Blue Ridge Parkway

 

The Blue Ridge is a mountain chain in the eastern United States, part of the Appalachian Mountains, forming their eastern front from Georgia to Pennsylvania. The mountains are well known for their bluish color when seen from a distance. To the west of the Blue Ridge, between it and the bulk of the Appalachians, lies the Great Valley, bordered on the west by the Ridge and Valley province.

 

Blue Ridge Mountains

 

Although the term "Blue Ridge" is sometimes applied exclusively to the eastern edge or front range of the Appalachian Mountains, in which range Grandfather Mountain is the highest peak, the geological definition of the Blue Ridge province extends westward to the Ridge and Valley area, encompassing the Great Smoky Mountains, the Great Balsams, the Roans, the Brushy Mountains (a "spur" of the Blue Ridge) and other mountain ranges.

 

The Blue Ridge extends north into Pennsylvania as South Mountain. While South Mountain dwindles to mere hills between Gettysburg and Harrisburg, the band of ancient rocks that forms the core of the Blue Ridge continues northeast through the New Jersey and Hudson River highlands, eventually reaching The Berkshires of Massachusetts and the Green Mountains of Vermont.

 

The highest peak in the Blue Ridge and the Appalachian chain is Mt. Mitchell in North Carolina at 6,684 feet (2,037 m). There are 39 peaks in North Carolina and Tennessee higher than 6,000 feet (1,829 m); by comparison, the northern portion of the Appalachian chain contains only one 6,000 foot peak, New Hampshire's Mt. Washington.

 

The Blue Ridge Parkway runs 469 miles (750 km) along the crests of the Southern Appalachians and links two national parks: Shenandoah and Great Smoky Mountains. In many places along the parkway, there are metamorphic rocks (gneiss) with folded bands of light-and dark-colored minerals, which sometimes look like the folds and swirls in a marble cake.

 

Most of the rocks that form the Blue Ridge Mountains are ancient granitic charnockites, metamorphosed volcanic formations, and sedimentary limestones.

 

Recent studies completed by Richard Tollo, a professor and geologist at the George Washington University, provide greater insight into the petrologic and geochronologic history of the Blue Ridge basement suites. Modern studies have found that the basement geology of the Blue Ridge is made of compositionally unique gneisses and granitoids, including orthopyroxene-bearing charnockites. Analyses of zircon minerals in the granites completed by John Aleinikoff at the U.S. Geological Survey have provided more detailed emplacement ages.

 

Many of the features found in the Blue Ridge and documented by Tollo and others have confirmed that the rocks exhibit many similar features in other North American Grenville-age terranes. The lack of a calc-alkaline affinity and zircon ages less than 1,200 Ma suggest that Blue Ridge are unique from the Adirondacks, Green Mountains, and possibly the New York-New Jersey Highlands. The petrologic and geochronologic data suggest that the Blue Ridge basement is a composite orogenic crust that was emplaced during several episodes from a crustal magma source. Field relationships further illustrate that rocks emplaced prior to 1,078-1,064 Ma preserve deformational features. Those emplaced post-1,064 Ma generally have a massive texture and missed the main episode of Mesoproterozoic compression.

 

source: wikipedia.org