stripes
The Oktyabr'skii massif, formerly called the Mariupol or Azov Sea coastal massif, is one of the best explored alkaline massifs of the Ukrainian shield (Morozewicz, 1930; Ainberg, 1933; Tsarovsky, 1954; Yeliseev et al., 1965) and the most representative one of the gabbro-syenite series. The massif is widely known through the studies of Morozewicz, who described from here the rock type mariupolite, and it is the type locality for the minerals beckelite and taramite. The massif is oval in plan and emplaced in various granitoids including normal granites, granites of the rapakivi group and enderbite charnockites, and comprises subalkaline (titanaugite) basic and ultrabasic rocks (gabbro, pyroxenites, peridotites) and alkaline and nepheline syenites (foyaites, mariupolites). Pegmatites, veins and dykes of alkaline rocks are also encountered. Agpaitic phonolites, containing eudialyte and astrophyllite, and dykes of nepheline syenite are the youngest intrusions of the complex (Krivdik and Tkachuk, 1989 and 1990). The complex has an indistinctly pronounced concentric, zonal structure. The outer zone is represented by a discontinuous ring of basic and ultrabasic rocks and syenites, while in the inner zone an arcuate body of foyaites is present. The succession of differentiates, namely subalkaline gabbro and pyroxenites - syenites - pulaskites - foyaites - mariupolites - agpaitic nepheline syenites, shows an increase in alkalinity and Fe:Mg ratios of rocks and mafic minerals. Pyroxene in gabbro and pyroxenites is represented by titanaugite, in outer zone syenites by aegirine-bearing ferrosalite and aegirine-ferrosalite, and in foyaites, mariupolites, agpaitic phonolite and nepheline syenites by aegirine-hedenbergite and aegirine. Changes in the composition of Zr-bearing minerals are also regular: in gabbro and outer zone syenites they are represented by baddeleyite and zircon, in foyaites and mariupolites by zircon and in agpaitic phonolites by eudialyte. The last differentiates, mariupolites, agpaitic phonolites and foyaites, accumulated rare elements (Zr, Nb, RE) forming separate mineral phases including pyrochlore, britholite (beckelite), zircon and eudialyte The content of Ba and Sr decreases correspondingly. The data presented above might suggest that the fractional crystallization of original alkali basaltic magma was the main petrogenic mechanism in the formation of the Oktyabr'skii massif leading to the formation of alkaline rocks, including the agpaitic nepheline-bearing rocks.
AINBERG, L.F. 1933. The Azov region alkaline massif. Trudy Vsesoyuznogo Geologo-Razvedochnogo Ob'edineniya. 196: 48-64.
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*KRIVDIK, S.G. and TKACHUK, V.I. 1989. Eudialyte-bearing agpaitic phonolites and dike nepheline syenites in the October intrusion, Ukrainian shield. Geochemistry International, 26(3): 54-60.
KRIVDIK, S.G. and TKACHUK, V.I. 1990. Petrology of the alkaline rocks of the Ukrainian Shield. Naukova Dumka, Kiev. 407 pp.
MOROZEWICZ, J. 1930. Der mariupolit und seine Blutaverwandten. Mineralogisch und Petrographisches. Mittelunden, Nue Folge B.40, H, V-VI-S. 335-436.
SEMENENKO, N.P. SAVCHENKO, N.A. and BRITCHENKO, A.D. 1977. Cycles of volcanism of the Dneiper-Donetz basin and Donbass and metal-bearing problems of the northern slope of the Ukrainian Shield. In: Volcanism and ore-formations of the Dneprovo-Donetz basin and Donbass. AN Ukraine SSR, 156 pp.
TSAROVSKY, I.D. 1954. Geological types of structures of alkaline rocks of the Ukraine SSR. Izvestiya Akademii Nauk SSSR, Seriya Geologicheskaya, 4: 101-12.
VINOGRADOV, A.P., TUGARINOV, A.I., FEDOROVA, V.A. and ZYKOV, S.I. 1957. Age of the Precambrian rocks of the Ukraine. Geokhimiya, Communication 3, 7: 559-66.
YELISEEV, N.A., KUSHEV, V.G. and VINOGRADOV, D.P. 1965. Proterozoic intrusive complex of the eastern Priazov region. Nauka, Moscow and Leningrad, 204 pp
