Geochemical and radiogenic isotope (Sr-Nd) characteristics of Paleoproterozoic anorthositic and granitoid rocks in the Umiakoviarusek Lake region, Labrador, Canada.

Recent work in the north-central Labrador has identified Paleoproterozoic a northositic and granitoid rocks that are spatially associated with, yet tem porally distinct from, younger Mesoproterozoic intrusions of the Nain Pluto nic Suite. The Umiakoviarusek Lake (UL) region of Labrador contains several of these Paleoproterozoic intrusions and provides an opportunity to study their geochemical and radiogenic isotope (Sr-Nd) characteristics. Geochemic ally, the anorthositic and granitoid rocks have features consistent with co ntemporary anorthositic and granitoid rocks from other anorthosite-mangerit e-charnockite-granite complexes. The anorthositic rocks contain elevated co ntents of Al2O3, CaO, Sr, and Eu with low Ba, Rb, K, Zr, total rare earth e lements (REE), and light REE. The granitoid rocks, on the other hand, conta in lower concentrations of these elements along with elevated SiO2 and K2O. Isotopic data at 2050 Ma for the anorthositic rocks (I-Sr = 0.7048-0.7082; epsilon Nd = -4.1 to -15.9) and granitoid rocks (I-Sr = 0.7036-0.7094, eps ilon Nd = -5.1 to -9.7) are consistent with variable crustal and mantle con tributions to their genesis. The relatively unradiogenic Sr and slightly ev olved Nd isotopic data from the UL granitoid rocks is consistent with a sig nificant juvenile mantle component, possibly derived from an underplating m antle plume; this component may also be present in the anorthositic rocks. The Nd and Sr isotopic data are also consistent with crustal contamination from Archean source materials; however, based on the existing isotopic data base for the Nain Province gneisses, it is not possible to delineate a spec ific gneiss component. Furthermore, it is also quite possible that an Arche an source, unlike any described at present, was a crustal source component in the UL intrusive rocks.