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

The Kivalliq Igneous Suite (1.77-1.73 Ga) includes the Nueltin Granite intrusions; gabbro and anorthosite intrusions; three swarms of mafic dykes; and basalt, rhyolite and pyroclastic rocks of the Pitz Formation (Wharton Group, middle Dubawnt Supergroup). It was emplaced in the reworked Archaean hinterland of the trans-Hudson orogen, in the central western Churchill Province (WCP) of the Canadian Shield. The Nueltin granites have field relations, mineral assemblages, and compositions typical of metaluminous to peraluminous, Proterozoic to Recent rapakivi granites, and the suite comprises a classic bimodal anorogenic province. Kivalliq rhyolites/granites were erupted/emplaced in a N-S band (the Nueltin corridor) about 700 km long and 300 km wide, with volcanic rocks and dykes concentrated at the north end and coarse plutonic rocks to the south. The McRae Lake dyke swarm originates among three prominent gabbro/anorthosite intrusions inside the corridor, and forms a narrow array extending a minimum of 600 km to the NE along the central axis of the WCP. Early mafic rocks (intrusions and some lavas, 1.77 Ga) had an alkali basalt parent, with subalkaline basalts (sills, dykes, and mafic enclaves) present at the peak time of granite emplacement (1.75 Ga). Average initial epsilon(Nd) of basaltic rocks at 1.75 Ga is -4.0, indicating a significant crustal component. Sm-Nd depleted mantle model ages of granites and rhyolites (average initial epsilon(Nd) = -8.7) range from 2.2 to 3 Ga, consistent with melted Archaean crust variably mixed with juvenile basalt. Metallogenic prospects of the Kivalliq Suite include U-Th-Zr-Y-REE enriched granite and syenite, epithermal Ag/Au at silicic centres (including mafic/felsic ring complexes), and Pb-Cu sulphides associated with mafic intrusions. Topaz rhyolites are present, but Sn-enriched rocks have not been observed. The Kivalliq Suite is one of about 15 prominent anorogenic provinces and dyke swarms which erupted within the Nuna supercontinent at ca. 1.75 Ga, and the thermal effects of the Kivalliq event are recorded in U-Pb and K-Ar data throughout most of the western Churchill Province. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.