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 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.

Duplex system

Thrust fault hangingwall and footwall ramps and flats…

Fault-Propagation Fold 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-tip Folds Fault-propagation fold (non-parallel fold) Detachment fold (folding is always non-parallel) Fault-propagation Fold (parallel fold)

‘Drag folds’ Footwall rocks are commonly deformed into synclines Could also relate to fault propagation

Footwall syncline in the Canadian Cordillera

Let’s practice…

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

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

Recumbent tight similar syncline and anticline similar fold parallel fold from: http://earth.leeds.ac.uk/learnstructure/index.htm from: http://www.stmarys.ca/academic/science/geology/structural/ Recumbent tight similar syncline and anticline Upright open parallel syncline

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

Example from the Argentinian Cordillera

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 Fault-tip Fold Fault-bend Fold http://earth.leeds.ac.uk/learnstructure/index.htm

A case study of a fold and thrust belt: The North Tian Shan Piemont (Charreau et al, 2008)

Growth strata record of Kink Band migration (Huerguosi Anticline) (Charreau et al, 2008) (Suppe et al., 1997; Hubert-Ferrari et al, 2007)

Modeling 12 equations ex: Kinematic model (Charreau et al, 2008)

(Charreau et al, 2008)

Modeling dip angles Bedding expected from the pure Fault-bend fold model Bedding measured in surface Bedding expected from the fault-bend fold model with growth strata (Charreau et al, 2008)

Long Term History of Shortening (Charreau et al, 2008)

Sedimentation History Accumulation rates– Piggy back Accumulation rates- magnetostratigraphy (Charreau et al, 2008)