1) shear-stresses or frictional erosional; (2) wallrock "bursting" due to massive wall stresses; (3) wall melting or condensation of particles due to heat transfer; or (4) changes in applied stresses. Preliminary thermodynamic and fluid mechanical analysis suggests some initial cooling during ascent resulting from exsolution and expansion of volatiles, thermally buffered by freezing, Conduit contraction may occur, and so evolution towards a deep, gas-filled plume chamber is difficult to accommodate without evoking a co-incidental process. Conduit flaring occurs near the surface where velocities are greatest, enhancing erosion. Here, viscous dissipative heating exceeds adiabatic cooling, and so some boiling (a few wt%) may occur. In contrast with silicate volcanism, decompression to below the triple point will occur within conduit, vent or jet, resulting in rapid freezing and boiling of the remaining water at a 6.8:1 ratio. Subsequent isentropic or adiabatic expansion within erupting jets may result in a few percent net of condensation or sublimation. These effects combined lead to ~4:1-7:1 solid:vapor ratios in the jet for most eruption conditions. These figures are consistent with the ~6:1 inferred in Enceladus' jets, supporting the hypothesis that the Enceladus plume draws from a subsurface body of liquids through a conduit. Similar results are anticipated if cryovolcanic plumes are confirmed on Europa. However, eruption from an ocean is more challenging there, as far greater volatile contents would be required to facilitate mass continuity from an initial fracture, and hence eruption, from the higher pressure source. Shallower sources, such as proposed under chaos, are less challenging.

Anatomy of a late spring snowfall on sea ice

NASA Astrophysics Data System (ADS)

Perovich, Donald; Polashenski, Christopher; Arntsen, Alexandra; Stwertka, Carolyn

2017-03-01

Spring melt initiation is a critical process for Arctic sea ice. Melting conditions decrease surface albedo at a time of high insolation, triggering powerful albedo feedback. Weather events during melt initiation, such as new snowfalls, can stop or reverse the albedo decline, however. Here we present field observations of such a snow event and demonstrate its enduring impact through summer. Snow fell 3-6 June 2014 in the Chukchi Sea, halting melt onset. The snow not only raised albedo but also provided a significant negative latent heat flux, averaging -51 W m-2 from 3 to 6 June. The snowfall delayed sustained melt by 11 days, creating cascading impacts on surface energy balance that totaled some 135 MJ/m2 by mid-August. The findings highlight the sensitivity of sea ice conditions on seasonal time scales to melt initiation processes.

Comparison of clinical outcomes in decompression and fusion versus decompression only in patients with ossification of the posterior longitudinal ligament: a meta-analysis.

PubMed

Mehdi, Syed K; Alentado, Vincent J; Lee, Bryan S; Mroz, Thomas E; Benzel, Edward C; Steinmetz, Michael P

2016-06-01

OBJECTIVE Ossification of the posterior longitudinal ligament (OPLL) is a pathological calcification or ossification of the PLL, predominantly occurring in the cervical spine. Although surgery is often necessary for patients with symptomatic neurological deterioration, there remains controversy with regard to the optimal surgical treatment. In this systematic review and meta-analysis, the authors identified differences in complications and outcomes after anterior or posterior decompression and fusion versus after decompression alone for the treatment of cervical myelopathy due to OPLL. METHODS A MEDLINE, SCOPUS, and Web of Science search was performed for studies reporting complications and outcomes after decompression and fusion or after decompression alone for patients with OPLL. A meta-analysis was performed to calculate effect summary mean values, 95% CIs, Q statistics, and I(2) values. Forest plots were constructed for each analysis group. RESULTS Of the 2630 retrieved articles, 32 met the inclusion criteria. There was no statistically significant difference in the incidence of excellent and good outcomes and of fair and poor outcomes between the decompression and fusion and the decompression-only cohorts. However, the decompression and fusion cohort had a statistically significantly higher recovery rate (63.2% vs 53.9%; p < 0.0001), a higher final Japanese Orthopaedic Association score (14.0 vs 13.5; p < 0.0001), and a lower incidence of OPLL progression (< 1% vs 6.3%; p < 0.0001) compared with the decompression-only cohort. There was no statistically significant difference in the incidence of complications between the 2 cohorts. CONCLUSIONS This study represents the only comprehensive review of outcomes and complications after decompression and fusion or after decompression alone for OPLL across a heterogeneous group of surgeons and patients. Based on these results, decompression and fusion is a superior surgical technique compared with posterior decompression alone in patients with OPLL. These results indicate that surgical decompression and fusion lead to a faster recovery, improved postoperative neurological functioning, and a lower incidence of OPLL progression compared with posterior decompression only. Furthermore, decompression and fusion did not lead to a greater incidence of complications compared with posterior decompression only.

Optic Nerve Decompression

MedlinePlus

... Nerve Decompression Dacryocystorhinostomy (DCR) Disclosure Statement Printer Friendly Optic Nerve Decompression John Lee, MD Introduction Optic nerve decompression is a surgical procedure aimed at ...

Melt fracturing and healing: A mechanism for degassing and origin of silicic obsidian

USGS Publications Warehouse

Cabrera, A.; Weinberg, R.F.; Wright, H.M.N.; Zlotnik, S.; Cas, Ray A.F.

2011-01-01

We present water content transects across a healed fault in pyroclastic obsidian from Lami pumice cone, Lipari, Italy, using synchrotron Fourier transform infrared spectroscopy. Results indicate that rhyolite melt degassed through the fault surface. Transects define a trough of low water content coincident with the fault trace, surrounded on either side by high-water-content plateaus. Plateaus indicate that obsidian on either side of the fault equilibrated at different pressure-temperature (P-T) conditions before being juxtaposed. The curves into the troughs indicate disequilibrium and water loss through diffusion. If we assume constant T, melt equilibrated at pressures differing by 0.74 MPa before juxtaposition, and the fault acted as a low-P permeable path for H2O that diffused from the glass within time scales of 10 and 30 min. Assuming constant P instead, melt on either side could have equilibrated at temperatures differing by as much as 100 ??C, before being brought together. Water content on the fault trace is particularly sensitive to post-healing diffusion. Its preserved value indicates either higher temperature or lower pressure than the surroundings, indicative of shear heating and dynamic decompression. Our results reveal that water contents of obsidian on either side of the faults equilibrated under different P-T conditions and were out of equilibrium with each other when they were juxtaposed due to faulting immediately before the system was quenched. Degassing due to faulting could be linked to cyclical seismic activity and general degassing during silicic volcanic activity, and could be an efficient mechanism of producing low-water-content obsidian. ?? 2011 Geological Society of America.

Origin of depleted basalts during subduction initiation and early development of the Izu-Bonin-Mariana island arc: Evidence from IODP expedition 351 site U1438, Amami-Sankaku basin

NASA Astrophysics Data System (ADS)

Hickey-Vargas, R.; Yogodzinski, G. M.; Ishizuka, O.; McCarthy, A.; Bizimis, M.; Kusano, Y.; Savov, I. P.; Arculus, R.

2018-05-01

The Izu-Bonin-Mariana (IBM) island arc formed following initiation of subduction of the Pacific plate beneath the Philippine Sea plate at about 52 Ma. Site U1438 of IODP Expedition 351 was drilled to sample the oceanic basement on which the IBM arc was constructed, to better understand magmatism prior to and during the subduction initiation event. Site U1438 igneous basement Unit 1 (150 m) was drilled beneath 1460 m of primarily volcaniclastic sediments and sedimentary rock. Basement basalts are microcrystalline to fine-grained flows and form several distinct subunits (1a-1f), all relatively mafic (MgO = 6.5-13.8%; Mg# = 52-83), with Cr = 71-506 ppm and Ni = 62-342 ppm. All subunits are depleted in non-fluid mobile incompatible trace elements. Ratios such as Sm/Nd (0.35-0.44), Lu/Hf (0.19-0.37), and Zr/Nb (55-106) reach the highest values found in MORB, while La/Yb (0.31-0.92), La/Sm (0.43-0.91) and Nb/La (0.39-0.59) reach the lowest values. Abundances of fluid-mobile incompatible elements, K, Rb, Cs and U, vary with rock physical properties, indicating control by post-eruptive seawater alteration, but lowest abundances are typical of fresh, highly depleted MORBs. Mantle sources for the different subunits define a trend of progressive incompatible element depletion. Inferred pressures of magma segregation are 0.6-2.1 GPa with temperatures of 1280-1470 °C. New 40Ar/39Ar dates for Site U1438 basalts averaging 48.7 Ma (Ishizuka et al., 2018) are younger that the inferred age of IBM subduction initiation based on the oldest ages (52 Ma) of IBM forearc basalts (FAB) from the eastern margin of the Philippine Sea plate. FAB are hypothesized to be the first magma type erupted as the Pacific plate subsided, followed by boninites, and ultimately typical arc magmas over a period of about 10 Ma. Site U1438 basalts and IBM FABs are similar, but Site U1438 basalts have lower V contents, higher Ti/V and little geochemical evidence for involvement of slab-derived fluids. We hypothesize that the asthenospheric upwelling and extension expected during subduction initiation occurred over a broad expanse of the upper plate, even as hydrous fluids were introduced near the plate edge to produce FABs and boninites. Site U1438 basalts formed by decompression melting during the first 3 Ma of subduction initiation, and were stranded behind the early IBM arc as mantle conditions shifted to flux melting beneath a well-defined volcanic front.

Modeling Continental Rifts and Melting Under Precambrian Mantle Conditions: Effects of Mantle Potential Temperature and Rheology

NASA Astrophysics Data System (ADS)

Hansen, M.; Moucha, R.; Rooney, T. O.; Stein, S.; Stein, C. A.

2016-12-01

The Mid-Continent Rift System (MCRS) is a 2000 kilometer-long failed rift which formed within the Precambrian continent of Laurentia ca. 1.1 Ga. The MCRS is part of the Keweenaw large igneous province (LIP), and is dominantly composed of flood basalts, with subordinate rhyolite. While continental rifts and LIPs are frequently spatially related, it is unusual for a rift to be filled with flood basalts. Existing work has suggested that the presence of large volumes of flood basalts within the MCRS is the result of the rift interacting with anomalously hot mantle material, possibly a mantle plume. However, ambient mantle conditions were much hotter during the late Proterozoic than in the modern mantle. This raises the question - could rifting alone generate the significant volume of decompressive melt from the ambient atmosphere without the need for a mantle plume? In this contribution, we utilize a 2D particle-in-cell thermomechanical visco-elasto-plastic code (e.g. Gerya, 2010; & references therein) to numerically explore the parameter space: specifically, the mantle potential temperature, plume excess temperature and volume, extension rates and rheology, and estimate the amount of melt produced in a Precambrian continental rift setting. *This submission is a result of Hansen's participation in GLADE, a nine week summer REU program directed by Dave Stegman (SIO/UCSD).

How do the radiative effects of springtime clouds and water vapor modulate the melt onset of Arctic sea ice?

NASA Astrophysics Data System (ADS)

Huang, Y.; Dong, X.; Xi, B.; Deng, Y.

2017-12-01

Earlier studies show that there is a strong positive correlation between the mean onset date of snow melt north of 70°N and the minimum Arctic sea ice extent (SIE) in September. Based on satellite records from 1980 to 2016, the September Arctic SIE minimum is most sensitive to the early melt onset over the Siberian Sea (73°-84°N, 90°-155°), which is defined as the area of focus (AOF) in this analysis. The day with melt onset exceeding 10% area of the AOF is marked as the initial melt date for a given year. With this definition, a strong positive correlation (r=0.59 at 99% confidence level) is found between the initial melt date over the AOF and the September SIE minimum over the Arctic. Daily anomalies of cloud and radiation properties are compared between six years with earliest initial melt dates (1990, 2012, 2007, 2003, 1991, 2016) and six years with latest initial melt dates (1996, 1984, 1983, 1982, 1987, 1992) using the NASA MERRA-2 reanalysis. Our results suggest that higher cloud water path (CWP) and precipitable water vapor (PWV) are clearly associated with early melt onset years through the period of mid-March to August. Major contrasts in CWP are found between the early and late onset years in a period of approximately 30 days prior to the onset to 30 days after the onset. As a result, the early melt onset years exhibit positive anomalies for downward longwave flux at the surface and negative anomalies for downward shortwave flux, shortwave cloud radiative effect (CRE) as well as net CRE. The negative net CRE is over-compensated by the positive longwave flux anomaly associated with elevated PWV, contributing to early melt onsets. The temporal evolution of CRE and PWV radiative effect during the entire melting season will be documented together with an analysis tracing the dynamical, mid-latitude origins of increased CWP and PWV prior to initial melt onsets.

Melt generation in the West Antarctic Rift System: the volatile legacy of Gondwana subduction?

NASA Astrophysics Data System (ADS)

Aviado, K.; Rilling-Hall, S.; Mukasa, S. B.; Bryce, J. G.; Cabato, J.

2013-12-01

The West Antarctic Rift System (WARS) represents one of the largest extensional alkali volcanic provinces on Earth, yet the mechanisms responsible for driving rift-related magmatism remain controversial. The failure of both passive and active models of decompression melting to explain adequately the observed volume of volcanism has prompted debate about the relative roles of thermal plume-related melting and ancient subduction-related flux melting. The latter is supported by roughly 500 Ma of subduction along the paleo-Pacific margin of Gondwana, although both processes are capable of producing the broad seismic anomaly imaged beneath most of the Southern Ocean. Olivine-hosted melt inclusions from basanitic lavas provide a means to evaluate the volatile budget of the mantle responsible for active rifting beneath the WARS. We present H2O, CO2, F, S and Cl concentrations determined by SIMS and major oxide compositions by EMPA for olivine-hosted melt inclusions from lavas erupted in Northern Victoria Land (NVL) and Marie Byrd Land (MBL). The melt inclusions are largely basanitic in composition (4.05 - 17.09 wt % MgO, 37.86 - 45.89 wt % SiO2, and 1.20 - 5.30 wt % Na2O), and exhibit water contents ranging from 0.5 up to 3 wt % that are positively correlated with Cl and F. Coupling between Cl and H2O indicates metasomatic enrichment by subduction-related fluids produced during dehydration reactions; coupling between H2O and F, which is more highly retained in subducting slabs, may be related to partial melting of slab remnants [1]. Application of source lithology filters [2] to whole rock major oxide data shows that primitive lavas (MgO wt % >7) from the Terror Rift, considered the locus of on-going tectonomagmatic activity, have transitioned from a pyroxenite source to a volatilized peridotite source over the past ~4 Ma. Integrating the volatile data with the modeled characteristics of source lithologies suggests that partial melting of lithosphere modified by subduction processes is the source of pyroxenite and volatiles in the mantle beneath the present-day rift. The earliest magmatic activity preferentially removed the most readily fusible components from the mantle, resulting in transition to a metasomatized peridotite source over time. [1] Straub & Layne, 2003, GCA; [2] Herzberg & Asimow, 2008, G3; [3] Rilling et al., 2009, JGR.

Generation of alkaline magmas in subduction zones by melting of mélange diapirs

NASA Astrophysics Data System (ADS)

Cruz-Uribe, A. M.; Marschall, H.; Gaetani, G. A.; Le Roux, V.

2016-12-01

Alkaline lavas occur globally in subduction-related volcanic arcs. Existing explanations for the occurrence of alkaline lavas in volcanic arcs invoke at least one - and in some cases multiple - `metasomatic' events in addition to the traditional three-component mixing of altered oceanic crust (AOC), sediment melt, and depleted mantle, in order to explain the range of rock types found in a given region. These multi-stage models posit the existence of metasomatized mantle wedge peridotite containing phlogopite or amphibole-enriched veins, which partially melt when fluxed by the addition of materials from the subducted slab. The mélange diapir model is informed by observations and modeling of the subduction side of the arc system, and predicts the generation of alkaline arc magmas by advection of buoyant material from the slab-wedge interface into the mantle wedge below arcs. Here we report results from experiments in which natural mélange materials partially melted at upper mantle conditions were found to produce alkaline magmas compositionally similar to those found in arcs worldwide. The starting material for our experiments is a chlorite-omphacite fels (SY400) from the island of Syros, Greece, that is representative of a hybrid rock containing AOC, sediment, and mantle components. Melting experiments were performed using a piston cylinder apparatus at conditions relevant to the heating-decompression path of mélange diapirs (1000-1300 °C, 1.5-2.5 GPa). The compositions of experimentally produced melts range from 51-61 wt% SiO2, and fall within the trachyte and tephrite-phonolite series (7.5-12.9 wt% Na2O+K2O). Restitic phases in equilibrium with melt include clinopyroxene, garnet (at high P), phlogopite (at high P), amphibole, olivine, rutile, and ilmenite. Partial melts produced in our experiments have trace-element abundance patterns that are typical of alkaline arc lavas, such as enrichment in large ion lithophile elements (Cs, Rb, Ba, Pb, Sr) and alkalis (K and Na), and depletion in Nb and Ta. The presence of a light rare earth element (LREE)-bearing accessory phase results in trace element fractionation by a factor of 4.2 for Nd/Hf and 2.6 for Sr/Nd. Melting of mélange diapirs provides a simple, single-stage model for the origin of alkaline magmatism in the arc and backarc regions of subduction zones.

Initial experience with endoscopic side cutting aspiration system in pure neuroendoscopic excision of large intraventricular tumors.

PubMed

Mohanty, Aaron; Thompson, Bobbye Jo; Patterson, Joel

2013-11-01

Conventionally, neuroendoscopic excision of intraventricular tumors has been difficult and time consuming because of lack of an effective decompression system that can be used through the working channel of the endoscope. The authors report their initial experience in purely endoscopic excision of large intraventricular tumors with the minimally invasive NICO Myriad system. The NICO Myriad is a side cutting soft tissue aspiration system that uses an inner reciprocating cannula and an outer stationary sheath with a side port. During decompression, applied suction approximates the tumor into the lumen of the outer sheath, with the inner cannula excising the tissue by oscillation of the cutting edge. The tumor is then removed by aspiration through the inner sheath. Three patients with large intraventricular tumors were operated by a purely endoscopic approach using a GAAB rigid endoscope and the NICO Myriad system. Of these, two had intraventricular craniopharyngiomas and one had a lateral ventricular subependymoma. The tumor size varied between 1.9 and 4.5 cm in the largest diameter. A relatively firm and solid tumor was encountered in two and a multicystic tumor with thick adherent walls in one. The tumor could be subtotally removed in one and near totally in two. There were no long-term complications. The NICO Myriad is a highly effective tumor decompression system that can be effectively used in a purely endoscopic approach to intraventricular lesions. Copyright © 2013 Elsevier Inc. All rights reserved.

Experimental Constraints on Alkali Volatilization during Chondrule Formation: Implications for Early Solar System Heterogeneity

NASA Astrophysics Data System (ADS)

Ustunisik, G. K.; Ebel, D. S.; Nekvasil, H.

2014-12-01

The chemical variability of chondrule volatile element contents provide a wealth of information on the processes that shaped the early solar system and its compositional heterogeneity. An essential observation is that chondrule melts contain very low alkalies and other volatile elements (e.g., Cl). The reason for this depletion is the combined effects of cooling rates (10 to 1000K/h), the small size of chondrules, and their high melting temperatures (~1700 to 2100 K) resulting in extensive loss of volatiles at canonical pressures (e.g., 10-4bar). However, we observe some chondrules with significant concentrations of volatiles (Na, Cl), that differ markedly from chondrules dominated by refractory elements. Could such heterogeneity arise from loss of alkalis and Cl to a gas phase that itself later condenses, thereby yielding variations in volatile enrichments in chondrules? Does Cl enhance volatility of the alkalis to varying extents? Experiments on Cl-bearing and Cl-free melts of equivalent composition for 10 min, 4 h, and 6 h reveal systematic effects of Cl on alkali volatility. Cl-bearing melts lose 48% of initial Na2O, 66% of K2O, 96% of Cl within the first 10 minutes of degassing. Then the amount of alkali loss decreases due to the absence of Cl. Cl-free melts loses only 15% of initial Na2O and 33% K2O. After 4 hours, melts lose 1/3 of initial Na2O and 1/2 of K2O. For both systems, Na2O is more compatible in the melt relative to K2O. Therefore, the vapor given off has a K/Na ratio higher than the melt through time in spite of the much higher initial Na abundance in the melt. Enhanced vaporization of alkalis from Cl-bearing melt suggests that Na and K evaporate more readily as volatile chlorides than as monatomic gases. Cl-free initial melts with normative plagioclase of An50Ab44Or6 evolved into slightly normal zoned ones (An49Ab50Or1) while Cl-bearing initial melts normative to albitic plagioclase (An46Ab50Or4) evolved to reverse zoned ones (An54Ab45Or1). The vapor phase over Cl-bearing chondrule melts may have a bimodal character over time. The heteregeneous volatile contents of chondrules may result from quenching of melt droplets at different stages of repeated heating, chondrule fragment recycling, and recondensation of exsolved volatiles.

Chiari malformation and central sleep apnea syndrome: efficacy of treatment with adaptive servo-ventilation*

PubMed Central

do Vale, Jorge Marques; Silva, Eloísa; Pereira, Isabel Gil; Marques, Catarina; Sanchez-Serrano, Amparo; Torres, António Simões

2014-01-01

The Chiari malformation type I (CM-I) has been associated with sleep-disordered breathing, especially central sleep apnea syndrome. We report the case of a 44-year-old female with CM-I who was referred to our sleep laboratory for suspected sleep apnea. The patient had undergone decompressive surgery 3 years prior. An arterial blood gas analysis showed hypercapnia. Polysomnography showed a respiratory disturbance index of 108 events/h, and all were central apnea events. Treatment with adaptive servo-ventilation was initiated, and central apnea was resolved. This report demonstrates the efficacy of servo-ventilation in the treatment of central sleep apnea syndrome associated with alveolar hypoventilation in a CM-I patient with a history of decompressive surgery. PMID:25410846

Origin and Role of Recycled Crust in Flood Basalt Magmatism: Case Study of the Central East Greenland Rifted Margin

NASA Astrophysics Data System (ADS)

Brown, E.; Lesher, C. E.

2015-12-01

Continental flood basalts (CFB) are extreme manifestations of mantle melting derived from chemically/isotopically heterogeneous mantle. Much of this heterogeneity comes from lithospheric material recycled into the convecting mantle by a range of mechanisms (e.g. subduction, delamination). The abundance and petrogenetic origins of these lithologies thus provide important constraints on the geodynamical origins of CFB magmatism, and the timescales of lithospheric recycling in the mantle. Basalt geochemistry has long been used to constrain the compositions and mean ages of recycled lithologies in the mantle. Typically, this work assumes the isotopic compositions of the basalts are the same as their mantle source(s). However, because basalts are mixtures of melts derived from different sources (having different fusibilities) generated over ranges of P and T, their isotopic compositions only indirectly represent the isotopic compositions of their mantle sources[1]. Thus, relating basalts compositions to mantle source compositions requires information about the melting process itself. To investigate the nature of lithologic source heterogeneity while accounting for the effects of melting during CFB magmatism, we utilize the REEBOX PRO forward melting model[2], which simulates adiabatic decompression melting in lithologically heterogeneous mantle. We apply the model to constrain the origins and abundance of mantle heterogeneity associated with Paleogene flood basalts erupted during the rift-to-drift transition of Pangea breakup along the Central East Greenland rifted margin of the North Atlantic igneous province. We show that these basalts were derived by melting of a hot, lithologically heterogeneous source containing depleted, subduction-modified lithospheric mantle, and <10% recycled oceanic crust. The Paleozoic mean age we calculate for this recycled crust is consistent with an origin in the region's prior subduction history, and with estimates for the mean age of recycled crust in the modern Iceland plume[3]. These results suggest that this lithospheric material was not recycled into the lower mantle before becoming entrained in the Iceland plume. [1] Rudge et al. (2013). GCA, 114, p112-143; [2] Brown & Lesher (2014). Nat. Geo., 7, p820-824; [3] Thirlwall et al. (2004). GCA, 68, p361-386

Chiari decompression outcomes using ligamentum nuchae harvest and duraplasty in pediatric patients with Chiari malformation type I.

PubMed

Cools, Michael J; Quinsey, Carolyn S; Elton, Scott W

2018-04-13

OBJECTIVE The choice of graft material for duraplasty in decompressions of Chiari malformations remains a matter of debate. The authors present a detailed technique for harvesting ligamenta nuchae, as well as the clinical and radiographic outcomes of this technique, in a case series. METHODS The authors conducted a retrospective study evaluating the outcomes of Chiari malformation type I decompression and duraplasty in children aged 0-18 years at a single institution from 2013 to 2016. They collected both intraoperative and postoperative variables and compared them qualitatively to published data. RESULTS During the study period, the authors performed 25 Chiari malformation decompressions with ligamentum nuchae graft duraplasties. Of the 25 patients, 10 were females, and the mean age at surgery was 8.6 years (range 13 months to 18 years). The median operative time was 163 minutes (IQR 152-187 minutes), with approximately 10 minutes needed by a resident surgeon to harvest the graft. The mean length of stay was 3 nights (range 2-6 nights), and the mean follow-up was 12.6 months (range 0.5-43.5 months). One patient (4%) developed a CSF leak that was repaired using an oversewing patch. There were no postoperative pseudomeningoceles or infections. Of the 19 patients presenting with a syrinx, imaging showed improvement in 10 (53%) and 8 (42%) had stable syrinx size on imaging. Of 16 patients presenting with a symptomatic Chiari malformation, 14 (87.5%) experienced resolution of symptoms and in 1 (4%) symptoms remained the same. One patient (4%) presented with worsening syrinx and symptoms 1.5 months after initial surgery and underwent repeat decompression. CONCLUSIONS The authors describe a series of clinical and imaging outcomes of patients who underwent Chiari malformation decompression and duraplasty with a harvested ligamentum nuchae. The rates of postoperative CSF leak are similar to established techniques of autologous and artificial grafts, with similarly successful outcomes. Further study will be needed with larger patient cohorts to more directly compare duraplasty graft outcomes.

Vapor-Saturated Melting of Fertile Peridotite Revisited: A new Experimental Approach and Re-evaluation of the Hydrous Peridotite Solidus

NASA Astrophysics Data System (ADS)

Grove, T. L.

2001-12-01

The vapor-saturated melting relations of peridotite have been determined for a fertile mantle composition of Hart and Zindler (1986, Chem Geol 57: 247) over the pressure range of 1.2 to 2.4 GPa. For example, at 1.2 GPa melt is present at a temperature of 980° C and at 2.4 GPa melt is present at 920° C. These temperatures should be viewed as maximum values for the vapor-saturated solidus (although see below) because the initial melting temperature of multi-phase, multicomponent systems can often be difficult to detect. At 2.4 GPa the melt composition is highly silica-undersaturated and very aluminous ( ~ 21 wt. % Al2O3). Wet mantle melts are thought to be high in silica, but this is not the case for these hydrous melts. At 1.2 GPa, melt fractions are too small to allow reliable analysis. The experiments have been carried out in a piston cylinder apparatus using Au capsules. The starting material is an oxide mixture containing 14.5 wt. % H2O added as brucite. Free water present in the experiment after quenching indicates subsolidus conditions. The absence of fluid in experiments above the vapor-saturated solidus shows that all of the free H2O is dissolved in the melt. The high H2O content of the starting material moves the bulk composition close to the vapor-saturated melt composition, therefore increasing the amount of melt produced close to the solidus and making detection of low melt fraction possible. Studies of the hydrous peridotite solidus carried out between 1970 and 1975 by Mysen and Boettcher, Kushiro and others, Green and Millhollen and others at 2.0 GPa ranged from < 800 to ~ 1000° C, a variation of over 200 degrees. In a subduction zone environment a fluid-rich component released from the slab ascends into hotter overlying mantle and melting initiates at the vapor-saturated solidus. Melting would begin at a depth of ~ 75 km in the mantle wedge, for a realistic thermal structure. Melting would continue as these initial H2O-rich buoyant melts ascend into hotter, shallower mantle and re-equilibrate with their surroundings. The initiation of melting deep in the mantle wedge has implications for both chemical and mechanical processes in the subduction zone environment.

Isolation and Characterization of Erythrocyte and Parasite Membranes from Rhesus Red Cells Infected with P. knowlesi.

DTIC Science & Technology

1981-06-01

initiated experiments to separate and isolate the vacuolar membrane and the parasite plasma menbrane . For this, the surfaces of intact schizonts...controlled nitrogen decompression (1) is surrounded by two membranes, its own plasma membrane and the membrane of the parasitophorous vacuole. We have

Early formation and long-term stability of continents resulting from decompression melting in a convecting mantle

NASA Astrophysics Data System (ADS)

De Smet, J.; Van den Berg, A. P.; Vlaar, N. J.

2000-07-01

The origin of stable old continental cratonic roots is still debated. We present numerical modelling results which show rapid initial formation during the Archaean of continental roots of ca. 200 km thick. These results have been obtained from an upper mantle thermal convection model including differentiation by pressure release partial melting of mantle peridotite. The upper mantle model includes time-dependent radiogenic heat production and thermal coupling with a heat reservoir representing the Earth's lower mantle and core. This allows for model experiments including secular cooling on a time-scale comparable to the age of the Earth. The model results show an initial phase of rapid continental root growth of ca. 0.1 billion year, followed by a more gradual increase of continental volume by addition of depleted material produced through hot diapiric, convective upwellings which penetrate the continental root from below. Within ca. 0.6 Ga after the start of the experiment, secular cooling of the mantle brings the average geotherm below the peridotite solidus thereby switching off further continental growth. At this time the thickness of the continental root has grown to ca. 200 km. After 1 Ga of secular cooling small scale thermal instabilities develop at the bottom of the continental root causing continental delamination without breaking up the large scale layering. This delaminated material remixes with the deeper layers. Two more periods, each with a duration of ca. 0.5 Ga and separated by quiescent periods were observed when melting and continental growth was reactivated. Melting ends at 3 Ga. Thereafter secular cooling proceeds and the compositionally buoyant continental root is stabilized further through the increase in mechanical strength induced by the increase of the temperature dependent mantle viscosity. Fluctuating convective velocity amplitudes decrease to below 10 mma -1 and the volume average temperature of the sub-continental convecting mantle has decreased ca. 340 K after 4 Ga. Surface heatflow values decrease from 120 to 40 mW m -2 during the 4 Ga model evolution. The surface heatflow contribution from an almost constant secular cooling rate was estimated to be 6 mW m -2, in line with recent observational evidence. The modelling results show that the combined effects of compositional buoyancy and strong temperature dependent rheology result in continents which overall remain stable for a duration longer than the age of the Earth. Tracer particles have been used for studying the patterns of mantle differentiation in greater detail. The observed ( p, T, F, t)-paths are consistent with proposed stratification and thermo-mechanical history of the depleted continental root, which have been inferred from mantle xenoliths and other upper mantle samples. In addition, the particle tracers have been used to derive the thermal age of the modelled continental root, defined by a hypothetical closing temperature.

Comparative incidences of decompression illness in repetitive, staged, mixed-gas decompression diving: is 'dive fitness' an influencing factor?

PubMed

Sayer, Martin Dj; Akroyd, Jim; Williams, Guy D

2008-06-01

Wreck diving at Bikini Atoll consists of a relatively standard series of decompression dives with maximum depths in the region of 45-55 metres' sea water (msw). In a typical week of diving at Bikini, divers can perform up to 12 decompression dives to these depths over seven days; on five of those days, divers can perform two decompression dives per day. All the dives employ multi-level, staged decompression schedules using air and surface-supplied nitrox containing 80% oxygen. Bikini is serviced by a single diving operator and so a relatively precise record exists both of the actual number of dives undertaken and of the decompression illness incidents both for customer divers and the dive guides. The dive guides follow exactly the dive profiles and decompression schedules of the customers. Each dive guide will perform nearly 400 decompression dives a year, with maximum depths mostly around 50 msw, compared with an average of 10 (maximum of 12) undertaken typically by each customer diver in a week. The incidence of decompression illness for the customer population (presumed in the absence of medical records) is over ten times higher than that for the dive guides. The physiological reasons for such a marked difference are discussed in terms of customer demographics and dive-guide acclimatization to repetitive decompression stress. The rates of decompression illness for a range of diving populations are reviewed.

Intraoperative Computed Tomography for Cervicomedullary Decompression of Foramen Magnum Stenosis in Achondroplasia: Two Case Reports

PubMed Central

Arishima, Hidetaka; Tsunetoshi, Kenzo; Kodera, Toshiaki; Kitai, Ryuhei; Takeuchi, Hiroaki; Kikuta, Ken-ichiro

2013-01-01

The authors report two cases of cervicomedullary decompression of foramen magnum (FM) stenosis in children with achondroplasia using intraoperative computed tomography (iCT). A 14-month-old girl with myelopathy and retarded motor development, and a 10-year-old girl who had already undergone incomplete FM decompression was presented with myelopathy. Both patients underwent decompressive sub-occipitalcraniectomy and C1 laminectomy without duraplasty using iCT. It clearly showed the extent of FM decompression during surgery, which finally enabled sufficient decompression. After the operation, their myelopathy improved. We think that iCT can provide useful information and guidance for sufficient decompression for FM stenosis in children with achondroplasia. PMID:24140778

Intraoperative computed tomography for cervicomedullary decompression of foramen magnum stenosis in achondroplasia: two case reports.

PubMed

Arishima, Hidetaka; Tsunetoshi, Kenzo; Kodera, Toshiaki; Kitai, Ryuhei; Takeuchi, Hiroaki; Kikuta, Ken-Ichiro

2013-01-01

The authors report two cases of cervicomedullary decompression of foramen magnum (FM) stenosis in children with achondroplasia using intraoperative computed tomography (iCT). A 14-month-old girl with myelopathy and retarded motor development, and a 10-year-old girl who had already undergone incomplete FM decompression was presented with myelopathy. Both patients underwent decompressive sub-occipitalcraniectomy and C1 laminectomy without duraplasty using iCT. It clearly showed the extent of FM decompression during surgery, which finally enabled sufficient decompression. After the operation, their myelopathy improved. We think that iCT can provide useful information and guidance for sufficient decompression for FM stenosis in children with achondroplasia.

The Microwave Properties of Simulated Melting Precipitation Particles: Sensitivity to Initial Melting

NASA Technical Reports Server (NTRS)

Johnson, B. T.; Olson, W. S.; Skofronick-Jackson, G.

2016-01-01

A simplified approach is presented for assessing the microwave response to the initial melting of realistically shaped ice particles. This paper is divided into two parts: (1) a description of the Single Particle Melting Model (SPMM), a heuristic melting simulation for ice-phase precipitation particles of any shape or size (SPMM is applied to two simulated aggregate snow particles, simulating melting up to 0.15 melt fraction by mass), and (2) the computation of the single-particle microwave scattering and extinction properties of these hydrometeors, using the discrete dipole approximation (via DDSCAT), at the following selected frequencies: 13.4, 35.6, and 94.0GHz for radar applications and 89, 165.0, and 183.31GHz for radiometer applications. These selected frequencies are consistent with current microwave remote-sensing platforms, such as CloudSat and the Global Precipitation Measurement (GPM) mission. Comparisons with calculations using variable-density spheres indicate significant deviations in scattering and extinction properties throughout the initial range of melting (liquid volume fractions less than 0.15). Integration of the single-particle properties over an exponential particle size distribution provides additional insight into idealized radar reflectivity and passive microwave brightness temperature sensitivity to variations in size/mass, shape, melt fraction, and particle orientation.

Needle Decompression of Tension Pneumothorax with Colorimetric Capnography.

PubMed

Naik, Nimesh D; Hernandez, Matthew C; Anderson, Jeff R; Ross, Erika K; Zielinski, Martin D; Aho, Johnathon M

2017-11-01

The success of needle decompression for tension pneumothorax is variable, and there are no objective measures assessing effective decompression. Colorimetric capnography, which detects carbon dioxide present within the pleural space, may serve as a simple test to assess effective needle decompression. Three swine underwent traumatically induced tension pneumothorax (standard of care, n = 15; standard of care with needle capnography, n = 15). Needle thoracostomy was performed with an 8-cm angiocatheter. Similarly, decompression was performed with the addition of colorimetric capnography. Subjective operator assessment of decompression was recorded and compared with true decompression, using thoracoscopic visualization for both techniques. Areas under receiver operating curves were calculated and pairwise comparison was performed to assess statistical significance (P < .05). The detection of decompression by needle colorimetric capnography was found to be 100% accurate (15 of 15 attempts), when compared with thoracoscopic assessment (true decompression). Furthermore, it accurately detected the lack of tension pneumothorax, that is, the absence of any pathologic/space-occupying lesion, in 100% of cases (10 of 10 attempts). Standard of care needle decompression was detected by operators in 9 of 15 attempts (60%) and was detected in 3 of 10 attempts when tension pneumothorax was not present (30%). True decompression, under direct visualization with thoracoscopy, occurred 15 of 15 times (100%) with capnography, and 12 of 15 times (80%) without capnography. Areas under receiver operating curves were 0.65 for standard of care and 1.0 for needle capnography (P = .002). Needle decompression with colorimetric capnography provides a rapid, effective, and highly accurate method for eliminating operator bias for tension pneumothorax decompression. This may be useful for the treatment of this life-threatening condition. Copyright © 2017 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.

The effect of growth rate on the production of Ti-enriched rims of quartz phenocrysts in the Bishop magma bodies.

NASA Astrophysics Data System (ADS)

Pamukcu, A. S.; Ghiorso, M. S.; Gualda, G. A. R.

2015-12-01

Quartz commonly displays cathodoluminescence (CL) zoning correlated with elevated Ti concentrations. This zoning has been attributed to changes in magmatic intensive variables, suggesting for example, that in the Bishop Tuff (BT) magma bodies, bright-CL rims on quartz phenocrysts grew during a late-stage eruption-triggering thermal event. Yet, these rims are not ubiquitous, discounting their origin by variation in equilibrium growth conditions. Huang & Audetat (2012) suggest that Ti contents in quartz depend strongly on growth rate. Diffusion chronometry indicates that BT bright-CL quartz rims crystallized rapidly (days-weeks) at growth rates of 10-7-10-8 m/s, while interiors grew over centennial-millennial timescales (10-11-10-13 m/s). This result is consistent with CSD analyses that suggest eruptive decompression began <1 year before eruption. We use a numerical model based on the crystal growth equation of Lasaga (1982) to test if BT bright-CL rims could have resulted from elevated syn-eruptive growth rates. Results indicate that Ti contents at the quartz-melt boundary are strongly dependent on growth rate if it exceeds ~10-9 m/s. At 10-8 m/s, enrichment of 1.5-2.5 times the initial concentration is achieved at the boundary in a time frame of days-a week. At 10-7 m/s, enrichment jumps to 4-8 times over the same period. BT quartz interiors contain ~50 ppm Ti, while bright-CL rims have ~75-100 ppm (Wark et al. 2007). Our modeling successfully reproduces these concentrations using the growth rates, and over the timescales, indicated by diffusion chronometry. It also suggests that the rims grew chiefly at a rate of ~10-8 m/s; slower rates do not produce enrichment, and faster rates result in over-enrichment, relative to that observed in natural crystals. We conclude that high-Ti, bright-CL rims on BT quartz resulted from increased growth rates due to eruptive decompression, rather than late-stage fluctuations in magmatic intensive variables, over timescales of days to weeks.

Potential Fifty Percent Reduction in Saturation Diving Decompression Time Using a Combination of Intermittent Recompression and Exercise

NASA Technical Reports Server (NTRS)

Gernhardt, Michael I.; Abercromby, Andrew; Conklin, Johnny

2007-01-01

Conventional saturation decompression protocols use linear decompression rates that become progressively slower at shallower depths, consistent with free gas phase control vs. dissolved gas elimination kinetics. If decompression is limited by control of free gas phase, linear decompression is an inefficient strategy. The NASA prebreathe reduction program demonstrated that exercise during O2 prebreathe resulted in a 50% reduction (2 h vs. 4 h) in the saturation decompression time from 14.7 to 4.3 psi and a significant reduction in decompression sickness (DCS: 0 vs. 23.7%). Combining exercise with intermittent recompression, which controls gas phase growth and eliminates supersaturation before exercising, may enable more efficient saturation decompression schedules. A tissue bubble dynamics model (TBDM) was used in conjunction with a NASA exercise prebreathe model (NEPM) that relates tissue inert gas exchange rate constants to exercise (ml O2/kg-min), to develop a schedule for decompression from helium saturation at 400 fsw. The models provide significant prediction (p < 0.001) and goodness of fit with 430 cases of DCS in 6437 laboratory dives for TBDM (p = 0.77) and with 22 cases of DCS in 159 altitude exposures for NEPM (p = 0.70). The models have also been used operationally in over 25,000 dives (TBDM) and 40 spacewalks (NEPM). The standard U.S. Navy (USN) linear saturation decompression schedule from saturation at 400 fsw required 114.5 h with a maximum Bubble Growth Index (BGI(sub max)) of 17.5. Decompression using intermittent recompression combined with two 10 min exercise periods (75% VO2 (sub peak)) per day required 54.25 h (BGI(sub max): 14.7). Combined intermittent recompression and exercise resulted in a theoretical 53% (2.5 day) reduction in decompression time and theoretically lower DCS risk compared to the standard USN decompression schedule. These results warrant future decompression trials to evaluate the efficacy of this approach.

Cardiopulmonary Changes with Moderate Decompression in Rats

NASA Technical Reports Server (NTRS)

Robinson, R.; Little, T.; Doursout, M.-F.; Butler, B. D.; Chelly, J. E.

1996-01-01

Sprague-Dawley rats were compressed to 616 kPa for 120 min then decompressed at 38 kPa/min to assess the cardiovascular and pulmonary responses to moderate decompression stress. In one series of experiments the rats were chronically instrumented with Doppler ultrasonic probes for simultaneous measurement of blood pressure, cardiac output, heart rate, left and right ventricular wall thickening fraction, and venous bubble detection. Data were collected at base-line, throughout the compression/decompression protocol, and for 120 min post decompression. In a second series of experiments the pulmonary responses to the decompression protocol were evaluated in non-instrumented rats. Analyses included blood gases, pleural and bronchoalveolar lavage (BAL) protein and hemoglobin concentration, pulmonary edema, BAL and lung tissue phospholipids, lung compliance, and cell counts. Venous bubbles were directly observed in 90% of the rats where immediate post-decompression autopsy was performed and in 37% using implanted Doppler monitors. Cardiac output, stroke volume, and right ventricular wall thickening fractions were significantly decreased post decompression, whereas systemic vascular resistance was increased suggesting a decrease in venous return. BAL Hb and total protein levels were increased 0 and 60 min post decompression, pleural and plasma levels were unchanged. BAL white blood cells and neutrophil percentages were increased 0 and 60 min post decompression and pulmonary edema was detected. Venous bubbles produced with moderate decompression profiles give detectable cardiovascular and pulmonary responses in the rat.

Petrologic Modeling of Magmatic Evolution in The Elysium Volcanic Province

NASA Astrophysics Data System (ADS)

Susko, D.; Karunatillake, S.; Hood, D.

2017-12-01

The Elysium Volcanic Province (EVP) on Mars is a massive expanse of land made up of many hundreds of lava flows of various ages1. The variable surface ages within this volcanic province have distinct elemental compositions based on the derived values from the Gamma Ray Spectrometer (GRS) suite2. Without seismic data or ophiolite sequences on Mars, the compositions of lavas on the surface provide some of the only information to study the properties of the interior of the planet. The Amazonian surface age and isolated nature of the EVP in the northern lowlands of Mars make it ideal for analyzing the mantle beneath Elysium during the most recent geologic era on Mars. The MELTS algorithm is one of the most commonly used programs for simulating compositions and mineral phases of basaltic melt crystallization3. It has been used extensively for both terrestrial applications4 and for other planetary bodies3,5. The pMELTS calibration of the algorithm allows for higher pressure (10-30 kbars) regimes, and is more appropriate for modeling melt compositions and equilibrium conditions for a source within the martian mantle. We use the pMELTS program to model how partial melting of the martian mantle could evolve magmas into the surface compositions derived from the GRS instrument, and how the mantle beneath Elysium has changed over time. We attribute changes to lithospheric loading by long term, episodic volcanism within the EVP throughout its history. 1. Vaucher, J. et al. The volcanic history of central Elysium Planitia: Implications for martian magmatism. Icarus 204, 418-442 (2009). 2. Susko, D. et al. A record of igneous evolution in Elysium, a major martian volcanic province. Scientific Reports 7, 43177 (2017). 3. El Maarry, M. R. et al. Gamma-ray constraints on the chemical composition of the martian surface in the Tharsis region: A signature of partial melting of the mantle? Journal of Volcanology and Geothermal Research 185, 116-122 (2009). 4. Ding, S. & Dasgupta, R. The fate of sulfide during decompression melting of peridotite - implications for sulfur inventory of the MORB-source depleted upper mantle. Earth and Planetary Science Letters 459, 183-195 (2017). 5. Sakaia, R., Nagaharaa, H., Ozawaa, K. & Tachibanab, S. Composition of the lunar magma ocean constrained by the conditions for the crust formation. Icarus 229, 45-56 (2014).

Evaluation of thermobarometry for spinel lherzolite fragments in alkali basalts

NASA Astrophysics Data System (ADS)

Ozawa, Kazuhito; Youbi, Nasrrddine; Boumehdi, Moulay Ahmed; McKenzie, Dan; Nagahara, Hiroko

2017-04-01

Geothermobarometry of solid fragments in kimberlite and alkali basalts, generally called "xenoliths", provides information on thermal and chemical structure of lithospheric and asthenospheric mantle, based on which various chemical, thermal, and rheological models of lithosphere have been constructed (e.g., Griffin et al., 2003; McKenzie et al., 2005; Ave Lallemant et al., 1980). Geothermobarometry for spinel-bearing peridotite fragments, which are frequently sampled from Phanerozoic provinces in various tectonic environments (Nixon and Davies, 1987), has essential difficulties, and it is usually believed that appropriated barometers do not exist for them (O'Reilly et al., 1997; Medaris et al., 1999). Ozawa et al. (2016; EGU) proposed a method of geothermobarometry for spinel lherzolite fragments. They applied the method to mantle fragments in alkali basalts from Bou Ibalhatene maars in the Middle Atlas in Morocco (Raffone et al. 2009; El Azzouzi et al., 2010; Witting et al., 2010; El Messbahi et al., 2015). Ozawa et al. (2016) obtained 0.5GPa pressure difference (1.5-2.0GPa) for 100°C variation in temperatures (950-1050°C). However, it is imperative to verify the results on the basis of completely independent data. There are three types of independent information: (1) time scale of solid fragment extraction, which may be provided by kinetics of reactions induced by heating and/or decompression during their entrapment in the host magma and transportation to the Earth's surface (Smith, 1999), (2) depth of the host basalt formation, which may be provided by the petrological and geochemical studies of the host basalts, and (3) lithosphere-asthenosphere boundary depths, which may be estimated by geophysical observations. Among which, (3) is shown to be consistent with the result in Ozawa et al. (2016). We here present that the estimated thermal structure just before the fragment extraction is fully supported by the information of (1) and (2). Spera (1984) reviewed various method of estimation of ascent rate of mantle fragments in kimberlite and alkali basalt; one based on fluid dynamics of transportation of entrapped fragments by giving the maximum size and viscosity of magma as a minimum estimate (Spera, 1980) and the other by coupling depth of fragment residence before the entrapment in a magma and time scale of heating by the magma. The depth of entrapment, however, is the least known parameter for spinel lherzolite. Because of nearly adiabatic ascent of magmas loaded with solid fragments, all the fragments underwent the same heating and decompression history with difference in entrapment depth and thus heating duration, from which the depth of their residence just before the extraction may be estimated if ascent rate is known. Therefore, extent of chemical and textural modification induced by heating and decompression may provide independent test for pressure estimation. We have used several reactions for this purpose: (1) Mg-Fe exchange reaction between spinel and olivine (Ozawa, 1983; 1984), (2) Ca zoning in olivine (Takahashi, 1980), (3) partial dissolution of clinopyroxene, (4) partial dissolution of spinel, and (5) formation of melt frozen as glass, which is related to (3) and (4). The depth of melt generation is constrained to be deeper than 70km by modeling the trace element compositions of the host magmas using the methods of McKenzie and O'Nions (1991) and data from El Azzouzi et al. (2010). The host magmas can be produced by melting the convecting upper mantle without requirement of any input from the continental lithosphere. This is consistent with the positive gravity anomalies in the NW Africa showing shallow upwelling in this region allowing decompressional melting owing to the thinner lithosphere in the Middle Atlas.

Shock Initiation Characteristics of an Aluminized DNAN/RDX Melt-Cast Explosive

NASA Astrophysics Data System (ADS)

Cao, Tong-Tang; Zhou, Lin; Zhang, Xiang-Rong; Zhang, Wei; Miao, Fei-Chao

2017-10-01

Shock sensitivity is one of the key parameters for newly developed, 2,4-dinitroanisole (DNAN)-based, melt-cast explosives. For this paper, a series of shock initiation experiments were conducted using a one-dimensional Lagrangian system with a manganin piezoresistive pressure gauge technique to evaluate the shock sensitivity of an aluminized DNAN/cyclotrimethylenetrinitramine (RDX) melt-cast explosive. This study fully investigated the effects of particle size distributions in both RDX and aluminum, as well as the RDX's crystal quality on the shock sensitivity of the aluminized DNAN/RDX melt-cast explosive. Ultimately, the shock sensitivity of the aluminized DNAN/RDX melt-cast explosives increases when the particle size decreases in both RDX and aluminum. Additionally, shock sensitivity increases when the RDX's crystal quality decreases. In order to simulate these effects, an Ignition and Growth (I&G) reactive flow model was calibrated. This calibrated I&G model was able to predict the shock initiation characteristics of the aluminized DNAN/RDX melt-cast explosive.

Crustal-scale degassing and igneous mush re-organisation: a generic concept applied to episodic volcanism at the Soufrière Hills Volcano Montserrat

NASA Astrophysics Data System (ADS)

R Stephen J, S.; Cashman, K. V.

2015-12-01

A complete theory of episodic volcanism is lacking. Melt generation related to large scale tectonic processes is likely continuous but surface volcanic activity is typically episodic; for most volcanoes short-lived eruptions alternate with long periods of dormancy. Many models of volcanic activity and geophysical unrest are framed by a conceptual model of shallow magma chamber recharge, in which various phenomena are attributed to magma transport from deeper levels. While many aspects of volcanism are explained by this concept it has little explanatory power for key aspects of volcanism, including time scales of dormancy, eruption duration and eruption magnitude. Extensive trans-crustal igneous systems develop beneath active volcanoes in which much of the system is in a mushy state in which buoyancy-driven segregation of melt and magmatic fluid occurs to form layers, which are inherently unstable. We postulate that such systems are prone to destabilisation in which segregating layers amalgamate to form ephemeral magma chambers and in which melts and magmatic fluids decouple. Periods of dormancy relate to slow processes of segregation while short periods of volcanic unrest and eruption relate to episodic and rapid processes of destabilisation of the mush system. In this conceptual framework volatiles rather than magma recharge plays the key role in the dynamics of the shallow parts of the magmatic systems. Magma ascent during episodes of destabilisation does not itself cause pressurisation because melts and crystals are near incompressible, while volatile exsolution and decompression results in major pressure changes that can lead to unrest and eruption. These concepts are applied to the interpretation of stratigraphic, geochronological, geophysical, geochemical, petrological and volcanological data of volcanic activity at the Soufrière Hills Volcano (SHV), Montserrat.

Ogilvie's syndrome in a case of myxedema coma.

PubMed

Yanamandra, Uday; Kotwal, Narendra; Menon, Anil; Nair, Velu

2012-05-01

Ogilvie's syndrome [acute colonic pseudo-obstruction (ACPO)] presents as massive colonic dilatation without a mechanical cause, usually in critically ill patients due to imbalanced sympathetic and parasympathetic activity. The initial therapy remains conservative with supportive measures (correction of metabolic, infectious or pharmacologic factors) followed by neostigmine and decompressive colonoscopy. Surgery is reserved for patients with clinical deterioration or with evidence of colonic ischemia or perforation. A 60-year-old lady presented with fever, altered sensorium, obstipation, bradycardia and abdominal distension. Investigation revealed hyponatremia and acute colonic pseudo-obstruction. Supportive measures and decompressive colonoscopy were not of great benefit. Thyroid profile was suggestive of primary hypothyroidism. Colonic motility was restored only on starting thyroxin. The case is illustrative of the need to consider hypothyroidism, a common endocrine disorder, in the differential diagnosis of Ogilvie's.

Experimental Evidence for Fast Lithium Diffusion and Isotope Fractionation in Water-bearing Rhyolitic Melts at Magmatic Conditions

NASA Astrophysics Data System (ADS)

Cichy, S. B.; Till, C. B.; Roggensack, K.; Hervig, R. L.; Clarke, A. B.

2015-12-01

The aim of this work is to extend the existing database of experimentally-determined lithium diffusion coefficients to more natural cases of water-bearing melts at the pressure-temperature range of the upper crust. In particular, we are investigating Li intra-melt and melt-vapor diffusion and Li isotope fractionation, which have the potential to record short-lived magmatic processes (seconds to hours) in the shallow crust, especially during decompression-induced magma degassing. Hydrated intra-melt Li diffusion-couple experiments on Los Posos rhyolite glass [1] were performed in a piston cylinder at 300 MPa and 1050 °C. The polished interfaces between the diffusion couples were marked by addition of Pt powder for post-run detection. Secondary ion mass spectrometry analyses indicate that lithium diffuses extremely fast in the presence of water. Re-equilibration of a hydrated ~2.5 mm long diffusion-couple experiment was observed during the heating period from room temperature to the final temperature of 1050 °C at a rate of ~32 °C/min. Fractionation of ~40‰ δ7Li was also detected in this zero-time experiment. The 0.5h and 3h runs show progressively higher degrees of re-equilibration, while the isotope fractionation becomes imperceptible. Li contamination was observed in some experiments when flakes filed off Pt tubing were used to mark the diffusion couple boundary, while the use of high purity Pt powder produced better results and allowed easier detection of the diffusion-couple boundary. The preliminary lithium isotope fractionation results (δ7Li vs. distance) support findings from [2] that 6Li diffuses substantially faster than 7Li. Further experimental sets are in progress, including lower run temperatures (e.g. 900 °C), faster heating procedure (~100 °C/min), shorter run durations and the extension to mafic systems. [1] Stanton (1990) Ph.D. thesis, Arizona State Univ., [2] Richter et al. (2003) GCA 67, 3905-3923.

Decompression scenarios in a new underground transportation system.

PubMed

Vernez, D

2000-10-01

The risks of a public exposure to a sudden decompression, until now, have been related to civil aviation and, at a lesser extent, to diving activities. However, engineers are currently planning the use of low pressure environments for underground transportation. This method has been proposed for the future Swissmetro, a high-speed underground train designed for inter-urban linking in Switzerland. The use of a low pressure environment in an underground public transportation system must be considered carefully regarding the decompression risks. Indeed, due to the enclosed environment, both decompression kinetics and safety measures may differ from aviation decompression cases. A theoretical study of decompression risks has been conducted at an early stage of the Swissmetro project. A three-compartment theoretical model, based on the physics of fluids, has been implemented with flow processing software (Ithink 5.0). Simulations have been conducted in order to analyze "decompression scenarios" for a wide range of parameters, relevant in the context of the Swissmetro main study. Simulation results cover a wide range from slow to explosive decompression, depending on the simulation parameters. Not surprisingly, the leaking orifice area has a tremendous impact on barotraumatic effects, while the tunnel pressure may significantly affect both hypoxic and barotraumatic effects. Calculations have also shown that reducing the free space around the vehicle may mitigate significantly an accidental decompression. Numeric simulations are relevant to assess decompression risks in the future Swissmetro system. The decompression model has proven to be useful in assisting both design choices and safety management.

The partitioning behavior of silver in a vapor brine rhyolite melt assemblage

NASA Astrophysics Data System (ADS)

Simon, Adam C.; Pettke, Thomas; Candela, Philip A.; Piccoli, Philip M.

2008-03-01

The partitioning of silver in a sulfur-free rhyolite melt-vapor-brine assemblage has been quantified at 800 °C, pressures of 100 and 140 MPa and f≈NNO (nickel-nickel oxide). Silver solubility (±2 σ) in rhyolite increases 5-fold from 105 ± 21 to 675 ± 98 μg/g as pressure increases from 100 to 140 MPa. Nernst-type partition coefficients (DAgi,j±2σ) describing the mass transfer of silver at 100 MPa between vapor and melt, brine and melt and vapor and brine are 32 ± 30, 1151 ± 238 and 0.026 ± 0.004, respectively. At 140 MPa, values for DAgi,j(±2σ) for vapor and melt, brine and melt, and vapor and brine are 32 ± 10, 413 ± 172 and 0.06 ± 0.03, respectively. Apparent equilibrium constant values (±2 σ) describing the exchange of silver and sodium between vapor and melt, KAg,Nav/m, at 100 and 140 MPa are 105 ± 68 and 14 ± 6. The average values (±2 σ) for silver and sodium exchange between brine and melt, KAg,Nab/m, at 100 and 140 MPa are 313 ± 288 and 65 ± 12. These data indicate that the mass transfer of silver from rhyolite melt to an exsolved volatile phase(s) is enhanced at 100 MPa relative to 140 MPa, suggesting that decompression increases the silver ore-generative potential of an evolving silicate magma. Model calculations using the new data suggest that the evolution of low-density, aqueous fluid (i.e., vapor) may be responsible for the the silver tonnage of many porphyry-type and perhaps epithermal-type ore deposits. For example, Halter et al. (Halter W. E., Pettke T. and Heinrich C. A. (2002) The origin of Cu/Au ratios in porphyry-type ore deposits. Science296, 1842-1844) used detailed silicate and sulfide melt inclusion and vapor and brine fluid inclusions analyses to estimate a melt volume on the order of 15 km 3 to satisfy the copper budget at the Bajo de la Alumbrera copper-, gold-, silver-ore deposit. Using their melt volume estimate with the data presented here, model calculations for a 15-km 3 felsic melt, saturated with pyrrhotite and magnetite, suggest that a low-salinity magmatic vapor may scavenge on the order of 7 × 10 12 g of silver from the melt. This quantity of silver exceeds the discovered 2 × 10 9 g of Ag at Alumbrera. Calculated tonnages for numerous other deposits yield similar results. The excess silver in the vapor, remaining after porphyry formation, is then available to precipitate at lower PTconditions in the stratigraphically higher epithermal environment. These data suggest that silver, and perhaps other ore metals, in the porphyry-epithermal continuum may be derived solely from the time-integrated flux of dominantly low-salinity vapor exsolved from a series of sequential magma batches.

Use of the impedance threshold device improves survival rate and neurological outcome in a swine model of asphyxial cardiac arrest*.

PubMed

Pantazopoulos, Ioannis N; Xanthos, Theodoros T; Vlachos, Ioannis; Troupis, Georgios; Kotsiomitis, Evangelos; Johnson, Elisabeth; Papalois, Apostolos; Skandalakis, Panagiotis

2012-03-01

To assess whether intermittent impedance of inspiratory gas exchange improves hemodynamic parameters, 48-hr survival, and neurologic outcome in a swine model of asphyxial cardiac arrest treated with active compression-decompression cardiopulmonary resuscitation. Prospective, randomized, double-blind study. Laboratory investigation. Thirty healthy Landrace/Large-White piglets of both sexes, aged 10 to 15 wks, whose average weight was 19 ± 2 kg. At approximately 7 mins following endotracheal tube clamping, ventricular fibrillation was induced and remained untreated for another 8 mins. Before initiation of cardiopulmonary resuscitation, animals were randomly assigned to either receive active compression-decompression cardiopulmonary resuscitation plus a sham impedance threshold device (control group, n = 15), or active compression-decompression cardiopulmonary resuscitation plus an active impedance threshold device (experimental group, n = 15). Electrical defibrillation was attempted every 2 mins until return of spontaneous circulation or asystole. Return of spontaneous circulation was observed in six (40%) animals treated with the sham valve and 14 (93.3%) animals treated with the active valve (p = .005, odds ratio 21.0, 95% confidence interval 2.16-204.6). Neuron-specific enolase and S-100 levels increased in the ensuing 4 hrs post resuscitation in both groups, but they were significantly elevated in animals treated with the sham valve (p < .01). At 48 hrs, neurologic alertness score was significantly better in animals treated with the active valve (79.1 ± 18.7 vs. 50 ± 10, p < .05) and was strongly negatively correlated with 1- and 4-hr postresuscitation neuron-specific enolase (r = -.86, p < .001 and r = -.87, p < .001, respectively) and S-100 (r = -.77, p < .001 and r = -0.8, p = .001) values. In this model of asphyxial cardiac arrest, intermittent airway occlusion with the impedance threshold device during the decompression phase of active compression-decompression cardiopulmonary resuscitation significantly improved hemodynamic parameters, 24- and 48-hr survival, and neurologic outcome evaluated both with clinical and biochemical parameters (neuron-specific enolase, S-100).

Effect of Orbital Decompression on Corneal Topography in Patients with Thyroid Ophthalmopathy

PubMed Central

Kim, Su Ah; Jung, Su Kyung; Paik, Ji Sun; Yang, Suk-Woo

2015-01-01

Objective To evaluate changes in corneal astigmatism in patients undergoing orbital decompression surgery. Methods This retrospective, non randomized comparative study involved 42 eyes from 21 patients with thyroid ophthalmopathy who underwent orbital decompression surgery between September 2011 and September 2014. The 42 eyes were divided into three groups: control (9 eyes), two-wall decompression (25 eyes), and three-wall decompression (8 eyes). The control group was defined as the contralateral eyes of nine patients who underwent orbital decompression surgery in only one eye. Corneal topography (Orbscan II), Hertel exophthalmometry, and intraocular pressure were measured at 1 month before and 3 months after surgery. Corneal topographic parameters analyzed were total astigmatism (TA), steepest axis (SA), central corneal thickness (CCT), and anterior chamber depth (ACD). Results Exophthalmometry values and intraocular pressure decreased significantly after the decompression surgery. The change (absolute value (|x|) of the difference) in astigmatism at the 3 mm zone was significantly different between the decompression group and the controls (p = 0.025). There was also a significant change in the steepest axis at the 3 mm zone between the decompression group and the controls (p = 0.033). An analysis of relevant changes in astigmatism showed that there was a dominant tendency for incyclotorsion of the steepest axis in eyes that underwent decompression surgery. Using Astig PLOT, the mean surgically induced astigmatism (SIA) was 0.21±0.88 D with an axis of 46±22°, suggesting that decompression surgery did change the corneal shape and induced incyclotorsion of the steepest axis. Conclusions There was a significant change in corneal astigmatism after orbital decompression surgery and this change was sufficient to affect the optical function of the cornea. Surgeons and patients should be aware of these changes. PMID:26352432

Plastification of polymers in twin-screw-extruders: New visualization technic using high-speed imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knieper, A., E-mail: Alexander.Knieper@lbf.fraunhofer.de, E-mail: Christian.Beinert@lbf.fraunhofer.de; Beinert, C., E-mail: Alexander.Knieper@lbf.fraunhofer.de, E-mail: Christian.Beinert@lbf.fraunhofer.de

The initial melting of the first granules through plastic energy dissipation (PED) at the beginning of the melting zone, in the co-rotating twin-screw extruder is visualized in this work. The visualization was created through the use of a high speed camera in the cross section of the melting zone. The parameters screw speed, granule-temperature, temperature-profile, type of polymer and back pressure were examined. It was shown that the screw speed and the temperature-profile have significant influence on the rate of initial melting.

A comparative evaluation of two decompression procedures for technical diving using inflammatory responses: compartmental versus ratio deco.

PubMed

Spisni, Enzo; Marabotti, Claudio; De Fazio, Luigia; Valerii, Maria Chiara; Cavazza, Elena; Brambilla, Stefano; Hoxha, Klarida; L'Abbate, Antonio; Longobardi, Pasquale

2017-03-01

The aim of this study was to compare two decompression procedures commonly adopted by technical divers: the ZH-L16 algorithm modified by 30/85 gradient factors (compartmental decompression model, CDM) versus the 'ratio decompression strategy' (RDS). The comparison was based on an analysis of changes in diver circulating inflammatory profiles caused by decompression from a single dive. Fifty-one technical divers performed a single trimix dive to 50 metres' sea water (msw) for 25 minutes followed by enriched air (EAN50) and oxygen decompression. Twenty-three divers decompressed according to a CDM schedule and 28 divers decompressed according to a RDS schedule. Peripheral blood for detection of inflammatory markers was collected before and 90 min after diving. Venous gas emboli were measured 30 min after diving using 2D echocardiography. Matched groups of 23 recreational divers (dive to 30 msw; 25 min) and 25 swimmers were also enrolled as control groups to assess the effects of decompression from a standard air dive or of exercise alone on the inflammatory profile. Echocardiography at the single 30 min observation post dive showed no significant differences between the two decompression procedures. Divers adopting the RDS showed a worsening of post-dive inflammatory profile compared to the CDM group, with significant increases in circulating chemokines CCL2 (P = 0.001) and CCL5 (P = 0.006) levels. There was no increase in chemokines following the CDM decompression. The air scuba group also showed a statistically significant increase in CCL2 (P < 0.001) and CCL5 (P = 0.003) levels post dive. No cases of decompression sickness occurred. The ratio deco strategy did not confer any benefit in terms of bubbles but showed the disadvantage of increased decompression-associated secretion of inflammatory chemokines involved in the development of vascular damage.

Jurassic rifting at the Eurasian Tethys margin: Geochemical and geochronological constraints from granitoids of North Makran, southeastern Iran

NASA Astrophysics Data System (ADS)

Hunziker, Daniela; Burg, Jean-Pierre; Bouilhol, Pierre; von Quadt, Albrecht

2015-03-01

This study focuses on an east-west trending belt of granitic to intermediate intrusions and their volcanic cover in the northern Dur Kan Complex, a continental slice outcropping to the north of the exposed Makran accretionary wedge in southeastern Iran. Field observations, petrographic descriptions, trace element, and isotope analyses combined with U-Pb zircon geochronology are presented to determine the time frame of magmatism and tectonic setting during the formation of these rocks. Results document three magmatic episodes with different melt sources for (1) granites, (2) a diorite-trondhjemite-plagiogranite sequence, and (3) diabases and lavas. Granites, dated at 170-175 Ma, represent crystallized melt with a strong continental isotopic contribution. The diorite-trondhjemite-plagiogranite sequence is 165-153 Ma old and derives from a mantle magma source with minor continental contribution. East-west trending diabase dikes and bodies intruded the granitoids, which were eroded and then covered by Valanginian (140-133 Ma) alkaline lavas and sediments. Alkaline dikes and lavas have a mantle isotopic composition. Temporal correlation with plutonites of the Sanandaj-Sirjan Zone to the northwest defines a narrow, NW-SE striking and nearly 2000 km long belt of Jurassic intrusions. The increasing mantle influence in the magma sources is explained by thinning of continental lithosphere and related mantle upwelling/decompression melting. Accordingly, the formation of the studied igneous rocks is related to the extension of the Iranian continental margin, which ultimately led to the formation of the Tethys-related North Makran Ophiolites.

Magma heating by decompression-driven crystallization beneath andesite volcanoes.

PubMed

Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

2006-09-07

Explosive volcanic eruptions are driven by exsolution of H2O-rich vapour from silicic magma. Eruption dynamics involve a complex interplay between nucleation and growth of vapour bubbles and crystallization, generating highly nonlinear variation in the physical properties of magma as it ascends beneath a volcano. This makes explosive volcanism difficult to model and, ultimately, to predict. A key unknown is the temperature variation in magma rising through the sub-volcanic system, as it loses gas and crystallizes en route. Thermodynamic modelling of magma that degasses, but does not crystallize, indicates that both cooling and heating are possible. Hitherto it has not been possible to evaluate such alternatives because of the difficulty of tracking temperature variations in moving magma several kilometres below the surface. Here we extend recent work on glassy melt inclusions trapped in plagioclase crystals to develop a method for tracking pressure-temperature-crystallinity paths in magma beneath two active andesite volcanoes. We use dissolved H2O in melt inclusions to constrain the pressure of H2O at the time an inclusion became sealed, incompatible trace element concentrations to calculate the corresponding magma crystallinity and plagioclase-melt geothermometry to determine the temperature. These data are allied to ilmenite-magnetite geothermometry to show that the temperature of ascending magma increases by up to 100 degrees C, owing to the release of latent heat of crystallization. This heating can account for several common textural features of andesitic magmas, which might otherwise be erroneously attributed to pre-eruptive magma mixing.

Pictorial essay: Role of ultrasound in failed carpal tunnel decompression.

PubMed

Botchu, Rajesh; Khan, Aman; Jeyapalan, Kanagaratnam

2012-01-01

USG has been used for the diagnosis of carpal tunnel syndrome. Scarring and incomplete decompression are the main causes for persistence or recurrence of symptoms. We performed a retrospective study to assess the role of ultrasound in failed carpal tunnel decompression. Of 422 USG studies of the wrist performed at our center over the last 5 years, 14 were for failed carpal tunnel decompression. Scarring was noted in three patients, incomplete decompression in two patients, synovitis in one patient, and an anomalous muscle belly in one patient. No abnormality was detected in seven patients. We present a pictorial review of USG findings in failed carpal tunnel decompression.

Pictorial essay: Role of ultrasound in failed carpal tunnel decompression

PubMed Central

Botchu, Rajesh; Khan, Aman; Jeyapalan, Kanagaratnam

2012-01-01

USG has been used for the diagnosis of carpal tunnel syndrome. Scarring and incomplete decompression are the main causes for persistence or recurrence of symptoms. We performed a retrospective study to assess the role of ultrasound in failed carpal tunnel decompression. Of 422 USG studies of the wrist performed at our center over the last 5 years, 14 were for failed carpal tunnel decompression. Scarring was noted in three patients, incomplete decompression in two patients, synovitis in one patient, and an anomalous muscle belly in one patient. No abnormality was detected in seven patients. We present a pictorial review of USG findings in failed carpal tunnel decompression. PMID:22623813

Enhanced and asymmetric melting beneath the southern Mariana back-arc spreading ridge under the influence of the Pacific plate subduction

NASA Astrophysics Data System (ADS)

Matsuno, T.; Seama, N.; Shindo, H.; Nogi, Y.; Okino, K.

2017-12-01

Back-arc spreading ridges in the southern Mariana Trough are slow-spreading ridges but have features suggesting enhanced melting beneath the ridges and influences on seafloor spreading processes by fluid derived from the subducted Pacific slab underlying the ridges. To reveal melting and dehydration processes and dynamics in the upper mantle in the southern Mariana Trough, we conducted a marine magnetotelluric (MT) experiment along a 120 km-length transect across a ridge segment at 13°N. We obtained electromagnetic field data at 9 stations along the transect, and analyzed them for estimating MT responses, striping seafloor topographic distortion from the responses, and imaging a 2-D electrical resistivity structure by 2-D inversion of TM-mode responses. A resultant 2-D inversion model showed 1) a conductive area at 10-20 km depth beneath the ridge center, the center of which slightly offsets to the trench side, 2) a moderately conductive area expanding asymmetrically around and under the conductor of 1), 3) a resistive area thickening from the ridge center up to about 40 km on the remnant arc side, and 4) a resistive area with a constant thickness of about 150 km on the trench side. These model features suggest 1) a melt body beneath the ridge center, possibly containing slab-derived water 2) water- and melt-retained mantle area produced by hydration of the back-arc mantle wedge and asymmetric passive decompression melting in the hydrous mantle wedge, 3) cooled and residual lithospheric mantle off the ridge center, and 4) mantle wedge and subducted Pacific lithospheric mantle that are both cold and depleted. The electrical resistivity structure obtained in the southern Mariana Trough, which clearly contrasts with the structure of the central Mariana Trough at 18°N in that this lacks a conductor beneath the ridge center, provides insights on the mantle dynamics and its relation to the characteristic tectonics and many kinds of observational results in the southern Mariana Trough.

Contrasting melt equilibration conditions across Anatolia

NASA Astrophysics Data System (ADS)

Reid, Mary; Delph, Jonathan; Schleiffarth, W. Kirk; Cosca, Michael

2017-04-01

The widespread mafic volcanism, elevated crustal temperatures, and plateau-type topography in Central Anatolia, Turkey, could collectively be the result of lithospheric delamination, mantle upwelling, and tectonic escape in response to Arabian-Anatolian plate collision. We used the results from basalt geochemistry and a passive-source broadband seismic experiment obtained as part of an international collaborative effort (Continental Dynamics - Central Anatolia Tectonics) to investigate the crust-mantle structure and melting conditions associated with the Quaternary Hasandag Monogenic Cluster (HMC) south and west of Hasandag volcano. The HMC is unusually mafic, not only for Central Anatolia but globally, enabling meaningful comparisons between geochemical and seismic interpretations of mantle conditions. HMC basalts are characterized by orogenic signatures that could have originated (1) in mantle wedge that, after stagnating because of collision, was remobilized south and upward as a result of rollback of the African slab or, alternatively (2) by piecemeal foundering of residual mantle lithosphere into convecting upper mantle, producing small-scale convection and associated decompression melting. Melt equilibration conditions for the HMC are hot (TP ˜1335-1250˚ C, assuming 1-4 wt.% H2O) and shallow (P = 1.1 to 1.6 GPa), approaching those for MORB. Shear wave velocities are relatively constant at ˜4.1 km/s between the Moho and a depth of ˜45-50 km (˜1.4 GPa; Fig. 6), below which Vs increases with increasing depth. We infer that a melt-perfused mantle lid could be locally present between 40 and 55 km. In contrast to Central Anatolia, estimated equilibration conditions for Western Anatolia and Eastern Anatolia (east of the Inner Tauride Suture) mantle melts are hotter (by ≥60˚ C) and deeper (mostly by 0.6-1.0 GPa). They also have chemical signatures that, unlike Central Anatolia, are similar to those of intraplate basalts. These differences are likely related to the presence of a fragmenting, if quite deep, Cyprus slab beneath Central Anatolia, in contrast to absence of the Arabian slab beneath Eastern Anatolia since at least 10 Ma, and flow of deep-seated asthenosphere through a tear in the African plate under Western Anatolia. .

Petrogenesis and tectonic implications of Triassic mafic complexes with MORB/OIB affinities from the western Garzê-Litang ophiolitic mélange, central Tibetan Plateau

NASA Astrophysics Data System (ADS)

Liu, Bin; Ma, Chang-Qian; Guo, Yu-Heng; Xiong, Fu-Hao; Guo, Pan; Zhang, Xin

2016-09-01

Although numerous Paleo-Tethyan ophiolites with mid-oceanic ridge basalts (MORB) and/or oceanic-island basalt (OIB) affinities have been reported in the central Tibetan Plateau (CTP), the origin and tectonic nature of these ophiolites are not well understood. The petrogenesis, mantle sources and geodynamic setting of the mafic rocks from these ophiolites are unclear, which is the main reason for this uncertainty. In this paper, we present new geochronological, mineralogical and Sr-Nd isotopic data for the Chayong and Xiewu mafic complexes in the western Garzê-Litang suture zone (GLS), a typical Paleo-Tethyan suture crossing the CTP. Zircon LA-ICP-MS U-Pb ages of 234 ± 3 Ma and 236 ± 2 Ma can be interpreted as formation times of the Chayong and Xiewu mafic complexes, respectively. The basalts and gabbros of the Chayong complex exhibit enriched MORB (E-MORB) compositional affinities except for a weak depletion of Nb, Ta and Ti relative to the primitive mantle, whereas the basalts and gabbros of the Xiewu complex display distinct E-MORB and OIB affinities. The geochemical features suggest a probable fractionation of olivine ± clinopyroxene ± plagioclase as well as insignificant crustal contamination. The geochemical and Sr-Nd isotopic data reveal that the Chayong mafic rocks may have been derived from depleted MORB-type mantle metasomatized by crustal components and Xiewu mafic rocks from enriched lithospheric mantle metasomatized by OIB-like components. The ratios of Zn/Fet, La/Yb and Sm/Yb indicate that these mafic melts were produced by the partial melting of garnet + minor spinel-bearing peridotite or spinel ± minor garnet-bearing peridotite. We propose that back-arc basin spreading associated with OIB/seamount recycling had occurred in the western GLS at least since the Middle Triassic times, and the decompression melting of the depleted MORB-type asthenosphere mantle and partial melting of sub-continental lithosphere were metasomatized by plume-related melts, such as OIB s, which led to the generation of the Chayong and Xiewu mafic melts.

A theoretical method for selecting space craft and space suit atmospheres.

PubMed

Vann, R D; Torre-Bueno, J R

1984-12-01

A theoretical method for selecting space craft and space suit atmospheres assumes that gas bubbles cause decompression sickness and that the risk increases when a critical bubble volume is exceeded. The method is consistent with empirical decompression exposures for humans under conditions of nitrogen equilibrium between the lungs and tissues. Space station atmospheres are selected so that flight crews may decompress immediately from sea level to station pressure without preoxygenation. Bubbles form as a result of this decompression but are less than the critical volume. The bubbles are absorbed during an equilibration period after which immediate transition to suit pressure is possible. Exercise after decompression and incomplete nitrogen equilibrium are shown to increase bubble size, and limit the usefulness of one previously tested stage decompression procedure for the Shuttle. The method might be helpful for evaluating decompression procedures before testing.

Petrogenesis and tectonic significance of the late Triassic mafic dikes and felsic volcanic rocks in the East Kunlun Orogenic Belt, Northern Tibet Plateau

NASA Astrophysics Data System (ADS)

Hu, Yan; Niu, Yaoling; Li, Jiyong; Ye, Lei; Kong, Juanjuan; Chen, Shuo; Zhang, Yu; Zhang, Guorui

2016-02-01

We present zircon U-Pb ages and geochemical data on the late Triassic mafic dikes (diabase) and felsic volcanic rocks (rhyolite and rhyolitic tuffs) in the East Kunlun Orogenic Belt (EKOB). These rocks give a small age window of 228-218 Ma. The mafic dikes represent evolved alkaline basaltic melts intruding ~ 8-9 Myrs older and volumetrically more abundant A-type granite batholith. Their rare earth element (REE) and multi-element patterns are similar to those of the present-day ocean island basalts (OIBs) except for a weak continental crustal signature (i.e., enrichment of Rb and Pb and weak depletion of Nb, Ta and Ti). Their trace element characteristics together with the high 87Sr/86Sr (0.7076-0.7104), low εNd(t) (- 2.18 to - 3.46), low εHf(t) (- 2.85 to - 4.59) and variable Pb isotopic ratios are consistent with melts derived from metasomatized subcontinental lithospheric mantle with crustal contamination. The felsic volcanic rocks are characterized by high LREE/HREE (e.g., [La/Yb]N of 5.71-17.00) with a negative Eu anomaly and strong depletion in Sr and P, resembling the model upper continental crust (UCC). Given the high 87Sr/86Sr (0.7213-0.7550) and less negative εNd(t) (- 3.83 to - 5.09) and εHf(t) (- 3.06 to - 3.83) than the UCC plus the overlapping isotopes with the mafic dikes and high Nb-Ta rhyolites, the felsic volcanic rocks are best interpreted as resulting from melting-induced mixing with 45-50% crustal materials and 50-55% mantle-derived mafic melts probably parental to the mafic dikes. Such mantle-derived melts underplated and intruded the deep crust as juvenile crustal materials. Partial melting of such juvenile crust produced felsic melts parental to the felsic volcanic rocks in the EKOB. We hypothesize that the late Triassic mafic dikes and felsic volcanic rocks are associated with post-collisional extension and related orogenic collapse. Such processes are probably significant in causing asthenospheric upwelling, decompression melting, induced melting of the prior metasomatized mantle lithosphere and the existing crust. This work represents our ongoing effort in understanding the origin of the juvenile crust and continental crustal accretion through magmatism in the broad context of orogenesis from seafloor subduction to continental collision and to post-collisional processes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hermes, Robert E.

An encapsulated composition for polymerization includes an initiator composition for initiating a polymerization reaction, and a capsule prepared from an elemental metal or fusible alloy having a melting temperature from about 20.degree. C. to about 200.degree. C. A fluid for polymerization includes the encapsulated composition and a monomer. When the capsule melts or breaks open, the initiator is released.

Mantle Plumes and Geologically Recent Volcanism on Mars

NASA Astrophysics Data System (ADS)

Kiefer, W. S.

2013-12-01

Despite its small size, Mars has remained volcanically active until the geologically recent past. Crater retention ages on the volcanos Arsia Mon, Olympus Mons, and Pavonis Mons indicate significant volcanic activity in the last 100-200 million years. The radiometric ages of many shergottites, a type of igneous martian meteorite, indicate igneous activity at about 180 million years ago. These ages correspond to the most recent 2-4% of the age of the Solar System. The most likely explanation for this young martian volcanism is adiabatic decompression melting in upwelling mantle plumes. Multiple plumes may be active at any time, with each of the major volcanos in the Tharsis region being formed by a separate plume. Like at least some terrestrial mantle plumes, mantle plumes on Mars likely form via an instability of the thermal boundary layer at the base of the mantle. Because Mars operates in the stagnant lid convection regime, the temperature difference between mantle and core is lower than on Earth. This reduces the temperature contrast between mantle and core, resulting in mantle plumes on Mars that are about 100 K hotter than the average mantle. The chemical composition of the martian meteorites indicates that the martian mantle is enriched in both iron and sodium relative to Earth's mantle. This lowers the dry solidus on early Mars by 30-40 K relative to Earth. Migration of sodium to the crust over time decreases this difference in solidus temperature to about 15 K at present, but that is sufficient to increase the current plume magma production rate by a factor of about 2. Hydrous phases in the martian meteorites indicate the presence of a few hundred ppm water in the mantle source region, roughly the same as Earth. Finite element simulations of martian plumes using temperature-dependent viscosity and realistic Rayleigh numbers can reproduce the geologically recent magma production rate that is inferred from geologic mapping and the melt fraction inferred from trace element studies of martian meteorites. These plumes can also reproduce the observed spatial variability in elastic lithosphere thickness between regions of plume upwelling and regions that are far from the plumes. Melting in these models occurs at pressures of 3-5 GPa (250-400 km depth), reflecting the presence of a thick thermal lithosphere on present-day Mars. Meteorite evidence indicates that the martian mantle has about 10 times as much isotopic heterogeneity as Earth, which has sometimes been interpreted as evidence that the martian mantle is not convecting. This conclusion is incorrect, as the observed volcanos require some form of decompression melting and thus a convecting mantle. Few strike slip faults are observed on Mars, which indicates that flow in the mantle is almost entirely poloidal in nature, with little or no toroidal motion. The absence of toroidal flow on Mars makes convective mixing much less efficient than on Earth and permits the preservation of high levels of isotopic heterogeneity within a convecting mantle.

A benchmark initiative on mantle convection with melting and melt segregation

NASA Astrophysics Data System (ADS)

Schmeling, Harro; Dohmen, Janik; Wallner, Herbert; Noack, Lena; Tosi, Nicola; Plesa, Ana-Catalina; Maurice, Maxime

2015-04-01

In recent years a number of mantle convection models have been developed which include partial melting within the asthenosphere, estimation of melt volumes, as well as melt extraction with and without redistribution at the surface or within the lithosphere. All these approaches use various simplifying modelling assumptions whose effects on the dynamics of convection including the feedback on melting have not been explored in sufficient detail. To better assess the significance of such assumptions and to provide test cases for the modelling community we initiate a benchmark comparison. In the initial phase of this endeavor we focus on the usefulness of the definitions of the test cases keeping the physics as sound as possible. The reference model is taken from the mantle convection benchmark, case 1b (Blanckenbach et al., 1989), assuming a square box with free slip boundary conditions, the Boussinesq approximation, constant viscosity and a Rayleigh number of 1e5. Melting is modelled assuming a simplified binary solid solution with linearly depth dependent solidus and liquidus temperatures, as well as a solidus temperature depending linearly on depletion. Starting from a plume free initial temperature condition (to avoid melting at the onset time) three cases are investigated: Case 1 includes melting, but without thermal or dynamic feedback on the convection flow. This case provides a total melt generation rate (qm) in a steady state. Case 2 includes batch melting, melt buoyancy (melt Rayleigh number Rm), depletion buoyancy and latent heat, but no melt percolation. Output quantities are the Nusselt number (Nu), root mean square velocity (vrms) and qm approaching a statistical steady state. Case 3 includes two-phase flow, i.e. melt percolation, assuming a constant shear and bulk viscosity of the matrix and various melt retention numbers (Rt). These cases should be carried out using the Compaction Boussinseq Approximation (Schmeling, 2000) or the full compaction formulation. Variations of cases 1 - 3 may be tested, particularly studying the effect of melt extraction. The motivation of this presentation is to summarize first experiences, suggest possible modifications of the case definitions and call interested modelers to join this benchmark exercise. References: Blanckenbach, B., Busse, F., Christensen, U., Cserepes, L. Gun¬kel, D., Hansen, U., Har¬der, H. Jarvis, G., Koch, M., Mar¬quart, G., Moore D., Olson, P., and Schmeling, H., 1989: A benchmark comparison for mantle convection codes, J. Geo¬phys., 98, 23 38. Schmeling, H., 2000: Partial melting and melt segregation in a convecting mantle. In: Physics and Chemistry of Partially Molten Rocks, eds. N. Bagdassarov, D. Laporte, and A.B. Thompson, Kluwer Academic Publ., Dordrecht, pp. 141 - 178.

Influence of long-term intermittent exposures to hypoxia on decompression-induced pulmonary haemorrhage.

PubMed Central

Fang, H S; Chen, C F

1976-01-01

Healthy male rats were acclimatized by being placed in a decompression chamber at a simulated altitude of 18 000 feet (5486 m) for three hours daily for 84 days. The altitude acclimatized rats paired with unacclimatized rats were rapidly decompressed together. The range of decompression was performed from on atmospheric pressure to an ambient pressure of 30 mmHg in 0-2 seconds. It was found that in control rats, 14 of 20 lung (70%) exhibited pulmonary haemorrhage following rapid decompression. In altitude acclimatized rats, however, only 6 of 20 (30%) revealed decompression-induced haemorrhage. The difference was statistically significant. The present findings indicate that long-term intermittent exposures to hypoxia might increase the resistance of pulmonary tissue to rapid decompression, resulting in a decrease in frequency and severity of pulmonary haemorrhage. The possible mechanism of such a phenomenon is discussed. PMID:1257942

Deformation-related microstructures in magmatic zircon and implications for diffusion

NASA Astrophysics Data System (ADS)

Reddy, Steven Michael; Timms, Nicholas E.; Hamilton, Patrick Joseph; Smyth, Helen R.

2009-02-01

An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation. A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous zircon yields a SHRIMP U-Pb crystallisation age of 9.3 ± 0.2 Ma. Quantitative microstructural analysis of zircon by electron backscatter diffraction (EBSD) shows no deformation in the inherited xenocrysts, but intragrain orientation variations of up to 30° in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD maps. Less common <100> misorientation axes account for minor components of crystallographic dispersion. These observations are consistent with zircon deformation by dislocation creep and the formation of tilt and twist boundaries associated with the operation of <001>{100} and <100>{010} slip systems. The restriction of deformation microstructures to large glomerocrysts and the young magmatic zircon population, and the absence of deformation within the host igneous rock and inherited zircon grains, indicate that zircon deformation took place within a low-melt fraction (<5% melt), mid-lower crustal cumulate prior to fragmentation during magmatic disaggregation and entrainment of xenocrystic zircons during magmatic decompression. Tectonic stresses within the compressional Sunda Arc at the time of magmatism are considered to be the probable driver for low-strain deformation of the cumulate in the late stages of initial crystallisation. These results provide the first evidence of crystal plastic dislocation creep in zircon associated with magmatic crystallisation and indicate that the development of crystal-plastic microstructures in zircon is not restricted to high-strain rocks. Such microstructures have previously been shown to enhance bulk diffusion of trace elements (U, Th and REE) in zircon. The development of deformation microstructures, and therefore multiple diffusion pathways in zircon in the magmatic environment, has significant implications for the interpretation of geochemical data from igneous zircon and the trace element budgets of melts due to the potential enhancement of bulk diffusion and dissolution rates.

Snow Peak, OR: Miocene and Pliocene Tholeiitic Volcanism in the Cascadia Forearc

NASA Astrophysics Data System (ADS)

Hatfield, A. K.; Kent, A. J.; Nielsen, R. L.; Rowe, M. C.; Duncan, R. A.

2007-12-01

Snow Peak is a voluminous (>150 km3), glacially dissected shield volcano located approximately 50 km southeast of Salem, OR, with a summit height of 1,310 m above sea level. Snow Peak lies approximately 60 km west of the current High Cascade arc axis. Lavas from the southeast face of Snow Peak have been previously dated using K-Ar at ~3 Ma. New Ar-Ar dating indicates that lavas from the northwest face are ~5.4 Ma, and the summit plug is ~6 Ma. Snow Peak volcanics unconformably overlie western Cascade volcanics aged from middle to late Miocene (~10- 17 Ma). The age of Snow Peak is broadly contemporaneous with the initiation of modern High Cascade volcanism. Snow Peak's location provides a rare opportunity to study magmas produced within the modern High Cascades forearc region. The goal of this investigation is to characterize the composition and timing of volcanism at Snow Peak and the role of volatiles in magma genesis. Hypotheses for the formation of Snow Peak include flux melting associated with the Cascadia subduction zone and/or decompression melting associated with extensional faulting. Preliminary geochemical data on the basalts from Snow Peak indicate that they are low-to-medium-K tholeiites (SiO2 47.9-51.7 wt.%, MgO 5.5- 8.3 wt.%, K2O, 0.36-0.55 wt.%) and that they range from primitive to moderately evolved (Mg# 0.51-0.61). Common phenocryst phases are plagioclase, olivine, and clinopyroxene. Textures are typically hypocrystalline, and fine-grained to porphyritic. Mantle-normalized multi-element plots indicate Snow Peak lavas are generally HFSE depleted and LILE enriched. These data are consistent with a preliminary interpretation of a subduction zone signature, yet the major element composition most closely resembles high alumina olivine tholeiite (HAOT), more indicative of extensional environments. The degree of LILE enrichment is significantly lower than in calc alkaline lavas from the High Cascades and western Cascades. Determining the petrogenesis of this forearc center will include a comprehensive analysis of the volcano's major and trace element geochemistry, and additional age dating to constrain eruption rates. Direct measurement of volatiles in olivine-hosted melt inclusions will complement the major and trace element geochemistry in order to measure pre-eruptive water contents.

Does pain relief by CT-guided indirect cervical nerve root injection with local anesthetics and steroids predict pain relief after decompression surgery for cervical nerve root compression?

PubMed

Antoniadis, Alexander; Dietrich, Tobias J; Farshad, Mazda

2016-10-01

The relationship of pain relief from a recently presented CT-guided indirect cervical nerve root injection with local anesthetics and steroids to surgical decompression as a treatment for single-level cervical radiculopathy is not clear. This retrospective study aimed to compare the immediate and 6-week post-injection effects to the short- and long-term outcomes after surgical decompression, specifically in regard to pain relief. Patients (n = 39, age 47 ± 10 years) who had undergone CT-guided indirect injection with local anesthetics and steroids as an initial treatment for single cervical nerve root radiculopathy and who subsequently needed surgical decompression were included retrospectively. Pain levels (VAS scores) were monitored before, immediately after, and 6 weeks after injection (n = 34), as well as 6 weeks (n = 38) and a mean of 25 months (SD ± 12) after surgical decompression (n = 36). Correlation analysis was performed to find potential associations of pain relief after injection and after surgery to investigate the predictive value of post-injection pain relief. There was no correlation between immediate pain relief after injection (-32 ± 27 %) and 6 weeks later (-7 ± 19 %), (r = -0.023, p = 0.900). There was an association by tendency between immediate pain relief after injection and post-surgical pain relief at 6 weeks (-82 ± 27 %), (r = 0.28, p = 0.08). Pain relief at follow-up remained high at -70 ± 21 % and was correlated with the immediate pain amelioration effect of the injection (r = 0.37, p = 0.032). Five out of seven patients who reported no pain relief from injection had a pain relief from surgery in excess of 50 %. The amount of immediate radiculopathic pain relief after indirect cervical nerve root injection is associated with the amount of pain relief achieved at long-term follow-up after surgical decompression of single-level cervical radiculopathy. Patients can still expect sufficient pain relief from surgery even if they did not respond to the cervical infiltration.

Preoperative retrolisthesis as a predictive risk factor of reoperation due to delayed-onset symptomatic foraminal stenosis after central decompression for lumbar canal stenosis without fusion.

PubMed

Ikegami, Daisuke; Hosono, Noboru; Mukai, Yoshihiro; Tateishi, Kosuke; Fuji, Takeshi

2017-08-01

For patients diagnosed with lumbar central canal stenosis with asymptomatic foraminal stenosis (FS), surgeons occasionally only decompress central stenosis and preserve asymptomatic FS. These surgeries have the potential risk of converting preoperative asymptomatic FS into symptomatic FS postoperatively by accelerating spinal degeneration, which requires reoperation. However, little is known about delayed-onset symptomatic FS postoperatively. This study aimed to evaluate the rate of reoperation for delayed-onset symptomatic FS after lumbar central canal decompression in patients with preoperative asymptomatic FS, and determine the predictive risk factors of those reoperations. This study is a retrospective cohort study. Two hundred eight consecutive patients undergoing posterior central decompression for lumbar canal stenosis between January 2009 and June 2014 were included in this study. The number of patients who had preoperative FS and the reoperation rate for delayed-onset symptomatic FS at the index levels were the outcome measures. Patients were divided into two groups with and without preoperative asymptomatic FS at the decompressed levels. The baseline characteristics and revision rates for delayed-onset symptomatic FS were compared between the two groups. Predictive risk factors for such reoperations were determined using multivariate logistic regression and receiver operating characteristics analyses. Preoperatively, 118 patients (56.7%) had asymptomatic FS. Of those, 18 patients (15.3%) underwent reoperation for delayed-onset symptomatic FS at a mean of 1.9 years after the initial surgery. Posterior slip in neutral position and posterior extension-neutral translation were significant risk factors for reoperation due to FS. The optimal cutoff values of posterior slip in neutral position and posterior extension-neutral translation for predicting the occurrence of such reoperations were both 1 mm; 66.7% of patients who met both of these cutoff values had undergone reoperation. This study demonstrated that 15.3% of patients with preoperative asymptomatic FS underwent reoperation for delayed-onset symptomatic FS at the index levels at a mean of 1.9 years after central decompression, and preoperative retrolisthesis was a predictive risk factor for such a reoperation. These findings are valuable for establishing standards of appropriate treatment strategies in patients with lumbar central canal stenosis with asymptomatic FS. Copyright © 2017 Elsevier Inc. All rights reserved.

Evaluation of safety of hypobaric decompressions and EVA from positions of probabilistic theory

NASA Astrophysics Data System (ADS)

Nikolaev, V. P.

Formation and subsequent evolution of gas bubbles in blood and tissues of subjects exposed to decompression are casual processes in their nature. Such character of bubbling processes in a body predetermines probabilistic character of decompression sickness (DCS) incidence in divers, aviators and astronauts. Our original probabilistic theory of decompression safety is based on stochastic models of these processes and on the concept of critical volume of a free gas phase in body tissues. From positions of this theory, the probability of DCS incidence during single-stage decompressions and during hypobaric decompressions under EVA in particular, is defined by the distribution of possible values of nucleation efficiency in "pain" tissues and by its critical significance depended on the parameters of a concrete decompression. In the present study the following is shown: 1) the dimensionless index of critical nucleation efficiency for "pain" body tissues is a more adequate index of decompression stress in comparison with Tissue Ratio, TR; 2) a priory the decompression under EVA performed according to the Russian protocol is more safe than decompression under EVA performed in accordance with the U.S. protocol; 3) the Russian space suit operated at a higher pressure and having a higher "rigidity" induces a stronger inhibition of mechanisms of cavitation and gas bubbles formation in tissues of a subject located in it, and by that provides a more considerable reduction of the DCS risk during real EVA performance.

Decompression management by 43 models of dive computer: single square-wave exposures to between 15 and 50 metres' depth.

PubMed

Sayer, Martin D J; Azzopardi, Elaine; Sieber, Arne

2014-12-01

Dive computers are used in some occupational diving sectors to manage decompression but there is little independent assessment of their performance. A significant proportion of occupational diving operations employ single square-wave pressure exposures in support of their work. Single examples of 43 models of dive computer were compressed to five simulated depths between 15 and 50 metres' sea water (msw) and maintained at those depths until they had registered over 30 minutes of decompression. At each depth, and for each model, downloaded data were used to collate the times at which the unit was still registering "no decompression" and the times at which various levels of decompression were indicated or exceeded. Each depth profile was replicated three times for most models. Decompression isopleths for no-stop dives indicated that computers tended to be more conservative than standard decompression tables at depths shallower than 30 msw but less conservative between 30-50 msw. For dives requiring decompression, computers were predominantly more conservative than tables across the whole depth range tested. There was considerable variation between models in the times permitted at all of the depth/decompression combinations. The present study would support the use of some dive computers for controlling single, square-wave diving by some occupational sectors. The choice of which makes and models to use would have to consider their specific dive management characteristics which may additionally be affected by the intended operational depth and whether staged decompression was permitted.

Monazite behaviours during high-temperature metamorphism: a case study from Dinggye region, Tibetan Himalaya

NASA Astrophysics Data System (ADS)

Wang, Jia-Min; Wu, Fu-Yuan; Rubatto, Daniela; Liu, Shi-Ran; Zhang, Jin-Jiang

2017-04-01

Monazite is a key accessory mineral for metamorphic geochronology, but its growth mechanisms during melt-bearing high-temperature metamorphism is not well understood. Therefore, the petrology, pressure-temperature and timing of metamorphism have been investigated in pelitic and psammitic granulites from the Greater Himalayan Crystalline Complex (GHC) in Dinggye, southern Tibet. These rocks underwent an isothermal decompression process from pressure conditions of >10 kbar to <5 kbar with constant temperatures of 750-830°C, and recorded three metamorphic stages of kyanite-grade (M1), sillimanite-grade (M2) and cordierite-spinel grade (M3). Monazite and zircon crystals were analyzed for ages by microbeam techniques either in mounts or thin sections. Ages were linked to specific conditions of mineral growth by comprehensive studies on zoning patterns, trace element signatures, index mineral inclusions (melt inclusions, sillimanite and K-feldspar) in dated domains and textural correlations with coexisting minerals. The results show that inherited domains (500-400 Ma) are common in monazite even at granulite-facies conditions. Few monazites formed at the M1-stage ( 30-29 Ma) and recorded heterogeneous Th, Y, and HREE compositions, which formed by recrystallization related to muscovite dehydration melting reaction. These monazite grains were protected from dissolution or lateral overprinting mainly by the armour effect of matrix crystals (biotite and quartz). Most monazite grains formed at the M3-stage (21-19 Ma) through either dissolution-reprecipitation or recrystallization that was related to biotite dehydration melting reaction. These monazite grains record HREE and Y signatures in local equilibrium with different reactions involving either garnet breakdown or peritectic garnet growth. Another peak of monazite growth occurs during melt crystallization ( 15 Ma), and these monazites are unzoned and have homogeneous compositions. Our results documented the widespread recrystallization to account for monazite growth during high-temperature metamorphism and related melting reactions that trigger monazite recrystallization. In a regional sense, our P-T-t data along with published data indicate that the pre-M1 eclogite-facies metamorphism occurred at 39-30 Ma in the Dinggye Himalaya. Our results are in favour of a steady exhumation of the GHC rocks since Oligocene that was contributed by partial melting. Key words: U-Th-Pb geochronology, Monazite, Recrystallization, Pelitic granulite, Himalaya

Igneous rocks formed by hypervelocity impact

NASA Astrophysics Data System (ADS)

Osinski, Gordon R.; Grieve, Richard A. F.; Bleacher, Jacob E.; Neish, Catherine D.; Pilles, Eric A.; Tornabene, Livio L.

2018-03-01

Igneous rocks are the primary building blocks of planetary crusts. Most igneous rocks originate via decompression melting and/or wet melting of protolith lithologies within planetary interiors and their classification and compositional, petrographic, and textural characteristics, are well-studied. As our exploration of the Solar System continues, so too does the inventory of intrusive and extrusive igneous rocks, settings, and processes. The results of planetary exploration have also clearly demonstrated that impact cratering is a ubiquitous geological process that has affected, and will continue to affect, all planetary objects with a solid surface, whether that be rock or ice. It is now recognized that the production of igneous rocks is a fundamental outcome of hypervelocity impact. The goal of this review is to provide an up-to-date synthesis of our knowledge and understanding of igneous rocks formed by hypervelocity impact. Following a brief overview of the basics of the impact process, we describe how and why melts are generated during impact events and how impact melting differs from endogenic igneous processes. While the process may differ, we show that the products of hypervelocity impact can share close similarities with volcanic and shallow intrusive igneous rocks of endogenic origin. Such impact melt rocks, as they are termed, can display lobate margins and cooling cracks, columnar joints and at the hand specimen and microscopic scale, such rocks can display mineral textures that are typical of volcanic rocks, such as quench crystallites, ophitic, porphyritic, as well as features such as vesicles, flow textures, and so on. Historically, these similarities led to the misidentification of some igneous rocks now known to be impact melt rocks as being of endogenic origin. This raises the question as to how to distinguish between an impact versus an endogenic origin for igneous-like rocks on other planetary bodies where fieldwork and sample analysis may not be possible and all that may be available is remote sensing data. While the interpretation of some impact melt rocks may be relatively straightforward (e.g., for clast-rich varieties and those with clear projectile contamination) we conclude that distinguishing between impact and endogenic igneous rocks is a non-trivial task that ultimately may require sample investigation and analysis to be conducted. Caution is, therefore, urged in the interpretation of igneous rocks on planetary surfaces.

Receiver function imaging of mantle transition zone discontinuities beneath the Tanzania Craton and the Eastern and Western Branches of the East African Rift System

NASA Astrophysics Data System (ADS)

Sun, M.; Liu, K. H.; Fu, X.; Gao, S. S.

2017-12-01

To investigate the mechanism of initiation and development of the Eastern African Rifting System (EARS) circumfluent the Tanzania Craton (TC), over 7,100 P-to-S radial receiver functions (RFs) recorded by 87 broadband seismic stations are stacked to map the topography of mantle transition zone (MTZ) discontinuities beneath the TC and the Eastern and Western Branches of the EARS. After time-depth conversion using the 1-D IASP91 Earth model, the resulting 410 km (d410) and 660 km (d660) discontinuity apparent depths are found to be greater than the global averages beneath the whole study area, implying slower than normal upper mantle velocities. The mean thickness of the MTZ beneath the Western Branch and TC is about 252 km, which is comparable to the global average and is inconsistent with the existence of present-day thermal upwelling originating from the lower mantle. In contrast, beneath the Eastern Branch, an 30 km thinning of the MTZ is observed from an up to 50 km and 20 km apparent depression of the d410 and d660, respectively. On the basis of previous seismic tomographic results and empirical relationships between velocity and thermal anomalies, we propose that the most plausible explanation for the observations beneath the volcanic Eastern Branch is the existence of a low-velocity layer extending from the surface to the upper MTZ, probably caused by decompression partial melting associated with continental rifting. The observations are in general agreement with an upper mantle origin for the initiation and development of both the Western and Eastern Branches of the EARS beneath the study area.

46 CFR Appendix A to Part 197 - Air No-Decompression Limits

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 7 2012-10-01 2012-10-01 false Air No-Decompression Limits A Appendix A to Part 197... STANDARDS GENERAL PROVISIONS Pt. 197, App. A Appendix A to Part 197—Air No-Decompression Limits The following table gives the depth versus bottom time limits for single, no-decompression, air dives made...

46 CFR Appendix A to Part 197 - Air No-Decompression Limits

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 7 2013-10-01 2013-10-01 false Air No-Decompression Limits A Appendix A to Part 197... STANDARDS GENERAL PROVISIONS Pt. 197, App. A Appendix A to Part 197—Air No-Decompression Limits The following table gives the depth versus bottom time limits for single, no-decompression, air dives made...

46 CFR Appendix A to Part 197 - Air No-Decompression Limits

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 7 2011-10-01 2011-10-01 false Air No-Decompression Limits A Appendix A to Part 197... STANDARDS GENERAL PROVISIONS Pt. 197, App. A Appendix A to Part 197—Air No-Decompression Limits The following table gives the depth versus bottom time limits for single, no-decompression, air dives made...

46 CFR Appendix A to Part 197 - Air No-Decompression Limits

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 7 2010-10-01 2010-10-01 false Air No-Decompression Limits A Appendix A to Part 197... STANDARDS GENERAL PROVISIONS Pt. 197, App. A Appendix A to Part 197—Air No-Decompression Limits The following table gives the depth versus bottom time limits for single, no-decompression, air dives made...

Trace-element record in zircons during exhumation from UHP conditions, North-East Greenland Caledonides

USGS Publications Warehouse

McClelland, W.C.; Gilotti, J.A.; Mazdab, F.K.; Wooden, J.L.

2009-01-01

Coesite-bearing zircon formed at ultrahigh-pressure (UHP) conditions share general characteristics of eclogite-facies zircon with trace-element signatures characterized by depleted heavy rare earth elements (HREE), lack of an Eu anomaly, and low Th/ U ratios. Trace-element signatures of zircons from the Caledonian UHP terrane in North-East Greenland were used to examine the possible changes in signature with age during exhumation. Collection and interpretation of age and trace-element analyses of zircon from three samples of quartzofeldspathic gneiss and two leucocratic intrusions were guided by core vs. rim zoning patterns as imaged by cathodoluminesence. Change from igneous to eclogite-facies metamorphic trace-element signature in protolith zircon is characterized by gradual depletion of HREE, whereas newly formed metamorphic rims have flat HREE patterns and REE concentrations that are distinct from the recrystallized inherited cores. The signature associated with eclogite-facies metamorphic zircon is observed in coesite-bearing zircon formed at 358 ?? 4 Ma, metamorphic rims formed at 348 ?? 5 Ma during the initial stages of exhumation, and metamorphic rims formed at 337 ?? 5 Ma. Zircons from a garnet-bearing granite emplaced in the neck of an eclogite boudin and a leucocratic dike that cross-cuts amphibolite-facies structural fabrics have steeply sloping HREE patterns, variably developed negative Eu anomalies, and low Th/U ratios. The granite records initial decompression melting and exhumation at 347 ?? 2 Ma and later zircon rim growth at 329 ?? 5. The leucocratic dike was likely emplaced at amphibolite-facies conditions at 330 ?? 2 Ma, but records additional growth of compositionally similar zircon at 321 ??2 Ma. The difference between the trace-element signature of metamorphic zircon in the gneisses and in part coeval leucocratic intrusions indicates that the zircon signature varies as a function of lithology and context, thus enhancing its ability to aid in the interpretation of U-Pb data and track the exhumation history of UHP terranes. The differences may reflect variation in elemental availability through breakdown reactions in quartzofeldpathic gneiss vs. availability during melt production and/or crystallization. UHP rocks in North-East Greenland began exhumation by 347 ?? 2 Ma, were still at HP eclogite-facies conditions at 337 ?? 5 Ma and were at amphibolite-facies conditions by 330 ?? 2 Ma. ?? 2009 E. Schweizerbart'sche Verlagsbuchhandlung.

Gas embolization of the liver in a rat model of rapid decompression.

PubMed

L'Abbate, Antonio; Kusmic, Claudia; Matteucci, Marco; Pelosi, Gualtiero; Navari, Alessandro; Pagliazzo, Antonino; Longobardi, Pasquale; Bedini, Remo

2010-08-01

Occurrence of liver gas embolism after rapid decompression was assessed in 31 female rats that were decompressed in 12 min after 42 min of compression at 7 ATA (protocol A). Sixteen rats died after decompression (group I). Of the surviving rats, seven were killed at 3 h (group II), and eight at 24 h (group III). In group I, bubbles were visible in the right heart, aortic arch, liver, and mesenteric veins and on the intestinal surface. Histology showed perilobular microcavities in sinusoids, interstitial spaces, and hepatocytes. In group II, liver gas was visible in two rats. Perilobular vacuolization and significant plasma aminotransferase increase were present. In group III, liver edema was evident at gross examination in all cases. Histology showed perilobular cell swelling, vacuolization, or hydropic degeneration. Compared with basal, enzymatic markers of liver damage increased significantly. An additional 14 rats were decompressed twice (protocol B). Overall mortality was 93%. In addition to diffuse hydropic degeneration, centrilobular necrosis was frequently observed after the second decompression. Additionally, 10 rats were exposed to three decompression sessions (protocol C) with doubled decompression time. Their mortality rate decreased to 20%, but enzymatic markers still increased in surviving rats compared with predecompression, and perilobular cell swelling and vacuolization were present in five rats. Study challenges were 1) liver is not part of the pathophysiology of decompression in the existing paradigm, and 2) although significant cellular necrosis was observed in few animals, zonal or diffuse hepatocellular damage associated with liver dysfunction was frequently demonstrated. Liver participation in human decompression sickness should be looked for and clinically evaluated.

Surgical decompression is associated with decreased mortality in patients with sepsis and ureteral calculi.

PubMed

Borofsky, Michael S; Walter, Dawn; Shah, Ojas; Goldfarb, David S; Mues, Adam C; Makarov, Danil V

2013-03-01

The combination of sepsis and ureteral calculus is a urological emergency. Traditional teaching advocates urgent decompression with nephrostomy tube or ureteral stent placement, although published outcomes validating this treatment are lacking. National practice patterns for such scenarios are currently undefined. Using a retrospective study design, we defined the surgical decompression rate in patients admitted to the hospital with severe infection and ureteral calculi. We determined whether a mortality benefit is associated with this intervention. Patient demographics and hospital characteristics were extracted from the 2007 to 2009 Nationwide Inpatient Sample. We identified 1,712 patients with ureteral calculi and sepsis. Multivariate logistic regression was performed to determine the association between mortality and surgical decompression. Of the patients 78% underwent surgical decompression. Mortality was higher in those not treated with surgical decompression (19.2% vs 8.82%, p <0.001). Lack of surgical decompression was independently associated with an increased OR of mortality even when adjusting for patient demographics, comorbidities and geographic region of treatment (OR 2.6, 95% CI 1.9-3.7). Absent surgical decompression is associated with higher odds of mortality in patients with sepsis and ureteral calculi. Further research to determine predictors of surgical decompression is necessary to ensure that all patients have access to this life saving therapy. Copyright © 2013 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Cardiovascular Pressures with Venous Gas Embolism and Decompression

NASA Technical Reports Server (NTRS)

Butler, B. D.; Robinson, R.; Sutton, T.; Kemper, G. B.

1995-01-01

Venous gas embolism (VGE) is reported with decompression to a decreased ambient pressure. With severe decompression, or in cases where an intracardiac septal defect (patent foramen ovale) exists, the venous bubbles can become arterialized and cause neurological decompression illness. Incidence rates of patent foramen ovale in the general population range from 25-34% and yet aviators, astronauts, and deepsea divers who have decompression-induced venous bubbles do not demonstrate neurological symptoms at these high rates. This apparent disparity may be attributable to the normal pressure gradient across the atria of the heart that must be reversed for there to be flow potency. We evaluated the effects of: venous gas embolism (0.025, 0.05 and 0.15 ml/ kg min for 180 min.) hyperbaric decompression; and hypobaric decompression on the pressure gradient across the left and right atria in anesthetized dogs with intact atrial septa. Left ventricular end-diastolic pressure was used as a measure of left atrial pressure. In a total of 92 experimental evaluations in 22 dogs, there were no reported reversals in the mean pressure gradient across the atria; a total of 3 transient reversals occurred during the peak pressure gradient changes. The reasons that decompression-induced venous bubbles do not consistently cause serious symptoms of decompression illness may be that the amount of venous gas does not always cause sufficient pressure reversal across a patent foramen ovale to cause arterialization of the venous bubbles.

Influence of surgical decompression on the expression of inflammatory and tissue repair biomarkers in periapical cysts.

PubMed

Rodrigues, Janderson Teixeira; Dos Santos Antunes, Henrique; Armada, Luciana; Pires, Fábio Ramôa

2017-12-01

The biologic effects of surgical decompression on the epithelium and connective tissues of periapical cysts are not fully understood. The aim of this study was to evaluate the expression of tissue repair and inflammatory biomarkers in periapical cysts before and after surgical decompression. Nine specimens of periapical cysts treated with decompression before undergoing complete enucleation were immunohistochemically analyzed to investigate the expression of interleukin-1β, tumor necrosis factor-α, transforming growth factor-β1, matrix metalloproteinase-9, Ki-67, and epidermal growth factor receptor. Expression of the biomarkers was classified as positive, focal, or negative. Ki-67 immunoexpression was calculated as a cell proliferation index. The expression of the biomarkers was compared in the specimens from decompression and from the final surgical procedure. Computed tomography demonstrated that volume was reduced in all cysts after decompression. There were no differences in the immunoexpression of the proinflammatory and tissue repair biomarkers when comparing the specimens obtained before and after the decompression. Surgical decompression was efficient in reducing the volume of periapical cysts before complete enucleation. When comparing the specimens obtained from surgical decompression and from complete surgical removal, the immunohistochemical analysis did not show a decrease in proinflammatory biomarkers; neither did it show an increase in tissue repair biomarkers. Copyright © 2017 Elsevier Inc. All rights reserved.

Orbital Decompression

MedlinePlus

... A Complications of Sinusitis Epistaxis (Nosebleeds) Allergic Rhinitis (Hay Fever) Headaches and Sinus Disease Disorders of Smell & ... DCR) Disclosure Statement Printer Friendly Orbital Decompression John Lee, MD INTRODUCTION Orbital decompression is a surgical procedure ...

Frequency of decompression illness among recent and extinct mammals and "reptiles": a review

NASA Astrophysics Data System (ADS)

Carlsen, Agnete Weinreich

2017-08-01

The frequency of decompression illness was high among the extinct marine "reptiles" and very low among the marine mammals. Signs of decompression illness are still found among turtles but whales and seals are unaffected. In humans, the risk of decompression illness is five times increased in individuals with Patent Foramen Ovale; this condition allows blood shunting from the venous circuit to the systemic circuit. This right-left shunt is characteristic of the "reptile" heart, and it is suggested that this could contribute to the high frequency of decompression illness in the extinct reptiles.

Frequency of decompression illness among recent and extinct mammals and "reptiles": a review.

PubMed

Carlsen, Agnete Weinreich

2017-08-01

The frequency of decompression illness was high among the extinct marine "reptiles" and very low among the marine mammals. Signs of decompression illness are still found among turtles but whales and seals are unaffected. In humans, the risk of decompression illness is five times increased in individuals with Patent Foramen Ovale; this condition allows blood shunting from the venous circuit to the systemic circuit. This right-left shunt is characteristic of the "reptile" heart, and it is suggested that this could contribute to the high frequency of decompression illness in the extinct reptiles.

Melting in Superheated Silicon Films Under Pulsed-Laser Irradiation

NASA Astrophysics Data System (ADS)

Wang, Jin Jimmy

This thesis examines melting in superheated silicon films in contact with SiO2 under pulsed laser irradiation. An excimer-laser pulse was employed to induce heating of the film by irradiating the film through the transparent fused-quartz substrate such that most of the beam energy was deposited near the bottom Si-SiO2 interface. Melting dynamics were probed via in situ transient reflectance measurements. The temperature profile was estimated computationally by incorporating temperature- and phase-dependent physical parameters and the time-dependent intensity profile of the incident excimer-laser beam obtained from the experiments. The results indicate that a significant degree of superheating occurred in the subsurface region of the film. Surface-initiated melting was observed in spite of the internal heating scheme, which resulted in the film being substantially hotter at and near the bottom Si-SiO2 interface. By considering that the surface melts at the equilibrium melting point, the solid-phase-only heat-flow analysis estimates that the bottom Si-SiO2 interface can be superheated by at least 220 K during excimer-laser irradiation. It was found that at higher laser fluences (i.e., at higher temperatures), melting can be triggered internally. At heating rates of 1010 K/s, melting was observed to initiate at or near the (100)-oriented Si-SiO2 interface at temperatures estimated to be over 300 K above the equilibrium melting point. Based on theoretical considerations, it was deduced that melting in the superheated solid initiated via a nucleation and growth process. Nucleation rates were estimated from the experimental data using Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Interpretation of the results using classical nucleation theory suggests that nucleation of the liquid phase occurred via the heterogeneous mechanism along the Si-SiO2 interface.

Oculomotor nerve palsy by posterior communicating artery aneurysms: influence of surgical strategy on recovery.

PubMed

Güresir, Erdem; Schuss, Patrick; Seifert, Volker; Vatter, Hartmut

2012-11-01

Resolution of oculomotor nerve palsy (ONP) after clipping of posterior communicating artery (PCoA) aneurysms has been well documented. However, whether additional decompression of the oculomotor nerve via aneurysm sac dissection or resection is superior to pure aneurysm clipping is the subject of much debate. Therefore, the objective in the present investigation was to analyze the influence of surgical strategy--specifically, clipping with or without aneurysm dissection--on ONP resolution. Between June 1999 and December 2010, 18 consecutive patients with ruptured and unruptured PCoA aneurysms causing ONP were treated at the authors' institution. Oculomotor nerve palsy was evaluated on admission and at follow-up. The electronic database MEDLINE was searched for additional data in published studies of PCoA aneurysms causing ONP. Two reviewers independently extracted data. Overall, 8 studies from the literature review and 6 patients in the current series (121 PCoA aneurysms) met the study inclusion criteria. Ninety-four aneurysms were treated with simple aneurysm neck clipping and 27 with clipping plus aneurysm sac decompression. The surgical strategy, simple aneurysm neck clipping versus clipping plus oculomotor nerve decompression, had no effect on full ONP resolution on univariate (p = 0.5) and multivariate analyses. On multivariate analysis, patients with incomplete ONP at admission were more likely to have full resolution of the palsy than were those with complete ONP at admission (p = 0.03, OR = 4.2, 95% CI 1.1-16). Data in the present study indicated that ONP caused by PCoA aneurysms improves after clipping without and with oculomotor nerve decompression. The resolution of ONP is inversely associated with the initial severity of ONP.

Intradiscal pressure study of percutaneous disc decompression with nucleoplasty in human cadavers.

PubMed

Chen, Yung C; Lee, Sang-heon; Chen, Darwin

2003-04-01

Intradiscal pressure was measured after percutaneous disc decompression by nucleoplasty in human cadavers with different degrees of disc degeneration. To assess intradiscal pressure change after disc decompression, and to analyze the influence of degeneration on the intradiscal pressure change. Partial removal of the nucleus has been shown to decompress herniated discs, relieving pressure on nerve roots and, in some cases, offering relief from disc pain. Nucleoplasty, a new minimally invasive procedure using patented Coblation technology, combines coagulation and ablation for partial removal of the nucleus. Coblated channels remove the tissue volume and may decrease the disc pressure. Three fresh human cadaver spinal specimens (T8-L5; age, 54-84 years; mean age, 70.7 years) were used in this investigation. The intradiscal pressure was measured at three points: before treatment, after each channel was created, and after treatment using a 25-guage 6-inch needle connected to a Merit Medical Systems Intellisystem Inflation Monitor. The needles were calibrated initially to approximately 30 pounds per square inch. For the control, the change in disc pressure was recorded by the same procedure without using Coblation energy. To evaluate the effectiveness of nucleoplasty, disc pressure changes were compared between treatment with and without Coblation energy. Intradiscal pressure was markedly reduced in the younger, healthy disc cadaver. In the older, degenerative disc cadavers, the change in intradiscal pressure after nucleoplasty was very small. There was an inverse correlation between the degree of disc degeneration and the change in intradiscal pressure. Pressure reduction through nucleoplasty is highly dependent on the degree of spine degeneration. Nucleoplasty markedly reduced intradiscal pressure in nondegenerative discs, but had a negligible effect on highly degenerative discs.

Needle Decompression of Tension Pneumothorax Tactical Combat Casualty Care Guideline Recommendations

DTIC Science & Technology

2012-07-06

SUBJECT: Needle Decompression of Tension Pneumothorax Tactical Combat Casualty Care Guideline Recommendations 2012-05 2 demonstrating the...Decompression of Tension Pneumothorax Tactical Combat Casualty Care Guideline Recommendations 2012-05 3 needle may be too short to reliably reach the...at the AAL as the preferred site for needle decompression of a presumed tension pneumothorax . Further, studies evaluating chest wall thickness are

Factors associated with spinal fusion after posterior fossa decompression in pediatric patients with Chiari I malformation and scoliosis.

PubMed

Mackel, Charles E; Cahill, Patrick J; Roguski, Marie; Samdani, Amer F; Sugrue, Patrick A; Kawakami, Noriaki; Sturm, Peter F; Pahys, Joshua M; Betz, Randal R; El-Hawary, Ron; Hwang, Steven W

2016-12-01

OBJECTIVE The authors performed a study to identify clinical characteristics of pediatric patients diagnosed with Chiari I malformation and scoliosis associated with a need for spinal fusion after posterior fossa decompression when managing the scoliotic curve. METHODS The authors conducted a multicenter retrospective review of 44 patients, aged 18 years or younger, diagnosed with Chiari I malformation and scoliosis who underwent posterior fossa decompression from 2000 to 2010. The outcome of interest was the need for spinal fusion after decompression. RESULTS Overall, 18 patients (40%) underwent posterior fossa decompression alone, and 26 patients (60%) required a spinal fusion after the decompression. The mean Cobb angle at presentation and the proportion of patients with curves > 35° differed between the decompression-only and fusion cohorts (30.7° ± 11.8° vs 52.1° ± 26.3°, p = 0.002; 5 of 18 vs 17 of 26, p = 0.031). An odds ratio of 1.0625 favoring a need for fusion was established for each 1° of increase in Cobb angle (p = 0.012, OR 1.0625, 95% CI 1.0135-1.1138). Among the 14 patients older than 10 years of age with a primary Cobb angle exceeding 35°, 13 (93%) ultimately required fusion. Patients with at least 1 year of follow-up whose curves progressed more 10° after decompression were younger than those without curve progression (6.1 ± 3.0 years vs 13.7 ± 3.2 years, p = 0.001, Mann-Whitney U-test). Left apical thoracic curves constituted a higher proportion of curves in the decompression-only group (8 of 16 vs 1 of 21, p = 0.002). CONCLUSIONS The need for fusion after posterior fossa decompression reflected the curve severity at clinical presentation. Patients presenting with curves measuring > 35°, as well as those greater than 10 years of age, may be at greater risk for requiring fusion after posterior fossa decompression, while patients less than 10 years of age may require routine monitoring for curve progression. Left apical thoracic curves may have a better response to Chiari malformation decompression.

Decompression Surgery Alone Versus Decompression Plus Fusion in Symptomatic Lumbar Spinal Stenosis: A Swiss Prospective Multicenter Cohort Study With 3 Years of Follow-up.

PubMed

Ulrich, Nils H; Burgstaller, Jakob M; Pichierri, Giuseppe; Wertli, Maria M; Farshad, Mazda; Porchet, François; Steurer, Johann; Held, Ulrike

2017-09-15

Retrospective analysis of a prospective, multicenter cohort study. To estimate the added effect of surgical fusion as compared to decompression surgery alone in symptomatic lumbar spinal stenosis patients with spondylolisthesis. The optimal surgical management of lumbar spinal stenosis patients with spondylolisthesis remains controversial. Patients of the Lumbar Stenosis Outcome Study with confirmed DLSS and spondylolisthesis were enrolled in this study. The outcomes of this study were Spinal Stenosis Measure (SSM) symptoms (score range 1-5, best-worst) and function (1-4) over time, measured at baseline, 6, 12, 24, and 36 months follow-up. In order to quantify the effect of fusion surgery as compared to decompression alone and number of decompressed levels, we used mixed effects models and accounted for the repeated observations in main outcomes (SSM symptoms and SSM function) over time. In addition to individual patients' random effects, we also fitted random slopes for follow-up time points and compared these two approaches with Akaike's Information Criterion and the chi-square test. Confounders were adjusted with fixed effects for age, sex, body mass index, diabetes, Cumulative Illness Rating Scale musculoskeletal disorders, and duration of symptoms. One hundred thirty-one patients undergoing decompression surgery alone (n = 85) or decompression with fusion surgery (n = 46) were included in this study. In the multiple mixed effects model the adjusted effect of fusion compared with decompression alone surgery on SSM symptoms was 0.06 (95% confidence interval: -0.16-0.27) and -0.07 (95% confidence interval: -0.25-0.10) on SSM function, respectively. Among the patients with degenerative lumbar spinal stenosis and spondylolisthesis our study confirms that in the two groups, decompression alone and decompression with fusion, patients distinctively benefited from surgical treatment. When adjusted for confounders, fusion surgery was not associated with a more favorable outcome in both SSM scores as compared to decompression alone surgery. 3.

Effect of oxygen-breathing during a decompression-stop on bubble-induced platelet activation after an open-sea air dive: oxygen-stop decompression.

PubMed

Pontier, J-M; Lambrechts, K

2014-06-01

We highlighted a relationship between decompression-induced bubble formation and platelet micro-particle (PMP) release after a scuba air-dive. It is known that decompression protocol using oxygen-stop accelerates the washout of nitrogen loaded in tissues. The aim was to study the effect of oxygen deco-stop on bubble formation and cell-derived MP release. Healthy experienced divers performed two scuba-air dives to 30 msw for 30 min, one with an air deco-stop and a second with 100% oxygen deco-stop at 3 msw for 9 min. Bubble grades were monitored with ultrasound and converted to the Kisman integrated severity score (KISS). Blood samples for cell-derived micro-particle analysis (AnnexinV for PMP and CD31 for endothelial MP) were taken 1 h before and after each dive. Mean KISS bubble score was significantly lower after the dive with oxygen-decompression stop, compared to the dive with air-decompression stop (4.3 ± 7.3 vs. 32.7 ± 19.9, p < 0.001). After the dive with an air-breathing decompression stop, we observed an increase of the post-dive mean values of PMP (753 ± 245 vs. 381 ± 191 ng/μl, p = 0.003) but no significant change in the oxygen-stop decompression dive (329 ± 215 vs. 381 +/191 ng/μl, p = 0.2). For the post-dive mean values of endothelial MP, there was no significant difference between both the dives. The Oxygen breathing during decompression has a beneficial effect on bubble formation accelerating the washout of nitrogen loaded in tissues. Secondary oxygen-decompression stop could reduce bubble-induced platelet activation and the pro-coagulant activity of PMP release preventing the thrombotic event in the pathogenesis of decompression sickness.

Pasta Nucleosynthesis: Molecular dynamics simulations of nuclear statistical equilibrium

NASA Astrophysics Data System (ADS)

Caplan, Matthew; Horowitz, Charles; da Silva Schneider, Andre; Berry, Donald

2014-09-01

We simulate the decompression of cold dense nuclear matter, near the nuclear saturation density, in order to study the role of nuclear pasta in r-process nucleosynthesis in neutron star mergers. Our simulations are performed using a classical molecular dynamics model with 51 200 and 409 600 nucleons, and are run on GPUs. We expand our simulation region to decompress systems from initial densities of 0.080 fm-3 down to 0.00125 fm-3. We study proton fractions of YP = 0.05, 0.10, 0.20, 0.30, and 0.40 at T = 0.5, 0.75, and 1 MeV. We calculate the composition of the resulting systems using a cluster algorithm. This composition is in good agreement with nuclear statistical equilibrium models for temperatures of 0.75 and 1 MeV. However, for proton fractions greater than YP = 0.2 at a temperature of T = 0.5 MeV, the MD simulations produce non-equilibrium results with large rod-like nuclei. Our MD model is valid at higher densities than simple nuclear statistical equilibrium models and may help determine the initial temperatures and proton fractions of matter ejected in mergers.

Early Versus Delayed Surgical Decompression of Spinal Cord after Traumatic Cervical Spinal Cord Injury: A Cost-Utility Analysis.

PubMed

Furlan, Julio C; Craven, B Catharine; Massicotte, Eric M; Fehlings, Michael G

2016-04-01

This cost-utility analysis was undertaken to compare early (≤24 hours since trauma) versus delayed surgical decompression of spinal cord to determine which approach is more cost effective in the management of patients with acute traumatic cervical spinal cord injury (SCI). This study includes the patients enrolled into the Surgical Timing in Acute Spinal Cord Injury Study (STASCIS) and admitted at Toronto Western Hospital. Cases were grouped into patients with motor complete SCI and individuals with motor incomplete SCI. A cost-utility analysis was performed for each group of patients by the use of data for the first 6 months after SCI. The perspective of a public health care insurer was adopted. Costs were estimated in 2014 U.S. dollars. Utilities were estimated from the STASCIS. The baseline analysis indicates early spinal decompression is more cost-effective approach compared with the delayed spinal decompression. When we considered the delayed spinal decompression as the baseline strategy, the incremental cost-effectiveness ratio analysis revealed a saving of US$ 58,368,024.12 per quality-adjusted life years gained for patients with complete SCI and a saving of US$ 536,217.33 per quality-adjusted life years gained in patients with incomplete SCI for the early spinal decompression. The probabilistic analysis confirmed the early-decompression strategy as more cost effective than the delayed-decompression approach, even though there is no clearly dominant strategy. The results of this economic analysis suggests that early decompression of spinal cord was more cost effective than delayed surgical decompression in the management of patients with motor complete and incomplete SCI, even though no strategy was clearly dominant. Copyright © 2016 Elsevier Inc. All rights reserved.

Reducing intraocular-pressure spike after intravitreal-bevacizumab injection with ocular decompression using a sterile cotton swab soaked in proparacaine 0.5%: A quasi-experimental study.

PubMed

Qureshi, Naveed A; Mansoor, Hassan; Ahmad, Sabihuddin; Zafar, Sarah; Asif, Muhammad

2016-01-01

The study was conducted to determine the effect of preinjection ocular decompression by a cotton swab soaked in local anesthetic on the immediate postinjection rise in intraocular pressure (IOP) after intravitreal bevacizumab (IVB). A nonrandomized, quasi-experimental interventional study was conducted at Al-Shifa Trust Eye Hospital, Pakistan, from August 1, 2013 to July 31, 2014. One hundred ( n = 100) patients receiving 0.05-mL IVB injection for the first time were assigned to two preinjection anesthetic methods: one with ocular decompression using a sterile cotton swab soaked in proparacaine 0.5%, and the other without ocular decompression using proparacaine 0.5% eyedrops. The IOP was recorded in the eye receiving IVB at three time intervals: Time 1 (preinjection), Time 2 (immediately after injection), and Time 3 (30 minutes after injection). There was a significant difference in the mean IOP change (between Time 1 and Time 2) for the group injected with ocular decompression [ M = 1.00, standard deviation (SD) = 1.47] and the group injected without ocular decompression ( M = 5.00, SD = 2.38; t (68) = 9.761, p < 0.001). There was also a significant difference in the mean IOP change (between Time 1 and Time 3) for the group injected with ocular decompression ( M = 0.428, SD = 1.58) and the group injected without ocular decompression ( M = 4.318, SD = 3.34; t (58) = 7.111, p < 0.001). Patients receiving IVB injections with ocular-decompression soaking in proparacaine 0.5% experience significantly lower postinjection IOP spike, and that too for a considerably shorter duration as compared to those receiving IVB without ocular decompression.

Multiple Small Diameter Drillings Increase Femoral Neck Stability Compared with Single Large Diameter Femoral Head Core Decompression Technique for Avascular Necrosis of the Femoral Head.

PubMed

Brown, Philip J; Mannava, Sandeep; Seyler, Thorsten M; Plate, Johannes F; Van Sikes, Charles; Stitzel, Joel D; Lang, Jason E

2016-10-26

Femoral head core decompression is an efficacious joint-preserving procedure for treatment of early stage avascular necrosis. However, postoperative fractures have been described which may be related to the decompression technique used. Femoral head decompressions were performed on 12 matched human cadaveric femora comparing large 8mm single bore versus multiple 3mm small drilling techniques. Ultimate failure strength of the femora was tested using a servo-hydraulic material testing system. Ultimate load to failure was compared between the different decompression techniques using two paired ANCOVA linear regression models. Prior to biomechanical testing and after the intervention, volumetric bone mineral density was determined using quantitative computed tomography to account for variation between cadaveric samples and to assess the amount of bone disruption by the core decompression. Core decompression, using the small diameter bore and multiple drilling technique, withstood significantly greater load prior to failure compared with the single large bore technique after adjustment for bone mineral density (p< 0.05). The 8mm single bore technique removed a significantly larger volume of bone compared to the 3mm multiple drilling technique (p< 0.001). However, total fracture energy was similar between the two core decompression techniques. When considering core decompression for the treatment of early stage avascular necrosis, the multiple small bore technique removed less bone volume, thereby potentially leading to higher load to failure.

Ti-rich komatiites from northern Norway

NASA Astrophysics Data System (ADS)

Barnes, Sarah-Jane; Often, Morten

1990-06-01

Komatiites of the Karasjok Greenstone Belt, northern Norway, show two unusual features: they have certain compositional differences compared with other komatiites, and they are largely volcaniclastic in origin. Their geological setting suggests that the komatiites were crupted into shallow water, thus permitting phreatomagmatic eruption, in a small ocean basin that opened in the Baltic Shield. The major oxides (except for TiO2), the trace elements Y, Sc, V, heavy rare earth elements (HREE), Cr, Co, Ni and the platinum group elements (PGE) cover similar ranges to those observed in other komatiites, but TiO2, Sm, Zr and Hf (Ti-associated elements, TAE) are enriched compared with abundances commonly reported for komatiites. Thus, the Karasjok komatiites have interelement ratios 2 to 3 times greater than chondritic between the TAE and the HREE, PGE, Sc, V, Y, Al (HRE-associated elements, HAE). The light rare earth elements (LREE), Ta and Th are enriched in some samples relative to Ti, Sm, Zr, and Hf, but are depleted in others. One group of rocks that is similar to the Karasjok komatiites both in terms of geological setting and geochemistry is the Baffin Bay picrites. The reason for the high concentrations of TAE in the Karasjok komatiites could be that they formed at lower degrees of partial melting than most komatiites. The greater-than-chondritic TAE/HAE ratios indicate that garnet was a residual phase during their formation, requiring that the melt formed at a pressure greater than 40 kb. A model involving decompression melting of a mantle plume rising in a rifting environment, can explain the main features of the Karasjok komatiites.

The geochemistry and tectonic setting of late Cretaceous Caribbean and Colombian volcanism

NASA Astrophysics Data System (ADS)

Kerr, Andrew C.; Tarney, John; Marriner, Giselle F.; Nivia, Alvaro; Klaver, Gerard Th.; Saunders, Andrew D.

1996-03-01

Late Cretaceous mafic volcanic sequences in Western Colombia and in the southern Caribbean have a striking coherence in their chemistry and compositional range which suggests they are part of the same magmatic province. The chemical characteristics of the majority of the mafic lavas are totally unlike those of island arc or marginal basin basalts, so the sequences cannot represent accreted arc terranes. On the other hand their trace element characteristics closely resemble those of Icelandic/Reykjanes Ridge basalts that represent an oceanic plateau formed by extensive decompression melting of an uprising deep mantle plume. The occurrence of komatiites on Gorgona and high-MgO picritic lavas in S.E. Colombia and on Curaçao, representing high temperature melts of the plume tail, confirms this analogy. Likewise, late stage rhyolites within the Colombian mafic volcanics may well be the equivalent of the extensive silicic magmas on Iceland and at Galapagos, possibly formed by remelting of the deep parts of the overthickened basaltic crust above the plume head. These volcanics, plus others around the Caribbean, including the floor of the Central Caribbean, probably all represent part of an oceanic plateau that formed rapidly at the Galapagos hotspot at 88 Ma, and that was too hot and buoyant to subduct beneath the margin of S. America as it migrated westwards with the opening of the South Atlantic, and so was imbricated along the continental margin. Minor arc-like volcanics, tonalites and hornblende leucogabbro veins may represent the products of subduction-flip of normal ocean crust against the buoyant plateau, or hydrous melts developed during imbrication/obduction.

Recurrent ‘universal tumour’ of the spinal cord

PubMed Central

O'Grady, John; Kaliaperumal, Chandrasekaran; O'Sullivan, Michael

2012-01-01

Lipoma is popularly known as the ‘universal tumour’ because of its ubiquitous presence anywhere in the body. This is the first documented case of recurrent thoracic spinal cord intramedullary lipoma in a 44-year-old man, with a background of spinal dysraphism, which recurred 15 years after initial surgery. He was followed up every 2 years and currently presented with an 8-month history of progressive weakness in his lower limbs. An MRI of the spine confirmed recurrence of lipoma. He underwent redo laminectomy and partial resection and spinal cord decompression with duroplasty. Lipoma, although a low-grade tumour, can cause significant neurological deficits because of its location. Surgical exploration and removal of lipoma is recommended. However, to preserve the functionality of the spinal cord, one may resort to partial resection and aim for spinal cord decompression. The literature on spinal cord lipoma is reviewed and the aetiopathogenesis of this rare occurrence is described. PMID:22675149

Multiple locations of nerve compression: an unusual cause of persistent lower limb paresthesia.

PubMed

Ang, Chia-Liang; Foo, Leon Siang Shen

2014-01-01

A paucity of appreciation exists that the "double crush" phenomenon can account for persistent leg symptoms even after spinal neural decompression surgery. We present an unusual case of multiple locations of nerve compression causing persistent lower limb paresthesia in a 40-year old male patient. The patient's lower limb paresthesia was persistent after an initial spinal surgery to treat spinal lateral recess stenosis thought to be responsible for the symptoms. It was later discovered that he had peroneal muscle herniations that had caused superficial peroneal nerve entrapments at 2 separate locations. The patient obtained much symptomatic relief after decompression of the peripheral nerve. The "double crush" phenomenon and multiple levels of nerve compression should be considered when evaluating lower limb neurogenic symptoms, especially after spinal nerve root surgery. Copyright © 2014 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Standard cardiopulmonary resuscitation versus active compression-decompression cardiopulmonary resuscitation with augmentation of negative intrathoracic pressure for out-of-hospital cardiac arrest: a randomised trial.

PubMed

Aufderheide, Tom P; Frascone, Ralph J; Wayne, Marvin A; Mahoney, Brian D; Swor, Robert A; Domeier, Robert M; Olinger, Michael L; Holcomb, Richard G; Tupper, David E; Yannopoulos, Demetris; Lurie, Keith G

2011-01-22

Active compression-decompression cardiopulmonary resuscitation (CPR) with decreased intrathoracic pressure in the decompression phase can lead to improved haemodynamics compared with standard CPR. We aimed to assess effectiveness and safety of this intervention on survival with favourable neurological function after out-of-hospital cardiac arrest. In our randomised trial of 46 emergency medical service agencies (serving 2·3 million people) in urban, suburban, and rural areas of the USA, we assessed outcomes for patients with out-of-hospital cardiac arrest according to Utstein guidelines. We provisionally enrolled patients to receive standard CPR or active compression-decompression CPR with augmented negative intrathoracic pressure (via an impedance-threshold device) with a computer-generated block randomisation weekly schedule in a one-to-one ratio. Adults (presumed age or age ≥18 years) who had a non-traumatic arrest of presumed cardiac cause and met initial and final selection criteria received designated CPR and were included in the final analyses. The primary endpoint was survival to hospital discharge with favourable neurological function (modified Rankin scale score of ≤3). All investigators apart from initial rescuers were masked to treatment group assignment. This trial is registered with ClinicalTrials.gov, number NCT00189423. 2470 provisionally enrolled patients were randomly allocated to treatment groups. 813 (68%) of 1201 patients assigned to the standard CPR group (controls) and 840 (66%) of 1269 assigned to intervention CPR received designated CPR and were included in the final analyses. 47 (6%) of 813 controls survived to hospital discharge with favourable neurological function compared with 75 (9%) of 840 patients in the intervention group (odds ratio 1·58, 95% CI 1·07-2·36; p=0·019]. 74 (9%) of 840 patients survived to 1 year in the intervention group compared with 48 (6%) of 813 controls (p=0·03), with equivalent cognitive skills, disability ratings, and emotional-psychological statuses in both groups. The overall major adverse event rate did not differ between groups, but more patients had pulmonary oedema in the intervention group (94 [11%] of 840) than did controls (62 [7%] of 813; p=0·015). On the basis of our findings showing increased effectiveness and generalisability of the study intervention, active compression-decompression CPR with augmentation of negative intrathoracic pressure should be considered as an alternative to standard CPR to increase long-term survival after cardiac arrest. US National Institutes of Health grant R44-HL065851-03, Advanced Circulatory Systems. Copyright © 2011 Elsevier Ltd. All rights reserved.

Validation of the CRASH model in the prediction of 18-month mortality and unfavorable outcome in severe traumatic brain injury requiring decompressive craniectomy.

PubMed

Honeybul, Stephen; Ho, Kwok M; Lind, Christopher R P; Gillett, Grant R

2014-05-01

The goal in this study was to assess the validity of the corticosteroid randomization after significant head injury (CRASH) collaborators prediction model in predicting mortality and unfavorable outcome at 18 months in patients with severe traumatic brain injury (TBI) requiring decompressive craniectomy. In addition, the authors aimed to assess whether this model was well calibrated in predicting outcome across a wide spectrum of severity of TBI requiring decompressive craniectomy. This prospective observational cohort study included all patients who underwent a decompressive craniectomy following severe TBI at the two major trauma hospitals in Western Australia between 2004 and 2012 and for whom 18-month follow-up data were available. Clinical and radiological data on initial presentation were entered into the Web-based model and the predicted outcome was compared with the observed outcome. In validating the CRASH model, the authors used area under the receiver operating characteristic curve to assess the ability of the CRASH model to differentiate between favorable and unfavorable outcomes. The ability of the CRASH 6-month unfavorable prediction model to differentiate between unfavorable and favorable outcomes at 18 months after decompressive craniectomy was good (area under the receiver operating characteristic curve 0.85, 95% CI 0.80-0.90). However, the model's calibration was not perfect. The slope and the intercept of the calibration curve were 1.66 (SE 0.21) and -1.11 (SE 0.14), respectively, suggesting that the predicted risks of unfavorable outcomes were not sufficiently extreme or different across different risk strata and were systematically too high (or overly pessimistic), respectively. The CRASH collaborators prediction model can be used as a surrogate index of injury severity to stratify patients according to injury severity. However, clinical decisions should not be based solely on the predicted risks derived from the model, because the number of patients in each predicted risk stratum was still relatively small and hence the results were relatively imprecise. Notwithstanding these limitations, the model may add to a clinician's ability to have better-informed conversations with colleagues and patients' relatives about prognosis.

Pore Formation and Mobility Investigation (PPMI): Description and Initial Analysis of Experiments Conducted aboard the International Space Station

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Anilkumar, A. V.; Lee, C. P.

2003-01-01

Flow visualization experiments during the controlled directional melt back and re-solidification of succinonitrile (SCN) and SCN-water mixtures were conducted using the Pore Formation and Mobility Investigation (PFMI) apparatus in the glovebox facility (GBX) aboard the International Space Station. The study samples were initially 'cast' on earth under 450 millibar of nitrogen into 1 cm ID glass sample tubes approximately 30 cm in length, containing 6 in situ thermocouples. During the Space experiments, the processing parameters and flow visualization settings are remotely monitored and manipulated from the ground Telescience Center (TSC). The ground solidified sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. Bubbles of different sizes are seen to initiate at the melt interface and, upon release from the melting solid, translate at different speeds in the temperature field ahead of them before coming to rest. Over a period of time these bubbles dissolve into the melt. The gas-laden liquid is then directionally solidified in a controlled manner, generally starting at a rate of 1 micron /sec. Observation and preliminary analysis of bubble formation and mobility in pure SCN samples during melt back and the subsequent structure resulting during gas generation upon re-solidification are presented and discussed.

Pore Formation and Mobility Investigation (PFMI): Description and Initial Analysis of Experiments Conducted aboard the International Space Station

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Anilkumar, A. V.; Lee, C. P.

2002-01-01

Flow visualization experiments during the controlled directional melt back and re-solidification of succinonitrile (SCN) and SCN-water mixtures were conducted using the Pore Formation and Mobility Investigation (PFMI) apparatus in the glovebox facility (GBX) aboard the International Space Station. The study samples were initially "cast" on earth under 450 millibar of nitrogen into 1 cm ID glass sample tubes approximately 30 cm in length, containing 6 in situ thermocouples. During the Space experiments, the processing parameters and flow visualization settings are remotely monitored and manipulated from the ground Telescience Center (TSC). The ground solidified sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. Bubbles of different sizes are seen to initiate at the melt interface and, upon release from the melting solid, translate at different speeds in the temperature field ahead of them before coming to rest. Over a period of time these bubbles dissolve into the melt. The gas-laden liquid is then directionally solidified in a controlled manner, generally starting at a rate of 1 micron /sec. Observation and preliminary analysis of bubble formation and mobility in pure SCN samples during melt back and the subsequent structure resulting during gas generation upon re-solidification are presented and discussed.

Effects of decompression on operator performance.

DOT National Transportation Integrated Search

1966-04-01

The study was performed to provide more quantitative estimates of degradation of pilot performance following decompression and the extent to which a decompression with mask donning interrupts the task of piloting. The experiments utilized a Scow comp...

Increased Mediterranean Magma Production and Volcanism Triggered by the Messinian Salinity Crisis

NASA Astrophysics Data System (ADS)

Sternai, P.; Caricchi, L.; Garcia-Castellanos, D.; Jolivet, L.; Sheldrake, T.; Castelltort, S.

2017-12-01

For more than four decades, large controversies about the causes, effects and timing of the Mediterranean Messinian Salinity Crisis (MSC) have evolved in the light of a continuously growing body of evidences. The igneous response to such extreme event, however, has remained largely unexplored despite known relationships between surface load variations and the production, transfer and eruption of magma. Here, we compile published geochemical data and recognize a two-fold increase of volcanic eruptions from pan-Mediterranean magmatic provinces coinciding with the proposed "shallow-water phase" of the MSC between 5.70-5.33 Ma. Estimates of surface load variations due to the desiccation event corrected for water density change and deposition of salt deposits suggest a net mean lithospheric unloading of up to 15 MPa during the shallow-water phase of the MSC. Because the timescale of interest is too short for changes of the Mediterranean tectonics to significantly affect the bulk of the magma production, we propose that such net surface unloading enhanced the mantle decompression melting and dike formation, in turn causing the observed increase of volcanic events. If correct, the Mediterranean magmatic record provides an independent validation of the "shallow-water" model for the formation of salt deposits and testifies the high sensitivity of the melting of the Earth's interior to the surface forcing.

Ultrafast syn-eruptive degassing and ascent trigger high-energy basic eruptions.

PubMed

Giuffrida, Marisa; Viccaro, Marco; Ottolini, Luisa

2018-01-09

Lithium gradients in plagioclase are capable of recording extremely short-lived processes associated with gas loss from magmas prior to extrusion at the surface. We present SIMS profiles of the 7 Li/ 30 Si ion ratio in plagioclase crystals from products of the paroxysmal sequence that occurred in the period 2011-2013 at Mt. Etna (Italy) in an attempt to constrain the final ascent and degassing processes leading to these powerful eruptions involving basic magma. The observed Li concentrations reflect cycles of Li addition to the melt through gas flushing, and a syn-eruptive stage of magma degassing driven by decompression that finally produce significant Li depletion from the melt. Modeling the decreases in Li concentration in plagioclase by diffusion allowed determination of magma ascent timescales that are on the order of minutes or less. Knowledge of the storage depth beneath the volcano has led to the quantification of a mean magma ascent velocity of ~43 m/s for paroxysmal eruptions at Etna. The importance of these results relies on the application of methods, recently used exclusively for closed-system volcanoes producing violent eruptions, to open-conduit systems that have generally quiet eruptive periods of activity sometimes interrupted by sudden re-awakening and the production of anomalously energetic eruptions.

Mechanism of Promoter Melting by the Xeroderma Pigmentosum Complementation Group B Helicase of Transcription Factor IIH Revealed by Protein-DNA Photo-Cross-Linking

PubMed Central

Douziech, Maxime; Coin, Frédéric; Chipoulet, Jean-Marc; Arai, Yoko; Ohkuma, Yoshiaki; Egly, Jean-Marc; Coulombe, Benoit

2000-01-01

The p89/xeroderma pigmentosum complementation group B (XPB) ATPase-helicase of transcription factor IIH (TFIIH) is essential for promoter melting prior to transcription initiation by RNA polymerase II (RNAPII). By studying the topological organization of the initiation complex using site-specific protein-DNA photo-cross-linking, we have shown that p89/XPB makes promoter contacts both upstream and downstream of the initiation site. The upstream contact, which is in the region where promoter melting occurs (positions −9 to +2), requires tight DNA wrapping around RNAPII. The addition of hydrolyzable ATP tethers the template strand at positions −5 and +1 to RNAPII subunits. A mutation in p89/XPB found in a xeroderma pigmentosum patient impairs the ability of TFIIH to associate correctly with the complex and thereby melt promoter DNA. A model for open complex formation is proposed. PMID:11027286

Multiple plagioclase crystal populations identified by crystal size distribution and in situ chemical data: Implications for timescales of magma chamber processes associated with the 1915 eruption of Lassen Peak, CA

USGS Publications Warehouse

Salisbury, M.J.; Bohrson, W.A.; Clynne, M.A.; Ramos, F.C.; Hoskin, P.

2008-01-01

Products of the 1915 Lassen Peak eruption reveal evidence for a magma recharge-magma mixing event that may have catalyzed the eruption and from which four compositional members were identified: light dacite, black dacite, andesitic inclusion, and dark andesite. Crystal size distribution, textural, and in situ chemical (major and trace element and Sr isotope) data for plagioclase from these compositional products define three crystal populations that have distinct origins: phenocrysts (long axis > 0??5 mm) that typically have core An contents between 34 and 36 mol %, microphenocrysts (long axis between 0??1 and 0??5 mm) that have core An contents of 66-69, and microlites (long axis < 0??1 mm) with variable An core contents from 64 to 52. Phenocrysts are interpreted to form in an isolated dacitic magma chamber that experienced slow cooling. Based on textural, compositional, and isotopic data for the magma represented by the dacitic component, magma recharge was not an important process until just prior to the 1915 eruption. Average residence times for phenocrysts are in the range of centuries to millennia. Microphenocrysts formed in a hybrid layer that resulted from mixing between end-member reservoir dacite and recharge magma of basaltic andesite composition. High thermal contrast between the two end-member magmas led to relatively high degrees of undercooling, which resulted in faster crystal growth rates and acicular and swallowtail crystal habits. Some plagioclase phenocrysts from the dacitic chamber were incorporated into the hybrid layer and underwent dissolution-precipitation, seen in both crystal textures and rim compositions. Average microphenocryst residence times are of the order of months. Microlites may have formed in response to decompression and/ or syn-eruptive degassing as magma ascended from the chamber through the volcanic conduit. Chemical distinctions in plagioclase microlite An contents reveal that melt of the dark andesite was more mafic than the melt of the other three compositions. We suggest that mixing of an intruding basaltic andesite and reservoir dacite before magma began ascending in the conduit allowed formation of a compositionally distinct microlite population. Melt in the other three products was more evolved because it had undergone differentiation during the months following initial mixing; as a consequence, melt and microlites among these three products have similar compositions. The results of this study highlight the integrated use of crystal size distribution, textural, and in situ chemical data in identifying distinct crystal populations and linking these populations to the thermal and chemical characteristics of complex magma bodies. ?? The Author 2008. Published by Oxford University Press. All rights reserved.

Edema and elasticity of a fronto-temporal decompressive craniectomy

PubMed Central

Takada, Daikei; Nagai, Hidemasa; Moritake, Kouzo; Akiyama, Yasuhiko

2012-01-01

Background: Decompressive craniectomy is undertaken for relief of brain herniation caused by acute brain swelling. Brain stiffness can be estimated by palpating the decompressive cranial defect and can provide some relatively subjective information to the neurosurgeon to help guide care. The goal of the present study was to objectively evaluate transcutaneous stiffness of the cranial defect using a tactile resonance sensor and to describe the values in patients with a decompressive window in order to characterize the clinical association between brain edema and stiffness. Methods: Data were prospectively collected from 13 of 37 patients who underwent a decompressive craniectomy in our hospital during a 5-year period. Transcutaneous stiffness was measured as change in frequency and as elastic modulus. Results: Stiffness variables of the decompressive site were measured without any adverse effect and subsequent calculations revealed change in frequency = 101.71 ± 36.42 Hz, and shear elastic modulus = 1.99 ± 1.11 kPa. Conclusions: The elasticity of stiffness of a decompressive site correlated with brain edema, cisternal cerebrospinal fluid pressure, and brain shift, all of which are related to acute brain edema. PMID:22347679

[Two-wall decompression without resection of the medial wall. Effect on squint angle].

PubMed

Bertelmann, E; Rüther, K

2011-11-01

Postoperative new onset diplopia can be a disadvantage for surgical orbital decompression in patients with exophthalmos in thyroid eye disease. The various modifications of decompression (number and combination of walls) differ in their influence on the postoperative squint angle. We report on postoperative diplopia in a modified 2 wall decompression strategy (lateral wall and floor). This study was a retrospective analysis of 36 consecutive 2-wall decompressions performed between 2006-2010 in 24 patients with 6 months of stable exophthalmos in thyroid eye disease after medical therapy and radiotherapy. The preoperative and postoperative squint angle in prism cover test (PCT), motility, induction of diplopia, reduction of exophthalmos, visual acuity and complications were evaluated. In all 36 decompressions the postoperative squint angle was equal to or less than before surgery. In 8 eyes additional squint surgery was performed. The mean reduction in exopthalmos was 4.3 mm. An adverse effect of decompression on the postoperative squint angle was not evident in this study. New induction of diplopia was not observed at all. One possible explanation is the preservation of the medial wall.

Dynamics of diffusive bubble growth and pressure recovery in a bubbly rhyolitic melt embedded in an elastic solid

USGS Publications Warehouse

Chouet, Bernard A.; Dawson, Phillip B.; Nakano, Masaru

2006-01-01

We present a model of gas exsolution and bubble expansion in a melt supersaturated in response to a sudden pressure drop. In our model, the melt contains a suspension of gas bubbles of identical sizes and is encased in a penny-shaped crack embedded in an elastic solid. The suspension is modeled as a three-dimensional lattice of spherical cells with slight overlap, where each elementary cell consists of a gas bubble surrounded by a shell of volatile-rich melt. The melt is then subjected to a step drop in pressure, which induces gas exsolution and bubble expansion, resulting in the compression of the melt and volumetric expansion of the crack. The dynamics of diffusion-driven bubble growth and volumetric crack expansion span 9 decades in time. The model demonstrates that the speed of the crack response depends strongly on volatile diffusivity in the melt and bubble number density and is markedly sensitive to the ratio of crack thickness to crack radius and initial bubble radius but is relatively insensitive to melt viscosity. The net drop in gas concentration in the melt after pressure recovery represents only a small fraction of the initial concentration prior to the drop, suggesting the melt may undergo numerous pressure transients before becoming significantly depleted of gases. The magnitude of pressure and volume recovery in the crack depends sensitively on the size of the input-pressure transient, becoming relatively larger for smaller-size transients in a melt containing bubbles with initial radii less than 10-5 m. Amplification of the input transient may be large enough to disrupt the crack wall and induce brittle failure in the rock matrix surrounding the crack. Our results provide additional basis for the interpretation of volume changes in the magma conduit under Popocatépetl Volcano during Vulcanian degassing bursts in its eruptive activity in April–May 2000.

Levodopa in Treatment of Decompression Sickness and of Air Embolism Induced Paraplegia in Rats.

DTIC Science & Technology

1981-08-28

nitrosoureas (BCNU, CCNU) made additional progress in the treatment of brain tumors. A lipid soluble agent , 1,3-bis (2-Chloroethyl)-l- Nitrosourea (BCNU...mechanisms of levodopa and some other agents in the prevention and in the recovery of rats from decompression sickness. For better clarity the...brain occurring in decompression sickness. B. Decompression Sickness Studies. We have shown that gelatin, an agent that protects platelets during freezing

Xenon Blocks Neuronal Injury Associated with Decompression

PubMed Central

Blatteau, Jean-Eric; David, Hélène N.; Vallée, Nicolas; Meckler, Cedric; Demaistre, Sebastien; Lambrechts, Kate; Risso, Jean-Jacques; Abraini, Jacques H.

2015-01-01

Despite state-of-the-art hyperbaric oxygen (HBO) treatment, about 30% of patients suffering neurologic decompression sickness (DCS) exhibit incomplete recovery. Since the mechanisms of neurologic DCS involve ischemic processes which result in excitotoxicity, it is likely that HBO in combination with an anti-excitotoxic treatment would improve the outcome in patients being treated for DCS. Therefore, in the present study, we investigated the effect of the noble gas xenon in an ex vivo model of neurologic DCS. Xenon has been shown to provide neuroprotection in multiple models of acute ischemic insults. Fast decompression compared to slow decompression induced an increase in lactate dehydrogenase (LDH), a well-known marker of sub-lethal cell injury. Post-decompression administration of xenon blocked the increase in LDH release induced by fast decompression. These data suggest that xenon could be an efficient additional treatment to HBO for the treatment of neurologic DCS. PMID:26469983

Xenon Blocks Neuronal Injury Associated with Decompression.

PubMed

Blatteau, Jean-Eric; David, Hélène N; Vallée, Nicolas; Meckler, Cedric; Demaistre, Sebastien; Lambrechts, Kate; Risso, Jean-Jacques; Abraini, Jacques H

2015-10-15

Despite state-of-the-art hyperbaric oxygen (HBO) treatment, about 30% of patients suffering neurologic decompression sickness (DCS) exhibit incomplete recovery. Since the mechanisms of neurologic DCS involve ischemic processes which result in excitotoxicity, it is likely that HBO in combination with an anti-excitotoxic treatment would improve the outcome in patients being treated for DCS. Therefore, in the present study, we investigated the effect of the noble gas xenon in an ex vivo model of neurologic DCS. Xenon has been shown to provide neuroprotection in multiple models of acute ischemic insults. Fast decompression compared to slow decompression induced an increase in lactate dehydrogenase (LDH), a well-known marker of sub-lethal cell injury. Post-decompression administration of xenon blocked the increase in LDH release induced by fast decompression. These data suggest that xenon could be an efficient additional treatment to HBO for the treatment of neurologic DCS.

[Theoretical evaluation of the risk of decompression illness during simulated extravehicular activity].

PubMed

Nikolaev, V P

2008-01-01

Theoretical analysis of the risk of decompression illness (DI) during extravehicular activity following the Russian and NASA decompression protocols (D-R and D-US, respectively) was performed. In contrast to the tradition approach to decompression stress evaluation by the factor of tissue supersaturation with nitrogen, our probabilistic theory of decompression safety provides a completely reasoned evaluation and comparison of the levels of hazard of these decompression protocols. According to this theory, the function of cumulative DI risk is equal to the sum of functions of cumulative risk of lesion of all body tissues by gas bubbles and their supersaturation by solute gases. Based on modeling of dynamics of these functions, growth of the DI cumulative risk in the course of D-R and D-US follows essentially similar trajectories within the time-frame of up to 330 minutes. However, further extension of D-US but not D-R raises the risk of DI drastically.

Crystallographic effects during radiative melting of semitransparent materials

NASA Astrophysics Data System (ADS)

Webb, B. W.; Viskanta, R.

1987-10-01

Experiments have been performed to illustrate crystallogrpahic effects during radiative melting of unconfined vertical layers of semitransparent material. Radiative melting of a polycrystalline paraffin was performed and the instantaneous layer weight and transmittance were measured using a cantilever beam technique and thermopile radiation detector, respectively. The effects of radiative flux, initial solid subcooling, spectral distribution of the irradiation, and crystal structure of the solid as determined qualitatively by the sample solidification rate were studied. Experimental results show conclusively the dominant influence of cystallographic effects in the form of multiple internal scattering of radiation during the melting process. A theoretical model is formulated to predict the melting rate of the material. Radiation transfer is treated by solving the one-dimensional radiative transfer equation for an absorbing-scattering medium using the discrete ordinates method. Melting rate and global layer reflectance as predicted by the model agree well with experimental data. Parametric studies conducted with the model illustrate the sensitivity of the melting behavior to such variables as incident radiative flux, initial layer opacity (material extinction coefficient), and scattering asymmetry factor.

Melt onset over Arctic sea ice controlled by atmospheric moisture transport

NASA Astrophysics Data System (ADS)

Mortin, Jonas; Svensson, Gunilla; Graversen, Rune G.; Kapsch, Marie-Luise; Stroeve, Julienne C.; Boisvert, Linette N.

2016-06-01

The timing of melt onset affects the surface energy uptake throughout the melt season. Yet the processes triggering melt and causing its large interannual variability are not well understood. Here we show that melt onset over Arctic sea ice is initiated by positive anomalies of water vapor, clouds, and air temperatures that increase the downwelling longwave radiation (LWD) to the surface. The earlier melt onset occurs; the stronger are these anomalies. Downwelling shortwave radiation (SWD) is smaller than usual at melt onset, indicating that melt is not triggered by SWD. When melt occurs early, an anomalously opaque atmosphere with positive LWD anomalies preconditions the surface for weeks preceding melt. In contrast, when melt begins late, clearer than usual conditions are evident prior to melt. Hence, atmospheric processes are imperative for melt onset. It is also found that spring LWD increased during recent decades, consistent with trends toward an earlier melt onset.

An evaluation of potential decompression hazards in small pressurized aircraft.

DOT National Transportation Integrated Search

1967-06-01

Over 300 decompression tests were conducted to determine potential hazards of ejection or incapacitating or fatal head injuries in small volume pressurized aircraft in the event of sudden decompression following the loss of a window, emergency exit, ...

Volcanic processes recorded by inclusions in sanidine megacrystals ejected from Quaternary Rockeskyll volcano, Eifel, Germany

NASA Astrophysics Data System (ADS)

Eilhard, Nicole; Schreuer, Jürgen; Stöckhert, Bernhard

2016-04-01

Sanidine megacrystals were ejected by a late stage explosive eruption at the Quaternary Rockeskyll volcanic complex, Eifel volcanic field, Germany. The homogeneous distribution of barium (about 1 % wt BaO equivalent to about 2 mole % celsian component) indicates that the nearly perfect single crystals must have crystallized in the Ostwald-Miers range from a huge reservoir, probably in the roof of a magma chamber. Irregularities during crystal growth caused trapping of hydrous melt inclusions, which are the objective of the present study. The inclusions show a characteristic concentric microstructure, in the following described from the sanidine host towards the inclusion center: (1) Ba is enriched by a factor of 2 to 3 in a ca. 0.01 mm wide rim, compared to the otherwise homogeneous sanidine host; (2) inwards, the continuous rim is overgrown by a thin crust of Ba enriched sanidine with irregular surface; (3) a layer of glass with a composition similar to sanidine; (4) a second, thinner layer of glass slightly reduced in Na2O and K2O, separated from the first glass layer by a sharp interface with approximately spherical shape; (5) a bubble containing a fluid phase, composed of H2O and minor CO2. This record is interpreted as follows: After crystallization of the sanidine megacrystals, a rise in temperature within the magmatic system caused some re-melting of the Ba-rich sanidine around the inclusions. Partitioning of Ba between the small included melt reservoir and the host caused formation of the Ba-rich rim (layer 1) by diffusive exchange. The onset of cooling lead to crystallization of the thin sanidine crust (layer 2). Finally, very rapid decompression and cooling during the subsequent explosive eruption caused sequential phase separation (two stages) in the remaining melt, the denser melt phase (layers 3 and 4) quenched to glass, the complementary low-density volatile-rich phase forming the central bubble. In summary, the microstructure and phase composition of the inclusions in the sanidine megacrystals recorded information on the history of the volcanic system prior to and during explosive eruption.

Kyanite-bearing migmatites in the central Adirondack Mountains: Implications for late to post-orogenic metamorphism and melting in a collisional orogen

NASA Astrophysics Data System (ADS)

Reeder, J.; Metzger, E. P.; Bickford, M. E.; Leech, M. L.

2016-12-01

Sillimanite-rich felsic migmatites exposed at Ledge Mountain in the Central Adirondack Highlands (AH) represent the only location in the AH where kyanite is found. The texturally young kyanite is overprinted on sillimanite in largely undeformed pegmatitic leucosomes, suggesting a late episode of melting taking place deeper than previously thought, and requiring a counter-clockwise P-T path. A final phase of anatexis ca. 1050 Ma in the Eastern AH is consistent with an influx of fluid or decompression from extension in sillimanite-bearing migmatites. Temperatures both from this study and previous work are consistent with granulite-facies metamorphism; however, the presence of kyanite requires higher pressure conditions corresponding to deeper burial of rocks exposed in the central Adirondacks. The Adirondacks are associated with the Grenville Province of eastern North America, that formed during four orogenic events. The most recent (Grenville) orogeny consisted of two stages: crustal thickening and granulite facies metamorphism during the Ottawan phase (ca 1090-1020) then metamorphism and melting in the kyanite field during the much shorter Rigolet pulse (ca 1005-980 Ma). Preliminary U-Pb SHRIMP zircon ages from Ledge Mountain kyanite-bearing migmatites suggest that melting in the Central AH persisted into the Rigolet phase. On the basis of mineral composition and chemistry and the presence of distinctive quartz-sillimanite nodules, the Ledge Mountain migmatites closely resemble the K-rich phase of the Ottawan-age Lyon Mountain granite (LMG) and may represent LMG that was metamorphosed to sillimanite grade and then overprinted by a higher pressure, lower temperature assemblage. Kyanite-bearing felsic anatectites of Rigolet age have previously been observed only in the western portion of the Grenville Province. Documentation of a counterclockwise P-T path and post-Ottawan melting in the Ledge Mountain migmatites requires re-evaluation of current tectonic models for the Grenville Province and its Adirondacks outlier. Further analysis of age, geochemical, and petrographic data will help develop a better-defined P-T-t path and may lead to the development of a new tectonic model to be compared with other collisional orogens such as Himalaya or the Bohemian Massif of the Variscan orogenic belt.

In Situ XANES of U and Th in Silicate Liquids at High Pressure and Temperature

NASA Astrophysics Data System (ADS)

Mallmann, G.; Wykes, J.; Berry, A.; O'Neill, H. S.; Cline, C. J., II; Turner, S.; Rushmer, T. A.

2016-12-01

Although the chemical environments of elements in silicate melts at specific conditions of temperature, pressure and oxygen fugacity (fO2) are often inferred from measurements after quenching the melts to glasses, it is widely recognized that changes may occur during the quenching process, making measurements in situ at high pressure and temperature highly desirable. A case of importance in geochemistry is the speciation of uranium in silicate melts as a function of pressure. Evidence from mineral-melt partitioning and XANES (X-ray Absorption Near-Edge Structure) spectroscopy of glasses suggests that U5+ may be stable at low pressures in the Earth's crust (along with U4+ or U6+, depending on fO2) where basaltic liquids crystallize, but not in the Earth's upper mantle where peridotite partially melts to produce such liquids. To test these observations we recorded in situ transmission U and Th L3-edge XANES spectra of U and Th-doped silicate liquids at 1.6 GPa and 1350°C using the D-DIA apparatus at the X-ray Absorption Spectroscopy Beamline of the Australian Synchrotron. Data for thorium, which occurs exclusively as a tetravalent cation under terrestrial fO2 conditions, were collected as a `control' to monitor for changes in coordination. The cell assembly consisted of a boron-epoxy cube as pressure medium, alumina sleeve and cylindrical graphite heater. The starting mix, a powdered synthetic average MORB silicate glass doped with 2 wt.% of U and Th, was loaded into San Carlos olivine capsules along with solid oxygen buffers (either Re-ReO2 or Ru-RuO2) in a sandwich arrangement. The capsule was then placed inside the graphite heater and insulated with crushable MgO powder. Temperature was monitored using a type D thermocouple. U and Th L3-edge XANES spectra were recorded throughout the heating/compression cycle and then after quenching. Our preliminary assessment indicates that the U-XANES spectra recorded for the liquid in situ at high pressure and temperature and subsequently for the quenched glass are very similar, which would suggest no apparent change in uranium coordination and/or valence state on cooling/decompression.

Cell therapy versus simultaneous contralateral decompression in symptomatic corticosteroid osteonecrosis: a thirty year follow-up prospective randomized study of one hundred and twenty five adult patients.

PubMed

Hernigou, Philippe; Dubory, Arnaud; Homma, Yasuhiro; Guissou, Isaac; Flouzat Lachaniette, Charles Henri; Chevallier, Nathalie; Rouard, Hélène

2018-05-09

Symptomatic osteonecrosis related to corticosteroids has a high risk of progression to collapse in absence of treatment. The purposes of this study were to evaluate the results of autologous bone marrow grafting of the symptomatic hip in adult patients with osteonecrosis and to compare the results with core decompression alone in the contralateral symptomatic hip. A total of 125 consecutive patients (78 males and 47 females) with bilateral osteonecrosis (ON) and who had both hips symptomatic and at the same stage on each side (stage I or II) were included in this study from 1988 to 1998. The volume of osteonecrosis was measured with MRI in both hips; the smaller size ON was treated with core decompression, and the contralateral hip with the larger ON was treated with percutaneous mesenchymal cell (MSC) injection obtained from bone marrow concentration. The average total number of MSCs (counted as number of colony forming units-fibroblast) injected in each hip was 90,000 ± 25,000 cells (range 45,000 to 180,000 cells). At the most recent FU (average 25 years after the first surgery, range 20 to 30 years), among the 250 hips included in the study, 35 hips (28%) had collapsed at the most recent follow-up after bone marrow grafting, and 90 (72%) after core decompression (CD). Ninety-five hips (76%) in the CD group underwent total hip replacement and 30 hips (24%) in the bone marrow graft group (p < 0.0001). Hips undergoing only CD were approximately three times more likely to undergo a primary THA (odds ratio: 10.0278; 95% CI: 5.6117 to 17.9190; p < 0.0001) as compared with hips undergoing an initial bone marrow grafting. For the 90 hips treated with bone marrow injection and without collapse, the mean volume of repair evaluated by MRI at the most recent follow-up was 16.4 cm 3 (range 12 to 21 cm 3 ) corresponding to a decrease of the pre-operative average volume from 22.4 cm 3 (range 35-15 cm 3 ) to 6 cm 3 (range 12-0 cm 3 ); as percentage of the volume of the femoral head, the decrease moved from 44.8 to 12%. Core decompression with bone marrow injection improved the outcome of the disease as compared with core decompression alone in the same patient.

Laboratory experiments on fragmentation of highly-viscous bubbly syrup

NASA Astrophysics Data System (ADS)

Kurihara, H.; Kameda, M.; Ichihara, M.

2006-12-01

Fragmentation of vesicular magma by rapid decompression is a key process in explosive eruptions. To determine the fragmentation criteria, we carried out laboratory experiments on magma fragmentation using analogous materials. We used commercial syrup as an analogous material of magma, because the viscosity was widely altered by adding or subtracting water contents in the syrup. We made the bubbly syrup by adding hydrogen peroxide with manganese oxide in the syrup. The amount of hydrogen peroxide is proportional to the gas volume fraction in the syrup. We measured the rheological properties of the syrup. Zero shear viscosity η was measured by a rotating viscometer and a fiber elongation technique. Glass transition temperature was measured by differential scanning calorimetry. The measured data indicated that the temperature dependence of viscosity was described well using Williams-Landel-Ferry (WLF) equation. The solid content of syrup alters the viscosity as well as the glass transition temperature, though it may hardly affect the rigidity μ, which was measured by ultrasonic test in our previous work. We used a pressurized vertical tube with a large vacuum vessel to apply the rapid decompression on the material. An acrylic container, filled with the bubbly syrup, was placed in the bottom of the pressurized tube. By rupturing the diaphragms inserted between the tube and the vacuum vessel, the bubbly syrup is rapidly decompressed due to expansion of the pressurized gas in the tube. A high-speed video camera was used to obtain sequential images of the materials. Pressure transducers were mounted on the sidewall of the tube and the bottom of the container. The initial pressure was varied from 1 MPa to 5 MPa. The gas-volume fraction of the syrup under pressure was fixed as 2 % to 20%. The viscosity varied from 105 Pa·s to 108 Pa·s. We successfully observed three principal behaviors using the present analogous material; brittle fragmentation, partial fracture and ductile expansion without crack initiation. From all the experimental data, in conclusion, the fragmentation is observed when the pressure drop Δ p reaches a critical value within the order of relaxation time of syrup, which is defined as η/μ. Simultaneously, the initial gas volume fraction should be larger than a critical value, which decreases as the initial high-pressure is larger.

Lithosphere erosion and continental breakup: Interaction of extension, plume upwelling and melting

NASA Astrophysics Data System (ADS)

Lavecchia, Alessio; Thieulot, Cedric; Beekman, Fred; Cloetingh, Sierd; Clark, Stuart

2017-06-01

We present the results of thermo-mechanical modelling of extension and breakup of a heterogeneous continental lithosphere, subjected to plume impingement in presence of intraplate stress field. We incorporate partial melting of the extending lithosphere, underlying upper mantle and plume, caused by pressure-temperature variations during the thermo-mechanical evolution of the conjugate passive margin system. Effects of melting included in the model account for thermal effects, causing viscosity reduction due to host rock heating, and mechanical effects, due to cohesion loss. Our study provides better understanding on how presence of melts can influence the evolution of rifting. Here we focus particularly on the role of melting for the temporal and spatial evolution of passive margin geometry and rift migration. Depending on the lithospheric structure, melt presence may have a significant impact on the characteristics of areas affected by lithospheric extension. Pre-existing lithosphere heterogeneities determine the location of initial breakup, but in presence of plumes the subsequent evolution is more difficult to predict. For small distances between plume and area of initial rifting, the development of symmetric passive margins is favored, whereas increasing the distance promotes asymmetry. For a plume-rifting distance large enough to prevent interaction, the effect of plumes on the overlying lithosphere is negligible and the rift persists at the location of the initial lithospheric weakness. When the melt effect is included, the development of asymmetric passive continental margins is fostered. In this case, melt-induced lithospheric weakening may be strong enough to cause rift jumps toward the plume location.

Effect of Inert Gas Switching at Depth on Decompression Outcome in Rats

DTIC Science & Technology

1989-01-01

Indcuae Security Classification) Effect Of inert gas switching at depth on decompression outcome in rats Liil RVRcCall1urn M~E 16. SUPPLEMENTARY...CLASSIrICATrIONOF TI PAGE All other edition% -ate obsfee UNCLASSIFIED Effect of inert gas switching at depth on decompression outcome in rats R. S... Effect of inert gas Although various models of inert gas transport in the switching at depth on decompression outcome in rats. J. Appl

[Patent foramen ovale and decompression illness in divers].

PubMed

Sivertsen, Wiebke; Risberg, Jan; Norgård, Gunnar

2010-04-22

About 25 % of the population has patent foramen ovale, and the condition has been assumed to be a causal factor in decompressive illness. Transcatheter closure is possible and is associated with a relatively low risk, but it has not been clarified whether there is an indication for assessment and treatment of the condition in divers. The present study explored a possible relationship between a patent foramen ovale and the risk for decompression illness in divers, if there are categories of divers that should be screened for the condition and what advice should be given to divers with this condition. The review is based on literature identified through a search in Pubmed and the authors' long clinical experience in the field. The risk of decompression illness for divers with a persistent foramen ovale is about five times higher than that in divers without this condition, but the absolute risk for decompression illness is only 2.5 after 10,000 dives. A causal association has not been shown between patent foramen ovale and decompression illness. Even if closure of patent foramen ovale may be done with relatively small risk, the usefulness of the procedure has not been documented in divers. We do not recommend screening for patent foramen ovale in divers because the absolute risk of decompression illness is small and transcatheter closure is only indicated after decompression illness in some occupational divers.

Pseudotachylitic breccia from the Dhala impact structure, north-central India: Texture, mineralogy and geochemical characterization

NASA Astrophysics Data System (ADS)

Pati, J. K.; Reimold, W. U.; Greshake, A.; Schmitt, R. T.; Koeberl, C.; Pati, P.; Prakash, K.

2015-05-01

Pseudotachylitic breccia (PTB) occurs in a drill core from the crater floor of the 11 km diameter, Proterozoic Dhala impact structure, India. PTBs were intersected in late Archean granitoids between 348.15 m and 502.55 m depth in the MCB-10 drill core from the center of the Dhala structure. The breccias comprise both cataclastic-matrix as well as melt breccias. The presence of microlites and vesicles in the groundmass and a widely observed flow fabric in the PTB support the presence of melt in the groundmass of some samples. Clasts in PTB are derived from the Archean granitoid basement. PTB matrix, the matrix of impact melt breccia also occurring between 256.50 m and 502.55 m depth, and the target granitoids vary in terms of silica, total alkali, magnesium and iron oxide contents. Chondrite-normalized REE patterns of PTB and target granitoids are similar, but the elemental abundances in the PTB are lower. The restricted size of PTB as veins and pods of up to 2.5 cm width, their occurrence at varied depths over a core length of 150 m, the clast population, and the chemical relationships between PTB and their host rocks all suggest the derivation of these breccias locally from the fractured basement granitoids involving in-situ melting. We favor that this took place due to rapid decompression during the collapse and modification stage of impact cratering, with, locally, additional energy input from frictional heating. Locally, amphibolite and dioritic mylonite occur in the host granitoids and their admixture could have contributed to the comparatively more mafic composition of PTB. Alteration of these crater floor rocks could have involved preferential reduction of silica and alkali element abundances, possibly due to impact-induced hydrothermal activity at crater floor level. This process, too, could have resulted in more mafic compositions.

Himalayan gneiss dome formation in the middle crust and exhumation by normal faulting: New geochronology of Gianbul dome, northwestern India

USGS Publications Warehouse

Horton, Forrest; Lee, Jeffrey; Hacker, Bradley; Bowman-Kamaha'o, Meilani; Cosca, Michael A.

2015-01-01

A general lack of consensus about the origin of Himalayan gneiss domes hinders accurate thermomechanical modeling of the orogen. To test whether doming resulted from tectonic contraction (e.g., thrust duplex formation, antiformal bending above a thrust ramp, etc.), channel flow, or via the buoyant rise of anatectic melts, this study investigates the depth and timing of doming processes for Gianbul dome in the western Himalaya. The dome is composed of Greater Himalayan Sequence migmatite, Paleozoic orthogneiss, and metasedimentary rock cut by multiple generations of leucogranite dikes. These rocks record a major penetrative D2 deformational event characterized by a domed foliation and associated NE-SW–trending stretching lineation, and they are flanked by the top-down-to-the-SW (normal-sense) Khanjar shear zone and the top-down-to-the-NE (normal sense) Zanskar shear zone (the western equivalent of the South Tibetan detachment system). Monazite U/Th-Pb geochronology records (1) Paleozoic emplacement of the Kade orthogneiss and associated granite dikes; (2) prograde Barrovian metamorphism from 37 to 33 Ma; (3) doming driven by upper-crustal extension and positive buoyancy of decompression melts between 26 and 22 Ma; and (4) the injection of anatectic melts into the upper levels of the dome—neutralizing the effects of melt buoyancy and potentially adding strength to the host rock—by ca. 22.6 Ma on the southwestern flank and ca. 21 Ma on the northeastern flank. As shown by a northeastward decrease in 40Ar/39Ar muscovite dates from 22.4 to 20.2 Ma, ductile normal-sense displacement within the Zanskar shear zone ended by ca. 22 Ma, after which the Gianbul dome was exhumed as part of a rigid footwall block below the brittle Zanskar normal fault, tilting an estimated 5°–10°SW into its present orientation.

Sulfur and Metal Fertilization of the Lower Continental Crust

NASA Technical Reports Server (NTRS)

Locmelis, Marek; Fiorentini, Marco L.; Rushmer, Tracy; Arevalo, Ricardo, Jr.; Adam, John; Denyszyn, Steven W.

2015-01-01

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.

Upper extremity palsy following cervical decompression surgery results from a transient spinal cord lesion.

PubMed

Hasegawa, Kazuhiro; Homma, Takao; Chiba, Yoshikazu

2007-03-15

Retrospective analysis. To test the hypothesis that spinal cord lesions cause postoperative upper extremity palsy. Postoperative paresis, so-called C5 palsy, of the upper extremities is a common complication of cervical surgery. Although there are several hypotheses regarding the etiology of C5 palsy, convincing evidence with a sufficient study population, statistical analysis, and clear radiographic images illustrating the nerve root impediment has not been presented. We hypothesized that the palsy is caused by spinal cord damage following the surgical decompression performed for chronic compressive cervical disorders. The study population comprised 857 patients with chronic cervical cord compressive lesions who underwent decompression surgery. Anterior decompression and fusion was performed in 424 cases, laminoplasty in 345 cases, and laminectomy in 88 cases. Neurologic characteristics of patients with postoperative upper extremity palsy were investigated. Relationships between the palsy, and patient sex, age, diagnosis, procedure, area of decompression, and preoperative Japanese Orthopaedic Association score were evaluated with a risk factor analysis. Radiographic examinations were performed for all palsy cases. Postoperative upper extremity palsy occurred in 49 cases (5.7%). The common features of the palsy cases were solely chronic compressive spinal cord disorders and decompression surgery to the cord. There was no difference in the incidence of palsy among the procedures. Cervical segments beyond C5 were often disturbed with frequent multiple segment involvement. There was a tendency for spontaneous improvement of the palsy. Age, decompression area (anterior procedure), and diagnosis (ossification of the posterior longitudinal ligament) are the highest risk factors of the palsy. The results of the present study support our hypothesis that the etiology of the palsy is a transient disturbance of the spinal cord following a decompression procedure. It appears to be caused by reperfusion after decompression of a chronic compressive lesion of the cervical cord. We recommend that physicians inform patients and surgeons of the potential risk of a spinal cord deficit after cervical decompression surgery.

Dynamics of gas-driven eruptions: Experimental simulations using CO2-H2O-polymer system

NASA Astrophysics Data System (ADS)

Zhang, Youxue; Sturtevant, B.; Stolper, E. M.

1997-02-01

We report exploratory experiments simulating gas-driven eruptions using the CO2-H2O system at room temperature as an analog of natural eruptive systems. The experimental apparatus consists of a test cell and a large tank. Initially, up to 1.0 wt% of CO2 is dissolved in liquid water under a pressure of up to 735 kPa in the test cell. The experiment is initiated by suddenly reducing the pressure of the test cell to a typical tank pressure of 10 kPa. The following are the main results: (1) The style of the process depends on the decompression ratio. There is a threshold decompression ratio above which rapid eruption occurs. (2) During rapid eruption, there is always fragmentation at the liquid-vapor interface. Fragmentation may also occur in the flow interior. (3) Initially, the top of the erupting column ascends at a constant acceleration (instead of constant velocity). (4) Average bubble radius grows as t2/3. (5) When viscosity is 20 times that of pure water or greater, a static foam may be stable after expansion to 97% vesicularity. The experiments provide several insights into natural gas-driven eruptions, including (1) the interplay between bubble growth and ascent of the erupting column must be considered for realistic modeling of bubble growth during gas-driven eruptions, (2) buoyant rise of the bubbly magma is not necessary during an explosive volcanic eruption, and (3) CO2-driven limnic eruptions can be explosive. The violence increases with the initial CO2 content dissolved in water.

Decompression models: review, relevance and validation capabilities.

PubMed

Hugon, J

2014-01-01

For more than a century, several types of mathematical models have been proposed to describe tissue desaturation mechanisms in order to limit decompression sickness. These models are statistically assessed by DCS cases, and, over time, have gradually included bubble formation biophysics. This paper proposes to review this evolution and discuss its limitations. This review is organized around the comparison of decompression model biophysical criteria and theoretical foundations. Then, the DCS-predictive capability was analyzed to assess whether it could be improved by combining different approaches. Most of the operational decompression models have a neo-Haldanian form. Nevertheless, bubble modeling has been gaining popularity, and the circulating bubble amount has become a major output. By merging both views, it seems possible to build a relevant global decompression model that intends to simulate bubble production while predicting DCS risks for all types of exposures and decompression profiles. A statistical approach combining both DCS and bubble detection databases has to be developed to calibrate a global decompression model. Doppler ultrasound and DCS data are essential: i. to make correlation and validation phases reliable; ii. to adjust biophysical criteria to fit at best the observed bubble kinetics; and iii. to build a relevant risk function.

The mechanics of granitoid systems and maximum entropy production rates.

PubMed

Hobbs, Bruce E; Ord, Alison

2010-01-13

A model for the formation of granitoid systems is developed involving melt production spatially below a rising isotherm that defines melt initiation. Production of the melt volumes necessary to form granitoid complexes within 10(4)-10(7) years demands control of the isotherm velocity by melt advection. This velocity is one control on the melt flux generated spatially just above the melt isotherm, which is the control valve for the behaviour of the complete granitoid system. Melt transport occurs in conduits initiated as sheets or tubes comprising melt inclusions arising from Gurson-Tvergaard constitutive behaviour. Such conduits appear as leucosomes parallel to lineations and foliations, and ductile and brittle dykes. The melt flux generated at the melt isotherm controls the position of the melt solidus isotherm and hence the physical height of the Transport/Emplacement Zone. A conduit width-selection process, driven by changes in melt viscosity and constitutive behaviour, operates within the Transport Zone to progressively increase the width of apertures upwards. Melt can also be driven horizontally by gradients in topography; these horizontal fluxes can be similar in magnitude to vertical fluxes. Fluxes induced by deformation can compete with both buoyancy and topographic-driven flow over all length scales and results locally in transient 'ponds' of melt. Pluton emplacement is controlled by the transition in constitutive behaviour of the melt/magma from elastic-viscous at high temperatures to elastic-plastic-viscous approaching the melt solidus enabling finite thickness plutons to develop. The system involves coupled feedback processes that grow at the expense of heat supplied to the system and compete with melt advection. The result is that limits are placed on the size and time scale of the system. Optimal characteristics of the system coincide with a state of maximum entropy production rate. This journal is © 2010 The Royal Society

The effect of exercise on venous gas emboli and decompression sickness in human subjects at 4.3 psia

NASA Technical Reports Server (NTRS)

Conkin, Johnny; Waligora, James M.; Horrigan, David J., Jr.; Hadley, Arthur T., III

1987-01-01

The contribution of upper body exercise to altitude decompression sickness while at 4.3 psia after 3.5 or 4.0 hours of 100% oxygen prebreathing at 14.7 psia was determined by comparing the incidence and patterns of venous gas emboli (VGE), and the incidence of Type 1 decompression sickness (DCS) in 43 exercising male subjects and 9 less active male Doppler Technicians (DT's). Each subject exercised for 4 minutes at each of 3 exercise stations while at 4.3 psia. An additional 4 minutes were spent monitoring for VGE by the DT while the subject was supine on an examination cot. In the combined 3.5 and 4.0 hour oxygen prebreathe data, 13 subjects complained of Type 1 DCS compared to 9 complaints from DT's. VGE were detected in 28 subjects compared to 14 detections from DT's. A chi-square analysis of proportions showed no statistically significantly difference in the incidence of Type 1 DCS or VGE between the two groups; however, the average time to detect VGE and to report Tyep 1 DCS symptoms were statistically different. It was concluded that 4 to 6 hours of upper body exercise at metabolic rates simulating EVA metabolic rates hastens the initial detection of VGE and the time to report Type 1 DCS symptoms as compared to DT's.

Pasta nucleosynthesis: Molecular dynamics simulations of nuclear statistical equilibrium

NASA Astrophysics Data System (ADS)

Caplan, M. E.; Schneider, A. S.; Horowitz, C. J.; Berry, D. K.

2015-06-01

Background: Exotic nonspherical nuclear pasta shapes are expected in nuclear matter at just below saturation density because of competition between short-range nuclear attraction and long-range Coulomb repulsion. Purpose: We explore the impact nuclear pasta may have on nucleosynthesis during neutron star mergers when cold dense nuclear matter is ejected and decompressed. Methods: We use a hybrid CPU/GPU molecular dynamics (MD) code to perform decompression simulations of cold dense matter with 51 200 and 409 600 nucleons from 0.080 fm-3 down to 0.00125 fm-3 . Simulations are run for proton fractions YP= 0.05, 0.10, 0.20, 0.30, and 0.40 at temperatures T = 0.5, 0.75, and 1.0 MeV. The final composition of each simulation is obtained using a cluster algorithm and compared to a constant density run. Results: Size of nuclei in the final state of decompression runs are in good agreement with nuclear statistical equilibrium (NSE) models for temperatures of 1 MeV while constant density runs produce nuclei smaller than the ones obtained with NSE. Our MD simulations produces unphysical results with large rod-like nuclei in the final state of T =0.5 MeV runs. Conclusions: Our MD model is valid at higher densities than simple nuclear statistical equilibrium models and may help determine the initial temperatures and proton fractions of matter ejected in mergers.

Premature melt solidification during mold filling and its influence on the as-cast structure

NASA Astrophysics Data System (ADS)

Wu, M.; Ahmadein, M.; Ludwig, A.

2018-03-01

Premature melt solidification is the solidification of a melt during mold filling. In this study, a numerical model is used to analyze the influence of the pouring process on the premature solidification. The numerical model considers three phases, namely, air, melt, and equiaxed crystals. The crystals are assumed to have originated from the heterogeneous nucleation in the undercooled melt resulting from the first contact of the melt with the cold mold during pouring. The transport of the crystals by the melt flow, in accordance with the socalled "big bang" theory, is considered. The crystals are assumed globular in morphology and capable of growing according to the local constitutional undercooling. These crystals can also be remelted by mixing with the superheated melt. As the modeling results, the evolutionary trends of the number density of the crystals and the volume fraction of the solid crystals in the melt during pouring are presented. The calculated number density of the crystals and the volume fraction of the solid crystals in the melt at the end of pouring are used as the initial conditions for the subsequent solidification simulation of the evolution of the as-cast structure. A five-phase volume-average model for mixed columnar-equiaxed solidification is used for the solidification simulation. An improved agreement between the simulation and experimental results is achieved by considering the effect of premature melt solidification during mold filling. Finally, the influences of pouring parameters, namely, pouring temperature, initial mold temperature, and pouring rate, on the premature melt solidification are discussed.

From Mush to Eruption in 1000 Years: Rapid Assembly of the Super-Sized Oruanui Magma Body

NASA Astrophysics Data System (ADS)

Allan, A. S.; Morgan, D. J.; Wilson, C. J.; Millet, M.

2012-12-01

The mush model is useful in explaining how large volumes of evolved silicic melt can be generated in and extracted from a crystal-rich source to form crystal-poor rhyolite magma bodies at shallow crustal levels. It is unclear, however, how processes of melt extraction and/or formation of the melt-dominant magma body might be reflected in the crystal record, and what physical and temporal constraints can be applied. Textural observations and in situ geochemical fingerprints in crystals from pumices of the ~25.4 ka Oruanui eruption (Taupo, New Zealand), offer new perspectives on the processes, physical conditions and timing of the melt extraction and accumulation. Almost all orthopyroxene (opx) and plagioclase (plag) cores have textures showing a period of disequilibrium (partial dissolution and/or resorption) followed by stable conditions (infilling of raddled cores; euhedral rim overgrowths). Trace element contents in amphibole (amph), which was stable and actively crystallizing in all but the most evolved parcels of Oruanui magma, complement textural evidence showing that Mn and Zn liberated by opx dissolution were preferentially sequestered in amph. Concentrations of these opx-loving elements show a prominent inflection when plotted against indices of melt evolution (e.g. Eu/Eu* in amph) marking a return to opx stability and subsequent crystallization. Plagioclase, the most abundant crystal phase, records a more complex history with significant inheritance, but textural and chemical evidence suggests that at least some of Oruanui plag crystals experienced the same departure from and return to stability as the opx. Amphibole trace element data are linked to in situ estimates of P-T-fO2 and melt H2O determined via the Ridolfi et al. (2010: Contrib Mineral Petrol 160, 45) thermobarometer. Textural and geochemical evidence combined with P-T-H2O model values indicate that three major Oruanui crystal phases (opx, amph, plag) record a significant decompression event (from ~250 to ~150 MPa) with associated cooling (from ~900 to 820°C) coupled with the destabilization of opx. We interpret this event to reflect the extraction of rhyolitic melt plus crystals from a mush-like reservoir to form the Oruanui melt-dominant body. This body grew within model pressures of 90-150 MPa (~4-6 km depth) held at 760-800°C, with a generally homogeneous melt composition, as reflected in the consistent rim compositions of the three mineral phases. Fe-Mg diffusion modelling of core-rim boundaries in opx implies that accumulation of the ~530 km3 melt dominant body began only ca. 1000 years before eruption. The traditionally envisaged quasi-static drivers of the mush model (crystal settling, gas sparging, etc.) are difficult to reconcile with the rapidity of this timeframe, and a more dynamic, external influence (e.g. from extensional tectonics) is implied.

Critical Appraisal on Orbital Decompression for Thyroid Eye Disease: A Systematic Review and Literature Search.

PubMed

Boboridis, Konstadinos G; Uddin, Jimmy; Mikropoulos, Dimitrios G; Bunce, Catey; Mangouritsas, George; Voudouragkaki, Irini C; Konstas, Anastasios G P

2015-07-01

Orbital decompression is the indicated procedure for addressing exophthalmos and compressive optic neuropathy in thyroid eye disease. There are an abundance of techniques for removal of orbital bone, fat, or a combination published in the scientific literature. The relative efficacy and complications of these interventions in relation to the specific indications remain as yet undocumented. We performed a systematic review of the current published evidence for the effectiveness of orbital decompression, possible complications, and impact on quality of life. We searched the current databases for medical literature and controlled trials, oculoplastic textbooks, and conference proceedings to identify relevant data up to February 2015. We included randomized controlled trials (RCTs) comparing two or more interventions for orbital decompression. We identified only two eligible RCTs for inclusion in the review. As a result of the significant variability between studies on decompression, i.e., methodology and outcome measures, we did not perform a meta-analysis. One study suggests that the transantral approach and endonasal technique had similar effects in reducing exophthalmos but the latter is safer. The second study provides evidence that intravenous steroids may be superior to primary surgical decompression in the management of compressive optic neuropathy requiring less secondary surgical procedures. Most of the published literature on orbital decompression consists of retrospective, uncontrolled trials. There is evidence from those studies that removal of the medial and lateral wall (balanced) and the deep lateral wall decompression, with or without fat removal, may be the most effective surgical methods with only few complications. There is a clear unmet need for controlled trials evaluating the different techniques for orbital decompression. Ideally, future studies should address the effectiveness, possible complications, quality of life, and cost of each intervention.

Predictors of surgical revision after in situ decompression of the ulnar nerve.

PubMed

Krogue, Justin D; Aleem, Alexander W; Osei, Daniel A; Goldfarb, Charles A; Calfee, Ryan P

2015-04-01

This study was performed to identify factors associated with the need for revision surgery after in situ decompression of the ulnar nerve for cubital tunnel syndrome. This case-control investigation examined all patients treated at one institution with open in situ decompression for cubital tunnel syndrome between 2006 and 2011. The case patients were 44 failed decompressions that required revision, and the controls were 79 randomly selected patients treated with a single operation. Demographic data and disease-specific data were extracted from the medical records. The rate of revision surgery after in situ decompression was determined from our 5-year experience. A multivariate logistic regression model was used based on univariate testing to determine predictors of revision cubital tunnel surgery. Revision surgery was required in 19% (44 of 231) of all in situ decompressions performed during the study period. Predictors of revision surgery included a history of elbow fracture or dislocation (odds ratio [OR], 7.1) and McGowan stage I disease (OR, 3.2). Concurrent surgery with in situ decompression was protective against revision surgery (OR, 0.19). The rate of revision cubital tunnel surgery after in situ nerve decompression should be weighed against the benefits of a less invasive procedure compared with transposition. When considering in situ ulnar nerve decompression, prior elbow fracture as well as patients requesting surgery for mild clinically graded disease should be viewed as risk factors for revision surgery. Patient factors often considered relevant to surgical outcomes, including age, sex, body mass index, tobacco use, and diabetes status, were not associated with a greater likelihood of revision cubital tunnel surgery. Copyright © 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

Binary Colloidal Alloy Test-5: Three-Dimensional Melt

NASA Technical Reports Server (NTRS)

Yodh, Arjun G.

2008-01-01

Binary Colloidal Alloy Test - 5: Three-Dimensional Melt (BCAT-5-3DMelt) photographs initially randomized colloidal samples in microgravity to determine their resulting structure over time. BCAT-5-3D-Melt will allow the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-3D-Melt will look at the mechanisms of melting using three-dimensional temperature sensitive colloidal crystals. Results will help scientists develop fundamental physics concepts previously shadowed by the effects of gravity.

Viscosity Measurement for Tellurium Melt

NASA Technical Reports Server (NTRS)

Lin, Bochuan; Li, Chao; Ban, Heng; Scripa, Rosalia N.; Su, Ching-Hua; Lehoczky, Sandor L.

2006-01-01

The viscosity of high temperature Te melt was measured using a new technique in which a rotating magnetic field was applied to the melt sealed in a suspended ampoule, and the torque exerted by rotating melt flow on the ampoule wall was measured. Governing equations for the coupled melt flow and ampoule torsional oscillation were solved, and the viscosity was extracted from the experimental data by numerical fitting. The computational result showed good agreement with experimental data. The melt velocity transient initiated by the rotating magnetic field reached a stable condition quickly, allowing the viscosity and electrical conductivity of the melt to be determined in a short period.

Mantle ingredients for making the fingerprint of Etna alkaline magmas: implications for shallow partial melting within the complex geodynamic framework of Eastern Sicily

NASA Astrophysics Data System (ADS)

Viccaro, Marco; Zuccarello, Francesco

2017-09-01

Mantle ingredients responsible for the signature of Etnean Na- and K-alkaline magmas and their relationships with short-term geochemical changes of the erupted volcanic rocks have been constrained through a partial melting model that considers major, trace elements and water contents in the produced liquids. Characteristics of the Etnean source for alkaline magmas have been supposed similar to those of the mantle accessible at a regional scale, namely below the Hyblean Plateau. The assumption that the Etnean mantle resembles the one beneath the Hyblean Plateau is justified by the large geochemical affinities of the Etnean hawaiites/K-trachybasalts and the Hyblean hawaiites/alkali basalts for what concerns both trace elements and isotope systematics. We have modeled partial melting of a composite source constituted by two rock types, inferred by lithological and geochemical features of the Hyblean xenoliths: 1) a spinel lherzolite bearing metasomatic, hydrous phases and 2) a garnet pyroxenite in form of veins intruded into the spinel lherzolite. The partial melting modeling has been applied to each rock type and the resulting primary liquids have been then mixed in various proportions. These compositions have been compared with some Etnean alkaline magmas of the post ∼60 ka activity, which were firstly re-equilibrated to mantle conditions through mass balance calculations. Our results put into evidence that concentrations of major and trace elements along with the water obtained from the modeling are remarkably comparable with those of Etnean melts re-equilibrated at primary conditions. Different proportions of the spinel lherzolite with variable modal contents of metasomatic phases and of the garnet pyroxenite can therefore account for the signature of a large spectrum of Etnean alkaline magmas and for their geochemical variability through time, emphasizing the crucial role played by compositional small-scale heterogeneity of the source. These heterogeneities are able to produce magmas with variable compositions and volatile contents, which can then undergo distinct histories of ascent and evolution, leading to the wide range of eruptive styles observed at Mt. Etna volcano. Being partial melting confined in the spinel facies of the mantle, our model implies that the source of Mt. Etna magmas might be rather shallow (<2 GPa; i.e., lesser than ca. 60 km), excluding the presence of deep, plume-like mantle structures responsible for magma generation. Partial melting should occur consequently as a response of mantle decompression within the framework of regional tectonics affecting the Eastern Sicily, which could be triggered by extensional tectonics and/or subduction-induced mantle upwelling.

"White Cord Syndrome" of Acute Hemiparesis After Posterior Cervical Decompression and Fusion for Chronic Cervical Stenosis.

PubMed

Antwi, Prince; Grant, Ryan; Kuzmik, Gregory; Abbed, Khalid

2018-05-01

"White cord syndrome" is a very rare condition thought to be due to acute reperfusion of chronically ischemic areas of the spinal cord. Its hallmark is the presence of intramedullary hyperintense signal on T2-weighted magnetic resonance imaging sequences in a patient with unexplained neurologic deficits following spinal cord decompression surgery. The syndrome is rare and has been reported previously in 2 patients following anterior cervical decompression and fusion. We report an additional case of this complication. A 68-year-old man developed acute left-sided hemiparesis after posterior cervical decompression and fusion for cervical spondylotic myelopathy. The patient improved with high-dose steroid therapy. The rare white cord syndrome following either anterior cervical decompression and fusion or posterior cervical decompression and fusion may be due to ischemic-reperfusion injury sustained by chronically compressed parts of the spinal cord. In previous reports, patients have improved following steroid therapy and acute rehabilitation. Copyright © 2018 Elsevier Inc. All rights reserved.

Chronic Decompression Illness Cognitive Dysfunction Improved with Hyperbaric Oxygen: A Case Report

DTIC Science & Technology

2018-11-09

Altitude chamber exposures are used for training to allow aircrew to experience their hypoxia and pressure effect symptoms. Decompression illness ...chamber decompression illness is around 0.25% (1). Because the evolution of gas within the tissue or vasculature is being treated upon recompression

High-velocity frictional properties of gabbro

NASA Astrophysics Data System (ADS)

Tsutsumi, Akito; Shimamoto, Toshihiko

High-velocity friction experiments have been performed on a pair of hollow-cylindrical specimens of gabbro initially at room temperature, at slip rates from 7.5 mm/s to 1.8 m/s, with total circumferential displacements of 125 to 174 m, and at normal stresses to 5 MPa, using a rotary-shear high-speed friction testing machine. Steady-state friction increases slightly with increasing slip rate at slip rates to about 100 mm/s (velocity strengthening) and it decreases markedly with increasing slip rate at higher velocities (velocity weakening). Steady-state friction in the velocity weakening regime is lower for the non-melting case than the frictional melting case, due perhaps to severe thermal fracturing. A very large peak friction is always recognized upon the initiation of visible frictional melting, presumably owing to the welding of fault surfaces upon the solidification of melt patches. Frictional properties thus change dramatically with increasing displacement at high velocities, and such a non-linear effect must be incorporated into the analysis of earthquake initiation processes.

The dynamics of nucleation and growth of a particle in the ternary alloy melt with anisotropic surface tension.

PubMed

Chen, Ming-Wen; Li, Lin-Yan; Guo, Hui-Min

2017-08-28

The dynamics of nucleation and growth of a particle affected by anisotropic surface tension in the ternary alloy melt is studied. The uniformly valid asymptotic solution for temperature field, concentration field, and interface evolution of nucleation and particle growth is obtained by means of the multiple variable expansion method. The asymptotic solution reveals the critical radius of nucleation in the ternary alloy melt and an inward melting mechanism of the particle induced by the anisotropic effect of surface tension. The critical radius of nucleation is dependent on isotropic surface tension, temperature undercooling, and constitutional undercooling in the ternary alloy melt, and the solute diffusion melt decreases the critical radius of nucleation. Immediately after a nucleus forms in the initial stage of solidification, the anisotropic effect of surface tension makes some parts of its interface grow inward while some parts grow outward. Until the inward melting attains a certain distance (which is defined as "the melting depth"), these parts of interface start to grow outward with other parts. The interface of the particle evolves into an ear-like deformation, whose inner diameter may be less than two times the critical radius of nucleation within a short time in the initial stage of solidification. The solute diffusion in the ternary alloy melt decreases the effect of anisotropic surface tension on the interface deformation.

Optimization of heat transfer during the directional solidification process of 1600 kg silicon feedstock

NASA Astrophysics Data System (ADS)

Hu, Chieh; Chen, Jyh Chen; Nguyen, Thi Hoai Thu; Hou, Zhi Zhong; Chen, Chun Hung; Huang, Yen Hao; Yang, Michael

2018-02-01

In this study, the power ratio between the top and side heaters and the moving velocity of the side insulation are designed to control the shape of the crystal-melt interface during the growth process of a 1600 kg multi-crystalline silicon ingot. The power ratio and insulation gap are adjusted to ensure solidification of the melt. To ensure that the crystal-melt interface is slightly convex in relation to the melt during the entire solidification process, the power ratio should be augmented gradually in the initial stages while being held to a constant value in the middle stages. Initially the gap between the side and the bottom insulation is kept small to reduce thermal stress inside the seed crystals. However, the growth rate will be slow in the early stages of the solidification process. Therefore, the movement of the side insulation is fast in the initial stages but slower in the middle stages. In the later stages, the side insulation gap is fixed. With these modifications, the convexity of the crystal-melt interface in relation to the melt can be maintained during the growth process with an approximately 41% reduction in the thermal stress inside the growing ingot and an 80% reduction in dislocation density along the center line of the ingot compared with the original case.

A current review of core decompression in the treatment of osteonecrosis of the femoral head.

PubMed

Pierce, Todd P; Jauregui, Julio J; Elmallah, Randa K; Lavernia, Carlos J; Mont, Michael A; Nace, James

2015-09-01

The review describes the following: (1) how traditional core decompression is performed, (2) adjunctive treatments, (3) multiple percutaneous drilling technique, and (4) the overall outcomes of these procedures. Core decompression has optimal outcomes when used in the earliest, precollapse disease stages. More recent studies have reported excellent outcomes with percutaneous drilling. Furthermore, adjunct treatment methods combining core decompression with growth factors, bone morphogenic proteins, stem cells, and bone grafting have demonstrated positive results; however, larger randomized trial is needed to evaluate their overall efficacy.

Decompression Device Using a Stainless Steel Tube and Wire for Treatment of Odontogenic Cystic Lesions: A Technical Report.

PubMed

Jung, Eun-Joo; Baek, Jin-A; Leem, Dae-Ho

2014-11-01

Decompression is considered an effective treatment for odontogenic cystic lesions in the jaw. A variety of decompression devices are successfully used for the treatment of keratocystic odontogenic tumors, radicular cysts, dentigerous cysts, and ameloblastoma. The purpose of these devices is to keep an opening between the cystic lesion and the oral environment during treatment. The aim of this report is to describe an effective decompression tube using a stainless steel tube and wire for treatment of jaw cystic lesions.

Prevention of decompression sickness during extravehicular activity in space: a review.

PubMed

Tokumaru, O

1997-12-01

Extended and more frequent extravehicular activity (EVA) is planned in NASA's future space programs. The more EVAs are conducted, the higher the incidence of decompression sickness (DCS) that is anticipated. Since Japan is also promoting the Space Station Freedom project with NASA, DCS during EVA will be an inevitable complication. The author reviewed the pathophysiology of DCS and detailed four possible ways of preventing decompression sickness during EVA in space: (1) higher pressure suit technology; (2) preoxygenation/prebreathing; (3) staged decompression; and (4) habitat or vehicle pressurization. Among these measures, development of zero-prebreathe higher pressure suit technology seems most ideal, but because of economic and technical reasons and in cases of emergency, other methods must also be improved. Unsolved problems like repeated decompression or oxygen toxicity were also listed.

Decompression sickness in breath-hold divers: a review.

PubMed

Lemaitre, Frederic; Fahlman, Andreas; Gardette, Bernard; Kohshi, Kiyotaka

2009-12-01

Although it has been generally assumed that the risk of decompression sickness is virtually zero during a single breath-hold dive in humans, repeated dives may result in a cumulative increase in the tissue and blood nitrogen tension. Many species of marine mammals perform extensive foraging bouts with deep and long dives interspersed by a short surface interval, and some human divers regularly perform repeated dives to 30-40 m or a single dive to more than 200 m, all of which may result in nitrogen concentrations that elicit symptoms of decompression sickness. Neurological problems have been reported in humans after single or repeated dives and recent necropsy reports in stranded marine mammals were suggestive of decompression sickness-like symptoms. Modelling attempts have suggested that marine mammals may live permanently with elevated nitrogen concentrations and may be at risk when altering their dive behaviour. In humans, non-pathogenic bubbles have been recorded and symptoms of decompression sickness have been reported after repeated dives to modest depths. The mechanisms implicated in these accidents indicate that repeated breath-hold dives with short surface intervals are factors that predispose to decompression sickness. During deep diving, the effect of pulmonary shunts and/or lung collapse may play a major role in reducing the incidence of decompression sickness in humans and marine mammals.

Orbital fat decompression for thyroid eye disease: retrospective case review and criteria for optimal case selection.

PubMed

Prat, Marta Calsina; Braunstein, Alexandra L; Dagi Glass, Lora R; Kazim, Michael

2015-01-01

The purpose of this study is to identify the subgroups of thyroid eye disease (TED) patients most likely to benefit from orbital fat decompression. This retrospective study reviews 217 orbits of 109 patients who underwent orbital fat decompression for proptosis secondary to thyroid eye disease. Charts were reviewed for demographic, radiographic, clinical, and surgical data. Three groups of patients were defined for the purposes of statistical analysis: those with proptosis secondary to expansion of the fat compartment (group I), those with proptosis secondary to enlargement of the extraocular muscles (group II), and those with proptosis secondary to enlargement of both fat and muscle (group III). Groups I and II, and those patients with greater preoperative proptosis and those with a history of radiation therapy were most likely to benefit from orbital fat decompression. However, even those in group III or with lesser proptosis appreciated significant benefit. While orbital fat decompression can and, at times, should be combined with bone decompression to treat proptosis resulting from thyroid eye disease, orbital fat decompression alone is associated with lower rates of surgical morbidity, and is especially effective for group I and II patients, those with greater preoperative proptosis, and those with a history of radiation.

Biomechanics of the lower thoracic spine after decompression and fusion: a cadaveric analysis.

PubMed

Lubelski, Daniel; Healy, Andrew T; Mageswaran, Prasath; Benzel, Edward C; Mroz, Thomas E

2014-09-01

Few studies have evaluated the extent of biomechanical destabilization of thoracic decompression on the upper and lower thoracic spine. The present study evaluates lower thoracic spinal stability after laminectomy, unilateral facetectomy, and unilateral costotransversectomy in thoracic spines with intact sternocostovertebral articulations. To assess the biomechanical impact of decompression and fixation procedures on lower thoracic spine stability. Biomechanical cadaveric study. Sequential surgical decompression (laminectomy, unilateral facetectomy, unilateral costotransversectomy) and dorsal fixation were performed on the lower thoracic spine (T8-T9) of human cadaveric spine specimens with intact rib cages (n=10). An industrial robot was used to apply pure moments to simulate flexion-extension (FE), lateral bending (LB), and axial rotation (AR) in the intact specimens and after decompression and fixation. Global range of motion (ROM) between T1-T12 and intrinsic ROM between T7-T11 were measured for each specimen. The decompression procedures caused no statistically significant change in either global or intrinsic ROM compared with the intact state. Instrumentation, however, reduced global motion for AR (45° vs. 30°, p=.0001), FE (24° vs. 19°, p=.02), and LB (47° vs. 36°, p=.0001) and for intrinsic motion for AR (17° vs. 4°, p=.0001), FE (8° vs. 1°, p=.0001), and LB (12° vs. 1°, p=.0001). No significant differences were identified between decompression of the upper versus lower thoracic spine, with trends toward significantly greater ROM for AR and lower ROM for LB in the lower thoracic spine. The lower thoracic spine was not destabilized by sequential unilateral decompression procedures. Addition of dorsal fixation increased segment rigidity at intrinsic levels and also reduced overall ROM of the lower thoracic spine to a greater extent than did fusing the upper thoracic spine (level of the true ribs). Despite the lack of true ribs, the lower thoracic spine was not significantly different compared with the upper thoracic spine in FE and LB after decompression, although there were trends toward significance for greater AR after decompression. In certain patients, instrumentation may not be needed after unilateral decompression of the lower thoracic spine; further validation and additional clinical studies are warranted. Copyright © 2014 Elsevier Inc. All rights reserved.

Lithosphere destabilization by melt percolation during pre-oceanic rifting: Evidence from Alpine-Apennine ophiolitic peridotites

NASA Astrophysics Data System (ADS)

Piccardo, Giovanni; Ranalli, Giorgio

2017-04-01

Orogenic peridotites from Alpine-Apennine ophiolite Massifs (Lanzo, Voltri, External and Internal Ligurides, - NW Italy, and Mt. Maggiore - Corsica) derive from the mantle lithosphere of the Ligurian Tethys. Field/structural and petrologic/geochemical studies provide constraints on the evolution of the lithospheric mantle during pre-oceanic passive rifting of the late Jurassic Ligurian Tethys ocean. Continental rifting by far-field tectonic forces induced extension of the lithosphere by means of km-scale extensional shear zones that developed before infiltration of melts from the asthenosphere (Piccardo and Vissers, 2007). After significant thinning of the lithosphere, the passively upwelling asthenosphere underwent spinel-facies decompression melting along the axial zone of the extensional system. Silica-undersaturated melt fractions percolated through the lithospheric mantle via diffuse/focused porous flow and interacted with the host peridotite through pyroxenes-dissolving/olivine-precipitating melt/rock reactions. Pyroxene dissolution and olivine precipitation modified the composition of the primary silica-undersaturated melts into derivative silica-saturated melts, while the host lithospheric spinel lherzolites were transformed into pyroxene-depleted/olivine-enriched reactive spinel harzburgites and dunites. The derivative liquids interacted through olivine-dissolving/orthopyroxene+plagioclase-crystallizing reactions with the host peridotites that were impregnated and refertilized (Piccardo et al., 2015). The saturated melts stagnated and crystallized in the shallow mantle lithosphere (as testified by diffuse interstitial crystallization of euhedral orthopyroxene and anhedral plagioclase) and locally ponded, forming orthopyroxene-rich/olivine-free gabbro-norite pods (Piccardo and Guarnieri, 2011). Reactive and impregnated peridotites are characterized by high equilibration temperatures (up to 1250 °C) even at low pressure, plagioclase-peridotite facies conditions. This indicates that thermal advection by percolation of hot asthenospheric melts significantly heated the lithospheric mantle column above the melting asthenosphere. Numerical and analogue models show that infiltration of melts results in considerable softening of mantle rocks. Total ithospheric strength can be decreased from 10 to 1 TN m-1 as orders of magnitude and the sin-rift thermo-mechanical erosion of the lithospheric mantle induces significant rheological softening along the axial zone of extension (Corti et al., 2007; Ranalli et al., 2007). Softening of the lithospheric mantle may lead to whole lithospheric failure and consequently to transition from continental extension to oceanic spreading. Therefore, rheological softening caused destabilization of the lithospheric mantle between the future continental margins (Piccardo et al., 2014; Piccardo, 2016) of the Ligurian Tethys. The wedge of destabilized lithosphere favored faster divergence of the continental blocks and enhanced doming and thermal buoyancy of deeper/hotter asthenosphere that rose between the future continental margins and originated aggregated MORB melts (i.e., the oceanic magmatism that formed olivine-gabbro intrusions and pillowed basalt extrusions). Lithosphere destabilization by melt percolation can play a fundamental role in the geodynamic evolution of lithosphere extension causing transition from continental extension to continental break-up to oceanic spreading. Corti, G., Bonini, M., Innocenti, F., Manetti, P., Piccardo, G.B., Ranalli, G., 2007. Journal of Geodynamics, 43, 465-483. Piccardo, G.B., Padovano, M., Guarnieri, L. 2014. Earth-Science Reviews, 138, 409-434. Piccardo, G.B., 2016. Gondwana Research, 39, 230-249. Piccardo, G.B., Vissers, R.L.M., 2007. Journal of Geodynamics, 43, 417-449. Piccardo, G.B., Guarnieri, L., 2011. Lithos, 124, 210-214. Ranalli, G., Piccardo, G.B., Corona-Chavez, P., 2007. Journal of Geodynamics, 43, 450-464.

Dendrite Array Disruption by Bubbles during Re-melting in a Microgravity Environment

NASA Technical Reports Server (NTRS)

Grugel, Richard N.

2012-01-01

As part of the Pore Formation and Mobility Investigation (PFMI), Succinonitrile Water alloys consisting of aligned dendritic arrays were re-melted prior to conducting directional solidification experiments in the microgravity environment aboard the International Space Station. Thermocapillary convection initiated by bubbles at the solid-liquid interface during controlled melt back of the alloy was observed to disrupt the initial dendritic alignment. Disruption ranged from detaching large arrays to the transport of small dendrite fragments at the interface. The role of bubble size and origin is discussed along with subsequent consequences upon reinitiating controlled solidification.

Melting and dissolution of subducting crust at high pressures: the key role of white mica

NASA Astrophysics Data System (ADS)

Schmidt, Max W.; Vielzeuf, Daniel; Auzanneau, Estelle

2004-11-01

Conditions of melting in the crust are generally controlled by the availability of aqueous fluid and, in the absence of fluid, by the stability of hydroxylated minerals. To depths of 80-90 km, melting is controlled by amphibole and biotite. At greater depths, both phases are unstable in crustal compositions. Simultaneous experiments on a mid-ocean ridge basalt (MORB), a greywacke, and a pelite with excess H2O of 0.4-1.4 wt.% demonstrate that, at >100 km depth (≥3.5 GPa), all three bulk compositions are composed of garnet+clinopyroxene+phengite+coesite±kyanite±rutile, phengitic white mica being the only hydrous mineral present at near-melting temperatures. At 4 GPa, melting reactions, temperatures, and initial melt compositions are thus similar in the entire subducted crust. Fluid-saturated initial melting takes place near 850 °C and melt productivities are proportional to phengite contents. All three bulk compositions produce initially slightly peraluminous potassic Si-rich granites with K:Na molar ratios of 1.4-2.0 and containing 8-13 wt.% H2O. The relatively low Na-contents of these melts result from clinopyroxene/melt partitioning coefficients (Dcpx/melt) of 2.2-4.0 at near solidus temperatures. At higher pressures (≥6.5 GPa), we infer that classical melting does not take place. Instead, the bulk H2O-contents (1.5-2.1 wt.%) in the starting materials, although low, are apparently sufficient to dissolve phengite entirely near 1050 °C. This suggests that pressure conditions beyond the singular endpoint (or second critical point) which terminates the wet solidus as defined by Ricci in 1951 [J.E. Ricci, The phase rule and heterogeneous equilibrium, Dover Publications, Inc. New York (1951) 505 p.] were reached for all three bulk compositions. Extraction of these "supercritical" solute-rich (but Na-poor) melts, which contain about 30-40% H2O, or extraction of the potassic granite melts at lower pressure leave an anhydrous garnet+clinopyroxene±coesite±kyanite±rutile residue. Our results suggest that, except for extremely cold subduction zones, the subducting crust will lose all its potassium (and most of B, Be, Rb, and Ba, and other phengite-hosted trace elements) through leaching or melting during its descent to 300 km. The potassium-rich silica-saturated liquids will immediately react with the peridotite when entering the mantle wedge thus creating source regions for ultrapotassic magmas.

Geodynamics of kimberlites on a cooling Earth: Clues to plate tectonic evolution and deep volatile cycles

NASA Astrophysics Data System (ADS)

Tappe, Sebastian; Smart, Katie; Torsvik, Trond; Massuyeau, Malcolm; de Wit, Mike

2018-02-01

Kimberlite magmatism has occurred in cratonic regions on every continent. The global age distribution suggests that this form of mantle melting has been more prominent after 1.2 Ga, and notably between 250-50 Ma, than during early Earth history before 2 Ga (i.e., the Paleoproterozoic and Archean). Although preservation bias has been discussed as a possible reason for the skewed kimberlite age distribution, new treatment of an updated global database suggests that the apparent secular evolution of kimberlite and related CO2-rich ultramafic magmatism is genuine and probably coupled to lowering temperatures of Earth's upper mantle through time. Incipient melting near the CO2- and H2O-bearing peridotite solidus at >200 km depth (1100-1400 °C) is the petrologically most feasible process that can produce high-MgO carbonated silicate melts with enriched trace element concentrations akin to kimberlites. These conditions occur within the convecting asthenospheric mantle directly beneath thick continental lithosphere. In this transient upper mantle source region, variable CHO volatile mixtures control melting of peridotite in the absence of heat anomalies so that low-degree carbonated silicate melts may be permanently present at ambient mantle temperatures below 1400 °C. However, extraction of low-volume melts to Earth's surface requires tectonic triggers. Abrupt changes in the speed and direction of plate motions, such as typified by the dynamics of supercontinent cycles, can be effective in the creation of lithospheric pathways aiding kimberlite magma ascent. Provided that CO2- and H2O-fluxed deep cratonic keels, which formed parts of larger drifting tectonic plates, existed by 3 Ga or even before, kimberlite volcanism could have been frequent during the Archean. However, we argue that frequent kimberlite magmatism had to await establishment of an incipient melting regime beneath the maturing continents, which only became significant after secular mantle cooling to below 1400 °C during post-Archean times, probably sometime shortly after 2 Ga. At around this time kimberlites replace komatiites as the hallmark mantle-derived magmatic feature of continental shields worldwide. The remarkable Mesozoic-Cenozoic 'kimberlite bloom' between 250-50 Ma may represent the ideal circumstance under which the relatively cool and volatile-fluxed cratonic roots of the Pangea supercontinent underwent significant tectonic disturbance. This created more than 60% of world's known kimberlites in a combination of redox- and decompression-related low-degree partial melting. Less than 2% of world's known kimberlites formed after 50 Ma, and the tectonic settings of rare 'young' kimberlites from eastern Africa and western North America demonstrate that far-field stresses on cratonic lithosphere enforced by either continental rifting or cold subduction play a crucial role in enabling kimberlite magma transfer to Earth's surface.

When Is Melting Not Really Melting?

ERIC Educational Resources Information Center

Mangiaracina, Mike

2017-01-01

This 5E cycle of lessons takes students through a fun and thorough study of Silly Putty's properties, progressing from an initial observation of a "melting snowman" toy in the Engage phase to making and "marketing" their own homemade putty in the Evaluate phase. Along the way, students use evidence to construct their own…

Size-Dependent Melting Behavior of Colloidal In, Sn, and Bi Nanocrystals

PubMed Central

Liu, Minglu; Wang, Robert Y.

2015-01-01

Colloidal nanocrystals are a technologically important class of nanostructures whose phase change properties have been largely unexplored. Here we report on the melting behavior of In, Sn, and Bi nanocrystals dispersed in a polymer matrix. This polymer matrix prevents the nanocrystals from coalescing with one another and enables previously unaccessed observations on the melting behavior of colloidal nanocrystals. We measure the melting temperature, melting enthalpy, and melting entropy of colloidal nanocrystals with diameters of approximately 10 to 20 nm. All of these properties decrease as nanocrystal size decreases, although the depression rate for melting temperature is comparatively slower than that of melting enthalpy and melting entropy. We also observe an elevated melting temperature during the initial melt-freeze cycle that we attribute to surface stabilization from the organic ligands on the nanocrystal surface. Broad endothermic melting valleys and very large supercoolings in our calorimetry data suggest that colloidal nanocrystals exhibit a significant amount of surface pre-melting and low heterogeneous nucleation probabilities during freezing. PMID:26573146

Surgical decompression for space-occupying cerebral infarction (the Hemicraniectomy After Middle Cerebral Artery infarction with Life-threatening Edema Trial [HAMLET]): a multicentre, open, randomised trial.

PubMed

Hofmeijer, Jeannette; Kappelle, L Jaap; Algra, Ale; Amelink, G Johan; van Gijn, Jan; van der Worp, H Bart

2009-04-01

Patients with space-occupying hemispheric infarctions have a poor prognosis, with case fatality rates of up to 80%. In a pooled analysis of randomised trials, surgical decompression within 48 h of stroke onset reduced case fatality and improved functional outcome; however, the effect of surgery after longer intervals is unknown. The aim of HAMLET was to assess the effect of decompressive surgery within 4 days of the onset of symptoms in patients with space-occupying hemispheric infarction. Patients with space-occupying hemispheric infarction were randomly assigned within 4 days of stroke onset to surgical decompression or best medical treatment. The primary outcome measure was the modified Rankin scale (mRS) score at 1 year, which was dichotomised between good (0-3) and poor (4-6) outcome. Other outcome measures were the dichotomy of mRS score between 4 and 5, case fatality, quality of life, and symptoms of depression. Analysis was by intention to treat. This trial is registered, ISRCTN94237756. Between November, 2002, and October, 2007, 64 patients were included; 32 were randomly assigned to surgical decompression and 32 to best medical treatment. Surgical decompression had no effect on the primary outcome measure (absolute risk reduction [ARR] 0%, 95% CI -21 to 21) but did reduce case fatality (ARR 38%, 15 to 60). In a meta-analysis of patients in DECIMAL (DEcompressive Craniectomy In MALignant middle cerebral artery infarction), DESTINY (DEcompressive Surgery for the Treatment of malignant INfarction of the middle cerebral arterY), and HAMLET who were randomised within 48 h of stroke onset, surgical decompression reduced poor outcome (ARR 16%, -0.1 to 33) and case fatality (ARR 50%, 34 to 66). Surgical decompression reduces case fatality and poor outcome in patients with space-occupying infarctions who are treated within 48 h of stroke onset. There is no evidence that this operation improves functional outcome when it is delayed for up to 96 h after stroke onset. The decision to perform the operation should depend on the emphasis patients and relatives attribute to survival and dependency.

Comparison of V-4 and V-5 Exercise/Oxygen Prebreathe Protocols to Support Extravehicular Activity in Microgravity

NASA Technical Reports Server (NTRS)

Pollock, N. W.; Natoli, M. J.; Vann, R. D.; Gernhardt, M. L.; Conkin, Johnny

2007-01-01

The Prebreathe Reduction Program (PRP) used exercise during oxygen prebreathe to reduce necessary prebreathe time prior to depressurizing to work in a 4.3 psi suit during extravehicular activity (EVA). Initial testing produced a two-hour protocol incorporating ergometry exercise and a 30 min cycle of depress/repress to 10.2 psi where subjects breathed 26.5% oxygen/balance nitrogen (Phase II - 10 min at 75% peak oxygen consumption [VO2 peak] followed by 40 min intermittent light exercise [ILE] [approx. 5.8 mL-per kilogram- per minute], then 50 min of rest). The Phase II protocol (0/45 DCS) was approved for operations and has been used on 40 EVAs, providing significant time savings compared to the standard 4 h resting oxygen prebreathe. The Phase V effort focused on performing all light in-suit exercise. Two oxygen prebreathe protocols were tested sequentially: V-4) 160 min prebreathe with 150 min of continuous ILE. The entire protocol was completed at 14.7 psi. All exercise involved upper body effort. Exercise continued until decompression. V-5) 160 min prebreathe with 140 min of ILE - first 40 min at 14.7 psi, then 30 min at 10.2 psi (breathing 26.5% oxygen) after a 20 min depress, simulating a suit donning period. Subjects were then repressed to 14.7 psi and performed another 50 min of lower body ILE, followed by 50 min rest before decompression. The V-4 protocol was rejected with 3 DCS/6 person-exposures. Initial V-5 testing has produced 0 DCS/11 person-exposures (ongoing trials). The difference in DCS rate was significant (Fisher Exact p=0.029). The observations of DCS were significantly lower in early V-5 trials than in V-4 trials. Additional studies are required to evaluate the relative contribution of the variables in exercise distribution, the 10.2 psi depress/repress component, pre-decompression rest, or possible variation in total oxygen consumption.

Determining OCT structure and COB Location of the Omani Gulf of Aden Continental Margin from Gravity Inversion, Residual Depth Anomaly and Subsidence Analysis.

NASA Astrophysics Data System (ADS)

Cowie, Leanne; Kusznir, Nick; Leroy, Sylvie; Manatshal, Gianreto

2013-04-01

Knowledge and understanding of the ocean-continent transition (OCT) structure and continent-ocean boundary (COB) location, the distribution of thinned continental crust and lithosphere, its distal extent and the start of unequivocal oceanic crust are of critical importance in evaluating rifted continental margin formation and evolution. In order to determine the OCT structure and COB location for the eastern Gulf of Aden, along the Oman margin, we use a combination of gravity inversion, subsidence analysis and residual depth anomaly (RDA) analysis. Gravity inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning; subsidence analysis has been used to determine the distribution of continental lithosphere thinning; and RDAs have been used to investigate the OCT bathymetric anomalies with respect to expected oceanic bathymetries at rifted margins. The gravity inversion method, which is carried out in the 3D spectral domain, incorporates a lithosphere thermal gravity anomaly and includes a correction for volcanic addition due to decompression melting. Reference Moho depths used in the gravity inversion have been calibrated against seismic refraction Moho depths. RDAs have been calculated by comparing observed and age predicted oceanic bathymetries, using the thermal plate model predictions from Crosby and McKenzie (2009). RDAs have been computed along profiles and have been corrected for sediment loading using flexural back-stripping and decompaction. In addition, gravity inversion crustal basement thicknesses together with Airy isostasy have been used to predict a synthetic RDA. The RDA results show a change in RDA signature and may be used to estimate the distal extent of thinned continental crust and where oceanic crust begins. Continental lithosphere thinning has been determined using flexural back-stripping and subsidence analysis assuming the classical rift model of McKenzie (1978) with a correction for volcanic addition due to decompression melting based on White & McKenzie (1989). Gravity inversion and the "synthetic" gravity derived RDA both show generally normal thickness oceanic crust, with some localised thin oceanic crust. Continental lithosphere thinning factors determined from gravity inversion and subsidence analysis are in good agreement and have been used to constrain COB location along the profile lines. These techniques show that the OCT in the eastern Gulf of Aden, is relatively narrow, with the distance between the COB and the margin hinge measuring less than 100km.

The effects of venting and decompression on Yellow Tang (Zebrasoma flavescens) in the marine ornamental aquarium fish trade

PubMed Central

Tissot, Brian N.; Heidel, Jerry R.; Miller-Morgan, Tim

2015-01-01

Each year, over 45 countries export 30 million fish from coral reefs as part of the global marine ornamental aquarium trade. This catch volume is partly influenced by collection methods that cause mortality. Barotrauma in fish resulting from forced ascent from depth can contribute to post-collection mortality. However, implementing decompression stops during ascent can prevent barotrauma. Conversely, venting (puncturing the swim bladder to release expanded internal gas) following ascent can mitigate some signs of barotrauma like positive buoyancy. Here, we evaluate how decompression and venting affect stress and mortality in the Yellow Tang (Zebrasoma flavescens). We examined the effects of three ascent treatments, each with decompression stops of varying frequency and duration, coupled with or without venting, on sublethal effects and mortality using histology and serum cortisol measurements. In fish subjected to ascent without decompression stops or venting, a mean post-collection mortality of 6.2% occurred within 24 h of capture. Common collection methods in the fishery, ascent without decompression stops coupled with venting, or one long decompression stop coupled with venting, resulted in no mortality. Histopathologic examination of heart, liver, head kidney, and swim bladder tissues in fish 0d and 21d post-collection revealed no significant barotrauma- or venting-related lesions in any treatment group. Ascent without decompression stops resulted in significantly higher serum cortisol than ascent with many stops, while venting alone did not affect cortisol. Future work should examine links in the supply chain following collection to determine if further handling and transport stressors affect survivorship and sublethal effects. PMID:25737809

The floating anchored craniotomy

PubMed Central

Gutman, Matthew J.; How, Elena; Withers, Teresa

2017-01-01

Background: The “floating anchored” craniotomy is a technique utilized at our tertiary neurosurgery institution in which a traditional decompressive craniectomy has been substituted for a floating craniotomy. The hypothesized advantages of this technique include adequate decompression, reduction in the intracranial pressure, obviating the need for a secondary cranioplasty, maintained bone protection, preventing the syndrome of the trephined, and a potential reduction in axonal stretching. Methods: The bone plate is re-attached via multiple loosely affixed vicryl sutures, enabling decompression, but then ensuring the bone returns to its anatomical position once cerebral edema has subsided. Results: From the analysis of 57 consecutive patients analyzed at our institution, we have found that the floating anchored craniotomy is comparable to decompressive craniectomy for intracranial pressure reduction and has some significant theoretical advantages. Conclusions: Despite the potential advantages of techniques that avoid the need for a second cranioplasty, they have not been widely adopted and have been omitted from trials examining the utility of decompressive surgery. This retrospective analysis of prospectively collected data suggests that the floating anchored craniotomy may be applicable instead of decompressive craniectomy. PMID:28713633

Cutting-edge endonasal surgical approaches to thyroid ophthalmopathy.

PubMed

Tyler, Matthew A; Zhang, Caroline C; Saini, Alok T; Yao, William C

2018-04-01

Thyroid orbitopathy is a poorly understood extrathyroidal manifestation of Graves' disease that can cause disfiguring proptosis and vision loss. Orbital decompression surgery for Graves' orbitopathy (GO) can address both cosmetic and visual sequelae of this autoimmune condition. Endonasal endoscopic orbital decompression provides unmatched visualization and access to inferomedial orbital wall and orbital apex. This review examines the state of the art approaches employed in endonasal endoscopic orbital decompression for GO. Review of literature evaluating novel surgical maneuvers for GO. Studies examining the efficacy of endonasal endoscopic orbital decompression are heterogenous and retrospective in design; however, they reveal this approach to be a safe and effective technique in the management of GO. Subtle variations in endoscopic techniques significantly affect postsurgical outcomes and can be tailored to the specific clinical indication in GO making endonasal endoscopic decompression the most versatile approach available. NA.

Dynamic cervicomedullary cord compression and alterations in cerebrospinal fluid dynamics in children with achondroplasia: review of an 11-year surgical case series.

PubMed

Mukherjee, Debraj; Pressman, Barry D; Krakow, Deborah; Rimoin, David L; Danielpour, Moise

2014-09-01

Achondroplasia may be associated with compression at the cervicomedullary junction. Determining which patients are at greatest risk for neurological complications of cervicomedullary compression can be difficult. In the current study the authors reviewed their records to determine the incidence and clinical significance of dynamic cervicomedullary stenosis and obstruction of CSF flow along with surgical outcomes following posterior fossa decompression. The authors reviewed 34 consecutive cases involving symptomatic children with achondroplasia undergoing cervicomedullary decompression performed by a single surgeon over 11 years. Of these patients, 29 had undergone preoperative dynamic MRI of the cervicomedullary junction with cine (cinema) CSF flow studies; 13 of these patients underwent postoperative dynamic MRI studies. Clinical outcomes included changes in polysomnography, head circumference percentile, and fontanel characteristics. Radiographic outcomes included changes in dynamic spinal cord diameter, improvement in CSF flow at the foramen magnum, and change in the Evans ratio. Patients were predominantly female, with a mean age at presentation of 6.6 years and mean follow-up of 3.7 years (range 1-10 years). All patients had moderate to excellent improvement in postoperative polysomnography, slight decrease in average head circumference percentile (from 46.9th percentile to 45.7th percentile), and no subjective worsening of fontanel characteristics. The Evans ratio decreased by 2%, spinal cord diameter increased an average of 3.1 mm, 5.2 mm, and 0.2 mm in the neutral, flexed, and extended positions, respectively, and CSF flow improved qualitatively in all 3 positions. There were no postoperative infections, CSF leaks, or other major complications. None of the patients undergoing initial foramen magnum decompression performed at our medical center required reoperation. Patients with achondroplasia and symptomatic cervicomedullary compression have increased risk of dynamic stenosis at the foramen magnum evident upon dynamic cine MRI. Operative decompression may be offered with low risk of complications or need for reoperation.

Painless motor radiculopathy of the cervical spine: clinical and radiological characteristics and long-term outcomes after operative decompression.

PubMed

Siller, Sebastian; Kasem, Rami; Witt, Thomas-Nikolaus; Tonn, Joerg-Christian; Zausinger, Stefan

2018-03-23

OBJECTIVE Various neurological diseases are known to cause progressive painless paresis of the upper limbs. In this study the authors describe the previously unspecified syndrome of compression-induced painless cervical radiculopathy with predominant motor deficit and muscular atrophy, and highlight the clinical and radiological characteristics and outcomes after surgery for this rare syndrome, along with its neurological differential diagnoses. METHODS Medical records of 788 patients undergoing surgical decompression due to degenerative cervical spine diseases between 2005 and 2014 were assessed. Among those patients, 31 (3.9%, male to female ratio 4.8 to 1, mean age 60 years) presented with painless compressive cervical motor radiculopathy due to neuroforaminal stenosis without signs of myelopathy; long-term evaluation was available in 23 patients with 49 symptomatic foraminal stenoses. Clinical, imaging, and operative findings as well as the long-term course of paresis and quality of life were analyzed. RESULTS Presenting symptoms (mean duration 13.3 months) included a defining progressive flaccid radicular paresis (median grade 3/5) without any history of radiating pain (100%) and a concomitant muscular atrophy (78%); 83% of the patients were smokers and 17% patients had diabetes. Imaging revealed a predominantly anterior nerve root compression at the neuroforaminal entrance in 98% of stenoses. Thirty stenoses (11 patients) were initially decompressed via an anterior surgical approach and 19 stenoses (12 patients) via a posterior surgical approach. Overall reoperation rate due to new or recurrent stenoses was 22%, with time to reoperation shorter in smokers (p = 0.033). Independently of the surgical procedure chosen, long-term follow-up (mean 3.9 years) revealed a stable or improved paresis in 87% of the patients (median grade 4/5) and an excellent general performance and quality of life. CONCLUSIONS Painless cervical motor radiculopathy predominantly occurs due to focal compression of the anterior nerve root at the neuroforaminal entrance. Surgical decompression is effective in stabilizing or improving motor function with a resulting favorable long-term outcome.

Heterogeneous dissemination of projectile materials in the impact melts from Wabar crater, Saudi Arabia

NASA Astrophysics Data System (ADS)

Horz, F.; See, T. H.; Murali, A. V.; Blanchard, D. P.

The initial observations of Spencer (1933) that two distinct impact melts coexist at the 90-m-diameter Wabar crater, Saudi Arabia, is confirmed. A dark or 'black' melt contains on the order of 4 percent meteoritic contamination, while the transparent or 'white' melt contains less than 1 percent. The Fe/Ni ratios in both varieties exhibit considerable scatter on electron-microprobe scales, akin to those reported by others for metal spherules in the black melt. If the meteoritic component is subtracted, both melts are chemically very similar. Clasts engulfed by the Wabar melts were investigated also, as they represent the progenitor lithologies from which the melts formed. Bulk compositions for these clasts reveal subtle differences in modal feldspar content within the quartz-rich Wabar target. Both melts require that a minimum of two target lithologies be present in the Wabar melt zone.

Operative colonoscopic endoscopy.

PubMed

Van Gossum, A; Bourgeois, F; Gay, F; Lievens, P; Adler, M; Cremer, M

1992-01-01

There are several conditions where operative colonoscopy is useful. Acute colonic pseudo-obstruction or Ogilvie's syndrome is characterized by a acute distension of the colon. Although medical management may be sufficient in many cases, endoscopic decompression must be performed when colonic distension is greater than 12 cm. Insertion of decompression tube to avoid rapid recurrence seems to be adequate. In case of massive lower intestinal hemorrhage, colonoscopy seems to be more accurate than mesenteric angiography. Such endoscopic examination requires an experienced endoscopist. Colonoscopic polypectomy has become the standard method for removal of colonic polyps. Factors influencing the rate of complications have been studied. While the number of complications was very low, we have observed that all the major hemorrhages were immediate when the blended current was used, but delayed when the pure coagulation current was applied. Endoscopic laser photocavitation is a valuable palliative method treating rectal adenocarcinoma in well selected patients. Indeed, if the patients survive sufficiently long after initial therapy, it becomes increasingly difficult to achieve persistent palliation with laser therapy.

The risk of developing decompression sickness during air travel following altitude chamber flight.

PubMed

Rush, W L; Wirjosemito, S A

1990-11-01

Approximately 35,000 students are trained annually in United States Air Force (USAF) altitude chambers. Students who depart the training site via aircraft on the same day as their altitude chamber exposure may place themselves at increased risk for decompression sickness (DCS). Air travel as a passenger in the immediate post-chamber flight period is unrestricted by current USAF regulations. A retrospective study was conducted to assess the potential risk involved in such post-chamber flight travel. During the years 1982-87, there were 292 cases of DCS involving altitude chamber students which were subsequently treated with hyperbaric oxygen therapy. Only seven cases were found wherein the student was asymptomatic prior to air travel and subsequently developed DCS. Because the percentage of students who postpone travel is unknown, a precise relative risk could not be determined. Although the number of cases where sequential chamber and aircraft hypobaric exposures has initiated DCS is small, the potential for such occurrences remains a health concern.

[Combined surgical and physical treatment in traumatic painful syndromes of the cervical spine].

PubMed

Stachowski, B; Kaczmarek, J; Nosek, A; Kocur, L

1976-01-01

Clinical observations suggest the need for changing therapeutic management to a more active one in cases of cervical spine injury with damage to the spinal cord and nerve roots or brachial plexus. In 248 patients with these injuries treated initially conservatively the incidence of cervicobrachial pain was analysed. Neuralgic pains were present in 31.5% of cases, causalgic pains in 2.4% and sympathalgic pains in 2%. Conservative treatment conducted in these patients (89 cases) during many months after trauma had no effect on return of mobility. Long-term application of physioterapy prevented only temporarily the development of trophic changes and only partially relieved pains. Only surgical decompression of the spinal cord or spinal nerves with stabilization of damaged vertebrae caused disappearance of painful syndromes and improvement in the motor activity of the extremities. These observations show that early surgical intervention for decompression of the spinal cord, roots or brachial plexus should be advocated in these cases.

Multiple optimization of chemical components and texture of purple maize expanded by IVDV treatment using the response surface methodology.

PubMed

Mrad, Rachelle; Debs, Espérance; Maroun, Richard G; Louka, Nicolas

2014-12-15

A new process, Intensification of Vaporization by Decompression to the Vacuum (IVDV), is proposed for texturizing purple maize. It consists in exposing humid kernels to high steam pressure followed by a decompression to the vacuum. Response surface methodology with three operating parameters (initial water content (W), steam pressure (P) and processing time (T)) was used to study the response parameters: Total Anthocyanins Content, Total Polyphenols Content, Free Radical Scavenging Activity, Expansion Ratio, Hardness and Work Done. P was the most important variable, followed by T. Pressure drop helped the release of bound phenolics arriving to their expulsion outside the cell. Combined with convenient T and W, it caused kernels expansion. Multiple optimization of expansion and chemical content showed that IVDV resulted in good texturization of maize while preserving the antioxidant compounds and activity. Optimal conditions were: W=29%, P=5 bar and T=37s. Copyright © 2014 Elsevier Ltd. All rights reserved.

Acute deterioration in occult Chiari malformation following missile spinal trauma. Case report.

PubMed

Shahlaie, Kiarash; Hartman, Jonathan; Utter, Garth H; Schrot, Rudolph J

2008-04-01

Patients with Chiari malformation (CM) Type I typically experience chronic, slowly progressive symptoms. Rarely, however, do they suffer acute neurological deterioration following an iatrogenic decrease in caudal cerebrospinal fluid pressure due to, for example, a lumbar puncture. To our knowledge, acute neurological deterioration following missile spinal injury in CM has not been previously described. The authors report on a 16-year-old girl who was shot in the abdomen and lumbar spine. Although neurologically intact on initial workup, she developed precipitous quadriplegia and apnea in a delayed fashion. Tonsillar herniation with medullary compression and cerebellar infarction was diagnosed on magnetic resonance imaging. Suboccipital decompression resulted in significant neurological improvement. Well-formed tonsillar ectopia diagnosed at surgery suggested a preexisting CM. The authors conclude that missile spinal trauma can precipitate medullary compression and acute neurological decline, especially in patients with preexisting tonsillar ectopia. Immediate operative decompression to relieve impaction at the cervicomedullary junction can result in significant neurological recovery.

Influence of heat-piping on the initiation and evolution of plate tectonics

NASA Astrophysics Data System (ADS)

Tosi, N.; Baumeister, P. A.

2017-12-01

The onset of plate tectonics on Earth is believed to be caused by local weakening of the lithosphere. If the convective stress locally exceeds a critical value, a plate-breaking event may occur and initiate plate tectonics. Heat-piping is a heat transport process in which a large amount of melt produced at depth migrates either to the surface (extrusive volcanism) or the base of the crust and lithosphere (intrusive volcanism) due to positive buoyancy and over-pressure in the melting region. As a result of melt being extruded and compacted at the surface or within the crust and lithosphere, cold, near surface material is advected downwards. This mechanism, which effectively cools the mantle, has been proposed to dominate the early phases of the Earth's evolution preventing the onset of plate tectonics by leveling the slope of the lithosphere (e.g. Moore & Webb, 2013, Kankanamge & Moore, 2016). This in turn prevents the formation of lithospheric undulations that are necessary to locally build up sufficient stress to initiate a plate-breaking event. In this work we explore the effects of both extrusive and intrusive heat-piping on the critical yield stress needed to start a plate-breaking event and maintain a regime of surface mobilization over long timescales. We use a two-dimensional cylindrical model of compressible thermal convection. The melt generated at depth is extracted instantaneously according to a defined ratio between extrusive and intrusive volcanism. Extrusive melt is deposited at the surface, whereas intrusive melt is assumed to migrate to a depth dependent on the pressure distribution in the column above the melt region. Considering heat piping tends to increase the episodicity in the mobilization of the surface due to the additional local cooling caused by melt extraction but does not affect significantly the critical yield stress necessary to induce lid failure. Our models indicate that the evolution of plate mobility is a stochastic process, strongly dependent on the choice of the initial conditions. Heat-piping does not seem to be a controlling factor for the onset of plate tectonics.

Studies Relating to EVA

NASA Technical Reports Server (NTRS)

1997-01-01

In this session, Session JA1, the discussion focuses on the following topics: The Staged Decompression to the Hypobaric Atmosphere as a Prophylactic Measure Against Decompression Sickness During Repetitive EVA; A New Preoxygenation Procedure for Extravehicular Activity (EVA); Metabolic Assessments During Extra-Vehicular Activity; Evaluation of Safety of Hypobaric Decompressions and EVA From Positions of Probabilistic Theory; Fatty Acid Composition of Plasma Lipids and Erythrocyte Membranes During Simulation of Extravehicular Activity; Biomedical Studies Relating to Decompression Stress with Simulated EVA, Overview; The Joint Angle and Muscle Signature (JAMS) System - Current Uses and Future Applications; and Experimental Investigation of Cooperative Human-Robotic Roles in an EVA Work Site.

Redistribution of Decompression Stop Time from Shallow to Deep Stops Increases Incidence of Decompression Sickness in Air Decompression Dives

DTIC Science & Technology

2011-07-22

year old active duty male diver surfaced from a 170/30 air dive at <corr>12:11<corr> on 24AUG06 using MK 20 FFM and following the A-2 “deep stops...effort, and this episode responded immediately to pressure. AGE is unlikely due to the experience of the diver, the MK 20 FFM characteristics, and...from a 170/30 air dive at <corr>12:11<corr> on 24AUG06 using MK 20 FFM and following the A-2 “deep stops” experimental decompression profile

Unusual Clinical Presentation and Role of Decompressive Craniectomy in Herpes Simplex Encephalitis.

PubMed

Singhi, Pratibha; Saini, Arushi Gahlot; Sahu, Jitendra Kumar; Kumar, Nuthan; Vyas, Sameer; Vasishta, Rakesh Kumar; Aggarwal, Ashish

2015-08-01

Decompressive craniectomy in pediatric central nervous infections with refractory intracranial hypertension is less commonly practiced. We describe improved outcome of decompressive craniectomy in a 7-year-old boy with severe herpes simplex encephalitis and medically refractory intracranial hypertension, along with a brief review of the literature. Timely recognition of refractory intracranial hypertension and surgical decompression in children with herpes simplex encephalitis can be life-saving. Additionally, strokelike atypical presentations are being increasingly recognized in children with herpes simplex encephalitis and should not take one away from the underlying herpes simplex encephalitis. © The Author(s) 2014.

Enhanced Perfusion During Advanced Life Support Improves Survival With Favorable Neurologic Function in a Porcine Model of Refractory Cardiac Arrest

PubMed Central

Debaty, Guillaume; Metzger, Anja; Rees, Jennifer; McKnite, Scott; Puertas, Laura; Yannopoulos, Demetris; Lurie, Keith

2016-01-01

Objective To improve the likelihood for survival with favorable neurologic function after cardiac arrest, we assessed a new advanced life support approach using active compression-decompression cardiopulmonary resuscitation plus an intrathoracic pressure regulator. Design Prospective animal investigation. Setting Animal laboratory. Subjects Female farm pigs (n = 25) (39 ± 3 kg). Interventions Protocol A: After 12 minutes of untreated ventricular fibrillation, 18 pigs were randomized to group A—3 minutes of basic life support with standard cardiopulmonary resuscitation, defibrillation, and if needed 2 minutes of advanced life support with standard cardiopulmonary resuscitation; group B—3 minutes of basic life support with standard cardiopulmonary resuscitation, defibrillation, and if needed 2 minutes of advanced life support with active compression-decompression plus intrathoracic pressure regulator; and group C—3 minutes of basic life support with active compression-decompression cardiopulmonary resuscitation plus an impedance threshold device, defibrillation, and if needed 2 minutes of advanced life support with active compression-decompression plus intrathoracic pressure regulator. Advanced life support always included IV epinephrine (0.05 μg/kg). The primary endpoint was the 24-hour Cerebral Performance Category score. Protocol B: Myocardial and cerebral blood flow were measured in seven pigs before ventricular fibrillation and then following 6 minutes of untreated ventricular fibrillation during sequential 5 minutes treatments with active compression-decompression plus impedance threshold device, active compression-decompression plus intrathoracic pressure regulator, and active compression-decompression plus intrathoracic pressure regulator plus epinephrine. Measurements and Main Results Protocol A: One of six pigs survived for 24 hours in group A versus six of six in groups B and C (p = 0.002) and Cerebral Performance Category scores were 4.7 ± 0.8, 1.7 ± 0.8, and 1.0 ± 0, respectively (p = 0.001). Protocol B: Brain blood flow was significantly higher with active compression-decompression plus intrathoracic pressure regulator compared with active compression-decompression plus impedance threshold device (0.39 ± 0.23 vs 0.27 ± 0.14 mL/min/g; p = 0.03), whereas differences in myocardial perfusion were not statistically significant (0.65 ± 0.81 vs 0.42 ± 0.36 mL/min/g; p = 0.23). Brain and myocardial blood flow with active compression-decompression plus intrathoracic pressure regulator plus epinephrine were significantly increased versus active compression-decompression plus impedance threshold device (0.40 ± 0.22 and 0.84 ± 0.60 mL/min/g; p = 0.02 for both). Conclusion Advanced life support with active compression-decompression plus intrathoracic pressure regulator significantly improved cerebral perfusion and 24-hour survival with favorable neurologic function. These findings support further evaluation of this new advanced life support methodology in humans. PMID:25756411

The Seismic Velocity In Gas-charged Magma

NASA Astrophysics Data System (ADS)

Sturton, S.; Neuberg, J. W.

2001-12-01

Long-period and hybrid events, seen at the Soufrière Hills Volcano, Montserrat, show dominant low frequency content suggesting the seismic wavefield is formed as a result of interface waves at the boundary between a fluid and a solid medium. This wavefield will depend on the impedance contrast between the two media and therefore the difference in seismic velocity. For a gas-charged magma, increasing pressure with depth reduces the volume of gas exsolved, increasing the seismic velocity with depth in the conduit. The seismic radiation pattern along the conduit can then be modelled. Where single events merge into tremor, gliding lines can sometimes be seen in the spectra and indicate either changes in the seismic parameters with time or varying triggering rates of single events.The differential equation describing the time dependence of bubble growth by diffusion is solved numerically for a stationary magma column undergoing a decompression event. The volume of gas is depth dependent and increases with time as the bubbles grow and expand. It is used to calculate the depth and time dependence of the density, pressure and seismic velocity. The effect of different viscosities associated with different magma types and concentration of water in the melt on the rate of bubble growth is explored. Crystal growth, which increases the concentration of water in the melt, affects the amount of gas that can be exsolved.

Direct Observation of Pore Formation and Bubble Mobility during Controlled Melting and Resolidification in Microgravity

NASA Technical Reports Server (NTRS)

Grugel, Richard N.; Anilkumar, A. V.; Lee, C. P.

2004-01-01

Detailed studies on the controlled melting and subsequent re-solidification of succinonitrile were conducted in the microgravity environment aboard the International Space Station (ISS) using the PFMI apparatus (Pore Formation and Mobility Investigation) located in the ISS glovebox facility (GBX). Samples were initially prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. During Space processing, experimental parameters like temperature gradient and translation speed, for melting and solidification, were remotely monitored and controlled from the ground Telescience Center (TSC) at the Marshall Space Flight Center. Real time visualization during controlled melting revealed bubbles of different sizes initiating at the solid/liquid interface, and traveling up the temperature gradient ahead of them. Subsequent controlled re-solidification of the SCN revealed the details of porosity formation and evolution. A preliminary analysis of the melt back and re- solidification and its implications to future microgravity materials processing is presented and discussed.

Core decompression of the equine navicular bone: an in vivo study in healthy horses.

PubMed

Jenner, Florien; Kirker-Head, Carl

2011-02-01

To determine the physiologic response of the equine navicular bone to core decompression surgery in healthy horses. Experimental in vivo study. Healthy adult horses (n=6). Core decompression was completed by creating three 2.5-mm-diameter drill channels into the navicular bone under arthroscopic control. The venous (P(V)), arterial (P(A)), articular (P(DIPJ)), and intraosseous pressures (IOP) were recorded before and after decompression drilling. Each IOP measurement consisted of a baseline (IOP(B)) and a stress test (intramedullary injection of saline solution, IOP(S)) recording. Lameness was assessed subjectively and using force plate gait analysis. Fluorochrome bone labeling was performed. Horses were euthanatized at 12 weeks. Navicular bone mineral density (BMD) was measured, and bone histology evaluated. Peak IOP (IOP(max)) after stress testing was significantly (P<.05) reduced immediately after core decompression; however, the magnitude of these effects was decreased at 3 and 6 weeks after decompression. A significant (P<.05) correlation existed between IOP(max) and BMD. No lameness was observed beyond the first week after surgery. Substantial remodeling and neovascularization was evident adjacent the surgery sites. Navicular bone core decompression surgery reduced IOP(max), and, with the exception of a mild short-lived lameness, caused no other adverse effects in healthy horses during the 12-week study period. © Copyright 2011 by The American College of Veterinary Surgeons.

Decompression of keratocystic odontogenic tumors leading to increased fibrosis, but without any change in epithelial proliferation.

PubMed

Awni, Sarah; Conn, Brendan

2017-06-01

The aim of this study was to investigate whether decompression treatment induces changes in the histology or biologic behavior of keratocystic odontogenic tumor (KCOT). Seventeen patients with KCOT underwent decompression treatment with or without enucleation. Histologic evaluation and immunohistochemical expression of p53, Ki-67, and Bcl-2 were analyzed by using conventional microscopy. KCOT showed significantly increased fibrosis (P = .01) and a subjective reduction in mitotic activity (P = .03) after decompression. There were no statistically significant changes in the expression of proliferation markers. An increase in daughter-cysts or epithelial rests was seen after decompression (P = .04). Recurrence was noted in four of 16 cases, and expression of p53 was strongly correlated with prolonged duration of treatment (P = .01) and intense inflammatory changes (P = .02). Structural changes in the KCOT epithelium or capsule following decompression facilitate surgical removal of the tumor. There was no statistical evidence that decompression influences expression of proliferation markers in the lining, indicating that the potential for recurrence may not be restricted to the cellular level. The statistically significant increase of p53 expression with increased duration of treatment and increase of inflammation may also indicate the possibility of higher rates of recurrence with prolonged treatment and significant inflammatory changes. Crown Copyright © 2016. Published by Elsevier Inc. All rights reserved.

Changes in optical coherence tomography measurements after orbital wall decompression in dysthyroid optic neuropathy.

PubMed

Park, Kyung-Ah; Kim, Yoon-Duck; Woo, Kyung In

2018-06-01

The purpose of our study was to assess changes in peripapillary retinal nerve fiber layer (RNFL) thickness after orbital wall decompression in eyes with dysthyroid optic neuropathy (DON). We analyzed peripapillary optical coherence tomography (OCT) images (Cirrus HD-OCT) from controls and patients with DON before and 1 and 6 months after orbital wall decompression. There was no significant difference in mean preoperative peripapillary retinal nerve fiber layer thickness between eyes with DON and controls. The superior and inferior peripapillary RNFL thickness decreased significantly 1 month after decompression surgery compared to preoperative values (p = 0.043 and p = 0.022, respectively). The global average, superior, temporal, and inferior peripapillary RNFL thickness decreased significantly 6 months after decompression surgery compared to preoperative values (p = 0.015, p = 0.028, p = 0.009, and p = 0.006, respectively). Patients with greater preoperative inferior peripapillary RNFL thickness tended to have better postoperative visual acuity at the last visit (p = 0.024, OR = 0.926). Our data revealed a significant decrease in peripapillary RNFL thickness postoperatively after orbital decompression surgery in patients with DON. We also found that greater preoperative inferior peripapillary RNFL thickness was associated with better visual outcomes. We suggest that RNFL thickness can be used as a prognostic factor for DON before decompression surgery.

40 CFR 63.7734 - How do I demonstrate initial compliance with the emissions limitations that apply to me?

Code of Federal Regulations, 2013 CFR

2013-07-01

... used to demonstrate compliance. (1) For each electric arc metal melting furnace, electric induction metal melting furnace, or scrap preheater at an existing iron and steel foundry, (i) The average PM... not exceed 0.0002 gr/dscf. (4) For each electric induction metal melting furnace or scrap preheater at...

40 CFR 63.7734 - How do I demonstrate initial compliance with the emissions limitations that apply to me?

Code of Federal Regulations, 2010 CFR

2010-07-01

... used to demonstrate compliance. (1) For each electric arc metal melting furnace, electric induction metal melting furnace, or scrap preheater at an existing iron and steel foundry, (i) The average PM... not exceed 0.0002 gr/dscf. (4) For each electric induction metal melting furnace or scrap preheater at...

40 CFR 63.7734 - How do I demonstrate initial compliance with the emissions limitations that apply to me?

Code of Federal Regulations, 2012 CFR

2012-07-01

... used to demonstrate compliance. (1) For each electric arc metal melting furnace, electric induction metal melting furnace, or scrap preheater at an existing iron and steel foundry, (i) The average PM... not exceed 0.0002 gr/dscf. (4) For each electric induction metal melting furnace or scrap preheater at...

40 CFR 63.7734 - How do I demonstrate initial compliance with the emissions limitations that apply to me?

Code of Federal Regulations, 2014 CFR

2014-07-01

... used to demonstrate compliance. (1) For each electric arc metal melting furnace, electric induction metal melting furnace, or scrap preheater at an existing iron and steel foundry, (i) The average PM... not exceed 0.0002 gr/dscf. (4) For each electric induction metal melting furnace or scrap preheater at...

40 CFR 63.7734 - How do I demonstrate initial compliance with the emissions limitations that apply to me?

Code of Federal Regulations, 2011 CFR

2011-07-01

... used to demonstrate compliance. (1) For each electric arc metal melting furnace, electric induction metal melting furnace, or scrap preheater at an existing iron and steel foundry, (i) The average PM... not exceed 0.0002 gr/dscf. (4) For each electric induction metal melting furnace or scrap preheater at...

Abnormal Eu behavior at formation of H2O- and Cl-bearing fluids during degassing of granite magmas

NASA Astrophysics Data System (ADS)

Lukanin, Oleg

2010-05-01

One of the important features of REE behavior in the process of decompression degassing of granite melts is the presence of europium anomalies in REE spectrum of forming fluid phase. Negative Eu anomaly in REE spectrum of fluids enriched by chlorine that were formed under high pressures at early stages of degassing relative to REE spectrum of granite melts may take place. Negative Eu anomaly in fluid is replaced by positive one with pressure decrease and decline of Cl concentration in fluid [1, 2]. Observable unique features of europium redistribution between fluid and melt find an explanation in such a fact that Eu in contrast to the other REE under oxidation-reduction conditions, being typical for magmatic process, is present in acidic silica-alumina melts in two valency forms Eu3+ and Eu2+ whereas the dominant form for the other REE in such a melts is (REE)3+ [3, 4]. From the analysis of melt-fluid exchange reactions with participation of two valency forms of europium Eu3+ and Eu2+ follows that the total distribution coefficient of Eu between fluid and melt D(Eu)f-m is equal as a first approximation to [5, 6]: D(Eu)f-m = a1α [C(Cl)f]3 + a2 (1 - α)[C(Cl)f]2, where C(Cl)f - the concentration of Cl in fluid, α = Eu3+/(Eu3+ + Eu2+), i.e. fraction of Eu3+ from the general amount of europium in the melt, and, a1anda2- constants that can be approximately estimated from empirical data upon Eu fluid/melt distribution. The equation given allows to estimate the influence of oxidizing condition of europium on sign and size of Eu anomaly, which is expressed by Eu/Eu# ratio, where Eu is real concentration of europium in fluid being in equilibrium with melt with constant Eu3+/(Eu3+ + Eu2+) ratio, and Eu# is possible "virtual" concentration of europium that could be in the same fluid provided that all europium as other REE as well were exclusively present in trivalent form. The sign and size of Eu anomaly in fluid depends upon Cl concentration in fluid and Eu3+/Eu2+ ratio in melt. The abnormal behavior of Eu shows itself the stronger, the lower fO2and, accordingly, the more fraction of Eu2+is present in melt. The work is supported of the Geosciences Department of the Russian Academy of Science (the program 2- 2010) and RFBR (grant 08-05-00022). References [1] Reed M.J., Candela Ph.A., Piccoli Ph.M. Contrib. Mineral. Petrol. 2000. V. 140. P. 251-262. [2] Lukanin O.A., Dernov-Pegarev V.F. Vestnik Otd. Nauk Zemle RAN, No 1(25)'2007 URL: http://www.scgis.ru/russian/cp1251/h_dgggms/1-2007/informbul-1_2007/term-30e.pdf [3] Drake M.J. Geochim. Cosmochim. Acta. 1975. V. 39. P. 55-64. [4] Wilke M. Behrens H. Contrib. Mineral. Petrol. 1999. V. 137. P. 102-114. [5] Lukanin O.A. Vestnik Otd. Nauk o Zemle RAN, No 1(26)'2008. URL: http://www.scgis.ru/russian/cp1251/h_dgggms/1-2008/informbul-1_2008/magm-20e.pdf [6] Lukanin O.A., Dernov-Pegarev V.F. Geochemistry International, 2010 (in press)

The evolution of passive rifting: contributions from field and laboratory studies to the interpretation of modelling results

NASA Astrophysics Data System (ADS)

Piccardo, Giovanni; Ranalli, Giorgio

2015-04-01

Direct field/laboratory, structural/petrologic investigations of mantle lithosphere from orogenic peridotites in Alpine-Apennine ophiolites provide significant constraints to the rift evolution of the Jurassic Ligurian Tethys ocean (Piccardo et al., 2014, and references therein). These studies have shown that continental extension and passive rifting were characterized by an important syn-rift "hidden" magmatic event, pre-dating continental break-up and sea-floor spreading. Occurrence of km-scale bodies of reactive spinel-harzburgites and impregnated plagioclase-peridotites, formed by melt/peridotite interaction, and the lack of any extrusive counterpart, show that the percolating magmas remained stored inside the mantle lithosphere. Petrologic-geochemical data/modelling and mineral Sm/Nd age constraints evidence that the syn-rift melt infiltration and reactive porous-flow percolation through the lithosphere were induced by MORB-type parental liquids formed by decompression melting of the passively upwelling asthenosphere. Melt thermal advection through, and melt stagnation within the lithosphere, heated the mantle column to temperatures close to the dry peridotite solidus ("asthenospherization" of mantle lithosphere). Experimental results of numerical/analogue modelling of the Ligurian rifting, based on field/laboratory constraints, show that: (1) porous flow percolation of asthenospheric melts resulted in considerable softening of the mantle lithosphere, decreasing total strength TLS from 10 to 1 TN m-1 as orders of magnitude (Ranalli et al. 2007), and (2) the formation of an axial lithospheric mantle column, with softened rheological characteristics (Weakened Lithospheric Mantle - WLM), induced necking instability in the extending lithosphere and subsequent active upwelling of the asthenosphere inside the WLM zone (Corti et al., 2007). Therefore, the syn-rift hidden magmatism (melt thermo-chemical-mechanical erosion, melt thermal advection and melt storage) caused important compositional and rheological modifications in the mantle lithosphere and played a fundamental role in the evolution of rifting, favouring, in particular, faster divergence of future continental margins and active upwelling of deeper/hotter asthenosphere. Active divergent forces probably changed the extension regime from passive to active rifting (as envisaged by Huismans et al., 2001). Accordingly, melt thermal advection and melt storage, and the rheological modifications induced in the mantle lithosphere, had a fundamental role in the evolution of the Ligurian rifting (Piccardo, 2014; Piccardo et al., 2014). Observations from the natural laboratory are pivotal when interpreting modelling results on the formation of rifted continental margins by extension of continental lithosphere leading to seafloor spreading. The rheological characteristics of the melt-modified mantle lithosphere can provide natural constraints for the interpretation of variously termed components ("oceanic lithosphere, Huismans & Beaumont, 2014; "oceanic and syn-rift lithospheric mantle", Whitmarsh & Manatschal, 2012), located in some models at non-oceanic, sub-continental settings, either below the extending continental crust or between the sub-continental lithosphere and the upwelling asthenosphere. Corti, G., Piccardo, G.B., Ranalli, G., et al., 2007. J. Geodynamics, 43, 465-483. Huismans, R.S., Beaumont, C., 2014. EPSL, 407, 148-162. Huismans, R.S., Podladchikov, Y.Y., Cloetingh, S., 2001, J. Geophys. Res. 106(11), 271-291. Piccardo, G.B., 2014. Geol. Soc. London, Spec. Publ., online 413, http://dx.doi.org/10.1144/SP413.7. Piccardo, G.B., et al., 2014. Earth-Science Reviews, http://dx.doi.org/10.1016/j.earscirev.2014.07.002. Ranalli, G., Piccardo, G.B., Corona-Chavez, P., 2007. J. Geodynamics, 43, 450-464. Whitmarsh, R.B., Manatschal, G., 2012. Roberts & Bally (eds), http://eprints.soton.ac.uk/id/eprint/358832.

Decompression Mechanisms and Decompression Schedule Calculations.

DTIC Science & Technology

1984-01-20

phisiology - The effects of altitude. Handbook of Physiology, Section 3: Respiration, Vol. II. W.O. Fenn and H. Rahn eds. Wash, D.C.; Am. Physiol. Soc. 1 4...decompression studies from other laboratories. METHODS Ten experienced and physically qualified divers ( ages 22-42) were compressed at a rate of 60...STATISTICS* --- ---------------------------------------------------------- EXPERIMENT N AGE (yr) HEIGHT (cm) WEIGHT (Kg) BODY FAT

Spreading Depressions as Secondary Insults after Traumatic Injury to the Human Brain

DTIC Science & Technology

2012-09-01

earlier and larger craniotomies and better outcomes, despite being similar in initial injury characteristics compared to KCH patients. VCU patients also...enrolled patients with acute TBI who met the following inclusion criteria: clinical decision for craniotomy for lesion evacuation, de compression, or... craniotomies for evacuation of intracranial mass lesions or cerebral decompression, a median of 9·9 h (IQR 4·5–26·3) after trauma

Zero-gravity venting of three refrigerants

NASA Technical Reports Server (NTRS)

Labus, T. L.; Aydelott, J. C.; Amling, G. E.

1974-01-01

An experimental investigation of venting cylindrical containers partially filled with initially saturated liquids under zero-gravity conditions was conducted in the NASA Lewis Research Center 5-second zero-gravity facility. The effect of interfacial mass transfer on the ullage pressure response during venting was analytically determined, based on a conduction analysis applied to an infinitely planer (flat) liquid-vapor interface. This pressure response was compared with both the experimental results and an adiabatic decompression computation.

Enough positive rate of paraspinal mapping and diffusion tensor imaging with levels which should be decompressed in lumbar spinal stenosis.

PubMed

Chen, Hua-Biao; Zhong, Zhi-Wei; Li, Chun-Sheng; Bai, Bo

2016-07-01

In lumbar spinal stenosis, correlating symptoms and physical examination findings with decompression levels based on common imaging is not reliable. Paraspinal mapping (PM) and diffusion tensor imaging (DTI) may be possible to prevent the false positive occurrences with MRI and show clear benefits to reduce the decompression levels of lumbar spinal stenosis than conventional magnetic resonance imaging (MRI) + neurogenic examination (NE). However, they must have enough positive rate with levels which should be decompressed at first. The study aimed to confirm that the positive of DTI and PM is enough in levels which should be decompressed in lumbar spinal stenosis. The study analyzed the positive of DTI and PM as well as compared the preoperation scores to the postoperation scores, which were assessed preoperatively and at 2 weeks, 3 months 6 months, and 12 months postoperatively. 96 patients underwent the single level decompression surgery. The positive rate among PM, DTI, and (PM or DTI) was 76%, 98%, 100%, respectively. All post-operative Oswestry Disability Index (ODI), visual analog scale for back pain (VAS-BP) and visual analog scale for leg pain (VAS-LP) scores at 2 weeks postoperatively were measured improvement than the preoperative ODI, VAS-BP and VAS-LP scores with statistically significance (p-value = 0.000, p-value = 0.000, p-value = 0.000, respectively). In degenetive lumbar spinal stenosis, the positive rate of (DTI or PM) is enough in levels which should be decompressed, thence using the PM and DTI to determine decompression levels will not miss the level which should be operated. Copyright © 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.

Original endoscopic orbital decompression of lateral wall through hairline approach for Graves' ophthalmopathy: an innovation of balanced orbital decompression.

PubMed

Gong, Yi; Yin, Jiayang; Tong, Boding; Li, Jingkun; Zeng, Jiexi; Zuo, Zhongkun; Ye, Fei; Luo, Yongheng; Xiao, Jing; Xiong, Wei

2018-01-01

Orbital decompression is an important surgical procedure for treatment of Graves' ophthalmopathy (GO), especially in women. It is reasonable for balanced orbital decompression of the lateral and medial wall. Various surgical approaches, including endoscopic transnasal surgery for medial wall and eye-side skin incision surgery for lateral wall, are being used nowadays, but many of them lack the validity, safety, or cosmetic effect. Endoscopic orbital decompression of lateral wall through hairline approach and decompression of medial wall via endoscopic transnasal surgery was done to achieve a balanced orbital decompression, aiming to improve the appearance of proptosis and create conditions for possible strabismus and eyelid surgery afterward. From January 29, 2016 to February 14, 2017, this surgery was performed on 41 orbits in 38 patients with GO, all of which were at inactive stage of disease. Just before surgery and at least 3 months after surgery, Hertel's ophthalmostatometer and computed tomography (CT) were used to check proptosis and questionnaires of GO quality of life (QOL) were completed. The postoperative retroversion of eyeball was 4.18±1.11 mm (Hertel's ophthalmostatometer) and 4.17±1.14 mm (CT method). The patients' QOL was significantly improved, especially the change in appearance without facial scar. The only postoperative complication was local soft tissue depression at temporal region. Obvious depression occurred in four cases (9.76%), which can be repaired by autologous fat filling. This surgery is effective, safe, and cosmetic. Effective balanced orbital decompression can be achieved by using this original and innovative surgery method. The whole manipulation is safe and controllable under endoscope. The postoperative scar of endoscopic surgery through hairline approach is covered by hair and the anatomic structure of anterior orbit is not impacted.

Percutaneous laser disc decompression versus conventional microdiscectomy for patients with sciatica: Two-year results of a randomised controlled trial.

PubMed

Brouwer, Patrick A; Brand, Ronald; van den Akker-van Marle, M Elske; Jacobs, Wilco Ch; Schenk, Barry; van den Berg-Huijsmans, Annette A; Koes, Bart W; Arts, Mark A; van Buchem, M A; Peul, Wilco C

2017-06-01

Background Percutaneous laser disc decompression is a minimally invasive treatment, for lumbar disc herniation and might serve as an alternative to surgical management of sciatica. In a randomised trial with two-year follow-up we assessed the clinical effectiveness of percutaneous laser disc decompression compared to conventional surgery. Materials and methods This multicentre randomised prospective trial with a non-inferiority design, was carried out according to an intent-to-treat protocol with full institutional review board approval. One hundred and fifteen eligible surgical candidates, with sciatica from a disc herniation smaller than one-third of the spinal canal, were randomly allocated to percutaneous laser disc decompression ( n = 55) or conventional surgery ( n = 57). The main outcome measures for this trial were the Roland-Morris Disability Questionnaire for sciatica, visual analogue scores for back and leg pain and the patient's report of perceived recovery. Results The primary outcome measures showed no significant difference or clinically relevant difference between the two groups at two-year follow-up. The re-operation rate was 21% in the surgery group, which is relatively high, and with an even higher 52% in the percutaneous laser disc decompression group. Conclusion At two-year follow-up, a strategy of percutaneous laser disc decompression, followed by surgery if needed, resulted in non-inferior outcomes compared to a strategy of microdiscectomy. Although the rate of reoperation in the percutaneous laser disc decompression group was higher than expected, surgery could be avoided in 48% of those patients that were originally candidates for surgery. Percutaneous laser disc decompression, as a non-surgical method, could have a place in the treatment arsenal of sciatica caused by contained herniated discs.

Paraspinal muscle impingement causing acute Brown-Sequard syndrome after posterior cervical decompression.

PubMed

Jost, Patrick W; Marawar, Satyajit; O'Leary, Patrick F

2010-04-01

A case report. To present a previously unreported cause of neurologic compromise after cervical spine surgery. Several different causes of postoperative neurologic deficit have been reported in the literature. The authors present a case of acute postoperative paralysis after posterior cervical decompression by a mechanism that has not yet been reported in the literature. A 54-year-old muscular, short-statured man underwent posterior cervical laminectomy from C3-C5 without instrumentation and left C5 foraminotomy. Within hours of leaving the operating room, he began to develop postoperative neurologic deficits in his extremities, which progressed to a classic Brown-Sequard syndrome. Magnetic resonance imaging revealed regional kyphosis and large swollen paraspinal muscles impinging on the spinal cord without epidural hematoma. Emergent operative re-exploration confirmed these findings; large, swollen paraspinal muscles, a functioning drain, and no hematoma were found. The patient was treated with immediate corticosteroids at the time of initial diagnosis, and emergent re-exploration and debulking of the paraspinal muscles. The patient had complete recovery of neurologic function to his preoperative baseline after the second procedure but required a third procedure in which anterior discectomy and fusion at C4-C5 was performed, which led to improvement of his preoperative symptoms. When performing posterior cervical decompression, surgeons must be aware of the potential for loss of normal lordosis and anterior displacement of paraspinal muscles against the spinal cord, especially in muscular patients.

Fictitious Supercontinent Cycles

NASA Astrophysics Data System (ADS)

Marvin Herndon, J.

2014-05-01

"Supercontinent cycles" or "Wilson cycles" is the idea that before Pangaea there were a series of supercontinents that each formed and then broke apart and separated before colliding again, re-aggregating, and suturing into a new supercontinent in a continuing sequence. I suggest that "supercontinent cycles" are artificial constructs, like planetary orbit epicycles, attempts to describe geological phenomena within the framework of problematic paradigms, namely, planetesimal Earth formation and plate tectonics' mantle convection. The so-called 'standard model of solar system formation' is problematic as it would lead to insufficiently massive planetary cores and necessitates additional ad hoc hypotheses such as the 'frost line' between Mars and Jupiter to explain planetary differences and whole-planet melting to explain core formation from essentially undifferentiated matter. The assumption of mantle convection is crucial for plate tectonics, not only for seafloor spreading, but also for continental movement; continent masses are assumed to ride atop convection cells. In plate tectonics, plate collisions are thought to be the sole mechanism for fold-mountain formation. Indeed, the occurrence of mountain chains characterized by folding which significantly predate the breakup of Pangaea is the primary basis for assuming the existence of supercontinent cycles with their respective periods of ancient mountain-forming plate collisions. Mantle convection is physically impossible. Rayleigh Number justification has been misapplied. The mantle bottom is too dense to float to the surface by thermal expansion. Sometimes attempts are made to obviate the 'bottom heavy' prohibition by adopting the tacit assumption that the mantle behaves as an ideal gas with no viscous losses, i.e., 'adiabatic'. But the mantle is a solid that does not behave as an ideal gas as evidenced by earthquakes occurring at depths as great as 660 km. Absent mantle convection, plate tectonics is not valid and there is no motive force for driving supercontinent cycles. The reasonable conclusion one must draw, as in the case of epicycles, is there must exist a new and fundamentally different geoscience paradigm which obviates the problems inherent in plate tectonics and in planetesimal Earth formation and yet better explains geological features. I have disclosed a new indivisible geoscience paradigm, called Whole-Earth Decompression Dynamics (WEDD), that begins with and is the consequence of our planet's early formation as a Jupiter-like gas giant and which permits deduction of: (1) Earth's internal composition and highly-reduced oxidation state; (2) Core formation without whole-planet melting; (3) Powerful new internal energy sources, protoplanetary energy of compression and georeactor nuclear fission energy; (4) Mechanism for heat emplacement at the base of the crust; (5) Georeactor geomagnetic field generation; (6) Decompression-driven geodynamics that accounts for the myriad of observations attributed to plate tectonics without requiring physically-impossible mantle convection, and; (7) A mechanism for fold-mountain formation that does not necessarily require plate collision. The latter obviates the necessity to assume supercontinent cycles. The fundamental basis of geodynamics is this: In response to decompression-driven Earth volume increases, cracks form to increase surface area and mountain ranges characterized by folding form to accommodate changes in curvature. Resources at NuclearPlanet.com .

[Theoretical analysis of recompression-based therapies of decompression illness].

PubMed

Nikolaev, V P; Sokolov, G M; Komarevtsev, V N

2011-01-01

Theoretical analysis is concerned with the benefits of oxygen, air and nitrogen-helium-oxygen recompression schedules used to treat decompression illness in divers. Mathematical modeling of tissue bubbles dynamics during diving shows that one-hour oxygen recompression to 200 kPa does not diminish essentially the size of bubble enclosed in a layer that reduces tenfold the intensity of gas diffusion from bubbles. However, these bubbles dissolve fully in all the body tissues equally after 2-hr. air compression to 800 kPa and ensuing 2-d decompression by the Russian navy tables, and 1.5-hr. N-He-O2 compression to this pressure followed by 5-day decompression. The overriding advantage of the gas mixture recompression is that it obviates the narcotic action of nitrogen at the peak of chamber pressure and does not create dangerous tissue supersaturation and conditions for emergence of large bubbles at the end of decompression.

Cutting‐edge endonasal surgical approaches to thyroid ophthalmopathy

PubMed Central

Tyler, Matthew A.; Zhang, Caroline C.; Saini, Alok T.

2018-01-01

Objective Thyroid orbitopathy is a poorly understood extrathyroidal manifestation of Graves' disease that can cause disfiguring proptosis and vision loss. Orbital decompression surgery for Graves' orbitopathy (GO) can address both cosmetic and visual sequelae of this autoimmune condition. Endonasal endoscopic orbital decompression provides unmatched visualization and access to inferomedial orbital wall and orbital apex. This review examines the state of the art approaches employed in endonasal endoscopic orbital decompression for GO. Methods Review of literature evaluating novel surgical maneuvers for GO. Results Studies examining the efficacy of endonasal endoscopic orbital decompression are heterogenous and retrospective in design; however, they reveal this approach to be a safe and effective technique in the management of GO. Conclusion Subtle variations in endoscopic techniques significantly affect postsurgical outcomes and can be tailored to the specific clinical indication in GO making endonasal endoscopic decompression the most versatile approach available. Level of Evidence NA. PMID:29721541

Structural Confirmation of a Bent and Open Model for the Initiation Complex of T7 RNA Polymerase

PubMed Central

Turingan, Rosemary S.; Liu, Cuihua; Hawkins, Mary E.; Martin, Craig T.

2008-01-01

T7 RNA polymerase is known to induce bending of its promoter DNA upon binding, as evidenced by gel-shift assays and by recent end-to-end fluorescence energy transfer distance measurements. Crystal structures of promoter-bound and initially transcribing complexes, however, lack downstream DNA, providing no information on the overall path of the DNA through the protein. Crystal structures of the elongation complex do include downstream DNA and provide valuable guidance in the design of models for the complete melted bubble structure at initiation. In the current study, we test a specific structural model for the initiation complex, obtained by alignment of the C-terminal regions of the protein structures from both initiation and elongation and then simple transferal of the downstream DNA from the elongation complex onto the initiation complex. FRET measurement of distances from a point upstream on the promoter DNA to various points along the downstream helix reproduce the expected helical periodicity in the distances and support the model’s orientation and phasing of the downstream DNA. The model also makes predictions about the extent of melting downstream of the active site. By monitoring fluorescent base analogs incorporated at various positions in the DNA we have mapped the downstream edge of the bubble, confirming the model. The initially melted bubble, in the absence of substrate, encompasses 7–8 bases and is sufficient to allow synthesis of a 3 base transcript before further melting is required. The results demonstrate that despite massive changes in the N-terminal portion of the protein and in the DNA upstream of the active site, the DNA downstream of the active site is virtually identical in both initiation and elongation complexes. PMID:17253774

Hf isotope evidence for effective impact melt homogenisation at the Sudbury impact crater, Ontario, Canada

NASA Astrophysics Data System (ADS)

Kenny, Gavin G.; Petrus, Joseph A.; Whitehouse, Martin J.; Daly, J. Stephen; Kamber, Balz S.

2017-10-01

We report on the first zircon hafnium-oxygen isotope and trace element study of a transect through one of the largest terrestrial impact melt sheets. The differentiated melt sheet at the 1.85 Ga, originally ca. 200 km in diameter Sudbury impact crater, Ontario, Canada, yields a tight range of uniform zircon Hf isotope compositions (εHf(1850) of ca. -9 to -12). This is consistent with its well-established crustal origin and indicates differentiation from a single melt that was initially efficiently homogenised. We propose that the heterogeneity in other isotopic systems, such as Pb, in early-emplaced impact melt at Sudbury is associated with volatility-related depletion during the impact cratering process. This depletion leaves the isotopic systems of more volatile elements more susceptible to contamination during post-impact assimilation of country rock, whereas the systems of more refractory elements preserve initial homogeneities. Zircon oxygen isotope compositions in the melt sheet are also restricted in range relative to those in the impacted target rocks. However, they display a marked offset approximately one-third up the melt sheet stratigraphy that is interpreted to be a result of post-impact assimilation of 18O-enirched rocks into the base of the cooling impact melt. Given that impact cratering was a more dominant process in the early history of the inner Solar System than it is today, and the possibility that impact melt sheets were sources of ex situ Hadean zircon grains, these findings may have significance for the interpretation of the early zircon Hf record. We speculate that apparent εHf-time arrays observed in the oldest terrestrial and lunar zircon datasets may be related to impact melting homogenising previously more diverse crust. We also show that spatially restricted partial melting of rocks buried beneath the superheated impact melt at Sudbury provided a zircon crystallising environment distinct to the impact melt sheet itself.

How to make a craton

NASA Astrophysics Data System (ADS)

Lee, C.; Chin, E. J.; Erdman, M.; Gaschnig, R. M.; Lederer, G. W.; Savage, P. S.; Zhong, S.; Zincone, S.

2013-12-01

Most Archean cratons are underlain by long-lived 200-300 km thick thermal boundary layers, significantly thicker than oceanic boundary layers, which eventually subduct. The longevity of cratons is perplexing because cold thermal boundary layers should be gravitationally unstable or should thermally erode with time. However, it is agreed that thermal contraction of the cratonic root is compensated by intrinsic compositional buoyancy due to extreme melt depletion. This melt depletion is also thought to have dehydrated the peridotitic residue, strengthening the cratonic mantle, making it resistant to thermo-mechanical erosion. Exactly how cratonic mantle arrives at this chemically buoyant and dehydrated state is unknown. Possible scenarios include formation by melting within a large plume head, accretion of oceanic lithosphere, and accretion of sub-arc mantle. The high degrees of melting would seem to imply formation in hot plume heads, but low Al and heavy rare earth element contents suggest formation in the spinel stability field, implying formation at shallower depths than their current equilibration pressures. We present a new thermobarometer designed to estimate the average melting pressures and temperatures of residual peridotites using whole rock major element compositions. We find that the average melting pressures and temperatures of cratonic peridotites range between 3-4 GPa and 1600 °C. If cratonic peridotites melted via adiabatic decompression, these average pressures represent maximum bounds on the final pressures of melt extraction. Currently, cratonic peridotites derive from 4-7 GPa, implying that the building blocks of peridotites experienced an increase of 1-3 GPa, equivalent to 30-90 km of overburden. Our results thus imply that cratonic mantle most likely formed by tectonic thickening of oceanic or arc lithospheres. But because both arc and oceanic lithospheres might be expected to be wet due to hydrous flux melting and serpentinization, respectively, cratons should be weak. This dilemma can be reconciled by considering the thermal and magmatic evolution of juvenile crust formed in the Archean. Thickening of juvenile crust increases total heat production within the upper part of the nascent lithosphere. With higher heat production in the past, such thickening causes the crust to heat up on timescales of 100 Myr, resulting in a post-orogenic thermal pulse that generates a wave of crustal anatexis and downward heating of the lithospheric mantle, driving off residual water and increasing the kinetics of grain growth, both of which strengthen the lithosphere. Crustal melting will also advectively concentrate radiogenics towards the surface with no observable change in surface heat flow. This upward migration of radiogenics will be followed by cooling of the lower crust and lithospheric mantle, causing further strengthening. With secular cooling of the ambient convecting mantle over much longer timescales, cratons emerge in elevation, leading to erosion of the radiogenically enriched upper crust and leaving behind a continental block with the low surface heat flow characteristic of cratons today. In summary, cratons form by tectonic thickening of cold building blocks, followed by a thermal pulse that further dehydrates and anneals the cratonic mantle. The last step requires sufficient radiogenics to operate, which may explain why cratons formed early in Earth's history.

Melt extraction and mantle source at a Southwest Indian Ridge Dragon Bone amagmatic segment on the Marion Rise

NASA Astrophysics Data System (ADS)

Gao, Changgui; Dick, Henry J. B.; Liu, Yang; Zhou, Huaiyang

2016-03-01

This paper works on the trace and major element compositions of spatially associated basalts and peridotites from the Dragon Bone amagmatic ridge segment at the eastern flank of the Marion Platform on the ultraslow spreading Southwest Indian Ridge. The rare earth element compositions of basalts do not match the pre-alteration Dragon Bone peridotite compositions, but can be modeled by about 5 to 10% non-modal batch equilibrium melting from a DMM source. The Dragon Bone peridotites are clinopyroxene-poor harzburgite with average spinel Cr# 27.7. The spinel Cr# indicates a moderate degree of melting. However, CaO and Al2O3 of the peridotites are lower than other abyssal peridotites at the same Mg# and extent of melting. This requires a pyroxene-poor initial mantle source composition compared to either hypothetical primitive upper mantle or depleted MORB mantle sources. We suggest a hydrous melting of the initial Dragon Bone mantle source, as wet melting depletes pyroxene faster than dry. According to the rare earth element patterns, the Dragon Bone peridotites are divided into two groups. Heavy REE in Group 1 are extremely fractionated from middle REE, which can be modeled by 7% fractional melting in the garnet stability field and another 12.5 to 13.5% in the spinel stability field from depleted and primitive upper mantle sources, respectively. Heavy REE in Group 2 are slightly fractionated from middle REE, which can be modeled by 15 to 20% fractional melting in the spinel stability field from a depleted mantle source. Both groups show similar melting degree to other abyssal peridotites. If all the melt extraction occurred at the middle oceanic ridge where the peridotites were dredged, a normal 6 km thick oceanic crust is expected at the Dragon Bone segment. However, the Dragon Bone peridotites are exposed in an amagmatic ridge segment where only scattered pillow basalts lie on a partially serpentinized mantle pavement. Thus their depletion requires an earlier melting occurred at other place. Considering the hydrous melting of the initial Dragon Bone mantle source, we suggest the earlier melting event occurred in an arc terrain, prior to or during the closure of the Mozambique Ocean in the Neproterozoic, and the subsequent assembly of Gondwana. Then, the Al2O3 depleted and thus buoyant peridotites became the MORB source for Southwest Indian Ridge and formed the Marion Rise during the Gondwana breakup.

Graphics processing unit-assisted lossless decompression

DOEpatents

Loughry, Thomas A.

2016-04-12

Systems and methods for decompressing compressed data that has been compressed by way of a lossless compression algorithm are described herein. In a general embodiment, a graphics processing unit (GPU) is programmed to receive compressed data packets and decompress such packets in parallel. The compressed data packets are compressed representations of an image, and the lossless compression algorithm is a Rice compression algorithm.

Delayed facial nerve decompression for Bell's palsy.

PubMed

Kim, Sang Hoon; Jung, Junyang; Lee, Jong Ha; Byun, Jae Yong; Park, Moon Suh; Yeo, Seung Geun

2016-07-01

Incomplete recovery of facial motor function continues to be long-term sequelae in some patients with Bell's palsy. The purpose of this study was to investigate the efficacy of transmastoid facial nerve decompression after steroid and antiviral treatment in patients with late stage Bell's palsy. Twelve patients underwent surgical decompression for Bell's palsy 21-70 days after onset, whereas 22 patients were followed up after steroid and antiviral therapy without decompression. Surgical criteria included greater than 90 % degeneration on electroneuronography and no voluntary electromyography potentials. This study was a retrospective study of electrodiagnostic data and medical chart review between 2006 and 2013. Recovery from facial palsy was assessed using the House-Brackmann grading system. Final recovery rate did not differ significantly in the two groups; however, all patients in the decompression group recovered to at least House-Brackmann grade III at final follow-up. Although postoperative hearing threshold was increased in both groups, there was no significant between group difference in hearing threshold. Transmastoid decompression of the facial nerve in patients with severe late stage Bell's palsy at risk for a poor facial nerve outcome reduced severe complications of facial palsy with minimal morbidity.

Electromagnetic image-guided orbital decompression: technique, principles, and preliminary experience with 6 consecutive cases.

PubMed

Servat, Juan J; Elia, Maxwell Dominic; Gong, Dan; Manes, R Peter; Black, Evan H; Levin, Flora

2014-12-01

To assess the feasibility of routine use of electromagnetic image guidance systems in orbital decompression. Six consecutive patients underwent stereotactic-guided three wall orbital decompression using the novel Fusion ENT Navigation System (Medtronic), a portable and expandable electromagnetic guidance system with multi-instrument tracking capabilities. The system consists of the Medtronic LandmarX System software-enabled computer station, signal generator, field-generating magnet, head-mounted marker coil, and surgical tracking instruments. In preparation for use of the LandmarX/Fusion protocol, all patients underwent preoperative non-contrast CT scan from the superior aspect of the frontal sinuses to the inferior aspect of the maxillary sinuses that includes the nasal tip. The Fusion ENT Navigation System (Medtronic™) was used in 6 patients undergoing maximal 3-wall orbital decompression for Graves' orbitopthy after a minimum of six months of disease inactivity. Preoperative Hertel exophthalmometry measured more than 27 mm in all patients. The navigation system proved to be no more difficult technically than the traditional orbital decompression approach. Electromagnetic image guidance is a stereotactic surgical navigation system that provides additional intraoperative flexibility in orbital surgery. Electromagnetic image-guidance offers the ability to perform more aggressive orbital decompressions with reduced risk.

Interaction of tungsten with tungsten carbide in a copper melt

NASA Astrophysics Data System (ADS)

Bodrova, L. E.; Goida, E. Yu.; Pastukhov, E. A.; Marshuk, L. A.; Popova, E. A.

2013-07-01

The chemical interaction between tungsten and tungsten carbide in a copper melt with the formation of W2C at 1300°C is studied. It is shown that the mechanical activation of a composition consisting of copper melt + W and WC powders by low-temperature vibrations initiates not only the chemical interaction of its solid components but also their refinement.

Human Mitochondrial Transcription Factor B2 Is Required for Promoter Melting during Initiation of Transcription.

PubMed

Posse, Viktor; Gustafsson, Claes M

2017-02-17

The mitochondrial transcription initiation machinery in humans consists of three proteins: the RNA polymerase (POLRMT) and two accessory factors, transcription factors A and B2 (TFAM and TFB2M, respectively). This machinery is required for the expression of mitochondrial DNA and the biogenesis of the oxidative phosphorylation system. Previous experiments suggested that TFB2M is required for promoter melting, but conclusive experimental proof for this effect has not been presented. Moreover, the role of TFB2M in promoter unwinding has not been discriminated from that of TFAM. Here we used potassium permanganate footprinting, DNase I footprinting, and in vitro transcription from the mitochondrial light-strand promoter to study the role of TFB2M in transcription initiation. We demonstrate that a complex composed of TFAM and POLRMT was readily formed at the promoter but alone was insufficient for promoter melting, which only occurred when TFB2M joined the complex. We also show that mismatch bubble templates could circumvent the requirement of TFB2M, but TFAM was still required for efficient initiation. Our findings support a model in which TFAM first recruits POLRMT to the promoter, followed by TFB2M binding and induction of promoter melting. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Melt structure and self-nucleation of ethylene copolymers

NASA Astrophysics Data System (ADS)

Alamo, Rufina G.

A strong memory effect of crystallization has been observed in melts of random ethylene copolymers well above the equilibrium melting temperature. These studies have been carried out by DSC, x-ray, TEM and optical microscopy on a large number of model, narrow, and broad copolymers with different comonomer types and contents. Melt memory is correlated with self-seeds that increase the crystallization rate of ethylene copolymers. The seeds are associated with molten ethylene sequences from the initial crystals that remain in close proximity and lower the nucleation barrier. Diffusion of all sequences to a randomized melt state is a slow process, restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. Self-seeds dissolve above a critical melt temperature that demarcates homogeneity of the copolymer melt. There is a critical threshold level of crystallinity to observe the effect of melt memory on crystallization rate, thus supporting the correlation between melt memory and the change in melt structure during copolymer crystallization. Unlike binary blends, commercial ethylene-1-alkene copolymers with a range in inter-chain comonomer composition between 1 and about 15 mol % display an inversion of the crystallization rate in a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. With decreasing the initial melt temperature, broadly distributed copolymers show enhanced crystallization followed by a decrease of crystallization rate. The inversion demarcates the onset of liquid-liquid phase separation (LLPS) and a reduction of self-nuclei due to the strong thermodynamic drive for molecular segregation inside the binodal. The strong effect of melt memory on crystallization rate can be used to identify liquid-liquid phase separation in broadly distributed copolymers, and offers strategies to control the state of copolymer melts in ways of technological relevance for melt processing of LLDPE and other random olefin copolymers. References: B. O. Reid, et al., Macromolecules 46, 6485-6497, 2013 H. Gao, et al., Macromolecules 46, 6498-6506, 2013 A. Mamun et al., Macromolecules 47, 7958-7970, 2014 X. Chen et al., Macromol. Chem. Phys. 216, 1220 -1226, 2015 M. Ren et al., Macromol. Symp. 356, 131-141, 2015 Work supported by the NSF (DMR1105129).

Decompression to altitude: assumptions, experimental evidence, and future directions.

PubMed

Foster, Philip P; Butler, Bruce D

2009-02-01

Although differences exist, hypobaric and hyperbaric exposures share common physiological, biochemical, and clinical features, and their comparison may provide further insight into the mechanisms of decompression stress. Although altitude decompression illness (DCI) has been experienced by high-altitude Air Force pilots and is common in ground-based experiments simulating decompression profiles of extravehicular activities (EVAs) or astronauts' space walks, no case has been reported during actual EVAs in the non-weight-bearing microgravity environment of orbital space missions. We are uncertain whether gravity influences decompression outcomes via nitrogen tissue washout or via alterations related to skeletal muscle activity. However, robust experimental evidence demonstrated the role of skeletal muscle exercise, activities, and/or movement in bubble formation and DCI occurrence. Dualism of effects of exercise, positive or negative, on bubble formation and DCI is a striking feature in hypobaric exposure. Therefore, the discussion and the structure of this review are centered on those highlighted unresolved topics about the relationship between muscle activity, decompression, and microgravity. This article also provides, in the context of altitude decompression, an overview of the role of denitrogenation, metabolic gases, gas micronuclei, stabilization of bubbles, biochemical pathways activated by bubbles, nitric oxide, oxygen, anthropometric or physiological variables, Doppler-detectable bubbles, and potential arterialization of bubbles. These findings and uncertainties will produce further physiological challenges to solve in order to line up for the programmed human return to the Moon, the preparation for human exploration of Mars, and the EVAs implementation in a non-zero gravity environment.

Piezosurgery in Modified Pterional Orbital Decompression Surgery in Graves Disease.

PubMed

Grauvogel, Juergen; Scheiwe, Christian; Masalha, Waseem; Jarc, Nadja; Grauvogel, Tanja; Beringer, Andreas

2017-10-01

Piezosurgery uses microvibrations to selectively cut bone, preserving the adjacent soft tissue. The present study evaluated the use of piezosurgery for bone removal in orbital decompression surgery in Graves disease via a modified pterional approach. A piezosurgical device (Piezosurgery medical) was used in 14 patients (20 orbits) with Graves disease who underwent orbital decompression surgery in additional to drills and rongeurs for bone removal of the lateral orbital wall and orbital roof. The practicability, benefits, and drawbacks of this technique in orbital decompression surgery were recorded. Piezosurgery was evaluated with respect to safety, preciseness of bone cutting, and preservation of the adjacent dura and periorbita. Preoperative and postoperative clinical outcome data were assessed. The orbital decompression surgery was successful in all 20 orbits, with good clinical outcomes and no postoperative complications. Piezosurgery proved to be a safe tool, allowing selective bone cutting with no damage to the surrounding soft tissue structures. However, there were disadvantages concerning the intraoperative handling in the narrow space and the efficiency of bone removal was limited in the orbital decompression surgery compared with drills. Piezosurgery proved to be a useful tool in bone removal for orbital decompression in Graves disease. It is safe and easy to perform, without any danger of damage to adjacent tissue because of its selective bone-cutting properties. Nonetheless, further development of the device is necessary to overcome the disadvantages in intraoperative handling and the reduced bone removal rate. Copyright © 2017 Elsevier Inc. All rights reserved.

Compressive Neuropathy of the Ulnar Nerve: A Perspective on History and Current Controversies.

PubMed

Eberlin, Kyle R; Marjoua, Youssra; Jupiter, Jesse B

2017-06-01

The untoward effects resulting from compression of the ulnar nerve have been recognized for almost 2 centuries. Initial treatment of cubital tunnel syndrome focused on complete transection of the nerve at the level of the elbow, resulting in initial alleviation of pain but significant functional morbidity. A number of subsequent techniques have been described including in situ decompression, subcutaneous transposition, submuscular transposition, and most recently, endoscopic release. This manuscript focuses on the historical aspects of each of these treatments and our current understanding of their efficacy. Copyright © 2017 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

H Diffusion in Olivine and Pyroxene from Peridotite Xenoliths and a Hawaiian Magma Speedometer

NASA Technical Reports Server (NTRS)

Peslier, A. H.; Bizimis, M.

2014-01-01

Hydrogen is present as a trace element in olivine and pyroxene and its content distribution in the mantle results from melting and metasomatic processes. Here we examine how these H contents can be disturbed during decompression. Hydrogen was analyzed by FTIR in olivine and pyroxene of spinel peridotite xenoliths from Salt Lake Crater (SLC) nephelinites which are part of the rejuvenated volcanism at Oahu (Hawaii) [1,2]. H mobility in pyroxene resulting from spinel exsolution during mantle upwelling Most pyroxenes in SLC peridotites exhibit exsolutions, characterized by spinel inclusions. Pyroxene edges where no exsolution are present have less H then their core near the spinel. Given that H does not enter spinel [3], subsolidus requilibration may have concentrated H in the pyroxene adjacent to the spinel exsolution during mantle upwelling. H diffusion in olivine during xenolith transport by its host magma and host magma ascent rates Olivines have lower water contents at the edge and near fractures compared to at their core, while the concentrations of all other chemical elements appear homogeneous. This suggests that some of the initial water has diffused out of the olivine. Water loss from the olivine is thought to occur during host-magma ascent and xenolith transport to the surface [4-6]. Diffusion modeling matches best the data when the initial water content used is that measured at the core of the olivines, implying that mantle water contents are preserved at the core of the olivines. The 3225 cm(sup -1) OH band at times varies independantly of other OH bands, suggesting uneven H distribution in olivine defects likely acquired during mantle metasomatism just prior to eruption and unequilibrated. Diffusion times (1-48 hrs) combined with depths of peridotite equilibration or of magma start of degassing allow to calculate ascent rates for the host nephelinite of 0.1 to 27 m/s.

Ascent Rates of Rhyolitic Magma During the Opening Stages of Explosive Caldera-Forming Eruptions

NASA Astrophysics Data System (ADS)

Myers, M.; Wallace, P. J.; Wilson, C. J. N.; Watkins, J. M.; Liu, Y.; Morgan, D. J.

2016-12-01

We investigate the timescales of rhyolitic magma ascent for three supereruptions that show contrasting eruptive behavior at eruption onset: (1) the Bishop Tuff, CA where early fallout graded directly into climactic eruption, (2) the Oruanui eruption, Taupo NZ, which experienced a significant time break between the initial fallout and subsequent activity and (3) the Huckleberry Ridge, Yellowstone where initial activity was episodic, with eruptive pauses totaling days to weeks. During ascent, decompression causes volatile exsolution from the host melt, creating H2O and CO2 gradients in reentrants (REs; unsealed inclusions) that can be modeled to estimate ascent timescales1,2,3. Using a code1 refined to include an error minimization function, we present modeled ascent rates for REs from Huckleberry Ridge (n=10), Bishop (n=14), and Oruanui (n=4), measured using FTIR (20 μm resolution, 4-15 points per RE). Best-fit profiles for the Bishop REs give ascent rates of 0.6-30 m/s, which overlap with those of the Huckleberry (0.3-5.5 m/s), but extend to higher values. Although ascent rate and initial eruptive behavior are somewhat decoupled, there is an increase in the number of faster ascent rates and greater starting depths with higher stratigraphic height in the Huckleberry Ridge and Bishop fall deposits. Preliminary work on Oruanui REs indicates rates of 0.15-2.0 m/s, which overlie the lower end of the Bishop and Huckleberry REs, in agreement with previous data1. Overall, there is significant overlap between the three datasets (average 4±7 m/s). Our calculated ascent rates fall towards the lower end of ascent rates that have been estimated (5-40 m/s4) using theoretical and numerical modeling of conduit flow for Plinian rhyolitic eruptions below the fragmentation depth. 1 Liu Y et al. 2007: J Geophys Res 112, B06204; 2 Humphreys MCS et al. 2008: Earth Planet Sci Lett 270, 25; 3 Lloyd et al., 2014: J Volcanol Geotherm Res 283, 1; 4Rutherford MJ 2008: Rev Mineral Geochem 69, 241.

Aligning petrology with geophysics: the Father's Day intrusion and eruption, Kīlauea Volcano, Hawai`i

NASA Astrophysics Data System (ADS)

Salem, L. C.; Edmonds, M.; Maclennan, J.; Houghton, B. F.; Poland, M. P.

2016-12-01

The Father's Day 2007 eruption at Kīlauea Volcano, Hawai`i, is an unprecedented opportunity to align geochemical techniques with the exceptionally detailed volcano monitoring data collected by the Hawaiian Volcano Observatory (HVO). Increased CO2 emissions were measured during a period of inflation at the summit of Kilauea in 2003-2007, suggesting that the rate of magma supply to the summit had increased [Poland et al., 2012]. The June 2007 Father's Day eruption in the East Rift Zone (ERZ) occurred at the peak of the summit inflation. It offers the potential to sample magmas that have ascended on short timescales prior to 2007 from the lower crust, and perhaps mantle, with limited fractionation in the summit reservoir. The bulk rock composition of the lavas erupted are certainly consistent with this idea, with >8.5 wt% MgO compared to a typical 7.0-7.5 wt% for contemporaneous Pu`u`O`o ERZ lavas. However, our analysis of the major and trace element chemistry of olivine-hosted melt inclusions shows that the melts are in fact relatively evolved, with Mg# <53, compared to up to 63 for some high fountaining eruptions, e.g. Kīlauea Iki. The magma evidently entrained a crystal cargo of more primitive olivines, compositionally typical of summit eruption magma (with 81-84 mol% Fo). The melt inclusion chemistry shows homogenized and narrowly distributed trace element ratios, medium/low CO2 abundances and high concentrations of sulfur (unlike typical ERZ magmas). However, the chemistry is unlike melts that have partially bypassed the summit reservoir, e.g. those erupted at Kīlauea Iki, Mauna Ulu. We suggest that the Father's Day magma had been resident in the magma reservoir prior to the 2003-2007 inflation, and was evacuated from the reservoir into the ERZ in response to the increased rate of intrusion of magma from depth. Dissolved volatile contents along profiles in embayments ("open" melt inclusions) were measured and compared to diffusion models to predict timescales of magma decompression prior to eruption. These are compared to timescales of lateral dike intrusion measured using tilt, GPS and seismology to refine our understanding of horizontal and vertical magma flow in dikes between the summit reservoir and ERZ.

Labrador Massif Anorthosites: Chasing the Liquids and Their Sources

NASA Astrophysics Data System (ADS)

Morse, S. A.

2004-05-01

1. Plagioclase Gets the Liquid. Plagioclase (PL) contains all 10 of the major elements of igneous rocks, five as majors and five (Ti, Fe, Mn, Mg, P) as traces. Precise bulk analyses of PL megacrysts (MCRs) by XRF give useful values for all these elements by integrating the exsolved mafic phases. In 5 intrusions of the Nain anorthosite-norite-troctolite suite (ANT), DARK low-K PL (with more mafic inclusions) is associated with olivine, and PALE high-K PL with hypersthene. On Nukasusutok I. a trapped liquid of olivine gabbronorite composition is caught among big PLs, near a block of almost pure anorthosite (AN). On a whim, we divide the composition of the AN block by that of the trapped liquid and after adjustment get 2 sets of EFFECTIVE partition coefficients, one for mafic (cotectic) L and one for felsic L. Using MCR compositions from the 5 intrusions, ALL the derived liquid compositions from the DARK, OL region are OL-norm and all but 2 from the PALE, HY region are Q-norm. The OL-norm liquids plot with the experimental 5-kb cotectic OL,PL melts of the Kiglapait intrusion. The MCRs reveal an olivine-normative parent even when taken from noritic upper layers inherited from troctolite fractionation. This uncanny result needs far more study. Seek the trapped liquids! 2. Classify Anorthosites, DARK to PALE: by silica activity before Fe-Ti oxide precipitation: (mela) troctolite, gabbro, gabbronorite, norite, quartz norite. Associated Fe-Ti oxide minerals: titanomagnetite, Ti-Mt+ilmenite, magnetite+ilmenite, ilmenite, hemoilmenite. 3. Linear Partitioning of PL/L yields robust estimates of XAn in parent liquids by the relation XAb(L)=XAb(S)/D, where D=KD*XAn(S)+XAb(S) and at 5kb, KD=0.524 (N=8) from experiments giving An(S)=68 to 28. Harp Lake data from Fram & Longhi (1992 AmMin 605) show a strong effect of P on KD, from 0.4 at 1 atm to >1.0 at 15 kb. If you know the liquid composition you can estimate P, but more likely vice versa. The P calibration of KD needs much more study. But do natural PLs crystallize at equilibrium? 4. Source Regions. The hottest, troctolitic magmas bracketing the Nain ANTs from Voisey's Bay (1333 Ma) to Kiglapait (1306 Ma) are Al-Fe mantle melts probably beginning to form in the garnet field and separating from a depleted lithospheric source near 10 kb, near the spinel-PL boundary. Melts in equilibrium with Al-Opx+Cpx+PL+Sp+Gt at high pressure crystallize OL+PL when decompressed. If ponded near the base of the crust and allowed to shed mafics, they can become felsic and transported as crystal mush diapirs to the site of emplacement. Longer deep-crustal residence favors noritic ANTs. If the melting environment was extensional (think failed Central North American Rift) the Ps of generation are not at the base of the (thinned) crust but well within the mantle; melting is aided by decompression and diapiric advection of hot source rocks into the corroded, attenuating lithosphere. 5. Deeper Roots. The LIP length scale of ANTs in NE No. America is comparable to that of the Cameroon line; the geographic jumpiness of age distribution, when scaled, is also similar. We should be thinking hotspots. Anorthositic magmatism recurs on a vast time scale at Laramie (~400 Ma interval) and Nain (~800 Ma interval) and maybe elsewhere. This bizarre discovery demands a reason for recurrence. Deep mantle plumes are back in vogue and have been imaged. The biggest superplumes are fixed in position and have generated Al-Fe source rocks in the middle to deep lithosphere at Premier. We should wonder where our favorite ANT terranes were in the past, relative to the biggest hotspots: we need paleogeography with precision.

Size-dependent melting modes and behaviors of Ag nanoparticles: a molecular dynamics study

NASA Astrophysics Data System (ADS)

Liang, Tianshou; Zhou, Dejian; Wu, Zhaohua; Shi, Pengpeng

2017-12-01

The size-dependent melting behaviors and mechanisms of Ag nanoparticles (NPs) with diameters of 3.5-16 nm were investigated by molecular dynamics (MD). Two distinct melting modes, non-premelting and premelting with transition ranges of about 7-8 nm, for Ag NPs were demonstrated via the evolution of distribution and transition of atomic physical states during annealing. The small Ag NPs (3.5-7 nm) melt abruptly without a stable liquid shell before the melting point, which is characterized as non-premelting. A solid-solid crystal transformation is conducted through the migration of adatoms on the surface of Ag NPs with diameters of 3.5-6 nm before the initial melting, which is mainly responsible for slightly increasing the melting point of Ag NPs. On the other hand, surface premelting of Ag NPs with diameters of 8-16 nm propagates from the outer shell to the inner core with initial anisotropy and late isotropy as the temperature increases, and the close-packed facets {111} melt by a side-consumed way which is responsible for facets {111} melting in advance relative to the crystallographic plane {111}. Once a stable liquid shell is formed, its size-independent minimum thickness is obtained, and a three-layer structure of atomic physical states is set up. Lastly, the theory of point defect-pair (vacancy-interstitial) severing as the mechanism of formation and movement of the solid-liquid interface was also confirmed. Our study provides a basic understanding and theoretical guidance for the research, production and application of Ag NPs.

Sub-diffraction Imaging via Surface Plasmon Decompression

DTIC Science & Technology

2014-06-08

of the local wavelength of a surface plasmon polariton supported by two adjoining curved metal surfaces. The views, opinions and/or findings...adiabatic decompression of the local wavelength of a surface plasmon polariton supported by two adjoining curved metal surfaces. Conference Name...diffraction imaging based on a process of adiabatic decompression of the local wavelength of a surface plasmon polariton supported by two adjoining curved

Hypobaric decompression prebreathe requirements and breathing environment

NASA Technical Reports Server (NTRS)

Webb, James T.; Pilmanis, Andrew A.

1993-01-01

To reduce incidence of decompression sickness (DCS), prebreathing 100 percent oxygen to denitrogenate is required prior to hypobaric decompressions from a sea level pressure breathing environment to pressures lower than 350 mm Hg (20,000 ft; 6.8 psia). The tissue ratio (TR) of such exposures equals or exceeds 1.7; TR being the tissue nitrogen pressure prior to decompression divided by the total pressure after decompression (((0.781)(14.697))/6.758). Designing pressure suits capable of greater pressure differentials, lower TR's, and procedures which limit the potential for DCS occurrence would enhance operational efficiency. The current 10.2 psia stage decompression prior to extravehicular activity (EVA) from the Shuttle in the 100 percent oxygen, 4.3 psia suit, results in a TR of 1.65 and has proven to be relatively free of DCS. Our recent study of zero-prebreathe decompressions to 6.8 psia breathing 100 percent oxygen (TR = 1.66) also resulted in no DCS (N = 10). The level of severe, Spencer Grades 3 or 4, venous gas emboli (VGE) increased from 0 percent at 9.5 psia to 40 percent at 6.8 psia yielding a Probit curve of VGE risk for the 51 male subjects who participated in these recent studies. Earlier, analogous decompressions using a 50 percent oxygen, 50 percent nitrogen breathing mixture resulted in one case of DCS and significantly higher levels of severe VGE, e.g., at 7.8 psia, the mixed gas breathing environment resulted in a 56 percent incidence of severe VGE versus 10 percent with use of 100 percent oxygen. The report of this study recommended use of 100 percent oxygen during zero-prebreathe exposure to 6.8 psia if such a suit could be developed. For future, long-term missions, we suggest study of the effects of decompression over several days to a breathing environment of 150 mmHg O2 and approximately 52 mmHg He as a means of eliminating DCS and VGE hazards during subsequent excursions. Once physiologically adapted to a 4 psia vehicle, base, or space station segment, crew members could use greatly simplified EVA suits with greater mobility and no prebreathe requirement.

Early Outcomes of Endoscopic Contralateral Foraminal and Lateral Recess Decompression via an Interlaminar Approach in Patients with Unilateral Radiculopathy from Unilateral Foraminal Stenosis.

PubMed

Kim, Hyeun Sung; Patel, Ravish; Paudel, Byapak; Jang, Jee-Soo; Jang, Il-Tae; Oh, Seong-Hoon; Park, Jae Eun; Lee, Sol

2017-12-01

Percutaneous endoscopic contralateral interlaminar lumbar foraminotomy (PECILF) for lumbar degenerative spinal stenosis is an established procedure. Better preservation of contralateral facet joint compared with that of the approach side has been shown with uniportal bilateral decompression. The aim of this retrospective case series was to analyze the early clinical and radiologic outcomes of stand-alone contralateral foraminotomy and lateral recess decompression using PECILF. Twenty-six consecutive patients with unilateral lower limb radiculopathy underwent contralateral foraminotomy and lateral recess decompression using PECILF. Their clinical outcomes were evaluated with visual analog scale leg pain score, Oswestry Disability Index, and the MacNab criteria. Completeness of decompression was documented with a postoperative magnetic resonance imaging. Mean age for the study group was 62.9 ± 9.2 years and the male/female ratio was 4:9. A total of 30 levels were decompressed, with 18 patients (60%) undergoing decompression at L4-L5, 9 at L5-S1 (30%), 2 at L3-L4 (6.7%), and 1 at L2-L3 (3.3%). Mean estimated blood loss was 27 ± 15 mL per level. Mean operative duration was 48 ± 12 minutes/level. Visual analog scale leg score improved from 7.7 ± 1 to 1.8 ± 0.8 (P < 0.0001). Oswestry Disability Index improved from 64.4 ± 5.8 to 21 ± 4.5 (P < 0.0001). Mean follow-up of the study was 13.7 ± 2.7 months. According to the MacNab criteria, 10 patients (38.5%) had good results, 14 patients (53.8%) had excellent results, and 2 patients (7.7%) had fair results. One patient required revision surgery. Facet-preserving contralateral foraminotomy and lateral recess decompression with PECILF is effective for treatment of lateral recess and foraminal stenosis. Thorough decompression with acceptable early clinical outcomes and minimal perioperative morbidity can be obtained with the contralateral endoscopic approach. Copyright © 2017 Elsevier Inc. All rights reserved.

Effect of the aggregate morphology on the dispersability of MWCNTs in polymer melts

NASA Astrophysics Data System (ADS)

de Luna, M. Salzano; Tito, A.; Citterio, A.; Mazzocchia, C.; Acierno, D.; Filippone, G.

2012-07-01

Polystyrene nanocomposites filled with multi-walled carbon nanotubes have been prepared through a masterbatch melt mixing method and subjected to morphological, rheological and dielectrical analyses. The role of the structure of the initial aggregates has been investigated by comparing commercially available and synthesized MWCNTs prepared through fluidized bed chemical vapor deposition method and purified through a scalable one-pot route. Electron microscopy analyses reveal a less compact structure of the synthesized particles, in which the nanotubes are arranged in less entangled bundles. This reduces the strength of the initial agglomerates, thus enhancing their dispersability inside the host polymer by means of melt compounding as confirmed by both rheological and dielectrical measurements.

Characterization of thermoplastic polyimide NEW-TPI

NASA Technical Reports Server (NTRS)

Hou, T. H.; Reddy, R. M.

1991-01-01

Thermal and rheological properties of a commercial thermoplastic polyimide, NEW-TPI, were characterized. The as-received material possesses initially a transient crystallite form with a bimodal distribution in peak melting temperatures. After the meltings of the initial crystallite structures, the sample can be recrystallized by various thermal treatments. A bimodal or single-modal melting peak distribution is formed for annealing temperatures below or above 360 C, respectively. The recrystallized crystallinities are all transient in nature. The polymers are unable to be recrystallized after being subjected to elevated temperature annealing above 450 C. The recrystallization mechanism was postulated, and a simple kinetics model was found to describe the behavior satisfactorily under conditions of prolonged thermal annealing.

Gas evolution in eruptive conduits: Combining insights from high temperature and pressure decompression experiments with steady-state flow modeling

USGS Publications Warehouse

Mangan, M.; Mastin, L.; Sisson, T.

2004-01-01

In this paper we examine the consequences of bubble nucleation mechanism on eruptive degassing of rhyolite magma. We use the results of published high temperature and pressure decompression experiments as input to a modified version of CONFLOW, the numerical model of Mastin and Ghiorso [(2000) U.S.G.S. Open-File Rep. 00-209, 53 pp.] and Mastin [(2002) Geochem. Geophys. Geosyst. 3, 10.1029/2001GC000192] for steady, two-phase flow in vertical conduits. Synthesis of the available experimental data shows that heterogeneous nucleation is triggered at ??P 120-150 MPa, and leads to disequilibrium degassing at extreme H2O supersaturation. In this latter case, nucleation is an ongoing process controlled by changing supersaturation conditions. Exponential bubble size distributions are often produced with number densities of 106-109 bubbles/cm3. Our numerical analysis adopts an end-member approach that specifically compares equilibrium degassing with delayed, disequilibrium degassing characteristic of homogeneously-nucleating systems. The disequilibrium simulations show that delaying nucleation until ??P =150 MPa restricts degassing to within ???1500 m of the surface. Fragmentation occurs at similar porosity in both the disequilibrium and equilibrium modes (???80 vol%), but at the distinct depths of ???500 m and ???2300 m, respectively. The vesiculation delay leads to higher pressures at equivalent depths in the conduit, and the mass flux and exit pressure are each higher by a factor of ???2.0. Residual water contents in the melt reaching the vent are between 0.5 and 1.0 wt%, roughly twice that of the equilibrium model. ?? 2003 Elsevier B.V. All rights reserved.

Loss of cabin pressurization in U.S. Naval aircraft: 1969-90.

PubMed

Bason, R; Yacavone, D W

1992-05-01

During the 22-year period from 1 January 1969 to 31 December 1990, there were 205 reported cases of loss of cabin pressure in US Naval aircraft; 21 were crew-initiated and 184 were deemed accidental. The ambient altitudes varied from 10,000 ft (3048 m) to 40,000 ft. (12192 m). The most common reason for crew-initiated decompression was to clear smoke and fumes from the cockpit/cabin (95%). The most common cause for accidental loss of cabin pressure was mechanical (73.37%), with aircraft structural damage accounting for the remaining 26.63%. Serious physiological problems included 1 pneumothorax, 11 cases of Type I decompression sickness, 23 cases of mild to moderate hypoxia with no loss of consciousness, 18 cases of hypoxia with loss of consciousness, and 3 lost aircraft with 4 fatalities due to incapacitation by hypoxia. In addition, 12 ejections were attributed to loss of cockpit pressure. Nine of the ejections were deliberate and three were accidental, caused by wind blast activation of the face curtain. Three aviators lost their lives following ejection and seven aircraft were lost. While the incidence of loss of cabin pressure in Naval aircraft appears low, it none-the-less presents a definite risk to the aircrew. Lectures on the loss of cabin/cockpit pressurization should continue during indoctrination and refresher physiology training.

Petrological processes in mantle plume heads: Evidence from study of mantle xenoliths in the late Cenozoic alkali Fe-Ti basalts in Western Syria

NASA Astrophysics Data System (ADS)

Sharkov, Evgenii

2015-04-01

It is consensus now that within-plate magmatism is considered with ascending of mantle plumes and adiabatic melting of their head. At the same time composition of the plumes' matter and conditions of its adiabatic melting are unclear yet. The major source of objective information about it can be mantle xenoliths in alkali basalts and basanites which represent fragments of material of the plume heads above magma-generation zone. They are not represent material in melting zone, however, carry important information about material of modern mantle plumes, its phase composition and components, involved in melting. Populations of mantle xenoliths in basalts are characterized by surprising sameness in the world and represented by two major types: (1) dominated rocks of ``green'' series, and (2) more rare rocks of ``black'' series, which formed veins in the ``green'' series matrix. It can evidence about common composition of plume material in global scale. In other words, the both series of xenoliths represent two types of material of thermochemical mantle plumes, ascended from core-mantle boundary (Maruyama, 1994; Dobretsov et al., 2001). The same types of xenoliths are found in basalts and basanites of Western Syria (Sharkov et al., 1996). Rocks of ``green'' series are represented by Sp peridotites with cataclastic and protogranular structures and vary in composition from dominated spinel lherzolites to spinel harzburgites and rare spinel pyroxenites (websterites). It is probably evidence about incomplete homogenizing of the plume head matter, where material, underwent by partial melting, adjoins with more fertile material. Such heterogeneity was survived due to quick cooling of upper rim of the plume head in contact with relatively cold lithosphere. Essential role among xenoliths of the ``black'' series play Al-Ti-augite and water-bearing phases like hornblende (kaersutute) and Ti-phlogopite. Rocks of this series are represented by wehrlite, clinopyroxenite, amphibole clinopyroxenite, hornbledite, etc. as well as megacrysts of Al-Ti-augite, kaersutite, ilmenite, sanidine, etc. Numerous vesicles often occurred in megacrysts, especially in kaersurtite. Sp peridotites of the matrix are sharply different on their geochemical features from the ``black series'' rocks (in this case, megacrysts of kaersutite) which are the most close to composition of xenoliths-bearing alkali basalts. From this follows that geochemistry of plume-related basalts was determined by mantle fluids which occurred in magma-generation zone. Very likely, that these fluids, enriched in Fe, Ti, LREE, alkalis, and incompatible elements, initially were parts of intergranular material of original mantle plume material and were released due to its decompression. Because their high mobility, the fluids percolated upwards and accumulated in the upper part of the mantle plume head, where promoted its melting by lowering of solidus of the matter. Excess of the fluids gathered beneath the cooled upper rim and penetrated in its rocks which led to appearance of centers of secondary melting (melt-pockets). Very likely, that these secondary melts formed rocks of the ``black series'' (Ismail et al., 2008;Ryabchkov et al., 2011; Ma et al., 2014). According to geobarometric estimations, Sp peridotite xenoliths from Syria derived from depths 24-42 km (0.8-1.4 GPa) under temperatures 896-980oC; formation of melt-pockets, enriched in volatiles, occurred at the depths 21-27 km (0.7-0.9 GPa) under 826-981oC (Sharkov et al., 1996; Ismail et al., 2008; Ma et al., 2014). From this follows that plumeheads reached depths approximately 21-30 km which is in agree with practically absence of lower-crustal xenoliths in the populations. One of the problems of plume-related magmatism is coexisting of alkali and tholeiitic basalts, which origin often considered with different PT conditions. However, these basalt not rarely interlayered, especially at low and middle levels of LIPs or in single volcanoes (Hawaii, Etna, etc.) which is not in a good agreement with such idea. We suggest that the situation can be more likely explained by nonuniform impregnation of peridotite matrix with fluid components which composition and/or quantity can play essential role in composition of smeltings. It is especially important because even small differences in their ñomposition near to plane of SiO2 saturation in ``basalt tetrahedron'' (Yoder and Tilley, 1962) lead to appearance of Ne-normative or Ne-free melts at practically similar PT conditions. Thus, judging on composition of the mantle xenoliths in basalts of all occurrences in the world, quite possible that Sp peridotites (mainly lherzolites) together with intergranular geochemical-enriched fluid components represent the matter of the modern thermochemical mantle plumes. Origin of two major types of the plume-related magmas, probably, considered with fluid regime in the plume head.

Reactive Melt Infiltration Of Silicon Into Porous Carbon

NASA Technical Reports Server (NTRS)

Behrendt, Donald R.; Singh, Mrityunjay

1994-01-01

Report describes study of synthesis of silicon carbide and related ceramics by reactive melt infiltration of silicon and silicon/molybdenum alloys into porous carbon preforms. Reactive melt infiltration has potential for making components in nearly net shape, performed in less time and at lower temperature. Object of study to determine effect of initial pore volume fraction, pore size, and infiltration material on quality of resultant product.

A Log Logistic Survival Model Applied to Hypobaric Decompression Sickness

NASA Technical Reports Server (NTRS)

Conkin, Johnny

2001-01-01

Decompression sickness (DCS) is a complex, multivariable problem. A mathematical description or model of the likelihood of DCS requires a large amount of quality research data, ideas on how to define a decompression dose using physical and physiological variables, and an appropriate analytical approach. It also requires a high-performance computer with specialized software. I have used published DCS data to develop my decompression doses, which are variants of equilibrium expressions for evolved gas plus other explanatory variables. My analytical approach is survival analysis, where the time of DCS occurrence is modeled. My conclusions can be applied to simple hypobaric decompressions - ascents lasting from 5 to 30 minutes - and, after minutes to hours, to denitrogenation (prebreathing). They are also applicable to long or short exposures, and can be used whether the sufferer of DCS is at rest or exercising at altitude. Ultimately I would like my models to be applied to astronauts to reduce the risk of DCS during spacewalks, as well as to future spaceflight crews on the Moon and Mars.

Analysis of direct costs of decompressive craniectomy in victims of traumatic brain injury.

PubMed

Badke, Guilherme Lellis; Araujo, João Luiz Vitorino; Miura, Flávio Key; Guirado, Vinicius Monteiro de Paula; Saade, Nelson; Paiva, Aline Lariessy Campos; Avelar, Tiago Marques; Pedrozo, Charles Alfred Grander; Veiga, José Carlos Esteves

2018-04-01

Decompressive craniectomy is a procedure required in some cases of traumatic brain injury (TBI). This manuscript evaluates the direct costs and outcomes of decompressive craniectomy for TBI in a developing country and describes the epidemiological profile. A retrospective study was performed using a five-year neurosurgical database, taking a sample of patients with TBI who underwent decompressive craniectomy. Several variables were considered and a formula was developed for calculating the total cost. Most patients had multiple brain lesions and the majority (69.0%) developed an infectious complication. The general mortality index was 68.8%. The total cost was R$ 2,116,960.22 (US$ 661,550.06) and the mean patient cost was R$ 66,155.00 (US$ 20,673.44). Decompressive craniectomy for TBI is an expensive procedure that is also associated with high morbidity and mortality. This was the first study performed in a developing country that aimed to evaluate the direct costs. Prevention measures should be a priority.

Decompression-Driven Superconductivity Enhancement in In2 Se3.

PubMed

Ke, Feng; Dong, Haini; Chen, Yabin; Zhang, Jianbo; Liu, Cailong; Zhang, Junkai; Gan, Yuan; Han, Yonghao; Chen, Zhiqiang; Gao, Chunxiao; Wen, Jinsheng; Yang, Wenge; Chen, Xiao-Jia; Struzhkin, Viktor V; Mao, Ho-Kwang; Chen, Bin

2017-09-01

An unexpected superconductivity enhancement is reported in decompressed In 2 Se 3 . The onset of superconductivity in In 2 Se 3 occurs at 41.3 GPa with a critical temperature (T c ) of 3.7 K, peaking at 47.1 GPa. The striking observation shows that this layered chalcogenide remains superconducting in decompression down to 10.7 GPa. More surprisingly, the highest T c that occurs at lower decompression pressures is 8.2 K, a twofold increase in the same crystal structure as in compression. It is found that the evolution of T c is driven by the pressure-induced R-3m to I-43d structural transition and significant softening of phonons and gentle variation of carrier concentration combined in the pressure quench. The novel decompression-induced superconductivity enhancement implies that it is possible to maintain pressure-induced superconductivity at lower or even ambient pressures with better superconducting performance. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Successful Treatment of Early Talar Osteonecrosis by Core Decompression Combined with Intraosseous Stem Cell Injection: A Case Report.

PubMed

Nevalainen, Mika T; Repo, Jussi P; Pesola, Maija; Nyrhinen, Jukka P

2018-01-01

Osteonecrosis of the talus is a fairly rare condition. Many predisposing factors have been identified including previous trauma, use of corticosteroids, alcoholism, and smoking. As a gold standard, magnetic resonance imaging (MRI) is the most sensitive and specific diagnostic examination to detect osteonecrosis. While many treatment options for talar osteonecrosis exist, core decompression is suggested on young patients with good outcome results. More recently, intraosseous stem cell and platelet-rich plasma (PRP) injection has been added to the core decompression procedure. We report a successful treatment of early talar osteonecrosis ARCO I (Association Research Circulation Osseous) by core decompression combined with stem cell and PRP injection. On 3-month and 15-month follow-up, MRI showed complete resolution of the osteonecrotic changes together with clinical improvement. This modified technique is a viable treatment option for early talar osteonecrosis. Nevertheless, future prospects should include a study comparing this combined technique with plain core decompression.

Decompressive craniectomy and hydrocephalus: proposal of a therapeutic flow chart.

PubMed

Peraio, Simone; Calcagni, Maria Lucia; Mattoli, Maria Vittoria; Marziali, Giammaria; DE Bonis, Pasquale; Pompucci, Angelo; Anile, Carmelo; Mangiola, Annunziato

2017-12-01

Decompressive craniectomy (DC) may be necessary to save the lives of patients suffering from intracranial hypertension. However, this procedure is not complication-free. Its two main complications are hydrocephalus and the sinking skin-flap syndrome (SSFS). The radiological findings and the clinical evaluation may be not enough to decide when and/or how to treat hydrocephalus in a decompressed patient. SSFS and hydrocephalus may be not unrelated. In fact, a patient affected by hydrocephalus, after the ventriculo-peritoneal shunt, can develop SSFS; on the other hand, SSFS per se can cause hydrocephalus. Treating hydrocephalus in decompressed patients can be challenging. Radiological findings and clinical evaluation may not be enough to define the most appropriate therapeutic strategy. Cerebrospinal fluid (CSF) dynamics and metabolic evaluations can represent important diagnostic tools for assessing the need of a CSF shunt in patients with a poor baseline neurologic status. Based on our experience, we propose a flow chart for treating decompressed patients affected by ventriculomegaly.

Water in orthopyroxene from abyssal spinel peridotites of the East Pacific Rise (ODP Leg 147: Hess Deep)

NASA Astrophysics Data System (ADS)

Hesse, Kirsten T.; Gose, Jürgen; Stalder, Roland; Schmädicke, Esther

2015-09-01

Abyssal spinel peridotites from Hess Deep, East Pacific Rise (ODP Leg 147) were investigated concerning their major, minor, and trace element mineral chemistry and the incorporation of structural water in orthopyroxene. The rocks are partially serpentinized harzburgites containing primary minerals of olivine, orthopyroxene, clinopyroxene, and spinel. Orthopyroxene is enstatitic with Mg# (Mg/(Mg + Fe)) between 0.90 and 0.92 and Al2O3 from 0.5 to 2.9 wt.%. The residual harzburgite experienced high degrees of melt removal in the spinel peridotite stability field. The average degree of partial melting was calculated to be 17.5% (range: 16.4-17.8%). Trace element data of ortho- and clinopyroxenes reflect this strong depletion, characteristic for the restitic nature of abyssal peridotites. Mantle re-equilibration temperatures around 1000 °C indicate that, after melt extraction and before exhumation to the ocean floor, the rocks experienced significant cooling in the spinel peridotite facies. Water contents of orthopyroxene range from 86 to 233 wt. ppm H2O with an average concentration of 142 wt. ppm H2O. These results represent the first data on water contents in the sub-pacific mantle obtained by direct measurements of sub-oceanic peridotite. The water contents are not related to mineral chemistry, stratigraphy, melting degree, mantle equilibrium conditions or oxidation state. Calculated post-melt peridotite water contents vary between 40 and 100 wt. ppm H2O. Compared to Mid-Atlantic Ridge peridotites, the East Pacific Rise samples of Leg 147 contain somewhat lower water concentrations than samples from Leg 153 and considerably higher contents than those of Leg 209 (Gose et al., 2009; Schmädicke et al., 2011). In Leg 147, the strongest OH absorbtion band occurs at 3420 cm- 1, wheras orthopyroxene from MAR peridotite (Legs 153 and 209) has its strongest absorbtion band at 3566 and 3522 cm- 1. The mantle equilibrium temperature of Leg 147 peridotites is lower than that of Leg 209 ( 1250 °C) but close to that of Leg 153 samples (950-1000 °C). The high degree of partial melting of Leg 147 peridotite samples overlaps with the Leg 209 samples. In accordance to this data we conclude that in order to obtain relatively high water contents of up to 233 wt. ppm in depleted peridotite, after melt removal water must have re-entered the orthopyroxene structure. We suggest that re-equilibration of water contents took place under spinel-facies conditions before exhumation of the tectonite, since elevated temperatures enhance diffusion and elevated pressures facilitate hydrogen uptake. The extended time span between melt removal and uplift inferred from significant isobaric cooling of at least 200 K at spinel-facies depth facilitates re-equilibration of water contents and may explain the high concentrations. Exhumation from spinel-facies depth was fast and accompanied by further cooling such that re-equilibration to lower pressure assemblages and decompression-induced water loss were prevented.

Numerical modelling of lithospheric flexure in front of subduction zones in Japan and its role to initiate melt extraction from the LVZ.

NASA Astrophysics Data System (ADS)

Bessat, A.; Pilet, S.; Duretz, T.; Schmalholz, S. M.

2017-12-01

Petit-spot volcanoes were found fifteen years ago by Japanese researchers at the top of the subducting plate in Japan (Hirano 2006). This discovery is of great significance as it highlights the importance of tectonic processes for the initiation of intraplate volcanism. The location of these small lava flows is unusual and seems to be related to the plate flexure, which may facilitate the extraction of low degree melts from the base of the lithosphere, a hypothesis previously suggested to explain changes in electric and seismic properties at 70-90 km depth, i.e. within the low velocity zone (LVS) (Sifré 2014). A critical question is related to the process associated with the extraction of this low degree melts from the LVZ. First models suggested that extension associated to plate bending allows large cracks to propagate across the lithosphere and could promote the extraction of low degree melts at the base of the lithosphere (Hirano 2006 & Yamamoto 2014). However, the study of petit-spot mantle xenoliths from Japan (Pilet 2016) has demonstrated that low degree melts are not directly extracted to the surface but percolate, interact and metasomatize the oceanic lithosphere. In order to understand the melt extraction process in the region of plate bending, we performed 2D thermo-mechanical simulations of Japanese-type subduction. The numerical model considers viscoelastoplastic deformation. This allows the quantification of state of the stress, strain rates, and viscosities which will control the percolation of melt initially stocked at the base of the lithosphere. Initial results show that plate flexure changes the distribution of the deformation mechanism in the flexure zone, between 40 km to 80 km depth. A change of the dominant deformation mechanism from diffusion creep to dislocation creep and from there to Peierls creep was observed about 200 to 300 km from the trench. These changes are linked to the augmentation of the stresses in the flexure zone. At the base of the lithosphere diffusion creep is observed as a thin layer (20 km), which becomes smaller (10 km) as the subduction progresses in favour of the dislocation creep. Further work will be necessary to prove whether the associated stress distributions is compatible with the development of porosity waves, a critical process to extract melts in low porosity media.

Oxygen Equipment and Rapid Decompression Studies

DTIC Science & Technology

1979-03-01

defined and discussed by Fritz Haber anti Hans Clamann (3) of the USAF School of Aviation Medicine.* These authors define two factors in a...for the pattern of airflow through the pene- tration; and (vi) maintenance of critical flow. The equation for rapid decompression as presented by Haber ...galley, controlling the pressure differential between the two compartments. Using the equation of Haber and Clamann (7), a decompression for the galley

Bilateral Ocular Decompression Retinopathy after Ahmed Valve Implantation for Uveitic Glaucoma.

PubMed

Flores-Preciado, Javier; Ancona-Lezama, David Arturo; Valdés-Lara, Carlos Andrés; Díez-Cattini, Gian Franco; Coloma-González, Itziar

2016-01-01

We report the case of a 29-year-old man who underwent Ahmed valve implantation in both eyes as treatment for uveitic glaucoma, subsequently presenting with bilateral ocular decompression retinopathy in the postoperative period. Ocular decompression retinopathy is a rare complication of filtering surgery in patients with glaucoma; however, the course is benign in most cases, with spontaneous resolution of bleedings and improvement of visual acuity.

Hazards of high altitude decompression sickness during falls in barometric pressure from 1 atm to a fraction thereof

NASA Technical Reports Server (NTRS)

Genin, A. M.

1980-01-01

Various tests related to studies concerning the effects of decompression sicknesses at varying pressure levels and physical activity are described. The tests indicate that there are no guarantees of freedom from decompression sicknesses when man transitions from a normally oxygenated normobaric nitrogen-oxygen atmosphere into an environment having a 0.4 atm or lower pressure and he is performing physical work.

A benchmark initiative on mantle convection with melting and melt segregation

NASA Astrophysics Data System (ADS)

Schmeling, Harro; Dannberg, Juliane; Dohmen, Janik; Kalousova, Klara; Maurice, Maxim; Noack, Lena; Plesa, Ana; Soucek, Ondrej; Spiegelman, Marc; Thieulot, Cedric; Tosi, Nicola; Wallner, Herbert

2016-04-01

In recent years a number of mantle convection models have been developed which include partial melting within the asthenosphere, estimation of melt volumes, as well as melt extraction with and without redistribution at the surface or within the lithosphere. All these approaches use various simplifying modelling assumptions whose effects on the dynamics of convection including the feedback on melting have not been explored in sufficient detail. To better assess the significance of such assumptions and to provide test cases for the modelling community we carry out a benchmark comparison. The reference model is taken from the mantle convection benchmark, cases 1a to 1c (Blankenbach et al., 1989), assuming a square box with free slip boundary conditions, the Boussinesq approximation, constant viscosity and Rayleigh numbers of 104 to 10^6. Melting is modelled using a simplified binary solid solution with linearly depth dependent solidus and liquidus temperatures, as well as a solidus temperature depending linearly on depletion. Starting from a plume free initial temperature condition (to avoid melting at the onset time) five cases are investigated: Case 1 includes melting, but without thermal or dynamic feedback on the convection flow. This case provides a total melt generation rate (qm) in a steady state. Case 2 is identical to case 1 except that latent heat is switched on. Case 3 includes batch melting, melt buoyancy (melt Rayleigh number Rm) and depletion buoyancy, but no melt percolation. Output quantities are the Nusselt number (Nu), root mean square velocity (vrms), the maximum and the total melt volume and qm approaching a statistical steady state. Case 4 includes two-phase flow, i.e. melt percolation, assuming a constant shear and bulk viscosity of the matrix and various melt retention numbers (Rt). These cases are carried out using the Compaction Boussinseq Approximation (Schmeling, 2000) or the full compaction formulation. For cases 1 - 3 very good agreement is achieved among the various participating codes. For case 4 melting/freezing formulations require some attention to avoid sub-solidus melt fractions. A case 5 is planned where all melt will be extracted and, reinserted in a shallow region above the melted plume. The motivation of this presentation is to summarize first experiences and to finalize the case definitions. References: Blankenbach, B., Busse, F., Christensen, U., Cserepes, L. Gunkel, D., Hansen, U., Harder, H. Jarvis, G., Koch, M., Marquart, G., Moore D., Olson, P., and Schmeling, H., 1989: A benchmark comparison for mantle convection codes, J. Geophys., 98, 23-38. Schmeling, H., 2000: Partial melting and melt segregation in a convecting mantle. In: Physics and Chemistry of Partially Molten Rocks, eds. N. Bagdassarov, D. Laporte, and A.B. Thompson, Kluwer Academic Publ., Dordrecht, pp. 141 - 178.

Experimental and computational studies on the femoral fracture risk for advanced core decompression.

PubMed

Tran, T N; Warwas, S; Haversath, M; Classen, T; Hohn, H P; Jäger, M; Kowalczyk, W; Landgraeber, S

2014-04-01

Two questions are often addressed by orthopedists relating to core decompression procedure: 1) Is the core decompression procedure associated with a considerable lack of structural support of the bone? and 2) Is there an optimal region for the surgical entrance point for which the fracture risk would be lowest? As bioresorbable bone substitutes become more and more common and core decompression has been described in combination with them, the current study takes this into account. Finite element model of a femur treated by core decompression with bone substitute was simulated and analyzed. In-vitro compression testing of femora was used to confirm finite element results. The results showed that for core decompression with standard drilling in combination with artificial bone substitute refilling, daily activities (normal walking and walking downstairs) are not risky for femoral fracture. The femoral fracture risk increased successively when the entrance point is located further distal. The critical value of the deviation of the entrance point to a more distal part is about 20mm. The study findings demonstrate that optimal entrance point should locate on the proximal subtrochanteric region in order to reduce the subtrochanteric fracture risk. Furthermore the consistent results of finite element and in-vitro testing imply that the simulations are sufficient. Copyright © 2014 Elsevier Ltd. All rights reserved.

Optic neuropathy in thyroid eye disease: results of the balanced decompression technique.

PubMed

Baril, Catherine; Pouliot, Denis; Molgat, Yvonne

2014-04-01

To determine the efficacy of combined endoscopic medial and external lateral orbital decompression for the treatment of compressive optic neuropathy (CON) in thyroid eye disease (TED). A retrospective review of all patients undergoing combined surgical orbital decompression for CON between 2000 and 2010 was conducted. Fifty-nine eyes of 34 patients undergoing combined surgical orbital decompression for CON. Clinical outcome measures included visual acuity, Hardy-Rand-Rittler (HRR) colour plate testing, relative afferent pupillary defect, intraocular pressure measurement, and Hertel exophthalmometry. A CON score was calculated preoperatively and postoperatively based on the visual acuity and the missed HRR plates. A higher CON score correlates with more severe visual dysfunction. All patients had improvement of their optic neuropathy after surgical decompression. CON score was calculated for 54 eyes and decreased significantly from a mean of 13.2 ± 10.35 preoperatively to a mean of 8.51 ± 10.24 postoperatively (p < 0.0001). Optic neuropathy was completely resolved in 93.22% (55/59 eyes). Eighteen of 34 patients (52.94%) experienced development of new-onset postoperative strabismus that required subsequent surgical intervention. Endoscopic medial combined with external lateral orbital decompression is an effective technique for the treatment of TED-associated CON. © 2013 Canadian Ophthalmological Society Published by Canadian Ophthalmological Society All rights reserved.

Exercise with prebreathe appears to increase protection from decompression sickness: Preliminary findings

NASA Technical Reports Server (NTRS)

Webb, James T.; Fischer, Michele D.; Heaps, Cristine L.; Pilmanis, Andrew A.

1994-01-01

Extravehicular activity (EVA) from the Space Shuttle involves one hour of prebreath with 100% oxygen, decompression of the entire Shuttle to 10.2 psia for at least 12 hours, and another prebreath for 40 minutes before decompression to the 4.3 psia suit pressure. We are investigating the use of a one-hour prebreathe with 100% oxygen beginning with a ten-minute strenuous exercise period as an alternative for the staged decompression schedule described above. The 10-minute exercise consists of dual-cycle ergometry performed at 75% of the subject's peak oxygen uptake to increase denitrogenation efficiency by increasing ventilation and perfusion. The control exposures were preceded by a one-hour prebreathe with 100% oxygen while resting in a supine position. The twenty-two male subjects were exposed to 4.3 psia for 4 hours while performing light to moderate exercise. Preliminary results from 22 of the planned 26 subjects indicate 76% DCS following supine, resting prebreathe and 38% following prebreathe with exercise. The staged decompression schedule has been shown to result in 23% DCS which is not significantly different from the exercise-enhanced prebreathe results. Prebreathe including exercise appears to be comparable to the protection afforded by the more lengthy staged decompression schedule. Completion of the study later this year will enable planned statistical analysis of the results.

Resolution of Tachyarrhythmia Following Posterior Fossa Decompression Surgery for Chiari Malformation Type I.

PubMed

Elia, Christopher; Brazdzionis, James; Tashjian, Vartan

2018-03-01

Chiari malformation (CM) type I commonly presents with symptoms such as tussive headaches, paresthesias, and, in severe cases, corticobulbar dysfunction. However, patients may present with atypical symptoms lending to the complexity in this patient population. We present a case of a CM patient presenting with atypical cardiac symptoms and arrhythmias, all of which resolved after surgical decompression. A 31-year-old female presented with atypical chest pain, palpitations, tachycardia, headaches, and dizziness for 2 years. Multiple antiarrhythmics and ultimately cardiac ablation procedure proved to be ineffective. Magnetic resonance imaging revealed CM, and the patient ultimately underwent surgical decompression with subsequent resolution of her symptoms. The surgical management of CM patients presenting with atypical symptoms can be challenging and often lead to delays in intervention. To our knowledge this is the only reported case of a patient presenting with tachyarrhythmia and atypical chest pain with resolution after Chiari decompression. We believe the dramatic improvement documented in the present case should serve to advance Chiari decompression in CM patients presenting with refractory tachyarrhythmia in whom no other discernable cause has been elucidated. Further studies are needed to better correlate the findings and to hopefully establish a criteria for patients that will likely benefit from surgical decompression. Copyright © 2017 Elsevier Inc. All rights reserved.

Decompressing recompression chamber attendants during Australian submarine rescue operations.

PubMed

Reid, Michael P; Fock, Andrew; Doolette, David J

2017-09-01

Inside chamber attendants rescuing survivors from a pressurised, distressed submarine may themselves accumulate a decompression obligation which may exceed the limits of Defense and Civil Institute of Environmental Medicine tables presently used by the Royal Australian Navy. This study assessed the probability of decompression sickness (P DCS ) for medical attendants supervising survivors undergoing oxygen-accelerated saturation decompression according to the National Oceanic and Atmospheric Administration (NOAA) 17.11 table. Estimated probability of decompression sickness (P DCS ), the units pulmonary oxygen toxicity dose (UPTD) and the volume of oxygen required were calculated for attendants breathing air during the NOAA table compared with the introduction of various periods of oxygen breathing. The P DCS in medical attendants breathing air whilst supervising survivors receiving NOAA decompression is up to 4.5%. For the longest predicted profile (830 minutes at 253 kPa) oxygen breathing at 30, 60 and 90 minutes at 132 kPa partial pressure of oxygen reduced the air-breathing-associated P DCS to less than 3.1 %, 2.1% and 1.4% respectively. The probability of at least one incident of DCS among attendants, with consequent strain on resources, is high if attendants breathe air throughout their exposure. The introduction of 90 minutes of oxygen breathing greatly reduces the probability of this interruption to rescue operations.

Basanite-nephelinite suite from early Kilauea: Carbonated melts of phlogopite-garnet peridotite at Hawaii's leading magmatic edge

USGS Publications Warehouse

Sisson, T.W.; Kimura, Jun-Ichi; Coombs, M.L.

2009-01-01

A basanite-nephelinite glass suite from early submarine Kilauea defines a continuous compositional array marked by increasing concentrations of incompatible components with decreasing SiO2, MgO, and Al2O3. Like peripheral and post-shield strongly alkalic Hawaiian localities (Clague et al. in J Volcanol Geotherm Res 151:279-307, 2006; Dixon et al. in J Pet 38:911-939, 1997), the early Kilauea basanite-nephelinite glasses are interpreted as olivine fractionation products from primary magnesian alkalic liquids. For early Kilauea, these were saturated with a garnet-phlogopite-sulfide peridotite assemblage, with elevated dissolved CO2 contents responsible for the liquids' distinctly low-SiO2 concentrations. Reconstructed primitive liquids for early Kilauea and other Hawaiian strongly alkalic localities are similar to experimental 3 GPa low-degree melts of moderately carbonated garnet lherzolite, and estimated parent magma temperatures of 1,350-1,400??C (olivine-liquid geothermometry) match the ambient upper mantle geotherm shortly beneath the base of the lithosphere. The ???3 GPa source regions were too hot for stable crystalline carbonate and may have consisted of ambient upper mantle peridotite containing interstitial carbonate-silicate or carbonatitic liquid, possibly (Dixon et al. in Geochem Geophys Geosyst 9(9):Q09005, 2008), although not necessarily, from the Hawaiian mantle plume. Carbonate-enriched domains were particularly susceptible to further melting upon modest decompression during upward lithospheric flexure beneath the advancing Hawaiian Arch, or by conductive heating or upward drag by the Hawaiian mantle plume. The early Kilauea basanite-nephelinite suite has a HIMU-influenced isotopic character unlike other Hawaiian magmas (Shimizu et al. in EOS Tran Amer Geophys Union 82(47): abstr V12B-0962, 2001; Shimizu et al. in Geochim Cosmochim Acta 66(15A):710, 2002) but consistent with oceanic carbonatite involvement (Hoernle et al. in Contrib Mineral Petrol 142:520-542, 2002). It may represent the melting products of a fertile domain in the ambient upper mantle impinged upon and perturbed by the sustained plume source that feeds later shield-stage magmatism. ?? US Government 2009.

Sulfur diffusion in dacitic melt at various oxidation states: Implications for volcanic degassing

NASA Astrophysics Data System (ADS)

Lierenfeld, Matthias Bernhard; Zajacz, Zoltán; Bachmann, Olivier; Ulmer, Peter

2018-04-01

The diffusivity of S in a hydrous dacitic melt (4.5-6.0 wt.% H2O) has been investigated in the temperature (T) and pressure (P) range of 950 °C to 1100 °C and 200 to 250 MPa, respectively. Three series of experiments were conducted at relatively low oxygen fugacity (fO2) conditions [0.8 log units below fayalite-magnetite-quartz equilibrium (FMQ -0.8); referred to as "low fO2"] and high fO2 conditions (FMQ +2.5; referred to as "high fO2") to determine if the diffusivity of S is affected by its oxidation state and speciation. Sulfur concentration profiles were measured by electron microprobe and the diffusion coefficient (D) was calculated by fitting these profiles. Sulfur diffusion is approximately one order of magnitude faster when S is dominantly present as sulfide species (low fO2) in comparison to the sulfate dominated experiments (high fO2). The following Arrhenian equations were obtained for high and low fO2 conditions at 200 MPa: high fO2: D = 10-5.92±0.86 * exp ({-137.3±21.5 kJ/mol}/{RT}) low fO2: D = 10-5.18±1.39 * exp ({-125.7±34.4 kJ/mol}/{RT}) where D is the average diffusion coefficient in m2 s-1, R is the gas constant in 8.3144 J mol-1 K-1 and T is the temperature in K. Our results demonstrate for the first time in natural melts that S diffusion is strongly sensitive to fO2. Our S diffusivities under low fO2 conditions are only slightly slower of those found for H2O, suggesting that S can be rather efficiently purged from reduced dacitic melts during volcanic eruptions. However, for more oxidized systems (e.g. subduction zones), S diffusion will be much slower and will hinder equilibrium syn-eruptive degassing during rapid decompression. Therefore, we conclude that the "excess" measured during many explosive volcanic eruptions in arcs is dominantly derived from S-rich bubble accumulation in the eruptible portion of the magma reservoir.

Volcanic Metal Emissions and Implications for Geochemical Cycling and Mineralization

NASA Astrophysics Data System (ADS)

Edmonds, M.; Mather, T. A.

2016-12-01

Volcanoes emit substantial fluxes of metals to the atmosphere in volcanic gas plumes in the form of aerosol, adsorbed onto silicate particles and even in some cases as gases.. A huge database of metal emissions has been built over the preceding decades, which shows that volcanoes emit highly volatile metals into the atmosphere, such as As, Bi, Cd, Hg, Re, Se, Tl, among others. Understanding the cycling of metals through the Solid Earth system has importance for tackling a wide range of Earth Science problems, e.g. (1) the environmental impacts of metal emissions; (2) the sulfur and metal emissions of volcanic eruptions; (3) the behavior of metals during subduction and slab devolatilization; (4) the influence of redox on metal behavior in subduction zones; (5) the partitioning of metals between magmatic vapor, brines and melts; and (6) the relationships between volcanism and ore deposit formation. It is clear, when comparing the metal composition and flux in the gases and aerosols emitted from volcanoes, that they vary with tectonic setting. These differences allow insights into how the magmatic vapor was generated and how it interacted with melts and sulfides during magma differentiation and decompression. Hotspot volcanoes (e.g. Kilauea, Hawaii; volcanoes in Iceland) outgas a metal suite that mirrors the sulfide liquid-silicate melt partitioning behaviors reconstructed from experiments (as far as they are known), suggesting that the aqueous fluids (that will later be outgassed from the volcano) receive metals directly from oxidation of sulfide liquids during degassing and ascent of magmas towards the surface. At arc volcanoes, the gaseous fluxes of metals are typically much higher; and there are greater enrichments in elements that partition strongly into vapor or brine from silicate melts such as Cu, Au, Zn, Pb, W. We collate and present data on volcanic metal emissions from volcanoes worldwide and review the implications of the data array for metal cycling through subduction, the potential link between the rise of plate tectonics, metal outgassing and biology, and what we can understand about metal sequestration into ore deposits from volcanic emissions.

In situ experimental study of subduction zone fluids using diamond anvil cells

NASA Astrophysics Data System (ADS)

Bureau, H.; Foy, E.; Somogyi, A.; Munsch, P.; Simon, G.; Kubsky, S.

2008-12-01

Experiments carried out in diamond anvil cells combined with in situ synchrotron light source measurements represent the only one issue to observe and study fluid equilibria in real time, at the pressure and temperature conditions of the subduction zones. We will present new results recently obtained at the DIFFABS beam line (SOLEIL Synchrotron) aiming at studying equilibria between silica-rich hydrous melts and aqueous fluids in the presence of U, Th, Pb, Ba and Br. We used synchrotron X-Ray fluorescence analysis performed in situ in Bassett-modified hydrothermal diamond anvil cells in order to monitor the chemical transfers of the studied elements between the phases in equilibrium at different pressures (up to 1.6 GPa) and temperatures (up to 900°C). We have calculated the partition coefficients for each studied element (i): Difluid/melt = Cifluid/Cimelt. Results show that U and Th exhibit more affinities for the silica-rich hydrous fluids in the presence or absence of Br, considered here such as an analogue for Cl, (i.e. 0.4 < DUfluid/melt < 0.7 depending on P,T conditions). Br partitioning shows that whereas this halogen element has very strong affinity to the aqueous fluid during magma degassing (DBrfluid/melt >> 10 after decompression) this coefficient decreases with pressure suggesting that Br would not be immediately washed out from the subducted plate during dehydration but may be recycled deeper in the mantle. These new data combined with previous ones obtained for Pb, Ba (Bureau et al., 2007, HPR vol 27, p. 235) and Rb, Sr, Zr (Bureau et al., 2004, Eos Trans. AGU, 85(47), V11C-05), allow us to propose a general outline of the fluid phase transfers through the subduction factory: (1) at shallow level: their nature and composition, the impact of the presence of halogens and the fertilizing role of such fluids in the mantle wedge, where the generation of arc magmas takes place (2) deeper in the mantle: where hydrous silica-rich supercritical fluids may also favour a deep recycling of a fraction of volatiles and trace elements present in the subducted oceanic crust.

Basanite-nephelinite suite from early Kilauea: carbonated melts of phlogopite-garnet peridotite at Hawaii's leading magmatic edge

NASA Astrophysics Data System (ADS)

Sisson, T. W.; Kimura, J.-I.; Coombs, M. L.

2009-12-01

A basanite-nephelinite glass suite from early submarine Kilauea defines a continuous compositional array marked by increasing concentrations of incompatible components with decreasing SiO2, MgO, and Al2O3. Like peripheral and post-shield strongly alkalic Hawaiian localities (Clague et al. in J Volcanol Geotherm Res 151:279-307, 2006; Dixon et al. in J Pet 38:911-939, 1997), the early Kilauea basanite-nephelinite glasses are interpreted as olivine fractionation products from primary magnesian alkalic liquids. For early Kilauea, these were saturated with a garnet-phlogopite-sulfide peridotite assemblage, with elevated dissolved CO2 contents responsible for the liquids’ distinctly low-SiO2 concentrations. Reconstructed primitive liquids for early Kilauea and other Hawaiian strongly alkalic localities are similar to experimental 3 GPa low-degree melts of moderately carbonated garnet lherzolite, and estimated parent magma temperatures of 1,350-1,400°C (olivine-liquid geothermometry) match the ambient upper mantle geotherm shortly beneath the base of the lithosphere. The ~3 GPa source regions were too hot for stable crystalline carbonate and may have consisted of ambient upper mantle peridotite containing interstitial carbonate-silicate or carbonatitic liquid, possibly (Dixon et al. in Geochem Geophys Geosyst 9(9):Q09005, 2008), although not necessarily, from the Hawaiian mantle plume. Carbonate-enriched domains were particularly susceptible to further melting upon modest decompression during upward lithospheric flexure beneath the advancing Hawaiian Arch, or by conductive heating or upward drag by the Hawaiian mantle plume. The early Kilauea basanite-nephelinite suite has a HIMU-influenced isotopic character unlike other Hawaiian magmas (Shimizu et al. in EOS Tran Amer Geophys Union 82(47): abstr V12B-0962, 2001; Shimizu et al. in Geochim Cosmochim Acta 66(15A):710, 2002) but consistent with oceanic carbonatite involvement (Hoernle et al. in Contrib Mineral Petrol 142:520-542, 2002). It may represent the melting products of a fertile domain in the ambient upper mantle impinged upon and perturbed by the sustained plume source that feeds later shield-stage magmatism.

The therapeutic effect of negative pressure in treating femoral head necrosis in rabbits.

PubMed

Zhang, Yin-gang; Wang, Xuezhi; Yang, Zhi; Zhang, Hong; Liu, Miao; Qiu, Yushen; Guo, Xiong

2013-01-01

Because negative pressure can stimulate vascular proliferation, improve blood circulation and promote osteogenic differentiation of bone marrow stromal cells, we investigated the therapeutic effect of negative pressure on femoral head necrosis (FHN) in a rabbit model. Animals were divided into four groups (n = 60/group): [1] model control, [2] core decompression, [3] negative pressure and [4] normal control groups. Histological investigation revealed that at 4 and 8 weeks postoperatively, improvements were observed in trabecular bone shape, empty lacunae and numbers of bone marrow hematopoietic cells and fat cells in the negative pressure group compared to the core decompression group. At week 8, there were no significant differences between the negative pressure and normal control groups. Immunohistochemistry staining revealed higher expression of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) in the femoral heads in the negative pressure group compared with the core decompression group. Transmission electron microscopy revealed that cell organelles were further developed in the negative pressure group compared with the core decompression group. Microvascular ink staining revealed an increased number of bone marrow ink-stained blood vessels, a thicker vascular lumen and increased microvascular density in the negative pressure group relative to the core decompression group. Real-time polymerase chain reaction revealed that expression levels of both VEGF and BMP-2 were higher in the negative pressure group compared with the core decompression group. In summary, negative pressure has a therapeutic effect on FHN. This effect is superior to core decompression, indicating that negative pressure is a potentially valuable method for treating early FHN.

The Therapeutic Effect of Negative Pressure in Treating Femoral Head Necrosis in Rabbits

PubMed Central

Zhang, Yin-gang; Wang, Xuezhi; Yang, Zhi; Zhang, Hong; Liu, Miao; Qiu, Yushen; Guo, Xiong

2013-01-01

Because negative pressure can stimulate vascular proliferation, improve blood circulation and promote osteogenic differentiation of bone marrow stromal cells, we investigated the therapeutic effect of negative pressure on femoral head necrosis (FHN) in a rabbit model. Animals were divided into four groups (n = 60/group): [1] model control, [2] core decompression, [3] negative pressure and [4] normal control groups. Histological investigation revealed that at 4 and 8 weeks postoperatively, improvements were observed in trabecular bone shape, empty lacunae and numbers of bone marrow hematopoietic cells and fat cells in the negative pressure group compared to the core decompression group. At week 8, there were no significant differences between the negative pressure and normal control groups. Immunohistochemistry staining revealed higher expression of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) in the femoral heads in the negative pressure group compared with the core decompression group. Transmission electron microscopy revealed that cell organelles were further developed in the negative pressure group compared with the core decompression group. Microvascular ink staining revealed an increased number of bone marrow ink-stained blood vessels, a thicker vascular lumen and increased microvascular density in the negative pressure group relative to the core decompression group. Real-time polymerase chain reaction revealed that expression levels of both VEGF and BMP-2 were higher in the negative pressure group compared with the core decompression group. In summary, negative pressure has a therapeutic effect on FHN. This effect is superior to core decompression, indicating that negative pressure is a potentially valuable method for treating early FHN. PMID:23383276

Technique for Mini-open Decompression of Chiari Type I Malformation in Adults.

PubMed

Pakzaban, Peyman

2017-08-01

The technique for decompression of Chiari type I malformation relies on open exposure of craniocervical junction for suboccipital craniectomy and upper cervical laminectomy with or without duraplasty. There is no detailed technical report of a minimally invasive approach for Chiari decompression in adults. To describe a mini-open technique for decompression of Chiari type I malformation (including duraplasty) in adults. Six consecutive adult patients with symptomatic Chiari type I malformation underwent decompression through a 3 to 4 cm midline incision via a speculum retractor. All patients underwent a limited suboccipital craniectomy and C1 laminectomy with an ultrasonic bone scalpel. All patients underwent duraplasty with a synthetic dural substitute. In the 2 patients with syringomyelia, the arachnoid was opened and intradural dissection was carried out. In the remaining 4 patients, the arachnoid was left intact. All operations were completed successfully through the mini-open exposure. Mean surgery time, blood loss, and length of stay were 114 min, 55 mL, and 1.3 days, respectively. Mean follow-up was 13.2 months (range 9-18). All patients had excellent clinical outcomes as defined by scores of 15 (3 patients) or 16 (3 patients) on Chicago Chiari Outcome Scale. There were no neurological complications or cerebrospinal fluid leaks. Postop computed tomography revealed good boney decompression. In the 2 patients with syringomyelia, MRI at 6 months revealed resolution of the syrinx. Decompression of Chiari type I malformation in adults can be performed safely and effectively through the mini-open exposure described in this report. Copyright © 2017 by the Congress of Neurological Surgeons

Parameter estimation of the copernicus decompression model with venous gas emboli in human divers.

PubMed

Gutvik, Christian R; Dunford, Richard G; Dujic, Zeljko; Brubakk, Alf O

2010-07-01

Decompression Sickness (DCS) may occur when divers decompress from a hyperbaric environment. To prevent this, decompression procedures are used to get safely back to the surface. The models whose procedures are calculated from, are traditionally validated using clinical symptoms as an endpoint. However, DCS is an uncommon phenomenon and the wide variation in individual response to decompression stress is poorly understood. And generally, using clinical examination alone for validation is disadvantageous from a modeling perspective. Currently, the only objective and quantitative measure of decompression stress is Venous Gas Emboli (VGE), measured by either ultrasonic imaging or Doppler. VGE has been shown to be statistically correlated with DCS, and is now widely used in science to evaluate decompression stress from a dive. Until recently no mathematical model has existed to predict VGE from a dive, which motivated the development of the Copernicus model. The present article compiles a selection experimental dives and field data containing computer recorded depth profiles associated with ultrasound measurements of VGE. It describes a parameter estimation problem to fit the model with these data. A total of 185 square bounce dives from DCIEM, Canada, 188 recreational dives with a mix of single, repetitive and multi-day exposures from DAN USA and 84 experimentally designed decompression dives from Split Croatia were used, giving a total of 457 dives. Five selected parameters in the Copernicus bubble model were assigned for estimation and a non-linear optimization problem was formalized with a weighted least square cost function. A bias factor to the DCIEM chamber dives was also included. A Quasi-Newton algorithm (BFGS) from the TOMLAB numerical package solved the problem which was proved to be convex. With the parameter set presented in this article, Copernicus can be implemented in any programming language to estimate VGE from an air dive.

Sagittal imbalance in patients with lumbar spinal stenosis and outcomes after simple decompression surgery.

PubMed

Shin, E Kyung; Kim, Chi Heon; Chung, Chun Kee; Choi, Yunhee; Yim, Dahae; Jung, Whei; Park, Sung Bae; Moon, Jung Hyeon; Heo, Won; Kim, Sung-Mi

2017-02-01

Lumbar spinal stenosis (LSS) is the most common lumbar degenerative disease, and sagittal imbalance is uncommon. Forward-bending posture, which is primarily caused by buckling of the ligamentum flavum, may be improved via simple decompression surgery. The objectives of this study were to identify the risk factors for sagittal imbalance and to describe the outcomes of simple decompression surgery. This is a retrospective nested case-control study PATIENT SAMPLE: This was a retrospective study that included 83 consecutive patients (M:F=46:37; mean age, 68.5±7.7 years) who underwent decompression surgery and a minimum of 12 months of follow-up. The primary end point was normalization of sagittal imbalance after decompression surgery. Sagittal imbalance was defined as a C7 sagittal vertical axis (SVA) ≥40 mm on a 36-inch-long lateral whole spine radiograph. Logistic regression analysis was used to identify the risk factors for sagittal imbalance. Bilateral decompression was performed via a unilateral approach with a tubular retractor. The SVA was measured on serial radiographs performed 1, 3, 6, and 12 months postoperatively. The prognostic factors for sagittal balance recovery were determined based on various clinical and radiological parameters. Sagittal imbalance was observed in 54% (45/83) of patients, and its risk factors were old age and a large mismatch between pelvic incidence and lumbar lordosis. The 1-year normalization rate was 73% after decompression surgery, and the median time to normalization was 1 to 3 months. Patients who did not experience SVA normalization exhibited low thoracic kyphosis (hazard ratio [HR], 1.04; 95% confidence interval [CI], 1.02-1.10) (p<.01) and spondylolisthesis (HR, 0.33; 95% CI, 0.17-0.61) before surgery. Sagittal imbalance was observed in more than 50% of LSS patients, but this imbalance was correctable via simple decompression surgery in 70% of patients. Copyright © 2016 Elsevier Inc. All rights reserved.

Shock melting and vaporization of metals.

NASA Technical Reports Server (NTRS)

Ahrens, T. J.

1972-01-01

The effect of initial porosity on shock induction of melting and vaporization is investigated for Ba, Sr, Li, Fe, Al, U, and Th. For the less compressible of these metals, it is found that for a given strong shock-generation system (explosive in contact, or flyer-plate impact) an optimum initial specific volume exists such that the total entropy production, and hence the amount of metal liquid or vapor, is a maximum. Initial volumes from 1.4 to 2.0 times crystal volumes, depending on the metal sample and shock-inducing system, will result in optimum post-shock entropies.

Research into the rationality and the application scopes of different melting models of nanoparticles

NASA Astrophysics Data System (ADS)

Fu, Qingshan; Xue, Yongqiang; Cui, Zixiang; Duan, Huijuan

2017-07-01

A rational melting model is indispensable to address the fundamental issue regarding the melting of nanoparticles. To ascertain the rationality and the application scopes of the three classical thermodynamic models, namely Pawlow, Rie, and Reiss melting models, corresponding accurate equations for size-dependent melting temperature of nanoparticles were derived. Comparison of the melting temperatures of Au, Al, and Sn nanoparticles calculated by the accurate equations with available experimental results demonstrates that both Reiss and Rie melting models are rational and capable of accurately describing the melting behaviors of nanoparticles at different melting stages. The former (surface pre-melting) is applicable to the stage from initial melting to critical thickness of liquid shell, while the latter (solid particles surrounded by a great deal of liquid) from the critical thickness to complete melting. The melting temperatures calculated by the accurate equation based on Reiss melting model are in good agreement with experimental results within the whole size range of calculation compared with those by other theoretical models. In addition, the critical thickness of liquid shell is found to decrease with particle size decreasing and presents a linear variation with particle size. The accurate thermodynamic equations based on Reiss and Rie melting models enable us to quantitatively and conveniently predict and explain the melting behaviors of nanoparticles at all size range in the whole melting process. [Figure not available: see fulltext.

High-Pressure γ-CaMgSi2O6: Does Penta-Coordinated Silicon Exist in the Earth's Mantle?

NASA Astrophysics Data System (ADS)

Hu, Yi; Kiefer, Boris; Bina, Craig R.; Zhang, Dongzhou; Dera, Przemeslaw K.

2017-11-01

In situ X-ray diffraction experiments with natural Fe- and Al- bearing diopside single crystals and density functional theory (DFT) calculations on diopside end-member composition indicate the existence of a new high-pressure γ-diopside polymorph with rare penta-coordinated silicon. On compression α-diopside transforms to the γ-phase at ˜50 GPa, which in turn, on decompression is observed to convert to the known β-phase below 47 GPa. The new γ-diopside polymorph constitutes another recent example of penta-coordinated silicon (VSi) in overcompressed metastable crystalline silicates, suggesting that VSi may exist in the transition zone and the uppermost lower mantle in appreciable quantities, not only in silicate glass and melts but also in crystalline phases contained in the coldest parts of subducted stagnant slabs. VSi may have significant influences on buoyancy, wave velocity anomalies, deformation mechanisms, chemical reactivity of silicate rocks, and seismicity within the slab.

Magma Fragmentation

NASA Astrophysics Data System (ADS)

Gonnermann, Helge M.

2015-05-01

Magma fragmentation is the breakup of a continuous volume of molten rock into discrete pieces, called pyroclasts. Because magma contains bubbles of compressible magmatic volatiles, decompression of low-viscosity magma leads to rapid expansion. The magma is torn into fragments, as it is stretched into hydrodynamically unstable sheets and filaments. If the magma is highly viscous, resistance to bubble growth will instead lead to excess gas pressure and the magma will deform viscoelastically by fracturing like a glassy solid, resulting in the formation of a violently expanding gas-pyroclast mixture. In either case, fragmentation represents the conversion of potential energy into the surface energy of the newly created fragments and the kinetic energy of the expanding gas-pyroclast mixture. If magma comes into contact with external water, the conversion of thermal energy will vaporize water and quench magma at the melt-water interface, thus creating dynamic stresses that cause fragmentation and the release of kinetic energy. Lastly, shear deformation of highly viscous magma may cause brittle fractures and release seismic energy.

Mobility of partially molten crust, heat and mass transfer, and the stabilization of continents

NASA Astrophysics Data System (ADS)

Teyssier, Christian; Whitney, Donna L.; Rey, Patrice F.

2017-04-01

The core of orogens typically consists of migmatite terrains and associated crustal-derived granite bodies (typically leucogranite) that represent former partially molten crust. Metamorphic investigations indicate that migmatites crystallize at low pressure (cordierite stability) but also contain inclusions of refractory material (mafic, aluminous) that preserve evidence of crystallization at high pressure (HP), including HP granulite and eclogite (1.0-1.5 GPa), and in some cases ultrahigh pressure (2.5-3.0 GPa) when the continental crust was subducted (i.e. Norwegian Caledonides). These observations indicate that the partially molten crust originates in the deep crust or at mantle depths, traverses the entire orogenic crust, and crystallizes at shallow depth, in some cases at the near-surface ( 2 km depth) based on low-T thermochronology. Metamorphic assemblages generally show that this nearly isothermal decompression is rapid based on disequilibrium textures (symplectites). Therefore, the mobility of partially molten crust results in one of the most significant heat and mass transfer mechanisms in orogens. Field relations also indicate that emplacement of partially molten crust is the youngest major event in orogeny, and tectonic activity essentially ceases after the partially molten crust is exhumed. This suggests that flow and emplacement of partially molten crust stabilize the orogenic crust and signal the end of orogeny. Numerical modeling (open source software Underworld; Moresi et al., 2007, PEPI 163) provides useful insight into the mechanisms of exhumation of partially molten crust. For example, extension of thickened crust with T-dependent viscosity shows that extension of the shallow crust initially drives the mobility of the lowest viscosity crust (T>700°C), which begins to flow in a channel toward the zone of extension. This convergent flow generates channel collision and the formation of a double-dome of foliation (two subdomes separated by a steep high strain zone). In turn, the rapid exhumation of low-viscosity deep crust within and between the two subdomes enhances localization of extension in the shallow crust; the positive feedback between exhumation of low-viscosity crust and localization of shallow crust extension explains the exhuming power of migmatite domes, the rapid isothermal decompression of dome rocks (order of 1.0-1.5 GPa), and the crystallization of melt at shallow depth followed by rapid cooling. Modeling results indicate that the mobility of low-viscosity (partially molten) crust is a major process for transferring heat and mass during the late stages of orogeny.

Muscovite-Dehydration Melting: A Textural Study of a Key Reaction in Transforming Continental Margin Strata Into a Migmatitic Orogenic Core

NASA Astrophysics Data System (ADS)

Dyck, B. J.; St Onge, M. R.; Waters, D. J.; Searle, M. P.

2015-12-01

Metamorphosed continental margin sedimentary sequences, which comprise the dominant tectonostratigraphic assemblage exposed in orogenic hinterlands, are crucial to understanding the architecture and evolution of collisional mountain belts. This study explores the textural effect of anatexis in amphibolite-grade conditions and documents the mineral growth mechanisms that control nucleation and growth of K-feldspar, sillimanite and silicate melt. The constrained textural evolution follows four stages: 1) Nucleation - K-feldspar is documented to nucleate epitaxially on isomorphic plagioclase in quartzofeldspathic (psammitic) domains, whereas sillimanite nucleates in the Al-rich (pelitic) domain, initially on [001] mica planes. The first melt forms at the site of muscovite breakdown. 2) Chemically driven growth - In the quartzofeldspathic domain, K-feldspar progressively replaces plagioclase by a K+ - Na+ cation transfer reaction, driven by the freeing of muscovite-bound K+ during breakdown of the mica. Sillimanite forms intergrowths with the remaining hydrous melt components, contained initially in ovoid clots. 3) Merge and coarsening - With an increase in pressure, melt and sillimanite migrate away from clots along grain boundaries. A melt threshold is reached once the grain-boundary network is wetted by melt, increasing the length-scale of diffusion, resulting in grain boundary migration and grain-size coarsening. The melt threshold denotes the transition to an open-system on the lithology scale, where melt is a transient phase. 4) Residual melt crystallization - Residual melt crystallizes preferentially on existing peritectic grains as anatectic quartz, plagioclase, and K-feldspar. As the system cools and closes, grain growth forces melt into the intersections of grain-boundaries, recognized as irregular shaped melt films, or as intergrowths of the volatile-rich phases (i.e. Tur-Ms-Ap). In the Himalayan metamorphic core these processes result in the formation of: pelitic K-feldspar augen gneiss, stockwork leucogranites, and an effective strengthening of the hinterland, as evidenced by a switch in tectonic deformation style, from thin-skinned cover sequence thrust imbrication and folding to out-of-sequence basement-involved thick-skinned thrusting and folding.

Alternative technique in atypical spinal decompression: the use of the ultrasonic scalpel in paediatric achondroplasia

PubMed Central

Woodacre, Timothy; Sewell, Matthew; Clarke, Andrew J; Hutton, Mike

2016-01-01

Spinal stenosis can be a very disabling condition. Surgical decompression carries a risk of dural tear and neural injury, which is increased in patients with severe stenosis or an atypical anatomy. We present an unusual case of symptomatic stenosis secondary to achondroplasia presenting in a paediatric patient, and highlight a new surgical technique used to minimise the risk of dural and neural injury during decompression. PMID:27288205

You’re the Flight Surgeon: Pulmonary Decompression Sickness

DTIC Science & Technology

2008-06-01

follow-up of this patient Diagnosis: Decompression sickness (DeS) with pulmonary symptoms (Type Il DeS, older nomenclature). Treatment: Hyperbaric ...is quite clear thai any case of suspected decompression sickness in the USAF be discussed with the hyperbariC medicine specialists at Brooks City...physician in as respectful manner as you can that you suspect the patient’s condition is likely related to his hypobaric exposure. B. Agree with

The Air Force Mobile Forward Surgical Team (MFST): Using the Estimating Supplies Program to Validate Clinical Requirement

DTIC Science & Technology

2004-12-01

conducted in an abbreviated, staged manner, such as laparotomies, decompression craniotomies , vascular shunts, or amputations. The FRSS provides...Performed at MFST Abbreviated laparotomy 36.29 Vascular shunt/ligate 32.84 Amputation 12.32 Decompression craniotomy 8.98 Thoracotomy 6.35...Vascular shunt/ligations 6 33 Abbreviated laparotomy 4 22 Amputation 3 16 Decompression craniotomy 3 16 Thoracotomy 2 10 Other 3 Total 18 100

Bilateral Ocular Decompression Retinopathy after Ahmed Valve Implantation for Uveitic Glaucoma

PubMed Central

Flores-Preciado, Javier; Ancona-Lezama, David Arturo; Valdés-Lara, Carlos Andrés; Díez-Cattini, Gian Franco; Coloma-González, Itziar

2016-01-01

Case Report We report the case of a 29-year-old man who underwent Ahmed valve implantation in both eyes as treatment for uveitic glaucoma, subsequently presenting with bilateral ocular decompression retinopathy in the postoperative period. Discussion Ocular decompression retinopathy is a rare complication of filtering surgery in patients with glaucoma; however, the course is benign in most cases, with spontaneous resolution of bleedings and improvement of visual acuity. PMID:27920718

Minimally invasive lumbar foraminotomy.

PubMed

Deutsch, Harel

2013-07-01

Lumbar radiculopathy is a common problem. Nerve root compression can occur at different places along a nerve root's course including in the foramina. Minimal invasive approaches allow easier exposure of the lateral foramina and decompression of the nerve root in the foramina. This video demonstrates a minimally invasive approach to decompress the lumbar nerve root in the foramina with a lateral to medial decompression. The video can be found here: http://youtu.be/jqa61HSpzIA.

An atomistic model for cross-linked HNBR elastomers used in seals

NASA Astrophysics Data System (ADS)

Molinari, Nicola; Sutton, Adrian; Stevens, John; Mostofi, Arash

2015-03-01

Hydrogenated nitrile butadiene rubber (HNBR) is one of the most common elastomeric materials used for seals in the oil and gas industry. These seals sometimes suffer ``explosive decompression,'' a costly problem in which gases permeate a seal at the elevated temperatures and pressures pertaining in oil and gas wells, leading to rupture when the seal is brought back to the surface. The experimental evidence that HNBR and its unsaturated parent NBR have markedly different swelling properties suggests that cross-linking may occur during hydrogenation of NBR to produce HNBR. We have developed a code compatible with the LAMMPS molecular dynamics package to generate fully atomistic HNBR configurations by hydrogenating initial NBR structures. This can be done with any desired degree of cross-linking. The code uses a model of atomic interactions based on the OPLS-AA force-field. We present calculations of the dependence of a number of bulk properties on the degree of cross-linking. Using our atomistic representations of HNBR and NBR, we hope to develop a better molecular understanding of the mechanisms that result in explosive decompression.

A combined three-dimensional in vitro–in silico approach to modelling bubble dynamics in decompression sickness

PubMed Central

Stride, E.; Cheema, U.

2017-01-01

The growth of bubbles within the body is widely believed to be the cause of decompression sickness (DCS). Dive computer algorithms that aim to prevent DCS by mathematically modelling bubble dynamics and tissue gas kinetics are challenging to validate. This is due to lack of understanding regarding the mechanism(s) leading from bubble formation to DCS. In this work, a biomimetic in vitro tissue phantom and a three-dimensional computational model, comprising a hyperelastic strain-energy density function to model tissue elasticity, were combined to investigate key areas of bubble dynamics. A sensitivity analysis indicated that the diffusion coefficient was the most influential material parameter. Comparison of computational and experimental data revealed the bubble surface's diffusion coefficient to be 30 times smaller than that in the bulk tissue and dependent on the bubble's surface area. The initial size, size distribution and proximity of bubbles within the tissue phantom were also shown to influence their subsequent dynamics highlighting the importance of modelling bubble nucleation and bubble–bubble interactions in order to develop more accurate dive algorithms. PMID:29263127

Treatment of Large Periapical Cyst Like Lesion: A Noninvasive Approach: A Report of Two Cases

PubMed Central

Maheshwari, Neha; Gothi, Rajat; Sood, Niti

2015-01-01

ABSTRACT Periapical lesions develop as sequelae to pulp disease. Periapical radiolucent areas are generally diagnosed either during routine dental radiographic examination or following acute toothache. Various methods can be used in the nonsurgical management of periapical lesions: the conservative root canal treatment, decompression technique, active nonsurgical decompression technique, aspiration-irrigation technique, method using calcium hydroxide, lesion sterilization and repair therapy and the apexum procedure. Monitoring the healing of periapical lesions is essential through periodic follow-up examinations. The ultimate goal of endodontic therapy should be to return the involved teeth to a state of health and function without surgical intervention. All inflammatory periapical lesions should be initially treated with conservative nonsurgical procedures. Surgical intervention is recommended only after nonsurgical techniques have failed. Besides, surgery has many drawbacks, which limit its use in the management of periapical lesions. How to cite this article: Sood N, Maheshwari N, Gothi R, Sood N. Treatment of Large Periapical Cyst Like Lesion: A Noninvasive Approach: A Report of Two Cases. Int J Clin Pediatr Dent 2015;8(2):133-137. PMID:26379382

Treatment of Large Periapical Cyst Like Lesion: A Noninvasive Approach: A Report of Two Cases.

PubMed

Sood, Nikhil; Maheshwari, Neha; Gothi, Rajat; Sood, Niti

2015-01-01

Periapical lesions develop as sequelae to pulp disease. Periapical radiolucent areas are generally diagnosed either during routine dental radiographic examination or following acute toothache. Various methods can be used in the nonsurgical management of periapical lesions: the conservative root canal treatment, decompression technique, active nonsurgical decompression technique, aspiration-irrigation technique, method using calcium hydroxide, lesion sterilization and repair therapy and the apexum procedure. Monitoring the healing of periapical lesions is essential through periodic follow-up examinations. The ultimate goal of endodontic therapy should be to return the involved teeth to a state of health and function without surgical intervention. All inflammatory periapical lesions should be initially treated with conservative nonsurgical procedures. Surgical intervention is recommended only after nonsurgical techniques have failed. Besides, surgery has many drawbacks, which limit its use in the management of periapical lesions. How to cite this article: Sood N, Maheshwari N, Gothi R, Sood N. Treatment of Large Periapical Cyst Like Lesion: A Noninvasive Approach: A Report of Two Cases. Int J Clin Pediatr Dent 2015;8(2):133-137.

Demonstrating damage tolerance of composite airframes

NASA Technical Reports Server (NTRS)

Poe, Clarence C., Jr.

1993-01-01

Commercial transport aircraft operating in the United States are certified by the Federal Aviation Authority to be damage tolerant. On 28 April 1988, Aloha Airlines Flight 243, a Boeing 727-200 airplane, suffered an explosive decompression of the fuselage but landed safely. This event provides very strong justification for the damage tolerant design criteria. The likely cause of the explosive decompression was the linkup of numerous small fatigue cracks that initiated at adjacent fastener holes in the lap splice joint at the side of the body. Actually, the design should have limited the damage size to less than two frame spacings (about 40 inches), but this type of 'multi-site damage' was not originally taken into account. This cracking pattern developed only in the high-time airplanes (many flights). After discovery in the fleet, a stringent inspection program using eddy current techniques was inaugurated to discover these cracks before they linked up. Because of concerns about safety and the maintenance burden, the lap-splice joints of these high-time airplanes are being modified to remove cracks and prevent new cracking; newer designs account for 'multi-site damage'.

Endoscopic foraminal decompression for failed back surgery syndrome under local anesthesia.

PubMed

Yeung, Anthony; Gore, Satishchandra

2014-01-01

The most common causes of failed back surgery are residual or recurrent herniation, foraminal fibrosis and foraminal stenosis that is ignored, untreated, or undertreated. Residual back ache may also be from facetal causes or denervation and scarring of the paraspinal muscles.(1-6) The original surgeon may advise his patient that nothing more can be done on the basis of his opinion that the nerve was visually decompressed by the original surgery, supported by improved post-op imaging and follow-up studies such as EMG and conduction velocity studies. Post-op imaging or electrophysiological assessment may be inadequate to explain all the reasons for residual or recurrent symptoms. Treatment of Failed back surgery by repeat traditional open revision surgery usually incorporates more extensive decompression causing increased instability and back pain, therefore necessitating fusion. The authors, having limited their practice to endoscopic MIS surgery over the last 15-20 years, report on their experience gained during that period to relieve pain by endoscopically visualizing and treating unrecognized causative patho-anatomy in FBSS.(7.) Thirty consecutive patients with FBSS presenting with back and leg pain that had supporting imaging diagnosis of lateral stenosis and /or residual / recurrent disc herniation, or whose pain complaint was supported by relief from diagnostic and therapeutic injections (Figure 1), were offered percutaneous transforaminal endoscopic discectomy and foraminoplasty over a repeat open procedure. Each patient sought consultation following a transient successful, partially successful or unsuccessful open translaminar surgical treatment for disc herniation or spinal stenosis. Endoscopic foraminoplasty was also performed to either decompress the bony foramen for foraminal stenosis, or foraminoplasty to allow for endoscopic visual examination of the affected traversing and exiting nerve roots in the axilla, also known as the "hidden zone" of Macnab (Figure 2).(8, 9) The average follow up time was, average 40 months, minimum 12 months. Outcome data at each visit included Macnab, VAS and ODI. Fig. 1A diagnostic and therapeutic epidural gram may help identify unrecognized lateral recess stenosis underestimated by MRI. An excellent result from a therapeutic block lends excellent prognosis for a more lasting and "permanent" result from transforaminal endoscopic lateral recess decompression.Fig. 2Kambin's Triangle provides access to the "hidden zone" of Macnab by foraminoplasty. The foramen and lateral recess is decompressed by removing the ventral aspect and tip of the superior articular process to gain access to the axilla between the traversing and exiting nerve. FBSS contains patho-anatomy in the axilla between the traversing and exiting nerve that hides the pain generators of FBSS. The average pre-operative VAS improved from 7.2 to 4.0, and ODI 48% to 31%. While temporary dysesthesia occurred in 4 patients in the early post-operative period, all were happy, as all received additional relief of their pre-op symptoms. They were also relieved to be able to avoid "open" decompression or fusion surgery. The transforaminal endoscopic approach is effective for FBSS due to residual/recurrent HNP and lateral stenosis. Failed initial index surgery may involve failure to recognize patho-anatomy in the axilla of the foramen housing the traversing and the exiting nerve, including the DRG, which is located cephalad and near the tip of SAP.(10) The transforaminal endoscopic approach effectively decompresses the foramen and does not further destabilize the spine needing stabilization.(11) It also avoids going through the previous surgical site. Disc narrowing as a consequence of translaminar discectomy and progressive degenerative narrowing and spondylolisthesis (Figure 3) as a natural history of degenerative disc disease can lead to central and lateral stenosis. The MRI may underestimate the degree of stenosis from a bulging or a foraminal disc protrusion and residual lateral recess stenosis. Pain can be diagnosed and confirmed by evocative discography and by clinical response to transforaminal diagnostic and therapeutic steroid injections.(12) Foraminal endoscopic decompression of the lateral recess is a MIS technique that does not "burn bridges" for a more conventional approach and it adds to the surgical armamentarium of FBSS. Fig. 3Cadaver Illustration of Foraminal Stenosis (courtesy of Wolfgang Rauschning). As the disc narrows, the superior articular process impinges on the exiting nerve and DRG, creating lateral recess stenosis, lumbar spondylosis, and facet arthrosis.

Endoscopic Foraminal Decompression for Failed Back Surgery Syndrome under local Anesthesia

PubMed Central

Gore, Satishchandra

2014-01-01

Background The most common causes of failed back surgery are residual or recurrent herniation, foraminal fibrosis and foraminal stenosis that is ignored, untreated, or undertreated. Residual back ache may also be from facetal causes or denervation and scarring of the paraspinal muscles.1–6 The original surgeon may advise his patient that nothing more can be done on the basis of his opinion that the nerve was visually decompressed by the original surgery, supported by improved post-op imaging and follow-up studies such as EMG and conduction velocity studies. Post-op imaging or electrophysiological assessment may be inadequate to explain all the reasons for residual or recurrent symptoms. Treatment of Failed back surgery by repeat traditional open revision surgery usually incorporates more extensive decompression causing increased instability and back pain, therefore necessitating fusion. The authors, having limited their practice to endoscopic MIS surgery over the last 15-20 years, report on their experience gained during that period to relieve pain by endoscopically visualizing and treating unrecognized causative patho-anatomy in FBSS.7 Methods Thirty consecutive patients with FBSS presenting with back and leg pain that had supporting imaging diagnosis of lateral stenosis and /or residual / recurrent disc herniation, or whose pain complaint was supported by relief from diagnostic and therapeutic injections (Figure 1), were offered percutaneous transforaminal endoscopic discectomy and foraminoplasty over a repeat open procedure. Each patient sought consultation following a transient successful, partially successful or unsuccessful open translaminar surgical treatment for disc herniation or spinal stenosis. Endoscopic foraminoplasty was also performed to either decompress the bony foramen for foraminal stenosis, or foraminoplasty to allow for endoscopic visual examination of the affected traversing and exiting nerve roots in the axilla, also known as the “hidden zone” of Macnab (Figure 2).8, 9 The average follow up time was, average 40 months, minimum 12 months. Outcome data at each visit included Macnab, VAS and ODI. Fig. 1 A diagnostic and therapeutic epidural gram may help identify unrecognized lateral recess stenosis underestimated by MRI. An excellent result from a therapeutic block lends excellent prognosis for a more lasting and “permanent” result from transforaminal endoscopic lateral recess decompression. Fig. 2 Kambin's Triangle provides access to the “hidden zone” of Macnab by foraminoplasty. The foramen and lateral recess is decompressed by removing the ventral aspect and tip of the superior articular process to gain access to the axilla between the traversing and exiting nerve. FBSS contains patho-anatomy in the axilla between the traversing and exiting nerve that hides the pain generators of FBSS. Results The average pre-operative VAS improved from 7.2 to 4.0, and ODI 48% to 31%. While temporary dysesthesia occurred in 4 patients in the early post-operative period, all were happy, as all received additional relief of their pre-op symptoms. They were also relieved to be able to avoid “open” decompression or fusion surgery. Conclusions / Level of Evidence 3 The transforaminal endoscopic approach is effective for FBSS due to residual/recurrent HNP and lateral stenosis. Failed initial index surgery may involve failure to recognize patho-anatomy in the axilla of the foramen housing the traversing and the exiting nerve, including the DRG, which is located cephalad and near the tip of SAP.10 The transforaminal endoscopic approach effectively decompresses the foramen and does not further destabilize the spine needing stabilization.11 It also avoids going through the previous surgical site. Clinical Relevance Disc narrowing as a consequence of translaminar discectomy and progressive degenerative narrowing and spondylolisthesis (Figure 3) as a natural history of degenerative disc disease can lead to central and lateral stenosis. The MRI may underestimate the degree of stenosis from a bulging or a foraminal disc protrusion and residual lateral recess stenosis. Pain can be diagnosed and confirmed by evocative discography and by clinical response to transforaminal diagnostic and therapeutic steroid injections.12 Foraminal endoscopic decompression of the lateral recess is a MIS technique that does not “burn bridges” for a more conventional approach and it adds to the surgical armamentarium of FBSS. Fig. 3 Cadaver Illustration of Foraminal Stenosis (courtesy of Wolfgang Rauschning). As the disc narrows, the superior articular process impinges on the exiting nerve and DRG, creating lateral recess stenosis, lumbar spondylosis, and facet arthrosis. PMID:25694939

Magma ocean formation due to giant impacts

NASA Technical Reports Server (NTRS)

Tonks, W. B.; Melosh, H. J.

1992-01-01

The effect of giant impacts on the initial chemical and thermal states of the terrestrial planets is just now being explored. A large high speed impact creates an approximately hemispherical melt region with a radius that depends on the projectile's radius and impact speed. It is shown that giant impacts on large planets can create large, intact melt regions containing melt volumes up to a few times the volume of the projectile. These large melt regions are not created on asteroid sized bodies. If extruded to the surface, these regions contain enough melt to create a magma ocean of considerable depth, depending on the impact speed, projectile radius, and gravity of the target planet.

Origin of geochemical mantle components: Role of spreading ridges and thermal evolution of mantle

NASA Astrophysics Data System (ADS)

Kimura, Jun-Ichi; Gill, James B.; van Keken, Peter E.; Kawabata, Hiroshi; Skora, Susanne

2017-02-01

We explore the element redistribution at mid-ocean ridges (MOR) using a numerical model to evaluate the role of decompression melting of the mantle in Earth's geochemical cycle, with focus on the formation of the depleted mantle component. Our model uses a trace element mass balance based on an internally consistent thermodynamic-petrologic computation to explain the composition of MOR basalt (MORB) and residual peridotite. Model results for MORB-like basalts from 3.5 to 0 Ga indicate a high mantle potential temperature (Tp) of 1650-1500°C during 3.5-1.5 Ga before decreasing gradually to ˜1300°C today. The source mantle composition changed from primitive (PM) to depleted as Tp decreased, but this source mantle is variable with an early depleted reservoir (EDR) mantle periodically present. We examine a two-stage Sr-Nd-Hf-Pb isotopic evolution of mantle residues from melting of PM or EDR at MORs. At high-Tp (3.5-1.5 Ga), the MOR process formed extremely depleted DMM. This coincided with formation of the majority of the continental crust, the subcontinental lithospheric mantle, and the enriched mantle components formed at subduction zones and now found in OIB. During cooler mantle conditions (1.5-0 Ga), the MOR process formed most of the modern ocean basin DMM. Changes in the mode of mantle convection from vigorous deep mantle recharge before ˜1.5 Ga to less vigorous afterward is suggested to explain the thermochemical mantle evolution.

Foreland-forearc collisional granitoid and mafic magmatism caused by lower-plate lithospheric slab breakoff: The Acadian of Maine, and other orogens

USGS Publications Warehouse

Schoonmaker, A.; Kidd, W.S.F.; Bradley, D.C.

2005-01-01

During collisional convergence, failure in extension of the lithosphere of the lower plate due to slab pull will reduce the thickness or completely remove lower-plate lithosphere and cause decompression melting of the asthenospheric mantle; magmas from this source may subsequently provide enough heat for substantial partial melting of crustal rocks under or beyond the toe of the collisional accretionary system. In central Maine, United States, this type of magmatism is first apparent in the Early Devonian West Branch Volcanics and equivalent mafic volcanics, in the slightly younger voluminous mafic/silicic magmatic event of the Moxie Gabbro-Katahdin batholith and related ignimbrite volcanism, and in other Early Devonian granitic plutons. Similar lower-plate collisional sequences with mafic and related silicic magmatism probably caused by slab breakoff are seen in the Miocene-Holocene Papuan orogen, and the Hercynian-Alleghenian belt. Magmatism of this type is significant because it gives evidence in those examples of whole-lithosphere extension. We infer that normal fault systems in outer trench slopes of collisional orogens in general, and possibly those of oceanic subduction zones, may not be primarily due to flexural bending, but are also driven by whole-lithosphere extension due to slab pull. The Maine Acadian example suggests that slab failure and this type of magmatism may be promoted by pre-existing large margin-parallel faults in the lower plate. ?? 2005 Geological Society of America.

Sr isotope zoning in plagioclase from andesites at Cabo De Gata, Spain: Evidence for shallow and deep contamination

NASA Astrophysics Data System (ADS)

Waight, Tod E.; Tørnqvist, Jakob B.

2018-05-01

Plagioclase crystals in andesites from the Cabo De Gata region show generally radiogenic Sr isotope compositions and consistent core to rim increases in 87Sr/86Sr that are indicative of open system processes in the lithosphere and crustal contamination during crystallization. High-grade metamorphic rocks of the Alpujárride and Nevado-Filábride complexes represent the most likely crustal contaminants. The plagioclases are characterized by subtly zoned and resorbed calcic cores (An73-86). These cores also have radiogenic 87Sr/86Sr (0.7127-0.7129), although typically less radiogenic than plagioclase rims, groundmass plagioclase and whole rock compositions (up to 87Sr/86Sr = 0.7135). These cores are interpreted to represent early crystallization of plagioclase from hydrous melts emplaced into the lower crust. The parental melts to these andesites must therefore have already inherited their radiogenic Sr isotope compositions prior to entering the lower crust and before the onset of crystallization of plagioclase, which is inconsistent with previous models suggesting that the generally radiogenic nature of Sr in these volcanics reflects large amounts of crustal contamination. Instead, the isotope systematics are consistent with models invoked significant addition of a subducted sediment component to the mantle source. The high-An% plagioclase cores are characterized by resorption textures, which are consistent with dissolution during rapid decompression and/or devolatisation during magma migration from the lower crust into upper crustal magma chambers.

Dibutyryl cAMP effects on thromboxane and leukotriene production in decompression-induced lung injury

NASA Technical Reports Server (NTRS)

Little, T. M.; Butler, B. D.

1997-01-01

Decompression-induced venous bubble formation has been linked to increased neutrophil counts, endothelial cell injury, release of vasoactive eicosanoids, and increased vascular membrane permeability. These actions may account for inflammatory responses and edema formation. Increasing the intracellular cAMP has been shown to decrease eicosanoid production and edema formation in various models of lung injury. Reduction of decompression-induced inflammatory responses was evaluated in decompressed rats pretreated with saline (controls) or dibutyryl cAMP (DBcAMP, an analog of cAMP). After pretreatment, rats were exposed to either 616 kPa for 120 min or 683 kPa for 60 min. The observed increases in extravascular lung water ratios (pulmonary edema), bronchoalveolar lavage, and pleural protein in the saline control group (683 kPa) were not evident with DBcAMP treatment. DBcAMP pretreatment effects were also seen with the white blood cell counts and the percent of neutrophils in the bronchoalveolar lavage. Urinary levels of thromboxane B2, 11-dehydrothromboxane B2, and leukotriene E4 were significantly increased with the 683 kPa saline control decompression exposure. DBcAMP reduced the decompression-induced leukotriene E4 production in the urine. Plasma levels of thromboxane B2, 11-dehydrothromboxane B2, and leukotriene E4 were increased with the 683-kPa exposure groups. DBcAMP treatment did not affect these changes. The 11-dehydrothromboxane B2 and leukotriene E4 levels in the bronchoalveolar lavage were increased with the 683 kPa exposure and were reduced with the DBcAMP treatment. Our results indicate that DBcAMP has the capability to reduce eicosanoid production and limit membrane permeability and subsequent edema formation in rats experiencing decompression sickness.

Nerve Decompression Surgery After Total Hip Arthroplasty: What Are the Outcomes?

PubMed

Chughtai, Morad; Khlopas, Anton; Gwam, Chukwuwieke U; Elmallah, Randa K; Thomas, Melbin; Nace, James; Mont, Michael A

2017-04-01

The purpose of our study was to compare (1) muscle strength; (2) pain; (3) sensation; (4) various outcome measurement scales between post-total hip arthroplasty (THA) patients who had a sciatic nerve injury and did or did not receive decompression surgery for this condition; and (5) to compare these findings with current literature. Nineteen patients who had nerve injury after THA were reviewed. Patients were stratified into those who had a nerve decompression (n = 12), and those who had not (n = 7). Motor strength was evaluated using the Muscle Strength Testing Scale. Pain was evaluated by using the visual analogue scale. Systematic literature search was performed to compare the findings of this study with others currently published. The decompression group had a significant improvement in motor strength and the visual analog scale scores as compared with nonoperative group. Patients in decompression group had a significant larger increase in the mean Harris hip score and University of California Los Angeles score. There was no significant difference in the increase of Short Form-36 physical and mental scores between the 2 groups. Literature review for nonoperative management yielded 5 studies (93 patients), with 33% improvement. There were 7 studies (81 patients) on nerve decompression surgery, with 75% improvement. This study demonstrates the benefits of nerve decompression surgery in patients who had sciatic nerve injury after THA, as evidenced by results of standardized outcome measurement scales. It is possible to achieve improvements in terms of strength, pain, and clinical outcomes. Comparative studies with larger cohorts are needed to fully assess the best candidates for this procedure. Copyright © 2016 Elsevier Inc. All rights reserved.

A Start Toward Micronucleus-Based Decompression Models; Altitude Decompression

NASA Technical Reports Server (NTRS)

Van Liew, H. D.; Conkin, Johnny

2007-01-01

Do gaseous micronuclei trigger the formation of bubbles in decompression sickness (DCS)? Most previous instructions for DCS prevention have been oriented toward supersaturated gas in tissue. We are developing a mathematical model that is oriented toward the expected behavior of micronuclei. The issue is simplified in altitude decompressions because the aviator or astronaut is exposed only to decompression, whereas in diving there is a compression before the decompression. The model deals with four variables: duration of breathing of 100% oxygen before going to altitude (O2 prebreathing), altitude of the exposure, exposure duration, and rate of ascent. Assumptions: a) there is a population of micronuclei of various sizes having a range of characteristics, b) micronuclei are stable until they grow to a certain critical nucleation radius, c) it takes time for gas to diffuse in or out of micronuclei, and d) all other variables being equal, growth of micronuclei upon decompression is more rapid at high altitude because of the rarified gas in the micronuclei. To estimate parameters, we use a dataset of 4,756 men in altitude chambers exposed to various combinations of the model s variables. The model predicts occurrence of DCS symptoms quite well. It is notable that both the altitude chamber data and the model show little effect of O2 prebreathing until it lasts more than 60 minutes; this is in contrast to a conventional idea that the benefit of prebreathing is directly due to exponential washout of tissue nitrogen. The delay in response to O2 prebreathing can be interpreted as time required for outward diffusion of nitrogen; when the micronuclei become small enough, they are disabled, either by crushing or because they cannot expand to a critical nucleation size when the subject ascends to altitude.

Long-term effects of core decompression by drilling. Demonstration of bone healing and vessel ingrowth in an animal study.

PubMed

Simank, H G; Graf, J; Kerber, A; Wiedmaier, S

1997-01-01

Avascular necrosis of the femoral head is associated with bone marrow hyperpression. Although core decompression by drilling is an accepted treatment regimen, until today no experimental results exist concerning the physiological effects of this procedure. Published clinical data are controversial. In an animal study marrow decompression was carried out by drilling of both hips in 18 healthy male sheep. In the right hip of each animal a resorbable stent was implanted in order to prolong the duration of core decompression. Over a time period of 24 weeks the effects were studied by measurement of the intraosseous pressure, by the plastination method and by morphological examination with light and electron microscopy. Bone drilling is a procedure of high short-time efficacy in decompressing the bone marrow. But decompression lasts only for a short time period. Three weeks postoperatively the drill channel is sealed by hematoma and fibrous tissue in both hips (with/without stent) and no significant decompressive effect is measured. Ingrowth of vessels along the drill channel is found in all hips after a time period of 3 weeks. These vessels originate from the periosteum as well as from the bone marrow and form temporary anastomoses between the periostal-diaphyseal-metaphyseal and the epiphyseal-physeal circulatory system. In conclusion, for the first time an anastomosis induced by drilling between both circulatory systems of bone is demonstrated and the importance of the periosteum is confirmed. The time of decreased core pressure induced by drilling is too short for substitution of a necrotic area and could be the explanation of the inferior clinical results of the procedure.

Patient-specific core decompression surgery for early-stage ischemic necrosis of the femoral head

PubMed Central

Wang, Wei; Hu, Wei; Yang, Pei; Dang, Xiao Qian; Li, Xiao Hui; Wang, Kun Zheng

2017-01-01

Introduction Core decompression is an efficient treatment for early stage ischemic necrosis of the femoral head. In conventional procedures, the pre-operative X-ray only shows one plane of the ischemic area, which often results in inaccurate drilling. This paper introduces a new method that uses computer-assisted technology and rapid prototyping to enhance drilling accuracy during core decompression surgeries and presents a validation study of cadaveric tests. Methods Twelve cadaveric human femurs were used to simulate early-stage ischemic necrosis. The core decompression target at the anterolateral femoral head was simulated using an embedded glass ball (target). Three positioning Kirschner wires were drilled into the top and bottom of the large rotor. The specimen was then subjected to computed tomography (CT). A CT image of the specimen was imported into the Mimics software to construct a three-dimensional model including the target. The best core decompression channel was then designed using the 3D model. A navigational template for the specimen was designed using the Pro/E software and manufactured by rapid prototyping technology to guide the drilling channel. The specimen-specific navigation template was installed on the specimen using positioning Kirschner wires. Drilling was performed using a guide needle through the guiding hole on the templates. The distance between the end point of the guide needle and the target was measured to validate the patient-specific surgical accuracy. Results The average distance between the tip of the guide needle drilled through the guiding template and the target was 1.92±0.071 mm. Conclusions Core decompression using a computer-rapid prototyping template is a reliable and accurate technique that could provide a new method of precision decompression for early-stage ischemic necrosis. PMID:28464029

Microendoscopic posterior decompression for the treatment of thoracic myelopathy caused by ossification of the ligamentum flavum: a technical report.

PubMed

Baba, Satoshi; Oshima, Yasushi; Iwahori, Tomoyuki; Takano, Yuichi; Inanami, Hirohiko; Koga, Hisashi

2016-06-01

Ossification of the ligamentum flavum (OLF) is a common cause of progressive thoracic myelopathy in East Asia. Good surgical results are expected for patients who already show myelopathy. Surgical decompression using a posterior approach is commonly used to treat OLF. This study investigated the use of microendoscopic posterior decompression for the treatment of thoracic OLF. Microendoscopic posterior decompression was performed on 9 patients with myelopathy. Patients had a mean age of 59.8 years and single-level involvement, mostly at the T10-11 and T11-12 vertebrae. Computed tomography and magnetic resonance imaging were used to classify the OLF. A tubular retractor and endoscopic system were used for microendoscopic posterior decompression. Midline and unilateral paramedian approaches were performed in 2 and 7 patients, respectively. Intraoperative motor evoked potentials (MEPs) of 7 patients were monitored. Pre- and postoperative neurological status was evaluated using the modified Japanese Orthopaedic Association (mJOA) score. Thoracic OLF for all patients were classed as bilateral type with a round morphology. Improvement of MEPs at least one muscle area was recorded in all patients following posterior decompression. A dural tear in one patient was the only observed complication. The mean recovery rate was 44.9 %, as calculated from mJOA scores at a mean follow-up period of 20 months. Microendoscopic posterior decompression combined with MEP monitoring can be used to treat patients with thoracic OLF. The optimal surgical indication is OLF at a single vertebral level and of a unilateral or bilateral nature, without comma and tram track signs, and a round morphology.

Patient-specific core decompression surgery for early-stage ischemic necrosis of the femoral head.

PubMed

Wang, Wei; Hu, Wei; Yang, Pei; Dang, Xiao Qian; Li, Xiao Hui; Wang, Kun Zheng

2017-01-01

Core decompression is an efficient treatment for early stage ischemic necrosis of the femoral head. In conventional procedures, the pre-operative X-ray only shows one plane of the ischemic area, which often results in inaccurate drilling. This paper introduces a new method that uses computer-assisted technology and rapid prototyping to enhance drilling accuracy during core decompression surgeries and presents a validation study of cadaveric tests. Twelve cadaveric human femurs were used to simulate early-stage ischemic necrosis. The core decompression target at the anterolateral femoral head was simulated using an embedded glass ball (target). Three positioning Kirschner wires were drilled into the top and bottom of the large rotor. The specimen was then subjected to computed tomography (CT). A CT image of the specimen was imported into the Mimics software to construct a three-dimensional model including the target. The best core decompression channel was then designed using the 3D model. A navigational template for the specimen was designed using the Pro/E software and manufactured by rapid prototyping technology to guide the drilling channel. The specimen-specific navigation template was installed on the specimen using positioning Kirschner wires. Drilling was performed using a guide needle through the guiding hole on the templates. The distance between the end point of the guide needle and the target was measured to validate the patient-specific surgical accuracy. The average distance between the tip of the guide needle drilled through the guiding template and the target was 1.92±0.071 mm. Core decompression using a computer-rapid prototyping template is a reliable and accurate technique that could provide a new method of precision decompression for early-stage ischemic necrosis.

Orbital Decompression in Thyroid Eye Disease

PubMed Central

Fichter, N.; Guthoff, R. F.; Schittkowski, M. P.

2012-01-01

Though enlargement of the bony orbit by orbital decompression surgery has been known for about a century, surgical techniques vary all around the world mostly depending on the patient's clinical presentation but also on the institutional habits or the surgeon's skills. Ideally every surgical intervention should be tailored to the patient's specific needs. Therefore the aim of this paper is to review outcomes, hints, trends, and perspectives in orbital decompression surgery in thyroid eye disease regarding different surgical techniques. PMID:24558591

29 CFR Appendix A to Subpart S of... - Decompression Tables

Code of Federal Regulations, 2010 CFR

2010-07-01

... working period at 20 pounds gauge. Decompression Table No. 1: 20 pounds for 4 hours, total decompression... minutes per pound. Stage 2 (final) elapsed time 40 Total time 43 Example No. 2: 5-hour working period at... pressure p.s.i.g. Working period hours 1/2 1 11/2 2 3 4 5 6 7 8 Over 8 9 to 12 3 3 3 3 3 3 3 3 3 3 3 14 6 6...

Patterns and Variations in Microvascular Decompression for Trigeminal Neuralgia

PubMed Central

TODA, Hiroki; GOTO, Masanori; IWASAKI, Koichi

2015-01-01

Microvascular decompression (MVD) is a highly effective surgical treatment for trigeminal neuralgia (TN). Although there is little prospective clinical evidence, accumulated observational studies have demonstrated the benefits of MVD for refractory TN. In the current surgical practice of MVD for TN, there have been recognized patterns and variations in surgical anatomy and various decompression techniques. Here we provide a stepwise description of surgical procedures and relevant anatomical characteristics, as well as procedural options. PMID:25925756