Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published April 1972 | Published
Journal Article Open

Geologic Setting and Petrology of Apollo 15 Anorthosite (15415)

Abstract

Apollo 15 sample number 15415, popularly called the "Genesis Rock," is coarse-grained anorthosite composed largely of calcic plagioclase with small amounts of three pyroxene phases. The rock was found as a clast in a piece of friable soil breccia on the lip of Spur crater, a small young crater on the lower slopes of the Apennine Mountains. The mode of occurrence of sample 15415 indicates that it has undergone at least two, and possibly three or more, fragmentation events. These events are reflected in the texture of the rock by shattered and granulated minerals. An earlier thermal metamorphic event is represented by irregular bands of coarsely recrystallized plagioclase and minor pyroxene that cross larger plagioclase grains. Preliminary observations of textural relations of the large plagioclase grains are consistent either with accumulation of plagioclase followed by overgrowth of cumulus grains and post-cumulus crystallization of minor interstitial pyroxene, or with metamorphic recrystallization that eradicated original textures. Any of the events in the complex history of this rock may have affected apparent radiometric ages. Comparative abundance of similar, though smaller, pieces of anorthositic rock in the area and dominance of originally coarse-grained gabbroic-anorthositic clasts in breccia at Spur crater suggest that sample 15415 is the least-deformed member of a suite of similar rocks that were ejected from beneath the regolith at Spur crater.

Additional Information

© 1972, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. Manuscript received by the society October 28, 1971. We are greatly indebted to David R. Scott and James B. Irwin for discussions of the field relations of sample 15415. Open exchange of information on the mineralogy and petrology of the sample with David B. Stewart was very beneficial. We are grateful to Ray Sabala for his excellent drafting of the illustrations, to C. G. Utter for his expert photographic work, and K. A. Howard and D. C. Ross, U.S. Geological Survey, for critical review of the manuscript. This work was done under NASA contracts T-4738A and T-65253-G.

Attached Files

Published - i0016-7606-83-4-1083.pdf

Files

i0016-7606-83-4-1083.pdf
Files (1.3 MB)
Name Size Download all
md5:4f7b9cb00b417ca6235034f11af1946c
1.3 MB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023