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Journal of the Geological Society; 2008; v. 165; issue.1; p. 405-421;
DOI: 10.1144/0016-76492006-162
© 2008 Geological Society of London

Original Article

Age and evolution of late Mesozoic metamorphic core complexes in southern Siberia and northern Mongolia

T.V. DONSKAYA1, B.F. WINDLEY2, A.M. MAZUKABZOV1, A. KRöNER3, E.V. SKLYAROV1, D.P. GLADKOCHUB1, V.A. PONOMARCHUK4, G. BADARCH{dagger},5, M.K. REICHOW2 & E. HEGNER6

1 Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, 128 Lermontov St., Irkutsk 664033, Russia (e-mail: tanlen{at}crust.irk.ru)
2 Department of Geology, University of Leicester, Leicester LE1 7RH, UK
3 Institut für Geowissenschaften, Universität Mainz, 55099 Mainz, Germany
4 United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of the Russian Academy of Sciences, 3 Koptyug Pr., Novosibirsk 630090, Russia
5 Institute of Geology and Mineral Resources, Mongolian Academy of Sciences, 63 Peace Avenue, Ulaanbaatar 210357, Mongolia
AFF {dagger}Deceased
6 Department für Umwelt- und Geowissenschaften, Universität München, 41 Theresienstrasse, 80333 München, Germany

Numerous Cretaceous metamorphic core complexes (MCCs) extend from Transbaikalia in Russia to northern Mongolia within the Central Asian Orogenic Belt. We investigated the Buteel and Zagan MCCs in detail. Shear sense indicators in mylonitized rocks show footwall-to-the-NW tectonic transport. Single zircon dating of footwall rocks in the Buteel MCC establishes the emplacement of granitoid orthogneiss precursors at 240–211 Ma, a felsic metavolcanic rock at 265.0 ± 1.2 Ma, a syenite at 265.5 ± 1.2 Ma and a metarhyolite of the pre-granitoid basement at 553.6 ± 2.9 Ma. A peralkaline granite intruding orthogneisses of the Zagan MCC has a new U–Pb zircon age of 151.6 ± 0.7 Ma. 40Ar/39Ar ages of 133.5 ± 1.8 Ma of hornblende from amphibolite and 122.6 ± 1.8 Ma of biotite from mylonitized gabbro–dolerite of the Buteel MCC are interpreted as cooling ages representing the time of deformation in the footwall. Geological data suggest that the MCCs in Transbaikalia and northern Mongolia formed as a result of extension in a crust that had previously been thickened by abundant calc-alkaline magmatism in an Andean-type setting on the border of the closing Mongol–Okhotsk ocean, by widespread collisional to post-collisional thrusting, and by extensive alkaline–peralkaline magmatism.