Abstract Calcium carbonate (CaCO3) is one of the most abundant carbonates on Earth’s surface and transports carbon to Earth’s interior via subduction. Although some petrological observations support the preservation of CaCO3 in cold slabs to lower mantle depths, the geophysical properties and stability of CaCO3 at these depths are not known, due in part to complicated polymorphic phase transitions and lack of constraints on thermodynamic properties. Here we measured thermal equation of state of CaCO3-Pmmn, the stable polymorph of CaCO3 through much of the lower mantle, using synchrotron X‑ray diffraction in a laser-heated diamond-anvil cell up to 75 GPa and 2200 K. The room-temperature compression data for CaCO3-Pmmn are fit with third-order Birch-Murnaghan equation of state, yielding KT0 = 146.7 (±1.9) GPa and K0 = 3.4(±0.1) with V0 fixed to the value determined by ab initio calculation, 97.76 Å3. High-temperature compression data are consistent with zero-pressure thermal expansion αT = a0 + a1T with a0 = 4.3(±0.3)×10-5 K-1, a1 = 0.8(±0.2)×10-8 K-2, temperature derivative of the bulk modulus (∂KT/∂T)P = –0.021(±0.001) GPa/K; the Grüneisen parameter γ0 = 1.94(±0.02), and the volume independent constant q = 1.9(±0.3) at a fixed Debye temperature θ0 = 631 K predicted via ab initio calculation. Using these newly determined thermodynamic parameters, the density and bulk sound velocity of CaCO3-Pmmn and (Ca,Mg)-carbonate-bearing eclogite are quantitatively modeled from 30 to 80 GPa along a cold slab geotherm. With the assumption that carbonates are homogeneously mixed into the slab, the results indicate the presence of carbonates in the subducted slab is unlikely to be detected by seismic observations, and the buoyancy provided by carbonates has a negligible effect on slab dynamics.

中文翻译：

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文石后CaCO3-Pmmn状态热方程

摘要 碳酸钙（CaCO3）是地球表面最丰富的碳酸盐之一，通过俯冲作用将碳输送到地球内部。尽管一些岩石学观察支持将冷板坯中的 CaCO3 保存到较低的地幔深度，但在这些深度处 CaCO3 的地球物理特性和稳定性尚不清楚，部分原因是复杂的多晶相变和缺乏对热力学特性的限制。在这里，我们在高达 75 GPa 和 2200 K 的激光加热金刚石砧室中使用同步加速器 X 射线衍射测量了 CaCO3-Pmmn 状态的热方程，CaCO3 的稳定多晶型物穿过大部分下地幔。 CaCO3-Pmmn 的温度压缩数据符合三阶 Birch-Murnaghan 状态方程，得出 KT0 = 146.7 (±1.9) GPa 和 K0 = 3.4(±0. 1) V0 固定为从头计算确定的值，97.76 Å3。高温压缩数据与零压热膨胀一致 αT = a0 + a1T 且 a0 = 4.3(±0.3)×10-5 K-1, a1 = 0.8(±0.2)×10-8 K-2, 温度体积模量的导数 (∂KT/∂T)P = –0.021(±0.001) GPa/K；Grüneisen 参数 γ0 = 1.94(±0.02)，体积独立常数 q = 1.9(±0.3) 在固定的德拜温度 θ0 = 631 K 通过 ab initio 计算预测。使用这些新确定的热力学参数，CaCO3-Pmmn 和 (Ca,Mg)-碳酸盐榴辉岩的密度和体积声速沿冷板坯地温从 30 到 80 GPa 进行了定量建模。假设碳酸盐均匀地混合到板坯中，