USE OF GEOMETRIC AND KINEMATIC TESTS TO DETERMINE MECHANICAL FORMATION OF A REGIONAL SCALE FOOTWALL SYNCLINE

Historically, fold and thrust formation in the Valley and Ridge has been studied in hanging-wall anticlines and attributed to buckling. More recent cross sections through the Tennessee Valley and Ridge employ a kink geometry, implying a kinking mechanism acted during fold formation, although, little quantitative geometric, kinematic, and mechanical analysis of folds has actually been performed. Specifically, no dominant fold mechanism has been identified for foreland fold-thrust belt formation. Furthermore, certain well-accepted fold-related thrust models (e.g. fault-bend-folding) used to explain Valley and Ridge—type folding do not permit the footwall synclines that clearly exist here. Our purpose is to identify a mechanical model for the development of a regional scale footwall syncline using geometric and kinematic tests. The similarity of the Appalachian foreland to other forelands and good outcrop exposure makes it an ideal location to quantitatively study fold formation and mechanics. Data characterizing fold geometry, and kinematic data such as bulk shortening and slip on bedding have been collected and will be used to test possible mechanical models for folding and thrusting. Flexural-slip occurs at the mesoscopic scale and appears to be penetrative on the map scale. Geometric and kinematic tests of each model will identify models that do not match the field data and if possible establish a unique fold mechanism. At present, buckling (with flexural-slip) appears to be the dominant mechanism for fold formation. Valley and Ridge thrusts follow a classic ramp-flat geometry favoring neither fault-bend nor fault-propagation fold end members. Presence of major footwall synclines along several large thrusts in the Valley and Ridge (e.g. Saltville and Whiteoak Mountain) may exclude fault-bend folding and suggest some hybrid mechanism is responsible for fault and fold formation here.