Oxygen Fugacities of Super Mantle Rocks from Thermobarometry

这个项目是用一种新校准的温压计方法来确定上地幔氧逸度的不均匀程度。这将包括用显微探针和穆斯堡尔方法测量尖晶石二辉橄榄岩中共存的橄榄石、斜方辉石和尖晶石的组成。尖晶石二辉橄榄岩包体已经并正在从大陆和海洋板块的许多不同的地质区和构造环境中收集--不列颠哥伦比亚省、日本、法国中部山丘、美国西南部、东澳大利亚和夏威夷。从大西洋和印度洋裂隙带挖出的深海橄榄岩将进一步覆盖大洋岩石圈，并有助于区分次大陆和次大洋地幔的氧逸度。对最近俯冲地区(日本、不列颠哥伦比亚省)的样品进行分析，将为地幔通过俯冲衍生流体的作用而被氧化的假设提供检验。对石榴石和石榴石-尖晶石二辉橄榄岩的初步穆斯堡尔测量表明，在尖晶石稳定场以上的压力下，石榴石含有大量的铁。通过确定共存的尖晶石和石榴石之间的Fe3-Al分配，温压法将扩展到石榴石领域。

This project is to determine the extent of heterogeniety in upper-mantle oxygen fugacity using a newly calibrated thermobarometric method. This will involve measuring the compositions of coexisting olivine, orthopyroxene and spinel from spinel lherzolites by microprobe and Mossbauer methods. Spinel lherzolite xenoliths have been, and are being, collected from a number of different geologic areas and tectonic environments in both continental and oceanic plates - British Columbia, Japan, Massif Central of France, Southwestern Us., Eastern Australia and Hawaii. Abyssal peridotites dredged from fracture zones in the Atlantic and Indian Oceans will provide further coverage of oceanic lithosphere and facilitate distinction between subcontinental and suboceanic mantle with respect to oxygen fugacity. Analysis of samples from areas of recent subduction (Japan, British Columbia) will provide tests of the hypothesis that the mantle is becoming oxidized through the agency of subduction-derived fluids. Preliminary Mossbauer measurements of garnet and garnet-spinel lherzolites indicate that, at pressures above the spinel stability field, garnet contains substantial amounts of ferric iron. The thermobarometric method will be extended to the garnet field by determining Fe3-Al partitioning between coexisting spinel and garnet.