Oxidation state of the lithospheric mantle beneath Somerset Island, Rae Craton, Canada as a function of depth and its relation to metasomatism

• Applicant: Professor Dr. Alan Butler Woodland
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 393808454

The oxidation state of the Earths mantle, expressed as oxygen fugacity (fO2), is a fundamental parameter along with pressure and temperature that influences many geochemical and geophysical processes. For example, knowing how mantle fO2 varies both laterally and vertically is important for understanding global volatile cycles and the physical stability of mantle-crust domains, such as long-lived cratonic masses. Archean-age cratonic mantle is often observed to be stratified in terms of mineralogy and geochemical fertility, which reflects its compositional and tectonic evolution before, during and after cratonisation. Vertical variations in oxidation state can also be correlated with this stratification, although overprinting by metasomatic activity is often observed. In this way, oxidation through metasomatism can cause diamond to become locally unstable. Such variations have been well documented for the Slave craton (NW Canada), but no redox data are currently available for the neighboring Rae cratonic block that lies directly to the east and collided with the Slave 1.97 Ga ago. The aim of this study is to determine the oxidation state of the mantle lithosphere beneath the Rae craton, establishing a redox profile with depth. A suite of peridotite xenoliths from Somerset Island will be investigated. Fe3+/Fetot in garnet will be determined by Mössbauer spectroscopy and combined with major element analyses of garnet, olivine, orthopyroxene and clinopyroxene to compute fO2. Trace element concentrations of garnet and clinopyroxene will also be measured to check for possible metasomatic interactions. Results will be used to assess volatile speciation at depth and the potential for diamond stability/instability. In addition, results will be compared with published data for the neighboring Slave craton, to reveal differences in the evolution of the two cratonic blocks.

• DFG Programme: Research Grants
• International Connection: Canada
• Cooperation Partners: Bruce Kjarsgaard, Ph.D.; Professor David Graham Pearson, Ph.D.