Hydrous Volatiles in Upper Mantle Minerals

地球上地幔中挥发性组分的浓度和化学形态在地质过程中起着重要作用。尽管它们很重要，但我们对它们在各种地球化学储层中的实际储存方式知之甚少。此前，红外光谱被用来确定不同数量的OG存在于辉石、石榴石和橄榄石中，这些辉石、石榴石和橄榄石以包体的形式带到地球表面，形成碱性岩浆。初步迹象表明，这些矿物的OH浓度与其形成环境有关，因此可能反映了环境中的水合挥发活性。PIS计划确定重要地幔矿物的实际OH含量，主要集中在南部非洲的次大陆地幔。他们将使用各种方法来校准IR方法。这将使他们能够以绝对值量化这些岩石中OH的矿物间分配的丰度，并可能提供D/H比。为了将观测到的样品的羟基含量与源的挥发活性联系起来，他们将在活塞筒装置中测量在压力、温度和挥发活性受控条件下合成的石榴石的羟基含量。这一结果有望对了解挥发分在上地幔中的分布以及它们在熔体产生和俯冲过程中的行为具有重要意义。

The concentration and chemical speciation of volatile components in the Earth's upper mantle play an important role in geologic processes. Despite their importance, we know little about their actual modes of storage in the various geochemical reservoirs. Previously, infrared spectroscopy was used to establise that variable quantities of OG occur in pyroxenes, garnet and olivine brought to the Earth's surface as xenoliths in alkalic magmas. Preliminary indications are that the OH concentration of these minerals is correlated with their environmmet of formation and may thus reflect ambient hydrous volatioe activity. The PIs plan to determine the actual OH content of important mantle minerals, concentrating on the subcontinental mantle of southern Africa. They will calibrate the IR method using a variety of methods. This will allow them to quantify in absolute terms the abundance of inter-mineral partitioning of OH in these rocks and perhaps to provide D/H ratios. In order to relate the observed OH contents of the samples to volatile activity of the sources, they will measure the OH contents of garnets grown synthetically under controlled conditions of pressure, temperature and volatile activity in a piston cylinder apparatus. The results are expected to have an important bearing on understanding how volatiles are distributed in the upper mantle as well as how they behave int eh processes of melt generation and subduction.