•Detections of smectites, chlorites, carbonates and possible serpentine.•Alteration evidence of the first 7km of the crust between the Hellas and Isidis basins.•Evidence of carbonation of the martian crust. Recent investigations of alteration of martian crustal outcrops suggest putative crustal hydrothermal systems, which are favorable environments for the emergence of life. In this study, we perform an analysis of the CRISM targeted observations covering crustal outcrops in the region between the Hellas and Isidis basins with the goal of investigating the alteration phases. Over the wide studied region, we detect the presence of possible serpentines, chlorites, smectites and carbonates. These detections occur within ejecta blankets, crater walls and central uplifts of impact craters. We investigate the relation between the observed associations of minerals and the ages of the impact craters assessed by crater count. No clear relation is observed. We also investigate the relationship between the group of detected mineral and the pre-impact depth of the studied outcrops assessed from the size of the impact craters. This method allows us to reconstruct the pre-impact cross-section. We suggest that alteration of the first 7km of the crust between the Hellas and Isidis basins may have undergone alteration processes.