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Russian Geology and Geophysics

2004 year, number 2

GEODYNAMIC POSITION OF MIDDLE PALEOZOIC BASITE SERIES OF THE ALTAI, EXEMPLIFIED BY THE KARAOYUK AND TEREKTA COMPLEXES

V.A. Goverdovsky
Gorny-Altai Territorial Archive of Geological Information, 13 ul. Ulagasheva, Gorno-Altaisk, 649000, Russia
Keywords: Metadolerites, rhyolites, petrography, geochemistry, geodynamic setting, Gorny Altai
Pages: 193-203

Abstract

Geology and geochemistry of the Karaoyuk and Terekta complexes of the Gorny Altai are described. It has been established that the Karaoyuk complex (D3) is dominated by subalkalic metadolerites and rhyolites, which form a bimodal association typical of rifting zones. A conclusion is made that the rocks of this complex were formed from initial Cr-Co-Ni magma melts under conditions of back extension at the active continental margin.
The rocks of the Terekta complex (C1) are represented by metagabbro-dolerites and metadolerites. Despite the most primitive composition of the initial Fe-Ti-V magma, they also formed under extension conditions which are interpreted as extensions in the dome of a granite-gneiss asthenolens.
The distribution patterns of Nd, Eu, and some other elements (Co, Ni, V) suggest the fractionation of the initial magma melts having formed the rocks of the complexes. It is supposed that the dike complexes have their own intrusive "roots" exposed in the Altai geologic structures, which are erroneously considered part of other igneous complexes of the region. The formation of the explored dike complexes is related to the functioning of a mantle column in the zone of back-arc basin on the active continental margin and to tensions above the gently submerging slab during the interaction between the Middle Paleozoic Siberian continent and Irtysh-Zaisan fragment of the oceanic crust of the Paleotethys.