MINERALOGICAL MAPPING OF LIGHT-TONED, SULFATE-RICH DEPOSITS IN EASTERN VALLES MARINERIS, MARS

Numerous occurrences of aqueously-altered minerals have been identified on Mars including phyllosilicates-class minerals thought to form very early in Mars’ history and sulfate and iron oxides minerals thought to mark the transition from early to modern geochemical conditions (e.g., Bibring et al. 2006). In the Valles Marineris region, sulfate, hydrated silica, and iron oxide minerals are typically found associated with light-toned layered deposits (LTLDs). These deposits include large (1000s m thick) and small (100s m thick) interior layered deposits (ILDs) throughout Valles Marineris as well as draped LTLDs along canyon walls and floors. Several models have been proposed to explain the origin of LTLDs including eolian, lacustrine, volcanic, evaporitic, diagenetic, hydrothermal, glacial and salt tectonic processes (e.g., Chojnacki and Hynek 2008). The mineralogy and stratigraphy of ILDs are similar and thus, may have had similar origins. Other LTLDs differ in mineralogy, stratigraphy, and/or morphology; therefore, additional processes are likely involved.

Here we map and characterize the mineralogy and morphology of light-toned, sulfate-rich deposits in the chaos terrains of eastern Valles Marineris (study area: -15-0°N, 325-345°E) to assess the regional variability and compare to ILDs and other LTLDs in Valles Marineris. Deposits were mapped in Aurorae, Arsinoes, Aureum, and Iani Chaos terrains and consist of monohydrated sulfates either overlain by or interbedded with polyhdrated sulfates. The presence of hematite (and less commonly Fe-hydroxysulfate and jarosite) was variable, but found associated with both types of hydrated sulfates. This mineralogy is comparable to that found in Valles Marineris ILDs. However, mapped deposits are thinner and display erosional scours indicative of flow direction; these scours are likely caused by higher-energy fluvial erosion during the Hesperian-aged chaos terrain and outflow channel development. This morphology suggests ILD formation in the study area predates the final drainage of the region. Understanding the relative timing and modification of these deposits helps inform and constrain proposed formation and evolution mechanisms for deposits throughout Valles Marineris.