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== Formation and origin ==
== Formation and origin ==
[[File:Ashe Metamorphic Suite.jpg|alt=Ashe Metamoprhic Suite from Meat Camp, North Carolina.|thumb|Ashe Metamorphic Suite (AMS) amphibolite from [[Meat Camp, North Carolina|Meat Camp, NC]].]]Rankin suggested the Ashe Metamorphic Suite was deposited on a rifted continental margin with a [[Unconformity|nonconformable contact]] with the underlying Cranberry Gneiss.<ref>{{Cite journal|last=Skipper|first=Hannah|last2=Ranson|first2=William A.|date=2020|title=GEOLOGY AND BLUE RIDGE ESCARPMENT EVOLUTION ALONG BEARCAMP, BEAR, AND BEARWALLOW CREEKS IN SOUTHWESTERN NORTH CAROLINA AND NORTHWESTERN SOUTH CAROLINA|url=http://dx.doi.org/10.1130/abs/2020se-345247|publisher=Geological Society of America|doi=10.1130/abs/2020se-345247}}</ref> Raymond and Abott suggested the AMS to be a subduction-related mélange with the contact between the Cranberry Gneiss and the AMS to be a fault.<ref>{{Cite journal|last=Abbott|first=R. N.|last2=Raymond|first2=L. A.|date=1984-05-01|title=The Ashe Metamorphic Suite, Northwest North Carolina; metamorphism and observations on geologic history|url=http://www.ajsonline.org/cgi/doi/10.2475/ajs.284.4-5.350|journal=American Journal of Science|language=en|volume=284|issue=4-5|pages=350–375|doi=10.2475/ajs.284.4-5.350|issn=0002-9599}}</ref><ref>{{Cite journal|last=Greenawald|first=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|publisher=Geological Society of America|doi=10.1130/abs/2017am-305430}}</ref> While Misra and Conte proposed the unit was deposited as a [[back-arc basin]].<ref name=":0" /> The Ashe Metamorphic Suite is confined between the opening of the [[Iapetus Ocean|Iapetus sea]] at the beginning of the [[Cambrian]], and the closing of the ocean by in the Early [[Ordovician]].<ref>{{Cite journal|date=1993|title=The volcanogenic Mount Rogers Formation and the overlying glaciogenic Konnarock Formation; two late Proterozoic units in southwestern Virginia|url=http://dx.doi.org/10.3133/b2029}}</ref>
[[File:Ashe Metamorphic Suite.jpg|alt=Ashe Metamoprhic Suite from Meat Camp, North Carolina.|thumb|Ashe Metamorphic Suite (AMS) amphibolite from [[Meat Camp, North Carolina|Meat Camp, NC]].]]Rankin suggested the Ashe Metamorphic Suite was deposited on a rifted continental margin with a [[Unconformity|nonconformable contact]] with the underlying Cranberry Gneiss.<ref>{{Cite journal|last=Skipper|first=Hannah|last2=Ranson|first2=William A.|date=2020|title=GEOLOGY AND BLUE RIDGE ESCARPMENT EVOLUTION ALONG BEARCAMP, BEAR, AND BEARWALLOW CREEKS IN SOUTHWESTERN NORTH CAROLINA AND NORTHWESTERN SOUTH CAROLINA|url=http://dx.doi.org/10.1130/abs/2020se-345247|publisher=Geological Society of America|doi=10.1130/abs/2020se-345247}}</ref> Raymond and Abott suggested the AMS to be a subduction-related mélange with the contact between the Cranberry Gneiss and the AMS to be a fault.<ref>{{Cite journal|last=Abbott|first=R. N.|last2=Raymond|first2=L. A.|date=1984-05-01|title=The Ashe Metamorphic Suite, Northwest North Carolina; metamorphism and observations on geologic history|url=http://www.ajsonline.org/cgi/doi/10.2475/ajs.284.4-5.350|journal=American Journal of Science|language=en|volume=284|issue=4-5|pages=350–375|doi=10.2475/ajs.284.4-5.350|issn=0002-9599}}</ref><ref>{{Cite journal|last=Greenawald|first=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|publisher=Geological Society of America|doi=10.1130/abs/2017am-305430}}</ref> While Misra and Conte proposed the unit was deposited as a [[back-arc basin]].<ref name=":0" /> The Ashe Metamorphic Suite is confined between the opening of the [[Iapetus Ocean|Iapetus sea]] at the beginning of the [[Cambrian]], and the closing of the ocean by in the Early [[Ordovician]].<ref>{{Cite journal|date=1993|title=The volcanogenic Mount Rogers Formation and the overlying glaciogenic Konnarock Formation; two late Proterozoic units in southwestern Virginia|url=http://dx.doi.org/10.3133/b2029}}</ref><ref>{{Cite journal|last=Rankin|first=Douglas W.|date=1993|title=The volcanogenic Mount Rogers Formation and the overlying glaciogenic Konnarock Formation; two late Proterozoic units in southwestern Virginia|url=https://pubs.er.usgs.gov/publication/b2029|journal=USGS Professional Publication #something|doi=10.3133/b2029}}</ref>


== References ==
== References ==

Revision as of 19:11, 18 March 2021

Ashe Metamorphic Suite for editing

The Ashe Metamorphic Suite (AMS) also referred to as the Ashe Formation, was named after its type locality, Ashe County, North Carolina.[1] The Ashe Metamorphic Suite is located in the Eastern Blue Ridge providence that extends from North Carolina up to Virginia. It is a heterogeneous collection of metamorphic rocks. It has been assigned radiometric dates between 570 to 350 millions of years old. Being deposited during the Late Proterozoic and reaching its cooling age during the end of the Devonian. [(A photo taken at Elk Knob should be added here)]

Geographic situation

The Ashe Metamorphic Suite forms part of the Blue Ridge mountains running at a North-East to South-West direction from South-Western Virginia into North Carolina. It is intersected by the Grandfather Mountain window leaving a Northeastern and Southwestern region of the unit.[2] 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.[3][(Here a map of the Ashe Metamorphic Suite and Alligator Back Suite should be added w/ GM window shown)]

Geologic overview

The AMS is composed of a variety of different rocks such as metagreywackes, muscovite schist, quartzite[4], graphitic schist, and ultramafic rocks such as amphibolite and hornblende gneiss.[5] The unit is overwhelmingly composed of mica schist with the southwest having intrusions of the ultramafic rocks.[2] The AMS overlies the Chilhowee Group of North Carolina and Tennessee or the Blue Ridge basement complex. The Alligator Back Metamorphic Suite overlies the Ashe Metamorphic Suite.[3]

Petrological description

Chemical composition

The analyses by Conte and Misra [6] of 8 samples of Ashe Metamorphic Suite amphibolites demonstrating the chemical composition of these rocks. This analysis suggests a basalt origin for the amphibolites within the AMS showing a MOR basalt protolith.[6]

Oxide

Weight %

As-20 As-24 As-49 As-56 As-82 As-12 As-27 As-66
SiO2 51.69 50.67 49.31 49.85 51.00 47.89 50.79 50.93
TiO2 0.15 0.44 1.29 1.88 1.43 3.23 3.16 13.78
Al2O3 12.28 12.07 16.20 13.93 14.14 12.88 12.01 13.78
Fe2O3 12.89 14.88 10.66 14.15 12.15 16.44 16.06 15.03
MnO 0.15 0.18 0.16 0.20 0.17 0.21 0.22 0.20
MgO 8.83 7.95 7.35 6.68 7.22 12.78 5.54 4.31
CaO 11.64 11.13 9.38 10.03 10.32 9.79 9.24 6.76
Na2O 1.28 1.51 3.61 2.87 2.78 2.92 2.34 2.25
K2O 0.19 0.17 0.25 0.31 0.29 0.27 0.83 2.39
P2O5 0.02 0.06 0.17 0.33 0.27 0.44 0.43 0.84
Total 99.12 99.06 98.38 100.23 99.77 100.20 100.62 98.89

Formation and origin

Ashe Metamoprhic Suite from Meat Camp, North Carolina.
Ashe Metamorphic Suite (AMS) amphibolite from Meat Camp, NC.

Rankin suggested the Ashe Metamorphic Suite was deposited on a rifted continental margin with a nonconformable contact with the underlying Cranberry Gneiss.[7] Raymond and Abott suggested the AMS to be a subduction-related mélange with the contact between the Cranberry Gneiss and the AMS to be a fault.[8][9] While Misra and Conte proposed the unit was deposited as a back-arc basin.[3] The Ashe Metamorphic Suite is confined between the opening of the Iapetus sea at the beginning of the Cambrian, and the closing of the ocean by in the Early Ordovician.[10][11]

References

  1. ^ "Geolex — Ashe publications". ngmdb.usgs.gov. Retrieved 2021-03-18.
  2. ^ a b Raymond, Loren A. (10/2015). "FORMAL REVISION OF THE ASHE AND ALLIGATOR BACK FORMATION NAMES". Southeastern Geology. 51: 135–143. {{cite journal}}: Check date values in: |date= (help)
  3. ^ a b c Misra, Kula C.; Conte, Jonathan A. (1991-06-01). "Amphibolites of the Ashe and Alligator Back Formations, North Carolina: Samples of Late Proterozoic-early Paleozoic oceanic crust". GSA Bulletin. 103 (6): 737–750. doi:10.1130/0016-7606(1991)1032.3.CO;2. ISSN 0016-7606.
  4. ^ Bailey, Christopher M.; Coiner, Lorrie V. (2014-03-26). Elevating Geoscience in the Southeastern United States: New Ideas about Old Terranes: Field Guides for the GSA Southeastern Section Meeting, Blacksburg, Virginia, 2014. Geological Society of America. ISBN 978-0-8137-0035-9.
  5. ^ Misra, Kula C.; Conte, Jonathan A. (1991-06-01). "Amphibolites of the Ashe and Alligator Back Formations, North Carolina: Samples of Late Proterozoic-early Paleozoic oceanic crust". GSA Bulletin. 103 (6): 737–750. doi:10.1130/0016-7606(1991)1032.3.CO;2. ISSN 0016-7606.
  6. ^ a b Misra, Kula C.; Conte, Jonathan A. (1991-06-01). "Amphibolites of the Ashe and Alligator Back Formations, North Carolina: Samples of Late Proterozoic-early Paleozoic oceanic crust". GSA Bulletin. 103 (6): 737–750. doi:10.1130/0016-7606(1991)1032.3.CO;2. ISSN 0016-7606.
  7. ^ Skipper, Hannah; Ranson, William A. (2020). "GEOLOGY AND BLUE RIDGE ESCARPMENT EVOLUTION ALONG BEARCAMP, BEAR, AND BEARWALLOW CREEKS IN SOUTHWESTERN NORTH CAROLINA AND NORTHWESTERN SOUTH CAROLINA". Geological Society of America. doi:10.1130/abs/2020se-345247. {{cite journal}}: Cite journal requires |journal= (help)
  8. ^ Abbott, R. N.; Raymond, L. A. (1984-05-01). "The Ashe Metamorphic Suite, Northwest North Carolina; metamorphism and observations on geologic history". American Journal of Science. 284 (4–5): 350–375. doi:10.2475/ajs.284.4-5.350. ISSN 0002-9599.
  9. ^ Greenawald, David; Stewart, Kevin G.; Gaynor, Sean (2017). "AMPHIBOLITE ZIRCON U-PB GEOCHRONOLOGY IN THE ASHE METAMORPHIC SUITE, EASTERN BLUE RIDGE, NORTH CAROLINA". Geological Society of America. doi:10.1130/abs/2017am-305430. {{cite journal}}: Cite journal requires |journal= (help)
  10. ^ "The volcanogenic Mount Rogers Formation and the overlying glaciogenic Konnarock Formation; two late Proterozoic units in southwestern Virginia". 1993. {{cite journal}}: Cite journal requires |journal= (help)
  11. ^ Rankin, Douglas W. (1993). "The volcanogenic Mount Rogers Formation and the overlying glaciogenic Konnarock Formation; two late Proterozoic units in southwestern Virginia". USGS Professional Publication #something. doi:10.3133/b2029.
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