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A Numerical Approach to Model the Accretion of Icelandic Crust

A Numerical Approach to Model the Accretion of Icelandic Crust. Gabriele Marquart and Harro Schmeling. Bathymetry in the North Atlantic. Observations of crustal thickness. Darbyshire,2000. Thickness of the Icelandic crust from Gravity and seismic Data. Extraction. 1 cm/a. 1 cm/a.

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A Numerical Approach to Model the Accretion of Icelandic Crust

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

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

  3. Observations of crustal thickness Colloquium Prague, April, 2005

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

  5. Extraction 1 cm/a 1 cm/a Streamlines Melting rate 1. Model Crust is simply related to extracted melt Colloquium Prague, April, 2005

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

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

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

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

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

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

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

  14. The model concept for crustal accretion • Extrusives • fissures, magma chambers • deep dykes and sills • Underplating Colloquium Prague, April, 2005

  15. 1 cm/a 1 cm/a Streamlines Melting rate 3. Model Extracted melts are emplaced in a separate crustal model (with contstant rate...) Extraction Colloquium Prague, April, 2005

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

  17. 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 Colloquium Prague, April, 2005

  18. Visualization of the Accretion of Crust after 500 time steps • 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-4th order scheme Colloquium Prague, April, 2005

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

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

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

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

  23. Crustal structure at the rift axis Krustenstruktur aus Seismik Colloquium Prague, April, 2005

  24. Magma Chamber Deep Dykes Surface Lavas Temperature Temperature Temperature 40 C/km 30 C/km 20 C/km Location of profiles Horizontal velocity Horizontal velocity Horizontal velocity Vertical velocity Vertical velocity Vertical velocity Comparison of Different Accretion Types Colloquium Prague, April, 2005

  25. Riftzone 0 km 50 km Comparison to the Seismogenic Crust in Iceland ~ 500°C South Iceland Seismic zone Stefanson, 1998 Deep dykes Magma Chamber Lava flows Depth: 20 km 20 km 10 km 20 km 10 km 5 km 10 km 5 km Colloquium Prague, April, 2005

  26. Magma Chamber Deep Dykes Surface Lavas Temperature Temperature Temperature 40 C/km 30 C/km 20 C/km Location of profiles Horizontal velocity Horizontal velocity Horizontal velocity Vertical velocity Vertical velocity Vertical velocity Comparison of Different Accretion Types • Strong vertical and differential • horizontal velocities Colloquium Prague, April, 2005

  27. Seismic Azimuthal Anisotropy from Rayleigh waves 20-40 km 50-80 km Li & Detrick, EPSL2003 Colloquium Prague, April, 2005

  28. Preliminary Findings for the Accreton of Crust on Iceland • 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, 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 Colloquium Prague, April, 2005

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