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Thermoluminescence characteristics and chemical compositions of mesostases in ordinary chondrites

Abstract

Induced thermoluminescence (TL) images of ordinary chondrites, ALH-77214 (L3.4-3.5), Y-74191 (L3.6), ALH-77216 (L3.8) and ALH-78043 (L6), were measured by the TL spatial distribution readout system combined with a microscope and TL characteristics [peak temperature and peak width] of mesostases were analyzed. Their chemical compositions were also analyzed by an electron probe X-ray microanalyzer. We found that; (1) The mesostasis was responsible for much of the TL in the ordinary chondrites, (2) A mesostasis of normative anorthite compositions showed low peak temperature (∿90℃) and narrow width (∿65℃), while a mesostasis of normative albite compositions showed high peak temperature (∿125℃) and wide width (∿100℃), (3) A main phosphor in a low petrologic grade chondrite 3.5 was a high albite mesostasis, (4) Some chondrules in the same fragments of the type 3 chondrites showed no or weak TL emission and these mesostases had high normative albite. These facts suggest that in type 3 ordinary chondrites; (1) The post-accretional metamorphism cannot account for the coexistence of high albite mesostases with TL emission and no emission and a high anorthite mesostasis with TL emission, (2) Low petrologic grade chondrites 3.5 have a large population of slowly cooled chondrules

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