Mathematics – Logic
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........81b&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF ARKANSAS, 1992.Source: Dissertation Abstracts International, Volume: 53-08, Section: B, page: 398
Mathematics
Logic
Eucrites, Diogenites, Howardites, Mesosiderites, And The Moon
Scientific paper
Thermal histories of extraterrestrial basalts, involving metamorphic, shock, and brecciation processes on their parent bodies, were investigated by thermoluminescence (TL), cathodoluminescence (CL), thermal annealing, and acid washing experiments. The sample base included 66 basaltic achondrites and 20 lunar samples, along with 41 separated clasts and matrix samples from eucrites, howardites, and mesosiderites. Thermoluminescence peak temperatures show that meteoritic basaltic achondrites have suffered similar degrees of metamorphism compared to lunar highland samples, and more metamorphism than lunar mare rocks. Annealing experiments suggest that HEDs have either not been heated above 700 ^circC, or have cooled slowly below that temperature, while the mesosiderite matrix (but not large clasts) has been significantly annealed below 700^circC. TL sensitivity data show that eucrites have suffered a continuous range of metamorphic effects, and the data can be used to determine a petrologic type classification based on the degree of metamorphism experienced. The mare rocks show a similar dependence of TL sensitivity on thermal history, and a classification scheme similar to that for the eucrites may be feasible, but will require a larger data set. The howardites have seen very little post-brecciation metamorphism (CL images limit any heating to <500 ^circC), and their TL sensitivities reflect the abundance of eucritic material. Feldspar is the predominant phosphor in all these rocks, although luminescent silica (as SiO_2 ) is seen in eucrites and mesosiderites, and an undetermined phosphor, possible a phosphate, is present in lunar samples. CL images show that the mechanism of luminescence dependence on metamorphism affects existing crystalline feldspar, and may involve trace element concentrations. The images show the presence of two morphs of silica in eucrites, a euhedral green-luminescing silica and an anhedral red -luminescing silica which may be a reaction product. It seems likely that metamorphism on the HED parent body was associated with low-velocity impact and was uniformly distributed across the surface. This impact history was sufficient to homogenize the surface regolith on a local scale. The mesosiderite parent body may have been fragmented and reassembled by the addition on metal as a solid, and this event resulted in the metamorphism of its fine-grained matrix material.
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