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

Abstract

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 Paleoproterozoic 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) abundant calc-alkaline felsic volcanism and subvolcanic intrusions during the period 1870–1866 Ma, bracketed by five ages; (iii) intrusion of large calc-alkaline granitic plutons, including the Marian River batholith, dated by zircon and titanite from two samples at 1866 +2–3 Ma; and (iv) emplacement of the potassic Faber Lake rapakivi granite at 1856 +2–3 Ma. The arc was developed on the Hottah terrane due to easterly subduction of an oceanic plate under the amalgamated Slave craton – Hottah terrane. The oldest exposed rocks in the southern part of the arc are remnants of a Paleoproterozoic platformal sequence. They were regarded previously as equivalents of the initial passive margin sequence on the Slave craton, but are interpreted here 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 from 1875 to 1840 Ma and also identify two suites of compositionally and temporally 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.

Chronostratigraphy of the Hottah terrane and Great Bear magmatic zone of Wopmay Orogen, Canada, and exploration of a terrane translation model

“…2), to help resolve stratigraphic challenges that arose during bedrock mapping and to assess the temporal and petrological evolution of the Hottah terrane -Great Bear magmatic zone transition. The new and previously published data (Hildebrand et al 1983;Bowring 1984;Reichenbach 1991;Gandhi et al 2001;Bennett and Rivers 2006a) allow the construction of a time-constrained stratigraphic column that records the transition from Hottah terrane to Great Bear magmatic zone tectonics. Such constraints are needed to further evaluate the proposed models for the evolution of Wopmay Orogen.…”

“…Screens of volcanic rocks that range from andesite to trachyandesite to rhyolite are preserved in a sea of younger plutons that only rarely contain penetrative deformation fabrics. These plutonic rocks range in composition from gabbro to syenogranite, although they are predominantly monzonitic to monzogranitic (e.g., Fraser et al 1972;Badham 1973;Hildebrand et al 1987bHildebrand et al , 2010bGandhi 1994;Gandhi et al 2001;Ootes et al 2013).…”

“…Age determinations are in Ma (±2 uncertainty); Great Bear plutonic ages are not shown. Previously reported ages are italicized and from Bowring (1984), Reichenbach (1991), Gandhi et al (2001), and Bennett and Rivers (2006a). The detrital zircon (DZ) maximum depositional ages for the Holly Lake metamorphic complex are from Davis et al (2015), and the Treasure Lake Group are from Gandhi and van Breemen (2005) and Bennett and Rivers (2006b).…”

“…3F-3G) were erupted onto and intruded into the older Hottah terrane stratigraphy and dominate the bedrock exposures west of the Wopmay fault zone (Figs. 1, 2;Bowring 1984;Gandhi et al 2001;Hildebrand et al 2010b). Screens of volcanic rocks that range from andesite to trachyandesite to rhyolite are preserved in a sea of younger plutons that only rarely contain penetrative deformation fabrics.…”

“…West of Wopmay fault zone are the remnants of the >1.9 Ga Hottah terrane, which was extensively overprinted by ca. 1.875-1.85 Ga Great Bear magmatism (e.g., Fraser et al 1972;Badham 1973;Bowring 1984;Gandhi et al 2001;Hildebrand et al 2010b). Northeast-striking brittle faults dextrally offset all units and are transected by the ca.…”