Abstract

The Brevard zone is a narrow belt of steeply dipping low-grade metamorphic rocks known to extend for at least 375 miles from near Montgomery, Alabama, northeast to Mount Airy, North Carolina. It probably continues northeastward into Virginia, but its position there can only be inferred. The Brevard zone separates the Blue Ridge geologic belt on the northwest from the Inner Piedmont belt on the southeast, but it is only locally coincident with the physiographic boundary between the Blue Ridge and Piedmont.

The Brevard zone has previously been interpreted both as a narrow syncline of younger rocks infolded into a terrane of metamorphic and plutonic rocks and as a belt of retrogressively metamorphosed rocks along an overthrust fault (the Martic or Brevard overthrust).

Detailed mapping and petrographic studies southeast of the Grandfather Mountain window in North Carolina show that there the Brevard is a fault zone, and rocks along this fault zone display pervasive structural and metamorphic effects related to it across an outcrop width of as much as 5 miles. Latest movement along the zone occurred after major thrusting along the Linville Falls fault, which bounds the Grandfather Mountain window, and before emplacement of an unaltered diabase dike believed to be Late Triassic.

Reconnaissance field and petrographic studies along the zone in North Carolina, South Carolina, and northern Georgia support the conclusion that the Brevard is a fault zone. The linearity of the zone, the presence of blastomylonite and phyllonite within it, the horizontal cataclastic lineation associated with it, and the contrast in rocks across it suggest that the Brevard is a zone of strike-slip faulting of great magnitude. Right-lateral displacement of at least 135 miles is believed to have occurred in late Paleozoic or Early Triassic time or both.

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