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Williams, R. J.

Publications and source records attributed to Williams, R. J..

51 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

The system anorthite-forsterite-fayalite-silica to 2 kbar with lunar petrologic applications

Near-liquidus phase relations in the magnesium-rich portion of the system anorthite-forsterite-fayalite-silica have been determined from synthesis experiments at 1 atm and 2 kbar at oxygen fugacities near the iron-wuestite buffer. The major-element chemistries of KREEP basalts are similar to peritectic liquids, L/ol,px,an/, produced experimentally. The reaction L/ol,px,an/ is well-located at low pressures. It intersects the join anorthite-enstatite-ferrosilite at Fe/(Fe+Mg) equals 0.45 (atomic ratio), and is peritectic only for Fe/(Fe+Mg) not greater than 0.45. Although positions of the equilibria, L/an,ol/ and L/ol,px/, differ significantly at 1 atm from their positions at 2 kbar, the position of the piercing point, L/ol,px,an/, on the anorthite-enstatite-ferrosilite join is not sensitive to pressure. The composition of liquids produced by partial melting of troctolites and pyroxenites in the lunar crustal environment will be affected by pressure, whereas liquids derived from gabbroic assemblages will not.

Merrill, R. B.↗
NASA NTRS1975

Experimentally reproduced textures and mineral chemistries of high-titanium mare basalts

Many of the textures, morphologies, and mineral chemistries of the high-titanium mare basalts have been experimentally duplicated using single-stage cooling histories. Lunar high-titanium mare basalts are modeled in a 1 m thick gravitationally differentiating flow based on cooling rates, thermal models, and modal olivine contents. The low-pressure equilibrium phase relations of a synthetic high-titanium basalt composition were investigated as a function of oxygen fugacity, and petrographic criteria are developed for the recognition of phenocrysts which were present in the liquid at the time of eruption.

Usselman, T. M.↗
NASA NTRS1974

A refractory glass chondrule in the Vigarano chondrite

Vigarano, a type 3 carbonaceous chondrite, contains a chondrule composed of highly refractory Ca- and Al-rich glass with minor spinel. The chondrule formed from material similar to the Ca-, Al-, Ti-rich aggregates that are common in Vigarano and other type 3 chondrites and formation of these refractory aggregates must predate formation of some Vigarano chondrules. Experiments with synthetic analogs and a comparison with studies in the system CaO-MgO-Al2O3-SiO2 indicate a temperature for formation of the chondrule at or above 1700 C followed by very rapid cooling.

Reid, A. M.↗
NASA NTRS1972

A solid ceramic electrolyte system for measuring redox conditions in high temperature gas mixing studies

The details of the construction and operation of a gas mixing furnace are presented. A solid ceramic oxygen electrolyte cell is used to monitor the oxygen fugacity in the furnace. The system consists of a standard vertical-quench, gas mixing furnace with heads designed for mounting the electrolyte cell and with facilities for inserting and removing the samples. The system also contains the highinput impedance electronics necessary for measurements and a simplified version of standard gas mixing apparatus. The calibration and maintenance of the system are discussed.

Williams, R. J.↗
NASA NTRS1972

The origin and stability of lunar goethite, hematite and magnetite.

Extra-lunar contamination, fumarolic activity, and exposure to oxidizing gases from comet or carbonaceous meteorite impacts have been previously proposed as the causes of magnetite, hematite, and goethite in lunar materials. However, these minerals can occur in the stable low-temperature gas-solid equilibrium assemblages of lunar rocks. Below 600 C magnetite is in equilibrium with C-O-H gases with compositions compatible with high-temperature equilibrium with metallic iron; below 150 C hematite is stable in these same gases. Goethite is not stable in carbonaceous gases at low total pressure, and thus gases from impacting carbonaceous material cannot have produced it. Goethite is stable at low temperatures and pressures in almost pure H2-H2O gases. Its minimum stability against hematite is 2 bars total pressure at 130 C and 0.001 bars at 30 C for H2 to H2O ratios compatible with the high-temperature redox state of lunar materials. Thus the traces of magnetite, hematite, and goethite in lunar materials may be the result of normal low-temperature processes indigenous to the moon and not special processes.

Williams, R. J.↗
NASA NTRS1972

The lithification and metamorphism of lunar breccias.

Investigations regarding the textural and mineralogical classification of Apollo 14 breccias are considered together with some related experimental studies. The experiments can be used to construct a temperature scale which may be called the 'petrogenetic line' for lunar breccias. A model for the Fra Mauro formation is also discussed. The most interesting facts revealed by the discussion are the intensity of heating involved and the short times necessary to develop the physical properties of the Apollo 14 breccias. The purpose of the studies is to construct a scale of lunar metamorphic temperatures which is consistent with experimentally determined conditions necessary for the acquisition of certain properties by the lunar breccias.

Williams, R. J.↗