Michael R. Smith

Alteration of basaltic glasses from north-central British Columbia, Canada

Abstract Evidence of palagonitization (glass replacement by poorly crystallized, clay-like material) is seen on all glasses studied from three Pleistocene subglacial volcanoes in north-central British Columbia, Canada. Samples from foreset breccias of Tuya Butte are more highly palagonitized than those from the tephra cones of Ash Mountain and Southern Tuya. Extensive palagonitization is generally associated with authigenic mineralization (clays, zeolites). Palagonite composition varies widely relative to glass composition, and palagonite can be broadly categorized as either high-Al or low-Al, depending on whether Al was retained or lost to aqueous solutions during palagonitization. The lowest Al palagonites are those from the foreset breccias of Tuya Butte. Loss of Al during palagonitization is related to closed-system alteration, including precipitation of aluminosilicate authigenic cements. Low initial pH is suggested for Al depletion, consistent with the behavior of Ni, Co, and Cr, which are retained in high-Al and depleted in low-Al palagonite. Microenvironment appears to be more influential than macroenvironment in determining the composition of palagonite. Palagonite rinds are compositionally zoned, generally becoming progressively higher in Al and Ca, and lower in Fe and Mg, towards the innermost (later-formed) portions of the rinds. This apparently reflects changing solution composition (increasing pH) with time. Compositional zoning does not change the overall stoichiometry of palagonite which resembles smectite clay. Mineral paragenesis is related to the Ca content of the palagonite, with partial replacement of palagonite by smectite (Fe-saponite) occurring when Ca is retained in the rind. This replacement phenomenon occurs prior to zeolitization. No such replacement clay occurs with low-Ca palagonite, but a late-stage nontronite film overgrows zeolite. Phillipsite is the first zeolite formed, followed by chabazite. Analcime and calcite occur in the most highly palagonitized samples. Mass balance considerations indicate higher mass loss where palagonitization has not proceeded to the point where zeolite solubility limits were attained in the local solution. Zeolites occur in closed-system conditions (low flow rates), where little net system mass loss or gain has occurred. The colloidal nature of palagonite allows the effective adsorption of Rb, Cs, Sr, Ba, and REEs.

Impact melting of the Cachari eucrite 3.0 Gy ago

Both the host phase and glass veins of the Cachari eucrite have been analyzed by microprobe and neutron activation analysis for their chemical compositions and by mass spectrometry for their 39Ar-40Ar gas retention ages. Cachari is chemically similar to other non-cumulate eucrites. The vesicular glass veins vary from pure glass, to devitrified glass, to areas that are substantially crystalline. The glassy areas have nearly the same concentrations of major and trace elements as the unmelted portions of Cachari, but some differences, probably due to preferential dissolution, occur along melt contacts. The glass formed by shock melting of Cachari host or of rock identical to it. 39Ar-40Ar data for the host and glass suggest distinctly different ages of 3.04 ±.07 Gy and 3.47 ±.04 Gy, respectively. The time of glass formation, which may also be the time of brecciation, is most likely given by the 3.0 Gy age of the host. The higher age for the glass is interpreted to represent incomplete Ar degassing during the 3.0 Gy event due to the greater resistance to Ar diffusion shown by the glass compared to the host. Event ages significantly younger than 4.5 Gy have now been determined for several eucrites and howardites and suggest a long dynamic regolith history for the parent body.

Rapidly Deployable Video Analysis Sensor units for wide area surveillance

This paper presents an overview of self-contained automated video analytics units that are man-portable and constitute nodes of a large-scale distributed sensor network. The paper highlights issues with traditional video surveillance systems in volatile environments such as a battle field and provides solutions to them in the form of Rapidly Deployable Video Analysis sensors. We discuss scientific and engineering aspects of the system and present the outcome of a field deployment in an exercise conducted by the Office of Naval Research.