CLEMENTINE OBSERVATIONS OF THE ARISTARCHUS REGION OF THE MOON

Multispectral and topographic data acquired by the Clementine spacecra ft provide information on the composition and geologic history of the Aristarchus region of the moon. Altimetry profiles show;the Aristarchu s plateau dipping about 1 degrees to the north-northwest and rising ab out 2 kilometers above the surrounding lavas of Oceanus Procellarum to the south. Dark, reddish pyroclastic glass covers the plateau to aver age depths of 10 to 30 meters, as determined from the estimated excava tion depths of 100- to 1000-meter-diameter craters that have exposed m aterials below the pyroclastics. These craters and the walls of sinuou s rilles also show that mare basalts underlie the pyroclastics across much of the plateau. Near-infrared images of Aristarchus crater reveal olivine-rich materials and two kilometer-sized outcrops of anorthosit e in the central peaks. The anorthosite could be either a derivative o f local magnesium-suite magmatism or a remnant of the ferroan anorthos ite crust that formed over the primordial magma ocean.