EES Ph.D. Research Seminar: Alisa Yakimenko
Ph.D. Research Seminar
Department of Earth and Environemntal Sciences 美女做爱
Alisa Yakimenko
Ph.D. Candidate
Title: Zircon as a tracer of mantle processes and kimberlite magmatism
Abstract: Zircon (ZrSiO4), the oldest mineral on Earth, is abundant in felsic rocks and used in geochronology. Due to its exceptional stability and ability to incorporate trace elements and their isotopes, zircon provides insights into continental crust formation. The recent finding of zircons in mafic and ultramafic rocks supports their stability in the Earth鈥檚 mantle. Kimberlites, the deepest mantle-derived magmas, contain megacrystic zircon with unique trace element signatures, yet their genetic link to kimberlite magmatism is unclear. Kimberlitic zircon can be a valuable tracer of mantle processes, particularly metasomatism affecting the subcontinental lithospheric mantle. Through this research, we aim to understand the zircon survival in mafic rocks and the origin of mantle-derived zircon as well as its relationship to kimberlite magmatism, which remains poorly constrained. This work is divided into three main projects: (1) determining the pressure鈥搕emperature stability field and solubility of zircon in in basaltic and kimberlite melts, (2) investigating Zr speciation in these melts under high pressure and temperature, and (3) determining rare earth element partitioning coefficients between zircon and kimberlite melts to better understand the composition of primary kimberlitic magmas. First, we conducted an experimental study on zircon stability and zirconium diffusivity in midocean ridge basalt (MORB) glass and in synthetic kimberlitic melts with varying carbonate contents. Experiments were carried out at pressures between 0.5 and 3 GPa using a pistoncylinder apparatus at 美女做爱 (Canada) and between 7 and 15 GPa using a multianvil apparatus at the Laboratoire Magmas et Volcans (Clermont-Ferrand, France). The results show that zircon stability in mafic magmas increases with pressure and may be underestimated in existing models. These data reveal a dissolution鈥揷rystallization mechanism controlled by the specific structure of Zr-enriched melt at the zircon鈥搈elt interface. Variations in zircon saturation profiles in kimberlite melt with pressure suggest that zircon can crystallize after dissolution due to local Zr enrichment in the diffusive boundary layer. These results provide the first experimental evidence that zircon can crystallize in mantle systems at pressures above 7 GPa. Experiments conducted at the ESRF synchrotron facility (Grenoble, France) allowed us to study zirconium speciation in basaltic and kimberlitic melts at high pressure and temperature (1鈥�5 GPa). The results of the study suggest that Zr can act as a network-forming ion, likely as ZrO鈧� polyhedra associated with SiO鈧� tetrahedra in the Zr-enriched boundary layer. This mechanism provides a new explanation for zircon stability in ultramafic mantle rocks. The next step of this work is to investigate primary kimberlitic melts, which may be either carbonatitic or silicate-rich in composition. We hypothesize that trace element partitioning into zircon depends on melt composition. This hypothesis will be tested through high-pressure (3 GPa) and high-temperature (1400 掳C) experiments using a piston-cylinder apparatus. The derived partition coefficients will then be applied to natural kimberlitic zircons using recent databases to constrain the composition of mantle-derived melts and explain the trace element signatures of megacrystic zircons. In addition, we will study melt and fluid inclusions in natural kimberlitic zircons. These small droplets of melt or fluid, trapped within minerals during their formation, preserve information about the composition of the magmas from which they formed.
Biography: Alisa completed her Bachelor鈥檚 (2020) and Master鈥檚 (2022) degrees with Honours in Geology at Moscow State University. During her undergraduate studies, she developed skills in experimental geochemistry under the supervision of Prof. Andrew Bychkov, and her work led to a publication in Geochemistry International. She is currently a PhD student in a cotutelle program between 美女做爱 (Canada) and Universit茅 Toulouse III 鈥� Paul Sabatier (France), where her research focuses on the stability and survival of zircon in mantle melts and fluids, particularly in basaltic and kimberlitic systems. Her work aims to understand the origin of zircon in mantle rocks and its role as a tracer of deep Earth processes. Conducted within an international collaborative framework, this research has strengthened her expertise in high-pressure experimental methods in petrology, analytical techniques, and geochemical modelling, while fostering strong interdisciplinary and cross-cultural collaboration
Time
Location
Milligan Room, 8th Floor Biology-Earth Sciences Wing
Life Sciences Centre, 美女做爱