Lecture5- Geologic setting and evolution of LApujana/latin/PDFS... · Three kinds of rocks Igneous (cooled from magma) – Volcanic (cools at surface, ex: basalt) – Plutonic (cools

Geologic Setting and Evolution of Latin America

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)

Geologic History of Latin America

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)

South American Geologic Provinces

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

South American Platform

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

Topography of the S. American Platform

Precambrian (>540 Ma) Exposures in S. America

Oldest rock in Latin America: ~3.5 Ga

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.

Two ways to add crust at the margins of continents1) Magmatic additions to the crust

Thick crust beneath Andes is partly due to addition of magma to base of crust

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

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

2) Accretion and collisionTwo ways to add crust at the margins of continents

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

Continued collisions lead to formation of continent

Precambrian Orogenies produced the crust of South America

De Almeida et al. 2000 ESR 50

Lithospheric Root of Craton helps keep it stable

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

Most recent Supercontinent: Pangea

End Precambrian Supercontinent

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

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)

S. America and breakup of Gondwana

Gondwana ~200 Ma ago

Amazonia

WestAfrica

Rio de laPlata

ca. 550 Ma

Kalahari

São Fran. -W. Congo

Marshak, U. Illinois

Pangea = Laurasia + Gondwana

Laurasia = N. America and Asia

Gondwana = S. America, Africa, Antarctica, India, & Australia

http://pubs.usgs.gov/publications/text/historical.html

S. America and breakup of Gondwana

Gondwana ~200 Ma ago

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

Breakup of Gondwana produced Passive Margins on the flanks of the rifted continents - those facing the newly formed Atlantic Ocean

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

Passive Margins are very important because the thick accumulation of sediments holds much of the world’s future supply of oil and gas

The Gulf of Mexico Passive Margin

Patty Ganey, UTIG

Texas

Mexico

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

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

Passive Margins of the World

Moores & Twiss 1995

A Passive Margin in

the making: The Gulf

of California that began opening recently (about 5

Ma. Ago).

Evolution of the Caribbean

S. America

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

Evolution of the Caribbean

S. America