33 Geologic Maps, Digital Geologic Maps, and Derivatives from Geologic Maps (Posters)

Friday, 24 March 2006
8:00 AM - 12:00 PM

NEW CONSTRAINTS ON GEOCHEMICAL CORRELATIONS AND TECTONIC SETTING FOR VOLCANOGENIC TERRANES ON THE WESTERN FLANK OF THE WAKE-WARREN ANTICLINORIUM, NORTH CAROLINA EASTERN PIEDMONT

Paper number: 33-22
Program: THEME SESSIONS
Time: 8:00 AM – 12:00 PM

Authors

Abstract

In the North Carolina eastern Piedmont, a network of ductile dextral and normal fault zones and brittle normal faults that range from the late Paleozoic to Mesozoic extends 120 km along a corridor of 7.5-minute quadrangles mapped in the western Raleigh and Henderson 30x60-minute sheets for the NCGS STATEMAP project. These faults dissect the eastern portion of the Late Proterozoic to Cambrian Carolina Zone along the western flank of the Alleghanian Wake-Warren anticlinorium into discrete lithodemic terranes. In the Raleigh sheet, the Leesville fault separates the upper greenschist and amphibolite facies Carolina and Crabtree terranes, while the Falls Lake fault separates the amphibolite facies Falls Lake and Crabtree terranes. The Nutbush Creek and Middle Creek faults separate the Crabtree and greenschist facies Spring Hope terranes from the amphibolite facies Raleigh terrane. In the Henderson sheet, the ductile normal Upper Barton Creek fault separates the upper greenschist facies Carolina terrane from the Falls Lake terrane. The brittle normal Jonesboro fault divides the Carolina terrane into a northern lower greenschist facies portion and a southern upper greenschist to amphibolite facies portion, and separates the lower greenschist facies Carolina terrane from the amphibolite facies Crabtree terrane.

Because of these tectonothermal complexities and to test lithodemic correlations within terranes and across their bounding faults based on field relationships, petrography, and structural analysis, geochemical data from 255 samples along the western flank are evaluated. Major element concentrations support a bimodal mafic-felsic and tholeiitic to calc-alkaline island-arc trend for the greenschist and amphibolite facies metaigneous rocks in all terranes. REE and trace element concentration patterns substantiate correlations among rock types within and between terranes and reinforce an island-arc origin for all terranes. While most mafic and felsic petrogenetic discrimination diagrams further support an island-arc affinity for most samples, enrichment trends on specific diagrams suggest that continental contamination or continental arc formation, within-plate sources, and back-arc-basin rifting may have contributed to the geochemical signatures of some western flank lithodemes.