The Blue Ridge Province in southern and central Virginia is a complex slice of
Precambrian basement emplaced on the margin of Laurentia during collisional events in the
Paleozoic. This allochthonous basement is composed of Middle Proterozoic continental
crust, Late Proterozoic intrusives, and Late Proterozoic-early Paleozoic metasediments and
metavolcanics. Two distinct terranes within the Blue Ridge are separated by the northeasttrending
and southeast dipping Fries-Rockfish Valley Fault Zone, exposed as a 1-10 km
wide shear zone, formed during the middle Paleozoic Taconic Orogeny (425-450 Ma.).
These terranes are referred to as the Pedlar massif, a high-grade granulite terrane, to the
northwest and the Lovingston massif, a lower-grade amphibolite terrane to the southeast.
The connection between these terranes has been debated for decades.
A combined petrologic and geochemical approach has been applied in two transects
across the shear zone, four kilometers apart along strike near Roanoke, Virginia, to study
the geochemical and petrologic evidence of shearing along the fault and constrain the nature
and timing of possible retrogressive and fluid infiltration events that affected these
rocks. Mineral assemblages and microstructures at the northeastern Horsepen Mountain
and at the southwestern Explore Park transects indicate that deformation occurred along the
fault under greenshist facies conditions.
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