Geological Constraints
Lecture 6: GeodynamicsCarolina Lithgow-Bertelloni
Constraints
Mass distribution and changeGeoid and free air gravityTPW
Plate motions past and presentMagnetic anomalies
TopographyFlooding record
StressesSourcesMeasure strain
Record of volcanism
Mass Distribution
[Forte and Mitrovica, 2001]
Changes in Mass Distribution:True Polar Wander
Inertial interchanges
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Hotspots
[Steinberger et al., 2004]
Hotspot Tracks-Taking into account mantle wind-Letting hotspots move relative to each other-Taking into account plate deformation
Present-day plate motions
[Forsyth and Uyeda,1975]
Magnetic Anomalies
[Müller et al., 1994]
Plate Reconstructions:Cenozoic[10-25]
[25-43]
[43-48]
[48-56]
[56-64]
Plate Reconstructions: Mesozoic
[Lithgow-Bertelloni and Richards, 1998]
[64-74]
[74-84]
[84-94]
[94-100]
[100-119]
Topography
Continental flooding
•Ocean-volume variations•ice cap melting
•Changes in volume of ocean basins•spreading rates
•Isostatic balance of crust•Orogenesis (short uncompensated )
•Epeirogeny•long dynamic topography; tectonic uplift; post-glacial rebound
Sea-level
-150
-100
-50
0
50
100
150
200
250
300
0 100 200 300 400 500 600
Age (my)
Sealevel (m)
HAQ
HAQ
VAIL
Ages: 64 Ma
[Xu and Lithgow-Bertelloni, 2004]
Bathymetry and sea-level
[Conrad, Lithgow-Bertelloni and Xu, 2004]
Following Pitman (1978)
250
200
150
100
50
0
Sea Level (m)
6050403020100
Age (Ma)
[Haq et al.]
[Using G&J, 1986]
[Using Hall (2000) for Philippine plate]
Contributions to Topography
r
Mantle FlowFactors:Isostatic balance of crustOrogenesis
short uncompensated
EpeirogenyLong Tectonic uplift; post-glacial rebound; dynamic topography (Mitrovica et al., 1989; Gurnis, 1993)
Dynamic Topography
1
2r
hr/g
h
Mantle Flow
Surface Topography
Crustal Structure
[Laske et al., 2002]
Residual Topography Continents-Crust 2.0; Oceans-Bathymetry from IsostasyNo Depleted Mantle
Continents-Crust 2.0; Oceans-Bathymetry from AgeNo Depleted Mantle
Depleted Mantle
[De Koker and Lithgow-Bertelloni, 2004]
Lithospheric Stress Field
Contributions: Mantle Stresses; Crustal Heterogeneity
[Reinecker, J., Heidbach, O. and Mueller, B., 2003](available online at www.world-stress-map.org)
gInhomogeneityTopographyEdge TractionsBasal Tractions
Sources of Stress
Surface Topography
Crustal Structure
[Laske et al., 2002]
[Lithgow-Bertelloni & Guynn, 2004]
Mantle Tractions
Modeling the stress field
[Lithgow-Bertelloni and Guynn, 2004]
Combined effect of crustal contribution and mantle flow
LVC+TD0Fit to observations (Variance Reduction)Azimuth-59%Regime-61%
Episodic Crustal Production?
[Condie, 1998]
Plume Frequency3 Different Experiments
[Lithgow-Bertelloni et al., 2001]