COMPILATION OF LITHODEMIC AND STRUCTURAL DATA FROM THE EARLY DEVONIAN EASTERN RALEIGH TERRANE: A TRIBUTE TO THE RESEARCH OF AARON K. RICE AND THE NORTH CAROLINA GEOLOGICAL SURVEY

This abstract is submitted in honor of our friend and colleague Aaron Rice, who passed away in May 2021 while working for the NCGS.

The North Carolina eastern Piedmont exposes the infrastructural Raleigh terrane and its highly deformed amphibolite-facies rocks. Late Paleozoic tectonism is linked to transpression due to oblique Laurentian-Gondwanan convergence during Alleghanian orogenesis. Dextral strands of the Eastern Piedmont fault system (EPFS), an orogen-scale strike-slip network in the easternmost southern Appalachian hinterland, define the boundaries of the Raleigh terrane and subdivide it into western and eastern portions. Aaron compiled our NCGS STATEMAP and UNCW EDMAP structural data across an eight-quadrangle region to better understand the structural setting of the eastern Raleigh terrane.

EPFS shear strands juxtapose both infrastructural and suprastructural terranes against the Early Devonian eastern Raleigh terrane. The Lake Gordon shear zone marks the western boundary of the eastern Raleigh terrane with the infrastructural western Raleigh terrane of uncertain age. The Macon fault zone defines the eastern boundary of the eastern Raleigh terrane with the Neoproterozoic and supracrustal Spring Hope terrane. Between the high-strain zones, UNCW mappers identified hornblende-biotite-plagioclase-quartz and K-feldspar or plagioclase porphyroclastic biotite gneisses, and garnet-sillimanite-biotite-white mica schist in the eastern Raleigh terrane, forming an interlayered suite of meta-igneous and clastic metasedimentary rocks. Based on geometric and strain facies structural-kinematic domain analyses, these rocks share penetrative composite planar-linear shear fabrics, at least two fold generations, and west-side-north kinematic indicators recording regional deformation, ductile flow, and low-to-high-intensity strain during Alleghanian metamorphism. Compilation of regional and shear fabric data indicates that progressive, two-phase wrench and contractional strain overprinted the eastern Raleigh and northern Spring Hope terrane during dextral transpression. The eastern Raleigh terrane experienced moderately dipping, northeast translation along the Macon fault zone, potentially over the older western Spring Hope terrane, supporting data from prior studies.