Big Muley

The lunar rock sample 61016, known as Big Muley , was collected during the Apollo 16 mission in the Descartes Highlands in 1972 (coordinates: 8 ° 58 ′ 22.8 ″ S , 15 ° 30 ′ 0.7 ″ E ). At 11.7 kilograms, it is the heaviest sample brought back to Earth by the Apollo program . It is currently held in the Lunar Sample Laboratory Facility at the Lyndon B. Johnson Space Center . Moon -8.973011 15.500189

designation

The English name Big Muley (Großer Muley) refers to William R. Muehlberger , the head of the field geological team of the Apollo 16 mission.

description

NASA image of sample 61016

Big Muley is a dimictive breccia in which a smaller, shocked anorthosite fragment from a troctolithic impact melt is seated. The sample, which weighs 11745 grams, comes from the eastern edge of the Plum Crater in the Descartes highlands. It has an exposure age to cosmic rays of 1.84 million years and can therefore be associated with the ejecta of the South Ray Crater , which is 5 kilometers southwest of the landing site.

The sample was still partly in the lunar soil; its protruding, rounded top, exposed to the solar wind , was covered with a thin, brown patina and covered with tiny meteorite impact holes.

In the course of its history, the rock sample was so badly shocked by several impact events that the original plagioclase was converted into maskelynite and / or glass . The maximum pressures of the shock waves were determined using the diaplectic maskelynite and found mosaic structures with 30 to 40 gigapascals .

Petrography and Mineralogy

The Apollo 16 landing site with South Ray Crater in the lower left

Impact melt

The impact melt , the main component of Big Muley, has a high Al ₂ O ₃ (approx. 25%) and KREEP content. It consists of 16 percent by volume of fragment clasts and 84 percent by volume of matrix.

Clasts

Square to rounded plagioclases ( anorthites ), which can reach a grain size of 2 millimeters, act as clasts . The plagioclase loads are partially or completely converted into maskelynite . There are also glassy, lithic clasts, some of which are devitrified. These include light, coarse-grained, cataclastically deformed anorthosites and dark, fine-grained, dense mafites (troctolites) with mostly poikilitic olivine.

matrix

The semicrystalline matrix with a subophitic structure consists of tabular (0.1 to 0.2 millimeters) and lath-shaped (2 × 0.5 millimeters) maskelynite (42 percent by volume - with small spinel inclusions ), that with poikilitic, fine-grained (0.1 millimeter ), hypidiomorphic to idiomorphic olivine (43 percent by volume) is fused.

Gussets within the matrix are filled with a dark brown, glassy, ilmenite- bearing mesostasis (14 percent by volume). Relic plagioclase has a composition of An _92-98 and olivine is Fo _82-93 . There are also 1 to 2 percent by volume of meteoritic metal grains ( iron content 91 to 93%) with a nickel content of 4 to 8% and a cobalt content of 0.3 to 0.5%.

Anorthosite

The seated anorthosite is rich in iron and contains iron-rich pyroxene and olivine in addition to plagioclase . Its olivine has the composition Fo ₆₂ , its iron-rich pyroxene is Wo ₂ En ₆₃ Fo ₃₅ . The transition region to the sharply separated impact melt is formed from melted plagioclase.

Glass skin

The underside of Big Muley is covered by a skin of glass that probably once covered the entire handpiece. The sample is believed to be an ejection bomb from the South Ray Crater.

Chemism

The following table gives geochemical analysis values for the Big Muley, differentiated into three groups with different compositions: anorthosite, troctolite impact melt and glass (glassy mesostasis, glass skin, pseudotachylite- like veins, transition region)

Oxide wt.%	Impact melt	Anorthosite	Glass	Trace element ppm	Impact melt	Anorthosite	Glass
SiO ₂	42.9 -44.0	44.15-45.0	44.12-44.48	Sc	3.5-7.4	0; 5	3.75
TiO ₂	0.6-0.88	0.017-0.2	0.17-0.43	Cr	250-752	21-375	480-861
Al ₂ O ₃	23.9-26.26	33.19-34.85	29.83-31.74	Co	33-51	0.5	24
FeO	4.5-5.4	0.26-1.40	3.1-3.65	Sr	110-180	149-182	145
MgO	9.12-12.5	0.16-2.51	3.22-4.87	Ba	105-240	6.01-40.7	132
CaO	13.3-15.25	18.3-19.6	15.64-17.51	La	13.0-19.2	0.143-3.74	6.3-13.6
Na ₂ O	0.29-0.40	0.32-0.43	0.34-0.66	Eu	1.17-1.53	0.671-0.926	0.526-0.970
K ₂ O	0.067-0.13	0.0048-0.088	0.07-0.10	Nd	21.2-29.2	0.145-5.6	10.9
P ₂ O ₅	0.101-0.120	0.047-0.050	0.080	Rb	1.3-3.2	0.017-0.700	1,877

In the case of rare earths , the anorthosite has a clear, positive Europium anomaly, whereas the impact melt has a negative Eu anomaly. The glass only has a very weak negative Eu anomaly, but is generally much closer to the values of the impact melt. Compared to chondrites , the impact melt is strongly enriched in rare earths (20-80 times), whereas the anorthosite is slightly below the chondrite values.

Age

The age of Big Muley is given by Eugster (1999) to be 3970 ± 25 million years BP .

meaning

The importance of Big Muley lies in the fact that the sample combines the suspected three stem magma differentials of the primitive lunar crust. Their simultaneous occurrence in a limited space suggests that the sample was impacted several times, thereby melting, recrystallized and mechanically mixed by the impact energy, so that lithologies that were once separated from one another came to lie next to one another. In detail, the processes that led to the creation of Big Muley were very complex (for example, Stöffler assume four shock wave metamorphoses and a final impact event that ejected the sample from the South Ray Crater) and possibly followed the same pattern as in Descartes -Region.

Individual evidence

↑ Rao, MN et al. a .: Solar flare-implanted 4He / 3He and solar-proton-produced Ne and Ar concentration profiles preserved in lunar rock 61016 . In: Journal of Geophysical Research . tape 98 , 1993, pp. 7827-7835 .
↑ McGee, PE et al. a .: Introduction to the Apollo collections. Part II: Lunar Breccias . Curator's Office, JSC, 1979.
↑ ^a ^b Stöffler, D. u. a .: Rock 61016: Multiphase shock and crystallization history of a polymict troctolite-anorthosite breccias . In: Proc. 6th Lunar Sci. Conf. 1975, p. 673-692 .
↑ Misra, KC and Taylor, LA: Characteristics of metal particles in Apollo 16 rocks . In: Proc. 6th Lunar Sci. Conf. 1975, p. 615-639 .
^ Meyer, C .: Lunar Sample Compendium: 61016 . 2009.
^ Morris, RV et al. a .: Composition of the Cayley Formation at Apollo 16 as inferred from impact melt splashes . In: Journal of Geophysical Research . tape 90 , 1986, pp. E21-E42 .
^ Eugster, O .: Chronology of dimict breccias and the age of South Ray crater at the Apollo 16 site . In: Meteor. & Planet. Sci. tape 34 , 1999, pp. 385-391 .
^ Head, JW: The Moon . tape 11 , 1974, p. 77-99 .

[1] Rao, MN et al. a .: Solar flare-implanted 4He / 3He and solar-proton-produced Ne and Ar concentration profiles preserved in lunar rock 61016 . In: Journal of Geophysical Research . tape 98 , 1993, pp. 7827-7835 .

[2] McGee, PE et al. a .: Introduction to the Apollo collections. Part II: Lunar Breccias . Curator's Office, JSC, 1979.

[Stöffler-3] Stöffler, D. u. a .: Rock 61016: Multiphase shock and crystallization history of a polymict troctolite-anorthosite breccias . In: Proc. 6th Lunar Sci. Conf. 1975, p. 673-692 .

[4] Misra, KC and Taylor, LA: Characteristics of metal particles in Apollo 16 rocks . In: Proc. 6th Lunar Sci. Conf. 1975, p. 615-639 .

[5] Meyer, C .: Lunar Sample Compendium: 61016 . 2009.

[6] Morris, RV et al. a .: Composition of the Cayley Formation at Apollo 16 as inferred from impact melt splashes . In: Journal of Geophysical Research . tape 90 , 1986, pp. E21-E42 .

[7] Eugster, O .: Chronology of dimict breccias and the age of South Ray crater at the Apollo 16 site . In: Meteor. & Planet. Sci. tape 34 , 1999, pp. 385-391 .

[8] Head, JW: The Moon . tape 11 , 1974, p. 77-99 .