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NARROW
GeoRef Subject
-
all geography including DSDP/ODP Sites and Legs
-
Anglesey (1)
-
Asia (1)
-
Atlantic Ocean
-
North Atlantic
-
Gulf of Mexico (1)
-
Gulf of Saint Lawrence (3)
-
Northeast Atlantic
-
Porcupine Bank (1)
-
-
Northwest Atlantic (1)
-
-
-
Atlantic region (2)
-
Australasia
-
Australia
-
South Australia
-
Adelaide Australia (1)
-
-
-
-
Avalon Zone (17)
-
Caledonides (5)
-
Canada
-
Eastern Canada
-
Gander Zone (4)
-
Maritime Provinces
-
New Brunswick
-
Miramichi Bay (1)
-
-
Nova Scotia
-
Antigonish County Nova Scotia (1)
-
Cape Breton Island
-
Cape Breton Highlands (1)
-
-
Cobequid Fault (1)
-
Yarmouth County Nova Scotia (1)
-
-
-
Meguma Terrane (10)
-
Newfoundland and Labrador
-
Newfoundland
-
Avalon Peninsula (2)
-
Baie Verte Peninsula (3)
-
Burin Peninsula (1)
-
Humber Arm Allochthon (6)
-
Port au Port Peninsula (6)
-
-
-
Ontario (1)
-
Quebec
-
Anticosti Island (1)
-
Gaspe Peninsula (16)
-
Matapedia County Quebec (1)
-
Sherbrooke County Quebec (2)
-
-
-
-
Caribbean region
-
West Indies
-
Antilles
-
Greater Antilles
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Jamaica (1)
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Puerto Rico (1)
-
-
-
-
-
Dunnage Melange (1)
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Dunnage Zone (8)
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Europe
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Central Europe
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Bohemian Massif (1)
-
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Southern Europe
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Iberian Peninsula
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Ossa-Morena Zone (1)
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Tornquist-Teisseyre Zone (1)
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Western Europe
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Belgium
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Brabant Massif (1)
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Wallonia Belgium
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Namur Belgium (1)
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Dinant Basin (1)
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France
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Armorican Massif (2)
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Central Massif (1)
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Ireland
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Cork Ireland (1)
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Donegal Ireland (1)
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Kerry Ireland
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Dingle Peninsula (3)
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Sligo Ireland (1)
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United Kingdom
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Great Britain
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England
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Alston Block (1)
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Cumbria England (3)
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East Anglia (1)
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Leicestershire England (1)
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Scotland
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Great Glen Fault (1)
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Scottish Highlands
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Grampian Highlands (1)
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-
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Wales
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Caernarvonshire Wales
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Snowdonia (2)
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Gwynedd Wales
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Snowdonia (2)
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Welsh Basin (4)
-
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-
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-
Grand Canyon (1)
-
Green Mountains (1)
-
Hare Bay (2)
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Highland Boundary Fault (2)
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Hudson Bay Basin (1)
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Lake District (8)
-
Maritimes Basin (3)
-
Mexico
-
Puebla Mexico (1)
-
-
Midland Valley (1)
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Midlands (1)
-
North America
-
Appalachian Basin (11)
-
Appalachians
-
Appalachian Plateau (3)
-
Blue Ridge Mountains (4)
-
Blue Ridge Province (8)
-
Carolina slate belt (1)
-
Catskill Mountains (2)
-
Central Appalachians (2)
-
Northern Appalachians (47)
-
Piedmont
-
Inner Piedmont (6)
-
-
Southern Appalachians (15)
-
Valley and Ridge Province (3)
-
-
Canadian Shield
-
Grenville Province (1)
-
-
Humber Zone (8)
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Michigan Basin (3)
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North American Craton (1)
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Rocky Mountains
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U. S. Rocky Mountains (1)
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-
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Raleigh Belt (1)
-
South America
-
Amazonian Craton (2)
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Andes (1)
-
-
South Mountain Batholith (3)
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Southern Uplands (1)
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Sydney Basin (1)
-
United States
-
Alabama
-
Chilton County Alabama (2)
-
Clay County Alabama (1)
-
Coosa County Alabama (1)
-
-
Arizona (1)
-
Black Warrior Basin (1)
-
Blue Ridge Mountains (4)
-
Brevard Zone (3)
-
Bronson Hill Anticlinorium (5)
-
Carolina Terrane (4)
-
Catskill Delta (4)
-
Cincinnati Arch (1)
-
Connecticut
-
Fairfield County Connecticut (2)
-
Litchfield County Connecticut (1)
-
New Haven County Connecticut (1)
-
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Connecticut Valley (2)
-
Delaware (1)
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District of Columbia (1)
-
Eastern U.S. (3)
-
Georgia
-
Chattooga County Georgia (1)
-
Dade County Georgia (1)
-
Walker County Georgia (1)
-
Whitfield County Georgia (1)
-
-
Great Smoky Fault (2)
-
Great Smoky Mountains (1)
-
Hayesville Fault (1)
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Hudson Valley (2)
-
Illinois Basin (2)
-
Kentucky
-
Rowan County Kentucky (1)
-
-
Maine
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Aroostook County Maine (1)
-
Cumberland County Maine (1)
-
Franklin County Maine (1)
-
Kennebec County Maine (1)
-
Knox County Maine (2)
-
Lincoln County Maine (1)
-
Norumbega fault zone (2)
-
Piscataquis County Maine (2)
-
Sagadahoc County Maine (1)
-
Waldo County Maine (1)
-
Washington County Maine (1)
-
York County Maine (1)
-
-
Maryland
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Allegany County Maryland (1)
-
Baltimore County Maryland
-
Baltimore Maryland (1)
-
-
Montgomery County Maryland (1)
-
Washington County Maryland (1)
-
-
Massachusetts
-
Berkshire County Massachusetts (1)
-
Franklin County Massachusetts (4)
-
Hampden County Massachusetts (2)
-
Hampshire County Massachusetts (2)
-
Suffolk County Massachusetts
-
Boston Massachusetts (1)
-
-
Worcester County Massachusetts (2)
-
-
Merrimack Synclinorium (6)
-
Michigan (1)
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Midcontinent (1)
-
Midwest (1)
-
New England (23)
-
New Hampshire
-
Belknap County New Hampshire (2)
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Cheshire County New Hampshire (3)
-
Coos County New Hampshire (2)
-
Grafton County New Hampshire (12)
-
Hillsborough County New Hampshire (2)
-
Merrimack County New Hampshire (4)
-
Rockingham County New Hampshire (1)
-
Sullivan County New Hampshire (2)
-
-
New York
-
Albany County New York (1)
-
Catskill Mountains (2)
-
Erie County New York (1)
-
Finger Lakes (1)
-
Greene County New York (1)
-
Monroe County New York (1)
-
Orleans County New York (1)
-
Ulster County New York (1)
-
Wayne County New York (1)
-
Westchester County New York (2)
-
-
North Carolina
-
Mitchell County North Carolina (1)
-
Randolph County North Carolina (1)
-
Stanly County North Carolina (1)
-
Yancey County North Carolina (1)
-
-
Ohio (2)
-
Oklahoma
-
Wichita Uplift (1)
-
-
Pennsylvania
-
Clearfield County Pennsylvania (1)
-
Wayne County Pennsylvania (1)
-
-
Pine Mountain Window (1)
-
Potomac River (1)
-
Potomac River basin (1)
-
Rhode Island (1)
-
South Carolina (1)
-
Talladega Front (3)
-
Tennessee (3)
-
Texas
-
Amarillo Uplift (1)
-
-
U. S. Rocky Mountains (1)
-
Vermont
-
Orange County Vermont (2)
-
Windham County Vermont (3)
-
Windsor County Vermont (1)
-
-
Virginia
-
Fairfax County Virginia (1)
-
Highland County Virginia (1)
-
Loudoun County Virginia (1)
-
-
West Virginia
-
Grant County West Virginia (2)
-
Pendleton County West Virginia (1)
-
Pocahontas County West Virginia (1)
-
-
Yavapai Province (1)
-
-
White Bay (1)
-
White Mountains (1)
-
-
commodities
-
barite deposits (4)
-
brines (2)
-
metal ores
-
antimony ores (2)
-
arsenic ores (1)
-
base metals (4)
-
chromite ores (1)
-
cobalt ores (1)
-
copper ores (3)
-
gold ores (6)
-
iron ores (1)
-
lead-zinc deposits (3)
-
molybdenum ores (1)
-
nickel ores (1)
-
polymetallic ores (1)
-
silver ores (3)
-
tin ores (3)
-
tungsten ores (2)
-
uranium ores (2)
-
zinc ores (2)
-
-
mineral deposits, genesis (9)
-
mineral exploration (1)
-
oil and gas fields (1)
-
petroleum
-
natural gas
-
shale gas (1)
-
-
-
placers (1)
-
-
elements, isotopes
-
carbon
-
C-13/C-12 (4)
-
-
chemical ratios (1)
-
halogens
-
fluorine (1)
-
-
hydrogen
-
D/H (1)
-
deuterium (1)
-
-
isotope ratios (12)
-
isotopes
-
radioactive isotopes
-
Pb-206/Pb-204 (2)
-
Pb-207/Pb-204 (2)
-
Pb-208/Pb-204 (2)
-
Sm-147/Nd-144 (1)
-
-
stable isotopes
-
C-13/C-12 (4)
-
D/H (1)
-
deuterium (1)
-
Hf-177/Hf-176 (1)
-
Nd-144/Nd-143 (3)
-
O-18/O-16 (6)
-
Pb-206/Pb-204 (2)
-
Pb-207/Pb-204 (2)
-
Pb-208/Pb-204 (2)
-
S-34/S-32 (3)
-
Sm-147/Nd-144 (1)
-
Sr-87/Sr-86 (7)
-
-
-
Lu/Hf (2)
-
metals
-
actinides
-
uranium (1)
-
-
alkali metals
-
cesium (1)
-
lithium (1)
-
-
alkaline earth metals
-
strontium
-
Sr-87/Sr-86 (7)
-
-
-
antimony (1)
-
hafnium
-
Hf-177/Hf-176 (1)
-
-
iron (1)
-
lead
-
Pb-206/Pb-204 (2)
-
Pb-207/Pb-204 (2)
-
Pb-208/Pb-204 (2)
-
-
manganese (1)
-
niobium (1)
-
rare earths
-
europium (1)
-
lanthanum (1)
-
lutetium (2)
-
neodymium
-
Nd-144/Nd-143 (3)
-
Sm-147/Nd-144 (1)
-
-
samarium
-
Sm-147/Nd-144 (1)
-
-
ytterbium (1)
-
yttrium (2)
-
-
tantalum (1)
-
zirconium (1)
-
-
oxygen
-
O-18/O-16 (6)
-
-
sulfur
-
S-34/S-32 (3)
-
-
-
fossils
-
Graptolithina (1)
-
Invertebrata
-
Arthropoda
-
Trilobitomorpha
-
Trilobita (1)
-
-
-
Protista
-
Foraminifera (1)
-
-
-
microfossils
-
Chitinozoa (1)
-
-
palynomorphs
-
Chitinozoa (1)
-
miospores (1)
-
-
-
geochronology methods
-
Ar/Ar (26)
-
fission-track dating (2)
-
K/Ar (7)
-
Lu/Hf (2)
-
paleomagnetism (10)
-
Pb/Pb (2)
-
Pb/Th (2)
-
Rb/Sr (13)
-
Sm/Nd (2)
-
thermochronology (3)
-
U/Pb (35)
-
U/Th/Pb (4)
-
-
geologic age
-
Cenozoic
-
Tertiary
-
Paleogene
-
Eocene (1)
-
-
-
-
Dalradian (1)
-
Mesozoic
-
Cretaceous
-
Comanchean
-
Rodessa Formation (1)
-
-
Lower Cretaceous
-
Rodessa Formation (1)
-
-
-
Jurassic
-
Norphlet Formation (1)
-
Upper Jurassic
-
Haynesville Formation (1)
-
Kimmeridgian (1)
-
-
-
lower Mesozoic (1)
-
-
Paleozoic
-
Acatlan Complex (2)
-
Bedford Shale (1)
-
Berea Sandstone (1)
-
Bucksport Formation (1)
-
Cambrian
-
Acadian (11)
-
Lower Cambrian
-
Murphy Marble (1)
-
Rome Formation (1)
-
-
Middle Cambrian (5)
-
Upper Cambrian (1)
-
-
Cape Elizabeth Formation (1)
-
Carboniferous
-
Lower Carboniferous
-
Dinantian (3)
-
-
Mabou Group (2)
-
Middle Carboniferous (1)
-
Mississippian
-
Lower Mississippian
-
Kinderhookian (1)
-
Osagian (1)
-
Pocono Formation (1)
-
-
Macumber Formation (2)
-
Middle Mississippian
-
Visean (2)
-
-
Price Formation (2)
-
Redwall Limestone (1)
-
Windsor Group (5)
-
-
Pennsylvanian
-
Cumberland Group (2)
-
Middle Pennsylvanian
-
Allegheny Group (1)
-
-
Morien Group (1)
-
Pottsville Group (1)
-
Upper Pennsylvanian
-
Wescogame Formation (1)
-
-
Watahomigi Formation (1)
-
-
-
Casco Bay Group (2)
-
Catskill Formation (1)
-
Devonian
-
Genesee Group (1)
-
Lower Devonian
-
Emsian (3)
-
Littleton Formation (1)
-
Lochkovian (1)
-
Oriskany Sandstone (1)
-
Pragian (1)
-
Shap Granite (1)
-
-
Middle Devonian
-
Eifelian (3)
-
Elk Point Group (1)
-
Givetian (1)
-
Hamilton Group (2)
-
Ludlowville Formation (1)
-
Marcellus Shale (4)
-
Moscow Formation (1)
-
Onondaga Limestone (3)
-
Tully Limestone (4)
-
-
Old Red Sandstone (4)
-
Upper Devonian
-
Brallier Shale (1)
-
Cleveland Member (1)
-
Hampshire Formation (1)
-
Ohio Shale (1)
-
-
-
Helderberg Group (1)
-
Horton Group (4)
-
lower Paleozoic
-
Berwick Formation (1)
-
-
Matapedia Group (1)
-
Merrimack Group (2)
-
middle Paleozoic (6)
-
Ordovician
-
Lower Ordovician
-
Arenigian (1)
-
Tremadocian
-
Halifax Formation (1)
-
-
-
Meguma Group (2)
-
Middle Ordovician
-
Ammonoosuc Volcanics (2)
-
Cloridorme Formation (1)
-
Llanvirnian (1)
-
Normanskill Formation (2)
-
-
Miramichi Group (1)
-
Skiddaw Slates (2)
-
Trenton Group (1)
-
Upper Ordovician
-
Caradocian
-
Borrowdale Volcanic Group (1)
-
-
-
-
Permian
-
Coconino Sandstone (1)
-
Kaibab Formation (1)
-
Toroweap Formation (1)
-
-
Rangeley Formation (3)
-
Shawangunk Formation (1)
-
Silurian
-
Lockport Formation (1)
-
Lower Silurian
-
Llandovery (1)
-
-
Middle Silurian (1)
-
Niagaran (1)
-
Perry Mountain Formation (1)
-
Upper Silurian
-
Pridoli (1)
-
Salina Group (1)
-
-
-
Supai Formation (1)
-
Talladega Group (1)
-
Tippecanoe Sequence (1)
-
upper Paleozoic
-
Kaskaskia Sequence (1)
-
Pictou Group (2)
-
-
Wissahickon Formation (1)
-
-
Phanerozoic (1)
-
Precambrian
-
Archean (1)
-
Baltimore Gneiss (1)
-
Catoctin Formation (1)
-
upper Precambrian
-
Proterozoic
-
Coldbrook Group (1)
-
Lewisian (1)
-
Mesoproterozoic (3)
-
Neoproterozoic
-
Cryogenian (1)
-
Ediacaran (2)
-
Tonian (1)
-
Walden Creek Group (1)
-
-
Paleoproterozoic (2)
-
-
-
-
Rhenohercynian (1)
-
-
igneous rocks
-
igneous rocks
-
plutonic rocks
-
diorites
-
quartz diorites (1)
-
-
gabbros (3)
-
granites
-
felsite (1)
-
I-type granites (1)
-
leucogranite (2)
-
monzogranite (2)
-
S-type granites (1)
-
-
granodiorites (3)
-
lamprophyres (3)
-
pegmatite (5)
-
syenites (1)
-
ultramafics (3)
-
-
porphyry (1)
-
volcanic rocks
-
andesites (2)
-
basalts
-
mid-ocean ridge basalts (1)
-
-
pyroclastics
-
tuff (1)
-
-
rhyolites (1)
-
-
-
ophiolite (3)
-
volcanic ash (1)
-
-
metamorphic rocks
-
K-bentonite (2)
-
metamorphic rocks
-
amphibolites (4)
-
eclogite (4)
-
gneisses
-
granite gneiss (1)
-
orthogneiss (2)
-
paragneiss (2)
-
-
granulites (4)
-
marbles (1)
-
metaigneous rocks
-
meta-andesite (1)
-
metagabbro (3)
-
metagranite (1)
-
metarhyolite (1)
-
serpentinite (1)
-
-
metaplutonic rocks (3)
-
metasedimentary rocks
-
metachert (1)
-
metaconglomerate (2)
-
metapelite (9)
-
paragneiss (2)
-
-
metasomatic rocks
-
greisen (1)
-
serpentinite (1)
-
skarn (1)
-
-
metavolcanic rocks (6)
-
migmatites (2)
-
mylonites (10)
-
phyllites (3)
-
phyllonites (1)
-
quartzites (4)
-
schists (11)
-
slates (9)
-
-
ophiolite (3)
-
turbidite (4)
-
-
minerals
-
carbonates
-
calcite (3)
-
dolomite (2)
-
-
halides
-
fluorides
-
fluorite (1)
-
-
-
K-bentonite (2)
-
minerals (4)
-
native elements
-
graphite (2)
-
-
oxides
-
corundum (1)
-
ilmenite (4)
-
rutile (3)
-
sapphire (1)
-
spinel (2)
-
-
phosphates
-
apatite (2)
-
monazite (8)
-
-
silicates
-
aluminosilicates (1)
-
chain silicates
-
amphibole group
-
clinoamphibole
-
grunerite (1)
-
hornblende (8)
-
-
-
pyroxene group
-
clinopyroxene (1)
-
-
-
framework silicates
-
feldspar group
-
alkali feldspar
-
K-feldspar (4)
-
orthoclase (1)
-
perthite (1)
-
-
plagioclase
-
peristerite (1)
-
-
-
silica minerals
-
quartz (4)
-
-
-
orthosilicates
-
nesosilicates
-
garnet group (15)
-
kyanite (6)
-
sillimanite (6)
-
staurolite (3)
-
titanite group
-
titanite (1)
-
-
zircon group
-
zircon (35)
-
-
-
-
ring silicates
-
cordierite (1)
-
tourmaline group (1)
-
-
sheet silicates
-
chlorite group
-
chlorite (2)
-
-
illite (3)
-
mica group
-
biotite (12)
-
muscovite (12)
-
paragonite (1)
-
phengite (1)
-
phlogopite (1)
-
-
-
-
sulfates
-
barite (1)
-
-
sulfides
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Primary terms
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carbon
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Cenozoic
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Tertiary
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faults (93)
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Invertebrata
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Protista
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isostasy (3)
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lava (2)
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Mesozoic
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Cretaceous
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Lower Cretaceous
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Jurassic
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Upper Jurassic
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North America
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Inner Piedmont (6)
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Southern Appalachians (15)
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Valley and Ridge Province (3)
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Canadian Shield
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Humber Zone (8)
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oil and gas fields (1)
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orogeny (129)
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oxygen
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O-18/O-16 (6)
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paleoclimatology (6)
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paleogeography (24)
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paleomagnetism (10)
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Paleozoic
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Acatlan Complex (2)
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Bedford Shale (1)
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Berea Sandstone (1)
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Bucksport Formation (1)
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Cambrian
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Acadian (11)
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Lower Cambrian
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Murphy Marble (1)
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Rome Formation (1)
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Middle Cambrian (5)
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Upper Cambrian (1)
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Cape Elizabeth Formation (1)
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Carboniferous
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Lower Carboniferous
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Dinantian (3)
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Mabou Group (2)
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Middle Carboniferous (1)
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Lower Mississippian
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Kinderhookian (1)
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Osagian (1)
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Pocono Formation (1)
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Macumber Formation (2)
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Middle Mississippian
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Visean (2)
-
-
Price Formation (2)
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Redwall Limestone (1)
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Windsor Group (5)
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Pennsylvanian
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Cumberland Group (2)
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Middle Pennsylvanian
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Allegheny Group (1)
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Morien Group (1)
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Pottsville Group (1)
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Upper Pennsylvanian
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Wescogame Formation (1)
-
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Watahomigi Formation (1)
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-
-
Casco Bay Group (2)
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Catskill Formation (1)
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Devonian
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Genesee Group (1)
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Lower Devonian
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Emsian (3)
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Littleton Formation (1)
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Lochkovian (1)
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Oriskany Sandstone (1)
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Pragian (1)
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Shap Granite (1)
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Middle Devonian
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Eifelian (3)
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Elk Point Group (1)
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Givetian (1)
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Hamilton Group (2)
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Ludlowville Formation (1)
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Marcellus Shale (4)
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Moscow Formation (1)
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Onondaga Limestone (3)
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Tully Limestone (4)
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Old Red Sandstone (4)
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Upper Devonian
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Brallier Shale (1)
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Cleveland Member (1)
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Hampshire Formation (1)
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Ohio Shale (1)
-
-
-
Helderberg Group (1)
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Horton Group (4)
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lower Paleozoic
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Berwick Formation (1)
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Matapedia Group (1)
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Merrimack Group (2)
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middle Paleozoic (6)
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Ordovician
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Lower Ordovician
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Arenigian (1)
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Tremadocian
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Halifax Formation (1)
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-
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Meguma Group (2)
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Middle Ordovician
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Ammonoosuc Volcanics (2)
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Cloridorme Formation (1)
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Llanvirnian (1)
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Normanskill Formation (2)
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-
Miramichi Group (1)
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Skiddaw Slates (2)
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Trenton Group (1)
-
Upper Ordovician
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Caradocian
-
Borrowdale Volcanic Group (1)
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-
-
-
Permian
-
Coconino Sandstone (1)
-
Kaibab Formation (1)
-
Toroweap Formation (1)
-
-
Rangeley Formation (3)
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Shawangunk Formation (1)
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Silurian
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Lockport Formation (1)
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Lower Silurian
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Llandovery (1)
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Middle Silurian (1)
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Niagaran (1)
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Perry Mountain Formation (1)
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Upper Silurian
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Pridoli (1)
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Salina Group (1)
-
-
-
Supai Formation (1)
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Talladega Group (1)
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Tippecanoe Sequence (1)
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upper Paleozoic
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Kaskaskia Sequence (1)
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Pictou Group (2)
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Wissahickon Formation (1)
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palynology (1)
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palynomorphs
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paragenesis (10)
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petrology (11)
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phase equilibria (7)
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plate tectonics (43)
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pollution (1)
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Precambrian
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Catoctin Formation (1)
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upper Precambrian
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Proterozoic
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Coldbrook Group (1)
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Mesoproterozoic (3)
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Neoproterozoic
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Ediacaran (2)
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Tonian (1)
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Walden Creek Group (1)
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Paleoproterozoic (2)
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-
-
-
reefs (2)
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sea-floor spreading (1)
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sea-level changes (11)
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sedimentary rocks
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chemically precipitated rocks
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clastic rocks
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coal (1)
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sedimentary structures
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sedimentation (19)
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South America
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stratigraphy (24)
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United States
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graded bedding (1)
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bedding (2)
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cross-bedding (1)
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laminations (1)
-
ripple drift-cross laminations (1)
-
-
secondary structures
-
concretions (1)
-
-
soft sediment deformation
-
convoluted beds (1)
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olistostromes (2)
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-
-
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sediments
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sediments
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clastic sediments (1)
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-
Acadian Phase
Tectonics, geochronology, and petrology of the Walker Top Granite, Appalachian Inner Piedmont, North Carolina (USA): Implications for Acadian and Neoacadian orogenesis
ABSTRACT West Avalonia is a composite terrane that rifted from the supercontinent Gondwana in the Ordovician and accreted to Laurentia during the latest Silurian to Devonian Acadian orogeny. The nature and extent of West Avalonia are well constrained in Nova Scotia, New Brunswick, and Newfoundland, Canada, by U-Pb detrital zircon data and/or isotope geochemistry of (meta)sedimentary and igneous rocks. The southeastern New England Avalon terrane in eastern Massachusetts, Connecticut, and Rhode Island has generally been interpreted as an along-strike continuance of West Avalonia in Canada, but the ages and origins of metasedimentary units along the western boundary of the Avalon terrane in Massachusetts and Connecticut remain poorly constrained. In this study, new detrital zircon U-Pb and Lu-Hf laser-ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) data from three samples of metasedimentary units along the western boundary of the southeastern New England Avalon terrane in Connecticut and Massachusetts were compared with existing data to test whether these metasedimentary units can be correlated along strike. The data were also compared with existing detrital zircon U-Pb and εHf data in New England and Canada in order to constrain the extent and provenance of West Avalonia. The maximum depositional age of two of the three detrital zircon samples analyzed in this study, based on the youngest single grain in each sample (600 ± 28 Ma, n = 1; 617 ± 28 Ma, n = 1) and consistency with existing analyses elsewhere in the southeastern New England Avalon terrane, is Ediacaran, while that of the third sample is Tonian (959 ± 40 Ma, n = 4). Detrital zircon analyses of all three samples from this study showed similar substantial Mesoproterozoic and lesser Paleoproterozoic and Archean populations. Other existing detrital zircon U-Pb data from quartzites in the southeastern New England Avalon terrane show similar Tonian populations with or without Ediacaran grains or populations. Most published detrital zircon U-Pb data from (meta)sedimentary rocks in West Avalonia in Canada yielded Ediacaran youngest detrital zircon age populations, except for a quartzite unit within the Gamble Brook Formation in the Cobequid Highlands of Nova Scotia, which showed a Tonian maximum depositional age, and otherwise a nearly identical detrital zircon signature with rocks from the southeastern New England Avalon terrane. All samples compiled from the southeastern New England Avalon terrane and West Avalonia in Canada show main age populations between ca. 2.0 Ga and ca. 1.0 Ga, with major peaks at ca. 1.95, ca. 1.50, ca. 1.20, and ca. 1.00 Ga, and minor ca. 3.1–3.0 Ga and ca. 2.8–2.6 Ga populations. The εHf ( t ) values from the three samples yielded similar results to those from West Avalonia in Canada, suggesting that both regions were derived from the same cratonic sources. The εHf ( t ) values of all West Avalonian samples overlap with both Amazonia and Baltica, suggesting that there is a mixed signature between cratonic sources, possibly as a result of previous collision and transfer of basement fragments between these cratons during the formation of supercontinent Rodinia, or during subsequent arc collisions.
ABSTRACT The Paleozoic plate boundary zone between Laurussia and Gondwana in western Pangea hosts major magmatic and hydrothermal Sn-W-Ta, Au, and U mineralization. Individual mineral deposits represent the results of the superposition of a series of exogenic and endogenic processes. Exogenic processes controlled (1) the enrichment of the ore elements in sedimentary protoliths via residual enrichment during intense chemical weathering and via climatically or tectonically controlled redox traps, (2) the spatial distribution of fertile protoliths, and, thus, eventually (3) the spatial distribution of mineralization. Endogenic processes resulting in metamorphism and crustal melting controlled the mobilization of Sn-W, Au, and U from these enriched protoliths and, thus, account for the age distribution of Sn-W and Au mineralization and U-fertile granites. It is the sequence of exogenic and endogenic processes that eventually results in the formation of mineralization in particular tectonic zones. Whereas the endogenic processes were controlled by orogenic processes during the assembly of western Pangea itself, the exogenic processes were linked to the formation of suitable source rocks for later mineralization. The contrasting distribution of magmatic and hydrothermal Sn-W-Ta, Au, and U mineralization on the Laurussia and Gondwana sides of the plate boundary zone reflects the contrasting distribution of fertile protoliths and the contrasting tectonic situation on these margins. The Laurussian margin was an active margin during most of the Paleozoic, and the distribution of different mineralization types reflects the distribution of terranes of contrasting provenance. The Gondwanan margin was a passive margin during most of the Paleozoic, and the similar distribution of a wide range of different metals (Sn, W, Ta, Au, and U) reflects the fact that the protoliths for the various metals were diachronously accumulated on the same shelf, before the metals were mobilized during Acadian, Variscan, and Alleghanian orogenic processes.
ABSTRACT Avalonia and Ganderia are composite microcontinental fragments in the northern Appalachian orogen likely derived from Gondwanan sources. Avalonia includes numerous Neoproterozoic magmatic arc sequences that represent protracted and episodic subduction-related magmatism before deposition of an Ediacaran–Ordovician cover sequence of mainly siliciclastic rocks. We characterized the nature of the basement on which these arcs were constructed using zircon grains from arc-related magmatic rocks in Atlantic Canada that were analyzed for their Lu-Hf isotope composition. The majority of zircon grains from Avalonia are characterized by initial 176 Hf/ 177 Hf values that are more radiogenic than chondritic uniform reservoir, and calculated crust formation Hf T DM (i.e., depleted mantle) model ages range from 1.2 to 0.8 Ga. These data contrast with those from Ganderia, which show typically positive initial εHf values and Hf T DM model ages that imply magmatism was derived by melting of crustal sources with diverse ages ranging from ca. 1.8 to 1.0 Ga. The positive distribution of initial εHf values along with the pattern of Hf T DM model ages provide a clear record of two distinct subduction systems. Cryogenian–Ediacaran magmatism is interpreted to have resulted from reworking of an evolved Mesoproterozoic crustal component in a long-lived, subduction-dominated accretionary margin along the margin of northern Amazonia. A change in Hf isotope trajectory during the Ediacaran implies a greater contribution of isotopically evolved material consistent with an arc-arc–style collision of Ganderia with Avalonia. The shallow-sloping Hf isotopic pattern for Paleozoic Ganderian magmatism remains continuous for ~200 m.y., consistent with tectonic models of subduction in the Iapetus and Rheic Oceans and episodic accretion of juvenile crustal terranes to Laurentia.
ABSTRACT The Baie Verte Line in western Newfoundland marks a suture zone between (1) an upper plate represented by suprasubduction zone oceanic crust (Baie Verte oceanic tract) and the trailing continental Notre Dame arc, with related upper-plate rocks built upon the Dashwoods terrane; and (2) a lower plate of Laurentian margin metasedimentary rocks with an adjoining ocean-continent transition zone (Birchy Complex). The Baie Verte oceanic tract formed during closure of the Taconic seaway in a forearc position and started to be obducted onto the Laurentian margin between ca. 485 and 476 Ma (early Taconic event), whereas the Birchy Complex, at the leading edge of the Laurentian margin, was subducted to maximum depths as calculated by pseudosection techniques (6.7–11.2 kbar, 315–560 °C) by ca. 467–460 Ma, during the culmination of the Taconic collision between the trailing Notre Dame arc and Laurentia, and it cooled isobarically to 9.2–10.0 kbar and 360–450 °C by 454–449 Ma (M 1 ). This collisional wedge progressively incorporated upper-plate Baie Verte oceanic tract rocks, with remnants preserved in M 1 high-pressure, low-temperature greenschist-facies rocks (4.8–8.0 kbar, 270–340 °C) recording typical low metamorphic gradients (10–14 °C/km). Subsequently, the early Taconic collisional wedge was redeformed and metamorphosed during the final stages of the Taconic cycle. We relate existing and new 40 Ar/ 39 Ar ages between 454 and 439 Ma to a late Taconic reactivation of the structurally weak suture zone. The Taconic wedge on both sides of the Baie Verte suture zone was subsequently strongly shortened (D 2 ), metamorphosed (M 2 ), and intruded by a voluminous suite of plutons during the Salinic orogenic cycle. Calculated low- to medium-pressure, low-temperature M 2 conditions in the Baie Verte oceanic tract varied at 3.0–5.0 kbar and 275–340 °C, with increased metamorphic gradients of ~17–25 °C/km during activity of the Notre Dame arc, and correlate with M 2 assemblages in the Birchy Complex. These conditions are associated with existing Salinic S 2 white mica 40 Ar/ 39 Ar ages of ca. 432 Ma in a D 2 transpressional shear zone and synkinematic intrusions of comparable age. A third metamorphic event (M 3 ) was recorded during the Devonian with calculated low-pressure, low-temperature conditions of 3.2–3.8 kbar and 315–330 °C under the highest metamorphic gradients (23–30 °C/km) and associated with Devonian–early Carboniferous isotopic ages as young as 356 ± 5 Ma. The youngest ages are related to localized extension associated with a large-scale transtensional zone, which reused parts of the Baie Verte Line suture zone. Extension culminated in the formation of a Middle to Late Devonian Neoacadian metamorphic core complex in upper- and lower-plate rocks by reactivation of Baie Verte Line tectonites formed during the Taconic and Salinic cycles. The Baie Verte Line suture zone is a collisional complex subjected to repeated, episodic structural reactivation during the Late Ordovician Taconic 3, Silurian Salinic, and Early–Late Devonian Acadian/Neoacadian orogenic cycles. Deformation appears to have been progressively localized in major fault zones associated with earlier suturing. This emphasizes the importance of existing zones of structural weakness, where reactivation took place in the hinterland during successive collision events.
Latest Silurian syntectonic sedimentation and magmatism and Early Devonian orogenic gold mineralization, central Newfoundland Appalachians, Canada: Setting, structure, lithogeochemistry, and high-precision U-Pb geochronology
Paleozoic evolution of crustal thickness and elevation in the northern Appalachian orogen, USA
The deep magmatic cumulate roots of the Acadian orogen, eastern North America
ABSTRACT This trip explores three different occurrences of a diamictite-bearing unit in the transition between Upper Devonian redbeds of the Hampshire Formation (alluvial and fluvial deposits) and Mississippian sandstones and mudstones of the Price/Pocono Formations (deltaic deposits). Palynology indicates that all the diamictites examined are in the LE and LN miospore biozones, and are therefore of Late Devonian, but not latest Devonian, age. Their occurrence in these biozones indicates correlation with the Cleveland Member of the Ohio Shale, Oswayo Member of the Price Formation, and Finzel tongue of the Rockwell Formation in the central Appalachian Basin and with a large dropstone (the Robinson boulder) in the Cleveland Member of the Ohio Shale in northeastern Kentucky. Although several lines of evidence already support a glaciogenic origin for the diamictites, the coeval occurrence of the dropstone in open-marine strata provides even more convincing evidence of a glacial origin. The diamictites are all coeval and occur as parts of a shallow-marine incursion that ended Hampshire/Catskill alluvial-plain accumulation in most areas; however, at least locally, alluvial redbed accumulation continued after diamictite deposition ended. The diamictites are parts of nearshore, marginal-marine strata that accumulated during the Cleveland-Oswayo-Finzel transgression, which is related to global eustasy and to foreland deformational loading during the late Acadian orogeny. Detrital zircon data from clasts in a diamictite at Stop 3 (Bismarck, West Virginia) indicate likely Inner Piedmont, Ordovician plutonic sources and suggest major Acadian uplift of Inner Piedmont sources during convergence of the exotic Carolina terrane with the New York and Virginia promontories. Hence, the Acadian orogeny not only generated high mountain source areas capable of supporting glaciation in a subtropical setting, but also through deformational foreland loading, abetted regional subsidence and the incursion of shallow seas that allowed mountain glaciers access to the open sea.