Polymict breccias may have either a clastic matrix, a “melt” matrix which is crystallized or glassy, or a metamorphic matrix. Such breccias result from the mixing of different lithologies formed under different conditions at different selenological locations. Polymict (or polylithologic) breccias consist, of two main textural components which are termed matrix and clasts. The monomict breccias are cataclastic rocks formed by in-situ brecciation of a single lithology (monolithologic). 1980) classifies breccias as either monomict, polymict or dimict. This breccia type is termed regolith breccia because it closely resembles consolidated lunar soil.Ī committee report ( Stöffler et al. Sample 15299 is a vitric matrix breccia that is probably from a small crater in the local lunar regolith at the Apollo 15 site. Sample 72275 is a friable fragmental breccia from the edge of the Serenitatis basin. Poikilitic texture similar to that of sample 65015 was also typical of the large boulders at the Apollo 17 site ( fig. An example of a breccia from a large crater is the poikilitic rock 65015, which is thought to have originated as part of a melt sheet in a large lunar crater. Sample 14305 is a crystalline matrix, fragmental breccia typical of the Fra Mauro Formation, which is ejecta from the Imbrium basin. Sample 60025 is a cataclastic anorthosite that has already been discussed as a plutonic rock. This thin section set includes five different lunar breccias from the lunar highlands. Lunar breccias can originate from either large or small craters and/or from different radial distances from large craters. A wide range of crater sizes are found on the Moon, and it is easy to see why a wide range of breccia types is also present. These breccias have a wide variety of matrix textures - from fragmental to vitric to crystalline. In the Apollo collection, 59 breccia samples weigh over 500 g each, and there are many more samples with smaller sizes. A few breccias (sample 15405) are younger and were formed from the lunar regolith ( fig. Most of the breccias returned by the Apollo missions were formed in the ancient lunar highlands about 3900 to 4000 million years ago. Lunar breccias are the lithified aggregates of clastic debris and melt generated by meteorite bombardment of the lunar surface. (note the astronaut pushing his rover back uphill) Samples of this boulder are all breccias with a poikiloblastic texture typical of a melt sheet. Figure 44 - The large boulder at station 6, Apollo 17, has rolled down from the North Massif.
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