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The Brevard Fault Zone is a 700-km long and several km-wide
The Brevard Fault Zone is a 700-km long and several km-wide thrust fault
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.
Thrust geometry and nomenclature
Reverse faults
A thrust fault is a type of reverse fault that has a dip of 45 degrees or less.
If ...
that extends from the North Carolina-Virginia border, runs through the north metro Atlanta
Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton County, the most populous county in Georgia, but its territory falls in both Fulton and DeKalb counties. With a population of 498,71 ...
area, and ends near Montgomery
Montgomery refers to:
People
For people with the name Montgomery, see Montgomery (name)
Places Belgium
* Montgomery Square, Brussels
* Montgomery metro station, Brussels
Pakistan
* Montgomery (town), British India, former name of Sahiwal, Punja ...
, Alabama. It is an important Paleozoic
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon.
The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838
by combining the Greek words ''palaiós'' (, "old") and ' ...
era feature in the uplift of the Appalachian Mountains
The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. The ...
.
Discovery
Arthur Keith
Sir Arthur Keith FRS FRAI (5 February 1866 – 7 January 1955) was a British anatomist and anthropologist, and a proponent of scientific racism. He was a fellow and later the Hunterian Professor and conservator of the Hunterian Museum of the ...
from the United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
first identified an exposed segment of the Brevard Fault in 1905, believing it to be a syncline
In structural geology, a syncline is a fold with younger layers closer to the center of the structure, whereas an anticline is the inverse of a syncline. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimposed ...
. In 1932, Anna Jonas Stose
Anna Jonas Stose (August 17, 1881 – October 27, 1974) was a major geological pioneer, who worked for the American Museum of Natural History, Maryland Geological Survey, Pennsylvania Geological Survey, Virginia Geological Survey, and the United ...
’s used local petrology
Petrology () is the branch of geology that studies rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together ...
to identify the site as a thrust fault
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.
Thrust geometry and nomenclature
Reverse faults
A thrust fault is a type of reverse fault that has a dip of 45 degrees or less.
If ...
. Stose, the first to trace the fault, is also credited with identifying that the rocks in the area must have been formed through deformation
Deformation can refer to:
* Deformation (engineering), changes in an object's shape or form due to the application of a force or forces.
** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies.
* Defo ...
, placing the Brevard Fault in a regional perspective. Using modern methods of seismic reflection
Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic ...
and high-resolution profiling, geologists have since discovered that the Brevard Fault Zone has undergone both thrust and strike-slip
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tecton ...
movement.
Geology
The Brevard Fault Zone is a part of a much larger system of faults at the base of the Appalachian thrust sheet that played a key role in uplifting the Appalachian Mountains. The extent of its role remains uncertain because most of the fault is buried beneath Quaternary sediment. Many studies of the fault come fromGrandfather Mountain
Grandfather Mountain is a mountain, a non-profit attraction, and a North Carolina state park
near Linville, North Carolina. At 5,946 feet (1,812 m), it is the highest peak on the eastern escarpment of the Blue Ridge Mountains, one of the major ch ...
in the Linville Fall Quadrangle, which contains the exposed region that was first discovered by Arthur Keith. This region is only 1–3 km of its 700 km length.
The Brevard Fault experienced multiple phases of deformation and minimal stratigraphic displacement. The Brevard Fault Zone contains diverse lithologies
The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lith ...
, but it is primarily composed of mylonitic metagraywacke, schist
Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...
, amphibolite
Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flak ...
, and gneiss
Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...
that underwent metamorphism
Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ...
350–360 million years ago. The Fault Zone is characterized by ductile behavior as indicated by the widespread presence of mylonitic
Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a cl ...
and phyllonitic rocks.
See also
*Geology of Georgia (U.S. state)
The geology of Georgia consists of four distinct geologic regions, beginning in the northwest corner of the state and moving through the state to the southeast: the Valley and Ridge region and part of the Appalachian Plateau; the Blue Ridge; th ...
*Geology of North Carolina The geology of North Carolina includes ancient Proterozoic rocks belonging to the Grenville Province in the Blue Ridge. The region experienced igneous activity and the addition of new terranes and orogeny mountain building events throughout the Pal ...
Bibliography
* * *References
{{reflist Thrust faults Geology of Virginia Geology of Alabama Geology of Georgia (U.S. state) Seismic faults of the United States Appalachian Mountains