II. Basic Techniques in Structural Geology

• Field measurements and mapping

• Terminology on faults and folds

• Stereographic projections

• From maps to cross-sections

• Growth Strata

• Fault-related folds

• Seismic Imaging

Two types of fault-related fold(drawn here assuming flexural slip

folding)

Fault-bend fold Fault-propagation fold

Fault Bend Folds (FBF) =ramp anticlines

-throughgoing faults - slip is conserved.

-Fold amplitude is determined by the thickness above the lower hanging wall flat.

-Once the fold has achieved maximum amplitude, it only grows in width.

Fault-Bend Fold

Duplex system

Thrust fault hangingwall and footwall ramps and flats…

Fault Propagation Folds (FPF)

- fault slip is not conserved. Fault displacement is taken up by folding

- Fault tip is marked by a ductile ‘process zone’.

- Ideally, FPF’s evolve into FBF’s

Fault-Propagation Fold

Detachment fold

(folding is always non-parallel)

Fault-tip Folds

Fault-propagation Fold(parallel fold)

Fault-propagation fold(non-parallel fold)

Footwall rocks are commonly deformed into synclines

‘Drag folds’

Could also relate to fault propagation

Footwall syncline in the Canadian Cordillera

Let’s practice…

• Primary strucure due to cross-bedding stratification. Not related to deformation

Describe:

from: http://earth.leeds.ac.uk/learnstructure/index.htmfrom: http://www.stmarys.ca/academic/science/geology/structural/

similar fold

Recumbent tight similar syncline and anticline

parallel fold

Upright open parallel syncline

from: http://earth.leeds.ac.uk/learnstructure/index.htm

from: http://www.stmarys.ca/academic/science/geology/structural/

try to sketch: shallowly plunging, upright, tight, similar synclineAssume fold axis plunges toward N45E

Example from the Argentinian Cordillera

What is it?What is it?

Fault related Folds

all from: http://earth.leeds.ac.uk/learnstructure/index.htm

http://earth.leeds.ac.uk/learnstructure/index.htm

Fault related Folds

http://earth.leeds.ac.uk/learnstructure/index.htm

Fault-bend FoldFault-tip Fold

A B

A case study of a fold and thrust belt: The North Tian Shan Piemont

(Charreau et al, 2008)

(Suppe et al., 1997; Hubert-Ferrari et al, 2007)

A B

Growth strata record of Kink Band migration (Huerguosi Anticline)

(Charreau et al, 2008)

12 equations ex:

Modeling

Kinematic model

(Charreau et al, 2008)

(Charreau et al, 2008)

Bedding expected from the fault-bend foldmodel with growth strata

Modeling dip angles

Bedding measured in surfaceBedding expected from the pure Fault-bend fold model

(Charreau et al, 2008)

Long Term History of Shortening

(Charreau et al, 2008)

Accumulation rates– Piggy back

Accumulation rates- magnetostratigraphy

(Charreau et al, 2008)

Sedimentation History