DIVERSE HYDRATED MINERALS AND DEPOSITS AT NOCTIS LABYRINTHUS: IMPLICATIONS FOR LATE HESPERIAN TO AMAZONIAN AQUEOUS ACTIVITY ON MARS

We have targeted and analyzed both HiRISE and CRISM data of light-toned deposits within depressions of Noctis Labyrinthus and along the adjacent plataeu. Noctis Labyrinthus consists of a network of intersecting linear troughs and pits along the eastern Tharsis rise that connect eastward to the continuous chasmata of Valles Marineris. The age of Noctis Labyrinthus is thought to be Late Hesperian to Early Amazonian based upon disruption of the lava plains along the plateaus. Spectral information extracted from CRISM was combined with high-resolution imaging and Digital Terrain Models (DTMs) derived from HiRISE to map out geologic units, infer stratigraphy, and propose aqueous conditions to form these deposits. Numerous minerals have been identified within this region, including several kinds of sulfates (monohydrated (kieserite and szomolnokite) and polyhydrated sulfates, jarosite, and Ca-sulfates (gypsum, bassanite)), clays (Fe/Mg-smectites and Al-phyllosilicates), and hydrated silica/opal. We also identified a doublet feature between 2.2-2.3 µm in several of the depressions.

Our observations and analyses indicate a diverse range of deposits and minerals within the depressions of Noctis Labyrinthus and along portions of the plateau. While some depressions appear to have experienced the same aqueous conditions that produced similar minerals, most contain a distinct suite of minerals, suggesting that each depression underwent a unique depositional and alteration history. The presence of clays in many of the troughs indicates that water conditions were at times long-lived and habitable. Hydrothermal activity and the presence of volcanic ash are plausible conditions to explain many of the deposits observed in this region given their proximity to the Tharsis volcanoes. Young volcanic flows and channels have been identified in some of the troughs, indicating that heat was available in the Amazonian to melt ice and/or snow that may have accumulated in the troughs. The Late Hesperian to Amazonian ages of these deposits indicate that aqueous activity occurred within this region relatively late in martian history when conditions were thought to be cold and dry.