CALCIUM-RICH ULTRAMAFITES, ANKARAMITES, AND CLINOPYROXENE-PORPHYRIC GABBRO OF THE BIRKHIN MASSIF IN THE OL’KHON REGION: SOLUTION OF THE PROBLEM OF PRIMARY MELT AND FORMATION OF INTRUSION
E.V. Pushkarev1, A.V. Lavrenchuk2,3, I.A. Gottman1, E.V. Sklyarov4
1A.N. Zavaritsky Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences, Yekaterinburg, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
3Novosibirsk State University, Novosibirsk, Russia
4Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: Ankaramites, clinopyroxenites, chromian diopside, zoned clinopyroxene, differentiated series, primary melt, mantle sources, western Baikal area
Abstract
The paper presents new data on the chemical and mineral compositions of ultramafic rocks and various gabbro of the Birkhin massif in the Ol’khon region. Porphyric phenocrysts and zoned grains of clinopyroxene have been first found and studied in gabbronorite, which made it possible to reconstruct the entire melt crystallization trend from ultramafic to gabbro parageneses. Similar clinopyroxene trends have been established for clinopyroxenites and subvolcanic ankaramites, whose bodies and dikes have been recently discovered within the massif and in its environment. The total petrological data show that the magnesian high-Ca ankaramite melt corresponds in composition to the assumed primary melt for the Birkhin massif.
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