Peridotit xenoliths: a key to understanding exceptional depletion and re-enrichment of the lithospheric mantle beneath Greenland

• Applicant: Dr. Axel Gerdes
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 274106255

The Earths different ancient continental cores (cratons) show significant differences in their composition and structure. However, all cratons archive encrypted information on early Earth dynamics and environments that can be decoded by applying a variety of geochemical tools to exposed crustal samples or to lithospheric mantle samples entrained during sporadic magmatism. The cratonic part of Greenland has been a hotspot of scientific investigation since it was discovered that it contains some of the oldest crust on Earth and that the underlying lithosphere has significant diamond potential. We have in hand a newly recovered suite of fresh kimberlite-entrained peridotite xenoliths that range in lithology from dunites to harzburgites and highly metasomatised wehrlites. Using a detailed petrographic and in situ analytical approach for the acquisition of major and trace elements, as well as multiple radiogenic isotope systematics (Sr, Sm-Nd, Lu-Hf, Re-Os) of mineral separates and in situ, we would like to address the following questions that are directly relevant to early terrestrial dynamics: (1) What is the origin of the exceptional depletion of the mantle lithosphere beneath cratonic Greenland and what was the role of vertical (plumes) vs horizontal (subduction) processes during its nascence? (2) Was the formation of the crust and lithospheric mantle in cratonic Greenland coupled or decoupled? (3) What are the nature and timing of re-enrichment of mantle lithosphere and its link to regional tectonothermal events, in particular the formation of low-volume melts, such as diamondiferous kimberlites?

• DFG Programme: Research Grants
• International Connection: South Africa
• Co-Investigator: Dr. Sonja Aulbach
• Cooperation Partner: Professor Dr. Sebastian Tappe