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Petrologic history of the moon inferred from petrography, mineralogy, and petrogenesis of Apollo 11 rocks

Smith, J. V. and Anderson, A. T. and Newton, R. C. and Olsen, E. J. and Wyllie, P. J. and Crewe, A. V. and Isaacson, M. S. and Johnson, D. (1970) Petrologic history of the moon inferred from petrography, mineralogy, and petrogenesis of Apollo 11 rocks. In: Proceedings of the Apollo 11 Lunar Science Conference. Pergamon Press , New York, NY, pp. 897-925. ISBN 0080163920. https://resolver.caltech.edu/CaltechAUTHORS:20160209-101343274

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Abstract

The mineralogy and petrology of the Apollo 11 rocks are consistent with impact melting of ilmenite and pyroxene crystals plus liquid derived from fractional crystallization of basaltic magama. The complementary plagioclase accumulate should exist in the highlands. The ferrobasaltic magma is derived from a differentiated hot moon of modified chondritic composition. The one-sided distribution of large irregular seas is explained by tidal attraction of the last fraction of liquid to the near side of the moon and release of liquid by meteorite impact. The vesicular ferrobasalt lavas contain ilmenite, clinopyroxene and plagioclase and have textures similar to some terrestrial basalts. Delayed appearance of plagioclase indicates an unusual source of the magma. The iron-enrichment of the coarser microgabbros is extreme at the end of crystallization resulting in a new iron metasilicate, pyroxferroite. The oxygen fugacity at 1050°C of these rocks indicated by the composition of opaque oxides and troilite-iron intergrowths is 10^(-14)-10^(-16) compared to 10^(- 11) for terrestrial basalts and about 10^(16) for ordinary chondrites. Absence of hydrous minerals indicates loss of volatiles at some stage in the moon's history. The breccias and soil have the same mineralogy modified by shock. Plagioclase vitrophyres are probably melted cumulates and may derive from the highlands. Lithification of the breccia results principally from welding of debris discharged from a hot gas cloud created by meteorite impact. Small glass spheres have surface features consistent with a fiery rain of boiling silicate liquid rounded by surface tension and later impacted by high-velocity micrometeorites. Melting experiments of synthetic material of mean Apollo 11 rock composition revealed low liquidus temperature, delayed appearance of plagioclase and narrow crystal-liquid interval. These support the concept of advanced fractional crystallization of a basaltic liquid under reducing conditions leading to high iron enrichment. Flotation of plagioclase and sin king of ilmenite and pyroxene should occur in the liquid basalt. We propose that meteorite impact blasted away a plagioclase-rich crust, melting a mixture of fractionated basalt liquid and ilmenite plus pyroxene crystals. The new liquid formed the Sea of Tranquillity and yielded the near-surface lava flows represented by the ferrobasalts and microgabbros. This new liquid could yield plagioclase only after the extra ilmenite and pyroxene had crystallized. We propose that the original basalt liquid was derived by fractional crystallization of a molten moon of modified chondritic composition yielding a metallic core surrounded by pressure-stable Mg-rich o li vine and pyroxene. The fractionated liquid became Fe-rich resulting in an inverse density stratification. Primitive ultra basic crust should occur in the highlands, along with dominant plagio clase- rich cumulates. The temperature-time relations of the model are discussed qualitatively. Key factors are early removal of radioactive material from the center by fractional crystallization and possible enhancement of radiative heat transfer in volatile-free silicates. The moon rocks should be more refractory and rigid because of the low volatile content.


Item Type:Book Section
Additional Information:© 1970 Pergamon Press. Received 3 February 1970; accepted in revised form 4 March 1970. We thank P. B. MOORE and J. R. GOLDSMITH for scientific assistance, G. R. ZECHMAN and O. DRAUGHN for electron microprobe super vision and specimen preparation, Mrs. J. V. SMITH for bibliographic and editorial work, Mrs. I. BALTUSKA and Mrs. J. RJEFFEL for secretarial help, A. T. DEVITT for administration, R. BANOVICH for graphic arts, W. F. SCHMIDT for technical help, and J. R. ROBERTSON for photographic assistance. Financial assistance from NASA grant NAS 9-8086 was supplemented by NSF grants G-1658, GA-4420, GA-15718, and GA-1656, an Advanced Research Projects Agency grant, a grant-in-aid from Union Carbide Corporation, a Hertz Foundation fellowship and general funds of the University of Chicago. We particularly thank D. ANDERSON and J. WARNER of NASA for helpful cooperation in supply of specimens, and the LSPET team for their excellent basic description carried out under exceptionally difficult circumstances. We gratefully acknowledge the advice of C. FRONDEL and A. A. LEVINSON.
Funders:
Funding AgencyGrant Number
NASANAS 9-8086
NSFG-1658
NSFGA-4420
NSFGA-15718
NSFGA-1656
Advanced Research Projects Agency (ARPA)UNSPECIFIED
Union Carbide CorporationUNSPECIFIED
Fannie and John Hertz FoundationUNSPECIFIED
University of ChicagoUNSPECIFIED
Record Number:CaltechAUTHORS:20160209-101343274
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160209-101343274
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ID Code:64329
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 Feb 2016 19:51
Last Modified:03 Oct 2019 09:36

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