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Russian Geology and Geophysics

2005 year, number 4

BLUESCHISTS FROM THE UIMON ZONE AS EVIDENCE FOR ORDOVICIAN ACCRETIONARY-COLLISIONAL EVENTS IN GORNY ALTAI

N.I. Volkova, S.I. Stupakov*, G.A. Tret'yakov*, V.A. Simonov*, A.V. Travin**, and D.S. Yudin**
Institute of Mineralogy and Petrography, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Institute of Geology, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
** Analytical Centre of United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Blueschist, geochemistry, subduction, accretion, geochronology, Gorny Altai
Pages: 361-378

Abstract

Petrochemical study of metabasites from the Uimon Zone, Gorny Altai, shows essential differences in TiO2, MgO, Na2O, K2O, and P2O5 contents between glaucophane-bearing, winchite-actinolite, and actinolite schists. Geochemical discrimination of these rocks suggests that blueschists are comparable to alkaline basalts of oceanic islands (OIB), whereas greenschists correspond in composition to tholeiite basalts of N-MORB type and their tuffs. Mineralogical distinctions of the rocks (namely, the presence of glaucophane or actinolite) are stipulated by chemical compositions of their protoliths, instead of variations in P-T conditions of metamorphism. Under similar P-T conditions (350-400