TECTO-127064; No of Pages 13 Tectonophysics xxx (2016) xxx–xxx Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Lithospheric strength and elastic thickness of the Barents Sea and Kara Sea region Sébastien Gac a,⁎,PeterKlitzkeb,c, Alexander Minakov a,d, Jan Inge Faleide a, Magdalena Scheck-Wenderoth b,c a Department of Geosciences, University of Oslo, 0316 Oslo, Norway b Helmholtz Centre Potsdam, GFZ, German Research Centre for Geosciences, Potsdam, Germany c RWTH Aachen University, Department of Geology, Geochemistry of Petroleum and Coal, Aachen, Germany d VISTA Program, The Norwegian Academy of Sciences and Letters, Oslo, Norway article info abstract Article history: Interpretation of tomography data indicates that the Barents Sea region has an asymmetric lithospheric structure Received 30 June 2015 characterized by a thin and hot lithosphere in the west and a thick and cold lithosphere in the east. This suggests Received in revised form 7 April 2016 that the lithosphere is stronger in the east than in the west. This asymmetric lithosphere strength structure may Accepted 14 April 2016 have a strong control on the lithosphere response to tectonic and surface processes. In this paper, we present Available online xxxx computed strength and effective elastic thickness maps of the lithosphere of the Barents Sea and Kara Sea region. Those are estimated using physical parameters from a 3D lithospheric model of the Barents Sea and Kara Sea re- Keywords: Barents Sea gion. The lithospheric strength is computed assuming a temperature-dependent ductile and brittle rheology for Rheology sediments, crust and mantle lithosphere. Results show that lithospheric strength and elastic thickness are mostly Lithosphere controlled by the lithosphere thickness. The model generally predicts much larger lithospheric strength and Strength elastic thickness for the Proterozoic parts of the East Barents Sea and Kara Sea. Locally, the thickness and lithology Effective elastic thickness of the continental crust disturb this general trend. At last, the gravitational potential energy (GPE) is computed. Ridge push Our results show that the difference in GPE between the Barents Sea and the Mid-Atlantic Ridge provides a net horizontal force large enough to cause contraction in the western and central Barents Sea. © 2016 Elsevier B.V. All rights reserved. 1. Introduction generated by the difference in gravitational potential energy between elevated areas (the Knipovich Ridge and/or Iceland margin) and the The Barents Sea and Kara Sea region is located in the North European western Barents Sea margin, has been proposed to explain these obser- Arctic. The region is characterized by a west–east structural asymmetry vations (Fejerskov et al., 2000; Doré et al., 2008). Magnetic isochron in- (Fig. 1). The western Barents Sea is a shallow sedimentary platform terpretation (Fig. 2b) indicates that the onset of the Knipovich crisscrossed by Late Paleozoic–Mesozoic narrow rift basins (Johansen spreading ridge predates the contraction of Mid-Miocene sedimentary et al., 1992; Gudlaugsson et al., 1998) whereas the eastern part is strata (Faleide et al., 2010). To test the ridge push hypothesis, the net marked by a single wide and deep Late Paleozoic basin (Johansen force provided by difference in gravitational potential energy between et al., 1992). elevated areas and passive margins has to be compared with the litho- Cenozoic deformation structures are widespread in the Barents Sea. sphere strength. The entire Barents Sea was uplifted and eroded during Neogene time. Uplift and contractional structures are the mechanical response of The western Barents Sea experienced more erosion than the eastern the lithosphere when it is exposed to external forces. The lithosphere Barents Sea and Kara Sea (Dimakis et al., 1998; Henriksen et al., 2011; mechanical response is in turn controlled by its yield strength, i.e. the Sobolev, 2012). Seismic reflection data from the northeast Atlantic amount of stress necessary to trigger anelastic deformation. Knowledge passive margins indicate that Mid-Miocene and older sediments of the lithosphere yield strength structure is therefore an important (N16–18 Ma) are locally folded and form dome structures (Vågnes element to understand the Cenozoic deformation in the Barents Sea et al., 1998; Doré et al., 2008; Anell et al., 2009; Døssing et al., 2016). region. Such contractional structures are observed in sediment layers at the The purpose of the paper is to evaluate the present-day lithospheric Vestbakken margin (Fig. 2a) located on the western margin of the Ba- yield strength and effective elastic thickness for the Barents Sea and rents Sea (Faleide et al., 1988; Gabrielsen et al., 1997). Ridge push stress, Kara Sea region. We then use the modeled lithosphere strength to evaluate the potential of a ridge push mechanism to cause contraction in the Barents Sea region. ⁎ Corresponding author at: Department of Geosciences, University of Oslo, Postboks 1047, Blindern, 0316 Oslo, Norway. In this study we use an approach similar to Tesauro et al. (2012, E-mail address: [email protected] (S. Gac). 2013) to estimate present-day lithosphere yield strength and effective http://dx.doi.org/10.1016/j.tecto.2016.04.028 0040-1951/© 2016 Elsevier B.V. All rights reserved. Please cite this article as: Gac, S., et al., Lithospheric strength and elastic thickness of the Barents Sea and Kara Sea region, Tectonophysics (2016), http://dx.doi.org/10.1016/j.tecto.2016.04.028 2 S. Gac et al. / Tectonophysics xxx (2016) xxx–xxx a) Bathymetry and topography in the North-Atlantic o o o 84 84 -30 80 o o 30o 80 80 o o 76 76 o o 72 72 o o 68 68 o o 64 64 o o 60 60 o -40o 90o -30o 80o -20o 70o -10o 60o 0o 50o 10o 40o 20o 30o -3400 -1700 -300 -100 100 200 900 Topography (m) b) Bathymetry and topography in the Barents Sea 84 o o 10o 80o 84 o 70o 20 o o 30 40o 50o 60 82 o o 82 80 o o 80 Franz North 78 Joseph Kara Sea o o Svalbard Land 78 76 Fig. 8 o o 76 Vestbakken Knipovich Ridge NW Barents Sea 74 o o 74 Barents Sea 72 o o Fig. 2 72 South 70 SW Barents Sea o o Kara Sea 70 COB Novaya Zemlya o 10o 80 East Barents Sea basin Kola-Kanin monocline Fennoscandia o 20o 70 30o 60o 40o 50o -3809 -2494 -422 -272 -193 -111 -47 -12 27 105 384 Topography (m) Fig. 1. Bathymetry–topography map of a) the North-Atlantic region (top) and b) the Barents Sea and Kara Sea region. Main structural features are represented, basins (blue) and highs (red). The locations of transects (dashed lines) crossing the Vestbakken margin (see Fig. 2) and the Barents Sea from NW to SE (see Fig. 8) are shown. The political border between Norway (West) and Russia (East) is shown (dotted line). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) elastic thickness maps. The strength is computed assuming brittle and In the following, we first summarize the geology of the Barents Sea temperature-dependent ductile rheology for the crust and mantle and Kara Sea region. Second, we describe the rheological modeling lithosphere. The present-day thermal field is steady-state. Effective elas- approach. The computation of yield strength is based on a 3D tic thickness map is computed using the modeled lithosphere strength lithosphere-scale structural model (Klitzke et al., 2015) and thermal envelope (Burov and Diament, 1995). model of the region, consistent with seismic, gravity and tomography Please cite this article as: Gac, S., et al., Lithospheric strength and elastic thickness of the Barents Sea and Kara Sea region, Tectonophysics (2016), http://dx.doi.org/10.1016/j.tecto.2016.04.028 S. Gac et al. / Tectonophysics xxx (2016) xxx–xxx 3 a) Seismic profile crossing the Vestbakken margin 0 IQ = Intra Quartenary BQ = Base Quartenary 500 ?IUP = ?Intra Upper piocene IQ IUP = Intra Upper Pliocene BQ IUP ?BP ?BP = ?Base Pliocene 1000 ?IUP ILM ILM = Intra Lower Miocene BQ IO IO = Intra Oligocene 1500 IME ILO = Intra Lower Oligocene BO = Base Oligocene IME = Intra Mid Eocene depth (m) 2000 LME = Lower Mid Eocene 2500 LME 3000 3500 1600 1800 2000 2200 2400 2600 distance (km) b) Plate reconstruction of the Western Barents Sea margin from Oligocene to Present-day Chron 13 Chron 6 Chron 5 Present (0 Ma) (34 Ma - earliest Oligocene) (19 Ma - early Miocene) (10 ma - mid-late Miocene) modified from Faleide et al. (2010) Fig. 2. Seismic profile BV-04-86 (modified from Eidvin et al., 1988) crossing the Vestbakken margin (see Fig. 1 for location of the profile). The figure shows a) an interpretation of the migrated seismic profile. Mid-Miocene and older sediment layers are folded and b) a kinematic plate reconstruction of the western Barents Sea margin from Early Oligocene to Present-day (modified from Faleide et al., 2010). The reconstruction indicates that the Knipovich Ridge was established in early Oligocene. Additional time was needed to develop a prominent ridge complex sitting above the abyssal plain giving rise to a ridge push force. data (Klitzke et al., in press). We present a rheological model of the Ba- also constitutes the basement of the east Barents Sea basin. This inter- rents Sea–Kara Sea region and we identify trends in the lithosphere pretation is also supported by the 3D magnetic and gravity modeling strength structure of the region. We compute the gravitational potential of Marello et al. (2013). Their model suggests that parts of the east Ba- energy (GPE) of the region using two methods: double depth integral of rents Sea and Pechora Basin basement rocks have similar properties density distribution in the 3D lithospheric model of the Barents Sea and hence, lithologies: mainly island arc and oceanic basalts.