Magnesium carbonates have been identified within the landing site of the Perseverance rover mission. This study reviews terrestrial analog environments and textural, mineral assemblage, isotopic, and elemental analyses that have been applied to establish formation conditions of magnesium carbonates. Magnesium carbonates form in five distinct settings: ultramafic rock-hosted veins, the matrix of carbonated peridotite, nodules in soil, alkaline lake, and playa deposits, and as diagenetic replacements within lime—and dolostones. Dominant textures include fine-grained or microcrystalline veins, nodules, and crusts. Microbial influences on formation are recorded in thrombolites, stromatolites, crinkly, and pustular laminites, spheroids, and filamentous microstructures. Mineral assemblages, fluid inclusions, and carbon, oxygen, magnesium, and clumped isotopes of carbon and oxygen have been used to determine the sources of carbon, magnesium, and fluid for magnesium carbonates as well as their temperatures of formation. Isotopic signatures in ultramafic rock-hosted magnesium carbonates reveal that they form by either low-temperature meteoric water infiltration and alteration, hydrothermal alteration, or metamorphic processes. Isotopic compositions of lacustrine magnesium carbonate record precipitation from lake water, evaporation processes, and ambient formation temperatures. Assessment of these features with similar analytical techniques applied to returned Martian samples can establish whether carbonates on ancient Mars were formed at high or low temperature conditions in the surface or subsurface through abiotic or biotic processes. The timing of carbonate formation processes could be constrained by ¹⁴⁷Sm-¹⁴³Nd isochron, U-Pb concordia, ²⁰⁷Pb-²⁰⁶Pb isochron radiometric dating as well as ³He, ²¹Ne, ²²Ne, or ³⁶Ar surface exposure dating of returned Martian magnesium carbonate samples.

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地球上碳酸镁的形成及其对火星的影响


在毅力号火星车任务的着陆点内发现了碳酸镁。本研究回顾了陆地模拟环境以及用于确定碳酸镁形成条件的结构、矿物组合、同位素和元素分析。碳酸镁在五种不同的环境中形成：超镁铁质岩脉、碳化橄榄岩基质、土壤中的结核、碱性湖和普拉亚沉积物，以及石灰和白云岩内的成岩替代物。主要结构包括细粒或微晶脉、结节和结壳。微生物对形成的影响记录在凝块石、叠层石、褶皱和脓疱层板、球体和丝状微结构中。矿物组合、流体包裹体以及碳、氧、镁以及碳和氧的团块同位素已被用来确定碳、镁和碳酸镁流体的来源及其形成温度。超镁铁质岩石中的碳酸镁的同位素特征表明，它们是由低温大气水渗透和蚀变、热液蚀变或变质过程形成的。湖相碳酸镁的同位素组成记录了湖水的降水、蒸发过程和环境地层温度。使用返回火星样本的类似分析技术对这些特征进行评估，可以确定古代火星上的碳酸盐是否是在高温或低温条件下通过非生物或生物过程在地表或地下形成的。 碳酸盐形成过程的时间可能受到¹⁴⁷ Sm- ¹⁴³ Nd 等时线、U-Pb 等时线、 ²⁰⁷ Pb- ²⁰⁶ Pb 等时线放射性测年以及返回的³ He、 ²¹ Ne、 ²² Ne 或³⁶ Ar 表面暴露测年法的限制火星碳酸镁样品。