Oxidation state of the upper mantle beneath the northwestern part of the Arabian lithosphere

The Fe³⁺ contents of spinels from upper mantle lherzolite xenoliths occurring in the Pleistocene alkali basalts of northeast Jordan have been determined using ⁵⁷Fe Mössbauer spectroscopy at room temperature. The determined Fe³⁺ fractions were used to calculate oxygen fugacity. The calculated f{hook}_O2-T-P conditions are consistent with derivation of the lherzolite samples from a relatively oxidized source region dominated by CO₂ and/or H₂O fluid species. Calculated f{hook}_O2's range from 0.5 above to 1.1 log-units below the fayalite-magnetite-quartz (FMQ) buffer. Estimated Fe³⁺ Fe_total-ratios from microprobe analyses are 2-7% more than those determined from Mössbauer spectroscopy and can shift the computed oxygen fugacity by 0.1 to 0.6 log-units. Pressure and/or temperature does not contribute significantly in the calculated Δf{hook}_O2. The average Δf{hook}_O2 (relative to FMQ) is -0.29 ± 0.4 log-units. This is higher than that reported for western Europe (-0.89 ± 0.58), British Columbia (-1.05 ± 0.3), and eastern Australia (-1.78 ± 0.66).