DETAILED GEOLOGIC MAPPING AND A STRUCTURAL-KINEMATIC ANALYSIS ACROSS THE EASTERN RALEIGH, SPRING HOPE, AND TRIPLET TERRANE BOUNDARIES IN THE VIRGINIA EASTERN PIEDMONT

The Alberta and Lawrenceville 1:24K Quadrangles in the Virginia eastern Piedmont expose meta-igneous, metasedimentary, and plutonic rocks of the eastern Raleigh (eRt), Spring Hope (SHt), and Triplet (Tt) terranes. The Macon and Hollister fault strands of the Eastern Piedmont fault system (EPFS) juxtapose these third order lithotectonic elements. Both the faults and terranes record dextral wrench flow and partitioned contraction during Alleghanian transpression and Laurentian-Gondwanan continental collision. The Macon fault separates the eRt and SHt; the Hollister fault divides the SHt and eRt from the Tt. The eRt contains amphibolite facies (1^st sillimanite zone) white mica schist, biotite paragneiss, and biotite tonalitic and granitic orthogneiss intruded by tonalite and biotite granite. Greenschist facies (biotite zone) felsic and white mica-rich ultraphyllonite occur in the SHt; less deformed equivalents crop out just south of Lawrenceville. Pluton textures in the Tt range from massive to ultramylonitic. K-feldspar megacrystic biotite granite intrudes both the eRt and Tt whereas equigranular biotite granite crosscuts all terranes.

Fabric elements are subdivided into four strain facies based on strain intensity variations. Three structural-kinematic domains are classified by spatial variations among the strain facies. The western domain records tight to isoclinal upright F₂ folds that refold F₁ folds, S₀-S₁ gneissosity and schistosity, and a shallow L₁ stretching lineation in the eRt. Ultraphyllonite and granitic orthogneiss in the central domain record shallow to steep SW-dipping S₁S-S₁C-S₁C’ phyllonitic schistosity or mylonitic gneissosity in the eRt, SHt, and Tt, a shallow L₁ stretching lineation, and dextral kinematic indicators. The eastern domain records steep S₀-S₁ gneissosity and a shallow L₁ stretching lineation in Tt plutonic rocks. A white mica schist-phyllonite contact defines the western boundary of the Macon fault in the eRt; granitic mylonite and ultramylonite define the eastern boundary of the Hollister fault in the Tt. In the central domain, high-strain fabric elements overprint SHt ultraphyllonites, which terminate between the eRt and Tt where the Macon and Hollister faults merge. This Y-shear is the junction between strands of a dextral freeway within the EPFS.