日本地球惑星科学連合2018年大会

講演情報

[EJ] ポスター発表

セッション記号 P (宇宙惑星科学) » P-PS 惑星科学

[P-PS07] 火星と火星圏の科学

2018年5月20日(日) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:宮本 英昭(東京大学)、臼井 寛裕(東京工業大学地球生命研究所)、松岡 彩子(宇宙航空研究開発機構 宇宙科学研究所 太陽系科学研究系、共同)、Sushil K Atreya (University of Michigan Ann Arbor)

[PPS07-P06] 地球の鉄コンクリーションの形成メカニズムから読み解く火星の表層環境史

*長谷川 精1吉田 英一2勝田 長貴3城野 信一4丸山 一平4南 雅代5淺原 良浩4西本 昌司6山口 靖4Ichinnorov Niiden7Metcalfe Richard8 (1.高知大学理工学部、2.名古屋大学博物館、3.岐阜大学教育学部、4.名古屋大学環境学研究科、5.名古屋大学宇宙地球環境研究所、6.名古屋市科学館、7.モンゴル古生物地質研究所、8.Quintessa Limited, The Hub, Henley-on-Thames, Oxfordshire)

キーワード:コンクリーション、地球、火星、変質、炭酸塩

Spherical Fe-oxide concretions on Earth, in particular in Utah, U.S.A, have been investigated as an analogue of hematite spherules discovered in Meridiani Planum on Mars, in order to support interpretations of water-rock interactions in early Mars. Although several formation mechanisms have been proposed for the concretions on Earth and Mars, it is still unclear whether these mechanisms are viable because a precise formation process and precursor of the Fe-oxide concretions are missing. Here, we show evidence that Fe-oxide concretions in Utah and newly discovered Fe-oxide concretions in Mongolia, had spherical calcite (CaCO3) concretions as precursors. Observed different formation stages of calcite and Fe-oxide concretions, both in the Navajo Sandstone, Utah, and the Djadokhta Formation, Mongolia, indicate the formation process of Fe-oxide concretions as follows: (1) calcite concretions initially formed by groundwater evaporation within aeolian sandstone strata; (2) the calcite concretions were dissolved by infiltrating Fe-rich acidic waters; and (3) mobilized Fe in acidic waters was fixed to form spherical FeO(OH) (goethite) crusts on the pre-existing spherical calcite concretion surfaces due to the pH-buffering dissolution reaction. The similarity between these Fe-oxide concretions on Earth and the hematite spherule occurrences in Meridiani Planum, combined with evidence of acid sulfate water influences on Mars, suggests that the Martian spherules also formed from dissolution of pre-existing carbonate concretions. Formation of recently discovered spherical-shaped nodules in Gale crater on Mars can also be explained by a similar process, although evidence of acid water influence is not obvious in lower strata of the Gale crater. The hematite spherules in Meridiani Planum and spherical nodules in Gale crater are possibly relics of carbonate minerals formed under a dense thick carbon dioxide atmosphere in the past.