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

利用先进的多砧技术准确测定高达 35 GPa 的下地幔条件下原始橄榄岩的熔化关系

• 批准号: 461495683
• 负责人: Professor Dr. Tomoo Katsura
• 金额: --
• 依托单位: Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/461495683?language=en
• 关键词: Accurate; determination; melting; relations; primitive

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.

据认为，地球的地幔在其早期历史中经历了一次或多次广泛的融化；这种融化被称为陆地岩浆海。陆地岩浆海洋的凝固可能产生了成分分层，这应该为地幔的演化提供了初始状态。在各种相关参数中，下地幔条件下原始橄榄岩的熔融关系对了解岩浆海的凝固过程尤为重要；这些关系将在本项目中使用多砧压力机来确定。尽管已经进行了几项研究来确定原始橄榄岩的熔融关系，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造成了熔体与固体的偏析，导致了对凝固顺序的误解。(2)常规多砧压力机压力范围限制在25gpa。下地幔条件下相关压力区间仅为2 GPa。(3)常规多砧压机的温度范围限制在2800 K，不足以确定深部地幔的液态温度。(4)压力估计可能存在较大误差，因为在以往的研究中，压力校准是在比熔化实验低得多的温度下进行的，尽管在恒定的压力负荷下，压力随温度的升高而降低。(5)由于存在微量熔体，固相温度难以测定。为了克服这些问题，我们将采用以下先进的多砧技术。(1)样品室的温度梯度将被抑制到接近零，以防止熔体偏析使用我的研究小组开发的新炉设计。(2)通过我们的超高压生成技术，压力范围将扩大到35gpa，该技术使用的是带有硬质合金顶砧的多顶压机。(3)使用我课题组博士后开发的掺硼金刚石加热器，将温度范围扩大到4000 K。(4)采用原位x射线衍射法标定与熔化实验相同温度条件下高压池的样品压力。(5)固相温度将通过原位x射线衍射观察晶粒的突然生长来确定。利用这些技术，我们将确定接近干燥的原始橄榄岩“KLB-1”在25 GPa、30 GPa和35 GPa压力下从液相以上温度到低于固相温度的熔化关系。样品中的含水量将在亚固体运行中估计。