Compositional variation and petrogenesis of mare basalts in the Humorum basin: New insights from spectral analysis and crater counting

Abstract

Pyroxene chemistry estimated using a series of spectral parameters derived from Chandrayaan-I M3 data was used to divide the basalts of Mare Humorum into six compositional units. In order to understand the petrogenetic history of the Humorum basalts, first, the dominant pyroxene end-member composition in each unit is used to estimate the temperature of crystallization; and then crater counting is implemented using craters mapped from the high-resolution Kaguya Terrain Camera data to estimate the age of each unit. The spatial distributions of pyroxene composition and corresponding crystallization temperatures indicate that there is a difference in volcanic activity between the regions corresponding to Units 1–3 (Group I) and the regions corresponding to Units 4–6 (Group II). This observation is further reinforced by analyzing the variation of FeO and TiO2 content across the units. Hence two sources titanium-rich high calcic pyroxene (HCP) and less titanium high calcic pyroxene (HCP) correspond to two groups of basalts in the Humorum area. Furthermore, our new crater-counting analysis reveals that the magmatic activity probably continued until ca. 1.9 Ga in the Humorum basin. To the best of our knowledge, this younger age of volcanism has not been reported before.