Earth and Planetary Science Letters 386 (2014) 138–148 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Ferropicrite-driven reworking of the Ungava craton and the genesis of Neoarchean pyroxene-granitoids Dejan Milidragovic ∗ , Don Francis Earth and Planetary Sciences, McGill University, 3450 University St., Montreal, QC, H3A 2A7, Canada article info abstract Article history: Received 26 February 2013 Received in revised form 30 October 2013 Accepted 31 October 2013 Available online 25 November 2013 Editor: T.M. Harrison Keywords: Neoarchean AFC ferropicrite crustal growth charnockite Voluminous, pyroxene-bearing, intermediate to felsic plutons were emplaced during a 20–50 million year long, spatially extensive Neoarchean igneous event that culminated in the cratonization of North America’s ∼500 km-wide Ungava craton. The crystallization ages of pyroxene-bearing plutons coincide with the emplacement of numerous ca. 2.72–2.70 Ga, Fe-rich, ultramafic/mafic intrusions of the Qullinaaraaluk suite (Q-suite) that are scattered across the disparate domains of the Ungava craton. A high proportion of relatively sodic pyroxene-bearing granitoids with intermediate silica contents fall in a compositional gap between the Q-suite and pyroxene-free granitoids, suggesting that the pyroxene- granitoids may be formed by the simultaneous fractional crystallization and assimilation of older tonalitic and trondhjemitic (TT) crust by the Q-suite magmas. We estimate that pyroxene-granitoids containing ∼65 wt.% SiO 2 may reflect ∼40–50 wt.% contamination of mantle-derived picritic magma by trondhjemitic melts of the pre-2.74 Ga TTG crust. The craton-wide occurrence of the Q-suite intrusions and pyroxene-granitoids suggests that underplating by ferropicritic magmas played a key role in the cratonization of the Ungava craton at the end of Archean. A major contribution of mantle-derived magmas to the petrogenesis of the ca. 2.74–2.70 Ga pyroxene-granitoids is consistent with the proposed global generation of voluminous juvenile continental crust ca. 2.7 Ga.  2013 Elsevier B.V. All rights reserved. 1. Introduction The Neoarchean Ungava craton (Fig. 1A) is a largely plu- tonic domain of the Archean Superior Province composed of the pre-2.74 Ga tonalite–trondhjemite–granodiorite (TTG), and the 2.74 Ga high-K granite–granodiorite–monzogranite (GGM) and low-K pyroxene-granitoid suites (Boily et al., 2009; Maurice et al., 2009). Most of the pyroxene-granitoids and the GGM plutons of the Ungava craton were emplaced ca. 2.74–2.70 Ga, during an episode of extensive igneous activity, increased crustal contam- ination of mafic volcanic suites, and comprehensive reworking of the Ungava craton (Maurice et al., 2009). During this same time period, numerous, small, ultramafic to mafic intrusions (lo- cally termed the Qullinaaraaluk, Couture, and Chateguay suites, herein collectively referred to as the Q-suite) were emplaced across the width of the craton (Simard, 2008). These intrusions commonly contain peridotitic cores inferred to have crystallized from Fe-rich, high-Mg basaltic to picritic parental magmas (MgO = 10–14 wt.%). In this paper, we present a geochemical model in which the voluminous pyroxene-granitoid suites of the Un- gava craton are produced by craton-wide underplating by the * Corresponding author at: Department of Earth and Planetary Sciences, McGill University, Montreal, QC, H3A 2A7, Canada. E-mail address: dejan.milidragovic@mail.mcgill.ca (D. Milidragovic). mantle-derived magmas that were parental to the Q-suite. The pyroxene-granitoids are thus the mid-crustal expression of ju- venile, mantle-derived magmatism that drove the reworking of the Northeastern Superior Province during a time of enhanced global formation of continental crust at ca. 2.7 Ga (Condie, 2000; Hawkesworth et al., 2009). 2. Plutonic rocks of the Ungava craton The relatively sodic (K/(K + Na) = 0.20 + 0.29/−0.10) TTG suites of the Ungava craton have positive Sr anomalies and steep REE profiles (Bédard, 2006; Boily et al., 2009; Bédard et al., 2013), characteristic of the majority of Archean TTGs (Martin, 1986; Moyen and Stevens, 2006; Moyen and Martin, 2012). Al- though there is a broad consensus that the geochemical signa- ture of TTGs reflects an origin through fluid-absent partial melt- ing of metabasite at pressures >1000 MPa where garnet is sta- ble as a residual mineral, there are differing views regarding the geodynamic setting of Archean TTG (Moyen and Stevens, 2006; Moyen, 2011; Moyen and Martin, 2012). The end-member models call for: 1) A high pressure (2000 MPa) origin by partial melt- ing of subducted oceanic crust, requiring geothermal gradients lower than 10 ◦ C/km; 2) a medium pressure (1000–1500 MPa) ori- gin, requiring geotherms of 10–12 ◦ C; or 3) a low pressure origin (<1000 MPa) by partial melting of overthickened oceanic crust 0012-821X/$ – see front matter  2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.epsl.2013.10.051