Petrology and isotopic composition of a Grenvillian basement fragment in the northern Appalachian orogen: Blair River inlier, Nova Scotia, Canada

Mesoproterozoic metaplutonic rocks in northern Cape Breton Island, Nova Sco tia, occur in a tectonic inlier within the Appalachian orogen. Although the y have been multiply metamorphosed and variably deformed, the petrology and geochemistry of these rocks provide insight into the tectonomagmatic evolu tion of easternmost Laurentia. Anorthosite, syenite, and granitoid plutons (1100-980 Ma) intruded the Sailor Brok and Polletts Cove River gneisses. Ne w Nd isotopic data are presented from a biotite-rich part of the Sailor Bro ok gneiss (epsilon (Nd1) = -0.7), two anorthosite samples (epsilon Nd, = +2 .1 and +2.8), two anorthosite samples (epsilon Nd, = -0.4). New U-Pb zircon data from the anorthosite yield Pb-207/Pb-206 ages between 975 and 1095 Ma . Disrupted U-Pb systematics preclude a unique age interpretation, but the similar to 1095 Ma single-grain date is a minimum age for the anorthosite. Field relations, major and trace-element geochemistry, and isotopic charact eristics indicate that the anorthosite and charnockite were probably coexis ting melts, but not differentiates of a single parent magma. The lithologic al and chemical characteristics of the Lowland Brook Syenite are similar to those of a contemporaneous belt of ultrapotassic plutons in the southern G renville Province, and both have the chemical characteristics of certain mo dern continental-margin arc magmas. These data indicate that the Mesoproter ozoic units in the Blair River inlier were juvenile crustal additions to ea stern Laurentia during Grenville-related orogenic events.