ALLOCHTHONOUS 2.78 GA OCEANIC PLATEAU SLIVERS IN A 2.72 GA CONTINENTAL ARC SEQUENCE - VIZIEN GREENSTONE-BELT, NORTHEASTERN SUPERIOR PROVINCE, CANADA

Embedded within the vast granitoid terrane of the Minto block of north eastern Superior Province are Late Archean greenstone belts of the Gou dalie domain that preserve a long-lived record of continent-ocean inte raction. The Vizien greenstone belt is one such belt and it contains f our fault-bounded structural panels. The 2786 Ma mafic-ultramafic sequ ence is an allochthonous package of pillowed basaltic andesite, komati ite and volcaniclastic rocks cut by peridotite and gabbro sills. The m afic rocks are LREE-depleted tholeiites which have primitive mantle (P RIM)-normalized abundances of Tn < Nb < La, and epsilon(Nd) values of + 1.5 to + 3.2 reflecting extraction from a depleted mantle source. Th e 2724 Ma lac Lintelle continental calc-alkaline volcanic sequence con sists of massive basalt, plagioclase-porphyritic andesite, dacite, rhy olite, capped by quartz-rich sandstones/conglomerates with 2.97 Ga Nd model ages. Lac Lintelle volcanic rocks are LREE enriched, with low Ti O2 (< 1%) and Zr(< 200 ppm), PRIM-normalized enrichment in Tn > La > N b, and a range of epsilon(Nd) values from - 0.1 to + 1.7. The similar to 2722 Ma lac Serindac bimodal, subaerial tholeiitic volcanic sequenc e contains andesite (locally with tonalite xenoliths), basalt, gabbro sills, lenses of quartz-rich sedimentary rocks and a thick, upper rhyo lite sequence. The lac Serindac tholeiites are LREE-enriched, have PRI M-normalized Th > La > Nb, high Zr (to 300 ppm) and Ti contents, and l ow epsilon(Nd) values from + 0.8 in basalt to - 1.4 in rhyolite. The < 2718 Ma basement-cover sequence comprises 2.94 Ga tonalitic gneiss un conformably overlain by elastic sediments and a thin upper sequence of 2700 Ma gabbro, siliceous high-Mg basalt (SHMB) and andesite. The SHM B are characterised by LREE depletion and epsilon(Nd) values of + 2.6, whereas the andesite is LREE-enriched and has epsilon(Nd) 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 sequenc e represents a continental are formed on the eastern protocraton. The similar to 2722 Ma lac Serindac volcanic sequence represents late cont inental rift deposits. The various 2.8-2.7 Ga supracrustal sequences w ere accreted, deformed and metamorphosed to mid-amphibolite facies dur ing late-stage assembly of the Minto block between 2.718 and 2.693 Ga.