Accurate determination of the melting relations of primitive peridotite under lower-mantle conditions up to 35 GPa using advanced multi-anvil techniques

据认为，地球的地幔在其早期历史中经历了一次或多次大规模的熔融，这种熔融被称为陆地岩浆海洋。陆地岩浆海洋的凝固可能产生了成分分层，这应该为地球地幔的演化提供了初始状态。在各种相关参数中，原始橄榄岩在下地幔条件下的熔融关系对于了解岩浆海洋的凝固过程尤为重要，本项目将使用多砧压力机确定这些关系。尽管已经进行了几项确定原始橄榄岩熔融关系的研究，但这些研究遇到了一些局限性。(1)样品室中陡峭的温度梯度导致熔体与固体分离，导致对凝固顺序的误解。(2)传统多砧压机的压力范围限于25 GPa。下地幔条件下的相应压力区间仅为2GPa。(3)传统的多砧压力机的温度范围限于2800 K，这不足以确定深地幔中的液相线温度。(4)压力估计可能包含较大的误差，因为在以前的研究中，压力校准是在比熔化实验低得多的温度下进行的，尽管在恒定的压力载荷下压力随着温度的升高而降低。(5)由于存在微量的熔体，固相线温度很难确定。为了克服这些问题，我们将采用以下先进的多砧技术。(1)使用我的研究小组开发的新熔炉设计，样品室中的温度梯度将被抑制到接近零，以防止熔体偏析。(2)压力范围将扩大到35 GPa，通过我们的超高压产生技术，使用多砧压机与硬质合金砧。(3)利用我所在课题组博士后研制的掺硼金刚石加热器，将温度范围扩展到4000 K。(4)在相同的温度条件下，并在相同的高压池作为熔化实验的样品压力将通过在原位的X射线衍射进行校准。(5)利用原位X射线衍射技术，通过观察晶粒的突然生长，确定了近干原始橄榄岩“KLB-1”在25 GPa、30 GPa和35 GPa压力下从液相线以上到固相线以下的熔化关系。将在亚固相线运行中估计样品中的含水量。

It is thought that the Earth’s mantle experienced extensive melting one or more times in its early history; this melting is referred to as the terrestrial magma ocean. Solidification of the terrestrial magma ocean may have produced compositional layering, which should provide the initial state for the evolution of the Earth’s mantle. Of the various relevant parameters, the melting relations of primitive peridotite under lower-mantle conditions are particularly important to understand the solidification process of the magma ocean; these relations will be determined in this project using multi-anvil presses.Even though there have been several studies conducted to determine the melting relations of primitive peridotite, these studies have encountered several limitations. (1) Steep temperature gradients in the sample chambers have caused segregation of the melt from the solids, resulting in misinterpretations of the solidification sequence. (2) The pressure range of conventional multi-anvil presses is limited to 25 GPa. The relevant pressure interval under lower-mantle conditions is only 2 GPa. (3) The temperature range of conventional multi-anvil presses is limited to 2800 K, which is insufficient to determine liquidus temperatures in the deep mantle. (4) Pressure estimations likely contain large errors because, in previous studies, pressure calibrations were conducted at much lower temperatures than those of the melting experiments, despite the decrease in the pressure with increasing temperature at a constant press load. (5) Solidus temperatures are difficult to determine due to the trace amounts of melt present.To overcome these problems, we will adopt the following advanced multi-anvil techniques. (1) Temperature gradients in the sample chambers will be suppressed to nearly zero to prevent melt segregation using a new furnace design developed by my research group. (2) The pressure range will be expanded to 35 GPa via our ultrahigh-pressure generation technique using a multi-anvil press with hard carbide anvils. (3) The temperature range will be expanded to 4000 K using a boron-doped diamond heater developed by a postdoc in my research group. (4) Sample pressures at the same temperature conditions and in the same high-pressure cell as the melting experiments will be calibrated by means of in situ X-ray diffraction. (5) The solidus temperatures will be determined by observing sudden grain growth by means of in situ X-ray diffraction.Using these technologies, we will determine the melting relations of nearly dry primitive peridotite “KLB-1” from above-liquidus to below-solidus temperatures at pressures of 25 GPa, 30 GPa, and 35 GPa. The water content in the samples will be estimated in a sub-solidus run.