Hydrous Spinelloids and the Hydration State of the Mantle

SmythEAR-0229315氢可能是地球上约束最差的成分变量，但它对许多（如果不是大多数）地质过程具有控制作用。该提案旨在通过研究水合过渡带内及其附近发生的水合橄榄石、尖晶石和尖晶石相的稳定性、晶体化学和状态方程来增进对内部水合状态的理解。 我们将与巴伐利亚地质研究所 (Bayerisches Geoinstitut) 的同事合作，在相当于 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、电子微探针和红外光谱来表征这些材料。 我们将在科罗拉多大学的金刚石砧室 (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水合橄榄石、尖晶石和尖晶石相的压缩率（等温体积模量）和热膨胀。通过一年的资金，我们预计能够完成一系列含水尖晶石、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。因为体积模量与地震速度直接相关，如果这些相的压缩性与无水变体有很大不同，则可能对过渡带矿物中实际存在的 OH 量施加一些限制。 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，并向其他小组提供样品。

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.