image: This is a photomicrograph of a petrographic thin section of a piece of a coherent, crystalline impact melt breccia collected from landslide material at the base of the South Massif, Apollo 17 (sample 73217,84). Different mineral and lithic clasts, as well as impact melt phases are evident. Determining the ages of different melt components in such a complex rock requires carefully focused analyses within context of spatial and petrographic information such as this. In this study, laser microprobe 40Ar/39Ar analysis is used to investigate age relationships of three of the distinct generations of impact melt shown in this image. This material relates to a paper that appeared in the Feb. 13, 2015, issue of Science, published by AAAS. The paper, by C.M. Mercer at Arizona State University in Tempe, AZ, and colleagues was titled, "Refining lunar impact chronology through high spatial resolution 40Ar/39Ar dating of impact melts." view more
Credit: Brad Jolliff, Washington University in St. Louis