Planet Earth Week 3 (including lab notes!)
Planet Earth Week 3 (including lab notes!) Geol 105
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This 7 page Class Notes was uploaded by Abi Sommers on Friday September 9, 2016. The Class Notes belongs to Geol 105 at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months taught by John Platt in Fall 2016. Since its upload, it has received 21 views.
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Date Created: 09/09/16
Week 3 Notes : 9 7 Answers to last week’s pop quiz: 1. What term best describes the part of Earth that forms the tectonic plates? Lithosphere 2. The radius of the Earth’s core is about one sixth radius of the earth. False 3. Which is not correct? Earth’s mantle is made of liquid rock 4. Plate material is formed at divergent boundaries and destroyed at convergent boundaries. True 5. Boundaries of plates most clearly indicated by : distribution of earthquakes 6. The sun is the principal energy source that drives plate tectonics. False 7. Which statement is not correct : plate boundary in central california is a subduction zone 8. The East African Ridge and Mid Atlantic Ridge are both expressions of divergent plate boundaries. True Earth Materials II : Rocks Rocks : Rock Description: Mineral assemblage Grain size ( size of crystals) Texture Organization and structure ● These all give info that allow us to interpret how the rock formed Texture: Crystalline texture grains may have crystal faces and interpenetrate may result from growth of grains granite Sedimentary (Clastic) texture Rounded or angular grains Do not interpenetrate Separated by matrix Pebbly sandstone and conglomerate sediment deposited by rivers Clastic means segmented Granite: The main constituent of the continental crust An igneous rock , a crystallized rock made of mainly quartz and feldspar rich in Si , Al, Na, K Oxygen is most abundant element ! Peridotite: Main constituent of Earth’s mantle Crystalline texture Peridotite made up of mainly olivine ( also pyroxene, sometimes garnet) Mainly Si (less than in the crust) and Mg Oxygen is most abundant element! Classification of rocks by texture and origin I . Igneous rocks Crystalline texture Crystallize from a melt (magma) 2. Sedimentary rocks Clastic texture (mainly) Grains deposited by flowing water or wind 3. Metamorphic rocks Crystalline texture Growth of minerals in the solid state Form by modification of other types of rock Igneous rocks: Igneous rocks form by solidification from a liquid ( magma, molten rock). Magma may crystallize within the crust ( intrusive igneous rocks), or flow out at the surface as lava ( extrusive (volcanic) igneous rocks Intrusive igneous rocks Basalt dike, New Zealand Magma may be emplaced into the crust , forming igneous intrusions The magma cools more slowly (years to millions of years) Crystals have time to grow Rocks are medium or coarse grained, with a crystalline texture Plutonic rocks Granite, Sierra Nevada large crystals are kfeldspar large intrustion of igneuous rocks called plutons cool very slowly, coarsegrained ● Interpretation based on observation of the great size of the rocks Sedimentary Rocks : Grains transported by rivers, currents, tides, waves or wind are deposited to form clastic sedimentary rocks. ( Bedded conglomerates, Fish Canyon, California) Metamorphic Rocks : Start as one thing and end up as another Garnet amphibolite with garnet, hornblende, and feldspar Metamorphic rocks have a crystalline structure Mineralization: Water flows through pore spaces and fractures in rock Dissolves material Precipitates it as cement, and in fractures ( veins ) minerals deposit by fluids include quartz calcite many economically valuable minerals ( gold, silver, ore materials ) 9/9 Lecture (Monday’s quiz will not include this info) Exam Question of the Day : The theory of isostasy states that : D. Topography (surface elevation) is controlled by the density and thickness of the crust Extrusive igneous rocks : Magma extruded at surface solidifies to form fine grained or glassy volcanic rock; lava flows Glass is a noncrystalline solid Volcanic lava can cool to form a glass Some volcanic rock has “fine grained” or microscopic crystals Columnar jointing in basalt lava columnar joining in basalt County Antrim, Northern Ireland every point within lava flow pulls away for others points and breaks up into columns ( mud cracks and column jointing in lava produced by same physical process) ● If magma is ejected violently, may be deposited as ash ( pyroclastic rocks) Intrusive igneous rocks : 3 types ( important definitions! ) Dike a tabular intrusion that is discordant with surrounding rock Pluton a large intrusion ( usually discordant, but so big, hard to see) Sill a tabular intrusion that is concordant with the surrounding rocks Where and why does melting occur within the Earth? Where 1. At midocean ridges 2. In mantle plumes 3. Above subduction zones 4. In zones of mountain building Magmatism at midocean ridges: Melting is a result of decompression of mantle rock rising beneath ridge Occurs at 3060 km depth Melting of mantle peridotite Magma cools to form 6km thick ocean crust Forms distinctive sequence of intrusive and extrusive rocks Locally preserved on land : ophiolite Lava cooled fast, fine grained called : basalt Coarse grained Intrusion called : gabbro Melting at midocean ridges Melting of mantle peridotite beneath MOR Produces basalt magma : Low content of SiO2 High content of Fe and Mg melting is attributed to decompression, as the asthenosphere rises towards the surface ( see lecture diagram) Convection is the manner heat is conducted ;Hot material rises, cool material sinks, transaction occurring by transferring of heat Quiz Monday! Lab Week 3 ● The Earth’s mantle is higher because of isostasy 3 kinds of plate boundaries 1. Divergent ←- --> 2. Convergent > < 3. Transform > ←------ Divergent boundaries ; plates move apart; new seafloor is made Hot material within mantel reaches top and cools down at sea floor Forms new material and rocks at sea floor , new material pushes old apart, to left and right, creates mid atlantic ridge Convergent boundaries ; one plate is subducted (the denser plate) the Andes Mountains are an example of this 3 types of Convergent boundaries; OceanContinent collision (andes mountains and peruchile trench) Continentcontinent collision ( himalayas and tibetan plateau) Ocean ocean collision ( japanese islands and japan trench) Transform boundaries ; plates slide past each other along strike slip faults San andreas fault is an example of this The Pacific plate has been grinding horizontally past north american plate for 10 million years Hot spots Not related to plate tectonics Chain of volcanoes formed above a stationary magma chamber in mantle Can be used to determine plate motion rates and directions Hot spots are beneath active volcanoes