Geological Map of Proclus Crater, Moon

GEOLOGICAL MAP OF PROCLUS CRATER, MOON. L. Giacomini1 , C. Carli1, G. Serventi2 and M. Sgavetti2 1INAF, Istituto di Astrofisica e Planetologia Spaziali, Rome, Italy ([email protected]), 2 Dipartimento di Fisica e di Scienze della Terra, Università degli Studi di Parma, Parma, Italy. Introduction: Proclus craters has a diameter of 27 km and is located at a latitute of 16.1° N and a longitude of 47.0° E, on the northwest rim of Crisium basin and east of Palus Somni. It shows a fresh morphology and rayed ejecta, extending up to 600 km, that place the crater in the Copernican age. In the past, it was selected as possible landing site for the Apollo XV mission [1]. In this work we present the preliminary integrated map of this crater including both morphological and spectral information. Data and Methods: To compile the geomorphological map of Proclus crater, LROC (Lunar Reconnaissance Orbiter Camera) data were used. In particular, the LRO WAC mosaic of 100 m/pixel as well as a derived LROC NAC mosaic of 1 m/pixel served as main basemaps. Moreover, several high-resolution NAC images with a resolution of 0.8 m/pixel were processed and mosaicked with ISIS in order to have the most suitable illumination condition for mapping the wall and the floor of the crater. The projected images were imported in the ArcGIS® environment, and then, the geological features were digitalized as vector layers. The map was produced in equirectangular projection. To investigate the spectral properties of this crater we considered images from M3 spectrometer onboard Chandrayaan-1 which covers the 0.43-3.0 µm range [2]. In particular, we selected one image that covered all the crater, with a spatial resolution 140 m/px and its ejecta, whereas other images were used to verify the spectral retrieved data. The data were analyzed with ENVI ® to defined spectral endmembers and classify them, whereas Origin ® was used to plot spectra endmembers and apply the continuum removed for further mineralogical analysis. Finally, an integrated geological map was compiled merging the geomorphological and spectral maps in order to highlight correspondences between morphologies and spectral characteristics and to detect possible new units not discernible considering only the geomorphology. Proclus crater’s geomorphological map: In the map of Proclus crater the geological contacts, lineaments and geological units are shown (Fig.1a). The contacts define the boundary of geologic units, that are surfaces characterized by the same morphology/texture, albedo characteristic, and stratigraphic position. Contacts are classified in: certain, where the boundary between adjacent units is detected with confidence, and approximate, where it is not well defined. Lineaments include: i) crater rim, that defines the crest of craters ii) fractures, that have been mapped mainly on the crater floor, iii) terrace margins, mapped on the wall and on the slump masses within the floor, and iv) strata, that are bedding planes parallel to each other, and are mapped on the crater wall. The geomorphological map highlights as the Proclus crater’s floor is dominated by impact melt related features. The crater wall is affected of gravitational deposits of fine material although some outcrops of stratified rocks are still visible. Fig.1 Proclus crater maps. a) Geomorphological map based on LROC monochrome images highlighting the different surface textures of the crater. b) Spectral map based on M3 data showing the different spectral units that characterized the wall, floor, and ejecta. In the background is LROC WAC global mosaic. Proclus crater’s spectral map: A priori application of the Purity Pixel Index [3] permitted to define seven distinct endmembers. Application of the Spectral Angle Mapper [4] supported the identification of a large spectral variability for some endmemebers. This aspect suggested to introduce other endmembers, reducing the acceptance angle of the SAM, investigating unclassified regions. Finally, 6 main units could be identify, with two of them that could be divided in sub-units (Fig.1b). The units were populated by: A) Pl-dominated spectra; B) pl-px bearing units; C) Px-dominated; d) Ol-dominated; E) mineral mixing with ol-px and spinels with weak absortpions and low reflectance; F) featureless-space weathered material. Units A e B are larger regions mainly occurring on crater walls, units C and D indicates small outcrops in different position within the crater, unit E are partially covering the floor and ejecta, and Unit F is distributed within the floor. Proclus crater’s final integrated geological map: The geomorphological map was compared and integrated with the spectral map of Proclus. In this manner, new subunits within the geomorphological units, previously mapped, have been detected. In some cases these subunits have morphological counterparts. This was particularly evident in the crater’s floor. On the crater wall, the different spectral units helped us to better discern the areas where talus deposits are thicker from those where rock outcrops are dominant. Moreover, different spectral subunits can be inferred on the crater wall outcrop. The resulting map is a more complete geological map of Proclus crater that can give important new information about the crater’s formation. References: [1] El-Baz, F., Worden, A.M., 1972. Apollo 15 Preliminary Science Report 25-1–25-25 (NASA SP-289). [2] Pieters, C.M. et al. (2009) Current Sci., 96, 500-505. [3] Boardman, J.W. (1993) 4thJPL Air.Geosc.W. 11-14. [4] Kruse, F.A. et al. (1993) RSE, 44, 145-163.