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Volcanism on the passive margin of Laurentia: an early Paleozoic analogue of Cretaceous volcanism on the northeastern American margin: Reply

1990; NRC Research Press; Volume: 27; Issue: 11 Linguagem: Inglês

10.1139/e90-166

1480-3313

Stephen Kumarapeli, Karen St. Seymour, Hillar Pintson, Elizabeth Hasselgren,

Paleontology and Stratigraphy of Fossils

Allochthonous masses of basaltic lava flows and related tuffs are present in several localities in an approximately 30 km long segment of the western margin of the Granby Nappe, in southeastern Quebec. They occur either as numerous small blocks in the Drummondville wildflysch related to the nappe or as larger masses intercalated with sedimentary sequences of limestone and shale of probable Late Cambrian to Early Ordovician age. These latter occurrences and the associated sedimentary units form island-like areas within lithologies of the Granby Nappe consisting of Cambrian sediments that accumulated on the continental rise. Their overall characteristics suggest that they represent slabs derived from the shelf margin of Laurentia and incorporated into the cratonward-moving nappes during the Middle Ordovician Taconian Orogeny.The volcanic rocks are mainly transitional but include some alkali olivine basalts. There are some indications that their affinities are to basaltic rocks of seamount chains localized...