Kinematic implications of football structures

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Virginia Polytechnic Institute and State University


Folding prior to thrust-sheet emplacement is proposed to explain presence of overturned synclines in the footwalls of many thrust-faults in the Appalachian foreland fold- and thrust-belt of southwest Virginia. Investigation of relations in the footwalls of the Saltville and St. Clair thrust-sheets near the Southern-Central Appalachian juncture indicates presence of at least two distinct types of footwall structures: 1)isolated forelimbs of thrust-truncated asymmetric ramp-generated anticlines, and 2)areally extensive overturned subthrust synclines.

Mesoscopic fabric data and strain states indicate rotation of bedding by folding prior to thrust-sheet emplacement rather than drag folding during thrusting. Low angles between bedding and cleavage planes and low strain values on the back limbs of folds at thrust terminations (Sinking Creek anticline) and in hangingwall strata seems to indicate folding was largely accomplished by flexural flow in units of relatively low mechanical strength.