Late Cambrian to Early Ordovician volcanic and hypabyssal rocks in the NotreDame subzone, Newfoundland Appalachians, are generally considered to have formed in a series of island arcs and back arc basins on the Laurentian side of Iapetus. Our compilation of new geochemical and Nd isotopic data provides a more detailed look at the nature of magmatism in these environments than has heretofore been possible. Nd isotopic data constrain the nature of the magma sources for the various volcanic episodes and, in particular, allow us to track the early Paleozoic interaction of mantle and continental lithosphere at the Laurentian margin. New and published geochronological data permit us to assign a time sequence to the various events that we recognize.Geochemical data show that volcanic rocks in the Notre Dame subzone can be divided into several groups, most of which have well-documented analogs in modern plate environments. In nonarc environments, tholeiitic rocks with characteristics of N-MORB (normal mid-ocean basalt ridge) and E-MORB (enriched-MORB) are present, as are tholeiitic and alkalic basalts with characteristics of oceanic island basalts. The geochemical and isotopic data indicate derivation from time-integrated depleted mantle sources. We interpret these to have formed in ensimatic back arc basins.Arc volcanic rocks include island arc tholeiites, transitional island arc tholeiites, calc-alkalic basalt and/or andesite, boninites, and felsic volcanics. Geochemical and Nd isotopic data indicate that the tholeiitic rocks were derived from time integrated LREE-(light rare earth element-) depleted mantle sources contaminated by subducted, hydrous oceanic lithospheric and continentally derived sediments. Calc-alkalic rocks and associated felsic volcanic rocks have Nd isotopic compositions that indicate the direct involvement of continental lithosphere in their petrogenesis.Integration of geochemical, geological, and geochronological evidence suggests the following sequence of events: (1

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