Dikes of distinct composition intruded into Noachian‐aged crust exposed in the walls of Valles Marineris

Abstract

Valles Marineris represents the deepest natural incision in the Martian upper crust. Previous studies showed that the upper parts of the walls were made of finely layered probable basalts in most of the chasmata, while the base of the stratigraphy reveals primary Noachian crustal blocks. Exposures of pristine Noachian bedrock are rare on Mars, and mostly observed outside of their geological context. The occurrence of well‐preserved and extended outcrops of pristine material in this giant rift could bring valuable information on the early processes that took place at the surface of Mars. Analyses of high resolution data over the best exposures of lower walls in Coprates Chasma, central Valles Marineris, revealed the presence of multiple magmatic intrusions interpreted as dikes. These dikes intrude an old, massive, fractured bedrock interpreted as being preserved ancient Noachian crust. Their composition, determined using CRISM data, and distribution, limited to this ancient crust at the bottom walls, indicate that they might have formed early in the rift formation, and therefore represent exceptionally well‐preserved outcrops of the early history of Mars.