Download Parts of the Appalachians

Appalachians: Great Smoky and Acadia NPs
• Appalachian Mountains
extend from NE Canada to
Georgia
– Ouachitas (MS-AK) related in
origin
• Remains of deeply eroded,
ancient mountain chain once
larger than Himalayans
Parts of the Appalachians
• Coastal Plain (not part of
App) is exposed continental
shelf
• Fall Line = change to
metamorphic rocks of
piedmont.
– Abrupt change in topography
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Parts of the Appalachians
• Piedmont
– Metamorphic rocks
– Once the core of the
huge mountain chain
– Now extensively
eroded
• Blue ridge
– Runs from VA
through NC, SC and
GA
– Metamorphic rocks
formed beneath huge
mnts
– 1.1 Ga formed
during assembly of
Rodinia
– Exotic terrain (added
to Laurentia)
Parts of the Appalachians
• Valley and Ridge
– Large folds and thrust faults
– Differential weathering
produces the topography
• Ridges = resistant rocks
• Valleys = weak rocks
– Faults repeat the
stratigraphy and produce
the region of ridges and
valleys
• Appalachian Front =
westernmost folded rocks
• Appalachian Plateau = flatlying strata of the valley and
ridge
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Tectonic History of Appalachians
• 1.1 Ga Grenville
Orogeny builds Blue
Ridge Mountains
– Basement of entire
Appalachian province
• Assembles Rodinia
super continent
Tectonic History of Appalachians
• ~600 Ma Rodinia Rifts
– Forms Laurentia and
Gondwanaland
– Rift sediments and volcanics
(like East African Rift) fill the
valley
• Eastern margin of Laurentia
becomes passive
– Like today
– Becomes covered with
sandstones shales and
limestones (transgressive
sequence).
• The new ocean is called Iapetus
(proto-Atlantic)
• By Ordovician time (~490 Ma)
this passive margin becomes
active convergent margin
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Tectonic History of Appalachians
• Taconic Orogeny (~490 Ma)
– Avalonia and Baltica approach Laurentia
– Volcanic Islands are sutured to Laurentia (mountain building)
• Exotic terrains
• Igneous and metamorphic rocks produced and preserved in
New England (Acadia - Ellsworth Schist and Bar Harbor Fm)
• Mountains erode away before next event.
Tectonic History of Appalachians
• Acadian Orogeny ~425 Ma
– Baltica Collides with northern NA and Avalonia collides with eastern NA
– More igneous and metamorphic rocks result (granites of Acadia)
• These mountains then erode away before the next event
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Tectonic History of Appalachians
• Alleganian Orogen (~320 Ma)
– Euroamerica collides with Gondwanaland forming Pangaea
– Appalachian mountains form
– valley and ridge province produced
• These mountains then erode away too!
Tectonic History of Appalachians
• Pangaea rifts apart
– Begins in Triassic ~250 Ma
– Atlantic ocean forms ~180
Ma
– Uplifts the east coast of
North America
– This is the modern
Appalachian Mountains!
• Modern Continents form
from break-up of Pangaea
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Great Smoky National Park
Smoky from combination of fog/mist and oils from the trees
Great Smoky National Park
• Located on TN-NC boarder
• Highest peaks East of Black Hills SD
• Rolling topography from stream erosion controlled by fold and
fault orientations
– This are has not been glaciated
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Great Smoky National Park
• Blue Ridge = Grenville (1.1 Ga)
age metamorphic rocks
Great Smoky National Park
• Valley and Ridge
– Rocks are Precambrian rift
sediments (rifting of Rodinia)
– Cambrian marine sediments
(Chilhowee group = passive
margin)
– Ordovician Marine Limestones
(Knox Group)
• Ridges = resistant limestones
and sandstones
• Valleys = weaker rocks
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Acadia National Park
• Coastal islands of Maine
• Landscape is sculpted by glacial erosion
• Rocks are
– accreted terrains of volcanic islands and Avalon
microcontinent from Taconic and Acadian orogenies
– Igneous and metamorphic rocks of the Acadian orogeny
Acadia National Park
• This is classic glacial
topography:
– Fjords
– Roche Moutonnee
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Acadia National Park
Dike intruded during Acadian
orogeny cutting Silurian Sediments
Sea stack cut during highstand of sea level.
Ice Ages:
• Times of low global temperature
• Glaciers advance to low latitudes (&
altitudes)
• Current or Pleistocene ice age:
– Began ~2 m.y. ago
• ~ 20 cycles during Pleistocene
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Causes of Ice Ages:
Plate Tectonic Causes:
• Move continents to poles
• Disrupt ocean circulation
• Ice-house effect: mountain building
exposes more crust. Weathering
consumes CO2 and cools the
atmosphere
Causes of Ice Age:
• Milankovich (orbital) Cycles
– Eccentricity - 1x105 yrs
– Obliquity - 4.1x104 yrs
– Precesion - 2.6x104 yrs
• Coincidence of these cycles may
cause an ice age…
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Two types of Glaciers:
Valley (alpine) Glaciers
–
–
–
–
–
Form in mountains
Above snowline
Flows down slope
Ice 100s m thick
210,000 km3 water
Second type: Continental Ice Sheet
• Regional Scale
• > 70% of fresh water
• Polar regions
– Antarctica & Greenland
• 3 - 5 km thick
• Flow out from area of accumulation
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Glaciers move in two ways:
Plastic Flow
• D > 50 m
• Ductile
Deformation
– Deform crystal
– Or ‘creep’ or
sliding along
grain boundaries
Basal Slip
• Ice melts at high P (base of glacier)
• Lubricates surface
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Glaciers Erode too
• Plucking & abrasion
Abrasion polishes and scratches
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