Precambrian Ophiolites and Related Rocks Edited by Timothy M. Kusky Developments in Precambrian Geology, Vol.13 (K.C.Condie, Series Editor) 425 ©2004 Elsevier B.V. All rights reserved. Сhapter 14 2.8 GA BONINITEHOSTING PARTIAL SUPRASUBDUCTION ZONE OPHIOLITE SEQUENCES FROM THE NORTH KARELIAN GREENSTONE BELT, NE BALTIC SHIELD, RUSSIA A.A. SHCHIPANSKY a , A.V. SAMSONOV b , E.V. BIBIKOVA c , LI. BABARINA a , A.N. KONILOV a , K.A. KRYLOV a,1 , A.I. SLABUNOV d AND M.M. BOGINA b a Geological Institute of RAS, Pyzhevsky per., 7, Moscow, 109017, Russia b Institute of Ore Deposits, Petrography, Geochemistry and Mineralogy of RAS, Staromonetny per., 35, Moscow, 109017, Russia c Vernadsky Institute of Geochemistry and Analytical Chemistry of RAS, Kosygin St., 19, Moscow, 17975, Russia d Karelian Research Center of RAS, Institute of Geology, Pushkinskaya St., 11, Petrozavodsk, 185610, Karelia, Russia Neoarchean subductionrelated assemblages of the North Karelian greenstone belt, in the NE part of the Baltic Shield, Russia, contain the world's oldest known boninite series, occurring in at least in two areas of the belt. The first area, referred to here as the Khizo vaara structure, shows evidence of a late Archean oceanisland volcanic arc collage formed during two tectonic episodes nearly 2.8 Ga ago. The second area, named the Iringora struc ture, preserves distinctive features of an ophiolite pseudostratigraphy, including not only gabbro and lava units, but also remnants of a sheeted dike complex. The major and trace element chemistry of the Iringora ophiolitic gabbro, dike and lava units suggests a comag matic series with a continuous compositional variation from more primitive mafic to strictly boninitic melts. In terms of major and trace element abundance, the boninite series of the North Karelian greenstone belt is practically indistinguishable from the Group I and II of the Troodos upper pillow lavas. These occurrences strongly suggest that Neoarchean subductionrelated processes including boninitehosting suprasubduction zone ophiolites have not changed substantially over the past 2.8 Ga. 1 Present address: Department of Geological and Environment Sciences, Stanford University, CA 943052115, USA. DOI: 10.1016/S01662635(04)130144