CHLORIDE DEPOSITS ON MARS: CHLORINE FROM THE SKY, OR CHLORINE FROM THE ROCKS?
For a short duration (< 1 Mars yr) warming event (above freezing point), chlorapatite dissolution cannot provide sufficient Cl- to satisfy mass balance. High water-to-rock ratios (W/R) are also ruled out because sulfates would be transported into the lakes and precipitate close to or with the chlorides. If the source of chlorine was the weathering of volcanic Cl-phases (e.g. perchlorate), long warm events are not required, since the volcanic Cl-phases only reside in the top-most meters of soil/dust. For a ~ 1.4 × 1011 kg NaCl deposit near Miyamoto Crater in Meridiani Planum , we find that masses of degassed volcanic HCl reported by  are insufficient to form the deposit. However, chlorapatite weathering to a depth of ~ 15 m across the 1.2 × 109 m2basin (i.e. ~ 1 Mars yr) could form the deposit but would be inconsistent with seasonal melting.
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