LITHOS 0 ELSEVIER Lithos 37 (19961163-179 Allochthonous 2.78 Ga oceanic plateau slivers in a 2.72 Ga continental arc sequence: Vizien greenstone belt, northeastern Superior Province, Canada T. Skulski, J.A. Percival zyxwvutsrqponmlkjihgfedcbaZYXWVUTS Continental Geoscience Division, Geological Survey of Canada, 601 Booth St., Ottuwu, Ont. KIA OE8, Canadu Received 5 January 1995; accepted 25 July 1995 Abstract Embedded within the vast granitoid terrane of the Minto block of northeastern Superior Province are Late Archean greenstone belts of the Goudalie domain that preserve a long-lived record of continent-ocean interaction. The Vizien greenstone belt is one such belt and it contains four fault-bounded structural panels. The 2786 Ma mafic-ultramafic sequence is an allochthonous package of pillowed basaltic andesite, komatiite. and volcaniclastic rocks cut by peridot& and gabbro sills. The mafic rocks are LREE-depleted tholeiites which have primitive mantle (PRIM&normalized abundances of Th < Nb < La, and l Nd values of + 1.5 to +3.2 reflecting extraction from a depleted mantle source. The 2724 Ma lac Lintelle continental talc-alkaline volcanic sequence consists of massive basalt, plagioclase-potphyritic andesite, dacite, rhyolite, capped by quartz-rich sandstones/conglomerates with 2.97 Ga Nd model ages. Lac Lintelle volcanic rocks are LREE enriched, with low TiO, ( < 1%) and Zr ( < 200 ppm), PRIM-normalized enrichment in Th > La > Nb, and a range of l Nd values from - 0.1 to + 1.7. The * 2722 Ma lac Serindac bimodal, subaerial tholeiitic volcanic sequence contains and&e (locally with tonalite xenoliths), basalt, gabbro sills, lenses of quartz-rich sedimentary rocks and a thick, upper rhyolite sequence. The lac Serindac tholeiites are LREE-enriched, have PRIM-normalized Th > La > Nb, high Zr (to 300 ppm) and Ti contents, and low l Nd values from +0.8 in basalt to - 1.4 in rhyolite. The < 2718 Ma basement-cover sequence comprises 2.94 Ga tonalitic gneiss unconformably overlain by elastic sediments and a thin upper sequence of 2700 Ma gabbro, siliceous high-Mg basalt (SHMB) and andesite. The SHMB are characterised by LREE depletion and l Nd values of +2.6, whereas the andesite is LREE-enriched and has eNd values of -0.3. The 2786 Ma mafic-ultramafic sequence is interpreted as a sliver of plume-related oceanic plateau crust. The 2724 lac Lintelle sequence represents a continental arc formed on the eastern protocraton. The _ 2722 Ma lac Serindac volcanic sequence represents late continental rift deposits. The various 2.8-2.7 Ga supracrustal sequences were accreted, deformed and metamorphosed to mid-amphibolite facies during late-stage assembly of the Minto block between 2.718 and 2.693 Ga. 1. Introduction As the principal record of early magmatism on Earth, Archean greenstone belts provide a unique window on ancient tectonic environments. Data from belts of the Canadian Superior Province show growth by accretion of island arcs, oceanic plateaus, marginal basin crust and forearc prisms between 2.75 and 2.70 Ga onto a - 3.0 Ga northwestern cratonic nucleus (Langford and Morin, 1976; Card, 1990; Williams, 00244937/%/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 0024-4937(95)00035-6