- Field stop 2 -
Blue Ridge, Appalachian Mtns.
||The Roan Mtns, the Smokies, and the Unaka Mtns are all part of the
Blue Ridge region (Figure 1) of the Appalachian. Stop 2, in the Roan Mtns.
resides in the northeast corner of Tennessee. As in the Piedmont to the
east, these are metamorphic rocks. The rocks were once sediments, and later
sedimentary rocks. Compression resulting from the docking of North America
with Africa (i.e. the Alleghany orogeny) altered both the texture and composition
of those strata, producing medium- to high-grade metamorphism over a large
In Figure 2, the Blue Ridge is partially snow-covered and dominates the scene. The Piedmont of North Carolina is located in the lower-left corner of the photo, while Tennessee's Valley and Ridge lies to the upper-right. Gatlinburg, TN is near the center of the frame. The photo is oriented with North toward the right. You can clearly see that the terrain of the Blue Ridge is more rugged than that of the Piedmont. The rocks of the Blue Ridge have indeed stood the test of time. They are quartz rich, and very resistant to erosion. In fact, of the highest peaks in the eastern U.S., more reside in the Blue Ridge than any other area of the Appalachians.
|Figure 2. Space shuttle photo illustrating three regions of
the Appalachians in Tennessee and North Carolina. Courtesy of the Image
Science & Analysis Laboratory, NASA Johnson Space Center, Photo ISS006-E-14968.
Click on the image to view an enlargement.
Stop 2 - Roan Mountain, Tennessee/North Carolina
Roan Mtn. (Figure 3) lies on the border between Tennessee and North
Carolina. It contains five peaks, the highest of which (Roan High Knob,
located in NC) stands at an elevation of 1,916 m (6,285 feet). Roan Mtn.
is part of the Roan Highlands, which stretches for a distance of about
32 km (20 mi) along the state border.
|Figure 3. The Roan Highlands. The Roan Gneiss is visible in the foreground. Click on the image to view an enlargement.|
The Roan Highlands were raised primarily during the Alleghany orogeny
(i.e. the Late Paleozoic), the most recent mountain-building episode associated
with the assembly of Pangaea. However, the rocks of the Roan Highlands
are mostly Precambrian in age. For example, the Cranberry Gneiss is nearly
two billion (1,800 million) years old, making it one of the oldest rocks
in the eastern U.S., and the oldest rock in North Carolina and Tennessee.
|Figure 4. A peak in the Roan Highlands with the Roan Gneiss in the background and the darker colored Bakersville Gabbro (a plutonic rock) in the foreground. The intrusion of the gabbro likely resulted in contact metamorphism of the gneiss.|
Figures 4 & 5 illustrate younger (800 Ma) plutonic intrusions in
close proximity to older (1800 Ma) metamorphic rocks. As you know, the
intrusion of the magma into the country rock would produce contact metamorphism.
Compression during the Allegheny Orogeny (~ 325-250 Ma) also contributed
to regional metamorphism in this area. In fact, some hand samples of plutonic
rocks (e.g. gabbro) do exhibit foliation.
|Figure 5. Contact between the Roan Gneiss (top) and Bakersville Gabbro (bottom). There is little visible evidence of contact metamorphism. Click on the image to view an enlargement.|