A model for eruption behavior of a volcanic vent in eastern Mare Serenitatis

Homogeneous glass droplets with an ilmenite pyroxenite composition sampled at the Apollo 17 landing site were apparently formed by lava fountaining of a low-viscosity magma. The droplets studied were collected from the top and bottom of an 80-cm-deep section within a block of clastic material located on the rim of Shorty Crater. At a depth of 80 cm, the samples consist of mostly compound and simple droplets which are nearly all partly crystalline (sample 74001,2). Near the top of the section simple orange noncrystalline glass spheres predominate, although some are partly crystalline (sample 74220). Although texturally different, both samples have identical bulk compositions. Individual droplets within each of the grain size fractions for morphology, amount of glass, and olivine texture. It is clear that ranges of cooling rates varied by 2 or 3 orders of magnitude. It is also apparent that the droplets of the unit represented by sample 74001,2 cooled much more slowly on the average than those within the unit represented by 74220. The two samples may represent parts of an eruption sequence. In a well-collimated vertical fountain, many of the droplets would have fallen back into the fountain and been ''recycled'' to produce compound forms. Slower coolingmore » rates would have allowed time for crystal growth. The resulting deposit would have been relatively thick and centered near the vent. This may have been the eruptive phase during which sample 74001,2 was deposited. As the jet became more dispersed, melt droplets would have cooled rapidly and formed mainly simple glassy droplets. This phase of activity would have formed a thinner tephra blanket and may be represented by sample 74220 and orange glass spheres collected throughout the valley of Taurus-Littrow. 8 figs., 2 tables.« less