Lecture5- Geologic setting and evolution of LApujana/latin/PDFS... · Three kinds of rocks Igneous...
Transcript of Lecture5- Geologic setting and evolution of LApujana/latin/PDFS... · Three kinds of rocks Igneous...
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Geologic Setting and Evolution of Latin America
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Important events in the Geologic Evolution of Latin America
Formation of the Continental Crust (3.5-0.5Ga)Formation of Gondwana (~600 Ma)Break-up of Pangea (~250 Ma)Break-up of Gondwana (~120 Ma)Formation of the Caribbean (~70 Ma)
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Geologic History of Latin America
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Three kinds of rocks
Igneous (cooled from magma)– Volcanic (cools at surface, ex: basalt)– Plutonic (cools at depth, ex: granite)– Hypabyssal (cools below surface, but at shallow
depth)Sedimentary (deposited on earth’s surface by action of water or wind, ex. sandstone, limestone)Metamorphic (buried and heated sedimentary or igneous rocks)
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South American Geologic Provinces
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Craton, Shield, and Platform
All refer to the stable interiors of continentsCraton is ancient crust that has long been stable. Composed of igneous and metamorphic rocksShield is exposed cratonPlatform is the craton plus overlying sediments
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South American Platform
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South American Platform
Stable continental crust of S. America not affected by Cenozoic tectonics and orogenies
– Basically everything east of the Andes and south of the Caribbean
Consists of Archean and older Proterozoic nuclei surrounded by younger Proterozoic orogenic belts Exposed in 4 places:
– Guyana Shield– Guaporé Shield– Sao Francisco Craton– Rio de la Plata Craton
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Topography of the S. American Platform
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Precambrian (>540 Ma) Exposures in S. America
Oldest rock in Latin America: ~3.5 Ga
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Orogenies, Orogenic belts, and Orogens
Orogenies are episodes of crustal deformation that generate new crust and mountains– Also defined as “Growth of Continental Crust by
addition of material at the margins”– Cratons are not affected.
Orogenic belts are elongate zones of high relief and deformation, generally mountain chains like the AndesOrogens are crustal tracts that were subjected to orogeny at about the same time.
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Two ways to add crust at the margins of continents1) Magmatic additions to the crust
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Thick crust beneath Andes is partly due to addition of magma to base of crust
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Much of the high Andes are volcanoes, but not all!
Aconcagua is the highest mountain in the western hemisphere (6962m or 22841 feet).It is located in western Argentina, near the Chile border, and about 100 km east of Santiago.
Aconcagua “Fold-and-Thrust” Belt
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Machu Pichu, Peru
The ruins of Machu Pichu were rediscovered in 1911. The Inca people used the Andean mountain top (9060 feet elevation) from the early 1400's. The Spaniards never found Machu Picchu, even though they suspected its existence. Machu Pichu was abandoned some forty years after the Spanish took Cuzco in 1533.http://www.sacredsites.com/2nd56/21422.html
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2) Accretion and collisionTwo ways to add crust at the margins of continents
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Example of accretion: Himalayan-Tibetan OrogenyTallest mountain range in the world (Himalayas) and highest plateau (Tibetan Plateau) are due to collision of Indian and Asian continental crusts
Valdiya 1989
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Continued collisions lead to formation of continent
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Precambrian Orogenies produced the crust of South America
De Almeida et al. 2000 ESR 50
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Lithospheric Root of Craton helps keep it stable
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Latin America and the SupercontinentCycle
The supercontinent cycle refers to the episodic aggregation and dispersal of continental crustSupercontinent is when most of the continental crust is found in a single large mass and is associated with a ‘Superocean’Supercontinents form as the result of a protracted period of continent-continent collisionsCycle takes ~300-400 million yearsThree important supercontinents– 200 Ma, 600 Ma, and 1000 Ma
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Most recent Supercontinent: Pangea
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End Precambrian Supercontinent
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The South American Platform assembled when Gondwana formed at the end of the Precambrian (~550-630 Ma)
A: Cratonic nuclei (pre 730 Ma). B: Initial stage of assembly (collision of Rio de la Plata Craton with southern part of São Francisco–Congo Craton). BO =Brazilide Ocean, AO = Adamastor Ocean, SFC-C =São Francisco–Congo Craton. C: Intermediate stage of assembly (collision of remaining blocks). D: Final assembly. Alkim et al. 2001 Geology
BrasilianoOrogeny
Borborema
W.Africa
Amazonia
SF-C
ca. 630 Ma
C Neoprotero-zoic belts
SFC - C
BorboremaAmazonia
W.Africa
Rio de laPlata
ca. 550 Ma
D
1
Kalahari
2
4
6
5
3
São Francisco -Congo
Rio de la Plata
Amazonia
WestAfrica Borborema
Goiás massif
cratonicnucleus
continent
volcanic arc
A
SFC - CR. de la Plata
Borborema
Amazonia
W.Africa
ca. 730 Ma
B
AO
BO
Rio de laPlata
pre-730 Ma
7
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BrasilianoOrogen (~550-630 Ma) cements the older cratonsinto the South American platform
SãoFrancisco
Rio de laPlata
0°
craton (pre-Brasiliano)
Phanerozoic platform/basin
exposed Brasilianoorogens
Andean orogen
Patagonian platform
0 1000 km
São Luis
Amazon
S. Marshak (U. Illinois)
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S. America and breakup of Gondwana
Gondwana ~200 Ma ago
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Amazonia
WestAfrica
Rio de laPlata
ca. 550 Ma
Kalahari
São Fran. -W. Congo
Marshak, U. Illinois
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Pangea = Laurasia + Gondwana
Laurasia = N. America and Asia
Gondwana = S. America, Africa, Antarctica, India, & Australia
http://pubs.usgs.gov/publications/text/historical.html
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S. America and breakup of Gondwana
Gondwana ~200 Ma ago
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Global Plate Tectonics
Jurassic to Present Day
ByL.A. Lawver, M.F. Coffin, I.W.D. Dalziel
L.M. Gahagan, D.A. Campbell, and R.M. Schmitz
©2001, University of Texas Institute for GeophysicsFebruary 9, 2001
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Breakup of Gondwana produced Passive Margins on the flanks of the rifted continents - those facing the newly formed Atlantic Ocean
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Passive Margins
Passive Margins are equivalent to Continental shelvesThese are not plate margins but are important because they are where thick accumulations of sediment occur
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Passive Margins are very important because the thick accumulation of sediments holds much of the world’s future supply of oil and gas
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The Gulf of Mexico Passive Margin
Patty Ganey, UTIG
Texas
Mexico
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The Gulf of Mexico (and Central
Atlantic) opened along the
Carboniferous Suture between Gondwana and
Laurasia
Configuration at end of Paleozoic (~245 Ma) after Walper, 1972
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Opening of the Gulf of Mexico and Evolution of the Mojave-Sonora Megashear. This moved Mexico into its modern position.
S. America
N. America
Mojave-Sonora Megashear
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Passive Margins of the World
Moores & Twiss 1995
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A Passive Margin in
the making: The Gulf
of California that began opening recently (about 5
Ma. Ago).
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Evolution of the Caribbean
S. America
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QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.
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Evolution of the Caribbean
S. America