Paleomagnetism Tectonic Applications

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Paleomagnetism Tectonic Applications

• Tectonic reconstructions
• AMS
• Hand in assignment 1?

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Geocentric Axial Dipole (GAD) Hypothesis
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Plate motion
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Paleogeographic Reconstructions
See Butler Chapter 7 and 11 Tauxe Chapter 16
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Continental Break-up and Collision

• 400 Ma
• 400 180 Ma
• 180 Ma - today

• Eur-Am collision
• Eur-Am together
• Eur-Am Break-up

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Tectonics
Tectonic motion within one plate
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1. Latitudinal transport
Great Circle
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Small Circle
2. Vertical-axis rotation
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Polar projection
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Stereographic projection
Observed direction
Expected direction (pole)
R Rotation F Flattening 95 confidence
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AMS Anisotropy of Magnetic Susceptibility
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Preferred orientations in rocks
Schist 3.5xs showing foliated mineral grains.
Gneiss polished surface showing foliation.
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Deformation stress and strain
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Tectonic fabric
Sedimentary fabric
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Sedimentary fabric and paleocurrent
min
int
max
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Tauxe Chapter 13
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Applications
INDIA
ASIA
Tibetan Plateau
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Application the Altyn Tagh Fault
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Deformation is
Localized or distributed?
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Distributed or localized shear along the ATF?

• Arcuate thrusts
• Original structure of arcuate ramp or
• - Acquired structure through sinistral shear?

Dupont-Nivet et al. 2004, Tectonics
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Dupont-Nivet et al. 2004, Tectonics
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Application Eastern Plateau
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• Localized deformation
• Rotation of central parts.
• (Avouac et al. 1993 Chen et al. 2002)

• Distributed deformation
• Rotations limited to margins.
• (Dewey et al. 1988 Holt et al. 2000)

Dupont-Nivet et al., JGR 2003
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Basin rotation
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Regional Rotation
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Regional Rotation
Dupont-Nivet et al. 2004, JGR
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Tectonic model
Dupont-Nivet et al. 2002
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Application Tarim Basin
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15 CW rotation Local or entire basin?
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Principle of least astonishment15 CW rotation
of eastern end of Maza Tagh is probably local
rather than entire basin.
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25 inclination shallowing
AMS
ChRM
min
int
max
Geographic
Stratigraphic
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Applications the Indo-Asia Collision
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Persistently low Asian paleolatitudes between 50
and 20 Ma
50-20 Ma latitudes systematically low
Selection of only - Volcanics and -
Shallowing-corrected sediments shallow
inclination problem!
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55 Ma collision 4000 km total convergence since
collision 2000 km intra-continental shortening
in Asia in India