KINEMATIC HISTORY OF THE NORTH ANNA GNEISS DOME IN THE GOOCHLAND TERRANE, EASTERN PIEDMONT, VIRGINIA

The Goochland Terrane (GT) is an enigmatic fault-bounded block of Mesoproterozoic to Paleozoic crust in Virginia’s eastern Piedmont. The structural geometry of the eastern GT is dominated by three elongate gneiss domes that crop out to the west of the Hylas Zone. The domes are cored by the Mesoproterozoic State Farm gneiss, and surrounded by a heterogeneous sequence of biotite gneiss and amphibolite. Previous workers have interpreted the domes to be refolded basement-cored anticlines that were modified by late Paleozoic ductile deformation along the Hylas Zone. Our study focuses on understanding the geometry and kinematics of structures in the North Anna dome, the northernmost of the domes exposed in the GT.

The North Anna dome is an elongate structure that occupies an area of ~50 km² and is covered by Coastal Plain strata at its northeastern margin. Amphibolite to granulite facies foliations, both within the dome and in the surrounding biotite gneiss, dip gently. Mineral and elongation lineations, regardless of position in the dome, trend NE-SW and are gently plunging to subhorizontal. Mesoscale refolded recumbent folds and sheath folds occur in the cover sequence. Dextral sense-of-shear indicators are common and likely developed under general shear conditions.

Domes in the Goochland terrane may be the cumulative result of mid-crustal, orogen parallel-flow associated with transpressional collision during the Alleghanian that was followed by orogenic collapse and exhumation prior to Atlantic rifting in the early Mesozoic.