日本地球惑星科学連合2019年大会

講演情報

[J] ポスター発表

セッション記号 S (固体地球科学) » S-MP 岩石学・鉱物学

[S-MP33] 鉱物の物理化学

2019年5月29日(水) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:鎌田 誠司(東北大学学際科学フロンティア研究所)、鹿山 雅裕(東北大学大学院理学研究科地学専攻)

[SMP33-P09] Thermal conductivity anomaly of (Mg,Fe)CO3 solid solution across the spin transition

*趙 耕賢1謝 文斌1,2 (1.台湾中央研究院地球科学研究所、2.台湾国立台湾大学地質学科)

キーワード:スピン転移、熱伝導率、菱鉄苦土鉱、菱鉄鉱

Deep carbon cycle is a process carrying carbon into Earth’s interior by subduction of slabs and returning to Earth’s surface by volcanic activities. Given the abundance of iron in Earth’s interior, it is believed that (Mg,Fe)CO3 solid solution is an important candidate of carbon-hosting mineral in the mantle. Prior studies have shown that the iron in the (Mg,Fe)CO3 solid solution undergoes a pressure-induced spin transition at 40-55 GPa and the iron content has a minor effect on the onset pressure of spin transition. Across the spin transition, the physical properties of (Mg,Fe)CO3 solid solution, e.g. sound velocity and unit cell volume, typically change accordingly. Lattice thermal conductivity of mantle minerals is key to control the heat flux and temperature profile of the mantle. However, the thermal conductivity of (Mg,Fe)CO3 solid solution under relevant mantle pressure-temperature conditions remains largely unknown. Here we used Raman spectroscopy to characterize the extent of spin transition of natural (Fe0.18Mn0.01Mg0.80Ca0.01)CO3 ferromagnesite and time-domain thermoreflectance to measure its thermal conductivity from ambient conditions to 65 GPa. Our preliminary study shows that the thermal conductivity of (Fe0.18Mn0.01Mg0.80Ca0.01)CO3 ferromagnesite is 20 W m-1 K-1 at 40 GPa and drastically increases to 80 W m-1 K-1 at the beginning of spin transition, and then suddenly drops to 20 W m-1 K-1 during the middle period of spin transition, similar to its iron-rich counterpart, (Fe0.78Mg0.22)CO3 siderite, investigated in our previous work. Our results suggest that if the (Mg,Fe)CO3 carbonates can be transported by the subduction slabs to 1400-1800 km depth with iron contents of 18 to 78 %, their thermal conductivity anomalies across the spin transition may induce anomalies in local thermo-chemical profiles in subduction zones, which in turn alter the distribution fields of subducting minerals.