Hydrous Spinelloids and the Hydration State of the Mantle

SmythEAR-0229315氢气可能是地球上最不受约束的组成变量，但它对许多地质过程(如果不是大多数地质过程)具有控制作用。这是一项通过研究在含水过渡带及其附近可能出现的含水橄榄石、尖晶石和尖晶石相的稳定性、晶体化学和状态方程来提高对内部水化状态的理解的建议。我们将与巴伐利亚地质研究所(Bayerisches GeoInstitute)的同事合作，在对应于300至700公里深度的温度和压力下对含水橄榄岩成分进行合成实验。在科罗拉多大学，我们将通过单晶X射线衍射、电子探针和红外光谱对这些材料进行表征。我们将在科罗拉多大学的钻石顶压室(DAC)中使用单晶X射线衍射测量来测量在这些实验中观察到的含水橄榄石、尖晶石和尖晶石相的压缩系数(等温体弹性系数)和热膨胀。在一年的资助下，我们预计能够完成一系列含水环木、瓦兹利石和橄榄石的表征，并对其中几个样品进行高压压缩实验。由于体积模数与地震速度直接相关，如果这些相的可压缩性与无水修改有很大不同，则可能对过渡带矿物中实际存在的OH的量施加一些限制。此外，我们将继续开展布里渊光谱和GHz超声干涉测量弹性性能的合作研究，并将样品提供给其他小组。

SmythEAR-0229315Hydrogen is perhaps the most poorly constrained compositional variable in the Earth, yet it has a controlling effect on many if not most geologic processes. This is a proposal to improve the understanding of the hydration state of the interior by investigation of the stability, crystal chemistry and equation of state of hydrous olivine, spinel, and spinelloid phases that would occur in and near a hydrous Transition Zone. In collaboration with colleagues at the Bavarian Geological Institute (Bayerisches Geoinstitut), we will perform synthesis experiments on hydrous peridotite compositions at temperatures and pressures corresponding to depths of 300 to 700 km. At the University of Colorado, we will characterize these materials by single crystal X-ray diffraction, electron microprobe and IR spectroscopy. We will use single-crystal X-ray diffraction measurements in the diamond anvil cell (DAC) at the University of Colorado to measure compressibilities (isothermal bulk moduli) and thermal expansion of the hydrous olivine, spinel and spinelloid phases observed in these experiments. With a single year of funding, we expect to be able to complete characterization of a series of hydrous ringwoodites, wadsleyites and olivines and to perform high-pressure compression experiments on several of these samples. 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. In addition, we will continue our collaborative studies on measurement of elastic properties by Brillouin spectroscopy and GHz ultrasonic interferometry, and make samples available to other groups.