Abstract
Eastern Transbaikalia is a unique rare-metal province of Russia. Most of the studied deposits are associated with granitoid intrusions. Despite the high degree of knowledge of regional magmatism, a number of questions remain related to both the belonging of specific massifs to magmatic complexes and the correlation of certain complexes within various structural-formation zones. This paper compares the material composition and age of several petrotypical and parapetrotypical massifs classified as Late Mesozoic complexes distributed within the Aginskaya, Prishilkinskaya, and Argunskaya structural-formational zones of Eastern Transbaikalia. Based on the results of U-Pb dating, two stages of granitoid magmatism have been established: 1) the end of the Middle – the beginning of the Late Jurassic (163–156 million years ago) and 2) the beginning of the Early Cretaceous (142 million years ago). It is shown that the closely aged rocks of the Borshchovochny, Amudzhikano-Sretensky and Shakhtama complexes have similar material characteristics, while the rocks of the Kukulbey complex (from three massifs) vary in composition. Elevated δ18O values (from +10.8‰ to +11.9 ‰) for the rocks of the Jurassic complexes indicate their formation mainly due to the melting of crustal material, and lower δ18O values (from +9.8 ‰ up to +10.3‰) for the Early Cretaceous granitoids suggest the contribution of a mantle source to their genesis.
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