Study Guide for Quiz 4
Study Guide for Quiz 4 GEOL1005
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This 0 page Study Guide was uploaded by Kate Notetaker on Thursday February 18, 2016. The Study Guide belongs to GEOL1005 at George Washington University taught by Catherine A. Forster in Winter 2016. Since its upload, it has received 52 views. For similar materials see Historical Geology in Geology at George Washington University.
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Date Created: 02/18/16
Textbook Notes for the Quiz 0 Laurentia 0 Name given to the combination of Greenland and North America in the Proterozoic and most of Phanerozoic period 0 Gained territory by continental accretion Found this through Rocks obtained from wells that penetrate the Phanerozoic cover 0 Exposed rocks of the Canadian Shield Precambrian rocks that have been elevated by Phanerozoic mountain building in the American West Evidence appeared decades ago 0 Recognition of structural trends and regional occurrences of rock units Uraniumlead techniques 0 Dates obtained from crystalline rocks 0 Grew rapidly during Proterozoic time as other cratons became sutured to it 0 First stage Assembly of at least ve micro continents into a sizable craton 0 Micro continents had formed during Archean time Took place within about 100 million years 0 Between 195 billion and 185 billion years ago 0 Superior Province Largest of the Archean terranes Crops out as far south as Wisconsin Separated from smaller Archean terranes to the west by a broad zone of rocks that formed between 20 billion and 18 billion years ago 0 TransHudson Belt 0 Comprises both deepsea sediments squeezed up between the converging cratons and crystalline rocks produced by an igneous arc 0 South of the Archaen terranes between 2 Billion and 18 billion years ago Series of terranes whose addition expanded Laurentia eastward Clastic example of continental accretion Grenville orogeny Ended about a billion years ago Three successive orogenies Produced the Appalachian Mountains during the Paleozoic Era o Added more continental crust to eastern North America Sudbury impact 0 O O O O 185 billion years ago Extraterrestrial event Produced one of the largest bodies of metallic ores ever discovered Impact of an asteroid l crater in southern Canada Originally about 150 kilometers in diameter Shattered rocks to form breccias Some contain such large clasts that they are called megabreccias Pressure also shattered rocks in coneshaped radial patterns Shatter cones Point toward the impact site Tsunami deposits some cross bedded indicate that the impact happened in a marine setting Blasted chunks of rocks out of the sea oor Ejecta Some objects ew as far as 800 kilometers from the impact site Spherical sandsized grains that were originally glassy Formed by the rapid cooling of droplets of molten rock Larger elongated clasts Formed by the cooling of airborne globs of lava Sudbury ore deposits Rich in copper nickel platinum palladium and gold Derived from bedrock Heavy metals segregated from other molten materials when the heat of the impact melted a huge volume of rock Banded iron formations in the Lake Superior region 0 O O A lot of iron for the production of steel Deposition ended about 185 billion years ago Sudbury impact stirred up the ocean changing the concentration of oxygen near the sea oor and temporarily terminating iron deposition 0 Greatest disturbance of the central North American craton O O 0 Last 14 billion years Spreading center formed beneath the craton l begins to rift apart Lavas poured into elongate basins along a belt that extended from the Great Lakes region to Kansas Rifting ceased before the continent was split Left its mark in enormous volumes of mantlederived lavas Lavas produced basalts and felsic volcanic rocks 0 Had the crescentshaped zone of rifting extended to the southern margin of the craton Eastern US would have drifted away 0 Keweenawan Supergroup Con guration and composition indicate the presence of failed midcontinent rift Rocks that formed within rift include hardened lavas known as Keweenawan basalts Exposed near the southern border of the Canadian Shield 0 Associated with red siliciclastic rocks and alluvialfan conglomerates Contain ore deposits of native copper 0 Mineral consisting of elemental copper uncombined with other elements 0 Presence is associated with feature known as quotmidcontinental gravity highquot 0 Local increase in Earth39s gravitational eld as measured from the surface 00 Grenville Orogeny 0 Another step in the accretion of Laurentia Added a belt that stretched from northern Canada far down into the eastern United States 0 Stabilized a large volume of sediments that had accumulated along the margin of eastern North America 0 Crystalline rocks Best exposed in the Canadian portion of the Grenville Province 0 Grenville event collision of eastern Laurentia with a landmass that would later become northern South America Remnants of mountain systems that are the same age as the Grenville orogenic belt 0 The Canadian Shield 0 Large portion of the North American craton o Precambrian rocks underlie the interior of the continent farther south Overlain by a relatively thin veneer of Phanerozoic sedimentary rocks
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