P–V–T equation of state of siderite to 33 GPa and 1673 K

Abstract

Pressure–volume–temperature relations have been measured to 33GPa and 1673K for natural siderite (Fe0.95Mn0.05CO3) using synchrotron X-ray diffraction with a multianvil apparatus at the ‘SPring-8’ facility. A least-squares fit of the room-temperature compression data to a third-order Birch–Murnaghan equation of state (EOS) yielded K0=120±1GPa and K′=3.57±0.09, with fixed V0=293.4±0.1Å3. Further analysis of the high-temperature compression data yielded the temperature derivative of the bulk modulus (∂KT/∂T)P=−0.015±0.001GPa/K and zero-pressure thermal expansion α=a0+a1T with a0=3.57(9)×10−5K−1 and a1=0.06(14)×10−8K−2. The analysis of axial compressibility indicates that the c-axis is more compressible (KTc=59±1GPa at K′=2.7±0.1) than the a-axis (KTa=166±2GPa at K′=14.0±0.8). The present thermal EOS enables accurate calculation the density and thermodynamic properties of siderite to the deep mantle conditions.