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Fig. 6. Schematic diagram of the Cl cycle on Mars proposed here. Recent basalts erupt with phosphates with a δ37Cl of −0.6‰, which is representative of the bulk Martian mantle. When on or near the surface, these phosphates interact with halogen rich brines that have incorporated isotopically fractionated Cl, which occurred by photochemistry in the atmosphere (a minimum of −55 to a maximum of +5‰, Jackson et al., 2010) or the soil (which would have a similar composition). The perchlorate on the Martian surface that is likely incorporated into the Martian brines has a δ37Cl of −55 to −1‰ (Farley et al., 2016).

图6 本文提出的火星氯循环示意图。新近喷发的玄武岩携带的磷酸盐的δ37Cl值为-0.6‰，该值代表了火星整体地幔的同位素特征。当这些磷酸盐处于火星表面或近地表环境时，会与富含卤素的卤水发生相互作用；这类卤水的氯同位素已发生分馏，其分馏过程源于大气光化学作用（范围为-55‰至+5‰，Jackson等，2010）或土壤作用（土壤的氯同位素组成与之近似）。火星地表的高氯酸盐（perchlorate）大概率会进入火星卤水中，其δ37Cl值为-55‰至-1‰（Farley等，2016）。