Late high‐titanium basalts of the Western Maria: Geology of the Flamsteed REgion of Oceanus Procellarum

The Flamsteed region of Oceanus Procellarum is representative of an unsampled volcanic complex on the lunar nearside. The evolution of this region, as portrayed in the current surface, is investigated in detail. A synthesis of remote sensing data, including multispectral images (digital vidicon images and color composite photographs), spectral reflectance measurements, radar topographic maps, and orbital and earth‐based photography, is presented. Additional information is derived from crater degradation studies, radar backscatter, gravity measurements and orbital γ ray data. Seven spectrally distinct basaltic units, which range in age from 2.5±0.5 b.y. to 3.65±0.15 b.y., have been identified. Three have been formally named and related to the Procellarum lithostratigraphic nomenclature scheme. The earliest units within the mapped area are composed of highlands material and include partially flooded impact craters. Another early nonmare unit is spectrally distinct material that occurs as plains and domes and which, in part, is of probable extrusive origin. Small amounts of dark mantle material suggest the presence of an early Ti‐rich basalt (Repsold Formation) beneath the presently exposed mare basalts. The oldest surface exposed mare basalts are very low Ti basalts of the Telemann Formation. These are overlain by low to intermediate Ti basalts of the Hermann Formation. The youngest exposed basalts are the moderately Ti‐rich members of the Sharp Formation. The unsampled Flamsteed basalt, a young Ti‐rich unit defined here, is comparable to Apollo 11 basalts in many measurable parameters except the strength of an absorption feature at 1 μm. This distinction implies a fundamental difference in mineralogy of the two titanium‐rich units; the Flamsteed basalts may be more iron rich than the other lunar basalts. The total mare fill in the Flamsteed region is probably of the order of 400‐m average thickness. Ejecta from young craters such as Kepler and Copernicus overlie some basalts. The major deformation of these units, evidenced by tectonic rules and mare ridges, terminated prior to the emplacement of the youngest mare unit during the emplacement of the Hermann Formation. This complexity of emplacement history and wide variety of observed basalt types, largely unsampled by Apollo and Luna missions, provide additional details of basaltic volcanism on the moon and require models of lunar basalt petrogenesis to be reexamined.