Lunar breccia

Yanai K. (2000) Achondrite polymict breccia 1153 a new lunar meteorite classified to anorthositic regolith breccia. Lunar Planet. Sci. XXXI, 1101. Lunar and Planetary Institute, Houston (CD-ROM). 

Eichhorn, G., James, 0. B., Schaeffer, 0. A., and Muller, H. W., Laser 39Ar-40Ar Dating of Two Clasts From Consortium Breccia 73215, Proc. Lunar Planet. Conf. 9th, 1978, p. 855. 

Lunar Meteorites Highlands breccias Mare basalts... 

Samples returned by the Apollo and Luna missions can be readily distinguished based on their contents of FeO and thorium. This may seem like an unlikely choice of chemical components for classification, but they nicely discriminate rock types and are easily measured by remote sensing. The FeO and thorium contents of ferroan anorthosites, mare basalts, impact melt breccias, and lunar meteorites are shown by various symbols in Figure 13.4. 

As noted earlier, lunar meteorites are mostly breccias of ferroan anorthosite and related early crustal rocks, although a few mare basalt meteorites are known. The lunar meteorites likely sample the whole Moon. The absence of KREEP-rich breccias so common among Apollo samples collected from the nearside in the lunar meteorite collection implies that KREEP-rich rocks cover only a small area on the Moon. In fact, the lunar highlands meteorites appear to provide a closer match to the average lunar crust than do the Apollo highlands samples (Fig. 13.5), as measured by geochemical mapping (see below). 

Figure 2.12 Correlated isotopic variations observed in stepwise heating of lunar breccia 60019. The linear array suggests that only two components, in varying proportions, are present one is trapped solar wind, presumably near BEOC-12, the other is in situ cosmic ray-induced spallation, relatively rich in 124Xe and 126Xe.

To resolve the primordial terrestrial noble gas, it would be useful to examine major noble gas reservoirs in the early solar system, which could have supplied noble gases to the Earth. As we discussed in Chapter 3, two major noble gas components occur very widely in the solar system and can be a potential source for the terrestrial noble gas. They are solar noble gas (representative of the sun), which is generally assumed to be best represented by solar wind noble gas implanted on Al-foil target plates on the moon (elemental ratio) and on lunar breccia (isotopic ratio) (e.g., Ozima et al., 1998), and Q phase noble gas (see Wieler, 1994, for a review), which occurs very widely in various chondrites. Next we will compare the bulk Earth noble gas, which we assume to be represented by atmospheric noble gas with these two major noble gas components in the solar system. 

Black, D. C. (1972) On the origin of trapped helium, neon, and argon siotopic variations in meteorites - I. Gas-rich meteorites, lunar soil and breccia. Geochim. Cosmochim. Acta, 36, 347-75. 

Eberhardt, E, Geiss, X, Graf, H., Grogler, N., Mendia, M. D., Morgeli, M. U., Schwaller, H., Stettler, A. (1972) Trapped solar wind noble gases in Apollo 12 lunar fines 12001 and Apollo 11 breccia 10046. Proc. Third Lunar Science Conf., 2, 1821-56. 

Bell, J. F. Keil, K. (1988) Spectral alteration effects in chondritic gas-rich breccias implications for S-class and Q-class asteroids. Proc. 19th Lunar Planet. Sci. 

The enrichment in the fines and regolith breccias is thought to result from exposure on the lunar surface, resulting in either preferential removal of 12C or addition of 13C. A number of mechanisms have been proposed to explain these observations for the fines and must also be applicable to the regolith breccias. 

It has been suggested24 that the CH4 released by deuterated acid dissolution could arise from reaction of lunar carbide on grain surfaces with adsorbed terrestrial H2O. This has been shown to be unlikely exposure of the fines to D20 at 200 °C 5), or at ambient for periods up to several weeks47, failed to release CD4. Also, dissolution of freshly exposed chips of an Apollo 11 regolith breccia released CH4 and CD4in concentrations similar to those released from Apollo 11 fines47. ... 

The carbon chemistry of the regolith has been established as a significant indicator of exposure and reworking. In conjunction with other parameters indicative of exposure of the fines and breccias on the lunar surface, it should contribute to an understanding of the complex history of the regolith. 

With the exception of these small amounts of meteoritic matter, the lunar soil is derived from igneous rocks disrupted by impacts and gradually reduced to fine-grained dust. On all landing sites, the soil is much more abundant than rocks or breccias. Except on steep slopes, the whole Moon is covered with a layer dust of at least 5 m thick. The rock samples brought back are separate fragments embedded in the soil once part of the underlying bedrock, they were excavated by the impact of meteorites. 

Figure 31 Lunar meteorite North West Africa (NWA) 773 consists of two distinct lithologies cumulate olivine norite and regolith breccia. The cumulate portion is composed of olivine, pigeonite, augite, feldspar, and opaques (troilite, chromite, Fe-metal). The breccia portion contains fragments of cumulate portion as well as silica glass, hedenbergitic pyroxene, volcanic rocks, and unusual lithic clasts with fayalite + Ba-rich K-feldspar + silica + plagioclase (photograph courtesy of M. Killgore).

Keil K. (1982) Composition and origin of chondritic breccias. In Workshop on Lunar Breccias and Soils and their Meteoritic Analogs, LPI Technical Report 82-02 (eds. G. J. Taylor and L. L. Wilkening). The Lunar and Planetary Institute, Houston, pp. 65-83. 

Warren P. H., Taylor J. G., and Keil K. (1983) Regolith breccia Allan HiUs A81005 evidence of lunar origin, and petrography of pristine and nonpristine clasts. Geophys. Res. Lett 10, 779-782. 

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