Tectonic evolution of the west-central portion of the Newton window, North Carolina Inner Piedmont: Timing and implications for the emplacement of the Paleozoic Vale charnockite, Walker Top Granite, and mafic complexes
Date of Award
Master of Science
Robert D. Hatcher, Jr.
Harry Y. McSween, Theodore C. Labotka
Detailed geologic mapping of portions of the Banoak, Reepsville, Lincolnton West, and Cherryville 7.5-minute quadrangles has confirmed the easternmost exposure of the Brindle Creek fault, which frames the Newton window. The Brindle Creek fault is a terrane boundary that separates the overlying Siluro-Devonian assemblage of metasedimentary rocks and Devonian-Mississippian anatectic plutons of the Cat Square terrane from the Neoproterozoic(?)-Ordovician metasedimentary and igneous rocks of the Tugaloo terrane. Structures related to six deformational events have been identified in this portion of the Inner Piedmont. The Brindle Creek fault has been folded multiple times, resulting in a sinuous outcrop pattern and the formation of the Newton window and smaller Howards Creek window. Portions of three map-scale sheath folds have been identified by map patterns and orientation of dominant mineral lineations, fold axes, and shear-sense indicators. The discontinuity of map-scale bodies of metagraywacke, mafic complexes, and amphibolite is attributed to extension during sheath fold formation. Dominant foliation, mineral lineation, and fold-axis orientations suggest north-northwest directed flow occurred in this portion of the Inner Piedmont.
Zircon geochronology data indicate crystallization of the Vale charnockite at 366.4 ± 3.1 Ma and the enclosing Walker Top Granite at 356.5 ± 5.3 Ma. Zircon saturation thermometry estimates minimum magmatic temperatures for the granitoids at 800-840⁰ C. Whole-rock geochemical and isotopic data indicate the Vale charnockite and Walker Top Granite are genetically related and were derived from deep crustal melting of largely Proterozoic-affinity metasediments in an arc environment. Both granitoids crystallized from the same parent magma; the Vale charnockite is an autolith, or early crystallization of the melt, incorporated into the later crystallizing Walker Top Granite. Geochemical analyses of Cat Square terrane mafic complexes west of the Newton window suggest these bodies represent vestiges of oceanic crust formed in a back-arc basin setting or from both MORB and volcanic-arc sources as characterized by mixed N-MORB and calc-alkaline volcanic-arc signatures. This back-arc basin likely formed from east-dipping subduction during the development of Ordovician volcanic arcs outboard of Laurentia.
Byars, Heather Elizabeth, "Tectonic evolution of the west-central portion of the Newton window, North Carolina Inner Piedmont: Timing and implications for the emplacement of the Paleozoic Vale charnockite, Walker Top Granite, and mafic complexes. " Master's Thesis, University of Tennessee, 2010.