Alekseev, et al., report that the research history of allanite(Y) has been considered in this paper. The composition and genesis of this mineral is discussed with allowance for new findings in Li–F granites of the Russian Far East. Compositional anomalies in allanite(Y) reflect the metastable character of its structure. Types of zoning and trends in the chemical substitution of major components are described. Two crystal chemical modes of allanite(Y) formation and the two-step isomorphism of its components are suggested. The main tendencies in the chemical evolution of allanite(Ce) and allanite(Y) in granitic rocks of the Far East are pointed out. Allanite(Y) is formed in the anomalous geochemical setting that characterizes crystallization of fluid-saturated subalkaline granitic melt and is regarded as an index mineral of raremetal ongonite magmatism completing the Late Cretaceous Pacific Orogeny.
The authors concluded that:
1) The research history of allanite(Y) shows that this mineral is not abundant because its formation requires special geochemical conditions. Allanite(Y) is characterized by anomalous and steadily nonstoichiometric chemical composition. The enrichment in Y, HREE, and Fe2+ and depletion in Ca, Fe3+, Al, and Th are typical, as well as a yttrium-type chondrite normalized REE pattern with Dy and Nd anomalies.
2) The structure of allanite(Y) is metastable due to metamictization and the complex twostep isomorphism of HREE, Y, Ca, and Fe, which leads to formation of structural defects. Allanite(Y) was formed in two ways: allanite(Ce) → allanite(Y) and anomalous allanite(Y) → allanite(Y).
(3) The evolution of allanite composition reflects the geochemical evolution of the granitic series of the Far East, from highAl allanite(Ce) in early biotite granite to ferroan allanite(Y) in raremetal zinnwaldite granite. Allanite(Y) is formed in the anomalous geochemical setting inherent to crystallization of fluid-saturated subalkaline granitic melt and serves as a guide of rare-metal ongonitic magmatism completing the Late Cretaceous Pacific Orogeny
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