GEOLOGIC MAP OF THE GREENSBORO PORTION OF THE HYCO SHEAR ZONE.

The Hyco Shear Zone (HSZ) of North Carolina’s Piedmont region has been described as an Alleghanian ductile thrust zone separating the Ordovician Milton terrane to the west from the Neoproterozoic Carolina terrane to the east. We present new mapping along the Greensboro portion of the HSZ, where it forms a boundary between the Churchland Plutonic Suite to the west and the Carolina terrane/Greensboro Intrusive Suite to the east.

We present new U-Pb zircon (LA-ICP MS) ages for two major igneous complexes in the study area to constrain the timing of major pre-Alleghanian plutonism occurring along the HSZ. New U-Pb zircon ages of 332-331 Ma for the Churchland Plutonic Suite are consistent with samples of the Churchland from northeast of our study area. Collectively these data support Churchland emplacement in the middle Mississippian that temporally aligns with the ca. 335-330 Ma active period of the HSZ. Additionally, we provide new U-Pb zircon age dates of 598-611 Ma for the Greensboro Intrusive Suite, another major igneous complex in the eastern (hanging wall) portion of the study area.

The continuation of 1:50,000 scale bedrock mapping along the Greensboro portion of the HSZ presented here provides new structural measurements and thin-section petrography that further illustrate the effect of ductile deformation along the shear zone. Petrographic indicators in the Greensboro portion of the HSZ show the continuation of ductile deformation features with mylonitic foliations and winged or rotated feldspar porphyroclasts primarily displaying top-to-right shear that appears to overprint a minor top-to-left shear component. Collectively, these data support the idea of a complex ductile thrust regime with major plutonic bodies representing both pre- and possibly syn-tectonic intrusive events along the Hyco Shear Zone.