Chapter 4: Basins due to flexure

Chapter 4: Basins due to flexure

This presentation contains illustrations from Allen and Allen (2005)

Flexure at ocean trenches and foreland basinsFlexure Theory

Continuous plate and Broken plate under a distributed loadControls on rigidity

Oceanic lithosphereContinental lithosphere

Flexural BucklingTheoryIn nature and in experiments

Dynamics of Orogenic WedgesCritical taper TheoryAnalog modelsNumerical Models

Modeling Foreland BasinMoving tectonic loadErosion and deposition of bivergent margins

Basins due to flexure

Flexure at ocean trenches

• Ocean-continent and Ocean-ocean collision

Ocean-Continent across Chile Trench

From the following article:Measuring the onset of locking in the Peru−Chile trench with GPS and acoustic measurementsKatie Gagnon, C. David Chadwell and Edmundo NorabuenaNature 434, 205-208 (10 March 2005) doi: 10.1038/nature03412

http://www.nature.com/nature/journal/v434/n7030/full/nature03412.html


Key topographic featuresOuter ridge (forebulge)TrenchMountain range/volcanic chain


Local isostatic prediction



Trench should be shallower => held downGravity model supports this interpretation

Deformation in the overriding plate

Broad Zone of deformation

(1)Shortening in accretionary prism sometimes

extension

(3) Shortening near craton

700 km

Front of deformation zone in trench(www.geo.au.dk/.../Projects/juan/pic/jp_fig5.jpg)

Causes of earthquakes in the downgoing slab

(Isacks, 1969; Isacks and Molnar, 1971)

bendingextending

shortening

Basins associated with collisional margins

Peripheral foreland basin

Retro-arc foreland basin

Alpine Po Basin(Italy) -Northern Alpine Foreland of Bavaria

http://images.google.com/imgres?imgurl=http://www.paleoweb.net/algae/algae/ecology/ramp/img-europe.jpg&imgrefurl=http://www.paleoweb.net/algae/algae/ecology/ramp/ramp2.htm&h=300&w=300&sz=72&hl=en&start=3&tbnid=s6DXcRiWbZwS2M:&tbnh=116&tbnw=116&prev=/images%3Fq%3DaLPINE%2BFORELAND%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG

• http://www.peakware.com/encyclopedia/ranges/maps/images/europe_alps.gif

Alps Po Basin

http://www.peakware.com/encyclopedia/ranges/maps/images/europe_alps.gif

Development of bivergence

Kinematic marker

Continental lithosphere

Oceanic lithosphere


Mechanical decoupling





Retro-arc foreland basin

Peripheral foreland basin/trench/foredeep

Sevier Orogenic foreland

• http://jan.ucc.nau.edu/~rcb7/Sevier.jpg

http://jan.ucc.nau.edu/~rcb7/Sevier.jpg

http://www.colorado.edu/GeolSci/Resources/WUSTectonics/SevierLaramide/WestUS_Tectonics/Pics%20for%20presentation/

DeCelles_2004Fig19.jpg

Peripheral foreland basin/trench/foredeep

Back-arc extensiona

Subduction Zone Rollback

Pannonian Basin and Dinarides

http://www.ingeba.euskalnet.net/lurralde/lurranet/lur17/17klemen/17klem01.gif

Adriatic

C.M.


Line loadContinuous plate and Broken plate under a distributed load

Causes of rigidityOceanic lithosphereContinental lithosphere





Broken Plate and Distributed Load

Continuous (elastic) Plate vs. broken (elastic) plate

Deflection is continuous across the break, but there is no internal shear strength at within the plate (elastic) at the break

A “line” load

A theoretical counterpart very useful for first-order studies

Time just before t=0

Continuous plate

Broken plate

A “line” load

The geometry of the calculation will not match the details of good data

Time just after t=0

Continuous plate

Broken plate



Time just before t=0



An instant later …




Weaker plateNarrower, deeper basin

forebulge


Broken (elastic) plate


10 km

Trench is 2km deep100 km between trench and forebulge ( a few hundred meters)


Broken (elastic) plate

Trench is 2km deep 100 km between trench and forebulge ( a few hundred meters)



Controls of rigidityOceanic lithosphereContinental lithosphere





Controls on Rigidity-Oceanic Lithosphere

Controls on Rigitidy- Oceanic Lithosphere

• Depth to the 450 degree isotherm

Controls on Rigitidy- Continental Lithosphere

Controls on Rigitidy- Continental Lithosphere

• Temperature• Fluid pressure• Rate of deformation• Amount of deformation

(curvature)

Controls on Rigidity- Continental Lithosphere

• Temperature (As Temp increases, Teff decreases…)

• Fluid pressure (….Teff decreases…)• Rate of deformation (…Teff increases….)• Amount of deformation (curvature) (…Teff

decreases…)

Controls on RigidityDifferential stress

extensioncompression

Controls on RigidityDifferential stress

Mechanical Decoupling 10^-7 curvature








Lithospheric Buckling• Long-wavelength Buckling is more accepted

for oceanic lithosphere: Indian Ocean

http://myweb.dal.ca/klouden/ocean5110/Lectures/lect7/lect7.html








Critical Taper Theory

http://www.geology.um.maine.edu/geodynamics/analogwebsite/Projects2005/Barker_2005/Html/Results.html

Movies

Critical wedge in shortening

Creitical Wedge in extension

• http://terra.rice.edu/department/faculty/morganj/Movies/movie3a.html

Critical Wedge over salt

NO SALT

SALT

Critical Taper Theory

Basal friction

Coulomb wedge

Taper angle backstop








Simple flexure models (Teff=20km)

Get Matlab code HERE

Simple flexure models (Teff=80km)

Get Matlab code HERE

Bivergent margins-erosion

Documents

Chapter 4: Basins due to flexure