CRUSTAL GROWTH IN THE GEOLOGIC EVOLUTION OF THE BAIDARIK BLOCK, CENTRAL MONGOLIA - EVIDENCE FROM SM-ND ISOTOPIC SYSTEMATICS

The Sm-Nd isotopic systematics of supracrustal sequences and intrusive granitoid complexes of the Baidarik block in the Bayan-Khongor zone o f Early Caledonides of Central Mongolia (Dzabkhan microcontinent of th e Central Asian foldbelt) were used to recognize the principal periods of crustal growth: no earlier than 1.7 Ga, Early Proterozoic (1.8-2.5 Ga), and Archean (2.9-3.3 Ga). The isotopic structure of the continen tal crust of the Baidarik block is characterized by a vertical heterog eneity: the modern erosion level exposes rocks of the Archean continen tal crust, which rest on analogous rocks of mainly Riphean and, probab ly, Early Proterozoic age.