ИСТИНА

The rates of magmatic processes preceding eruption are not well understood yet. Oscillating zoning of Mg-Fe-Ni-Ca-Cr-Al-P in high-Mg olivine crystals from 7600 BP tuff ring of Shiveluch volcano, Kamchatka, enables reconstruction of the entire olivine crystallization history with characteristic times from mantle conditions to eruption. Bell-shaped Fo86–92 and Ni profiles in crystal cores were formed by diffusion after mixing with evolved magma. Diffusion proceeded to the centres of crystals and completely equilibrated Fo and Ni in some crystals. Diffusion times extracted from Fo and Ni core profiles range from 100 to 2000 days. During subsequent mixing with mafic mantle-equilibrated melt, the cores were partially dissolved and overgrown by Fo90 olivine. Times extracted from Fo and Ni diffusion profiles across the resorption interface between the core and its overgrowth range within 1–10 days, which corresponds to the time of magma ascent to the surface. The overgrowth shows identical smooth Fo-Ni decreasing zoning patterns for all crystals towards the margin, indicating that all crystals shared the same growth history after last mixing event prior to eruption. At the same time, Ca, and to an even greater extent Cr, Al, and P have oscillatory growth patterns in the crystals overgrowth. Our research shows that processes in mafic magmas that ascend from mantle source to surface during maar/tuff ring eruption may be quite complex and time of ascent from Moho depths can be very fast – just a few days. This research was supported by grants DFG Wo 362/51-1 and RFBR 16-55-12040.