Lithosphere-asthenosphere mixing in a transform-dominated late ...
Geologic Evolution of Latin Americapujana/latin/PDFS/Lecture 4- Plate... · Lithosphere and...
Transcript of Geologic Evolution of Latin Americapujana/latin/PDFS/Lecture 4- Plate... · Lithosphere and...
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Geologic Evolution of Latin America
Plate Tectonics: General Concepts & Applications to Latin America
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Structure of Earth:3 major divisions of Core, Mantle, and Crust
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Upper mantle differs in the way that it transports heat
Three ways to transport heat: radiation, convection,and conduction Uppermost 100-200 km of mantle is strong, cold, and transports heat by conductionBelow this the mantle is hotter, weaker, and transports heat by convection
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Lithosphere and Asthenosphere
Lithosphere: strong upper mantleAsthenosphere: Weaker mantle beneath lithosphereLithosphere = plate of plate tectonics– -Oceanic lithosphere thickens as it ages and
coolsAsthenosphere = what allows plates to move
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7 major and 6 minor plates
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a
b
c
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e f
Latin America occupies parts of 3 plates: N. America, Caribbean, and S. America
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“This Dynamic Earth” http://pubs.usgs.gov/publications/text/slabs.html
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Three types of Plate Boundaries
Where lithosphere is created: Divergent (Constructive) Plate BoundaryWhere lithosphere is destroyed: Convergent (Destructive) Plate BoundaryWhere lithosphere is neither created nor destroyed: Transform Plate Boundary
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Plate Tectonics
“This Dynamic Earth” http://pubs.usgs.gov/publications/text/Vigil.html
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Mantle convection
Sinking of dense lithosphere in Subduction Zones drives plate motions
Outer core(liquid)
Inner core(solid)
2885 km
5144km
6371km
Oceanic crustSpreading ridge
Asthenosphere
Lower mantle(Mesosphere)
370 km670 km
Hot spotArc volcano
Arc-trench complex
Transition zone
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Plate boundaries
TASA Graphics
Divergent = Mid-Ocean Ridge Spreading Convergent = Subduction ZoneTransform = plates slide past each other
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Divergent or Constructive Plate Boundaries= Mid-Ocean Ridges – Spreading Centers
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Constructive Plate boundary = Mid Ocean Ridge
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Mid-Ocean Ridge System (Constructive Plate Boundaries)
“This Dynamic Earth” http://pubs.usgs.gov/publications/text/baseball.html
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Oceanic crust and lithosphere is created at Mid-Ocean ridges and gets older away from the ridge
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The Mid-Atlantic Ridge comes on shore in Iceland
Krafla 1980“This Dynamic Earth” http://pubs.usgs.gov/publications/text/Krafla.html
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Mid-Ocean Ridges are mostly submarine
Research submarine “ALVIN” Hydrothermal vent “Black smoker”
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Several Mid-Ocean Ridges around LA
Mid-Atlantic RidgeS. SandwichEast Pacific RiseChile RidgeCocos RidgeCayman Trough
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Mantle Plumes and Hot Spot Volcanoes
Can occur anywhere within a plate or along a divergent plate boundaryCaused by upwelling material from deep in the mantleProduce chains of volcanic islands or seamounts
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‘Hot Spot’chains
Moving plate over
mantle plume
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Galapagos ‘Hot Spot’
Fernandinacaldera
Galapagos from space
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Galapagos & Darwin’s Theory of Evolution
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Galapagos Hot Spot trail
Gutscher et al. Earth and Planetary Science Letters 168 (1999) 255–270
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Transform Plate
Boundaries
Plates slide past each otherExample: San Andreas fault of California
http://pubs.usgs.gov/publications/text/dynamic.html
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Latin American Transform Plate Boundaries are in the Caribbean
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Convergent Plate Margins
Subduction ZonesTrenchesWadati-Benioff ZonesVolcanic arcs
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Convergent Margins, Subduction Zones:Trenches, Earthquakes, and Volcanoes
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55,000 km of Convergent Plate Margins; Lallemand 1999
Atlantic Ocean
Indian Ocean
Pacific Ocean
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Peru-Chile Trench(<8170m)
Middle America Trench (<6600m)
Trenches around Latin America
Challenger Deep in W. Pacific = 10,920 m (Deepest point on Earth’s surface)
PuertoRico Trench (<8605m)
South SandwichTrench (<8325m)
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Circum-Pacific “Ring of Fire”
“This Dynamic Earth” http://pubs.usgs.gov/publications/text/fire.html
Volcanic arcs and oceanic trenches partly encircling the Pacific Basin form the so-called Ring of Fire, a zone of frequent earthquakes and volcanic eruptions. The trenches are shown in blue-green. The volcanic arcs, although not labelled, are parallel to, and always landward of, the trenches.For example, the Andes volcanic arc is associated with the Peru-Chile Trench.
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Oceanic Arc: Common in Western Pacific
TASA Graphics
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‘Island’ Arc Volcanoes
Some are not even islands!
Anatahan, Marianas 5/03
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Lesser Antilles Island Arc
Pelee, Martinique 1902: 29,000 killed“Volcano World’ http://volcano.und.edu
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Arc volcanoes overly igneous intrusions in the crust
Primarypartialmelts
Active arc Forearc Back-arc
Interbedded lava flows& volcaniclastic deposits
H2O
CO2
CO2
CO2
CO2Mafic cumulate
rocks & sills
VolcaniclasticdepositsDistal Proximal
Sea level
Crustal delamination
Mafic pillow lavas & flows
Mid-crustal plutons Differentiatingmagma
chamber
Arc volcano
H2O H2O
Mafic underplating
0
30
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10
10 km No Vertical Exaggeration
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Half Dome, Yosemite
(California): A good
example of an ancient igneous intrusion
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Subduction Zones are associated with inclined earthquake zones (Wadati-Benioff Zones)
Earthquakes beneath Japan
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Earthquakes in Latin America
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Oceanic vs.
Continental Crust
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Two kinds of crust: Oceanic & Continental
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Continental Crust beneath Dallas (Texas)
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Arcs built on continental crust are “Andean-type” arcs
Tasa Graphics
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Isostasy
Greek for “Equal standing”Indicates that masses must be equivalent above a ‘compensation depth’(~asthenosphere)How can there be different elevations of Earth’s solid surface?
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Pratt vs. Airy models of Isostasy
Watts 2001
Different columns have different densities but reach the same depth
Different columns have the same density but different heights and depths
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Oceanic vs. Continental
crust
Watts 2001
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Thick crust of Central Andes
http://quake.wr.usgs.gov/research/structure/CrustalStructure/
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Why are the Andes so high?
Mountains of the Central Andes are the second highest range in the world (Himalayas are the highest with 100 peaks >8300m tall; Andes have 84 peaks over 6000m tall)Crust of Central Andes is the second thickest in the world (crust beneath the Himalayas and Tibet is the thickest)Isostasy! Thicker crust stands higher.
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Passive marginsPassive Margins are equivalent to continental shelvesCrustal boundary between continental and oceanic crustThese are not plate margins but are important because they are where thick accumulations of sediment occur
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Passive Margins of the World
Moores & Twiss 1995