Can the North Sea lower crustal body be explained by inherited subduction wedge petrology? Christine Fichler Tore Odinsen Håkon Rueslåtten Jens Emil Vindstad Susann Wienecke Odleiv Olesen 1 - Classification: Internal 2010-05-28 The content of this presentation is submitted to Tectonophysics for publication
Aim reveal inherited crustal structures in the northern North Sea Barents Sea Contents North Sea basement & tectonic history island arcs Norwegian Sea serpentinites & meta-peridotites Gravity and magnetic modelling North Sea Discussion & conclusions USGS 2 - Classification: Internal 2010-05-28
Basement information: Onshore: Ramberg et al, 2007 Petrology *** new * * Slagstad et al., in prep. from Olesen et al, 2006 ( KONTIKI, NGU) **Donato and Tully, 1986 ***NPD s Millenium atlas Granitoids *** ** * new 3 - Classification: Internal 2010-05-28
Tectonic history: 440 Ma 430 Ma 420 Ma future North Sea crust Ramberg et al., 2007 4 - Classification: Internal 2010-05-28
Island Arc petrology granitoids tholeitic / alkaline magmas Serpentinite mafic (basaltic/gabbroic) oceanic crust peridotite Fryer, P., Mud volcanoes of the Marianas, Scientific American, Feb. 1992, 46-52, 1992. 5 - Classification: Internal 2010-05-28
Island Arc petrology granitoids tholeitic / alkaline magmas 40 km 100 km Serpentinite mafic (basaltic/gabbroic) oceanic crust peridotite Fryer, P., Mud volcanoes of the Marianas, Scientific American, Feb. 1992, 46-52, 1992. 6 - Classification: Internal 2010-05-28
serp. serp. Keary and Wine, 1996. 7 - Classification: Internal 2010-05-28
Possible collision belt analog : Northern Central Africa Alpine Rif Belt (Morocco) Guiraud et al., 2005; Chalouan, A., Michard, A., 2004 Serpentinites 8 - Classification: Internal 2010-05-28
440 Ma S S S serpentinite 430 Ma S S 420 Ma S S S future North Sea crust Ramberg et al., 2007 What happens to the serpentinite during orogeny & rifting? 9 - Classification: Internal 2010-05-28
Prograde metamorphism of serpentinites (meta peridotites) Serpentinite peridotite + water + talcum - stable at low temperature up to high pressures - volume reduction of up to 30 % Temperature ( o C) Seibold and Schilling, 2003. 10 - Classification: Internal 2010-05-28
Prograde metamorphism of serpentinites (meta peridotites) Serpentinite peridotite + water + talcum - stable at low temperature up to high pressures 15 o C/km - volume reduction of up to 30 % 50 o C/km Temperature ( o C) Seibold and Schilling, 2003. 11 - Classification: Internal 2010-05-28
Example: Precambrian meta-peridotites in the Western Gneiss Region (Almkløvdalen ultramafic body) Kostenko et al., 2002. 12 - Classification: Internal 2010-05-28
Melange of different ultramafic petrologies Gravity model Kostenko et al., 2002. 13 - Classification: Internal 2010-05-28 Grønlie and Rost, 1974
PERIDOTITE Densities decreasing density with serpentinisation Susceptibilities increasing susceptibility Valid for both serpentinisation and deserpentinisation (e.g., Clark, 1995 for susceptibilities) SERPENTINITE Miller and Christensen, 1997 Escartin et al., 2001 14 - Classification: Internal 2010-05-28
MAGNETIC TMI (Verhoef et al. 1995) FREE AIR satellite gravity (GETECH reprocessed) 15 - Classification: Internal 2010-05-28
NSDP84-1 Christiansson et al., 2000. Christiansen et al., 2000. 16 - Classification: Internal 2010-05-28
modelled observed 2.82 g/cm3 Density 3.25 2.95 2601 µcgs 17 - Classification: Internal 2010-05-28 Susceptibility
modelled observed Far too coarse topography low density & low magnetic uppermost crust deeper layer(s) with different densities and magn. attributes needed 2.82 g/cm3 Density 3.25 2.95 2601 µcgs 18 - Classification: Internal 2010-05-28 Susceptibility
antikorrelation antikorrelation + + + + + + - + - + 2.82 g/cm3 Density 3.25 2.95 2601 µcgs 19 - Classification: Internal 2010-05-28 Susceptibility
D=2.65 D=2.814 D=2.814 High Low D=Density[g/cm 3 ] 20 - Classification: Internal 2010-05-28
D=2.65 S=300 D=2.814 D=2.814 S=0 High Low S=Susceptibility [µcgs] 21 - Classification: Internal 2010-05-28
D=2.65 S=300 D=2.814 D=2.814 Low density High susceptibility S=0 Intermediate density zero susceptibility 22 - Classification: Internal 2010-05-28
2.65, 400 2.88, 4400 2.65, 10000 2.67, 0 2.89, 0 3.18, 0 2.7, 600 2.75, 500 23 - Classification: Internal 2010-05-28 3.28, 0 Density (g/cm 3 ), susceptibility (µcgs) 2.95, 0
island arc crust (granitoid) cont.crust, intrusive serpentinite meta peridotite? 24 - Classification: Internal 2010-05-28 HP high pressure UHP ultra high pressure sediments metasediments gneiss Continental crust mantle gneiss
MAGNETIC TMI GETECH FREE AIR satellite gravity 64 km Periodicity of 50-100 km observed along oceanic Arc magmatism 25 - Classification: Internal 2010-05-28
Multilevel detachments (Odinsen, 2000) D1 D2 D3 - may be explained by serpentinite & meta-serpentinites - relevant for the discussion of decoupled upper and lower crustal extension island arc crust (granitoid) continental crust Serpentinite meta intrusive peridotite? mantle sediments metasediments D2 D2 level on top of serpentinite gneiss gneiss 26 - Classification: Internal 2010-05-28
Crustal thinning by metamorphisation of serpentinite will effect the Beta factor island arc crust (granitoid) continental crust Serpentinite meta intrusive peridotite? mantle HP melange* sediments metasediments gneiss continental crust UHP melange* Stratigraphically modelled Moho ( Odinsen et al., 2000) very similar to an Airy isostatic model 27 - Classification: Internal 2010-05-28
Conclusions 1. Large amounts of serpentinites are produced in forearc subduction mantle wedges and gathered during later collision. 2. Serpentinites survive in high pressure, low temperature environments (Caledonian orogeny). 3. Increased heatflow by later rifting will cause transition to meta peridotites. 4. Serpentinites and meta-peridotites have been detected by gravity & magnetic modelling along the NSDP 84-1 deep seismic line. 5. Geological consequences may include multilevel detachments, decoupled extension and biassed Beta factors. 28 - Classification: Internal 2010-05-28
Thank You for your attention! crystalline crust Acknowledgements: Statoil colleaques, especially Eli Aamot, Cato Wille, Martin Hovland and Erik Lundin Hans Konrad Johnsen Monte Swan Stan Keith Søren Naumann Statoil for allowing us to give this presentation. 29 - Classification: Internal 2010-05-28