The Effect of Flourine on the Liquidus of an Adirondack-class Martian

Introduction: This study presents first experimental results on the effect of fluorine on near-liquidus phase equilibria of an Adirondack-class Martian basalt. The basis of this study is our previous work on anhydrous [1] and chlorine bearing [2] systems which has already shown that: 1) the Adirondack-class basalts are evolved liquid compositions [1] and 2) that chlorine has a large effect on liquidus depression and is important for basalt genesis on Mars [2]. However , to date there is little experimental work on the effect of fluorine on martian basalts. Yet, fluorine-rich martian basaltic compositions are suggested from the fluorine-rich magmatic minerals in the SNC meteorites [3-6]. Therefore, fluorine may play an important role in Martian basalt genesis and crystallization. Evidence from martian meteorites: The martian meteorites show evidence for high fluorine concentrations in magmatic and alteration minerals. Magmatic inclusions within the SNC meteorites commonly contain magmatic amphibole which can readily accept F [3, 4]. Kaersutite, a Ti-rich amphibole, in the Chassigny meteorite contains 0.5 wt % F [3], and in NWA 2737 contains ~3 wt % F [4]. Also, within the melt-inclusions of the Chassigny meteorite there is rare Ti-biotite which contains 2.3 wt % F [3]. Using a D F biotite/melt ~ 5.5 [7], for a biotite with an Mg# ~ 65 [3], suggests that the parental liquid to the amphibole in the Chassigny meteorite had ~ 0.4 wt % F. Apatite is also a ubiquitous late stage mag-matic mineral in the SNC meteorites. It is a significant reservoir of halogens in the SNC meteorites and can be used to compare halogen budgets of different planets [5]. Patiño Douce and Roden [5] compared apatites within the SNC meteorites to apatites from terrestrial basalts. They suggested that martian rocks are water poor compared with terrestrial basalts but contain significant halogen contents. Others [6] have observed that within the Chassigny meteorite there are two populations of apatite: fluorine-rich, water-poor found in the melt-inclusions and chlorine-rich, water-poor found interstially [6]. They concluded that the F-rich apatite formed in a closed system process within the melt inclusions; while the chlor-fluor-apatite is created via open system fluid migration