GEOCHEMICAL AND PETROLOGICAL FEATURES OF THE ALKALINE GRANITES OF THE UKRAINIAN SHIELD

Abstract

Alkaline granites in the Ukrainian Shield are not widespread and are only revealed in two areas. To first one belong the alkaline (with aegirine and ribekite) varieties among Proterozoic biotite-alkalic feldspathic Perga granites. Second area is Azov megablock where are found hypabyssal bodies of Devonian grorudites. Grorudites are of more melanocratic composition and have higher agpaitic index while low magnesity is the typical features for both types of alkaline granites. Perga alkaline granites and grorudites have different geochemical peculiarities. Grorudites have increased content of Ti, V, Cr, Ni, while Perga granites are enriched in Sn, Mo, Be, Rb, U. Like to alkaline granites over world alkaline granites of the Ukrainian Shield are, on the one hand enriched in HFSE and REE and, on the other hand – depleted in Sr and Ba. Chondrite normalized REE patterns from Perga granites have deep negative Eu-anomalus and enriched in HREE in comparison to grorudites. Geochemical peculiarities indicate that Perga granites are genetically related to granitic magmas of Korosten pluton and their formation have been attended by intensive feldspar fractionation. At the same time generation of grorudites are connected with subalkaline and alkaline basaltic melts differentiation during of the Dnieper-Donetsk depression formation.