Thermoluminescence of Primitive Ordinary Chondrites, Semarkona and Bishunpur

Details Thermoluminescence of Primitive Ordinary Chondrites, Semarkona and Bishunpur Thermoluminescence of Primitive Ordinary Chondrites, Semarkona and Bishunpur

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.269n&link_type=abstract

Meteoritics, vol. 27, no. 3, volume 27, page 269

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Scientific paper

A thermoluminescence (TL) spatial distribution readout system attached to a microscope has been developed (1). This system has become a time-resolving spectroscopy system, substituting a spectroscope for the microscope (2). The induced TL sensitivity of ordinary chondrites increases by a factor of 10^5 with metamorphism and the primitive ordinary chondrites such as Semarkona (LL3.0) and Bishunpur (LL3.1) have the lowest TL sensitivities (3). However, we investigated induced TL images and glow curves of them by the TL spatial distribution readout system over a wide range of wavelengths with Corning 4-96 filter. A chondrule with anorthite-normative mesostasis in Semarkona, which is a porphyritic olivine chondrule [Fo(sub)99.5-99.7] of type IA according to Scott and Taylor (4), shows especially high induced TL intensity with a 300 degree C glow peak and a zonal structure. We measured high TL intensity although it would have the lowest TL sensitivity. The TL spectra from Semarkona were also measured by the time-resolving spectroscopy system. While the TL spectra of equilibrated ordinary chondrites are known to have a 450-nm peak in a low-temperature region and a 400-nm peak in a high-temperature region, they have a peak at ~570 nm and agree with those of some plagioclase feldspars in which Mn^2+ ions act as luminescence centers (5). The Corning 4-69 and 7-59 filter assemblies used in usual TL measuring systems limit the detection wavelength from 320 nm to 480 nm while the 4-96 filter transmits 570-nm emission. The "low TL sensitivity" of the primitive ordinary chondrites is in part due to limiting the detection wavelengths to ultraviolet-blue region. The cathodoluminescence of this chondrule was measured. This chondrule shows the yellow cathodoluminescence in anorthite- normative mesostasis and the zonal structure, and it is classified to group A1 of Sears et al. (6). The yellow cathodoluminescence is consistent with the ~570-nm TL emission. A barred olivine chondrule in Bishunpur shows also an unusual glow curve with a ~110 degrees C peak and a peak above 440 degrees C, different from the above glow curve. The TL spectra from Bishunpur have the same ~570-nm peaks. This barred olivine chondrule shows also the yellow cathodoluminescence in anorthite- normative mesostasis, and it is classified to group A1. On the other hand, a porphyritic olivine chondrule of type II in Bishunpur shows a usual glow curve with a ~170 degree C peak and blue cathodoluminescence in albite-normative mesostasis, and it is classifed to group A5. The results are that 1) some chondrules in Semarkona and Bishunpur show high TL intensities although such primitive ordinary chondrites would have low TL sensitivity, 2) these high TL intensities are due to ~570-nm emission, which is consistent with the yellow cathodoluminescences in anorthite-normative mesostases, beside the usual blue TL emissions from albite- normative mesostasis, 3) they show a variety of glow curve shapes inspite of the same yellow cathodoluminescence. References (1) Ninagawa et al. (1990) Proc. NIPR Symp. Ant. Met. 3, 244-253. (2) Ninagawa et al. (1986) Bull. Okayama Univ. Sci. 21A, 49-54. (3) Sears (1988) Nucl. Tracks Radiat. Meas. 14, 5-17. (4) Scott and Taylor (1983) Proc. LPSC 14, B275-B286. (5) Huntley et al. (1988) J. Lumin. 39, 123-136. (6) Sears et al. (1992) Nature, in press.

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