Evolution of an Archean greenstone belt in the Stormy Lake - Kawashegamuk Lake area (stratigraphy, structure and geochemistry) - Western Wabigoon Subprovince, Northwest Ontario /

330 km 2 of the easter-n part of the Archean Manitou Lakes - Stormy Lake metavolcanic - metasedimentary belt have been mapped and sampled. A large number of rocks ~.vere analyzed for the major and trace constituents including the rare-earth elements (REE). The Stormy Lake - Kawashegamuk Lake area may be subdivided into four major lithological groups of supracrustal rocks 1) A north-facing mafic assemblage, consisting of pillowed tholeiitic basalts and gabbro sills characterized by flat REE profiles, is exposed in the south part of the map area and belongs to a 8000 m thick homoclinal assemblage outside the map area. Felsic pyroclastic rocks believed to have been issued from a large central vent conformably overlie the tholeiites. 2) A dominantly epiclastic group facing to the north consists of terrestrial deposits interpreted to be an alluvial fan deposit ; a submarine facies is represented by turbiditic sediments. 3) The northeastern part of the study area consists of volcanic rocks belonging to two mafic - felsic cycles facing to the southuest ; andesitic flows with fractionated REE patterns make up a large part of the upper cycle, whereas the lower cycle has a stronger chemical polarity being represented by tholeiitic flows, with flat REE, which a r e succeeded by dacitic and rhyolitic pyroclasti cs. iii 4) A thick monotonous succession of tholeiitic pillmled basalt f lows and gabbro sills with flat REE represent the youngest supracrustal rocks. TIle entire belt underwent folding, faulting and granitic plutonism during a tectono-thermal event around 2700 Ma ago. Rocks exposed in the map area were subjected to regional greenschist facies metamorphism, but higher metamorphic grades are present near late granitic intrusions. Geochemical studies have been useful in 1) distinguishing the various rock units ; 2) relating volcanic and intrusive rocks 3) studying the significance of chemical changes due to post magmatic processes 4) determining the petrogenesis of the major volcanic rock types. In doing so, two major volcanic suites have been recognized : a) a tholeiitic suite, mostly represented by mafic rocks, was derived from partial melting of upper mantle material depleted in Ti, K and the light REE ; b) a calc-alkalic suite which evolved from partial melting of amphibolite in the lower crust. The more differentiated magma types have been produced by a multistage process involving partial melting and fractional crystallization to yield a continuum of compos i t i ons ranging from basaltic andesite to rhyolite. A model for the development of the eastern part of the Manitou Lakes - Stormy Lake belt has been proposed.

Molluscan carbonate geochemistry and paleoceanography of the Late Cretaceous western interior seaway of North America

North Amerlc8 W8S inundated by fJ major eplcontlnental sea during ihe C:retaceo.us Period. The sOljihw6rd transgression of th.e northern Boreal See along the ~\festern Interior Seaway resulted in a meetlng with the northward edv6nclng waters from the GUlf of Mexico (Obradovich and Cobban, 1975). Th1s link was 1n eXlstence by late Albien time and 6llowed for the comm1ngl1ng of the prol1ferous Arctic and Gulf rnar1ne faunas (F1g. 1). By early Campanlan time, there was a widening of B6ffln Bay wlth a slrnult8neous subsidence 1n the Arct1c Archlpelago and Sverdrup 6as1n (W11liam and Stelck, 1975). Williams and Burk (1964) found 6 break 1n the marines sedlmentatlon in the f1anltoba area, suggesting Bland corlnectlon from the Dlstrlct of Keewatln through eastern M6fl1toba to the lake Sl~perlor reglon, lmplying that the only dlrect connection between the Interlor Sea with Baffln Bay, was yia the Arct1c. This hiatus was also documented by Meek and Hayden (1861) ln the United states between the Niobrara and Pierre Format1ons. Jeletzky (1971) suggested that the retreat of the sea towards the east was by a serles of strong pulses resultlng in the regression of the Campanlan and M66str1chtlan seas. During ttle Cretaceous1 the r1s1ng Corl1111era caused the western shoreline of the Interlor Sea to migrate eastwards and the Cordillera'l detritus produced deltaic cornplexes from the Mackenzie Valley to Ne\N Mexlcoo The foreland basin was continually subslding and thls down\",arplng aided in the eastward m1gration of the western shorel1ne. Thls also lndicates that trle water 'tIes becom1ng deeper in the central Plains sect10n of the Seaway (Fig. 2).