DEXTRAL STRIKE-SLIP FAULTING IN THE EASTERN BLUE RIDGE NEAR BREVARD, NORTH CAROLINA: OBSERVATIONS, PROBLEMS, AND SPECULATIONS

A set of parallel northeast-southwest trending strike-slip faults crosscut the gneiss of the Ash Metamorphic Suite (AMS) in an area that lies northwest of the Brevard Zone. The faults are characterized as zones, up to several hundred meters wide, of phyllonite intermixed in an anastomosing pattern with domains of rock, generally of the mylonite-series. The composition of these domains indicates that their protoliths were both local country rock and also distant or exotic sources. The rock immediately adjacent to these zones is also of the mylonite-series, the fabric of which is overprinting previous metamorphic elements of earlier deformations. This overprinting is not uniform in intensity and is field recognizable only within a hundred meters or so of the principal zone of shear grading into rock more typical of the AMS. The faults lie about 3 to 4 km apart. The areas or domains between are each structurally and stratigraphically distinct though the gross lithology of each is similar.

The ~380 Ma Looking Glass pluton, which intrudes the AMS, is truncated on its northwest and southeast flanks by these faults thus constraining their age to late Paleozoic (Arcadian) or younger. The mineral elongations, especially that of hornblende, suggests amphibolite conditions but chlorite is also associated with the faults. Mesoscopic and microscopic kinematic indicators suggest a dextral, northwest to the northeast southeast to the southwest, sense of shear though some indicators are contrary to this. Similarly some of mineral elongations are oriented oblique to the trend of the faults. These could be due to inheritance from the AMS or block scale rotation during fault movement.

Collectively the faults and the inter-fault areas may represent a major shear zone. This shear zone roughly parallels the trend of the Brevard Zone though the Brevard Zone seems to truncate or overprint it. In the immediate area of Brevard, North Carolina the Brevard Zone seems to be a ‘mushwad' or tops to the northwest ductile duplex. Scattered outcroppings of mylonite-series rock similar in character to that of the faults occur along the northwest margin of the Brevard Zone suggesting the possibly that one of the faults of the shear zone may have been reactivated as the west-side buttress of this duplex.