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

Colloquium Prague, April, Bathymetry in the North Atlantic

Colloquium Prague, April, Observations of crustal thickness

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

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

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

Colloquium Prague, April, 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%)

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

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

Colloquium Prague, April, Kinematic model of Palmason, 1980

Colloquium Prague, April, Iceland Surface Tectonic Features

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

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

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

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

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

Colloquium Prague, April, 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, 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

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

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

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

Colloquium Prague, April, 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

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

Colloquium Prague, April, 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

Colloquium Prague, April, 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

Colloquium Prague, April, 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

Colloquium Prague, April, Seismic Azimuthal Anisotropy from Rayleigh waves Li & Detrick, EPSL km50-80 km

Colloquium Prague, April, ► 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 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