| dc.description.abstract | Spin transition and thermal conductivity of (Fe0.78Mg0.22CO3) siderite under high pressure
ABSTRACT
Deep carbon cycle is a cycle controlling the long-term budget of carbon on Earth’s surface and in Earth’s interior: the carbon is transported to the mantle by the subduction of slabs and recycled back to the Earth’s surface by the volcanic activities, respectively. Iron-bearing carbonate, for example, siderite, was proposed to be an important mantle carbon-hosting mineral in the deep carbon cycle. Previous literature showed that the siderite undergoes a pressure-induced iron spin transition (from high spin to low spin) around 40-55 GPa and the physical properties of siderite, such as elastic properties, change drastically across the spin transition. The thermal conductivity is a critical physical property that controls the heat flux flowing through a mineral when temperature gradient exists, and therefore, thermal conductivity controls the temperature profile and thermal structure evolution in Earth’s interior. However, the thermal conductivity of iron-bearing carbonate has never been investigated under relevant extreme temperature and pressure conditions due to the experimental difficulties. In this work, we combined the diamond anvil cell, Raman spectroscopy and time-domain thermoreflectance techniques to measure the thermal conductivity of siderite from ambient condition to 67 GPa, in particular across the spin transition. We found that the thermal conductivity varies drastically across the spin transition: when siderite is under 40-55 GPa, the thermal conductivity increases by three times as the fraction of low spin iron is estimated to be around 50-85% and suddenly drops to around 1/9 of its maximum value as the spin transition almost completes. These results imply that if the siderite could be transported to the depth of 1100-1500 km by the subduction of slabs, the thermal conductivity anomaly of siderite that varies drastically within a narrow pressure range might induce local heat flux and temperature anomalies, and therefore, influence the stability of local mineral phases. | en_US |