Hydrous Spinelloids and the Hydration State of the Mantle

这是一项研究可能发生在地幔过渡带（410- 670 km深度）的含水尖晶石和类尖晶石相的稳定性、晶体化学和状态方程的提议。研究人员将与巴伐利亚地质研究所（Bayerisches Geoinstitut）的同事合作，进行合成实验，以确定尖晶石V是否可能存在于地幔成分中，并更好地完善尖晶石IV（wadsleyite II）的压力-温度-成分场。在含水体系中的初步实验已经产生了足够尺寸的晶体用于单晶衍射方法，因此运行产品将通过这种方法进行分析。他们将在金刚石压砧单元（DAC）中使用单晶X射线衍射测量来测量这些实验中观察到的含水尖晶石的压缩模量（等温体积模量）和热膨胀。由于体积模量与地震速度直接相关，如果这些相的压缩系数与无水变形有很大不同，则可能对过渡带矿物中实际存在的OH量施加一些限制。还将通过各种光谱和超声波方法提供样品供合作研究之用。

Smyth EAR-0087279 This is a proposal to investigate the stability, crystal chemistry and equation of state of hydrous spinel and spinelloid phases that could occur in the Transition Zone of the mantle (410-670km depth). In collaboration with colleagues at the Bavarian Geological Institute (Bayerisches Geoinstitut), the investigators will perform synthesis experiments to see if spinelloid V may exist in mantle compositions and to better refine the pressure-temperature-composition field of spinelloid IV (wadsleyite II). Preliminary experiments in hydrous systems have produced crystals of sufficient size for single-crystal diffraction methods, so run products will be analyzed by this method. They will use single-crystal X-ray diffraction measurements in the diamond anvil cell (DAC) to measure compressibilities (isothermal bulk moduli) and thermal expansion of the hydrous spinelloid observed in these experiments. Because the bulk modulus is directly related to seismic velocity, if the compressibilities of these phases differ greatly from the anhydrous modifications, it may be possible to place some constraint on the amount of OH actually present in the minerals of the Transition Zone. Samples will also be made available for collaborative studies by various spectroscopic and ultrasonic methods.