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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 continents Craton is ancient crust that has long been stable. Composed of igneous and metamorphic rocks Shield is exposed craton Platform 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 Andes Orogens are crustal tracts that were subjected to orogeny at about the same time. Two ways to add crust at the margins of continents 1) 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 “Fold-and-Thrust” Belt 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. 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 Two ways to add crust at the margins of continents 2) Accretion and collision Example of accretion: HimalayanTibetan Orogeny Tallest 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 Supercontinent Cycle The supercontinent cycle refers to the episodic aggregation and dispersal of continental crust Supercontinent 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 collisions Cycle takes ~300-400 million years Three 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) pre-730 Ma A West Africa B Borborema W. Africa Amazonia Borborema BO Amazonia volcanic arc SFC - C Goiás massif Brasiliano Orogeny Rio de la Plata São Francisco Congo continent cratonic nucleus C AO R. de la Plata ca. 730 Ma D Neoproterozoic belts W. Africa W. Africa Borborema Amazonia 3 Amazonia Borborema 4 1 5 2 7 6 Rio de la Plata SF-C ca. 630 Ma Rio de la Plata SFC - C Kalahari ca. 550 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 Amazon Brasiliano Orogen (~550630 Ma) cements the older cratons into the South American platform S. Marshak (U. Illinois) 0° São Luis São Francisco Rio de la Plata 0 1000 km Andean orogen Phanerozoic platform/basin Patagonian platform exposed Brasiliano orogens craton (pre-Brasiliano) S. America and breakup of Gondwana Gondwana ~200 Ma ago ca. 550 Ma West Africa Amazonia São Fran. W. Congo Rio de la Plata Kalahari Marshak, U. Illinois Laurasia = N. America and Asia Gondwana = S. America, Africa, Antarctica, India, & Australia Pangea = Laurasia + Gondwana 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 By L.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 Geophysics February 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 shelves These 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 Texas Mexico Patty Ganey, UTIG 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. N. America Mojave-Sonora Megashear S. America 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