Sr and Nd isotopic and petrological evidence for the age and origin of the White Bear Arm Complex and associated units from the Grenville Province in eastern Labrador

Three major lithological units (the Paradise metasedimentary gneiss belt, the Paradise Arm granitoid pluton and the White Bear Arm gabbronorite complex) situated in the Grenville Province, eastern Labrador, were investigated using Rb-Sr and Sm-Nd isotopic techniques. The Paradise metasedimentary gneiss belt was metamorphosed to amphibolite facies prior to ca. 1655 Ma, and subsequently intruded by the White Bear Arm complex ca. 1650 Ma. The metasedimentary gneisses and gabbronorite complex were both intruded by the Paradise Arm pluton and other granitoid rocks. Sm-Nd data indicate that the White Bear Arm complex was extracted from a LREE-depleted mantle (εNd > +3.6). A radiogenically enriched Sr isotopic signature is interpreted to indicate (i) addition of crustally derived Sr, and (ii) secondary remobilization of the Rb-Sr system. The granitoid rocks were derived either by melting of lower crust by a mantle source, or by partial melting of the metasedimentary gneisses by the upwelling mafic complex. -from Authors