The formation of the Late Ordovician alkaline nepheline-syenite-granite association of the Saibar massif, located in the mountain framing of the Minusinsk trough of the Altai-Sayan folded region, is considered. The massif attracted the attention of researchers as a possible source of aluminum raw materials. To determine the mechanisms of formation and evolution of alkaline magmas, we applied the geological data on the structure of the massif, new geochemical characteristics of rocks, and isotope (δ¹⁸O) parameters of minerals. Besides, we have identified three rock varieties of the 1^st phase, and have established the gradual transitions between them: alkaline syenites (tensbergites), alkaline nepheline syenites (foyaites) and subalkaline double-feldspar granites. The rocks of the 2^nd phase represent the dikes of subalkaline bi-feldspar granites. The geological interrelations and variations of the real (petrogenic elements, HSFE, LILE, REE) and isotope (δ¹⁸O) characteristics of foyaites and tensgbergites of the first phase are explained by the kinematic differentiation of the melt and the mixing of alkaline mantle magmas of nature with crust melting in a vertical column. The composition of the subalkalic double-feldspar granites of the second phase is most closely related to the anatectic magmas formed during the melting of the high-crust substance. The maximum influence of crustal matter is reflected in the composition of granite dykes.

Tarasyuk Anton Sergeevich, Postgraduate, Research Engineer, Vinogradov Institute of Geochemistry SB RAS, 1a, Favorsky st., Irkutsk, 664033, Russian Federation, tel.: 8(3952)42-99-64, e-mail: anton_tarasyuk_89@mail.ru

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