Abstract Silicon is a major constituent of grasses, therefore, research was initiated to evaluate the use of the paraffin technique for electron probe microanalysis of Si in grass leaf tissue. Mature healthy leaves of a tropical grass, Wilmington bahiagrass (Paspalum notatum Flügge), and a cool season grass, tall fescuegrass (Festuca arundinacea Schred), were selected for study. Paradermal sections (10 μ) of paraffin impregnated leaf tissue were placed on sheet carbon that had been attached with Haupt's adhesive to 2.5 cm glass discs. The grass sections were fixed to the sheet carbon with Haupt's adhesive and the paraffin removed with xylene prior to microanalysis. Silicon was found to be highly concentrated in the epidermis of fescuegrass and bahiagrass. Short cells, many containing opal bodies, had the highest contents of Si of the epidermal cells. Large quantities of Si was also present in guard cells but long cells contained relatively small amounts.
The Fish Canyon Tuff is one of the largest currently recognized ash-flow tuffs (> 3000 km3). It is a crystal-rich quartz latite containing about 40 per cent phenocrysts of plagioclase, sanidine, biotite, hornblende, quartz, magnetite, sphene, and ilmenite. Pyrrhotite occurs as inclusions in magnetite, sphene, and hornblende. The consistency of mineralogy and whole rock chemistry confirms that the Fish Canyon tuff is remarkably homogeneous. Most chemical variations can be accounted for by phenocryst-matrix fractionation, probably due to glass winnowing during eruption and emplacement. The composition of the parent magma, corrected for such winnowing, is very similar to that of calc-alkaline batholiths such as the Boulder and the Sierra Nevada batholiths. Fe-Ti oxide geothermometers indicate temperatures of 800 ± 30 °C for most of the outflow tuff. No evidence for a regular thermal gradient in the magma chamber could be detected. Two feldspar and Fe-Ti oxide equilibria indicate that the magma developed at depths of 25 to 30 km (about 9 kb pressure), and was erupted without time for phenocryst re-equilibration. The reconstructed composition of the liquid in equilibrium with the phenocrysts also suggests a deep source for this ash flow. A late, upper package of flow units have mineralogical characteristics which may reflect partial re-equilibration in a shallower environment. Oxygen fugacities are moderately high (log fO2 = — 11.5 ±0.3) but are similar to those obtained from other continental calc-alkaline ash-flow tuffs. The water fugacity is limited by calculations using biotite equilibria and experimental work relating to the stability of the phenocryst assemblage. Best estimates are that water fugacity was 2000 ± 1000 bars. The activities of sulphurous gases are estimated at fSO2 = 2 to 4 bars, fso2 = 150 to 200 bars, fH2S = 70 to 80 bars. The Fish Canyon Tuff therefore came from a deep, homogeneous, granitic magma body of batholithic proportions. Calculations of its probable viscosity, density, and size indicate that the system should convect with any reasonable thermal gradient. Convective mixing may account for the homogeneity of the parent magma body.
New recalculation scheme based on models of ionic substitution, consistent with a new thermodynamic model for the pure Fe-Ti system. The new scheme tends to give temperature and log fO 2 values falling in the middle of the range of variation.--Modified journal abstract.
