The Aristarchus Plateau on the Moon: Mineralogical and structural study from integrated Clementine UV–Vis–NIR spectral data

Abstract

Combining UVVIS and NIR Clementine spectral data, we characterize the mineralogy of the different volcanic and crustal materials occurring on the Aristarchus Plateau and its close vicinity, in order to investigate their stratigraphic relationships and understand the nature of the crust in this region of the Moon. From an iterative linear mixture modeling, we provide a comprehensive description of the distribution and amount of surface mixture of the units, and document the stratigraphic relationships in the region of study. The determination of clear relationships and origin of the different units forming the structure of the Plateau is not obvious as the surface materials (to a depth less than 1 km) represent complex materials from the Imbrium impact event. In the Aristarchus region, we show that the Imbrium ejecta has a norite and anorthosite rich composition, with the presence of a clinopyroxene component in the uppermost layer (AER and NE units in the text). Alternatively, AER may form a rather thick horizon emplaced on an NE-rich unit, or AER and NE form a single thick horizon showing a gradational compositional change from AER to NE, from the south to the north of the Plateau. Due to its size, the Aristarchus crater must have penetrated through the Imbrium ejecta and exposed underlying layers formed by pre-Imbrian ejecta and/or the original crust. The regional crustal unit (AP for “Aristarchus peak” in the text), i.e., the deepest horizon exposed by the Aristarchus crater likely originates from a pluri kilometer depth, and is represented by feldspar-rich materials with clinopyroxene and olivine as mafic components. Other deep crustal units, at a stratigraphic level close to the deepest horizon AP, or intermediate between AP and the uppermost horizon AER, and locally distributed in the Aristarchus crater and its vicinity (Aristarchus A crater, and the scarp forming the southern edge of the Plateau), are represented by pyroxene-bearing anorthosite (SC unit) and olivine-rich (OL unit) composition. Although in low abundance, olivine-rich materials are found to be widespread in this region of the Moon. Volcanic pyroclastic deposits (DMD) are widely exposed on the Plateau, with high abundances and a fairly homogeneous composition. We suggest their emplacement could have possibly lasted up to the Eratosthenian, thus leading to a more important pyroclastic activity in time than previously thought, and a rather voluminous and stable reservoir for their source. Based on their UVVIS and NIR spectral characteristics, SW-type materials characterizing the mare basalts west of the Plateau are not detected as a major component across the Plateau. However, SW-type material is significantly present in the complex ejecta of the Aristarchus crater, probably due to the particular morphology of the target, straddling the edge of the Plateau which rises about 2 km above Oceanus Procellarum. The present study based on the integrated visible–near infrared Clementine dataset paves the way for high spatial resolution surveys based on recent photometric observations (e.g., AMIE/Smart-1) and/or upcoming detailed spectroscopic observations [LISM/Kaguya–Selene; M3 (Moon Mineralogy Mapper)/Chandraayan-1].