Mp. Mazurov et At. Titov, Magnesian skarns from the sites of layer-by-layer injections of basic magma into the evaporites of the platform's sedimentary cover, GEOL GEOFIZ, 40(1), 1999, pp. 82-89
Contact-reaction magnesian skarns formed at the magmatic and postmagmatic s
tages have been found, in addition to the earlier revealed autoreaction ska
rns, in the Angara-Ilim volcanotectonic structures in the intracontinental
paleorift zones of the Siberian Platform. The spinel-forsterite magnesian s
karns of the magmatic stage are confined to the overdome parts of doleritic
bodies and are the result of the interaction of massive dolomites with flu
ids released from liquid magma. The magnesian skarns of the postmagmatic st
age are localized in the marginal parts and on the front (outwedging) of do
leritic sills, apophyses, and the branches of intrusive bodies in a carbona
te-evaporite series. The skarns resemble gravel conglomerates with carbonat
e cement and have a banded structure. It has been established that the foun
d fragments are globules of disintegrated doleritic porphyrites, completely
or partially substituted by zonal magnesian skarns. The cryptocrystalline
mesostasis and phenocrysts of olivine, plagioclase, and pyroxene had underg
one dispersion and substitution. The unaltered core is in contact with a fa
ssaite zone, which passes first Into a spinel-fassaite zone and then into a
forsterite-magnetite zone and calciphyre. In paleoisland-arc and margin-co
ntinental regions, these skarns have no analogs in texture-structural pecul
iarities and the mechanism of deposit formation. Their origin was caused by
the speciality of intrusion and solidification of basic magma in chemicall
y active carbonate-evaporite series.