Solomatova Natalia V, Caracas Razvan
CNRS Ecole Normale Supérieure de Lyon Laboratoire de Géologie de Lyon LGLTPE UMR5276 Centre Blaise Pascal Lyon France.
The Center for Earth Evolution and Dynamics (CEED) University of Oslo Oslo Norway.
J Geophys Res Solid Earth. 2021 Feb;126(2):e2020JB021045. doi: 10.1029/2020JB021045. Epub 2021 Feb 10.
The early Earth was marked by at least one global magma ocean. Melt buoyancy played a major role for its evolution. Here we model the composition of the magma ocean using a six-component pyrolite melt, to which we add volatiles in the form of carbon as molecular CO or CO and hydrogen as molecular HO or through substitution for magnesium. We compute the density relations from first-principles molecular dynamics simulations. We find that the addition of volatiles renders all the melts more buoyant compared to the reference volatile-free pyrolite. The effect is pressure dependent, largest at the surface, decreasing to about 20 GPa, and remaining roughly constant to 135 GPa. The increased buoyancy would have enhanced convection and turbulence, and thus promoted the chemical exchanges of the magma ocean with the early atmosphere. We determine the partial molar volume of both HO and CO throughout the magma ocean conditions. We find a pronounced dependence with temperature at low pressures, whereas at megabar pressures the partial molar volumes are independent of temperature. At all pressures, the polymerization of the silicate melt is strongly affected by the amount of oxygen added to the system while being only weakly affected by the specific type of volatile added.
早期地球至少有一个全球岩浆海洋。熔体浮力在其演化过程中起主要作用。在这里，我们使用六组分的橄榄岩熔体来模拟岩浆海洋的成分，并以分子态CO或CO₂的形式添加碳挥发物，以分子态H₂O的形式或通过替代镁来添加氢挥发物。我们从第一性原理分子动力学模拟计算密度关系。我们发现，与不含挥发物的参考橄榄岩相比，添加挥发物使所有熔体更具浮力。这种效应与压力有关，在地表最大，在约20吉帕时减小，到135吉帕时大致保持不变。浮力增加会增强对流和湍流，从而促进岩浆海洋与早期大气的化学交换。我们确定了整个岩浆海洋条件下H₂O和CO₂的偏摩尔体积。我们发现在低压下与温度有明显的相关性，而在兆巴压力下偏摩尔体积与温度无关。在所有压力下，硅酸盐熔体的聚合受到添加到系统中的氧量的强烈影响，而仅受到添加的特定挥发物类型的微弱影响。
