Silica phase as a thermoluminescence phosphor in ALH-77214 (L3.4)chondrite

Abstract

The induced thermoluminescence (TL) images for a slice sample of ALH-77214 (L3.4) have been measured to examine TL phosphors in type 3 ordinary chondrites with low TL sensitivity, using a TL spatial distribution readout system combined with microscope. The chemical compositions of TL phosphors were analyzed by X-ray microanalyzer. The TL emissions due to silica phases have been newly observed in two pyroxene chondrules with silica inclusions (SiO_2=97-99wt%) and one porphyritic olivine chondrule with very silica-rich mesostasis (SiO_2=84wt%), in addition to those due to feldspar crystals formed in chondrule mesostases enriched in plagioclase component. The glow curves of the silica phases (the peaks around 240-280℃) are quite different from those of the usual chondrule mesostases (the peaks around 80-120℃). We have tried to utilize glow curves of induced TL for five silica phases (hydrothermal quartz, volcanic quartz, tridymite, cristobalite and silica glass). From similarities of the shape of glow curve, the silica phase was tentatively identified to be cristobalite. Utilizing silica phases as a common TL phosphor, we can make a comparative study of TL characteristics among chondritic meteorites