IAPETUS OCEAN-FLOOR STUFFED INTO A SUTURE ZONE - XENOLITH ND ISOTOPICEVIDENCE FOR DUNNAGE-EQUIVALENT BASEMENT IN CENTRAL NEWFOUNDLAND

Granulite-facies xenoliths from Late Jurassic alkaline lamprophyres ma y represent basement to the Dunnage Zone in north-central Newfoundland (Notre Dame Bay area). At 143 Ma the xenoliths had positive epsilon(N d) values between 0.9 and 4.7. They give Nd depleted mantle model ages around 700 Ma and have trace element and major element compositions r eminiscent of oceanic arc-related intermediate volcanic and sedimentar y rocks. Their positive epsilon(Nd) values and associated ''young'' Nd model ages argue against their representing Grenvillian crust. Simila rly, Gander Zone basement to the east produced granitic rocks with str ongly negative epsilon(Nd) values unlike those of the xenoliths. Posit ive epsilon(Nd) values for Avalonian granites indicate that the xenoli ths could represent Avalon-type basement; however, there are 100-200 k m of Gander and Dunnage zone rocks between the xenolith locality and t he Avalon Zone. Early orogenic volcanic rocks and some late orogenic t o postorogenic granitic rocks in the central to northern portion of th e Gander Zone have positive epsilon(Nd) values, consistent with extrac tion from a depleted mantle at the same time as material forming the x enoliths. Similarities between the xenolith chemistry and that of earl y orogenic (Cambrian) arc-related intermediate volcanic rocks of the D unnage Zone indicate that the xenoliths and basement in the Notre Dame Bay area are composed of Iapetus Ocean floor relies (volcanic or volc anic-rich sedimentary rocks) stuffed into a collisional suture zone du ring ocean closure.