Geophysical-petrological modelling of the East Greenland Caledonides – Isostatic support from crust and upper mantle Christian Schiffer a,c, ⁎, Niels Balling a , Jörg Ebbing b , Bo Holm Jacobsen a , Søren Bom Nielsen a a Department of Geoscience, Aarhus University, Høegh-Guldbergs gade 2, DK-8000 Aarhus C, Denmark b Department of Geoscience, Christian-Albrechts-University Kiel, Otto-Hahn-Platz 1, D-24118 Kiel, Germany c Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, UK abstract article info Article history: Received 16 January 2016 Received in revised form 13 May 2016 Accepted 18 June 2016 Available online xxxx Teleseismic receiver function analysis imaged a complex upper mantle structure in the Central Fjord Region of East Greenland, including an east-dipping high velocity layer and a mantle wedge of high crustal or low mantle velocities. This was interpreted as a fossil Caledonian subduction complex, including a slab of eclogitised mafic crust and an overlying wedge of serpentinised mantle. In this paper, we use a multi-disciplinary geophysical and petrological modelling approach to test this proposed fossil subduction model. The consistency of the obtained velocity model with the regional gravity field is tested by forward density modelling and isostatic calculations. The models show that the sub-crustal structure, given by the more buoyant mantle wedge and the dipping high velocity/density layer, yield in a markedly better fit as compared to a homogeneous mantle lithosphere. Petrological-geophysical modelling is performed by testing different upper mantle compositions with regard to topography, gravity and seismic velocities using Litmod2D. This suggests that the observed lower crustal/ uppermost mantle bodies could be a combination of mafic intrusions, serpentinised peridotite and metamor- phosed mafic crust. The preferred composition for the dipping structure is eclogitised mafic crust, and hydrated peridotite filling the overlying mantle wedge. Models lacking an eclogite layer or a hydrated upper mantle composition show an inferior fit and, therefore, are not favoured representatives. This supports the interpretation as a fossil subduction zone complex. The spatial relations with Caledonian structures suggest an early Caledonian origin. © 2016 Elsevier B.V. All rights reserved. Keywords: Geophysical-petrological modelling Gravity-isostatic modelling Fossil subduction East Greenland Caledonides 1. Introduction The North Atlantic Realm (NAR) experienced a number of major tectonic events during the past 500 Ma which shaped the present-day topographic and crustal and upper mantle structure of the North Atlantic passive margins. While the general geodynamic evolution is known, various issues are still a matter of discussion. This applies to details of accretionary events associated with the Palaeozoic Caledonian orogeny, deep processes in the mantle related to the formation of the North Atlantic Igneous Province and the present-day state of isostasy of the high topography along the magma-rich passive margins of East Greenland and Scandinavia. Recently, it has been suggested that remnants of an early Caledonian east-dipping subduction zone are entrained in the lithosphere of the Central Fjord (CF) region of East Greenland (Schiffer et al., 2014, 2015a). Teleseismic receiver functions of the CF array indicate eclogitised mafic crust in the dipping layer and an overlying serpentinised mantle wedge. This structure could be part of a once contiguous eastward dip- ping Caledonian (or older) subduction zone along the eastern margin of Laurentia, connected with the so-called “Flannan reflector”, offshore northern Scotland (Smythe et al., 1982; Snyder and Flack, 1990; Warner et al., 1996) that shows very similar geometrical and geophysical properties (Schiffer et al., 2015b). In this study, we will substantiate the interpretation of a fossil subduction zone in East Greenland, by a detailed multi-disciplinary approach, including density, isostatic and petrological modelling. In particular, we will quantitatively differentiate between a set of selected end-member models that include a fossil subduction setting and alter- native geometries and compositions. 2. Geological setting The geological and topographic expression of the North Atlantic Realm (NAR) is considered to be mainly shaped during the past 500 Ma, with the Palaeozoic Caledonian orogeny (circa 425 Ma), rifting, continental break-up accompanied by an extreme magmatic outburst Tectonophysics xxx (2016) xxx–xxx ⁎ Corresponding author at: Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, UK. E-mail address: christian.schiffer@zoho.com (C. Schiffer). TECTO-127161; No of Pages 14 http://dx.doi.org/10.1016/j.tecto.2016.06.023 0040-1951/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Please cite this article as: Schiffer, C., et al., Geophysical-petrological modelling of the East Greenland Caledonides – Isostatic support from crust and upper mantle, Tectonophysics (2016), http://dx.doi.org/10.1016/j.tecto.2016.06.023