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Geological Constraints
Lecture 6: Geodynamics
Carolina Lithgow-Bertelloni
Constraints
Mass distribution and change
Geoid and free air gravity
TPW
Plate motions past and present
Magnetic anomalies
Topography
Flooding record
Stresses
Sources
Measure strain
Record of volcanism
Mass Distribution
[Forte and Mitrovica, 2001]
Changes in Mass Distribution:
True Polar Wander
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Inertial interchanges
Hotspots
Hotspot Tracks
-Taking into account
mantle wind
-Letting hotspots move
relative to each other
-Taking into account
plate deformation
[Steinberger et al., 2004]
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
[64-74]
[94-100]
[74-84]
[100-119]
[84-94]
[Lithgow-Bertelloni and Richards, 1998]
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
300
Sealevel (m)
250
200
150
HAQ
100
50
HAQ
0
VAIL
-50
-100
-150
0
100
200
300
Age (my)
400
500
600
Ages: 64 Ma
[Xu and Lithgow-Bertelloni, 2004]
Bathymetry and sea-level
Following Pitman (1978)
250
200
[Using G&J, 1986]
[Using Hall (2000) for Philippine plate]
Sea Level (m)
[Haq et al.]
150
100
50
0
0
[Conrad, Lithgow-Bertelloni and Xu, 2004]
10
20
30
Age (Ma)
40
50
60
Contributions to Topography
Factors:
Isostatic balance of crust
Orogenesis
short  uncompensated
r
Mantle Flow
Epeirogeny
Long 
Tectonic uplift; post-glacial rebound; dynamic topography (Mitrovica et al., 1989; Gurnis, 1993)
Dynamic Topography
h=-
r/g
h
1
r
Mantle Flow
2
Surface Topography
Crustal Structure
[Laske et al., 2002]
Residual Topography
Continents-Crust 2.0; Oceans-Bathymetry from Age
No Depleted Mantle
Continents-Crust 2.0; Oceans-Bathymetry from Isostasy
No 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)
Sources of Stress
Inhomogeneity
Topography
Edge Tractions
Basal Tractions
g
Surface Topography
Crustal Structure
[Laske et al., 2002]
Mantle Tractions
[Lithgow-Bertelloni & Guynn, 2004]
LVC+TD0
Fit to observations (Variance Reduction)
Azimuth-59%
Regime-61%
Modeling the stress field
Combined effect of crustal contribution and mantle flow
[Lithgow-Bertelloni and Guynn, 2004]
Episodic Crustal Production?
[Condie, 1998]
Plume Frequency
3 Different Experiments
[Lithgow-Bertelloni et al., 2001]