II Basic Techniques in Structural Geology Field measurements

II. Basic Techniques in Structural Geology • • • Field measurements and mapping Terminology on folds and folds Stereographic projections From maps to cross-sections Growth Strata Seismic Imaging

Growth and pre-growth strata • The assumption of beds with constant thickness holds generally for ‘pregrowth’ strata. Syntectonic deposition will induce lateral variations of bed thickness. Such strata are called ‘growth strata’.

(Burbank and Verges, 1994)

Fault-bend folding … The non planar fault has a flat-ramp-flat geometry. Translation of the thrust sheet along that fault requires axial surfaces. Note the difference between the active and Courtesy of Frederic Perrier passive axial surfaces

Example: Structure of a Fault-bend fold with Growth strata Growth triangles (Suppe et al. , 1997; Hubert-Ferrari et al, 2007)

Pre-growth strata

Growth strata

Growth triangle…

foldscarp… buttress unconformity

growth axial surface as disconformity…

Buttress unconformity…

angular unconformity…

growth axial surface as unconformity…

2 growth unconformities…

Growth strata record of Folding A B (Charreau et al, 2008)

Growth strata record of Kink Band migration (Huerguosi Anticline) A B (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 measured in surface Bedding expected from the pure Fault-bend fold model 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 k te a r n Ac s– ac b gy Pig tio a l u m u c phy Ac tesa r n o i at cumul igra t a r t s to magne (Charreau et al, 2008)