Introduction Fault-bend folding Fault-propagation folding Detachment folding Buckles Fold-thrust complexes in multilayers Trishear

Problem imaging the forelimb… critical for evaluating the structural style

Problem imaging fore-limb from seismic… interpretations are commonly strongly model-driven

First-pass interp - steep faults..…not in vogue

Low-angle thrust (detachment at depth??)

Introduction Fault-bend folding Fault-propagation folding Detachment folding Buckles Fold-thrust complexes in multilayers Trishear

Simple fault-bend fold Suppe model

Suppe fault bend folding….. But is this too simplistic a style?

Introduction Fault-bend folding Fault-propagation folding Detachment folding Buckles Fold-thrust complexes in multilayers Trishear

Fault-bend folding Fault-propagation folding Panels of constant-dip strata, folds grow by hinge migration

Test kinematic models using growth strata Growth triangles

“growth fans” rather than “growth triangles are the usual style…. So are the fault- bend models applicable?

Introduction Fault-bend folding Fault-propagation folding Detachment folding Buckles Fold-thrust complexes in multilayers Trishear

Detachment fold

From Sherkati et al (Mar. Pet. Geol. )

McQuarrie 2004 J. Struct. Geol.

Structural styles in the Zagros….. Geomorphologic evolution suggests buckle sheet “detached” on Hormuz salt + minor internal detachments

Geomorphological studies of developing folds using Landsat images from the Zagros Mountains, Iran. (Henry Lickorish)

Fold collision

Fold interactions: Long cylindrical Abrupt plunges Collided folds Merged folds

Introduction Fault-bend folding Fault-propagation folding Detachment folding Buckles Fold-thrust complexes in multilayers Trishear

Fold train initiates If one fold amplifies slightly faster…it will weaken So strain transferred onto that fold - other folds slow down/stop. System experiences stress drop.

CONTROLS ON BUCKLE FOLD EVOLUTION?

Quantify through modelling by Martin Casey….

Buckle fold development Finite element modelling by Martin Casey

Viscosity ratio 10:1 Differential stress

Stress concentrated in hinge area Differential stress Stress drop on limbs

Example….

Chevron fold (Hartland Quay) Bed-parallel slip Strain in hinge

Structures on limbs shear fibres on bedding fractures in beds More models…..

Contrast with higher viscosity ratio...

Stress drop throughout

Viscosity ratio 10:1 Viscosity ratio 40:1 Longer wavelength (and lower diff stress) for higher viscosity contrast

Unloading limbs - can promote fracture here Stress history is complex But can be modelled…..

Modelling fracture potential and evolution Timing might be crucial…. Diagenetic “events” Fluid migration “events”

Buckling is important Stress history is complex Model in 3D… and…. Fold-thrust complexes

Introduction Fault-bend folding Fault-propagation folding Detachment folding Buckles Fold-thrust complexes in multilayers Trishear

Multilayers?

Examples from Champsaur

WNW ESE

WNW ESE

Thrust cuts through Ramp area folds Thrust breaks back ? continuum - localised slip plus distributed deformation

WNW ESE

Different predictions for sand connectivity Precursor buckling important….

Introduction Fault-bend folding Fault-propagation folding Detachment folding Buckles Fold-thrust complexes in multilayers Trishear

Strat YES Complex localisation orogenic interiors?

Introduction Fault-bend folding Fault-propagation folding Detachment folding Buckles Fold-thrust complexes in multilayers Trishear