Proclus crater: a study case to integrate compositional information and morpho-stratigraphic mapping on the Moon

Geological planetary mapping is mainly done by considering morphology and stratigraphic information, supported sometimes by color variation to define boundaries of superficial textures or highlight physical properties. In recent years more attention was used to integrate mineralogical indications from the visible to the near-infrared (VNIR) to the usual planetary geological mapping. Specifical examples has been tested on Mercury (e.g. Wrigth et al., ESS, 2024), on Mars (e.g. Giacomini et al., Icarus, 2012) and on the Moon (e.g. Tognon et al., JGR, 2024).

Here, we investigate the Proclus crater, a 28 km, simple and fresh crater, Copernican in age (Apollo 15 PSR), which shows a variegate VNIR reflectance properties. We have analyzed the M3 m3g20090202t024131 (onboard Chandrayaan-1 mission) image to study the composition of Proclus crater whereas a mosaic compiled with six LROC (Lunar Reconnaissance Orbiter Camera) NAC images, with a spatial resolution of 0.8 m/pixel, has been used to define the morpho-stratigraphic map of the area.

We first classified the crater in different spectral regions applying the Spectral Angle Mapper (Kruse et al., REMOTE SENS. ENVIRON., 1993) method and using image-driven end-members by Purity Pixel Index (PPI, Boardman,  7JPL-Air.Geos.W., 1993). PPI supports the definition of 7 end-members, integrated by other 4 end-members evaluating the spectral variability.

Representative spectrum of each Spectral Unit was deconvolved by Gaussian model and results on mineralogical detection were compared with well characterized terrestrial analogues. The 11 end-members support the definition of six main Spectral Units and 2 units were divided in sub-units from a mineralogical point of view.  The Spectral Units recognized from Proclus crater indicate that this crater is characterized by lithologies rich in plagioclase mixed with variable amount of different mafic phases.

Geomorphological mapping highlights as Proclus crater walls is affected by mass wasting deposits, mainly represented by taluses. The crater floor is instead dominated by impact melt with different surface texture: from smooth melt ponds to more hummocky and knobby deposits.

Finally, Spectral Units were used to improve the morpho-stratigraphic map and identify sub-units or new-units.

We acknowledge support from the Horizon 2020 program grant agreements 871149-GMAP and 776276-PLANMAP.