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NARROW
Format
Article Type
Journal
Publisher
Section
GeoRef Subject
-
all geography including DSDP/ODP Sites and Legs
-
Africa
-
Reguibat Ridge (1)
-
Southern Africa
-
South Africa (1)
-
-
West Africa
-
Guinea (2)
-
Liberia (1)
-
Mauritania (1)
-
Senegal (1)
-
Sierra Leone (1)
-
-
West African Craton (1)
-
-
Atlantic Ocean
-
North Atlantic
-
Blake Plateau (2)
-
-
-
Atlantic region (1)
-
Avalon Zone (1)
-
Caledonides (2)
-
Canada
-
Eastern Canada
-
Gander Zone (1)
-
Meguma Terrane (1)
-
Ontario
-
Ottawa Ontario (1)
-
-
-
-
Caribbean region (1)
-
Europe
-
Alps
-
Western Alps (1)
-
-
Western Europe
-
Scandinavia
-
Norway (1)
-
-
United Kingdom
-
Great Britain
-
England (1)
-
-
-
-
-
Grandfather Mountain (4)
-
Hunter Valley (1)
-
Kings Mountain (1)
-
North America
-
Appalachian Basin (3)
-
Appalachians
-
Appalachian Plateau (2)
-
Blue Ridge Mountains (29)
-
Blue Ridge Province (36)
-
Carolina slate belt (18)
-
Central Appalachians (28)
-
Cumberland Plateau (3)
-
Northern Appalachians (3)
-
Piedmont
-
Inner Piedmont (7)
-
-
Southern Appalachians (298)
-
Valley and Ridge Province (23)
-
-
Eastern Overthrust Belt (4)
-
Gulf Coastal Plain (6)
-
North American Cordillera (1)
-
North American Craton (1)
-
-
Pine Mountain Fault (1)
-
Pulaski Fault (2)
-
Raleigh Belt (2)
-
Rome Trough (1)
-
Saltville Fault (4)
-
Sierra Nevada (1)
-
South America
-
Amazonian Craton (1)
-
Argentina (1)
-
Precordillera (1)
-
-
United States
-
Alabama
-
Calhoun County Alabama (2)
-
Chambers County Alabama (2)
-
Chilton County Alabama (5)
-
Clay County Alabama (5)
-
Cleburne County Alabama (3)
-
Coosa County Alabama (6)
-
Greene County Alabama (1)
-
Jefferson County Alabama (4)
-
Lee County Alabama (2)
-
Macon County Alabama (1)
-
Randolph County Alabama (1)
-
Saint Clair County Alabama (1)
-
Shelby County Alabama (4)
-
Talladega County Alabama (7)
-
Tallapoosa County Alabama (3)
-
-
Arkansas (1)
-
Atlantic Coastal Plain
-
Southern Atlantic Coastal Plain (4)
-
-
Benton Uplift (1)
-
Black Warrior Basin (1)
-
Blue Ridge Mountains (29)
-
Brevard Zone (9)
-
California
-
Northern California (1)
-
-
Carolina Terrane (17)
-
Charlotte Belt (5)
-
Colorado (1)
-
Eastern U.S.
-
Southeastern U.S. (3)
-
-
Florida
-
Calhoun County Florida (1)
-
-
Georgia
-
Bartow County Georgia
-
Cartersville Georgia (1)
-
-
Catoosa County Georgia (1)
-
Chattooga County Georgia (1)
-
Cherokee County Georgia (1)
-
Columbia County Georgia (1)
-
Dade County Georgia (1)
-
DeKalb County Georgia (1)
-
Elbert County Georgia (1)
-
Fannin County Georgia (1)
-
Franklin County Georgia (1)
-
Gilmer County Georgia (1)
-
Habersham County Georgia (2)
-
Hall County Georgia (1)
-
Harris County Georgia (5)
-
Lincoln County Georgia (1)
-
Madison County Georgia (1)
-
Muscogee County Georgia (3)
-
Oglethorpe County Georgia (1)
-
Rabun County Georgia (2)
-
Seminole County Georgia (1)
-
Stephens County Georgia (2)
-
Talbot County Georgia (2)
-
Walker County Georgia (1)
-
Whitfield County Georgia (1)
-
-
Great Smoky Fault (2)
-
Great Smoky Mountains (6)
-
Hayesville Fault (4)
-
Illinois (1)
-
Illinois Basin (1)
-
Kentucky
-
Kentucky River Fault (1)
-
-
Kings Mountain Belt (4)
-
Kiokee Belt (5)
-
Maryland (1)
-
Massachusetts
-
Suffolk County Massachusetts
-
Boston Massachusetts (1)
-
-
-
Midcontinent (3)
-
Midwest (1)
-
Mississippi Valley (2)
-
Nevada (1)
-
New England (3)
-
New Hampshire (1)
-
New Jersey (1)
-
New Madrid region (2)
-
New York (1)
-
North Carolina
-
Ashe County North Carolina (2)
-
Cabarrus County North Carolina (2)
-
Caldwell County North Carolina (1)
-
Clay County North Carolina (4)
-
Cleveland County North Carolina (1)
-
Dare County North Carolina (1)
-
Davidson County North Carolina (3)
-
Durham County North Carolina (1)
-
Gaston County North Carolina (2)
-
Graham County North Carolina (1)
-
Haywood County North Carolina (1)
-
Henderson County North Carolina (1)
-
Lincoln County North Carolina (1)
-
Macon County North Carolina (7)
-
Madison County North Carolina (2)
-
Mecklenburg County North Carolina (1)
-
Mitchell County North Carolina (1)
-
Montgomery County North Carolina (1)
-
Nash County North Carolina (1)
-
Person County North Carolina (1)
-
Randolph County North Carolina (2)
-
Rowan County North Carolina (2)
-
Stanly County North Carolina (2)
-
Surry County North Carolina (1)
-
Swain County North Carolina (2)
-
Transylvania County North Carolina (1)
-
Union County North Carolina (1)
-
Watauga County North Carolina (1)
-
Wilkes County North Carolina (1)
-
Yancey County North Carolina (1)
-
-
Oklahoma (1)
-
Ouachita Mountains (3)
-
Pennsylvania (3)
-
Pine Mountain Window (11)
-
Pulaski thrust sheet (1)
-
Reading Prong (1)
-
South Carolina
-
Aiken County South Carolina (1)
-
Anderson County South Carolina (1)
-
Charleston County South Carolina (1)
-
Cherokee County South Carolina (1)
-
Chesterfield County South Carolina (1)
-
Fairfield County South Carolina (2)
-
Kershaw County South Carolina (3)
-
Lake Jocassee (2)
-
Lancaster County South Carolina (3)
-
Oconee County South Carolina (1)
-
Pickens County South Carolina (2)
-
Saluda County South Carolina (1)
-
Savannah River Site (1)
-
York County South Carolina (2)
-
-
Southern U.S. (1)
-
Talladega Front (10)
-
Tennessee
-
Blount County Tennessee (2)
-
Campbell County Tennessee (1)
-
Claiborne County Tennessee (2)
-
Giles County Tennessee (1)
-
Grainger County Tennessee (3)
-
Hancock County Tennessee (1)
-
Hawkins County Tennessee (1)
-
Jefferson County Tennessee (1)
-
Knox County Tennessee (2)
-
Monroe County Tennessee (1)
-
Polk County Tennessee
-
Ducktown Tennessee (4)
-
-
Sequatchie Valley (1)
-
Sevier County Tennessee (1)
-
Sullivan County Tennessee (2)
-
Washington County Tennessee (1)
-
-
Virginia
-
Botetourt County Virginia (2)
-
Buckingham County Virginia (1)
-
Campbell County Virginia (1)
-
Carroll County Virginia (1)
-
Craig County Virginia (2)
-
Giles County Virginia (3)
-
Grayson County Virginia (2)
-
Lee County Virginia (1)
-
Louisa County Virginia (1)
-
Montgomery County Virginia (2)
-
Patrick County Virginia (1)
-
Pittsylvania County Virginia (1)
-
Pulaski County Virginia (2)
-
Roanoke County Virginia (2)
-
Smyth County Virginia (1)
-
Spotsylvania County Virginia (1)
-
Stafford County Virginia (1)
-
Wythe County Virginia (1)
-
-
West Virginia (4)
-
Wiggins Arch (1)
-
Wyoming (1)
-
-
Yucatan Peninsula (1)
-
-
commodities
-
barite deposits (1)
-
coal deposits (1)
-
construction materials (1)
-
energy sources (3)
-
metal ores
-
base metals (2)
-
copper ores (5)
-
gold ores (9)
-
iron ores (1)
-
lead-zinc deposits (2)
-
polymetallic ores (1)
-
pyrite ores (2)
-
strontium ores (1)
-
zinc ores (3)
-
-
mineral deposits, genesis (14)
-
mineral exploration (3)
-
mineral resources (1)
-
petroleum
-
natural gas (4)
-
-
soapstone (1)
-
sulfur deposits (1)
-
-
elements, isotopes
-
carbon
-
C-13/C-12 (2)
-
-
hydrogen
-
D/H (1)
-
deuterium (1)
-
-
isotope ratios (17)
-
isotopes
-
radioactive isotopes
-
Be-10 (1)
-
Pb-206/Pb-204 (3)
-
Pb-207/Pb-204 (3)
-
Pb-208/Pb-204 (2)
-
Sm-147/Nd-144 (2)
-
-
stable isotopes
-
Ar-40 (1)
-
C-13/C-12 (2)
-
D/H (1)
-
deuterium (1)
-
Hf-177/Hf-176 (1)
-
Nd-144/Nd-143 (4)
-
O-18/O-16 (8)
-
Pb-206/Pb-204 (3)
-
Pb-207/Pb-204 (3)
-
Pb-208/Pb-204 (2)
-
S-34/S-32 (2)
-
Sm-147/Nd-144 (2)
-
Sr-87/Sr-86 (5)
-
-
-
Lu/Hf (2)
-
metals
-
alkaline earth metals
-
beryllium
-
Be-10 (1)
-
-
strontium
-
Sr-87/Sr-86 (5)
-
-
-
aluminum (3)
-
hafnium
-
Hf-177/Hf-176 (1)
-
-
lead
-
Pb-206/Pb-204 (3)
-
Pb-207/Pb-204 (3)
-
Pb-208/Pb-204 (2)
-
-
manganese (1)
-
rare earths
-
neodymium
-
Nd-144/Nd-143 (4)
-
Sm-147/Nd-144 (2)
-
-
samarium
-
Sm-147/Nd-144 (2)
-
-
yttrium (1)
-
-
tin (1)
-
zirconium (1)
-
-
noble gases
-
argon
-
Ar-40 (1)
-
-
-
oxygen
-
O-18/O-16 (8)
-
-
sulfur
-
S-34/S-32 (2)
-
-
-
fossils
-
bacteria (1)
-
cyanobacteria
-
Renalcis (1)
-
-
Graptolithina (2)
-
ichnofossils (2)
-
Invertebrata
-
Archaeocyatha (1)
-
Arthropoda
-
Mandibulata
-
Crustacea
-
Ostracoda (1)
-
-
-
Trilobitomorpha
-
Trilobita (5)
-
-
-
Brachiopoda
-
Articulata
-
Pentamerida (1)
-
-
-
Bryozoa (1)
-
Echinodermata
-
Crinozoa (1)
-
-
Mollusca
-
Gastropoda (1)
-
-
Protista
-
Foraminifera (1)
-
-
-
Metazoa (2)
-
microfossils
-
Conodonta (1)
-
-
palynomorphs
-
acritarchs (2)
-
-
Plantae
-
algae (4)
-
-
problematic fossils (2)
-
thallophytes (3)
-
-
geochronology methods
-
(U-Th)/He (1)
-
Ar/Ar (14)
-
K/Ar (7)
-
Lu/Hf (2)
-
Nd/Nd (1)
-
paleomagnetism (1)
-
Pb/Pb (1)
-
Pb/Th (2)
-
Rb/Sr (8)
-
Sm/Nd (7)
-
Th/U (1)
-
thermochronology (6)
-
U/Pb (42)
-
U/Th/Pb (2)
-
-
geologic age
-
Cenozoic
-
Quaternary (1)
-
Tertiary
-
Paleogene (1)
-
-
upper Cenozoic (1)
-
-
Mesozoic
-
Cretaceous
-
Upper Cretaceous (1)
-
-
Triassic (1)
-
-
Paleozoic
-
Cambrian
-
Acadian (3)
-
Conasauga Group (7)
-
Lower Cambrian
-
Chilhowee Group (5)
-
Murphy Marble (1)
-
Rome Formation (5)
-
Shady Dolomite (4)
-
-
Middle Cambrian (1)
-
Upper Cambrian
-
Copper Ridge Dolomite (3)
-
Dresbachian (1)
-
Maynardville Limestone (3)
-
-
-
Carboniferous
-
Lower Carboniferous
-
Dinantian (1)
-
-
Mississippian
-
Lower Mississippian
-
Pocono Formation (1)
-
-
Newman Limestone (1)
-
Price Formation (1)
-
Upper Mississippian
-
Hartselle Sandstone (2)
-
Monteagle Limestone (1)
-
Parkwood Formation (1)
-
-
-
Pennsylvanian
-
Middle Pennsylvanian
-
Allegheny Group (4)
-
-
Pottsville Group (1)
-
-
-
Catskill Formation (1)
-
Chattanooga Shale (1)
-
Devonian
-
Lower Devonian (1)
-
Upper Devonian
-
Brallier Shale (1)
-
Chemung Formation (1)
-
-
-
Knox Group (10)
-
lower Paleozoic
-
Ashe Formation (2)
-
Chopawamsic Formation (2)
-
Henderson Gneiss (1)
-
-
middle Paleozoic
-
Hillabee Chlorite Schist (3)
-
-
Ordovician
-
Chickamauga Group (3)
-
Lower Ordovician
-
Mascot Dolomite (1)
-
-
Middle Ordovician
-
Deicke Bentonite Bed (1)
-
Lenoir Limestone (2)
-
Millbrig Bentonite Bed (1)
-
-
Upper Ordovician
-
Juniata Formation (1)
-
-
-
Permian
-
Lower Permian
-
Cisuralian (1)
-
-
-
Silurian
-
Lower Silurian
-
Llandovery (1)
-
-
Rockwood Formation (2)
-
Upper Silurian
-
Pridoli (1)
-
-
-
Talladega Group (7)
-
upper Paleozoic (11)
-
-
Phanerozoic (1)
-
Precambrian
-
Archean (1)
-
Catoctin Formation (1)
-
Great Smoky Group (1)
-
upper Precambrian
-
Proterozoic
-
Mesoproterozoic (4)
-
Neoproterozoic
-
Ediacaran (3)
-
Lynchburg Formation (1)
-
Vendian (3)
-
Walden Creek Group (2)
-
-
-
-
-
-
igneous rocks
-
igneous rocks
-
plutonic rocks
-
diorites
-
trondhjemite (2)
-
-
gabbros
-
norite (1)
-
-
granites
-
adamellite (1)
-
monzogranite (1)
-
-
granodiorites (1)
-
pegmatite (1)
-
syenites (2)
-
ultramafics
-
pyroxenite
-
clinopyroxenite (1)
-
orthopyroxenite (1)
-
-
-
-
volcanic rocks
-
basalts
-
mid-ocean ridge basalts (1)
-
ocean-island basalts (1)
-
-
pyroclastics
-
ash-flow tuff (1)
-
tuff (1)
-
-
rhyolites (1)
-
-
-
ophiolite (7)
-
volcanic ash (1)
-
-
metamorphic rocks
-
K-bentonite (4)
-
metamorphic rocks
-
amphibolites
-
orthoamphibolite (1)
-
-
cataclasites (4)
-
eclogite (3)
-
gneisses
-
biotite gneiss (1)
-
granite gneiss (2)
-
orthogneiss (1)
-
paragneiss (3)
-
-
granulites (1)
-
metaigneous rocks
-
metabasalt (3)
-
metadacite (1)
-
metagabbro (3)
-
metagranite (2)
-
serpentinite (1)
-
-
metaplutonic rocks (2)
-
metasedimentary rocks
-
metachert (1)
-
metapelite (2)
-
paragneiss (3)
-
-
metasomatic rocks
-
rodingite (1)
-
serpentinite (1)
-
-
metavolcanic rocks (18)
-
migmatites (4)
-
mylonites
-
ultramylonite (1)
-
-
phyllites (3)
-
phyllonites (1)
-
quartzites (5)
-
schists
-
greenstone (6)
-
hornblende schist (1)
-
-
slates (3)
-
-
ophiolite (7)
-
turbidite (4)
-
-
minerals
-
carbonates
-
calcite (2)
-
dolomite (2)
-
-
halides
-
fluorides
-
fluorite (1)
-
-
-
K-bentonite (4)
-
minerals (4)
-
native elements
-
graphite (1)
-
-
oxides
-
goethite (1)
-
hematite (1)
-
rutile (1)
-
-
phosphates
-
apatite (1)
-
monazite (6)
-
-
silicates
-
chain silicates
-
amphibole group
-
clinoamphibole
-
hornblende (9)
-
-
-
pyroxene group
-
clinopyroxene
-
jadeite (1)
-
-
-
-
framework silicates
-
feldspar group
-
alkali feldspar
-
microcline (1)
-
-
plagioclase (5)
-
-
silica minerals
-
quartz (6)
-
-
-
orthosilicates
-
nesosilicates
-
garnet group
-
almandine (1)
-
andradite (1)
-
grossular (1)
-
-
olivine group
-
olivine (1)
-
-
sillimanite (1)
-
zircon group
-
zircon (39)
-
-
-
sorosilicates
-
epidote group
-
epidote (2)
-
-
-
-
ring silicates
-
cordierite (1)
-
-
sheet silicates
-
clay minerals
-
smectite (2)
-
-
illite (4)
-
mica group
-
biotite (7)
-
muscovite (5)
-
-
sericite (1)
-
-
-
sulfates
-
barite (1)
-
-
sulfides
-
galena (1)
-
molybdenite (1)
-
pyrite (2)
-
pyrrhotite (1)
-
sphalerite (2)
-
-
-
Primary terms
-
absolute age (63)
-
Africa
-
Reguibat Ridge (1)
-
Southern Africa
-
South Africa (1)
-
-
West Africa
-
Guinea (2)
-
Liberia (1)
-
Mauritania (1)
-
Senegal (1)
-
Sierra Leone (1)
-
-
West African Craton (1)
-
-
Atlantic Ocean
-
North Atlantic
-
Blake Plateau (2)
-
-
-
Atlantic region (1)
-
bacteria (1)
-
barite deposits (1)
-
bibliography (1)
-
biogeography (1)
-
biography (1)
-
Canada
-
Eastern Canada
-
Gander Zone (1)
-
Meguma Terrane (1)
-
Ontario
-
Ottawa Ontario (1)
-
-
-
-
carbon
-
C-13/C-12 (2)
-
-
Caribbean region (1)
-
Cenozoic
-
Quaternary (1)
-
Tertiary
-
Paleogene (1)
-
-
upper Cenozoic (1)
-
-
clay mineralogy (3)
-
climate change (1)
-
coal deposits (1)
-
construction materials (1)
-
continental drift (5)
-
crust (46)
-
crystal chemistry (1)
-
crystal growth (2)
-
crystal structure (1)
-
data processing (3)
-
deformation (35)
-
diagenesis (10)
-
earthquakes (16)
-
economic geology (23)
-
electron microscopy (1)
-
energy sources (3)
-
engineering geology (4)
-
epeirogeny (1)
-
Europe
-
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GeoRef Categories
Era and Period
Epoch and Age
Book Series
Date
Availability
Southern Appalachians
Silurian ocean island basalt magmatism and Devonian–Carboniferous polymetamorphism: 100 million years in the Western Blue Ridge, USA Available to Purchase
Petrology of the Halifax County complex, North Carolina, Southern Appalachians: constraints from petrography, mineral chemistry, and geothermobarometry Available to Purchase
Don't judge an orogen by its cover: Kinematics of the Appalachian décollement from seismic anisotropy Open Access
Ordovician–Silurian back-arc silicic magmatism in the southernmost Appalachians Available to Purchase
Detrital zircon geothermochronology reveals pre-Alleghanian exhumation of regional Mississippian sediment sources in the southern Appalachian Valley and Ridge Province Open Access
Tectonism and metamorphism along a southern Appalachian transect across the Blue Ridge and Piedmont, USA Available to Purchase
ABSTRACT The Appalachian Mountains expose one of the most-studied orogenic belts in the world. However, metamorphic pressure-temperature-time (P-T-t) paths for reconstructing the tectonic history are largely lacking for the southernmost end of the orogen. In this contribution, we describe select field locations in a rough transect across the orogen from Ducktown, Tennessee, to Goldville, Alabama. Metamorphic rocks from nine locations are described and analyzed in order to construct quantitative P-T-t paths, utilizing isochemical phase diagram sections and garnet Sm-Nd ages. P-T-t paths and garnet Sm-Nd ages for migmatitic garnet sillimanite schist document high-grade 460–411 Ma metamorphism extending south from Winding Stair Gap to Standing Indian in the Blue Ridge of North Carolina. In the Alabama Blue Ridge, Wedowee Group rocks were metamorphosed at biotite to staurolite zone, with only local areas of higher-temperature metamorphism. The Wedowee Group is flanked by higher-grade rocks of the Ashland Supergroup and Emuckfaw Group to the northwest and southeast, respectively. Garnet ages between ca. 357 and 319 Ma indicate that garnet growth was Neoacadian to early Alleghanian in the Blue Ridge of Alabama. The P-T-t paths for these rocks are compatible with crustal thickening during garnet growth.
Hydrology of a Southern Appalachian Hypocrene Spring-Fed Fen Available to Purchase
New paleontological evidence for complex middle Paleozoic tectonic evolution in the Appalachian western Blue Ridge Available to Purchase
Detrital garnet geochronology: Application in tributaries of the French Broad River, Southern Appalachian Mountains, USA Available to Purchase
Linking metamorphism, magma generation, and synorogenic sedimentation to crustal thickening during Southern Appalachian mountain building, USA Open Access
From the Alleghanian to the Atlantic: Extensional collapse of the southernmost Appalachian orogen Available to Purchase
A Notable Earthquake Swarm in Alabama: Natural or Anthropogenic? Available to Purchase
Evolution of the Blue Ridge basement complex in the eastern Great Smoky Mountains: Evidence from zircon U-Pb geochronology and Nd-Pb isotope geochemistry of basement gneisses Available to Purchase
ABSTRACT The eastern Great Smoky Mountains basement complex consists of the following components: (1) ca. 1350–1325 Ma orthogneiss and mafic xenoliths that represent some of the oldest crust in Appalachian Grenville massifs (similar to “pre-Grenville” basement components in the Adirondack, Green Mountain, Hudson Highland, and Shenandoah massifs); (2) ca. 1150 Ma augen orthogneisses and granitic orthogneisses correlating with the Shawinigan phase of Grenville magmatism; and (3) paragneisses (cover rocks) that have either pre- or syn-Grenville (i.e., Mesoproterozoic) versus post-Grenville (Neoproterozoic) depositional ages, and that experienced Taconian metamorphism and migmatization. Mesoproterozoic paragneisses contain major zircon age modes that require a component of Proterozoic crust in the source region. The Neoproterozoic paragneisses exhibit the archetypical “Grenville doublet” in detrital zircon age distributions that matches the age distribution of Ottawan and Shawinigan magmatic/metamorphic events in eastern Laurentia. Most zircon U-Pb age systematics exhibit variable lead loss interpreted to result from high-grade Taconian (ca. 450 Ma) regional metamorphism and migmatization. Neodymium mantle model ages (T DM) for ortho- and paragneisses range from 1.8 to 1.6 Ga, indicating that all rocks were derived from recycling of Proterozoic crust (i.e., they are not juvenile), which is consistent with Proterozoic detrital zircon ages in pre- to syn-Grenville paragneisses. Lead isotope compositions confirm the presence of an exotic (Amazonian) crustal component in the source region for the protoliths of the pre-Grenville orthogneisses and xenoliths, and that this exotic component was incorporated to varying degrees in the evolution of the basement complex. The oldest age component may represent an Amazonian pre-Grenville analog to the ca. 1.35 Ga native Laurentian crust present in Adirondack and northern Appalachian basement massifs.
Blue Ridge–Inner Piedmont geotraverse from the Great Smoky fault to the Inner Piedmont: Upper crust to upper-lower crust, terranes, large faults, and sutures Available to Purchase
ABSTRACT The southern Appalachian orogen is a Paleozoic accretionary-collisional orogen that formed as the result of three Paleozoic orogenies, Taconic, Acadian and Neoacadian, and Alleghanian orogenies. The Blue Ridge–Piedmont megathrust sheet exposes various crystalline terranes of the Blue Ridge and Inner Piedmont that record the different effects of these orogenies. The western Blue Ridge is the Neoproterozoic to Ordovician Laurentian margin. Constructed on Mesoproterozoic basement, 1.2–1.0 Ga, the western Blue Ridge transitions from two rifting events at ca. 750 Ma and ca. 565 Ma to an Early Cambrian passive margin and then carbonate bank. The Hayesville fault marks the Taconic suture and separates the western Blue Ridge from distal peri-Laurentian terranes of the central and eastern Blue Ridge, which are the Cartoogechaye, Cowrock, Dahlonega gold belt, and Tugaloo terranes. The central and eastern Blue Ridge terranes are dominantly clastic in composition, intruded by Ordovician to Mississippian granitoids, and contain ultramafic and mafic rocks, suggesting deposition on oceanic crust. These terranes accreted to the western Blue Ridge during the Taconic orogeny at 462–448 Ma, resulting in metamorphism dated with SHRIMP (sensitive high-resolution ion microprobe) U-Pb ages of metamorphic zircon. The Inner Piedmont, which is separated from the Blue Ridge by the Brevard fault zone, experienced upper amphibolite, sillimanite I and higher-grade metamorphism during the Acadian and Neoacadian orogenies, 395–345 Ma. These events also affected the eastern Blue Ridge, and parts of the western Blue Ridge. The Acadian and Neoacadian orogeny is the result of the oblique collision and accretion of the peri-Gondwanan Carolina superterrane overriding the Inner Piedmont. During this collision, the Inner Piedmont was a forced mid-crustal orogenic channel that flowed NW-, W-, and SW-directed from underneath the Carolina superterrane. The Alleghanian orogeny thrust these terranes northwestward as part of the Blue Ridge–Piedmont megathrust sheet during the collision of Gondwana (Africa) and the formation of Pangea.
Taconic suprasubduction zone magmatism in southern Laurentia: Evidence from the Dadeville Complex Available to Purchase
Paleozoic tectonic evolution of the western Blue Ridge, southern Appalachians: A critical examination of long-standing conflicts in a polydeformed system Available to Purchase
ABSTRACT The southern Appalachian western Blue Ridge preserves a Mesoproterozoic and mid-Paleozoic basement and Neoproterozoic to Ordovician rift-to-drift sequence that is metamorphosed up to sillimanite grade and dissected by northwest-directed thrust faults resulting from several Paleozoic orogenic events. Despite a number of persistent controversies regarding the age of some western Blue Ridge units, and the nature and extent of multiple Paleozoic deformational/metamorphic events, synthesis of several multidisciplinary data sets (detailed geologic mapping, geochronology and thermochronology, stable-isotope chemostratigraphy) suggests that the western Blue Ridge likely records the effects of two discrete orogenic events. The earlier Taconic (470–440 Ma) event involved a progression from open folding and emplacement of the Greenbrier–Rabbit Creek and Dunn Creek thrust sheets as a foreland fold-and-thrust to low-grade hinterland system (D 1A), followed by deep burial (>31 km), pervasive folding of the earlier-formed fault surfaces, and widespread Barrovian metamorphism (D 1B). Because this high-grade (D 1B) metamorphic event is recorded in Ordovician Mineral Bluff Group turbidites, this unit must have been deposited prior to peak orogenesis, possibly as a foreland basin or wedge-top unit in front of and/or above the developing fold-and-thrust belt. The later Alleghanian (325–265 Ma) event involved widespread northwest-directed brittle thrusting and folding related to emplacement of the Great Smoky thrust sheet (D 2 ; hanging wall of the Blue Ridge– Piedmont thrust). Mid-Paleozoic 40 Ar/ 39 Ar muscovite ages from western Blue Ridge samples likely record post-Taconic cooling (hornblende and some muscovite 40 Ar/ 39 Ar ages) and/or Alleghanian thrust-related exhumation and cooling (ca. 325 Ma muscovite 40 Ar/ 39 Ar and 300–270 Ma zircon fission-track ages), as opposed to resulting from a discrete Neoacadian thermal-deformational event. The lack of evidence for a discrete Neoacadian event further implies that all deformation recorded in the Silurian–Mississippian(?) Maggies Mill–Citico Formation must be Alleghanian. We interpret this structurally isolated sequence to have been derived from the footwall of the Great Smoky fault as an orphan slice that was subsequently breached through the Great Smoky hanging wall along the out-of-sequence Maggies Mill thrust.
Temporal and spatial distribution of Paleozoic metamorphism in the southern Appalachian Blue Ridge and Inner Piedmont delimited by ion microprobe U-Pb ages of metamorphic zircon Available to Purchase
ABSTRACT Ion microprobe U-Pb zircon rim ages from 39 samples from across the accreted terranes of the central Blue Ridge, eastward across the Inner Piedmont, delimit the timing and spatial extent of superposed metamorphism in the southern Appalachian orogen. Metamorphic zircon rims are 10–40 µm wide, mostly unzoned, and dark gray to black or bright white in cathodoluminescence, and truncate and/or embay interior oscillatory zoning. Black unzoned and rounded or ovoid-shaped metamorphic zircon morphologies also occur. Th/U values range from 0.01 to 1.4, with the majority of ratios less than 0.1. Results of 206 Pb/ 238 U ages, ±2% discordant, range from 481 to 305 Ma. Clustering within these data reveals that the Blue Ridge and Inner Piedmont terranes were affected by three tectonothermal events: (1) 462–448 Ma (Taconic); (2) 395–340 Ma (Acadian and Neoacadian); and (3) 335–322 Ma, related to the early phase of the Alleghanian orogeny. By combining zircon rim ages with metamorphic isograds and other published isotopic ages, we identify the thermal architecture of the southern Appalachian orogen: juxtaposed and superposed metamorphic domains have younger ages to the east related to the marginward addition of terranes, and these domains can serve as a proxy to delimit terrane accretion. Most 462–448 Ma ages occur in the western and central Blue Ridge and define a continuous progression from greenschist to granulite facies that identifies the intact Taconic core. The extent of 462–448 Ma metamorphism indicates that the central Blue Ridge and Tugaloo terranes were accreted to the western Blue Ridge during the Taconic orogeny. Zircon rim ages in the Inner Piedmont span almost 100 m.y., with peaks at 395–385, 376–340, and 335–322 Ma, and delimit the Acadian-Neoacadian and Alleghanian metamorphic core. The timing and distribution of metamorphism in the Inner Piedmont are consistent with the Devonian to Mississippian oblique collision of the Carolina superterrane, followed by an early phase of Alleghanian metamorphism at 335–322 Ma (temperature >500 °C). The eastern Blue Ridge contains evidence of three possible tectonothermal events: ~460 Ma, 376–340 Ma, and ~335 Ma. All of the crystalline terranes of the Blue Ridge–Piedmont megathrust sheet were affected by Alleghanian metamorphism and deformation.
Transition from B- to A-type subduction during closing of the Rheic remnant ocean: New geochronologic and geochemical data marking Acadian-Neoacadian orogenesis and accretion of the Carolina superterrane, southern Appalachians Available to Purchase
ABSTRACT The timing and kinematics of Paleozoic peri-Gondwanan terrane accretion along the southern and central Appalachian margin have long been debated. The Silurian–Devonian Concord plutonic suite intruded the western flank of the Carolina superterrane, suggesting east-dipping subduction of ocean crust beneath the Carolina superterrane just prior to accretion, based on Devonian–Mississippian plutonism and metamorphism in the adjacent Laurentian terranes. Geochemical and isotopic data support a subduction-related origin for the Concord plutonic suite, and our geochronologic data reveal the main pulse of plutonism occurred ca. 405 Ma. Our new sensitive high-resolution ion microprobe (SHRIMP) geochronologic data identify a suite of mafic plutons from the Carolinas to central Georgia that also belong to the Concord suite. These gabbros have U-Pb zircon ages of 372 ± 2 Ma (Gladesville contact aureole), 386 ± 5.7 Ma (Buffalo), 403.8 ± 3.7 Ma (Highway 200), 404.9 ± 6.9 Ma (Mecklenburg), and 416 ± 6.9 Ma (Calhoun Falls). The Ogden Gabbro has a U-Pb age from baddeleyite of 411.91 ± 0.25 Ma. In this study, we identified a previously unrecognized Alleghanian (Pennsylvanian) gabbro suite with U-Pb zircon ages of 308.2 ± 6.2 Ma (Farmington), 311 ± 6.2 Ma (Dutchman’s Creek), and 311 ± 6.5 Ma (Mount Carmel). These gabbros should henceforth not be included in the Concord suite. The ages of Concord suite plutons slightly predate the main phase of plutonism in the Cat Square terrane to the west, which we suggest represents the product of B-type subduction of ocean crust beneath the Carolina superterrane between 415 and 400 Ma. Arc-related magmatism terminated because of the switch to A-type subduction of the eastern Laurentian margin. Prograde upper-amphibolite- to granulite-facies metamorphism, wholesale migmatization, and extensive anatectic plutonism in the eastern Inner Piedmont occurred from Late Devonian into Mississippian time, shortly after cessation of Concord plutonic suite plutonism, which also supports this proposed model. These data, combined with the timing and geometry of foreland clastic wedges, provide compelling support for Devonian–Mississippian accretion of the Carolina superterrane via dextral transpressive obduction above the eastern Laurentian margin.
Geologic and kinematic insights from far-traveled horses in the Brevard fault zone, southern Appalachians Available to Purchase
ABSTRACT The Brevard fault zone is one of the largest faults in the Appalachians, extending from Alabama to Virginia. It had a very complex history of movement and reactivation, with three movement episodes: (1) Acadian-Neoacadian (403–345 Ma) movement accompanying the thermal peak of metamorphism and deformation with dextral, southwest-directed emplacement of the Inner Piedmont; (2) ductile dextral reactivation during the early Alleghanian (~280 Ma) under lower-greenschist-facies conditions; and (3) brittle dip-slip reactivation during the late Alleghanian (260 Ma?). The Brevard is comparable to other large faults with polyphase movement in other orogens worldwide, for example, the Periadriatic line in the Alps. Two types of far-traveled, fault-bounded horses have been identified in the Brevard fault zone in the Carolinas: (1) metasedimentary and granitoid horses located along the southeastern margin of the Alleghanian retrogressive ductile dextral Brevard fault zone in North and South Carolina; and (2) limestone/dolostone horses located along the brittle, late Alleghanian Rosman thrust, the contact between Blue Ridge and Brevard fault zone rocks in North and South Carolina. Field, stratigraphic, petrographic, and Sr-isotope data suggest the carbonate horses may be derived from Valley and Ridge carbonates in the Blue Ridge–Piedmont megathrust sheet footwall. The horses of metasedimentary and granitoid rocks occur along faults that cut klippen of the southwest-directed Inner Piedmont Acadian-Neoacadian Alto (Six Mile) allochthon. New laser ablation– inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb zircon analyses from the metasedimentary mylonite component yield a detrital zircon suite dominated by 600 and 500 Ma zircons, and a second zircon population ranging from 2100 to 1300 Ma, with essentially no Grenvillian zircons, suggesting a peri-Gondwanan provenance. The granitoid component has a sensitive high-resolution ion microprobe (SHRIMP) age of 421 ± 14 Ma, similar to the ~430 Ma plutonic suite in northern Virginia and Maryland—a prominent component of the Cat Square terrane detrital zircon suite in the Carolinas. Peri-Gondwanan Neoproterozoic to Cambrian Avalon–Carolina superterrane rocks are nowhere in contact with the Brevard fault zone at present erosion level. While these far-traveled metasedimentary and granitoid horses may have originated several hundred kilometers farther northeast in the central Appalachians, they could alternatively be remnants of Avalon–Carolina superterrane rocks that once formed the tectonic lid of the southwest-directed Neoacadian–early Alleghanian (Late Devonian–early Mississippian) orogenic channel formed during north-to-south zippered accretion of Avalon–Carolina. The remnant fossil subduction zone survives as the central Piedmont suture. Avalon–Carolina terrane rocks would have once covered the Inner Piedmont (and easternmost Blue Ridge) to depths of >20 km, and have since been eroded. Data from these two suites of horses provide additional insights into the mid- to late Paleozoic history and kinematics of the Brevard fault zone, Inner Piedmont, and Avalon–Carolina superterrane. It was six men of Indostan To learning much inclined, Who went to see the Elephant (Though all of them were blind), That each by observation Might satisfy his mind. … And so these men of Indostan Disputed loud and long, Each in his own opinion Exceeding stiff and strong, Though each was partly in the right, And all were in the wrong. —John Godfrey Saxe (1816–1887) “The Blind Men and the Elephant”