Experimental petrology of the Mars Pathfinder rock composition: Constraints on the interpretation of Martian reflectance spectra

Abstract

Experiments to determine the crystallization sequence of the Mars Pathfinder (MPF) rock composition have been carried out to explore the range of possible mineral assemblages in this SiO2‐rich (57.4 wt %) Martian igneous rock. Recent Mars Global Surveyor thermal emission spectrometer observations have suggested the presence of large volumes of andesitic lava covering the northern hemisphere of Mars, but this interpretation has been called into question. Experimentally produced mineral assemblages can be used to infer spectral characteristics that would exist in andesitic lavas similar in composition to the MPF rock. The inferred spectra could then be used with remotely sensed data to further constrain the identity of surface rock types on Mars. We performed a series of experiments at 0.1 MPa at the quartz‐fayalite‐magnetite and iron‐quartz‐fayalite oxygen buffers and 100 MPa at the Ni‐NiO oxygen buffer using the calculated soil free MPF composition. Potential mineralogies for a lava with the MPF composition would be SiO2 (57 wt %), FeO (18 wt %) rich glass, plagioclase, quartz, augite, and Fe‐Ti oxides. A contoured pyroxene quadrilateral (with band I and II minima) was used to predict pyroxene composition on the basis of reflectance spectra. Using the quadrilateral in reverse, the augite produced in the experimental series should have band I and II minima at 0.97 μm and 2.15 μm, respectively. The absence of the 1‐μm minima in the Imager for Mars Pathfinder (IMP) spectra could be due to masking phases, possibly the Fe‐Ti oxides produced in our experiments at 1000°C.