Ion Probe Studies of Mantle-Melting Run Products

该提案要求提供资金，以支持对现有的10千巴地幔熔融产物进行离子探针研究，P.I. 2001年秋天，他打算在伍兹霍尔海洋研究所休假期间继续研究。 这些运行产品代表了P.I.还有两个博士毕业生对10种橄榄岩起始材料进行了研究，每种材料都是通过以不同的模式重组手选和酸洗矿物分离物而构建的。其中五个利用矿物从肥沃的二辉橄榄岩捕虏体从基尔本洞，而其他五个利用矿物从一个组成中间二辉橄榄岩样品从山。努拉特，S.E.澳大利亚总共有54种含玻璃和橄榄石的产品，36种含cpx，41种含opx，47种含尖晶石。 计算的熔体分数范围为1-48 wt.所有实验都采用金刚石聚集体技术的变化（例如，Hirose和Kushiro，1993; Baker和Stolper，1994），其中用一层直径为70-100微米的玻璃态碳球代替粉末金刚石，以提供一种熔体槽，在该熔体槽中一些熔体可以与残留晶体隔离，从而防止在实验终止时其淬火改性。主要元素矿物和玻璃数据的所有起始材料的变化在一个系统的和敏感的方式与温度的增加，这一点，结合运行持续时间2-10天，支持一个接近平衡的实验中提出的工作的主要目标将是测量之间的分配系数熔体和cpx和opx的REE，Ti，V，Cr，Sr，Y，Sr（Be、B、Rb、Nb和Ba也将尝试，但在辉石中可能太低），并分析这些标称无水运行产物的水含量。据我所知，这将是第一个这样的数据密切相关的地幔熔融来自实验的橄榄岩，而不是玄武岩，散装组成。玄武岩系统的早期工作揭示了复杂的辉石/熔体Ds的成分依赖关系，表明使用单值Ds的建模研究是不合适的。我们的主要元素数据极大地扩展了实验所涵盖的组成空间，并将允许扩展和更好地定义这些依赖关系，从而改进预测模型。我们还拥有17种含cpx的运行产品，其熔体含量低于5%，其中一些熔体的Na 2 O和SiO2含量较高（Baker等人）。（1995）首次指出了近固相线地幔熔体的特征。考虑到大洋中脊环境中部分熔融的可能重要性，确定这些“外来”熔体和地幔辉石之间关键微量元素的分配行为将是至关重要的

JohnstonEAR-0105500This proposal requests funds to support an ion probe study of existing 10 kbar mantle-melting run products which the P.I. proposes to pursue while at Woods Hole Oceanographic Institution during his sabbatical in Fall, 2001. These run products represent 5+ years of NSF-funded work by the P.I. and two recent Ph.D. graduates. Ten peridotitic starting materials, each constructed by recombining hand-picked and acid-washed mineral separates in differing modes, were investigated. Five of these utilized minerals from a fertile lherzolite xenolith from Kilbourne Hole while the other five utilized minerals from a compositionally intermediate lherzolite sample from Mt. Noorat, S.E. Australia. In all, 54 glass- and olivine-bearing run products are available, 36 with cpx, 41 with opx, and 47 with spinel. Calculated melt fractions range from 1-48 wt. %; 22 contain less than 5 wt% melt.All experiments employed a variation of the diamond aggregate technique (e.g., Hirose and Kushiro, 1993; Baker and Stolper, 1994) in which a layer of 70-100 micron diameter vitreous carbon spheres was substituted in lieu of powdered diamond, to provide a melt sink in which some melt could be isolated from the residual crystals, thereby preventing its quench modification upon termination of the experiments. Major element mineral and glass data for all starting materials vary in a systematic and sensible manner with increasing temperature and this, combined with run durations of 2-10 days, supports a close approach to equilibrium in the experiments.The primary goals of the proposed work will be to measure the distribution coefficients between melt and cpx and opx for REE, Ti, V, Cr, Sr, Y, and Sr (Be, B, Rb, Nb, and Ba will also be attempted but will probably be too low in the pyroxenes), and to analyze the water contents of these nominally anhydrous run products. To my knowledge, these will be the first such data germane to mantle melting derived from experiments on peridotitic, as opposed to basaltic, bulk compositions. Earlier work in basaltic systems has revealed complex compositional dependencies of pyroxene/melt Ds demonstrating that the use of single-valued Ds in modeling studies is inappropriate. Our major element data greatly expand the composition space covered by experiment and will allow extension and better definition of these dependencies, thus improving predictive models. We also have 17 cpx-bearing run products with less than 5% melt and some of these melts have the elevated Na2O and SiO2 contents that Baker et. al. (1995) first noted characterize very near-solidus mantle melts. Given the likely importance of fractional melting in the mid-ocean ridge environment, determination of the partitioning behavior of key trace elements between these "exotic" melts and mantle pyroxenes will be critical