EMPLACEMENT OF THE GUPTON PLUTON: A LOBE OF THE ALLEGHANIAN ROLESVILLE BATHOLITH, EASTERN PIEDMONT, NORTH CAROLINA

The Gupton pluton is a prominent lobe on the NE margin of the ~2000 km³, Alleghanian-age Rolesville batholith in the eastern Piedmont of North Carolina. Batholith construction is spatially and temporally associated with slip on regional shear zones, including the Macon fault zone on the western margin of the Gupton pluton. The intrusion consists of mostly fine- to medium-grained granite. Plagioclase (35%), potassium feldspar (31%), and quartz (30%) dominate the rocks, with the remainder composed of biotite (3%) and other accessory minerals (1%). Foliation, defined by biotite, is occasionally visible in the field.

To test reliability of field observations of fabric, we compare field measurements with results of two laboratory fabric analysis techniques on oriented samples. Shape-preferred orientation analysis of slabbed specimens provides quantitative constraints on 3-d alignment of visible crystals. Anisotropy of magnetic susceptibility analysis of cored hand-samples provides a measure of the alignment of all mineral grains by quantifying how induced magnetization perturbs a known magnetic field. Results from these two independent techniques are compared with one another and field measurements to provide a check on the consistency of fabric results.

We hypothesize that the Gupton pluton was emplaced as an outward-flowing lobe from the main body of the Rolesville batholith. The Macon fault zone was active during emplacement of the pluton and likely influenced the location and growth of the intrusion. The Trawenagh Bay granite in northwestern Ireland and the magmatic flow lobes of the Tuolumne batholith in California provide analogous examples of the incremental batholith construction observed in the Rolesville batholith.