The Ashe Metamorphic Suite, also referred to as the Ashe Formation, was named after its type locality, Ashe County,

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and So ...

. The Ashe Metamorphic Suite is located in the Eastern Blue Ridge providence that extends from North Carolina up to South-Western

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

. It is a collection of metamorphic rocks of both sedimentary and volcanic origin. Zircon

dating Dating is a stage of romantic relationships in which two individuals engage in an activity together, most often with the intention of evaluating each other's suitability as a partner in a future intimate relationship. It falls into the categor ...

indicates an age of 470 to 335 Ma for the unit. The

protolith A protolith () is the original, unmetamorphosed rock from which a given metamorphic rock is formed. For example, the protolith of a slate is a shale or mudstone. Metamorphic rocks can be derived from any other kind of non-metamorphic rock and thu ...

of the Ashe Metamorphic Suite was deposited during the

Late Proterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is prec ...

and reaching its cooling age during the end of the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

. The Ashe Metamorphic Suite is overwhelmingly composed of amphibolites and mica schists.

Nomenclature and Equivalent Units

The Ashe Metamorphic Suite is thought to be correlative with a lower part of the Lynchburg Group in Virginia, the Mount Roger Formation in North Carolina and Virginia, and the Tallulah Falls Formation in

Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...

Geologic overview

The Ashe Metamorphic Suite is composed of a variety of different rocks such as metagreywackes,

muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavage ...

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 o ...

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...

, graphitic schist, and mafic rocks such as

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 (flaky ...

and

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks ...

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 an ...

. The unit is overwhelmingly composed of

mica 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 o ...

with the southwest having intrusions of the ultramafic rocks. The Ashe Metamorphic Suite overlies the

Chilhowee Group The Chilhowee Group is a sedimentary body composed of early Cambrian siliciclastic sedimentary rocks which crop out along the eastern margin of the Blue Ridge province in Alabama, Maryland, Tennessee, North Carolina, Virginia, and West Virginia. ...

of North Carolina and Tennessee or the mesoproterozoic Blue Ridge basement complex. The Alligator Back Metamorphic Suite structurally overlies the Ashe Metamorphic Suite. The Ashe Metamorphic Suite is intersected by the Grandfather Mountain window leaving a northeastern and southwestern region of the unit.

Petrology and Geochemistry

Chemical composition

A whole rock analyses of 8 samples of Ashe Metamorphic Suite amphibolites demonstrates a basaltic origin of the amhibolites suggesting a mid-ocean ridge basalt

Mafic Rocks

The mafic rocks of the Ashe Metamorphic Suite are composed primarily of hornblende schists and gneiss. The main minerals composing these rocks are hornblende, quartz and plagioclase with minor garnet, biotite, epidote-zoisite and magnetite being present.

Pelitic schists

The pelitic rocks of the Ashe Metamorohic Suite to the north of the Grandfather Mountain Window are primarily muscovite schists. Depending on the metamorphic grade, the pelitic rocks can be consist of quartz, plagioclase, biotite, garnet, chlorite, staurolite, and kyanite.

Formation and origin

The Ashe Metamorphic Suite is confined between the opening of the Iapetus sea at the beginning of the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

, and the closing of the ocean by in the Early

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

. It was initially suggested the Ashe Metamorphic Suite was deposited on a rifted continental margin with a nonconformable contact with the underlying Cranberry Gneiss. More recently the Ashe Metamorphic Suite is thought to be a subduction-related mélange with the contact between the Cranberry Gneiss and the Ashe Metamorphic Suite being a fault, or that the Ashe Metamorphic Suite was deposited as a

back-arc basin A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most of ...

.{{Cite journal, last1=Greenawald, first1=David, last2=Stewart, first2=Kevin G., last3=Gaynor, first3=Sean, date=2017, title=Amphibolite Zircon U-PB Geochronology in the Ashe Metamorphic Suite, Eastern Blue Ridge, North Carolina, url=http://dx.doi.org/10.1130/abs/2017am-305430, journal=, series=Geological Society of America Abstracts with Programs, publisher=Geological Society of America, doi=10.1130/abs/2017am-305430

References

Geologic formations of North Carolina Geologic formations of Virginia