GEOL 1425 1st EditionExam # 3 Study Guide Lectures: 13-17Lecture 13 (03/04) & Lecture 14 (03/06)History of the Continents and Clocks in the Rocks:1. Craton composition: continental shields and platforms that make up the most stable parts ofthe continental lithosphere and contain eroded remnants of ancient deformed rocks. Continental cratons underlain by thick layers of strong mantle that move with the plates during continental drif2. Age of Cratons: every continental craton contains regions of crust that were last deformed during the Archean Age (4.0-2.5 billion years ago)3. Komatiite: ultramafic volcanic rock found only in Archean crust; contain high percentages of magnesium oxide and much mantle melting; made of a spinitex structure4. Epeirogeny: gradual downward and upward movements of broad regions of crust without significant folding or faulting. Usually result in a set of flat-lying sediments5. Pangea (Laurasia and Gondwanaland): before the breakup of Pangaea, the Farallon Plate occupied most of the Eastern Pacific Ocean. Orogeny: the breakup of Pangaea sent the continental crust of Africa, Arabia, and India northward causing the Tethys Ocean to close as its lithosphere was subducted beneath Urasia. Pieces of Gondwanalda collided with Eurasia.6. Where mountain building (orogenies) occur: most involve plate convergence, when continent rides over oceanic plate, most intense is when two continental plates collide. 7. Wrangellia: an exotic terrain, formerly a large oceanic plateau, transported over 5000 km from Southern Hemisphere to now be in Alaska and Western Canada. 8. Continent growth rate: accretion is a process of continental growth in which pieces of crust are attached to continents during plate motions9. The Colorado Plateau: Located in North American Cordillera, an island of stability that has experiences no major extension or compression since Precambrian Period.10. Age of Cordilleran mountain building: began 15 million years ago and continues today11. Farallon plate: occupied most of eastern pacific ocean before the breakup of Pangaea and today all that is lef of it are small remnants12. Appalachian fold belt: along eastern side of north America’s stable interior are old eroded Appalachian mountains, contains slices of ancient Europe and Africa and a variety of exotic terrains, resulting from plate tectonic events from late Precambrian time to present. 13. Radiometric dating of rocks and important isotopes used in dating: isotopic clock begins when a mineral crystalizes or recrystallizes. Different isotopic dating methods contain uranium-lead, potassium-argon, rubidium-strontium, carbon-nitrogen. 14. The names of the various divisions of the earth’s history: divisions of geologic time include eras, periods, and epochs. 15. Cross cutting relationships: include faults and intrusions16. Disconformities: beneath the ocean, sedimentary beds accumulate in layers. Later tectonic forces cause a lif of the beds above sea-level. Erosion strips away top few layers leaving an irregular surface of hills and valleys17. Principles of stratigraphic succession: horizontality- when lef undisturbed the younger layers remain above the oldest. Superposition when sediments are deposited in horizontal layers and eventually become rock. Lecture 15 (03/18) & Lecture 16 (03/20)Volcanoes 1 &2:1. Andesite—type of lava; extrusive rock with an intermediate silica content. Andesititc magmas are erupted mainly in volcanic belts along active continental or oceanic margins above subduction zones2. Basaltic magma—when basaltic magma cools under water it forms pillow lavas, which are an important indicator that a region on dry land was once under water. Basalt is an extrusive rock of mafic composition with relatively low silica content; basaltic magmas are the most common type of melt. Its extremely fluid and flows downhill quickly. 2 types: Aa is lava that has lost its gases and consequently flows more slowly than pahoehoe, allowing a thick skin to form. 3. Gas content of lava: the more gas a lava contains, the more violent its eruption is likely to be. When gas is released into lava during eruption, it creates little bubbles that can be seenin volcanic rock. 4. Rhyolite: extrusive rock of felsic composition with silica content greater than 68%; produced in zones where heat from the mantle has melted large volumes of continental crust. The stickiest and least fluid of all lavas, and can flow as much as 10 times slower than basaltic. 5. Diorite: the intrusive equivalent of andesite. 6. Volcanic domes: bulbous masses of felsic lava, which are so viscous that instead of flowing, they pile up over the vent7. Lava viscosity: the more viscous the lava is, the slower it moves. Viscous lava has a high silica content and low temperature. 8. Vesicles: gas cavities from which water vapor and other dissolved gasses escape 9. Volcano collapse: flank (a volcano’s sides may become too steep and break or slip off, sliding downhill in a landslide) and caldera (infrequent but very destructive; a collapse of large calderas) collapse.10. Lithified pyroclastic deposits: Volcanic activity does not stop when lava or pyroclastic materials cease to flow. For decades or even centuries afer a major eruption, volcanoes continue to emit gas fumes, water, and steam through small vents called fumaroles. These emanations contain dissolved materials that precipitate onto surrounding surfaces as the water evaporates or cools, forming various encrusting deposits. Some precipitates can contain valuable minerals. 11. Lehars 12. Fumaroles: volcanoes emit steam through small vents called fumaroles13. Diatremes: a type of central eruption; the resulting structure from when magma from earth’s interior escapes explosively and the vent and feeder channel below it are ofen lef filled with volcanic breccia as the eruption wanes14. Pyroclastic flow: One particularly spectacular and ofen devastating form of eruption occurswhen hot ash, dust, and gases are ejected in a glowing cloud that rolls downhill at high speeds. The solid particles are buoyed up by the hot gases, so there is little frictional resistance.15. Fissure eruptions: the main style of volcanism along with mid-ocean ridges, where new oceanic crust is formed. Highly fluid basalt erupting from fissures forms widespread layers rather than mountains.16. Location of most active volcanoes: along mid-ocean rifs where new continental crust is being