AUTOMATED PARTICLE ANALYSIS OF APOLLO 17 REGOLITH: QUANTITATIVE INSIGHTS INTO THE COMPOSITION AND TEXTURES OF GLASS SPHERES FROM THE SHORTY CRATER SAMPLING SITE

Unusually colored (orange) lunar regolith was discovered and sampled by astronauts Jack Schmitt and Gene Cernan adjacent to Shorty crater during the 1972 Apollo 17 lunar mission. Both surface and double drive tube sampling methods were used to collect material at the sampling site. Samples from lower portions of the drive tubes were found to be generally black, while samples from higher in the tube were predominantly orange. Early studies of these materials revealed that this regolith is comprised of spheres and sphere fragments ranging from holohyaline (orange spherules) to crystal-rich (black spheres). Orange spheres have relatively high Ti-rich glass content, whereas black spheres have relatively high crystalline mineral content (abundant ilmenite quench crystals). It is hypothesized that the spheres are the result of fire fountain eruptions that occurred during the same time period as the bulk of mare basalt extrusion, and that they owe their unique colors to a combination of specific chemical compositions, quench crystallization, and devitrification processes. Thorough analyses of the fine-scale petrography and petrology of large quantities of individual spherules can be an arduous task. For the present study an automated particle analysis technology (QEMSCAN®) was used to study two drive tube samples (74002,181 and 74001,113) to further understand the phase compositions and textural relationships. Several thousand spheres were analyzed from five size fractions (-500/+250µm; 250/+150µm; -150/+90µm; -75/+45µm, and -45/+20µm) to generate modal mineralogy and textural data for each sample. This new quantitative and internally consistent dataset allows for the direct comparison between samples and size fractions. Results are consistent with those of earlier petrographic studies; i.e., spherules from the stratigraphically deeper region of the 74001/2 drive tubes are more devitrified than those closer to the present day surface, as evidenced by their black coloration, distinctive mineralogy, and textures. These data indicate that it is possible to quantify proportions of crystalline material (olivine, ilmenite, chromium spinel) and glass phases within spherules, even at very fine crystal sizes. It is also now possible to quantify differences in phase assemblages between orange and black samples despite its apparent compositional homogeneity.