THE AGE AND GEODYNAMIC SETTING OF FORMATION OF HIGH-TEMPERATURE METAMORPHIC COMPLEXES IN THE SOUTH MONGOLIAN BELT
I.K. Kozakov, E.B. Sal'nikova, A.N. Didenko*, V.P. Kovach, A.M. Fedoseenko, and S.Z. Yakovleva
Institute of Geology and Geochronology of the Precambrian, Russian Academy of Sciences, 2 nab. Makarova, Saint Petersburg, 199034, Russia
* Gamburtsev Institute of the Earth's Physics, Russian Academy of Sciences, 10 ul. Bol'shaya Gruzinskaya, Moscow, 123810, Russia
Keywords: Tectonics, metamorphism, geochronology, Hercynides, Indo-Sinides
Pages: 482-487
Abstract
Based on the first isotope-geochronological data obtained, the age of metamorphic processes in Hercynian crystalline complexes in southeastern Mongolia has been estimated. The average 207Pb/ 235U age of monazite from synmetamorphic granites is 224  1 Ma. The Sm-Nd age for the bulk rock and its mineral inclusions is 219.2 6.2 Ma. We have established that highly metamorphosed rocks of Early and Late Hercynian (Indo-Sinian) folded structures in the South Mongolian belt cannot be fragments of the Caledonian (or more ancient) ensialic basement. They resulted from the development of deep segments in the Earth's crust during the closure of the South Mongolian and the Inner Mongolian ocean basins. |
