Experimental investigation into the thermodynamic properties of halogens

Recent research has shown that the Earth accreted and differentiated over 30-40 Myr,ecoming more oxidised through time. Stable continental crust was then established relatively quickly. These processes led to the segregation of siderophile (iron-loving) elements to the Earths core and incompatible lithophile (rock-loving) elements to the crust. One of the most intriguing questions facing planetary science is whether the processes experienced by the growing Earth represent those which took place on other terrestrial planets or even exoplanets. The answer lies with Earths nearest neighbour: Mars.The Mars Exploration Rovers (MER) and orbital missions continue to deliver largevolumes of high-quality chemical and mineralogical data from the Martian surface, including bountiful measurements of halogens, including chlorine and bromine. In addition,the Mars Odyssey Gamma Ray Spectrometer (GRS) has mapped the equatorial and midlatitude distribution of elemental Cl abundances at the near-surface of Mars (Zhao and McLennan, 2012). These datasets show the upper few tens of centimetres of Mars is significantly enriched in Cl relative to Martian meteorites and estimates for the bulk composition of the planet. However, it is not homogenously distributed.Much of the focus on the Cl-rich mineralogy of Mars derives from studies of the nakhlite and chassignite meteorites, each containing a broad array of magmatic volatile bearing minerals including Cl-enrichment (Filiberto and Treiman 2009; Filberto, et al., 2014). According to McCubbin et al., (2009), there is a clear link between chlorine-rich hydrothermal uids and magmatic activity in Chassigny and MIL 03346, but it is presently unclear whether the Cl-rich uid was exogenous or endogenous to the magmatic system. M'dard and Grove (2008), found that on a molar basis, Cl is twice as effective as H2O in depressing the liquidus of basalts. Although this does suggest that the addition of Cl to the Martian mantle may lower the magma genesis temperature and potentially aid in the petrogenesis of Martian magmas, current experiments have only explored a basalt composition with a xed Cl concentration; hence, applying their results to the range of Cl concentrations in terrestrial and Martian magmas becomes problematic. Other experiments evaluate the intrinsic effects of dissolved chlorine on Fe3+/PFe and magnetite solubility in hydrous chloride-rich rhyodacitic liquids, and show Cl addition to the melt has two prominent effects on iron: (1) dissolved Cl perturbs the magnetite-melt equilibrium, such that greater FeO total contents are required to support magnetite saturation in Cl-bearing melts than in Cl-free melts of equivalent bulk compositions; and (2) a systematic and progressive decrease of the measured Fe3+/PFe as fO2 is increased. Hence, the two intimately related effects each have important implications for redox processes occurring in Cl-enriched arc magmas. It is, however, well established that the Martian planet is vastly more Fe-rich than rhyodacitic melts. Therefore, bulk composition with lower Al2O3 and higher FeO contents should be tested to further constrain its effect on the influence of chlorine on near-liquidus crystallisation.The solubility of Cl has only been investigated for felsic magmas as above, with few experiments on Martian magmas compositions, which differ significantly from terrestrial. Therefore, the effect of Martian enriched FeO magmas on the solubility of halogens such as Cl is poorly understood. As it is unknown what in infuences Cl solubility, deciphering the partitioning behaviours of the martian mantle will be key to understanding the magmatic activity on Mars.I therefore propose to study Cl solubility within the Martian mantle through experimental methodology, creating chemically similar compositions to assess, if, and the extent at which Fe influences solubility, as this will shed light on the Martia magmatism and evolution.