ANGARA-VITIM GRANITOID BATHOLITH: new geochemical, U-Pb and Lu-Hf isotopic data, petrogenetic implications
A.A. Tsygankov, G.N. Burmakina
Dobretsov Geological Institute of Siberian Branch of Russian Academy of Sciences, Ulan-Ude, Russia
Keywords: Angara-Vtitm batholith, U-Pb isotopic age, Lu-Hf, sources of magma sources, geodynamics, Western Transbaikalia.
Abstract
The Late Paleozoic granitoid province of Transbaikalia (Angara-Vitim batholith, AVB, Russia), located in the northeastern part of the Central Asian Orogenic Belt (CAOB), covers an area of about 200,000 km2 and is composed of rocks ranging in composition from monzonites and quartz syenites to leucocratic granites. This work is aimed at: 1) determination of the total duration and dynamics of the formation of granitoids of the Angara-Vitim batholith; 2) finding the causes that determined the spatial and temporal heterogeneity of granitoids; 3) reconstruction of the sources of salic (granitoid) magmas, assessment of the contribution of mantle-crustal interaction processes to the petrogenesis of granitoids. The article is based on new petro-geochemical, isotopic (Lu-Hf) and isotopic-geochronological (U-Pb) data on the northern part of the AVB. Combined with the results of previous studies, it has been established that one of the largest granitoid provinces on Earth (AVB) was formed ~ 45 million years ago (from 320 to 275 million years). About 90% of the batholith rocks were formed during this time. Mainly crustal metagravaccian protoliths were the source of salic magmas. Formation of monzonitoids, quartz syenites, and granodiorites is associated with melting of mixed protoliths, in which the proportion of juvenile mafic material could reach 40-50%. The Late Paleozoic granitoid magmatism of Transbaikalia began with the actual introduction of calcareous-alkaline granites, granodiorites, and quartz syenites, which make up the bulk of the first stage of magmatism. At the second stage, magmatism was concentrated in a relatively narrow (200-250 km) permeable zone of the northeastern strike. This zone drained crustal foci of salic magmas and favored the entry of mafic mantle melts into the upper horizons of the Earth's crust. The granitoids of the Angara-Vitim batholith were formed at the post-collisional stage of the evolution of the eastern segment of the CAOB under the influence of mantle plume on the crust of the young orogen.
|
