Program > Browse abstracts by speaker > Kovalskii Georgii

Silicate melts drive Earth's thermal and material evolution, influencing chemical differentiation, planetary cooling, and ore formation. Understanding melt formation in the lower mantle is crucial but remains inaccessible to direct observation (Elkins-Tanton, 2012).

This study examines the structural evolution of trace elements (Sr, Y) in silicate glasses and melts under extreme conditions using laser-heated diamond anvil cell experiments and X-ray absorption spectroscopy. High-resolution spectra were collected for synthesized glasses: AbDi-glass (16 wt% SrO, 5000 ppm Y₂O₃) (Krstulović M et al., 2021) and AnDi-glass (5 wt% SrO, 5 wt% Y₂O₃). Cold-compression spectra were obtained up to 117.5 GPa (Sr) and 130 GPa (Y), while laser-heated spectra for Sr in AbDi melts and glasses reached 24 GPa.

XAFS analysis (Winterer, 1997) revealed pressure-induced shortening of RSr–O and RY–O distances. In AbDi glass, RSr–O decreased from 2.62 Å (0 GPa) to 2.32 Å (117.5 GPa); in AnDi glass, from 2.60 Å (2 GPa) to 2.36 Å (59 GPa), following RCa–O trends in molten basalt from MD simulations (Sr analogue) (Karki et al., 2018). RY–O in AbDi glass decreased from 2.24 Å (1.7 GPa) to 2.16 Å (117.5 GPa) and in AnDi glass from 2.30 Å (2 GPa) to 2.10 Å (130 GPa). Constant RSr–O below 6 GPa and RY–O below 20 GPa suggest coordination changes, supported by XANES pre-edge variations. Sr-O pair distributions in AbDi melts show configurational disorder, while stable heating above 24 GPa proved difficult.

The results reveal a pressure-driven densification mechanism with reduced cation-oxygen distances and increased coordination numbers, affecting melt viscosity and diffusivity. These findings refine mantle dynamics and geochemical models, highlighting high-pressure spectroscopy's role in linking mineralogy to planetary processes.