Sm-Nd-Sr isotopic and geochemical signatures of mafic intrusive rocks in the Nigadoo River Syncline, northeastern New Brunswick: Implications for regional tectonics

Mafic dykes and sills occur throughout the Silurian–Devonian Nigadoo River Syncline of northern New Brunswick. These intrusive rocks are characterized by transitional to calc-alkaline compositions consistent with volcanic-arc and within-plate environments and have trends suggestive of fractional crystallization of a melt derived from a mantle source. The dykes are characterized by flat chondrite-normalized rare earth element patterns, positive Cs, Rb, and Pb and negative Th and Nb anomalies relative to primitive mantle, suggesting crustal contamination. The eNd values between 4.4 and 54.4 and depleted mantle ages between ca. 1056 and 1192 Ma for the dykes are consistent with derivation from Ganderian subcontinental lithospheric mantle. The eSr values are elevated and between 17.37 and 36.93. Geochemical similarities suggest that these dykes are likely equivalents to overlying basalts of the Dalhousie Group and upper part of the Tobique Group, which were emplaced in a transpressional rift environment following break-off of the Salinic slab preceding oblique collision of Avalonia during the Acadian orogenic cycle.