Constraints on the thermal and mixing history of lunar surface materials and comparisons with basaltic meteorites

Abstract

Abstract. We have measured the induced thermoluminescence (TL) properties of mare basalts, •:h.ighland rocks, glasses, regolith breccias, soils and core samples. We also performed a series of heating experiments and made cathodoluminescence (CL) observations of Apollo 16 soils. The data are readily interpreted in terms of feldspar being the dominant source of TL and CL, the known luminescence properties of feldspar and history of the samples. For example, the TL sensitivity of the mare basalts is lower than that of the highland basalts by about an order of magnitude, probably due to the differing FeO content of their feldspars. Similarly, the TL properties of regolith breccias can readily be explained in terms of thermal processes similar to those experienced by the soils and by mixing of highland and mare components. Our major new observations and interpretations include (1) that there are maturity-dependent variations in the TL and CL properties of the core samples which reflect thermal annealing and melting during regolith working, (2) that the most "primitive" material in lunar samples in terms of their thermal histories is located in the immature lunar soils, and (3) that there is no TL evidence for widespread longterm thermal metamorphism of lunar samples, TL being particularly sensitive to low-level metamorphism in extraterrestrial materials. In this latter respect, lunar samples differ from basaltic meteorites which otherwise have very similar properties and histories. We argue that this reflects a greater tendency toward thick regoliths on asteroid-sized bodies.

Photomosaics of the cathodoluminescence of 60 sections of meteorites and lunar samples

“…Images 56-60 ( Figures A56 -A60) are for samples taken from a variety of depths in the regolith. These images and TL sensitivity measurements were discussed by Batchelor et al [1997].…”

The metamorphic history of eucrites and eucrite‐related meteorites and the case for late metamorphism

“…The major exception is the highly anomalous eucrite, Ibitira, which is type 6 according to pyroxene properties and type 2 according to TL sensitivity (Batchelor and Sears, 1991b;Batchelor et al, 1997). It is a vesicular lava and, as this disagreement in assigned type indicates, should be compared with the other eucrites only with caution.…”

“…The TL sensitivity of whole-rock eucrites is related to their metamorphic history (Fig. 2;Batchelor and Sears, 1991%~). Cumulate eucrites tend to have higher TL sensitivities than equilibrated eucrites, which, in turn, have higher TL sensitivities than unequilibrated eucrites.…”

“…The TL sensitivities of bulk eucrite samples can be used to make quantitative petrographic type assignments that generally conform to the Takeda et al (1 983) types based on pyroxene composition and texture. The major exception is the highly anomalous eucrite, Ibitira, which is type 6 according to pyroxene properties and type 2 according to TL sensitivity (Batchelor and Sears, 1991b;Batchelor et al, 1997). It is a vesicular lava and, as this disagreement in assigned type indicates, should be compared with the other eucrites only with caution.…”

“…Exsolution structures, compositional trends in the pyroxenes (Reid and Barnard, 1979;Takeda et al, 1983) and induced thermoluminescence (TL) data (Batchelor and Sears, 1991a,b) suggest that eucrites and related meteorites have experienced significant levels of metamorphism on their parent bodies. In this respect, they differ from lunar samples that are similar in that many are also basalts from a relatively small airless planetary body Batchelor et al, 1997). Eight petrologic types of eucrite have been defined on the basis of the compositional heterogeneity and exsolution structures in the pyroxenes and TL sensitivity.…”