Highly oxidizing aqueous environments on early Mars inferred from scavenging pattern of trace metals on manganese oxides
Highly oxidizing aqueous environments on early Mars inferred from scavenging pattern of trace metals on manganese oxides
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根据锰氧化物上微量金属的清除模式推断早期火星上的高度氧化水环境
DOI：
10.1029/2018je005892
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Hartmann Jens
中科院分区：
文献类型：
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作者：
Noda Natsumi;Imamura Shoko;Sekine Yasuhito;Kurisu Minako;Fukushi Keisuke;Terada Naoki;Uesugi Soichiro;Numako Chiya;Takahashi Yoshio;Hartmann Jens
好奇号和机遇号探测车在盖尔陨石坑和奋进陨石坑的沉积岩脉中发现了锰（Mn）（氧化物）的沉积。由于Mn是一种氧化还原敏感元素，揭示Mn（水）氧化物的化学形态提供了沉积时近地表/地下水氧化还原状态的独特信息。在这里，我们报告了实验室实验的结果，研究了微量金属（锌、镍和铬）在不同锰（氢）氧化物上的清除模式，以限制火星上发现的锰沉淀的化学形式。我们的研究结果表明，二氧化锰（MnO2）对锌和镍有较好的清除作用，但对铬没有清除作用。这种清除模式与观测结果的一致强烈表明，在火星上发现的锰（氢）氧化物极有可能是二氧化锰。为了形成MnO2，需要氧化的水环境（例如，在pH ~ 8时，Eh > 0.5 V）。氧化剂的候选物包括分子氧、臭氧、硝酸盐和高氯酸；所有这些都被认为是由光化学过程产生的。沉积物中mno2脉的存在表明，这种大气中的高Eh氧化剂可能通过短暂变暖激活的水循环被供应到地下。
The Curiosity and Opportunity rovers have found depositions of manganese (Mn) (hydr)oxides within the veins of the sedimentary rocks at Gale and Endeavour craters. Since Mn is a redox sensitive element, revealing the chemical form of the Mn (hydr)oxide provides unique information on the redox state of the near‐surface/groundwater at the time of deposition. Here we report results of laboratory experiments that investigated scavenging patterns of trace metals (zinc, nickel, and chromium) on different Mn (hydr)oxides in order to constrain the chemical form of the Mn precipitates found on Mars. Our results show manganese dioxide (MnO2) scavenges zinc and nickel effectively but not for chromium. The agreement of this scavenging pattern with the observations strongly suggests that the Mn (hydr)oxides found on Mars are highly likely to be MnO2. To form MnO2, oxidizing aqueous environments are required (e.g., Eh > 0.5 V at pH ~ 8). The candidates of the oxidant include molecular oxygen, ozone, nitrates, and perchlorate acids; all of which are considered to be produced by photochemical processes. The presence of MnO2veins in sediments suggests that such atmospheric high‐Eh oxidants may have been supplied to the subsurface, possibly through hydrological cycles activated by transient warming.