GEOL 101: Evolution of the Continents: Lecture 17
GEOL 101: Evolution of the Continents: Lecture 17 101-017
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This 3 page Class Notes was uploaded by Natalee Stanton on Wednesday February 24, 2016. The Class Notes belongs to 101-017 at University of South Carolina taught by in Winter 2016. Since its upload, it has received 24 views. For similar materials see Geology 101-017 in Geology at University of South Carolina.
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GEOL 101: Evolution of the Continents I. Nature of continents Continents are made and deformed by plate tectonic processes Continental rocks are generally older than oceanic rocks Lithosphere floats on a viscous layer below the continents, the asthenosphere, within the Earth’s mantle II. Continental lithosphere Sedimentary cover Crystalline basement (igneous and metamorphic rocks) Uppermost mantle III. Tectonic of North America Portions of continents vary by tectonic province and age Long geologic history is recorded Tectonic setting may change over geologic time o No matter where you are on a continent, the rock will change over time IV. Continental components a. Stable cratons 1. Shields metamorphic and igneous rocks at the surface 2. Platforms – sedimentary deposits at the surface b. Folded mountain belts (orogens) Orogeny – a general term for mountainbuilding processes o Folding and thrusting of rock layer o Often accompanied by magmatic activity and metamorphism o Evidence of multiple orogenic events is typically preserved in continents V. Continental shield Central, older portions of continents (older rocks) Low elevation and relatively flat Crystalline basements of metamorphic and igneous rocks Composed of a series of zones that were once tectonically active VI. Stable platforms Shields covered with a sequences of horizontal sedimentary rocks o Sandstones, limestones, and shales deposited in ancient shallow seas Many transgressions and regressions caused by changed in spreading rate o The raising and lowering of sea level over time Sedimentary rocks are now preserved in large basins Folded mountain belts: The Appalachians Relatively narrow zones of folded rocks with associated magmatism Formed at convergent plate boundaries Two major active belts 1. Cordilleran –RockiesAndies 2. Alps Himalaya Older examples include Appalachians and the Urals Tectonic provinces of the West – North American Cordillera o Still active tectonically VII. How continents grow Magmatic differentiation – magma transferred form mantle to continents at subduction zones Continental accretion – buoyant fragments of crust attached t continents as the result of plate motions o Amalgamation or accretion of terranes o Exotic terranes (seem outofplace) 1. Accretion of island arcs – 2. Accretion of continental Fragments – Madagascar 3. Accretion along transform faults – San Anderas Fault 4. Accretion by continental collision/rifting VIII. How continents are modified Orogeny – mountain – building process of folding, faulting, magmatism, and metamorphism Epeirogeny – vertical motions of largely ….. o Vertical motions IX. The Wilson Cycle Repeated opening and closing of ocean basins, collision and rifting of continents X. Formation of Cratons Archean cratons o Granitegreenstone terrains o Highgrade metamorphic XI. Deep structure of the continents Structure of the craton o Continental crust o Cratonic keel – similar to an ice berg flaring in water Sample Exam Questions: When is it though that the big bang took place a. Approximately 4.5 million years ago b. Approximately 14 million years ago c. Approximately 4.5 billion years ago d. Approximately 14 billion years ago What mountain chain runs along the eastern margin of North America? a. The Andes b. The Appalachian c. The Caledonides d. The Cordillera What is meant by the tectonic age of a region? a. The oldest rocks in the region b. The oldest major deformation event in the region c. The youngest rocks in the region d. The youngest major deformation event in the region What is orogeny? a. A broad exposure of deformed metamorphic and igneous rocks b. A general term for mountainbuilding processes c. A special type of reverse fault d. A theory that explains the uplift of continents after large ice sheets melt