U-Pb ages of granitoid rocks in the northwestern Makkovik Province, Labrador: evidence for 175 million years of episodic synorogenic and postorogenicplutonism

New U-Pb zircon, titanite, and monazite ages reported here, along with exis ting age data, demonstrate that granitoid bodies in the northwestern segmen t of the Paleoproterozoic Makkovik Province, Labrador, are of three distinc t ages. The redefined Island Harbour Bay plutonic suite consists of varied dioritic to granitic units that were syntectonically emplaced into Archean crust of the Kaipokok domain between ca. 1895 Ma and 1870 +/- 2 Ma. This pl utonism occurred during the early stages of the Makkovikian Orogeny in an o bliquely convergent, Andean continental margin setting. The Hares Islands a nd Drunken Harbour granites form smaller, discrete plutons that were emplac ed in or adjacent to the Island Harbour Bay plutonic suite at 1805 +/- 5 Ma and 1791 +/- 2 Ma, respectively, during dextral strike-slip deformation th at accompanied accretion of an outboard juvenile terrane. Magmatic activity during this period was preferentially sited along active structural zones, but also occurred outside of these zones. The undeformed Blacklers Bight A -type granite was emplaced in the Kaipokok domain at 1716 +/- 1 Ma, late in the development of the orogen. A-type granites of this age form a signific ant component of the southeastern Makkovik Province, and their generation i s linked to mafic underplating and heterogeneous regional extension. The ne w age data support the conclusion of earlier workers that crustal growth vi a synorogenic and postorogenic plutonism was episodic, and allow, along wit h field and geochemical data, inferences to be made regarding the tectonic setting of individual plutonic events.