OPTICAL DATING PROPERTIES OF THENARDITE (NA2SO4): A POTENTIAL SULFUR SOURCE MINERAL IN MARTIAN SEDIMENTS

Thenardite is an anhydrous sodium sulfate salt (Na₂SO₄) that was identified in trace amounts in the Shergotty meteorite. Recent satellite data also suggests that thenardite may be a significant contributor to elevated sulfur concentrations at numerous locations across the surface of Mars. Optical (OSL) dating is an absolute dating method, which is based on solid-state dosimetric properties of mineral grains and is being developed for in-situ use on Mars. OSL dating is especially suited for dating sedimentary deposits, which will be vital to interpreting Martian geologic and climatic history. Quartz and feldspars are the primary minerals used for terrestrial OSL dating and the dating properties of these minerals are well documented. However, due to the limitations placed on in-situ experimental devices, mineralogical separations may not be feasible or practical on Mars. So it is essential for dating of Martian sediments to understand how accessory minerals, such as sulfates, may affect results obtained in-situ. In this project we have evaluated basic optical dating properties of thenardite, which include radiation dose response and OSL signal stability. Our results suggest that, while the OSL properties of Thenardite itself are complex due to multiple structural phase changes when heated and it's capacity to absorb water to become the hydrated form Mirabilite (Na₂SO₄•10H₂O), trace amounts of thenardite occurring at Martian surface conditions are unlikely to have a significant effect on in-situ optical dating of silicate minerals on Mars.