Oxygen Fugacities of Super Mantle Rocks from Thermobarometry

本项目旨在利用一种新的标定热气压法确定上地幔氧逸度的非均质程度。这将包括用微探针法和穆斯堡尔法测量尖晶石橄榄石、正辉石和尖晶石共存的成分。尖晶石-辉橄榄岩捕虏体已经并且正在从许多不同的地质区域和大陆和海洋板块的构造环境中收集-不列颠哥伦比亚省，日本，法国中部地块，美国西南部。澳大利亚东部和夏威夷。从大西洋和印度洋断裂带挖出的深海橄榄岩将进一步覆盖海洋岩石圈，并有助于区分次大陆和海底地幔的氧逸度。对最近俯冲地区（日本、不列颠哥伦比亚省）样品的分析将为地幔通过俯冲产生的流体作用而被氧化的假设提供检验。对石榴石和石榴石尖晶石橄榄岩的初步穆斯堡尔测量表明，在高于尖晶石稳定场的压力下，石榴石含有大量的铁。通过测定共存尖晶石和石榴石之间的Fe3-Al分配，将热压法扩展到石榴石领域。

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.