The Hercynian Ikat thrust in the Transbaikalian segment of the Central Asian Orogenic Belt

We present a comprehensive description of the blastomylonites of the Ikat thrust localized within the Ikat terrane in the East Transbaikalian branch of the Central Asian Orogenic Belt. The metamorphic rocks of the Garga block are thrust over the almost unmetamorphosed Cambrian deposits of the Ikat Formation. The geologic position of the thrust and the structure and mineral and petrochemical compositions of the blastomylonites in the suture zone are considered, and U-Pb dating of detrital zircon is carried out. The blastomylonites develop after the gneisses of the Garga block; the block protolith, admixed with felsic volcanic material, was no older than the Neoproterozoic (750–800 Ma). The 40Ar/39Ar age of the thrust is estimated at 282 ± 0.4 Ma based on metamorphic biotite from the blastomylonites. The thrust marks the transpression period during the Late Paleozoic processes of tectonometamorphic activity related to the subduction of the Mongol-Okhotsk oceanic crust beneath the Siberian continent.