--> ABSTRACT: Differences Between Fault-Propagation Folds and Detachment Folds and their Subsurface Implications, by W. K. Wallace and T. X. Homza; #91021 (2010)
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Differences Between Previous HitFaultNext Hit-Propagation Folds and Detachment Folds and their Subsurface Implications

WALLACE, WESLEY K., and THOMAS X. HOMZA

Previous HitFaultNext Hit-related anticlines with steep to overturned forelimbs commonly are assumed to be Previous HitfaultNext Hit-propagation folds based on their geometric similarity to popular models. Examples in the northern Brooks Range suggest that some such folds may not have originated as a result of Previous HitfaultNext Hit propagation but instead as detachment folds. The Brooks Range folds originated as buckles in a competent unit over an incompetent unit. Anticline growth was by rotation of the limbs about fixed hinges in the competent unit and by thickening of the incompetent unit, but without propagation of a Previous HitfaultNext Hit up a ramp. Commonly, the 1steep forelimbs of these anticlines were subsequently truncated by thrust faults as shortening continued.

Folds formed as detachment folds differ fundamentally from Previous HitfaultNext Hit- propagation folds. A detachment anticline is cored by an incompetent unit and, if the anticline has been truncated by a thrust Previous HitfaultNext Hit, a syncline is commonly present in the footwall ramp. In contrast, a Previous HitfaultNext Hit-propagation fold is more likely to form in dominantly competent rocks and to have a relatively little-deformed footwall ramp. The timing, distribution, and amount of strain also differs between a thrust-truncated detachment fold with rotating limbs and fixed hinges and a Previous HitfaultTop-propagation fold with fixed interlimb angles and some migrating hinges. Distinguishing between these two fold mechanisms thus has important implications for interpreting the amount and distribution of reservoir, seal,and trap, and the development and preservation of porosity and permeability.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.