Wilson cycle passive margins: Control of orogenic inheritance on continental breakup Kenni D. Petersen a, ⁎, Christian Schiffer a,b a Department of Geoscience, Aarhus University, 8000 Aarhus, Denmark b Department of Earth Sciences, Durham University, Durham DH1 3LE, United Kingdom abstract article info Article history: Received 1 March 2016 Received in revised form 9 June 2016 Accepted 19 June 2016 Available online 08 August 2016 Handling Editor: F. Pirajno Rifts and passive margins often develop along old suture zones where colliding continents merged during earlier phases of the Wilson cycle. For example, the North Atlantic formed after continental break-up along sutures formed during the Caledonian and Variscan orogenies. Even though such tectonic inheritance is generally appreciated, causative physical mechanisms that affect the localization and evolution of rifts and passive margins are not well understood. We use thermo-mechanical modeling to assess the role of orogenic structures during rifting and continental breakup. Such inherited structures include: 1) Thickened crust, 2) eclogitized oceanic crust emplaced in the mantle lithosphere, and 3) mantle wedge of hydrated peridotite (serpentinite). Our models indicate that the presence of inherited structures not only defines the location of rifting upon extension, but also imposes a control on their structural and magmatic evolution. For example, rifts developing in thin initial crust can preserve large amounts of orogenic serpentinite. This facilitates rapid continental breakup, exhumation of hydrated mantle prior to the onset of magmatism. On the contrary, rifts in thicker crust develop more focused thinning in the mantle lithosphere rather than in the crust, and continental breakup is therefore preceded by magmatism. This implies that whether passive margins become magma-poor or magma-rich, respectively, is a function of pre-rift orogenic properties. The models show that structures of orogenic eclogite and hydrated mantle are partially preserved during rifting and are emplaced either at the base of the thinned crust or within the lithospheric mantle as dipping structures. The former provides an alternative interpretation of numerous observations of ‘lower crustal bodies’ which are often regarded as igneous bodies. The latter is consistent with dipping sub-Moho reflectors often observed in passive margins. © 2016 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. Keywords: Wilson Cycle Passive Margins Magmatism Serpentinite Hyperextension Thermo-mechanical modeling 1. Introduction Passive margins form the transition between oceanic and continen- tal lithosphere and are the result of rifting and continental break-up. These processes represent one phase of the Wilson cycle (Wilson, 1966; Dewey and Spall, 1975) where continents recurrently disinte- grate and reassemble and oceanic crust and lithosphere form, subduct and recycle, a process that is likely to have been ongoing for around 3 Ga (Cawood, 2006; Shirey and Richardson, 2011). The present-day margins of the Central and North Atlantic are a manifestation of at least two complete Wilson cycles: The supercontinent of Rodinia was assembled at the end of the Mesoproterozoic Grenvillian orogeny (Piper, 2000; Thomas, 2006), which after break-up was divided by the newly forming Iapetus Ocean. The closure of the Iapetus Ocean leads to the Paleozoic Caledonian–Acadian orogeny in the North Atlantic region. This continent–continent collision involved the continents Laurentia, Baltica, Avalonia and further smaller continental fragments and terranes (Van Staal et al., 1998; Leslie et al., 2008) and formed a co- herent, Himalaya-type mountain range of at least 3000 km length and 1000 km width (Roberts, 2003; Gee et al., 2008). The subsequent Late Paleozoic Variscan orogeny assembled large parts of present day Central and Southern Europe partly overprinting the Caledonian Orogen in the Appalachians (Stamfli and Kozur, 2006). Most recently, Mesozoic and Cenozoic rifting caused the breakup of the supercontinent Pangea and the formation of the North Atlantic and passive margins (Skogseid et al., 2000). Remnant structures and lineaments of earlier mountain-building events are generally strike-parallel and mimic the present-day North Atlantic margins, implying ancestral control of the older orogens (Williams, 1995 and references therein). In a recent review by Buiter and Torsvik (2014) it is concluded that continental breakup generally occurs along former collision zones irrespective of their age. In another recent paper, Schiffer et al. (2015b) demonstrated that the plate tectonic Gondwana Research 39 (2016) 131–144 ⁎ Corresponding author. E-mail address: kenni@geo.au.dk (K.D. Petersen). http://dx.doi.org/10.1016/j.gr.2016.06.012 1342-937X/© 2016 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr