Mg-skarns enclosed in dunite cumulates of the Neo-Proterozoic
loko-Dovyren intrusion (northern Baikal region, Russia) can be traced to
silica-poor dolomitic host rock layers. The dominant minerals of the
skarns are brucite (pseudomorph after periclase), forsterite and Cr-poor
spinel. Rapid heating of quartz-poor dolomitic xenoliths led to the
formation of minor olivine, followed by the breakdown of dolomite to
calcite and periclase. Xenoliths were partially melted upon further
heating resulting in a calcite melt. This low-density melt was
quantitatively squeezed out, mixed with the surrounding mafic magma and
left behind periclase and olivine. This caused the crystallization of
new olivine with elevated CaO contents in zones above skarn-bearing
horizons. Mixing of calcite melt with the surrounding mafic magma also
resulted in the crystallization of Cats-rich clinopyroxene instead of
plagioclase. The mineralogy of contaminated dunite cumulates is
consistent with assimilation of approximately 4wt% CaO by the
loko-Dovyren mafic magma.