BONINITES AND OPHIOLITES: PROBLEMS OF THEIR RELATIONS AND PETROGENESIS OF BONINITES
E.V. Sklyarov1,2, V.P. Kovach3, A.B. Kotov3, A.B. Kuzmichev4, A.V. Lavrenchuk5,6, V.I. Perelyaev7, A.A. Shchipansky4
1Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences, ul. Sukhanova 8, Vladivostok, 690950, Russia
2Far Eastern Federal University
3Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, nab. Makarova 2, St. Petersburg, 199034, Russia
4Geological Institute, Russian Academy of Sciences, Pyzhevsky per. 7, Moscow, 119017, Russia
5V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
6Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
7Irkutsk State University, ul. Karla Marksa 1, Irkutsk, 664003, Russia
Keywords: Ophiolites, subduction zone, suprasubduction magmatism, southeastern Sayan
Abstract
There are four main types of boninites in ophiolite suites, which either spatially coexist with ophiolites, though belong to other tectonic units (1), or are present as later constituents of ophiolite sequences (crosscutting dikes or lavas on top) (2), or build ophiolite sequences together with island-arc tholeiites and basaltic andesites, followed by younger volcanics of MORB or BABB affinites (3), or occupy the whole mafic portion of ophiolite sequences, together with island-arc tholeiites and basaltic andesites (4). The latter type, considered in more detail for the case of ophiolites from the southeastern Sayan Mountains (Siberia, Russia), presents an example of inconsistency between the model of ophiolite formation in mid-ocean ridge settings and subduction-related island-arc fingerprints in ophiolitic mafic rocks. The patterns of boninites record several evolution models of oceanic systems, with melting and intrusion of boninites in forearc, arc, and back-arc settings. The existing models are controversial, possibly, because there is no single mechanism to account for all types of boninites.
|
