GEOCHRONOLOGY AND GEODYNAMIC SETTING OF THE ANGARA-VITIM BATHOLITH

Geochronological data are reported on the southwestern portion of the world's largest batholith-Angara-Vitim-whose age was traditionally con sidered Precambrian or Early Paleozoic. U-Pb data were obtained on the granitic rocks of the Barguzin Complex, which dominate in the batholi th, and rocks of the Zaza Complex, which are exposed within the study area but whose age is thought to be Middle Paleozoic. The U-Pb zircon age of the Barguzin Complex was estimated at 289.2 +/- 1 and 291.7 +/- 1 Ma, and analogous values on the Zaza Complex are 286 +/- 1.1 and 30 3.4 +/- 7.3 Ma. Analysis of our and preexisting data on the U-Pb and R b-Sr age of large plutons within the Angara-Vitim batholith indicates that granitoids of the Barguzin Complex and analogous locks of the you nger Zaza, Konkudera-Mamakan, Vitimkan, and Chivyrkui complexes were e mplaced in the batholith during Late Carboniferous time, mainly over t he time interval from 290 to 320 Ma. The complexes are considered intr insic components of the batholith. Correlations between regional proce sses of granite magmatism and other regional magmatic events testify t hat the batholith developed simultaneously with alkaline magmatic acti vity. The latter processes resulted in either autonomous massifs of al kaline rocks, which are affiliated with the Saizhen and Synnyr complex es, or synplutonic intrusions of alkaline mafic rocks, Proceeding from these data and considerations, we suggest that the Angara-Vitim batho lith resulted from the involvement of its host crustal segment into a zone of influence of a mantle plume and the subsequent crustal anatexi s.