Boron Isotope Variation During Subduction, Melting, and Ascent of Arc Magmas

9973040 hervigo将进行实验，以确定在俯冲带条件下硼同位素的行为。这些实验旨在测量a)基性硅酸盐熔体与含水流体和b)白云母与含水流体之间的硼同位素分馏，并测量熔体中硼同位素的自扩散系数。这些实验将允许对俯冲岩石、流体改变的地幔楔物质和弧岩浆本身进行硼同位素分析，以考虑在俯冲和喷发物质脱挥发过程中可能发生的同位素分馏。结合自然样品的分析，可以验证以下假设：1)脱挥发是质量传递到上覆地幔楔的主要机制；2)岩浆在上升过程中的脱气不改变熔体的硼同位素比值，因此原始和演化的熔体包裹体的硼同位素组成同样指示了源区。实验分析将使用次级离子质谱仪（SIMS，或离子微探针）进行，非常适合进行精确的硼同位素微分析。在实验背景下描述俯冲和喷发岩石的硼同位素组成，表明这些矿物和熔体中的硼同位素比率如何变化，将增加我们对俯冲带发生的过程和发生在会聚板块边缘的壳幔再循环机制的理解。

9973040HervigExperiments to determine the behavior of boron isotopes under conditions occurring in subduction zones will be performed. These experiments are designed to measure boron isotope fractionation between a) mafic silicate melts and hydrous fluid and b) muscovite and hydrous fluid and to measure self-diffusion coefficients for boron isotopes in melts. The experiments will allow boron isotope analyses of subducted rocks, mantle wedge materials altered by fluids, and the arc magmas themselves to be considered in the context of isotopic fractionation that may be occurring during the devolatilization of subducted and erupted materials. When combined with analyses of natural samples the following hypotheses can be tested: 1) devolatilization is the dominant mechanism for mass transfer into the overlying mantle wedge, 2) degassing of magmas during ascent does not alter the boron isotope ratio of melts and thus boron isotopic composition of primitive and evolved melt inclusions are equally indicative of the source region. The analyses of the experiments will be obtained using the secondary ion mass spectrometer (SIMS, or ion microprobe) ideally suited to obtain precise boron isotopic microanalyses. Characterizing the boron isotopic composition of subducted and erupted rocks in the context of experiments showing how boron isotope ratios in these minerals and melts change will increase our understanding of the processes occurring in subduction zones and the crust-mantle recycling mechanisms that occur at convergent plate margins.