Oxidation State of the Lithospheric Mantle Beneath Komsomolskaya–Magnitnaya Kimberlite Pipe, Upper Muna Field, Siberian Craton

Anna Dymshits,Zhe Liu,Nester Korolev,Igor Sharygin,Igor Yakovlev,Vladimir Malkovets,Yi-Gang Xu,Taisia Alifirova

doi:10.3390/min10090740

Abstract

The oxidation state of the mantle plays an important role in many chemical and physical processes, including magma genesis, the speciation of volatiles, metasomatism and the evolution of the Earth’s atmosphere. We report the first data on the redox state of the subcontinental lithospheric mantle (SCLM) beneath the Komsomolskaya–Magnitnaya kimberlite pipe (KM), Upper Muna field, central Siberian craton. The oxygen fugacity of the KM peridotites ranges from −2.6 to 0.3 logarithmic units relative to the fayalite–magnetite–quartz buffer (∆logfO2 (FMQ)) at depths of 120–220 km. The enriched KM peridotites are more oxidized (−1.0–0.3 ∆logfO2 (FMQ)) than the depleted ones (from −1.4 to −2.6 ∆logfO2 (FMQ)). The oxygen fugacity of some enriched samples may reflect equilibrium with carbonate or carbonate-bearing melts at depths >170 km. A comparison of well-studied coeval Udachnaya and KM peridotites revealed similar redox conditions in the SCLM of the Siberian craton beneath these pipes. Nevertheless, Udachnaya peridotites show wider variations in oxygen fugacity (−4.95–0.23 ∆logfO2 (FMQ)). This indicates the presence of more reduced mantle domains in the Udachnaya SCLM. In turn, the established difference in the redox conditions is a good explanation for the lower amounts of resorbed diamonds in the Udachnaya pipe (12%) in comparison with the KM kimberlites (33%). The obtained results advocate a lateral heterogeneity in the oxidation state of the Siberian SCLM.

Highlights

The redox state of the mantle is essential for understanding processes occurring in the Earth’s interior
The second described approach is accepted in the present study, in order to be consistent with other works on mantle peridotites
We classified the kimberlite pipe (KM) samples according to the nomenclature proposed by Pearson and Brooks [48], i.e., clinopyroxene-free peridotite was defined as harzburgite or dunite (Table 1)

Summary

Introduction

The redox state of the mantle is essential for understanding processes occurring in the Earth’s interior. The fugacity of oxygen (f O2 ) is a thermodynamic variable that indicates chemical potential. Minerals 2020, 10, 740 of the oxygen in reactions where both reagents and products contain the same element (s), but with different valence states. The oxygen fugacity affects the relative abundances of Fe3+ and Fe3+ in minerals, and the stability of carbon which can exist in reduced

Methods

Results

Conclusion