16 Geologic Maps, Geophysical Maps, Digital Geologic Maps, and Derivatives from Geologic and Geophysical Maps (Posters)

Thursday, 24 March 2011
1:30 PM - 5:30 PM
Exhibit Hall

THE STRUCTURE AND PETROLOGY OF THE PEDEN METAULTRAMAFIC BODY, NW NORTH CAROLINA, USA

Paper number: 16-18
Program: Theme Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

The Peden Metaultramafic body, a predominantly chlorite-amphibole schist mass, is a component of the Ashe Metamorphic Suite (AMS) of northwestern North Carolina, exposed in Allegheney County. Previously, the body has been mapped in reconnaissance together with the larger Rocky Ridge body exposed to the north (Rankin et al., 1972), from which it is separated by a thin septum of a variety of AMS rocks and possibly a ductile fault. It was later partly mapped as a series of small individual masses interpreted to be metasomatically altered amphibolite (Stapor et al., 2010). Our new map provides greater detail. The body is extremely elongate parallel to the regional foliation of N60°-70ºE, dips steeply SE, and has a minimum aspect ratio of 220:1. It is structurally interleaved with elongate masses of pelitic schist, quartz-feldspar semi-schist, and hornblende gneiss and schist. The contacts are structural, as indicated by local slickensides and truncated foliations in a well exposed cross section of the body along its probable extension to the NE. Internally, the body is dominated by body parallel foliations and the rocks have down-dip lineations.

Petrologically, the body consists of two main rock types — chlorite+Ca-amphibole schist and talc+Mg-amphibole schist. The contact between the two is abrupt and is marked petrographically by 1) a change in groundmass from chlorite to talc, 2) a decrease in amphibole size and character, and 3) an increase in amphibole abundance. Amphiboles vary in size from 5mm to 0.07mm, and with similarly oriented chlorite and talc, define the dominant foliation. Locally, the chlorite-amphibole schist is porphyroclastic, with larger (older) zoned amphiboles enclosed by a matrix of smaller amphiboles and chlorite. Three generations of amphiboles likely represent three amphibolite to greenschist facies metamorphic assemblages (modified equivalents of Raymond’s A3, A4, and A5 assemblages; Raymond, 1995 p.669; Swanson and Raymond, 2010): A3 = hornblende cores with abundant ilmenite and magnetite inclusions + biotite, A4 = clear amphibole rims + chlorite, and A5 = finer-grained matrix amphiboles + chlorite. The Peden body is polylithologic and has a polyphase metamorphic and deformational history, the clarification of which requires integrated field and petrologic study.