Nabiei Farhang, Badro James, Boukaré Charles-Édouard, Hébert Cécile, Cantoni Marco, Borensztajn Stephan, Wehr Nicolas, Gillet Philippe
Earth and Planetary Science Laboratory EPFL Lausanne Switzerland.
Electron Spectrometry and Microscopy Laboratory EPFL Lausanne Switzerland.
Geophys Res Lett. 2021 Jun 28;48(12):e2021GL092446. doi: 10.1029/2021GL092446. Epub 2021 Jun 15.
We carried out a series of silicate fractional crystallization experiments at lower mantle pressures using the laser-heated diamond anvil cell. Phase relations and the compositional evolution of the cotectic melt and equilibrium solids along the liquid line of descent were determined and used to assemble the melting phase diagram. In a pyrolitic magma ocean, the first mineral to crystallize in the deep mantle is iron-depleted calcium-bearing bridgmanite. From the phase diagram, we estimate that the initial 33%-36% of the magma ocean will crystallize to form such a buoyant bridgmanite. Substantial calcium solubility in bridgmanite is observed up to 129 GPa, and significantly delays the crystallization of the calcium silicate perovskite phase during magma ocean solidification. Residual melts are strongly iron-enriched as crystallization proceeds, making them denser than any of the coexisting solids at deep mantle conditions, thus supporting the terrestrial basal magma ocean hypothesis (Labrosse et al., 2007).
我们使用激光加热金刚石压腔，在下地幔压力条件下开展了一系列硅酸盐分离结晶实验。确定了共熔熔体和沿液相线下降的平衡固相的相平衡关系及成分演化，并用于构建熔融相图。在火成岩质岩浆海洋中，下地幔中首先结晶的矿物是贫铁含钙布里奇曼石。根据相图，我们估计岩浆海洋最初的33% - 36%将结晶形成这种浮力较大的布里奇曼石。在高达129 GPa的压力下，观察到布里奇曼石中具有显著的钙溶解度，这显著延迟了岩浆海洋固化过程中硅酸钙钙钛矿相的结晶。随着结晶过程的进行，残余熔体强烈富铁，使其在地幔深部条件下比任何共存的固相都更致密，从而支持了地球基性岩浆海洋假说（拉布罗斯等人，2007年）。
