Dynamics of Fold Growth and the Impact on Internal Fluid Flow: Examples from ancient and modern fold-thrust belts (Sawtooth Range, Montana, USA & Zagros Simply Folded Belt, Islamic Republic of Iran)

Caroline M Setchell

Department of Earth Science and Engineering, Imperial College London

UK

[email protected]

Shortening across convergent margins is accommodated in part by the formation of fold-thrust belts, typically containing detachment folds, fault-bend folds and fault-propagation folds. Two such features are the Simply Folded Belt of the Zagros and the Rocky Mountain Sevier/Laramide fold-thrust belt.

The evolution of periclinal detachment folds, such as those in the Zagros, can be defined by the rate of amplification and associated topographic uplift. This can be determined from the theoretical analyses of folding and varies both temporally and spatially. Thus at a specific point on the fold the uplift rate will vary with time and at a particular time the uplift rate will vary along the fold hinge.

Insight into the process of fold evolution can be gained from an examination of interactions between growing folds and stream networks using processed LandsatETM images. By considering examples of developing folds of each type, the growth histories can be determined and any differences and similarities established.

The geometry and kinematics of detachment folds are well constrained, thus a pair of fault bend folds at the front of the Sawtooth Range of the Montana Disturbed Belt, have been selected for detailed field mapping. The Cave Mountain Quadrangle will be mapped at 1:24,000 and a detailed study of the geometry and fracture patterns of the anticlines will be made. Comparison of the geometries and fracture patterns will be combined with the satellite-generated dataset to produce time variant models of fold development and fluid flow within the structures for the various fold types.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid