THE TECTONOMAGMATIC EVOLUTION OF STRUCTURE-LITHOLOGIC COMPLEXES IN THE TANNU-OLA ZONE, TUVA, IN THE LATE VENDIAN-EARLY CAMBRIAN ( from geochemical, Nd isotope, and geochronological data )
A.A. Mongusha, V.I. Lebedeva, V.P. Kovachb, E.B. Sal'nikovab, E.K. Druzhkovaa, S.Z. Yakovlevab, Yu.V. Plotkinab, N.Yu. Zagornayab, A.V. Travinc, and P.A. Serovd
a Tuvinian Institute of Complex Exploration of Natural Resources, Siberian Branch of the Russian Academy of Sciences, ul. Internatsional'naya 117a, Kyzyl, 667007, Russia
b Institute of the Precambrian Geology and Geochronology, nab. Makarova 2, St. Petersburg, 199034, Russia
c V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
d Geological Institute of the Kola Research Center, Russian Academy of Sciences, ul. Fersmana 14, Apatity, Murmansk Region, 184209, Russia
Keywords: Island arc, subduction, accretion, geodynamics, Vendian, Cambrian, Tuva
Pages: 503-516
Abstract
In the Tanuu-Ola zone, there are island-arc (Late Vendian) and subduction-accretionary (first half of the Early Cambrian) complexes whose mantle sources were generated fr om melts produced in suprasubduction conditions as a result of melting of mantle wedge peridotites. The island arc, whose fragment is present in the Tannu-Ola zone, formed tentatively at 570 Ma and ceased as an individual structure at the Vendian-Cambrian boundary, though the subduction continued till the middle Early Cambrian. From the Vendian-Cambrian boundary to the middle Early Cambrian, the accretion of island-arc, back-arc, oceanic, and metamorphic structure-lithologic complexes took place at this segment of the Central Asian Fold Belt. From middle to late Early Cambrian, the Tannu-Ola zone was an active continental margin, wh ere basalts with island-arc characteristics, quartz microdiorites of adakite composition, basalts, dolerites, and quartz microdiorites of intraplate type, and diorite-tonalite-plagiogranite association of island-arc type formed. To explain the spatial and temporal conjugation of different magmatism manifestations on the active margin, we applied the slab-window model.
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