M.V. Chibisova1, A.V.Rybin1, Yu.A. Martynov2, V.M. Okrugin3

1 Institute of Marine Geology and Geopysics FEB RAS, Yuzhno-Sakhalinsk, 693022; chibisova@imgg.ru
2 Far Eastern Geological Institute FEB RAS, Vladivostok, 690022
3 Institute of Volcanology and Seismology FEB RAS, Petropavlovsk-Kamchatskii, 683006

The paper presents data on the petrography, chemical and mineral composition of magnesian basalts (MgO content may reach 9 mass %) of Men'shii Brat volcano (Medvezh'ya caldera, Iturup Island, The Kuril Island Arc). The content of magnesian basalts and andesitic basalts in the front and axial zones of the Kuril Island Arc is very low. The article provides detailed data on the chemical composition of the rock-forming and accessory minerals (olivine, plagioclase, orto- and clinopyroxene, chromous spinel). High magnesian content, a peculiar composition of minerals (insets), olivine (Fo89-92) and chromous spinel (Kmg»50) associations allow concluding that the initial melts have a primitive nature.

Keywords: magnesian basalts, petrography, mineralogy, chromous spinel, Men'shii Brat, the Kuril Islands.