2,219 research outputs found
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PetroPlot: A plotting and data management tool set for Microsoft Excel
PetroPlot is a 4000-line software code written in Visual Basic for the spreadsheet program Excel that automates plotting and data management tasks for large amount of data. The major plotting functions include: automation of large numbers of multiseries XY plots; normalized diagrams (e.g., spider diagrams); replotting of any complex formatted diagram with multiple series for any other axis parameters; addition of customized labels for individual data points; and labeling flexible log scale axes. Other functions include: assignment of groups for samples based on multiple customized criteria; removal of nonnumeric values; calculation of averages/standard deviations; calculation of correlation matrices; deletion of nonconsecutive rows; and compilation of multiple rows of data for a single sample to single rows appropriate for plotting. A cubic spline function permits curve fitting to complex time series, and comparison of data to the fits. For users of Excel, PetroPlot increases efficiency of data manipulation and visualization by orders of magnitude and allows exploration of large data sets that would not be possible making plots individually. The source codes are open to all users
A hydrous melting and fractionation model for mid-ocean ridge basalts: Application to the Mid-Atlantic Ridge near the Azores
The major element, trace element, and isotopic composition of mid-ocean ridge basalt glasses affected by the Azores hotspot are strongly correlated with H2O content of the glass. Distinguishing the relative importance of source chemistry and potential temperature in ridge-hotspot interaction therefore requires a comprehensive model that accounts for the effect of H2O in the source on melting behavior and for the effect of H2O in primitive liquids on the fractionation path. We develop such a model by coupling the latest version of the MELTS algorithm to a model for partitioning of water among silicate melts and nominally anhydrous minerals. We find that much of the variation in all major oxides except TiO2 and a significant fraction of the crustal thickness anomaly at the Azores platform are explained by the combined effects on melting and fractionation of up to ~700 ppm H2O in the source with only a small thermal anomaly, particularly if there is a small component of buoyantly driven active flow associated with the more H2O-rich melting regimes. An on-axis thermal anomaly of ~35°C in potential temperature explains the full crustal thickness increase of ~4 km approaching the Azores platform, whereas a âĽ75°C thermal anomaly would be required in the absence of water or active flow. The polybaric hydrous melting and fractionation model allows us to solve for the TiO2, trace element and isotopic composition of the H2O-rich component in a way that self-consistently accounts for the changes in the melting and fractionation regimes resulting from enrichment, although the presence and concentration in the enriched component of elements more compatible than Dy cannot be resolved
Origins of chemical diversity of back-arc basin basalts: a segment-scale study of the Eastern Lau Spreading Center
We report major, trace, and volatile element data on basaltic glasses from the northernmost segment of the Eastern Lau Spreading Center (ELSC1) in the Lau back-arc basin to further test and constrain models of back-arc volcanism. The zero-age samples come from 47 precisely collected stations from an 85 km length spreading center. The chemical data covary similarly to other back-arc systems but with tighter correlations and well-developed spatial systematics. We confirm a correlation between volatile content and apparent extent of melting of the mantle source but also show that the data cannot be reproduced by the model of isobaric addition of water that has been broadly applied to back-arc basins. The new data also confirm that there is no relationship between mantle temperature and the wet melting productivity. Two distinct magmatic provinces can be identified along the ELSC1 axis, a southern province influenced by a âwet componentâ with strong affinities to arc volcanism and a northern province influenced by a âdamp componentâ intermediate between enriched mid-ocean ridge basalts (E-MORB) and arc basalts. Highâfield strength elements and rare earth elements are all mobilized to some extent by the wet component, and the detailed composition of this component is determined. It differs in significant ways from the Mariana component reported by E. Stolper and S. Newman (1994), particularly by having lower abundances of most elements relative to H_(2)O. The differences can be explained if the slab temperature is higher for the Mariana and the source from which the fluid is derived is more enriched. The ELSC1 damp component is best explained by mixing between the wet component and an E-MORB-like component. We propose that mixing between water-rich fluids and low-degree silicate melts occurs at depth in the subduction zone to generate the chemical diversity of the ELSC1 subduction components. These modified sources then rise independently to the surface and melt, and these melts mix with melts of the background mantle from the ridge melting regime to generate the linear data arrays characteristic of back-arc basalts. The major and trace element framework for ELSC1, combined with different slab temperatures and compositions for difference convergent margins, may be able to be applied to other back-arc basins around the globe
Space Charge Limited 2-d Electron Flow between Two Flat Electrodes in a Strong Magnetic Field
An approximate analytic solution is constructed for the 2-d space charge
limited emission by a cathode surrounded by non emitting conducting ledges of
width Lambda. An essentially exact solution (via conformal mapping) of the
electrostatic problem in vacuum is matched to the solution of a linearized
problem in the space charge region whose boundaries are sharp due to the
presence of a strong magnetic field. The current density growth in a narrow
interval near the edges of the cathode depends strongly on Lambda. We obtain an
empirical formula for the total current as a function of Lambda which extends
to more general cathode geometries.Comment: 4 pages, LaTex, e-mail addresses: [email protected],
[email protected]
Volcanic glasses at the Izu arc volcanic front : new perspectives on fluid and sediment melt recycling in subduction zones
Author Posting. Š American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 5 (2004): Q01007, doi:10.1029/2002GC000408.Volcanic glasses contained in distal fallout tephras from the Izu arc volcanic front (Izu VF) provide unique perspectives on general problems of arc volcanism. Unlike cogenetic lavas, these glasses are liquid compositions where element concentrations as well as ratios have significance. Isotopic evidence and previous work show that there is no sediment melt contribution to the sources of the Izu VF tephras, and hence their trace element characteristics permit determination of the trace element contents of slab fluids. The slab fluid is a composite of metasediment (âź5% of total fluid) and metabasalt (âź95%) component fluids, and carries large ion lithophile elements (LILE) with high LILE/Th and LILE/U, and low Th and U relative to source. Except for Sr and K, the metabasalt fluid is much less enriched than the metasediment fluid, but its large relative proportions make it an important carrier of many trace elements. The metabasalt fluid has the characteristics of the arc trace element signature, obviating the need for ubiquitous involvement of sediment in arc magma genesis. The fluid component in the tephras is remarkably constant in composition over fifteen million years, and hence appears to be a robust composition that may be applicable to other convergent margins. Assuming that the metabasalt fluid is a common component, and that distribution coefficients between sediment and fluid are similar from one arc to another, composite fluid compositions can be estimated for other arcs. Differences from this composition then would likely result from a sediment melt component. Comparison to arcs with sediment melt components in their source (Marianas, eastern Aleutians) shows that partial sediment melts may be so enriched, that they can completely mask the signature of the comingling slab fluids. Hence sediment melts can easily dominate the trace element and isotopic signature of many convergent margins. Since sediment melts inherit the LILE/LILE ratios of the trench sediment, Earth's surface processes must eventually influence the compositional diversity of arcs.This study was funded by the âDeutsche Forschungsgemeinschaftâ (grants Str 441/3 and 441/4). The Northeast National Ion Microprobe Facility at WHOI was supported by grants EAR-9628749 and EAR-990440 from the National Science Foundation
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Origins of Chemical Diversity of Back-Arc Basin Basalts: A Segment-Scale Study of the Eastern Lau Spreading Center
We report major, trace, and volatile element data on basaltic glasses from the northernmost segment of the Eastern Lau Spreading Center (ELSC1) in the Lau back-arc basin to further test and constrain models of back-arc volcanism. The zero-age samples come from 47 precisely collected stations from an 85 km length spreading center. The chemical data covary similarly to other back-arc systems but with tighter correlations and well-developed spatial systematics. We confirm a correlation between volatile content and apparent extent of melting of the mantle source but also show that the data cannot be reproduced by the model of isobaric addition of water that has been broadly applied to back-arc basins. The new data also confirm that there is no relationship between mantle temperature and the wet melting productivity. Two distinct magmatic provinces can be identified along the ELSC1 axis, a southern province influenced by a wet component with strong affinities to arc volcanism and a northern province influenced by a damp component intermediate between enriched mid-ocean ridge basalts (E-MORB) and arc basalts. High field strength elements and rare earth elements are all mobilized to some extent by the wet component, and the detailed composition of this component is determined. It differs in significant ways from the Mariana component reported by E. Stolper and S. Newman (1994), particularly by having lower abundances of most elements relative to . The differences can be explained if the slab temperature is higher for the Mariana and the source from which the fluid is derived is more enriched. The ELSC1 damp component is best explained by mixing between the wet component and an E-MORB-like component. We propose that mixing between water-rich fluids and low-degree silicate melts occurs at depth in the subduction zone to generate the chemical diversity of the ELSC1 subduction components. These modified sources then rise independently to the surface and melt, and these melts mix with melts of the background mantle from the ridge melting regime to generate the linear data arrays characteristic of back-arc basalts. The major and trace element framework for ELSC1, combined with different slab temperatures and compositions for difference convergent margins, may be able to be applied to other back-arc basins around the globe.Earth and Planetary Science
On the formation/dissolution of equilibrium droplets
We consider liquid-vapor systems in finite volume at parameter
values corresponding to phase coexistence and study droplet formation due to a
fixed excess of particles above the ambient gas density. We identify
a dimensionless parameter and a
\textrm{universal} value \Deltac=\Deltac(d), and show that a droplet of the
dense phase occurs whenever \Delta>\Deltac, while, for \Delta<\Deltac, the
excess is entirely absorbed into the gaseous background. When the droplet first
forms, it comprises a non-trivial, \textrm{universal} fraction of excess
particles. Similar reasoning applies to generic two-phase systems at phase
coexistence including solid/gas--where the ``droplet'' is crystalline--and
polymorphic systems. A sketch of a rigorous proof for the 2D Ising lattice gas
is presented; generalizations are discussed heuristically.Comment: An announcement of a forthcoming rigorous work on the 2D Ising model;
to appear in Europhys. Let
Transport across nanogaps using semiclassically consistent boundary conditions
Charge particle transport across nanogaps is studied theoretically within the
Schrodinger-Poisson mean field framework and the existence of limiting current
investigated. It is shown that the choice of a first order WKB wavefunction as
the transmitted wave leads to self consistent boundary conditions and gives
results that are significantly different in the non-classical regime from those
obtained using a plane transmitted wave. At zero injection energies, the
quantum limiting current density, J_c, is found to obey the local scaling law
J_c ~ (V_g)^alpha/(D)^{5-2alpha} with the gap separation D and voltage V_g. The
exponent alpha > 1.1 with alpha --> 3/2 in the classical regime of small de
Broglie wavelengths. These results are consistent with recent experiments using
nanogaps most of which are found to be in a parameter regime where classical
space charge limited scaling holds away from the emission dominated regime.Comment: 4 pages, 4 ps figure
Diffusion-limited reactions and mortal random walkers in confined geometries
Motivated by the diffusion-reaction kinetics on interstellar dust grains, we
study a first-passage problem of mortal random walkers in a confined
two-dimensional geometry. We provide an exact expression for the encounter
probability of two walkers, which is evaluated in limiting cases and checked
against extensive kinetic Monte Carlo simulations. We analyze the continuum
limit which is approached very slowly, with corrections that vanish
logarithmically with the lattice size. We then examine the influence of the
shape of the lattice on the first-passage probability, where we focus on the
aspect ratio dependence: Distorting the lattice always reduces the encounter
probability of two walkers and can exhibit a crossover to the behavior of a
genuinely one-dimensional random walk. The nature of this transition is also
explained qualitatively.Comment: 18 pages, 16 figure
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