Home – Home – Jornals – Russian Geology and Geophysics 2003 number 5

We studied interstitial glasses and melt inclusions in minerals of peridotites from Pliocene basanites of the Vitim volcanic field, Dzhilinda River basin. The glasses can be divided into two groups: A and B. The glasses of group A resulted from deep-level partial melting of mantle, and those of group B are the interaction products of the host basanite melt and peridotites. The heated glasses of group A in xenolith minerals are compositionally similar to experimental and model partial (<10%) melts of peridotites obtained at 10 kbar. They contain (wt.%): SiO₂ = 51-56, TiO₂ = 0.5-0.6, Al₂O₃ = 12-16, Cr₂O₃ = 0-0.5, FeO = 2-4, MgO = 7-10, CaO = 6-12, Na₂O = 3-7, and K₂O < 1.5. Glasses from Ti-rich peridotites contain 1.9-3.5 wt.% TiO₂. Glasses of group B have similar contents of SiO₂, Al₂O₃, and Na₂O, high TiO₂ and K₂O contents, and low Mg-number. Interstitial glasses of this group are abnormally enriched in K₂O (up to 10 wt.%). Glasses in spinel harzburgite are SiO₂-richest (up to 71 wt.%); their alkali concentration decreases with increasing SiO₂ content. These data are consistent with the model for the reaction of xenolith orthopyroxene with basaltic (or hybride) melt, producing olivine and medium- and high-silica glass. The regular compositional variations of olivine microlites with high Mg-number (up to 94) and coexisting glass suggest that they are in equilibrium. The coefficients of Fe/Mg partition between them are 0.25-0.33.