Water partitioning between coexisting olivine (ol) and wadsleyite (wads) and the effect of the OH-defect concentrations on the P-T-x coordinates of the ol-wads phase transformation

在地幔410公里深处的地震不连续被认为是由橄榄石（ol）向瓦德斯莱石（wads）的转变引起的（例如Dziewonski和Anderson， 1981）。最近的地震观测表明，不连续性不像实验中观察到的那样尖锐（例如Zhang和Herzberg， 1994），但显示出从约4公里（例如Benz和Vidale， 1993）到35公里（van der Meijde et al., 2003）的广泛厚度范围。van der Meijde et al.（2003）基于理论研究（Wood, 1995; Helffrich and Wood, 1996）将观测到的410 km不连续面加宽解释为共存的地幔矿物ol和wads中掺入了水。如果这是真的，不同厚度的不连续表明水在上地幔的变化和不均匀分布。然而，到目前为止，地幔矿物ol和wads中掺入的水如何影响矿物之间的相界还没有得到实验的肯定（Smyth and Frost, 2002; Chen et al., 2002）。为了充分了解地球的水循环及其对地球结构的影响，需要更多的实验数据。该项目的目标是通过实验确定(i)在地幔条件下共存的橄榄石和wadsleyite的含水饱和度，以及（ii）在淬火多砧实验中水对ol-wads相变的P-T-x坐标的影响，以及在激光加热金刚石砧实验中原位的影响。在这些研究的基础上，第二个申请期的未来项目将处理（iii）水对ol-wads相变机制和动力学的影响。

The seismic discontinuity at 410 km depth within the Earth¿s mantle is believed to be caused by the transformation of olivine (ol) to wadsleyite (wads) (e.g. Dziewonski and Anderson, 1981). Recent seismic observations indicate that the discontinuity is not as sharp as observed in experiments (e.g. Zhang and Herzberg, 1994) but shows a wide range of thicknesses from about 4 km (e.g. Benz and Vidale, 1993).) to 35 km (van der Meijde et al. (2003). Based on theoretical studies (Wood, 1995; Helffrich and Wood, 1996) van der Meijde et al. (2003) interpret the observed broadening of the 410 km discontinuity as being caused by water incorporation in the coexisting mantle minerals ol and wads. If this is true, varying thicknesses of the discontinuity indicate variable and inhomogenous distribution of water in the upper mantle. However, up to now it has not been confirmed unquestioningly by experiments how water incorporation into the mantle minerals ol and wads influence the phase boundaries between the minerals (Smyth and Frost, 2002; Chen et al., 2002). To fully understand the water cylcle of the Earth and its effect on the Earth¿s structure more experimental data are needed. The goals of this project are to experimentally determine (i) the water saturation of coexisting olivine and wadsleyite under mantle conditions, and (ii) the effect of water on the P-T-x coordinates of the ol-wads phase transition in quenched multi-anvil experiments as well as in-situ in laser heated diamond anvil experiments. On the base of these studies a future project in the second application period will deal with (iii) the influence of water on the mechanisms and kinetics of the ol-wads phase transition.