Experimental modeling of the cooling history of Apollo 12 olivine basaltsAn analog of the Apollo 12 olivine vitrophyres has been crystallized in a 1-atm gas-mixing furnace at cooling rates ranging between 1250 and 0.7 C/hr and isothermally at degrees of supercooling ranging from 10 C to 325 C. Mineral chemistry, crystal shapes, grain sizes and textures are systematically related to cooling rate and degree of supercooling. At linear cooling rates not exceeding 40 C/hr the texture is porphyritic - large olivine crystals are set in a groundmass of finer-grained pyroxene, plagioclase, and ilmenite; a later generation of olivine never crystallizes. There are three shapes of olivine crystals in the Apollo 12 olivine vitrophyres: glomerocrysts of subhedral crystals, large subequant skeletons, and highly elongate skeletons. These result from three generations of nucleation and a two-stage cooling history - a slow preeruption stage and a rapid continuously increasing posteruption stage. It seems likely that the Apollo 12 olivine basalt magmas were erupted with olivine crystals in suspension. The nucleation temperature of olivine in cooling-rate experiments is dependent on the experimental technique, and hence results of cooling experiments should be applied with caution.
Document ID
19780062740
Acquisition Source
Legacy CDMS
Document Type
Conference Proceedings
Authors
Donaldson, C. H. (Lunar and Planetary Institute Houston, Tex., United States)
Usselman, T. M. (Lunar and Planetary Inst. Houston, TX, United States)
Williams, R. J. (Lunar and Planetary Inst. Houston, TX, United States)
Lofgren, G. E. (NASA Johnson Space Center Houston, Tex., United States)