Precambrian Research 177 (2010) 199–211 Contents lists available at ScienceDirect Precambrian Research journal homepage: www.elsevier.com/locate/precamres Quantifying rates of dome-and-keel formation in the Barberton granitoid-greenstone belt, South Africa Cristiano Lana a,∗ , Eric Tohver b , Peter Cawood b a Department of Geology, Geography and Environmental Studies, Stellenbosch University, Cnr Ryneveld and Merriman Streets, Geology Building, Private Bag XI, Matieland 7602, Stellenbosch, WC, South Africa b School of Earth and Geographical Sciences, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia article info Article history: Received 24 October 2008 Received in revised form 20 November 2009 Accepted 3 December 2009 Keywords: Dome-and-keel Barberton Archean tectonics Greenstone belt Core-complex abstract The Barberton granitoid-greenstone belt is a classic dome-and-keel province, characterized by kilometer- scale gneiss domes and elongate keels of largely folded supracrustal rocks. Combined U–Pb SHRIMP data and structural mapping demonstrate that the geometry of the Barberton belt reflects events that occurred over ∼30 million year interval, from ca. 3230 and 3203 Ma. Early deformation with NW–SE shortening in the upper crust was accompanied by emplacement of tonalite-trondhjemite-granodiorite TTG magmas at 3234 ± 12 and 3226 ± 9 Ma. Much of the structural grain of the greenstone belt relates to a long episode of post-orogenic extension, with NE-directed extension in the lower crust leading to exhumation of high-grade gneisses in the southern Barberton terrane. Advective heat transfer during emplacement of kilometer-scale (TTG) plutons around the margins of the greenstone belt facilitated the infolding of the relatively denser and colder greenstone sequence. The end of this tectonic cycle is punctuated by the emplacement of the undeformed, 3203 ± 7 Ma Dalmein pluton, which sharply truncates not only anticlines and synclines in the greenstone belt but also the dominant fabric in the high-grade gneisses. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The Archean Barberton granite-greenstone belt in the Mpumalanga Province of South Africa (Fig. 1) is a classic dome- and-keel province that has featured in many debates over the role of vertical vs. horizontal tectonics in the Archean (Visser, 1956; Anhaeusser, 1969, 1984, 2001; Anhaeusser et al., 1981; De Wit et al., 1992; De Wit, 1998; Van Kranendonk et al., 2009). The geometry of the belt has been attributed to overturn of an inverted crustal density profile, in which vertical movement of the granitoid-gneiss domes was triggered primarily by magmatic processes in the mid- to upper-crusts (Viljoen and Viljoen, 1969; Anhaeusser et al., 1981; Jackson and Robertson, 1983; Van Kranendonk et al., 2009). This emphasis on vertical motion follows from the supposition that heat flows were 2–6 times higher in the Archean compared to modern environments, due to both the retention of primordial heat and higher radioactivity of ancient crust (e.g., Lambert, 1976). Other workers maintain that the dome-and-keel geometry reflects a more conventional tectonic regime dominated by horizontal motions during a major collisional event at 3230 Ma (e.g., De Wit et al., 1992; De Ronde and De Wit, 1994; Lowe, 1994; Schoene et al., 2008, 2009). In this interpretation, the steep structural fabrics ∗ Corresponding author. Tel.: +27 21 808 4820; fax: +27 21 808 3129. E-mail address: lana@sun.ac.za (C. Lana). are the result of refolding of the greenstone sequences around rigid granitoid ramparts during progressive shortening (e.g., De Wit, 1983, 1998; De Wit et al., 1992; De Ronde and De Wit, 1994; Lowe, 1994, 1999; Lowe et al., 1999; De Ronde and Kamo, 2000). A number of recent structural studies provide evidence that the granitoid-gneiss domes in the southern part of the belt were exhumed along a low-angle detachment surface (Figs. 1 and 2), fol- lowing the main orogenic phase. These studies focus on the high-P and low-T metamorphic assemblages found in association with the granitoids, which suggest exhumation from depths of 30–50 km. (Kisters et al., 2003; Diener et al., 2005; Moyen et al., 2006; Schoene et al., 2008; Lana et al., 2010). The relatively low strain intensi- ties and low apparent geotherms (<15–20 ◦ C/km) recorded in the high-grade rocks in this portion of the belt point to the presence of cold and rigid continental blocks that could, at least temporarily, sustain significant crustal stacking and overthickening (e.g., Diener et al., 2005; Lana et al., 2010). However, while the new kinematic and metamorphic data from the Barberton belt are consistent with a core-complex scenario, geochronological constraints to illus- trate the correct sequence of events are lacking. Consequently, the processes that shaped the geometry of the granitoid-greenstone belt have not been integrated with an accurate chronology of events. This study presents new SHRIMP ages of key structural/ magmatic events that elucidate the formation of the dome-and- keel geometry in the Barberton belt. The new dataset provides 0301-9268/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.precamres.2009.12.001