Grants and Contracts Details
Description
Regionally, the Appalachian thrust belt includes the gradually curved Tennessee salient,
convex toward the craton in the direction of thrust translation, and the more angular bend of the
Alabama recess, concave toward the craton. In northwestern Georgia, north-northeast-striking
thrust faults and related folds in the southern arm of the Tennessee salient intersect east-
northeast-striking thrust faults and related folds of the Alabama recess (Fig. 1). The primary
scientific objective of this project is to determine the structural history of the intersection
between two regionally extensive structural trends in the southern Appalachian thrust belt. Two
end-member alternative solutions may be suggested for such a junction of structural trends. One
involves two or more temporally successive episodes of deformation, each with a different
translation direction that corresponds to the observed structural trends, such that the younger set
of structures overprints the other with compressional interference structures. In contrast, the
other solution involves a single episode of deformation in which thrust-translated structures are
bent around a pre-existing footwall structure. Variations in strain distribution, deformation style,
and nature of structural overprinting should distinguish the two alternatives. Moreover,
variations in strain accommodation should occur not only laterally, but also vertically as a result
of contrasting mechanical properties between stratigraphic units. We hope to produce a restored
three-dimensional model that will delineate domains of strain accommodation. The proposed
geologic mapping area in Georgia (Fig. 2) is selected to help address questions of kinematics and
mechanisms of thrust translation in the Appalachian thrust belt. Brian Cook, a Ph.D. student at
the University of Kentucky, will conduct the field mapping.
In interpreting the cause (mechanism) of curvature, the most fundamental alternative is
the relation of slip direction to the shape of curvature. The construction of palinspastically
restorable, balanced structural cross sections (e.g., Dahlstrom, 1969; Thomas and Bayona, 2005)
relies on the assumption of slip direction approximately perpendicular to strike of frontal thrust
ramps and trends of compressional fold axes. A long-standing problem is the recognition that
palinspastic restoration in map view of a bend in a thrust belt commonly results in "gaps" or
"overlaps" in the area of any particular stratigraphic horizon, and that imbalance in map view
underscores the question of the orientation of slip direction with respect to strike of thrust-belt
structures. An array of cross sections around a structural bend may be restored and balanced
individually; however, restorations perpendicular to strike along intersecting thrust faults yield
an imbalance in the along-strike lengths of frontal ramps. The restoration leads to a similar
imbalance in the surface area of a stratigraphic horizon, reflecting a volume imbalance in three
dimensions.
Status | Finished |
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Effective start/end date | 9/1/08 → 8/31/09 |
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