The Electrical Conductivity of Subducted Continental Crust

俯冲带是地壳和岩石圈循环进入地幔的区域。虽然洋壳在俯冲板块中占主导地位，但大陆壳也可以俯冲。据推测，俯冲的大陆地壳可以解释在深度大于~300 km的某些俯冲带观测到的高电导率。这种高导电性以前被归因于含水流体的释放。在这里，研究人员调查了另一种可能性：高导电性是由于lieberman - nite的存在。这种矿物在深俯冲板块中普遍存在的极端压力下变得稳定。它可能占俯冲大陆地壳的很大一部分。具有相似结构的材料通常表现出超离子导电性。这种类型的电导率——电荷载体是离子和固体中的空位——不需要流体的存在。在这里，科考队在地幔普遍存在的极端条件下进行实验。他们使用一种能够产生超过20000atm压力的设备。它们量化了温度、压力和矿物成分对电导率的影响。它们逐渐揭示了利伯曼岩是否可以解释在俯冲带观察到的高导电性。该项目的成果可能会在地球科学以外的材料科学领域得到应用。该奖项支持来自科学界代表性不足群体的首席研究员。它涉及高中生，特别是来自代表性不足的群体。它还促进了对公众的教育推广。在这里，研究小组测量了（K,Na）AlSi3O8 libermanite的电导率。他们研究了纯k端成员以及K-Na固溶体的电导率。他们在一个多砧高压-高温装置中使用了阻抗光谱技术。为了补充电导率测量，他们在相似的压力和温度条件下进行了K自扩散和Na-K相互扩散测量。这为从电导率测量推断的传导机制提供了进一步的见解。这些结果为计算利伯曼矿电导率作为压力、温度和成分在大范围地幔深度范围内的函数提供了基础。这项研究还改进了对大陆地壳电导率的估计。它确定了“干”大陆地壳是否可以解释深度大于300公里的高导电性区域。该团队还研究了利伯曼镍中电导率的晶体取向依赖性。目的是评估俯冲的大陆地壳是否具有显著的电性各向异性。利用这些数据，连同先前公布的其他矿物数据，计算了俯冲带大陆地壳的电导率。这为大地电磁测量识别俯冲大陆地壳提供了更好的依据。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Subduction zones are regions where crust and lithosphere are recycled into the Earth’s mantle. While oceanic crust dominates in subducting plates, continental crust can also be subducted. It has been inferred that subducted continental crust may explain the high electrical conductivity observed in some subduction zones at depth greater than ~300 km. This high conductivity has previously been attributed to the release of hydrous fluids. Here, the researchers investigate an alternative possibility: that the high conductivity is due to the presence of liebermannite. This mineral becomes stable at the extreme pressure prevailing in deep subducted plates. It may account for a significant fraction of subducted continental crust. Materials with similar structures often display superionic conductivity. This type of conductivity - where charge carriers are ions and vacancies in the solid - does not require the presence of fluids. Here, the team carries out experiments at the extreme conditions prevailing in the mantle. They use an apparatus capable of generating pressures in excess of 200,000 atm. They quantify the effect of temperature, pressure, and mineral composition on electrical conductivity. They gradually unveil whether liebermannite can explain the high conductivities observed in subduction zones. Outcomes of this project may find applications beyond Earth Sciences in Materials Science. The award supports a principal investigator from a group underrepresented in science. It involves high-school students notably from underrepresented groups. It also promotes educational outreach toward the public.Here, the team measures the electrical conductivity of (K,Na)AlSi3O8 libermannite. They investigate the conductivity of the pure K-endmember, as well as that of K-Na solid solutions. They use the impedance spectroscopy technique in a multi-anvil high-pressure-temperature device. To complement the conductivity measurements, they perform K self-diffusion and Na-K interdiffusion measurements at similar conditions of pressure and temperature. This provides further insight on the conduction mechanism inferred from the conductivity measurements. The results provide the basis for calculating liebermannite conductivity as a function of pressure, temperature, and composition over a wide range of mantle depths. The study also improves estimates of the electrical conductivity of continental crust. It establishes whether “dry” continental crust may explain regions of high conductivity at depths greater than 300 km. The team also investigate the crystal orientation dependence of the electrical conductivity in liebermannite. The goal is to evaluate whether subducted continental crust may have significant electrical anisotropy. The data are used, along with previously published data on other minerals, to calculate the electrical conductivity of continental crust in subduction zone. It provides an improved basis for the identification of subducted continental crust by magnetotelluric measurements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.