Identification of Paleoproterozoic anorthositic and monzonitic rocks in the vicinity of the Mesoproterozoic Nain Plutonic Suite, Labrador: U-Pb evidence

Recent mapping along the northeast margin of the Mesoproterozoic Nain Plutonic Suite has revealed an important suite of locally deformed and variably altered anorthositic rocks. Uranium-lead zircon dating of one of these anorthositic rocks reveals a Paleoproterozoic emplacement age (2112 +5/-4 Ma), broadly equivalent to established ages of nearby 2135-2110 Ma granitic plutons in Nain craton. New Paleoproterozoic emplacement ages (2128 to 2109 Ma) are also reported here for variably foliated dioritic-monzonitic-granitic rocks in the immediate region, and together with the basic rocks belie the general lithological similarities shared with the younger anorogenic Nain Plutonic Suite plutonic assemblage. Emplacement of diabase dyke swarms at 2121 ± 1.5 Ma and (crosscutting leucogabbro) at ca. 2045 Ma further substantiate the regional importance of Paleoproterozoic basic magmatism. Leuconoritic and monzodioritic members of the northern Nain Plutonic Suite yield crystallization ages of 1322 ± 1 Ma and 1330 ± 1 Ma, respectively. Recognition of significant Paleoproterozoic anorthositic rocks within this dominantly Mesoproterozoic magmatic province imposes important new constraints on massif anorthosite petrogenesis.