Petrology and comparative thermal and mechanical histories of clasts in breccia 62236
Lunar breccia 62236 contains large lithic fragments of troctolite, norite, and anorthosite. The mafic phases, olivine, inverted pigeonite, and augite, fill interstitial areas between larger plagioclases and appear to be cumulate phases with extensive adcumulus growth. Pyroxene compositional homogeneity indicates that cation exchange during cooling was limited to an area of about 1 mm. Primary augite and pigeonite both contain 30 ..mu..m-wide lamellae of the other along '001'. Pigeonite inverted to orthopyroxene without retaining any crystallographic orientation and subsequently exsolved fine lamellae of augite on (100). Profiles across orthopyroxene-augite interfaces obtained in the analytical transmission electron microscope show an increase of approx.5% wollastonite in augite within 0.5 ..mu..m of the interface, suggesting that short-range cation exchange continued to temperatures below 500 /sup 0/C. The entire sample has undergone heterogeneous shock deformation. Shock melting of the troctolitic clast suggests pressures of 200-300 kb and well-developed basal twinning in augite from the norite clasts suggest pressures of 50-300 kbars. The present evidence indicates that 62236 contains parts of a slowly cooled microlayered accumulate that has been heterogeneously shocked several times and combined into the present breccia.
- Research Organization:
- 959 National Center, U. S. Geological Survey, Reston, Virginia 22092
- OSTI ID:
- 5939802
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 88:S1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
MOON
PETROLOGY
PLANETARY EVOLUTION
ANORTHOSITES
CHEMICAL COMPOSITION
DEFORMATION
LUNAR MATERIALS
MINERALOGY
OLIVINE
TWINNING
ALKALINE EARTH METAL COMPOUNDS
GABBROS
GEOLOGY
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MATERIALS
MINERALS
OXYGEN COMPOUNDS
PLUTONIC ROCKS
ROCKS
SATELLITES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SOLAR SYSTEM EVOLUTION
TRANSITION ELEMENT COMPOUNDS
640107* - Astrophysics & Cosmology- Planetary Phenomena