Continental arc magmatism along the southeast Hearne Craton margin in Saskatchewan,Canada: Comparison of the 1.92–1.91 Ga Porter Bay Complex and the 1.86–1.85 Ga Wathaman Batholith

Detailed mapping, coupled with geochronological and geochemical investigations, has revealed the presence of a 1917–1913 Ma gabbro–monzodiorite–monzonite suite along the southeast margin of the Hearne Craton in northern Saskatchewan, Canada. The predominantly plutonic suite is also characterised by 1915 Ma old trachyandesitic subvolcanic and volcaniclastic inclusions. The rocks are hornblende–epidote–titanite ± augite bearing and collectively termed the Porter Bay Complex. The plutonic rocks cut the 2569 Ma Lueaza River granitoid suite, a component of the Hearne Craton and are themselves intruded by 1859 Ma pegmatitic diorite, 1856 Ma layered gabbro-anorthosite, and 1853 Ma quartz-diorite belonging to the Wathaman Batholith, one of the world's largest Paleoproterozoic Andean-type continental arcs. Wholerock major element geochemistry characterises the Porter Bay Complex as calc-alkalic to alkali-calcic, metaluminous and variable from ferroan to magnesian. Trace element concentrations are characterised by negative high field strength element anomalies, suggesting emplacement along a destructive plate margin. The geochemical signatures of the Wathaman Batholith and the Porter Bay Complex are largely identical. The geographic location, map relationships, and geochronological, geochemical and petrographic constraints are consistent with the Porter Bay Complex having formed in a subduction-related continental arc setting. The southeastern margin of the Hearne Craton was therefore a long-lived active continental margin with two separate periods of continental arc magmatism between 1.92–1.91 Ga and 1.86–1.85 Ga.