Geochemistry of isotopes of carbon, oxygen, and rare-earth elements in metasediments of the Ol'khon metamorphic complex (Western Prebaikalia)

The isotopic compositions of carbon, oxygen, and strontium in marbles and q uartzites in various metamorphic zones of the Ol'khon metamorphic complex a nd the REE patterns of these rocks prove that the source rocks of the latte r formed in a shallow-sea environment under reducing conditions preventing a complete loss of organic relies. The variations in carbon isotope ratio i n graphites and calcites of marbles are related to isotope exchange between these minerals with increasing temperature of regional metamorphism. The c arbonate-free metasediments are most similar in isotopic composition of car bon to biogenic source rocks.