Understanding the evolution of Martian carbonates from a combined modelling and synthesis study

Introduction – There were several discoveries in 2008 regarding carbonates on Mars that are important in understanding the evolution of these salts. These include the identified CaCO3 by Phoenix’s TEGA and MECA instruments [1,2]. The Phoenix lander has also discovered the surrounding soils were pH alkaline (8.3 ± 0.5) [2] and enriched with subliming water ice, both conditions favourable to carbonate formation. Furthermore carbonates (in the form of MgCO3) were detected by reflectance spectra from the orbital IR and VNIR spectrometer CRISM [3]. Despite these discoveries, without material being brought back directly from Mars by a sample return mission, martian meteorites provide the best source for analysis of the finescale mineralogy of the martian surface. ALH84001 The origins of ALH84001 carbonates are of great importance for understanding the ancient martian environment. Thought to have formed ~3.9 Ga [4], they are assumed to have precipitated from fluids with neutral to alkaline pH in contact with CO2. Approximately 0.6 Ga separates primary crystallization of ALH84001 from formation of secondary mineral assemblages. The period in which the carbonates formed has been called the Phyllosian era, owing to the outcrops of phyllosilicates discovered by the OMEGA and CRISM spectrometers [5, 6]. Their ancient age, abundance and mineralogical variations make ALH84001 carbonates ideal candidates to provide insights into early martian environmental conditions.