Experimental Petrology of Garnet Lherzolite Melting

该程序使用八面体多锤装置研究了标称为无水的石榴石橄榄岩在3到5.5 Gpa之间的熔融。实验的目标是确定1)P-T空间中的高压凝固，2)近固相线熔体和晶体的组成，3)熔化反应的细节，以及4)确定熔体生产率所需的温度和熔体分数之间的函数关系。我们正在对一系列石榴石二辉橄榄岩成分进行实验，这些成分的单斜辉石比例不同。这些成分将典型的MORB地幔中橄榄岩熔融的观测基础扩展到可能的地幔类似物。这些实验使用微交换技术来表征低于0.1的熔体分数的组成，以及在较高的熔体分数时采用更经典的方法。我们实验室在3 Gpa以上进行的详尽的P-T校准工作确保了多顶锤装置的重复性和样品环境的可控性，类似于在较低压力下通常在活塞-圆筒装置中实现的水平。本研究获得的高压基本相平衡数据将有助于建立有限的石榴石橄榄岩熔融实验数据库。这些数据对于定量模拟大洋扩张脊、大洋岩石圈和大陆之下地幔上涌形成的橄榄岩熔融是必不可少的。

LesherEAR-0001245This program investigates melting of nominally anhydrous garnet peridotite between 3 and 5.5 GPa using the octahedral multianvil apparatus. The goals of the experiments are determination of 1) high pressure solidii in P-T space, 2) the compositions of near-solidus melts and crystals, 3) the specifics of the melting reaction, and 4) the functional relationships between temperature and melt fraction required to determine melt productivity. We are performing experiments on a range of garnet lherzolite compositions that differ in the proportion of clinopyroxene. These compositions extend the observational basis for peridotite melting of typical MORB mantle to possible analogs for plume mantle. The experiemts employ micro-exchange techniques to characterize the compositions of melt fractions below 0.1, and more classical approaches at higher melt fractions. Exhaustive P-T calibration work in our laboratory above 3 GPa ensures a level of reproducibility and control of sample environment in the multianvil apparatus similar to that routinely achieved in the piston-cylinder apparatus at lower pressures. The fundamental phase equilibrium data at high pressures obtained in this study will contribution to the very limited experimental database for garnet peridotite melting. Such data are essential for quantitative modeling of melting of peridotite by mantle upwelling beneath ocean spreading ridges, oceanic lithosphere, and continents.