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Russian Geology and Geophysics

2003 year, number 12

MAGMATISM AND GEODYNAMICS OF EARLY CALEDONIAN STRUCTURES OF THE CENTRAL ASIAN FOLD BELT (isotopic and geological data)

V.I. Kovalenko, V.V. Yarmolyuk, V.P. Kovach*, A.B. Kotov*, and E.B. Sal'nikova*
Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry,
Russian Academy of Sciences, 35 Staromonetnyi per., Moscow, 109017, Russia
* Institute of Geology and Geochronology of the Precambrian, Russian Academy of Sciences,
2 nab. Makarova, St. Petersburg, 199034, Russia
Keywords: Early Caledonian structures, isotopic composition of granitoids, Central Asian fold belt
Pages: 1235-1248

Abstract

The structure of the Caledonian area of the Central Asian fold belt is determined by Caledonian folded formations made up of Vendian-Cambrian ophiolite and island-arc complexes and by terranes or microcontinents of older crust, located between them. The corresponding structural zones differ in the Nd isotope composition of their crust, which is determined from analysis of granitoids. The crust of the Precambrian terranes is characterized by negative Nd(T) values. Most of the terranes (Hangayn, Barguzin-Vitim, Sangilen) have Nd(T) = +0.5...-10, thus corresponding to crust with a model Nd isotopic age TNd(DM-2st) = 1000-1700 Ma. This allows uniting the above terranes into a