2 Longstanding Problems and New Ideas About the Structure and Tectonic Evolution of the Southern Appalachians and Other Mountain Belts I: In Honor of the Career of Robert D. Hatcher Jr.

Thursday, 12 April 2018
8:00 AM - 12:00 PM
Room 301 C

THE BLUE RIDGE-PIEDMONT BOUNDARY IN VIRGINIA: A TRANSPRESSIONAL FRONTIER

Paper number: 2-10
Program: Symposia Sessions
Time: 10:40 AM – 11:00 AM

Authors

Abstract

In the southern Appalachians, the Blue Ridge-Piedmont boundary has long been a source of spirited debate as to its kinematic history and tectonic significance. In Virginia, the boundary between the Blue Ridge-Piedmont geologic provinces forms both a distinct and nebulous NE-SW trending fault zone that can be traced for >300 km from the North Carolina boundary to the Culpeper Mesozoic basin in north-central Virginia. From south to north, the fault zone is variously known as the Bowens Creek, Buckmarlson, and Mountain Run zones. These zones separate medium- to low-grained Neoproterozoic cover rocks with a Laurentian affinity from various western Piedmont terranes including the Smith River Allochthon, Hardware, and Potomac terranes. Although the character of this fault zone changes along strike, it delineates a major change in the deformation plan of the orogen. Blue Ridge rocks are dominated by NW-directed contractional structures that facilitated material transport towards the Appalachian foreland, whereas rocks at, and to the east, of this boundary record dextral transpression with both NW-directed shortening and significant strike-parallel elongation and material flow.

In central Virginia, the recently named Buckmarlson zone forms a 3- to 5-km-wide transition zone between the eastern Blue Ridge and western Piedmont. The Buckmarlson transition zone is a NE-SW–trending belt with steeply dipping fabrics that record a different kinematic history than rocks to the northwest and southeast. Rocks in the Buckmarlson transition zone experienced a complex general shear-dominated deformation, and are cut by later discrete low-angle normal faults. Late normal faulting may explain the juxtaposition of low-grade western Piedmont rocks with older (400 to 420 Ma) muscovite cooling ages on higher grade Blue Ridge rocks with younger (345 to 330 Ma) muscovite cooling ages.

Geological Society of America Abstracts with Programs. Vol. 50, No. 3

doi: 10.1130/abs/2018SE-313185

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