Carbonate and silicate-carbonate injection complexes in collision systems: The West Baikal region as an example

Two types of carbonate and carbonate-silicate rocks: synmetamorphic marble melange and veined bodies in amphibolites, gabbroic rocks, and syenites are recognized in the Early Paleozoic Ol’khon collision system in the West Baikal region. The marble melange is characterized by the various size of the fragments of the mafic granulite, gneisses, metagabbros, and granites. It is suggested that the melange was injected into the silicate matrix as a result of a ductile flow. The calcite, dolomite, and carbonate-silicate rocks are characterized by their massive and fine-grained texture. They are often associated with coeval granite and dolerite dikes and occasionally reveal indications of carbonate-silicate mingling. It is suggested that carbonate and carbonate-silicate rocks were injected at late stages of the synmetamorphic tectogenesis. In isotopic composition, geochemistry, and mineralogy, these carbonate rocks differ from mantle carbonatites, and their origin is most likely related to the melting of carbonate rocks in the lower crust in the presence of aqueous fluid according to the model proposed by Lentz [29]. The shearing facilitated drainage of the lower crust and the upper mantle and made it possible to inject carbonate material to the upper level as a melt and a ductile mixture along with crustal granitic and mantle-derived basic melts. The injection carbonate rocks have been described from other metamorphic complexes, e.g., in the Caledonides of Norway and in the Himalayan collision system.