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

Abstract

The Fe 3+ 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 Fe 3+ fractions were used to calculate oxygen fugacity. The calculated ƒ O 2-T-P conditions are consistent with derivation of the lherzolite samples from a relatively oxidized source region dominated by CO 2 and/or H 2O fluid species. Calculated ƒ O 2 's range from 0.5 above to 1.1 log-units below the fayalite-magnetite-quartz (FMQ) buffer. Estimated Fe 3+ 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 Δƒ O 2 . The average Δƒ O 2 (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).