1. Colloquium Prague, April, 2005 1 A Numerical Approach to Model the Accretion of Icelandic Crust Gabriele Marquart and Harro Schmeling

2. Colloquium Prague, April, 2005 2 Bathymetry in the North Atlantic

3. Colloquium Prague, April, 20053 Observations of crustal thickness

4. Colloquium Prague, April, 2005 4 Thickness of the Icelandic crust from Gravity and seismic Data Darbyshire,2000

5. Colloquium Prague, April, 20055 Crust is simply related to extracted melt 1. Model 1 cm/a Streamlines Melting rate Extraction

6. Colloquium Prague, April, 2005 6 Numerical Model of a Rising Plume with Melting Anomalous temperature Melt production rate melting 120 - 60 km depth Melting zone Rising velocity ( T. Ruedas )

7. Colloquium Prague, April, 2005 7 Predictions for crustal thickness T excess = 350 K (1%) T excess = 250 K ( 0.1%) T excess = 250 K (1%) T excess = 250 K (3%) T excess = 150 K (1%)

8. Colloquium Prague, April, 2005 8 Comparison to „observation“ Model crust Darbyshire

9. Colloquium Prague, April, 2005 9 Extrated material is fed back into the model Width of emplacement zone 50 km (Gauß) 1 cm/a Streamlines Melting rate 2. Model

10. Colloquium Prague, April, 2005 10 Kinematic model of Palmason, 1980

11. Colloquium Prague, April, 2005 11 Iceland Surface Tectonic Features

12. Colloquium Prague, April, 2005 12 Structure of the Crust in Iceland Seismic findings: - Distinct upper crust 5-10 km thick - Seismically fast lower crust down to 24-50 km - Poorly constrained transition to the mantle

13. Colloquium Prague, April, 2005 13 Crustal Structure from receiver functions Receiver functions Low Vp-velocities (  10%) beneath 40 km Schlindwein, 2001

14. Colloquium Prague, April, 200514 The model concept for crustal accretion Extrusives fissures, magma chambers deep dykes and sills Underplating

15. Colloquium Prague, April, 200515 1 cm/a Streamlines Melting rate Extraction Extracted melts are emplaced in a separate crustal model (with contstant rate...) 3. Model

16. Colloquium Prague, April, 2005 16 Modeling Crustal Accretion - Equations Energy conservation: Momentum conservation: Mass conservation: Physical Equations Source Functions

17. Colloquium Prague, April, 200517 Model assumptions ► 2D ► Constant viscosity ► Total accretion rate  2 cm/s spreading rate ►  T of surface lavas: 100 K ►  T of magma chambers: 600 K ►  T deep dykes: 300 K ► 3 models: 1) Dominated (60%) by deep accretion 2) Dominated (60%) by magma chamber accretion 3) Dominated (60%) by shallow accretion

18. Colloquium Prague, April, 2005 18 Visualization of the Accretion of Crust Accretion is traced by markers New markers are inserted at each time step Color indicates the source Number of markers is according to the strength of the source Markers are followed up for 10 Ma, after 1Ma the color is changed Marker positions are determined by a RK-4 th order scheme after 500 time steps

19. Colloquium Prague, April, 2005 19 Accretion dominated by deep dykes (60% M tot )

20. Colloquium Prague, April, 2005 20 Accretion dominated by magma chambers (60% M tot )

21. Colloquium Prague, April, 2005 21 Accretion dominated by surface lavas (60% M tot )

22. Colloquium Prague, April, 2005 22 Comparison of Different Accretion Styles Deep dykes Lava flows Magma chamber -Uniformly stratified hot crust (Gabbro, mantle mix?) - thin seismogenic zone - lateral variable crust - upper crust thinning in central region - hot in central region - vertical layering of the middle crust - cold crust - hot only in central region - downbuildung, with tilted layering

23. Colloquium Prague, April, 200523 Krustenstruktur aus Seismik Crustal structure at the rift axis

24. Colloquium Prague, April, 2005 24 Location of profiles Comparison of Different Accretion Types Deep Dykes Temperature Vertical velocity Horizontal velocity Magma Chamber Temperature Vertical velocity Horizontal velocity Surface Lavas Temperature Vertical velocity Horizontal velocity 40 C/km 20 C/km30 C/km

25. Colloquium Prague, April, 2005 25 Comparison to the Seismogenic Crust in Iceland Lava flowsDeep dykesMagma Chamber 5 km 10 km Depth: 20 km South Iceland Seismic zone Stefanson, 1998 Riftzone 50 km0 km 20 km 10 km 5 km 20 km 10 km ~ 500°C

26. Colloquium Prague, April, 2005 26 Location of profiles Comparison of Different Accretion Types Deep Dykes Temperature Vertical velocity Horizontal velocity Magma Chamber Temperature Vertical velocity Horizontal velocity Surface Lavas Temperature Vertical velocity Horizontal velocity 40 C/km 20 C/km30 C/km -Strong vertical and differential horizontal velocities

27. Colloquium Prague, April, 2005 27 Seismic Azimuthal Anisotropy from Rayleigh waves Li & Detrick, EPSL2003 20-40 km50-80 km

28. Colloquium Prague, April, 200528 ► Thermal & geometric structure depends strongly on accretional mode ► Iceland: shallow seismogenic zone, high thermal gradient suggests deep or intermediate accretion (deep dykes and magma chambers) as the dominating process (However, (However, the seismogenic upper crust of 10-15 km is produced by shallow fissure swarm intrusions and subairial lava flows) ► Then only moderate differential velocities and mixing of the different accretion zones Preliminary Findings for the Accreton of Crust on Iceland