The northern Blue Ridge of Virginia, as seen
from Shenandoah National Park
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n Virginia, the Blue Ridge province forms a basement massif
with Mesoproterozoic crystalline rock
in its core and Late Neoproterozoic to Early Paleozoic cover rock on its flanks. The Blue
Ridge province is allochthonous and has been thrust to the northwest over Paleozoic rocks of the Valley and Ridge province  . Although earlier
deformation events are recorded in the older igneous and metamorphic rocks, the Blue Ridge
is a contractional structure that experienced deformation
and crustal shortening during the Paleozoic.
The Blue Ridge experienced the intrusion of a diverse suite of plutons and granulite-facies metamorphism during the Grenvillian (1.2 - 1.0 Ga)
orogeny. Late Neoproterozoic (750-700 Ma) granitoids intrude the
Grenvillian rocks and are associated with an early phase of Iapetan
rifting. Late Neoproterozoic sedimentary rocks
range from non-marine alluvial conglomerates to deep-water distal turbidites and are
derived from Grenvillian basement exposed along a rifted continental
margin. In central and northern Virginia, the 570 Ma Catoctin metabasalts overlie the Late Neoproterozoic
sedimentary units.
By the early Cambrian, the Iapetus Ocean had opened to the east of the
Blue Ridge and a westward transgression occurred along the ancient
North American margin. In the western Blue Ridge, shallow marine siliclastics
of the Chilhowee Group were deposited in the early Cambrian
and eventually gave way to carbonates of Cambro-Ordovician age.
In central and northern Virginia the Blue Ridge mountains rise to elevations in excess of
1200 m (4000 ft). Local relief on the east side of the Blue Ridge
is up to 1000 m. In southern Virginia, the Blue Ridge forms a broad plateau-like upland
that rises over 500 m from the Piedmont along a prominent escarpment. Mt. Rogers (1746 m), in the southwestern Virginia Blue Ridge, is
the highest peak in Virginia.
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(11/4/98) |
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