FOUR- DIMENSIONAL KINEMATIC MODEL FOR BRITTLE FAULTING IN THE LITTLE NORTH MOUNTAIN FAULT ZONE, SOUTHERN AUGUSTA COUNTY, VIRGINIA

Recent 1:24,000 scale mapping of the Augusta Springs quadrangle in southern Augusta County, Virginia reveals previously unrecognized northeast-southwest striking thrust fault, herein called the Little North Mountain Fault (LNMF), located along the western flank of Little North Mountain. The LNMF is interpreted as a splay of the regional scale North Mountain Fault located just north of the quadrangle. The LNMF dips approximately 30 degrees to the southeast, has an apparent westward displacement of several hundred feet, and separates an anticline-syncline pair in a package of Ordovician to Devonian siliciclastics.

In the northeast portion of the Augusta Springs quadrangle near Pond Gap, the LNMF has been dissected into distinct fault blocks by a series of east-west striking cross faults. Breccia and associated iron ore deposits along the trace of the LNMF are predominantly located at the intersections with cross faults. In addition, the middle cross-fault in the Pond Gap area abruptly separates steeply inclined beds and plunging folds to the south, from gently-dipping beds and horizontal folds to the north, suggesting a component of rotational block movement.

Cross-sections and stereonet analysis were used to create a four-dimensional model for the geometry and kinematics of the Pond Gap area. Results indicate that during the Alleghanian Orogeny, northwest directed compressive stress (s1) was accommodated by folding and thrust faulting along the LNMF; concurrent extension (s3) was accommodated by rotational dip-slip displacement along cross faults.