Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92122;
Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058;
Proc Natl Acad Sci U S A. 2015 Jan 13;112(2):336-41. doi: 10.1073/pnas.1315615112. Epub 2014 Dec 22.
Carbonate minerals provide critical information for defining atmosphere-hydrosphere interactions. Carbonate minerals in the Martian meteorite ALH 84001 have been dated to ∼ 3.9 Ga, and both C and O-triple isotopes can be used to decipher the planet's climate history. Here we report Δ(17)O, δ(18)O, and δ(13)C data of ALH 84001 of at least two varieties of carbonates, using a stepped acid dissolution technique paired with ion microprobe analyses to specifically target carbonates from distinct formation events and constrain the Martian atmosphere-hydrosphere-geosphere interactions and surficial aqueous alterations. These results indicate the presence of a Ca-rich carbonate phase enriched in (18)O that formed sometime after the primary aqueous event at 3.9 Ga. The phases showed excess (17)O (0.7‰) that captured the atmosphere-regolith chemical reservoir transfer, as well as CO2, O3, and H2O isotopic interactions at the time of formation of each specific carbonate. The carbon isotopes preserved in the Ca-rich carbonate phase indicate that the Noachian atmosphere of Mars was substantially depleted in (13)C compared with the modern atmosphere.
碳酸盐矿物为确定大气-水圈相互作用提供了关键信息。火星陨石 ALH84001 中的碳酸盐矿物的形成时间可追溯到约 39 亿年前，C 和 O 三同位素都可用于解读火星的气候历史。在这里，我们报告了使用分步酸溶解技术与离子探针分析相结合的方法，对 ALH84001 中至少两种碳酸盐的 Δ(17)O、δ(18)O 和 δ(13)C 数据进行了分析，以专门针对来自不同形成事件的碳酸盐，并约束火星大气-水圈-岩石圈相互作用和表面水蚀变。这些结果表明，存在一种富 (18)O 的富钙碳酸盐相，它形成于 39 亿年前的主要水相事件之后。这些相表现出过量的 (17)O（0.7‰），捕获了大气-表岩化学储层转移，以及在每个特定碳酸盐形成时的 CO2、O3 和 H2O 同位素相互作用。富钙碳酸盐相中保存的碳同位素表明，与现代大气相比，火星的诺亚纪大气中 (13)C 大量耗尽。
