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]