We present optical-line gas metallicity diagnostics established by the combination of local SDSS galaxies and the largest compilation of extremely metal-poor galaxies (EMPGs) including new EMPGs identified by the Subaru EMPRESS survey. A total of 103 EMPGs are included, covering a large parameter space of magnitude (M-i = -19 to -7) and H beta equivalent width (10-600 angstrom), i.e., wide ranges of stellar mass and star formation rate. Using reliable metallicity measurements from the direct method for these galaxies, we derive the relationships between strong optical-line ratios and gas-phase metallicity over the range of 12 + log (O/H) similar or equal to 6.9-8.9, corresponding to 0.02-2 solar metallicity Z(circle dot). We confirm that the R23 index, ([O III]+[O II])/H beta, is the most accurate metallicity indicator with a metallicity uncertainty of 0.14 dex over the range among various popular metallicity indicators. The other metallicity indicators show large scatters in the metal-poor range (less than or similar to 0.1 Z(circle dot)). It is explained by our CLOUDY photoionization modeling that, unlike the R23 index, the other metallicity indicators do not use a sum of singly and doubly ionized lines and cannot trace both low- and high-ionization gas. We find that the accuracy of the metallicity indicators is significantly improved if one uses H beta equivalent width measurements that tightly correlate with ionization states. In this work, we also present the relation of physical properties with the UV-continuum slope beta and ionization production rate xi(ion) derived with GALEX data for the EMPGs and provide local anchors of galaxy properties together with the optical-line metallicity indicators that are available in the form of a machine-readable table and useful for forthcoming JWST spectroscopic studies.

A general formalism is described for predicting shifts in mineral O-18/O-16 attending changes in intensive and extensive thermochemical parameters during metamorphism. The method involves solving simultaneously linear differential equations describing changes in deltaO-18 with requisite mass balance and thermodynamic equations and can be modified to accommodate a variety of open and closed-system conditions. Analytical solutions for deltaO-18 as a function of reaction progress (xi) are presented for simple systems experiencing closed-system evolution, Rayleigh dehydration, and fluid infiltration. An example application involving deltaO-18 zoning in garnet illustrates that comparisons of predicted covariations among deltaO-18 values, cation concentrations, and mineral abundances to patterns preserved in natural rocks can be used to reconstruct metamorphic net-transfer reaction histories. Such comparisons also provide new tests useful for determining the relative importance of other processes, such as Ostwald ripening, during the textural evolution of metamorphic rocks. The presented methodology constitutes the necessary framework for evaluating small-scale variations in deltaO-18 in the context of parageneses in metamorphic rocks.

CO2 laser-heating in a fluorinating atmosphere was used to obtain O-18/O-16 analyses of coexisting garnet, staurolite, muscovite, chlorite, and quartz from a sample of the Gassetts schist, southeastern Vermont, USA. Garnet and quartz deltaO-18V-SMOW values vary on a millimeter scale while values for other minerals are uniform within analytical uncertainties. Garnets exhibit O-18/O-16 zoning with core deltaO-18 values of 10.9 +/- 0.3 parts per thousand and rim values of 10.1 +/- 0.2. The depletion of O-18 in garnet rims correlates with reversals in cation zonation and intracrystalline textural unconformities. Quartz plucked from a garnet core yields a deltaO-18 of 14.8 parts per thousand while vein quartz deltaO-18 values vary from 14.3 +/- 0.2 in centers to 13.8 +/- 0.1 at margins. Staurolite, muscovite, and chlorite have mean deltaO-18 values of 10.8, 11.9, and 10.3, respectively.

Competition among atomic or molecular species for occupancy of crystallographic sites exaggerates correlations among chemical elements in suites of mineral chemical data, a phenomenon known as closure. Such exaggerated correlations can lead to incorrect conclusions about ionic substitution mechanisms and the petrological forces that drive them. Expressing mineral compositions in terms of a single additive component and molar concentrations of exchange components, eliminates the effects of closure. Statistical analysis of data so transformed can, in some instances, lead to conclusions distinct from analysis of the same data expressed in terms of ionic abundances. The chemical variability of fictive and naturally occurring amphiboles serves to illustrate the potential difficulties brought about by closure and the benefits of its elimination.

In situ oxygen isotope analysis of silicate minerals has been validated by interlaboratory calibration using an excimer laser (KrF fill gas, 248 nm), F-2 gas fluorinating reagent, and O-2 gas as mass spectrometer analyte. A value of delta(18)O(SMOW) = 5.82 parts per thousand (+/-0.03, 4 analyses) was obtained for almandine UWG-2 compared to a recommended value of 5.8 parts per thousand (Valley et al., 1995). The interhalogen BrF5 was tested by comparing in situ analyses made alternatively with either BrFS or Fa gas on crystals of almandine, epidote, forsterite, tourmaline, and zircon. Results for different pressures of BrF5 (20 to 40 ton) in the reaction chamber show that delta(18)O values decrease by 1 permil for an increase of 10 ton in BrF5 pressure. In strong contrast, delta(18)O values measured with purified F-2 gas are precise and accurate over a range of from 15 to 150 ton F-2 gas pressure. Use of F-2 gives higher yields of O-2 than with BrF5. Values of delta(17)O and delta(18)O measured in situ on a variety of silicates all plot on the terrestrial mass fractionation line, provided that NF3 contamination is eliminated from the O-2 gas analyte. Copyright (C) 1997 Elsevier Science Ltd.