SIGNIFICANCE OF INTRUSIVE ROCKS ALONG THE CHARLOTTE-CAROLINA TERRANE BOUNDARY: EVIDENCE FOR THE TIMING OF DEFORMATION IN THE GOLD HILL FAULT ZONE NEAR WAXHAW, NC

Geologic mapping along the North Carolina-South Carolina border reveals that regional metavolcanic rocks are intruded by plutonic suites of contrasting age and composition. Near Waxhaw, NC, the heterogeneously deformed Waxhaw granite (WG) intrudes low-grade volcaniclastic rocks of the Carolina terrane. To the west, the WG intrudes and contains xenoliths of amphibolite correlated with the Charlotte terrane; indicating the WG is a stitching pluton between the two terranes. The WG is in the footwall of the Gold Hill fault zone (GHfz), which near Waxhaw, NC, is a steep NW-dipping, dextral-reverse fault system. The GHfz deforms rocks in both the Carolina and Charlotte terranes as it crosses the inferred contact between the two terranes at a high angle, precluding it as a terrane boundary in this region.

Several observations suggest that emplacement of the WG was late-synkinematic to deformation by the GHfz: 1) the WG bears a greenschist-grade foliation similar to that of volcaniclastic rocks deformed by the GHfz; 2) contact metamorphic porphyroblasts in rocks around the WG both overgrow and are deformed by the main foliation in the GHfz; and 3) contact metamorphic assemblages around the WG indicate isobaric heating followed by an increase in pressure in the footwall, consistent with NW over SE directed thrusting by the GHfz. Also intruding deformed volcaniclastic rocks around Waxhaw, NC, is a suite of gabbros that contain unaltered, primary igneous mineral assemblages. The undeformed state of these gabbros indicates they post-date deformation by the GHfz, and thus post-date the WG.

A precise age on the WG is critical to constraining the timing of fault movement between the Carolina and Charlotte terranes. New U-Pb zircon, monazite, and xenotime data from the WG indicate a crystallization age of 539.4 ± 1.4 Ma. Two titanite fractions are concordant at 400 Ma. These data indicate that Charlotte-Carolina terrane interaction was no later than the earliest Cambrian, and that the GHfz around Waxhaw, NC, was active during the earliest Cambrian. Gabbro around Waxhaw, NC, may be related to mafic rocks in the Early Devonian Concord Suite, located in central NC. If such an inference is correct, then the concordant titanite ages are likely related to the emplacement of the Waxhaw gabbroic suite.