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Russian Geology and Geophysics

2006 year, number 8

COMPOSITION, U-Pb AGE, AND GEODYNAMIC SETTING OF ISLAND-ARC GABBROIDS AND GRANITOIDS OF THE DZHIDA ZONE ( southwestern Transbaikalia, northern Mongolia )

I.V. Gordienko, V.P. Kovach*, D.V. Gorokhovsky, E.B. Sal'nikova*, A.B. Kotov*, S.Z. Yakovleva*, N.Yu. Zagornaya*, A.M. Fedoseenko*, and Yu.V. Plotkina*
Geological Institute, Siberian Branch of the RAS, 8 ul. Sakh'yanovoi, Ulan Ude, 670047, Russia
* Institute of Precambrian Geology and Geochronology, 2 nab. Makarova, St. Petersburg, 199034, Russia
Keywords: Paleoasian ocean, island arc, gabbroids, granitoids, isotope age, Dzhida Caledonide zone, Transbaikalia, northern Mongolia
Pages: 948-955

Abstract

First data on the U-Pb age of island-arc gabbroids and granitoids of the Dzhida Caledonide zone are presented. It has been established that these rocks formed at nearly the same time (506 ± 1 Ma, gabbroids, and 504 ± 2 Ma, granitoids) at the final stage of the evolution of ensimatic island arc. The low 87Sr/86Sr (0.7031-0.7033) and high positive ε Nd (T) (+6.7...+7.6) values and localization of sample points at the same isochron evidence that the studied igneous rocks belong to the same differentiated gabbro-diorite-tonalite series, which resulted from the melting of a primary depleted mantle source with the subordinate role of a long-lived crustal component.