V.A. Seliverstov

Earth sciences Museum, Lomonosov Moscow State University. Moscow, 119899; е-mail: vaseliverstov@gmail.com

The article gives a brief description for the geological peculiarities of the alkaline-ultramafic volcanic complex in Eastern Kamchatka (meimechites, lamproitoides, Na-alkaline basalts). The ultramafic rocks contain a number of thermobarophyillic minerals: olivine (Fo 92.47-93.51), Cr-diopsides, garnets (lilac, red, rose and orange pyropes), Cr-spinels and Ti-Cr-spinels, picroilmenite, ilmenite, Cr-ulvospinel, magnesioferrite, Ti-magnesioferrite, phlogopite and Ba-phlogopite, Ba-orthoclase, moissanite (polytype 6H), corundum, ruby and Cr-ruby (Cr2O3 up to 45 mass %), zircon, "exotic" glasses. The "exotic" glasses composition agrees the composition of orthopyroxene, clinopyroxene and andradite. The above minerals belong to certain paragenesises, including diomondiferous ones: garnet clinopyroxenites, lhertsolites and wherlites, ilmenite and spinel peridotites, eclogites, alpine-type ultramafites etc. The combination of the following processes determines the meimechites and lamproitoides genesis:
1 – Selective melting of primitive mantle and reactions between melt and pyrolite accompanied by coherent elements loss caused by mantle metasomatosis.
2 – Impact fragmentation and subtraction of the fragmented mantle ultramafic rocks and the dispersed melt into the upper lithosphere.
3 – Eruption of tuffs on the bottom of Cretaceous sea, their decompressed melting in the intermediate chambers and differentiation of the newly formed ultramafic magmas in the feeding systems of paleovolcanoes. The formation of the alkaline ultramafic complex on the deep differentiated crust concluded with the eruption of lamproitoides tuffs and effusion of nepheline basalt lavas.

Keywords: alkaline-ultramafic volcanic complex, Eastern Kamchatka.