THE ANGARA–VITIM GRANITOID BATHOLITH: NEW GEOCHEMICAL, U–Pb AND Lu–Hf ISOTOPE DATA ON ZIRCON AND PETROGENETIC CONSEQUENCES

The late Paleozoic granitoid province of Transbaikalia (Angara–Vitim batholith (AVB), Russia), located in the northeast of the Central Asian Orogenic Belt (CAOB), occupies an area of about 200,000 km2. It is composed of rocks varying in composition from monzonites and quartz syenites to leucocratic granites. This research work is aimed at: 1) determination of the total duration and dynamics of formation of the Angara–Vitim batholith granitoids; 2) clarification of the reasons that determined the spatiotemporal heterogeneity of granitoids; 3) reconstruction of the sources of salic (granitoid) magmas and assessment of the contribution of mantle–crust interaction to the petrogenesis of granitoids. The paper is based on new petrogeochemical, isotope (Lu–Hf), and isotope-geochronological (U–Pb) data on the northern part of the AVB. Combined with the results of previous studies, it has been established that the AVB, one of the Earth’s largest granitoid provinces, formed over about 45 million years (from 320 to 275 Ma). During this time, about 90% of the batholith rocks formed. Crustal metagraywacke protoliths were the main source of salic magmas. The formation of monzonitoids, quartz syenites, and granodiorites is associated with the melting of mixed protoliths, in which the proportion of juvenile mafic material could reach 40–50%. The late Paleozoic granitoid magmatism in Transbaikalia began with the areal intrusion of calc-alkaline granites, granodiorites, and quartz syenites, which were predominant at the first stage of magmatism. At the second stage, magmatism took place in a narrow (200–250 km) permeable zone of NE strike. This zone drained crustal chambers of salic magmas and favored the penetration of mafic mantle melts into the upper crustal horizons. The AVB granitoids formed at the postcollisional stage of evolution of the eastern segment of the CAOB under the impact of mantle plume on the crust of the young orogen.