Geology and tectonic setting of Paleoproterozoic granitoid suites in the Island Harbour Bay area, Makkovik Province, Labrador

Paleoproterozoic granitoid rocks in the Island Harbour Bay area (Kaipokok d omain, Makkovik Province, Labrador) are divided into four separate suites o n the basis of field relations, petrology, and age. The redefined Island Ha rbour Bay plutonic suite consists of ca. 1895-1870 Ma dioritic to granitic (mainly granodioritic and granitic) units. The rocks are variably foliated as a result of emplacement under amphibolite-facies conditions in a dextral transpressive regime during Andean-type subduction. The dominant mafic min eral is biotite, and accessory epidote, allanite, and titanite are abundant . The suite is calc-alkalic, but with rare-earth element patterns similar t o those of Archean tonalitic-trondhjemitic-granodioritic suites. It is inte rpreted to have formed deep in an Andean-type magmatic arc at the margin of the Nain continent. In contrast, the younger Hares Islands and Drunken Har bour granites (emplaced at ca. 1805 and 1790 Ma, respectively) were part of widespread late-orogenic magmatic activity in the Makkovik Province. In co ntrast to the Island Harbour Bay plutonic suite, these units retain igneous textures and are either unfoliated or display magmatic foliation, locally modified by emplacement in active shear zones. The ca. 1716 Ma Blacklers Bi ght granite varies from porphyritic to equigranular, is fluorite-bearing, a nd has chemical features approaching those of continental A-type granites. Similar granite occurs farther south in the Makkovik Province, reflecting w idespread anorogenic magmatic activity at that time, perhaps related to maf ic magma underplating. Variable interaction with Archean (Nain Province) cr ust by granitic magmas of all three ages is evidenced by epsilon(Nd) values ranging from -7.2 to -2.5.