Magmatic evolution of the southern Great Bear continental arc, northwestern Canadian Shield: geochronological constraints

The calc-alkaline Great Bear continental arc in the Wopmay Orogen developed after a collision ca. 1890 Ma of the Archean Slave craton with the Paleopr oterozoic Hottah terrane to the west. U-Pb zircon dating of three volcanic and six intrusive rocks from the southern part of the arc shows four stages of development: (i) intrusion of a few small sodic leucogranite plutons at 1873 +/- 2 Ma into a previously folded metasedimentary sequence; (ii) abun dant calc-alkaline felsic volcanism and subvolcanic intrusions during the p eriod 1870-1866 Ma, bracketed by five ages; (iii) intrusion of large calc-a lkaline granitic plutons, including the Marian River batholith, dated by zi rcon and titanite from two samples at 1866(-3)(+2) Ma; and (iv) emplacement of the potassic Faber Lake rapakivi granite at 1856(-3)(+2) Ma. The arc wa s developed on the Hottah terrane due to easterly subduction of an oceanic plate under the amalgamated Slave craton - Hottah terrane. The oldest expos ed rocks in the southern part of the arc are remnants of a Paleoproterozoic platformal sequence. They were regarded previously as equivalents of the i nitial passive margin sequence on the Slave craton, but are interpreted her e as part of the Hottah terrane. The ages reported here are comparable with earlier data from the northern part of the arc, which show an age range fr om 1875 to 1840 Ma and also identify two suites of compositionally and temp orally distinct granites. The age constraints show that the Great Bear arc evolved rapidly in time from sodic through calc-alkaline, and then, with a pause, to potassic composition.