The Brevard Fault Zone is a 700-km [1] long and several km-wide thrust fault that extends from the North Carolina-Virginia border, runs through the north metro Atlanta area, and ends near Montgomery, Alabama. It is an important Paleozoic era feature in the uplift of the Appalachian Mountains. [2]
Arthur Keith from the United States Geological Survey first identified an exposed segment of the Brevard Fault in 1905, [3] believing it to be a syncline. In 1932, Anna Jonas Stose’s used local petrology to identify the site as a thrust fault. [4] Stose, the first to trace the fault, is also credited with identifying that the rocks in the area must have been formed through deformation, [5] placing the Brevard Fault in a regional perspective. [3] Using modern methods of seismic reflection and high-resolution profiling, geologists have since discovered that the Brevard Fault Zone has undergone both thrust and strike-slip movement. [6]
The Brevard Fault Zone is a part of a much larger system of faults at the base of the Appalachian thrust sheet [1] 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. [7] Many studies of the fault come from Grandfather Mountain in the Linville Fall Quadrangle, [8] which contains the exposed region that was first discovered by Arthur Keith. This region is only 1-3 km of its 700 km length. [7]
The Brevard Fault experienced multiple phases of deformation and minimal stratigraphic displacement. [3] The Brevard Fault Zone contains diverse lithologies, but it is primarily composed of mylonitic metagraywacke, schist, amphibolite, and gneiss [9] that underwent metamorphism 350-360 million years ago. [1] The Fault Zone is characterized by ductile behavior as indicated by the widespread presence of mylonitic and phyllonitic rocks. [1]
An orogeny is an event that leads to both structural deformation and compositional differentiation of the Earth's lithosphere at convergent plate margins. An orogen or orogenic belt develops when a continental plate crumples and is uplifted to form one or more mountain ranges; this involves a series of geological processes collectively called orogenesis. A synorogenic event is one that occurs during an orogeny.
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.
The Antler orogeny was a tectonic event that began in the early Late Devonian with widespread effects continuing into the Mississippian and early Pennsylvanian. Most of the evidence for this event is in Nevada but the limits of its reach are unknown. A great volume of conglomeratic deposits of mainly Mississippian age in Nevada and adjacent areas testifies to the existence of an important tectonic event, and implies nearby areas of uplift and erosion, but the nature and cause of that event are uncertain and in dispute. Although it is known as an orogeny, some of the classic features of orogeny as commonly defined such as metamorphism, and granitic intrusives have not been linked to it. In spite of this, the event is universally designated as an orogeny and that practice is continued here. This article outlines what is known and unknown about the Antler orogeny and describes three current theories regarding its nature and origin.
The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, from Labrador to Mexico, as well as to Scotland.
The Sevier orogeny was a mountain-building event that affected western North America from northern Canada to the north to Mexico to the south.
John James Stevenson was an American geologist, born in New York City. He graduated from New York University in 1863, became professor of chemistry at West Virginia University for two years (1869–71), then served as professor of geology at New York University until 1909. During 1873–74 and from 1878 to 1880 he was geologist for the United States Geological Survey. He also served on the Pennsylvania Geological Survey from 1875 to 1878 and from 1881 to 1882. He was president of the Geological Society of America in 1898.
Décollement is a gliding plane between two rock masses, also known as a basal detachment fault. Décollements are a deformational structure, resulting in independent styles of deformation in the rocks above and below the fault. They are associated with both compressional settings and extensional settings.
The Walker Lane is a geologic trough roughly aligned with the California/Nevada border southward to where Death Valley intersects the Garlock Fault, a major left lateral, or sinistral, strike-slip fault. The north-northwest end of the Walker Lane is between Pyramid Lake in Nevada and California's Lassen Peak where the Honey Lake Fault Zone, the Warm Springs Valley Fault, and the Pyramid Lake Fault Zone meet the transverse tectonic zone forming the southern boundary of the Modoc Plateau and Columbia Plateau provinces. The Walker Lane takes up 15 to 25 percent of the boundary motion between the Pacific Plate and the North American Plate, the other 75 percent being taken up by the San Andreas Fault system to the west. The Walker Lane may represent an incipient major transform fault zone which could replace the San Andreas as the plate boundary in the future.
The Sonoma orogeny was a period of mountain building in western North America. The exact age and structure of the Sonoma orogeny is controversial. The orogeny is generally thought to have occurred during the Permian / Triassic transition, around 250 million years ago, following the Late Devonian Antler orogeny. The Sonoma orogeny was one of a sequence of accretionary events along the Cordilleran margin, possibly caused by the closure of the basin between the island arc of Sonomia and the North American continent. Evidence of this event has been reported throughout western North America, but most distinctly in northwest Nevada.
The Carolina Terrane, also called the Carolina Superterrane or Carolinia, is an exotic terrane running ~370 miles (600 km) approximately North-South from central Georgia to central Virginia in the United States. It constitutes a major part of the eastern Piedmont Province.
The geology of North America is a subject of regional geology and covers the North American continent, the third-largest in the world. Geologic units and processes are investigated on a large scale to reach a synthesized picture of the geological development of the continent.
The Hunton Group is a stratigraphic group in Oklahoma. It preserves fossils dating back to the Devonian period.
The Vinini Formation is a marine, deep-water, sedimentary deposit of Ordovician to Early Silurian age in Nevada, U.S.A. It is notable for its highly varied, mainly siliceous composition, its mineral deposits, and controversies surrounding both its depositional environment and structural history. The formation was named by Merriam and Anderson for an occurrence along Vinini Creek in the Roberts Mountains of central Nevada and that name is now used extensively in the State.
In geology, the term exhumation refers to the process by which a parcel of rock, approaches Earth's surface.
The Waits River Formation (WRF) is a late Silurian to early Devonian limestone containing lesser amounts of phyllite and schist. It is located in the northern Appalachian Mountains of North America. It ranges from Long Island Sound in Connecticut to the Gulf of St. Lawrence in Quebec, and its width ranges from 10-50 km. It is part of the Connecticut Valley–Gaspé Trough, which is present in eastern and northeastern Vermont.
Anna Jonas Stose 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 States Geological Survey. She is best known for her work mapping the Appalachian Mountain Range, documenting the structure of and exposure to the rock formations, and tracing crystalline rocks. Stose was among the first to implement petrographic and structural techniques to the Appalachian Mountains, which were still in development at the time. This was rare because women at this time didn't do physical work in the fields, and her hard efforts are now noted and appreciated. She contributed largely to the Geologic Map of Virginia and the Geologic Map of the United States.
The Superior Craton is a stable crustal block covering Quebec, Ontario, and southeast Manitoba in Canada, and northern Minnesota in the United States. It is the biggest craton among those formed during the Archean period. A craton is a large part of the Earth's crust that has been stable and subjected to very little geological changes over a long time. The size of Superior Craton is about 1,572,000 km2. The craton underwent a series of events from 4.3 to 2.57 Ga. These events included the growth, drifting and deformation of both oceanic and continental crusts.
The Ashe Metamorphic Suite, also referred to as the Ashe Formation, was named after its type locality, Ashe County, North Carolina. The Ashe Metamorphic Suite is located in the Eastern Blue Ridge providence that extends from North Carolina up to South-Western Virginia. It is a collection of metamorphic rocks of both sedimentary and volcanic origin. Zircon dating indicates an age of 470 to 335 Ma for the unit. The protolith of the Ashe Metamorphic Suite was deposited during the Late Proterozoic and reaching its cooling age during the end of the Devonian. The Ashe Metamorphic Suite is overwhelmingly composed of amphibolites and mica schists.
Blue Ridge Ophiolite is an ultramafic series of pods found in the Blue Ridge Mountains of the Appalachian mountain chain. The pods formed before the Taconic orogeny. Throughout the middle and late Ordovician era, the rocks were affected by regional metamorphism leading to resulting in altered mineralogy for some pods.
Diane Seward is a low temperature thermochronologist. She is currently a Teaching Fellow at Victoria University of Wellington and affiliated with GNS Science. Seward's work has predominantly focused on thermochronology applied to basin analysis and tectonic evolution. Her research has also been instrumental in developing dating of volcanic deposit through fission track analysis.
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