30,928 research outputs found
Adiabat_1ph: A new public front-end to the MELTS, pMELTS, and pHMELTS models
The program adiabat_1ph is a simple text-menu driver for subroutine versions of the algorithms MELTS, pMELTS, and pHMELTS [Asimow et al., 2004; Ghiorso et al., 2002; Ghiorso and Sack, 1995]. It may be used to calculate equilibrium assemblages along a thermodynamic path set by the user and can simultaneously calculate trace element distributions. The MELTS family of algorithms is suitable for multicomponent systems, which may be anhydrous, water-undersaturated, or water-saturated, with the options of buffering oxygen fugacity and/or water activity. A wide variety of calculations can be performed either subsolidus or with liquid(s) present; melting and crystallization may be batch, fractional, or continuous. The software is suitable for Linux, MacOS X, and Windows, and many aspects of program execution are controlled by environment variables. Perl scripts are also provided that may be used to invoke adiabat_1ph with some command line options and to produce output that may be easily imported into spreadsheet programs, such as Microsoft Excel. Benefits include a batch mode, which allows almost complete automation of the calculation process when suitable input files are written. This technical brief describes version 1.04, which is provided as ancillary material. Binaries, scripts, documentation, and example files for this and future releases may be downloaded at http://www.gps.caltech.edu/~asimow/adiabat. On a networked computer, adiabat_1ph automatically checks whether a newer version is available
Petrology of some oceanic island basalts: PRIMELT2.XLS software for primary magma calculation
PRIMELT2.XLS software is introduced for calculating primary magma composition and mantle potential temperature (TP) from an observed lava composition. It is an upgrade over a previous version in that it includes garnet peridotite melting and it detects complexities that can lead to overestimates in TP by >100°C. These are variations in source lithology, source volatile content, source oxidation state, and clinopyroxene fractionation. Nevertheless, application of PRIMELT2.XLS to lavas from a wide range of oceanic islands reveals no evidence that volatile-enrichment and source fertility are sufficient to produce them. All are associated with thermal anomalies, and this appears to be a prerequisite for their formation. For the ocean islands considered in this work, TP maxima are typically ~1450–1500°C in the Atlantic and 1500–1600°C in the Pacific, substantially greater than ~1350°C for ambient mantle. Lavas from the Galápagos Islands and Hawaii record in their geochemistry high TP maxima and large ranges in both TP and melt fraction over short horizontal distances, a result that is predicted by the mantle plume model
Melt homogenization and self-organization of chalcogenides glasses: evidence of sharp rigidity, stress and nanoscale phase separation transitions in the GexSe100-x binary
A Raman profiling method is used to monitor growth of GexSe100-x melts and
reveals a two step process of homogenization. Resulting homogeneous glasses
show the non-reversing enthalpy at Tg, {\Delta}Hnr(x), to show a square-well
like variation with x, with a rigidity transition near xc(1) = 19.5(5)% and
stress transition near xc(2) = 26.0(5)%) representing the boundaries of the
rigid but stress-free Intermediate Phase (IP). The square-well like variation
of {\Delta}Hnr(x) develops sloping walls, a triangular shape and eventually
disappears in glasses having an increasing heterogeneity. The {\Delta}Hnr term
ages over weeks outside the IP but not inside the IP. An optical analogue of
the reversibility window is observed with Raman spectra of as-quenched melts
and Tg cycled glasses being the same for glass compositions in the IP but
different for compositions outside the IP. Variations of Molar volumes, display
three regimes of behavior with a global minimum in the IP and a pronounced
increase outside that phase. The intrinsic physical behavior of dry and
homogeneous chalcogenides glasses can vary sharply with composition near
elastic and chemical phase transitions, showing that the physics of network
glasses requires homogeneous samples, and may be far more interesting than
hitherto recognized
Tetrahedrally coordinated carbonates in Earth's lower mantle
Carbonates are the main species that bring carbon deep into our planet
through subduction. They are an important rock-forming mineral group,
fundamentally distinct from silicates in Earth's crust in that carbon binds to
three oxygen atoms, while silicon is bonded to four oxygens. Here, we present
experimental evidence that under the sufficiently high pressures and high
temperatures existing in the lower mantle, ferromagnesian carbonates transform
to a phase with tetrahedrally coordinated carbons. Above 80 GPa, in situ
synchrotron infrared experiments show the unequivocal spectroscopic signature
of the high-pressure phase of (Mg,Fe)CO. Using ab-initio calculations, we
assign the new IR signature to C-O bands associated with tetrahedrally
coordinated carbon with asymmetric C-O bonds. Tetrahedrally coordinated
carbonates are expected to exhibit substantially different reactivity than low
pressure three-fold coordinated carbonates, as well as different chemical
properties in the liquid state. Hence this may have significant implications on
carbon reservoirs and fluxes and the global geodynamic carbon cycle
CO2-crystal wettability in potassic magmas. Implications for eruptive dynamics in light of experimental evidence for heterogeneous nucleation.
The volatile content in magmas is fundamental for the triggering and style of volcanic eruptions. Carbon dioxide, the second most abundant volatile component in magmas after H2O, is the first to reach saturation upon ascent and depressurization. We investigate experimentally CO2-bubble nucleation in trachybasalt and trachyte melts at high temperature and high pressure (HT and HP) through wetting-angle measurements on different (sialic, mafic or oxide) phenocryst phases. The presence of crystals lowers the supersaturation required for CO2- bubble nucleation up to 37 per cent (heterogeneous nucleation, HeN), with a minor role of mineral chemistry. Different from H2O-rich systems, feldspar crystals are effective in reducing required supersaturation for bubble nucleation. Our data suggest that leucite, the dominant liquidus phase in ultrapotassic systems at shallow depth (i.e. <100 MPa), facilitates late-stage, extensive magma vesiculation through CO2 HeN, which may explain the shifting of CO2-rich eruptive systems towards an apparently anomalous explosive behaviour
Self-diffusion in single-component Yukawa fluids
It was suggested in the literature that the self-diffusion coefficient of
simple fluids can be approximated as a ratio of the squared thermal velocity of
the atoms to the "fluid Einstein frequency," which can thus serve as a rough
estimate of the friction (momentum transfer) rate in the dense fluid phase. In
this article we test this suggestion using a single-component Yukawa fluid as a
reference system. The available simulation data on self-diffusion in Yukawa
fluids, complemented with new data for Yukawa melts (Yukawa fluids near the
freezing phase transition), are carefully analyzed. It is shown that although
not exact, this earlier suggestion nevertheless provides a very sensible way of
normalization of the self-diffusion constant. Additionally, we demonstrate that
certain quantitative properties of self-diffusion in Yukawa melts are also
shared by systems like one-component plasma and liquid metals at freezing,
providing support to an emerging dynamical freezing indicator for simple soft
matter systems. The obtained results are also briefly discussed in the context
of the theory of momentum transfer in complex (dusty) plasmas.Comment: 6 pages, 3 figure
Grain refinement in a AlZnMgCuTi alloy by intensive melt shearing: A multi-step nucleation mechanism
This is a post-print version of the article. Copyright @ 2010 Elsevier B.V.Direct chill (DC) cast ingots of wrought Al alloys conventionally require the deliberate addition of a grain refiner to provide a uniform as-cast microstructure for the optimisation of both mechanical
properties and processability. Grain refiner additions have been in widespread industrial use for more than half a century. Intensive melt shearing can provide grain refinement without the need for a specific grain refiner addition for both magnesium and aluminium based alloys. In this paper we
present experimental evidence of the grain refinement in an experimental wrought aluminium alloy achieved by intensive melt shearing in the liquid state prior to solidification. The mechanisms for high
shear induced grain refinement are correlated with the evolution of oxides in alloys. The oxides present in liquid aluminium alloys, normally as oxide films and clusters, can be effectively dispersed
by intensive shearing and then provide effective sites for the heterogeneous nucleation of Al3Ti phase. As a result, Al3Ti particles with a narrow size distribution and hence improved efficiency as active nucleation sites of alpha-aluminium grains are responsible for the achieved significant grain refinement. This is termed a multi-step nucleation mechanism.Funding was obtained from the EPRSC
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