An interlaboratory comparison of piston-cylinder pressure calibration using the albite-breakdown reaction

The pressure of the reaction albite=jadeite and quartz was measured at 600° C by workers in six geophysical laboratories for the purpose of comparing pressure calibration procedures for the solid-pressure piston-cylinder apparatus. All groups used the same starting mix of crystalline reactant and products and all obtained hydrothermal reversals of the equilibrium. Solid pressure media used included talc, NaCl, boron nitride, pyrophyllite, pyrex glass and crushable ceramic. Various means of calibration were used, including internal standardization by transitions in indicator substances and the piston-in, piston-out bracketing method.There was agreement among all groups—the average preferred value of 16.3 kilobars at 600° C is enclosed by all of the error brackets assigned by the various investigators. This average preferred value is lower by nearly two kilobars than the often-quoted extrapolation of Birch and LeComte's data (1960). It will be important for both petrology and high-pressure technology to test this result in a very high gas pressure apparatus.     

A statistical prediction technique for deriving contour maps from geophysical data

A technique for preparing contour maps is presented which has particular applicability for geophysical data. This technique derives from the assumption that each measured value is a sample from a statistical distribution which is taken to be valid in the area around that sample location. This distribution may be specified in the manner which best defines the relationship between the data and its spatial environment. Extending this principle to cover all areas to be mapped, and not just those measured, it is possible to predict values over a grid array of locations and hence to produce a contour map. Inherent in this simple procedure is: (i) the ability to adjust to the nature of the data being contoured; (ii) the elimination of edge effects; (iii) visual indication of the relative accuracy with which contours are located, at all points of the map; (iv) the automatic downgrading of data values which are in error; (v) the ability to contour combinations of measured data values without compounding errors; and (vi) a relatively simple extension to data spatially distributed in three dimensions.Research Council of Alberta Contribution No. 618.     

Reversed experimental calibration of the garnet-clinopyroxene Fe — Mg exchange thermometer

The temperature-sensitive Fe,Mg exchange equilibrium,

Methane and Carbon Dioxide Seasonal Cycles at Urban Brazilian Inland Sites

Methane and carbon dioxide seasonal cycles during years 1998 and 1999 at two Brazilian urban and inland sites are presented. The mixing ratio averages over the studied period of time were 1.80 ppm CH₄ and 384.7 ppm CO₂. A comparison is made between continental averages and theaverages of the three nearest global network background sites of NOAA-CMDL comprising Ascension Island, Namibia and Easter Island. Inland sites had 0.08 ppm or 4.9% more CH₄ and 19.0 ppm or 4.9% moreCO₂ than background over the same time span. The CH₄ summer minimum observed in remote sites was also detected inland. During the month of October 98 and 99 inland mixing ratios were frequently similar to background.     

Inversion of reflection data for layered media: a review of exact methods

Summary. This paper is a summary of known exact methods for inferring the acoustical impedance of a horizontally layered medium from its reflection response to a vertical sound signal. It includes reviews of linear and nonlinear methods in the time and frequency domains.