Nueltin granites and mafic rocks in the Tebesjuak Lake map area, Nunavut: new geochronological, petrological, and geophysical data

Abstract

We report new and refined legacy data on 1.77 to 1.74 Ga gabbros, basalts, and granites (Kivalliq Igneous Suite) in the Tebesjuak Lake map area (NTS 65-O). Uranium-lead (baddeleyite) ages for a coarse alkali gabbro at Mallery Lake (1769 ± 6 Ma) and for a subalkaline gabbro at the southwest-ern end of the McRae Lake dyke (1753.6 ± 1.2 Ma) were determined. Uranium-lead (zircon) ages of 1752.6 ± 4.1 Ma and 1746.7 ± 4.3 Ma were obtained for the Pamiutuq granite intrusion and a quartz-feldspar porphyry dyke, respectively. Gravimetric/magnetic modelling of the Mallery complex is con-sistent with a gabbroic ring dyke about 8 km in diameter and 1 km tall surrounding a granite core, with an underlying mafic sill or intrusive complex. Petrographic and geochemical data support a petrogenetic link between the Mallery gabbro, a coarse anorthosite body (Fish intrusion), and basaltic lavas in the map area, all of alkali basalt composition. These data indicate the presence of bimodal volcanism near the base of the Pitz Formation, and establish the oldest age of Kivalliq anorogenic igneous activity at ca. 1.77 Ga.

The Kivalliq Igneous Suite: Anorogenic bimodal magmatism at 1.75Ga in the western Churchill Province, Canada

“…A second magnetic anomaly ring in the map area lies at the end of an elongate rapakivi granite intrusion, but mafic rocks are not exposed at the surface. The Mallery Gabbro has been dated at 1769 ± 6 Ma (U-Pb baddeleyite; Peterson et al, 2014Peterson et al, , 2015 and is the oldest known body assigned to the KIS. The main phase is a coarse rock dominated by clinopyroxene phenocrysts (extensively replaced by amphibole) in an intercumulate matrix of plagioclase, amphibole, apatite, and magnetite.…”

“…The high-Nb Mallery Gabbro, Fish Intrusion, and one lava (all from NTS65O) are somewhat more enriched, and close in composition (ε Nd(1.75 Ga) = −3.98, −3.76, and −4.83, respectively). The lava (79LAAT-287) is interpreted as sourced from an extension of the Fish intrusion, and the Nd isotope Peterson et al (2015), and this paper (Table 3). data are consistent with the correlation made between these three samples on the basis of petrography and field relations.…”

The Contact uranium prospect, Kiggavik project, Nunavut (Canada): Tectonic history, structural constraints and timing of mineralization

“…The Archean to Paleoproterozoic rocks where intruded by felsic to mafic rocks of the late syn-orogenic Trans-Hudsonian suite and ca. 1750 Ma rapakivi-style Nueltin granite of the anorogenic Kivalliq igneous suite (Hoffman 1988;van Breemen et al, 2005;Peterson et al, 2015b;c.f., Scott et al, 2015). The age of the Thelon Formation is thus bracketed by the age of emplacement of the Nueltin granite suite, ca.…”

“…As observed on drillcores, the QB cross-cuts Hudson and Nueltin granites dated ca. 1750 Ma (Peterson et al, 2015b), and on outcrops, the QB is covered by the Thelon Formation, thus bracketing the brecciation / silicification event between 1750 Ma and 1667 Ma.…”

“…This age was obtained in several studies throughout the Western-Churchill province (Turner et al, 2003;Bridge et al, 2013;Gandhi et al, 2013;Dieng et al, 2013;Sheahan et al, 2015) and is possibly linked to a regional thermal event possibly reflecting a craton-scale process. If this thermal event has reset the U-Pb isotopic system (Davis et al, 2011;Peterson et al, 2015b), then the ages of the first stage of faulting and mineralization could be bracketed between ca. 1667 Ma and 1420 Ma; although this remains speculative to date.…”