Troctolite 76535

Description

Troctolite 76535 is a coarse-grained plutonic rock that is believed to have had a slow cooling history. The rock originates from early in the Moon's history. Geologists have described it as a coarse-grained olivine-plagioclase cumulate with a granular polygonal texture. Olivine and plagioclase are of about equal quantities within 76535, while the remaining approximately 4% is made up of primarily orthopyroxene. According to early studies, the sample cooled at a depth of about 10 -, as well as its reequilibration and annealing. Later work indicated that the rock formed at a depth of 47 kilometers, about the middle to lower crust of the Moon, Investigations have shown that the rock may have formed as a cumulate at depth, thus possibly making the sample an important link in the understanding of the geologic timeline of the Moon.

As Troctolite 76535 is the oldest known "unshocked" (meaning unaltered by meteor impacts) lunar rock, it has been used for thermochronological calculations in order to determine whether the Moon formed a metallic core or generated a core dynamo. The results of these studies have been shown to support the core dynamo hypothesis.

References

References

1. "Lunar Sample 76535". Lunar and Planetary Institute, Lunar Sample Atlas.
2. "76535 Troctolite". National Aeronautics and Space Administration.
3. Ahrens, L. H.. (1980). "Chemistry of the moon". Pergamon.
4. (1999). "Inferred Depths of Formation of Spinel Cataclasites and Troctolitic Granulite, 76535 Using New Thermodynamic Data for Cr-Spinel". Lunar and Planetary Science Conference.
5. Domeneghetti, M.C.. (2001). "Complex Cooling Histories of Lunar Troctolite 76535 and Stillwater Orthopyroxenite SC-936". Lunar and Planetary Science XXXII (2001).
6. Bogard, D. D.. (May 1975). "76535: An old lunar rock". Earth and Planetary Science Letters.
7. Garrick-Bethell, Ian. (January 2009). "Early Lunar Magnetism". Science.