Stratigraphy and Structure Across the Blue Ridge and Inner Piedmont in Central Virginia – Culpeper to Charlottesville, Field Trip Guidebook T207

Published by the American Geophysical Union as part of the Field Trip Guidebooks Series, Volume 207.

This field trip is based on reconnaissance geologic mapping in the Charlottesville 1 Degreesx2 Degrees quadrangle as part of a new edition of the Geologic Map of Virginia (Figure 1). The first day of the field trip will be spent examining high-rank Grenville-age basement rocks that make up the core of the Blue Ridge anticlinorium. The second day will be spent examining greenschist facies Precambrian and Early Paleozoic metasedimentary and metavolcanic cover rocks that unconformably overlie the Grenville basement and dip to the southeast, off the southeastern limb of the anticlinorium.

In the area of this field trip possibly pre-Grenville, high-rank banded gneisses and Grenville-age metaigneous rocks form the core of the Blue Ridge anticlinorium (Figure 2). These ancient core rocks have been intruded by Late Precambrian and younger granitic, basaltic, and gabbroic plutons and by felsic and mafic dikes of latest Precambrian to Early Paleozoic age and diabase dikes of Late Triassic-Early Jurassic age. The Grenville core is subdivided into a northwestern (granulite) terrane and a southeastern (retrograded) terrane that may also contain relict granulite facies rocks. These two terranes seem to have had different geologic histories and are separated from each other by the Rockfish Valley ductile deformation zone (Bartholomew and others, 1981). The Rockfish Valley is a major right-lateral shear zone that developed under greenschist-grade conditions and is of probable Taconic age. Both the Grenville-age core rocks and younger cover rocks have been subjected to greenschist grade metamorphism that probably occurred during this same Taconic orogenic event.