Gerald G. Schaber 1973 Orbital photographs taken at low-Sun illumination during both the Apollo 15 (ref. 30-14) and Apollo 17 missions have provided excellent data on the lava flows in the southwestern Mare Imbrium. These photographs have been used recently to present a detailed photogeologic evaluation of these flows and their role in mare volcanism of Eratosthenian age in the basin (ref. 30-15). Eruption of these flood basalts apparently took place in at least three major episodes with suggested dates of 3.0 ± 0.4 billion years (phase I), 2.7 ± 0.3 billion years (phase II), and 2.5 ± 0.3 billion years (phase III) using the mare age-dating method described by Soderblom and Lebofsky (ref. 30-16) and recent data by Soderblom and Boyce (ref. 30-17). application/pdf en National Aeronautics and Space Administration Volcanic studies: Part E: Eratosthenian volcanism in Mare Imbrium: source of youngest lava flows chapter