Investigating the formation of impact-exhumed hydrated sulfates in Tyrrhena Terra, Mars

Abstract

Understanding the distribution and provenance of hydrated minerals within Noachian terrains is essential to deciphering Mars' crustal formation and alteration history. The phyllosilicate and carbonate minerals typically found within Noachian geologic units, for instance, have been attributed to a warmer, wetter climate that preceded a transition to the sulfate-dominated, colder, drier, and more acidic conditions in the Hesperian and Amazonian. However, these broad associations may not hold true locally. In Tyrrhena Terra, the heart of the Noachian-aged cratered highlands, three isolated craters host an unusual occurrence of hydrated sulfates alongside a variety of other alteration minerals more typically associated with the Noachian era. This paper investigates the presence of these outcrops in order to understand their origin, relationship to these co-located minerals, and implications for aqueous history and crustal evolution of Mars. Using Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data along with other contextual remote sensing data, we present a mineralogical mapping and spectral analysis of primary and secondary minerals at each location where sulfates are observed. Based on our characterization, we have constrained the formation of the sulfates to be associated with epithermal alteration or sulfide oxidation rather than impact or mechanically induced alteration. This suggests a complex sequence of aqueous alteration, potentially involving one or more steps, which we intend to explore further in future studies. The discovery of these sulfate minerals within predominantly phyllosilicate and carbonate territories challenges the conventional timeline of Mars' climate evolution, hinting that transitions between climatic epochs may have overlapped or been more regionally varied than previously thought.

Plain language summary

This research looks at how certain minerals, called hydrated sulfates, formed on Mars and what they can tell us about the planet's history. Sulfate outcrops were found in a region called Tyrrhena Terra, which is very old and dates back to a time when Mars was warmer and wetter than it is now. By studying data from a special camera on a Mars orbiter, we find that these minerals were brought to the surface by meteor impacts. They were likely formed a long time ago, before the impacts happened. This research explores different ways these minerals could have formed. One idea is that they were created by hot water moving through the ground, while another suggests they formed from chemical reactions involving sulfides (another type of mineral). The findings suggest that Mars' crust in this area was not necessarily uniform but could have had patches of different materials. These patches were altered by water, leading to the formation of the sulfates we see today. Understanding these minerals helps scientists learn more about the ancient climate and water activity on Mars. It gives clues about how the planet's surface has changed over billions of years and helps us piece together the story of Mars' geological past.