The mineralogy of Ceres’ Nawish quadrangle

Abstract

Quadrangle Ac-H-08 Nawish is located in the equatorial region of Ceres (Lat 22°S-22°N, Lon 144°E-216°E), and it has variable mineralogy and geology. Here, we report on the mineralogy using spectra from the Visible and InfraRed (VIR) mapping spectrometer onboard the NASA Dawn mission. This quadrangle has two generally different regions: the cratered highlands of the central and eastern sector, and the eastern lowlands. We find this dichotomy is also associated with differences in the NH 4 -phyllosilicates distribution. The highlands, in the eastern part of the quadrangle, appear depleted in NH 4 -phyllosilicates, conversely to the lowlands, in the north-western side. The Mg-phyllosilicates distribution is quite homogeneous across Nawish quadrangle, except for few areas. The 2.7-µm band depth is lower in the south-eastern part, e.g. in the Azacca ejecta and Consus crater ejecta, and the band depth is greatest for the Nawish crater ejecta, and indicates the highest content of Mg-phyllosilicates of the entire quadrangle. Our analysis finds an interesting relationship between geology, mineralogy, ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T 3 topography, and the age in this quadrangle. The cratered terrains in the highlands, poor in NH 4 phyllosilicates r r Ga). Conversely, the smooth terrain, such as with Vindimia Planitia, is richer in ammonia-bearing phy s t s s y u r Ga). At the local scale, Ac-H-8 Nawish, displays several interesting mineralogical features, such as at Nawish crater, Consus crater, Dantu and Azzacca ejecta, which exhibit localized Na-carbonates deposits. This material is superimposed on the cratered terrains and smooth terrains and shows the typical depletion of phyllosilicates, already observed on Ceres in the presence of Na-carbonates.

The geology of the Nawish quadrangle of Ceres: The rim of an ancient basin

“…The southern lowlands are characterized by the Kerwan smooth material, which are the melted products of the Kerwan impact (Williams et al, 2018a, Kerwan paper), that have propagated radially and partly filled the Vendimia Planitia basin interior, where its emplacement was contained by the Vendimia wall/rim. The mineralogic data Carrozzo et al, 2018 in press) also show a westward trend of increasing band absorption values for the 3.1 µm band, meaning that the western lowlands terrains are characterized by a higher abundance of ammonia-bearing phyllosilicates compared to the older highlands. Thus, we propose that the Kerwan smooth material represents evidence of ancient hydrothermal rock-water interaction that can occur at low temperatures (Levinson and Day, 1968).…”