Alexander Hanamean Ms. Harro Mentor: Dr. Tom Perkins MD. PhD.
Colloquium Prague, April, 2005 1 A Numerical Approach to Model the Accretion of Icelandic Crust...
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Transcript of Colloquium Prague, April, 2005 1 A Numerical Approach to Model the Accretion of Icelandic Crust...
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 11
A Numerical Approach to Model the A Numerical Approach to Model the Accretion of Icelandic CrustAccretion of Icelandic Crust
Gabriele Marquart and Harro SchmelingGabriele Marquart and Harro Schmeling
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 22
Bathymetry in the North Atlantic
Colloquium Prague, April, 2005 3
Observations of crustal thickness
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 44
Thickness of the Icelandic crust from Thickness of the Icelandic crust from Gravity and seismic DataGravity and seismic Data
Darbyshire,2000
Colloquium Prague, April, 2005 5
Crust is simply related to extracted melt
1. Model
1 cm/a1 cm/a
Streamlines
Melting rate
Extraction
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 66
Numerical Model of a Rising Plume Numerical Model of a Rising Plume with Melting with Melting
Anomalous temperature
Melt production rate
melting
120 - 60 km depth
Melting zone
Rising velocity
(T. Ruedas)
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 77
Predictions for crustal thickness
Texcess= 350 K (1%)Texcess= 250 K ( 0.1%)Texcess= 250 K (1%)
Texcess= 250 K (3%)
Texcess= 150 K (1%)
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 88
Comparison to „observation“
Model crustDarbyshire
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 99
Extrated material is fed back into the model
Width of emplacement zone 50 km (Gauß)
1 cm/a1 cm/a
Streamlines
Melting rate
2. Model
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 1010
Kinematic model ofPalmason, 1980
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 1111
Iceland Surface Tectonic FeaturesIceland Surface Tectonic Features
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 1212
Structure of the Crust in IcelandStructure 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, 2005Colloquium Prague, April, 2005 1313
Crustal Structure from receiver Crustal Structure from receiver functionsfunctions
Receiver functionsLow Vp-velocities(10%) beneath 40 km
Schlindwein, 2001
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/a1 cm/a
Streamlines
Melting rate
Extraction
Extracted melts are emplaced in a separate crustal model (with contstant rate...)
3. Model
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 1616
Modeling Crustal Accretion - Modeling Crustal Accretion - EquationsEquations
Energy conservation:
Momentum conservation:
Mass conservation:
txsHTTvtT
s ,)( 2
0312 zeTRavvp
22
,
,bzax eeAzxs
txs=v
Physical Equations
Source Functions
Colloquium Prague, April, 2005 17
Model assumptionsModel assumptions
► 2D2D► Constant viscosityConstant viscosity► Total accretion rate Total accretion rate 2 cm/s spreading rate 2 cm/s spreading rate► T of surface lavas: 100 KT of surface lavas: 100 K► T of magma chambers: 600 KT of magma chambers: 600 K► T deep dykes: 300 KT deep dykes: 300 K► 3 models:3 models:
1) Dominated (60%) by deep accretion1) Dominated (60%) by deep accretion2) Dominated (60%) by magma chamber accretion2) Dominated (60%) by magma chamber accretion3) Dominated (60%) by shallow accretion3) Dominated (60%) by shallow accretion
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 1818
Visualization of the Accretion of Crust 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-4th order scheme
after 500 time steps
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 1919
Accretion dominated by deep dykes Accretion dominated by deep dykes (60% M(60% Mtottot))
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 2020
Accretion dominated by magma chambers Accretion dominated by magma chambers (60% M(60% Mtottot))
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 2121
Accretion dominated by surface lavas Accretion dominated by surface lavas (60% M(60% Mtottot))
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 2222
Comparison of Different Accretion Styles Comparison of Different Accretion Styles Deep dykes Lava flowsMagma 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, 2005 23
Krustenstruktur aus Seismik
Crustal structure at the rift axisCrustal structure at the rift axis
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 2424
Location of profiles
Comparison of Different Accretion Comparison of Different Accretion TypesTypes
Deep DykesTemperature
Vertical velocity
Horizontal velocity
Magma ChamberTemperature
Vertical velocity
Horizontal velocity
Surface LavasTemperature
Vertical velocity
Horizontal velocity
40 C/km 20 C/km30 C/km
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 2525
Comparison to the Seismogenic Crust in Comparison to the Seismogenic Crust in IcelandIceland
Lava flowsDeep dykes Magma Chamber
5 km
10 km
Depth: 20 km
South IcelandSeismic zone
Stefanson, 1998
Riftzone
50 km0 km
20 km
10 km5 km
20 km10 km
~ 500°C
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 2626
Location of profiles
Comparison of Different Accretion Comparison of Different Accretion TypesTypes
Deep DykesTemperature
Vertical velocity
Horizontal velocity
Magma ChamberTemperature
Vertical velocity
Horizontal velocity
Surface LavasTemperature
Vertical velocity
Horizontal velocity
40 C/km 20 C/km30 C/km-Strong vertical and differential
horizontal velocities
Colloquium Prague, April, 2005Colloquium Prague, April, 2005 2727
Seismic Azimuthal Anisotropy from Rayleigh Seismic Azimuthal Anisotropy from Rayleigh waveswaves
Li & Detrick, EPSL200320-40 km 50-80 km
Colloquium Prague, April, 2005 28
► Thermal & geometric structure depends Thermal & geometric structure depends strongly on accretional modestrongly on accretional mode
► Iceland: shallow seismogenic zone, high Iceland: shallow seismogenic zone, high thermal gradient suggests deep or thermal gradient suggests deep or intermediate accretion (deep dykes and intermediate accretion (deep dykes and magma chambers) as the dominating processmagma 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 Then only moderate differential velocities and mixing of the different accretion zonesmixing of the different accretion zones
Preliminary Findings for the Accreton of Preliminary Findings for the Accreton of Crust on Iceland Crust on Iceland