Late Cenozoic Reverse Faulting in the Fall Zone, Southeastern Virginia

Area of Science:

• Structural Geology
• Neotectonics
• Sedimentology

Background:

• The Old Hickory Heavy Mineral Deposit is situated in the Fall Zone of southeastern Virginia.
• This area features Paleozoic metamorphosed igneous rocks of the Piedmont and overlying late Cenozoic sediments.

Purpose of the Study:

• To analyze the structural characteristics and deformational history of faults at the Old Hickory Heavy Mineral Deposit.
• To investigate the relationship between faulting and sedimentation in the region.

Main Methods:

• Detailed geological mapping of fault structures.
• Analysis of rock units, including diorite of the eastern Slate Belt and Pliocene Yorktown Formation.
• Interpretation of fault displacement and movement (oblique dip-slip).

Main Results:

• A set of en-echelon reverse faults were identified, cutting both Paleozoic rocks and Cenozoic sediments.
• Diorite was faulted over nearshore to shore-face deposits of the Yorktown Formation.
• Faults exhibit NW-SE strike, oblique dip-slip movement with up to 6m displacement, and tip out along strike.
• Distinct cobble beds overlying faults suggest contemporaneous faulting and sediment deposition.

Conclusions:

• Deformation at Old Hickory likely resulted from the reactivation of pre-existing Paleozoic structures.
• The reactivation occurred under a regionally extensive compressional stress field consistent with modern tectonic forces.
• The findings provide insights into the complex interplay of ancient structures and recent tectonic activity in the Virginia Fall Zone.