Zircon as a tracer of mantle processes and kimberlite magmatism: an experimental study

Zircon (ZrSiO4), the oldest mineral found on Earth with some specimens dating > 3.5 Ga, preserves a unique record of geological processes through time. It hosts a plethora of geochemical tracers that record the sources, conditions and chronology of processes occurring at depth. These records are preserved upon the mineral transfer to the Earth's surface and exposure to weathering due to the extreme chemical and mechanical stability and very high closure temperatures of zircon. Zircon is a ubiquitous accessory mineral in silica-rich continental rocks, which has long been used as a tracer of processes in the continental crust. However, a growing number of findings of ZrSiO4 and ZrO2 in (ultra)-mafic rocks provides strong evidence for stability of zircon in mantle settings. It remains unclear whether zircon crystallization directly in the mantle is possible. Zircons found in kimberlites, the deepest mantle magmas that reach the Earth's surface and host major economic diamond deposits, are used for dating and provide probes into the processes in the asthenosphere and subcontinental lithospheric mantle. However, the origin and crystallization conditions of zircon in kimberlites are poorly understood. The proposed experimental study will test if the formation of zircon is not limited to silicic crustal systems but can happen in the mantle. The project will provide a breakthrough advance by constraining the origin, conditions and compositions of mantle melts/fluids parental to zircon, the mechanisms and physical-chemical conditions of its origin and geochemical sources. These data will help in building novel geodynamic models linking the planet interior with the surface. The project aims to better understand the origin of zircon in kimberlites, and, using the concentrations of trace elements in kimberlitic zircon, examine the composition of parental kimberlite melts. This new collaboration brings together expertise of Canadian and France teams to address important questions of evolution of continental roots, subcontinental mantle, origin of enigmatic kimberlite magmas, and processes of metasomatic enrichments of continental roots in rare elements critical for modern technologies.