Gordon Moore

Isotopic and elemental partitioning of boron between hydrous fluid and silicate melt

Abstract The fractionation of B and its isotopes between aqueous fluid and silicate melt has been studied from 550 to 1100 °C and 100-500 MPa. Fluid-melt partition coefficients are <1 for basaltic melt and >1 for rhyolite melt. This shows that B is not always strongly extracted from melts into hydrous fluids. Boron isotopic fractionation is large compared with the carbon and oxygen stable isotopic systems (especially at high T) and is most simply explained by differences in coordination (trigonal vs. tetrahedral) among coexisting phases. Combined with earlier measurements on illite-water (300- 350 °C), B isotopic fractionation defines a temperature-dependent trend from 300 to 1100 °C. Because of the large magnitude and apparent low sensitivity to bulk composition, B isotopic fractionation can be readily applied to studies of diagenesis, hydrothermal alteration of planetary bodies, subduction- zone processing and arc magma generation, and magma chamber evolution.

Calibration of a reflectance FTIR method for determination of dissolved CO2 concentration in rhyolitic glasses

Abstract A technique based upon infrared reflectance spectroscopy is developed as an alternative to the Fourier transform infrared (FTIR) transmission method for the quantitative measurement of dissolved molecular carbon dioxide in aluminosilicate glasses. The technique has the advantage that only a single sample surface need be polished, and no thickness measurement is necessary. The reflectance spectrum is analyzed by Kramers–Kronig relations or classical oscillator analysis to yield the optical constants and the absorption coefficient at 2350 cm −1 , due to the asymmetric stretching (ν 3 ) vibration of molecular CO 2 . The value obtained is in excellent agreement with values obtained by the transmission FTIR technique for a suite of rhyolitic glasses. For practical application of the method to rhyolites, an empirical correlation is developed between the normalized change in reflectance at 2350 cm −1 and the CO 2 content, up to ∼0.40 wt%.

Analyzing hydrogen (H2O) in silicate glass by secondary ion mass spectrometry and reflectance Fourier transform infrared spectroscopy

The water contents of silicate glasses can be measured by secondary ion mass spectrometry (SIMS) and Fourier transform infrared (FTIR) spectroscopy. For SIMS, one of the impediments to quantitative analysis is uncertainty in the effect of sample chemistry on calibration, while for FTIR, sample preparation is often the most difficult step. A wide range of hydrogen-implanted silicate glasses was tested to see if a general relation between sample chemistry and calibration factors for SIMS could be formulated. The results show that while some compositions are suitable for H implantation (matching earlier calibrations based on experimentally hydrated samples), other H-implanted compositions show very low H signals. We suggest that the difference in atomic environment between implanted H vs. dissolved H may cause low count rates. Using the reflected IR spectrum simplifies sample preparation. Reflection IR measurements of experimentally hydrated glasses show that the H2O content of basaltic, andesitic, and rhyolitic glasses can be quantified down to ≈0.5 wt.%. Lateral resolution is limited by intensities of current IR sources to ≈100μm.

A low-pressure–high-temperature technique for the piston-cylinder

Abstract A method for conducting successful low pressure (0.3-0.5 GPa) and high temperature (900-1200 °C) experiments in the 19 mm piston-cylinder is presented. The technique is capable of running high fluid/melt experiments with minimum hydrogen loss, attaining precise, reproducible pressures (±10%), and has fast initial quench rates (>150 °C/s). These abilities are invaluable when conducting low pressure, fluid-saturated experiments such as phase equilibria, volatile solubility, and dynamic degassing experiments that are relevant to sub-volcanic magma chamber processes. A double capsule construction is also described that uses a solid oxygen buffer, and minimizes both contamination of the sample by carbon and the loss of iron in the melt to the capsule walls.

Assessing Early Spanish Explorer Routes Through Authentication of Rock Inscriptions

Rock inscriptions containing both names and calendar dates provide place-specific data on travels of explorers, if those inscriptions are truly authentic. We exemplify here a new strategy for determining the authenticity of inscriptions in arid environments in two case studies. One is an inscription purportedly created during the Marcos de Niza expedition of 1539 through Arizona. The other might have been made by the Dominguez–Escalante expedition of 1776 through the Colorado Plateau and Great Basin. The rock inscription in Phoenix, Arizona, “Fr Marcos de Niza corona todo el nuebo Mexico a su costa ano de 1539,” is likely not authentic. Although the Marcos de Niza petroglyph was manufactured before the use of leaded gasoline about 1922, it was made after the Little Ice Age ended in the mid-nineteenth century. In contrast, the engraving “Paso Por Aqui—Año 1776” near Lake Powells Padre Bay in Glen Canyon National Recreation Area has a lead profile indicating that the engraving predates twentieth-century pollution and also contains a Little Ice Age signal, evidence that the engraving is likely authentic. Nearby graffiti and natural weathering often endangers rock inscriptions, necessitating conservation efforts of authentic engravings. Conservation efforts to protect the delicate condition of the Lake Powell engraving are justified by these findings. In contrast, unnecessary expenditures and effort can result from work on engravings that are not authentic.