Introduction to Earth Science 1030
Introduction to Earth Science 1030 GEOL 1050
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This 11 page Bundle was uploaded by Amore' Notetaker on Tuesday March 1, 2016. The Bundle belongs to GEOL 1050 at Middle Tennessee State University taught by Melissa Kay Lobegeier in Fall 2015. Since its upload, it has received 52 views. For similar materials see Historical Geology in Geology at Middle Tennessee State University.
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Date Created: 03/01/16
Metamorphic Rocks Metamorphism describes the processes that changes rock in the Earth’s interior. The rock is heated and pressured, but does not melt. Metamorphic rocks are produced from preexisting rocks. The old (original) rock is the parent rock. The new rock is a metamorphic rock. The mineral content is controlled by what is in the parent rock. Metamorphic agents: Temperature, Pressure, and Chemically active fluids. 1) Temperature-Heat is needed for metamorphic reactions. 2) Pressure- 2 types: Confining pressure and Differential stress (Directed Pressure) 3) Chemically Active Fluid-Mainly water and other volatiles. Promote recrystallization. Confining Pressure From burial. Same in all directions. Forces minerals grains together. Ex. 3.3 km (2 miles) under rock=1000 atmospheres of pressure Differential Stress Differential stress (or directed pressure) occurs when force is different in different directions. Changes the texture of the rock (e.g. flattened pebbles), causing it to have a foliated texture. Foliation Foliation is the parallel alignment of minerals due to differential stress (directed pressure). Minerals line up perpendicular to stress of forces on the rock. Metamorphic Grade The intensity of the metamorphism that formed the rock. Grade closely reflects the temperature of metamorphism. Two most common types of metamorphism Contact Metamorphism-Occurs when rocks come into contact with a heat source. Occurs close to magma. (Like making ceramics-heat but no pressure). Rock is “baked” by coming into contact with hot magmatic intrusion. Usually occurs close to earth’s surface. Pressure is low. Not foliated as no differential stress. Regional Metamorphism-Usually occurs deep below the earth’s surface, so differential stress and confining pressure can be high. Rock is usually foliated, indication differential stress. Produces greatest volume of metamorphic rock. Occurs during mountain building. Summary-Metamorphic rock forms from other rocks that have been subjected to high pressure and temperature or chemically active fluids. Types determined by foliation and parent rock. Earthquakes An earthquake is a shaking of the ground caused by the sudden release of energy by rocks in the Earth’s surface. Associated with movement along faults. Elastic Rebound Theory-Step 1 (Stress with no strain) Step 2 (Stress produces strain) Step 3 (Fault breaks-strain energy released as shaking). Correct process is 2,3,1,4 Seismic Waves Seismic waves-Shock waves caused by the earthquake Focus-the place within the Earth where earthquake waves originate Epicenter-The point on the Earth’s surface directly above the focus Types of seismic Waves 1) Body waves-Pass through the earth’s interior a) Primary waves (P-Waves) are compressional-the rock vibrates in a direction parallel to the direction of the wave-push pull b) Secondary Waves (S-Waves) are slower, transverse waves- up down 2) Surface waves-travel ALONG the earth’s surface. Cause the most earthquake damage a) Loves Waves-side to side motions b) Rayleigh waves-vertical motion Locating and measuring earthquakes Seismograph measures seismic waves and records them. This record is called a seismograph. P Waves arrives first (Primary wave) S Waves arrives second (Secondary waves) Surface waves arrive last, but are strongest (not amplitude) More distant seismographs will record the earthquake later Determining the location on an Earthquake Three stations required to determine earthquake position Circle equal to the epicenter distance is drawn around each station We look for where the circles intersect Measuring the size of earthquakes The Modified Mercalli Intensity Scale measures the intensity of earthquakes. Developed in 1902 by Guiseppe Mercalli, estimates the degree of shaking at a given locale based on the amount of damage. The Richter scale The Richter scale measures the strength of earthquakes 2.0 limit can be felt by most people 6.0 is significant 9.0 caused the 2004 tsunami Scale is logarithmic 10-fold increase in ground motion-so a magnitude 6 is 10 times bigger than a magnitude 5, which is 10 times bigger than a magnitude 4. 32 times increase in energy released. Does not have a maximum value, does not adequately estimate the size of very large earthquakes. The Great Chilean Earthquake may 22, 1960 magnitude of 9.3. Moment Magnitude Scale The Moment Magnitude Scale measures very large earthquakes. Derived from the amount of displacement that occurs along a fault zone, the area of the rupture surface, and the shear strength of the faulted rock. Earthquake Prediction We CANNOT predict when an earthquake will occur. Location is easier. Patterns have been observed. We can predict where it will occur. Effects of Earthquakes Ground motion, fire, landslides, liquefaction, land movement, tsunami Tsunami are not tidal waves, starts as a big wave, but when hitting inland it turns into a strong surge of water. Tsunamis are seismic sea waves-produced by a large earthquake with a sub-ocean epicenter. When a seafloor earthquake results in an uplift o [art of the seafloor the water above the seafloor is also uplifted starting a tsunami. Part of the tsunami races towards land growing larger as it comes in to shore. The other part heads across the ocean. There is often more than one wave and the first wave is often not the biggest. The tsunami can last for hours. Geohazards & Plate T ectonics What countries have volcanoes? USA (Hawaii, Washington, Montana, Oregon, Alaska), Ecuador, Greece, Italy, Indonesia, Japan, Iceland, Macedonia, Russia, Columbia, Chile, Mexico What countries have earthquakes? USA (California, Tennessee, Washington, Oklahoma Alaska) Haiti, Chile, China, Japan, PNG, Spain, Virginia, Taiwan, New Zealand, Indonesia, Pakistan, Philippines, Italy Alfred Wegener-Most people thought the complementary shapes were coincidence. Alfred proposed the hypothesis of Continental Drift. Published THE ORIGIN OF CONTINENTS AND OCEANS. Continental Drift Wegener suggested there had once been a supercontinent called PANGEA that began breaking apart 200 million years ago. His hypothesis stated that the continents drift slowly across the Earth’s surface. Evidence: Fit of South America and Africa. Patterns of: Glaciations (climate), Rock Types and structures, and Fossils Glaciations Glaciations leave marks on the landscape and leave marks on the ice, called striations. Evidence of glaciation about 250 million years ago. An unusual pattern for today but not for a rearranged set of continents. Rock Types and mountain belts Rock types and mountain belts can be matched on either side of the Atlantic Ocean. Fossils Mesosaurus Testing the Hypothesis How do the continents move? Tides or Centrifugal forces? Doesn’t work both are not strong enough to move continents. Wegener’s downfall: Lack of a Mechanism Support from scientists from the southern continents and some acceptance in Europe. Almost total skepticism in North America. Condemnation by American geophysicists. No mechanism, no progress. The Sea Floor New information about the Earth’s surface and about the seafloor gave us a mechanism for Wegener’s continental drift hypothesis. This became known as the seafloor spreading. Seafloor Topography The seafloor gets deeper as we move away from the coast. First gradually, and then more quickly. Until it flattens out to form level areas called abyss plains (2.5 miles below sea level) As we continue to move away from the continents we come to an underwater mountain range, called the oceanic ridge system (mid-ocean ridge). Oceanic Ridges Found in all of the world’s major oceans Compared to the abyssal plains, the seafloor along the ridges is relatively shallow. Source of volcanic activity. The Mid-Atlantic ridge, the oceanic ridge in the Atlantic, comes to the surface in Iceland. Deep-Ocean Trenches Found along the edges of some continents. Can be very long. Can be up to 6. Miles deep. Age of the Ocean Floor Drilling into the seafloor has helped us determine how old the seafloor is. Oldest oceanic rocks are less than 200 million years old. Oldest continental rocks are 4 billion (4000 million) years old. Youngest rocks are near the ridges and the oldest rocks are along the edges of the oceans. These ages are symmetrical on either side of the ridge. Age of the seafloor increase symmetrically moving away from the oceanic ridge system. Heat flow, Volcanoes, & Earthquakes Heat flow Heat is escaping from the Earth’s interior. Heat flow varies Heat flow is heist along the oceanic ridge systems Oceanic ridge systems are places where hot, melted rock, called magma, is erupting onto the seafloor. Made out of basalt. Volcanoes Most active volcanoes are located beside oceanic trenches Plate T ectonics 2 A New Hypothesis We take all this evidence: 1) Oceanic Ridge Systems, deep ocean trenches 2) Age of the seafloor (youngest at ridges) 3) Heat flow along ridges 4) Location of volcanoes and earthquakes A new hypothesis called Seafloor Spreading New Oceanic floor is being continuously formed along the ridge system by magma rising from below. As this occurs the existing rocks move away from the ridge. Ocean floor is consumed and destroyed as it descends into the Earth’s interior adjacent to ocean trenches. Layers of the Earth The Earth is composed of: The core (inner and outer), the mantle, and the crust. The outer core is the only liquid layer. Crust Crust can be separated into: Oceanic Crust-3.6 miles thick and made of basalt. Continental crust-10-50 miles thick and made of less dense rocks (like granite). Beneath the crust, is the mantle. Key Layers The mantle and crust are split into two layers Lithosphere Rigid outer layer Composed of crust and uppermost part of the mantle The lithosphere is composed of several individual pieces called plates, which move in relation to one another. The rigid lithosphere is thought to float on the slowly moving asthenosphere Asthenosphere Exists beneath the lithosphere Part of the mantle Hotter and weaker than lithosphere Allows for motion of lithosphere Plate Tectonics Theory that the Earth’s outer shell consists of individual plates that interact in various ways and produce earthquakes, volcanoes, mountains and the crust itself. Seafloor spreading is one process within plate tectonics. Plate Boundaries -All major interactions among plates occurs along their edges or boundaries. Divergent Boundaries Two plates move apart or diverging Includes continental rifting and new seafloor construction Also called constructive margins Continental Rifting- 1Starts with crustal upwarping (Rift valley is formed- volcanic activity starts) Ex. East African Rift. 2Linear sea then forms- new floor is created. Ex. Red Sea. 3Then Ocean basin forms-ocean ridge system is at the center (Example-Mid-Atlantic Ridge). New seafloor is continually created at ridge. Rifts broke up the earlier supercontinent of Pangea into two continents, Laurasia and Gondwana. Eventually those broke into the continents we know today. Most divergent boundaries occur at oceanic ridges New seafloor is created at oceanic ridges and this is called seafloor spreading Seafloor spreading rates are 5-9 cm/yr. Earthquakes occurs along he oceanic ridges Convergent Boundaries Two plates collide Sometimes seafloor is destroyed Also called destructive margins What happens when tow plates collide? IT depends on what the plates are made out of! Oceanic lithosphere (thin, denser) or continental lithosphere (thicker, lighter). Subduction-When old lithosphere is thrust into the mantle to be destroyed. Only oceanic plates can be subducted. This process explains the age of oceanic plates. Oceanic-Continental Convergence Denser oceanic lithosphere is subducted underneath continental lithosphere. Continental volcanic arcs are produced (Example-Cascade or Andes Mountains). There is no trench and a continental volcanic arc. Benioff zone of earthquakes as plates scrape against each other. Subducted rocks melts to form magma that creates volcanism. Oceanic-Oceanic Convergence Two oceanic plates collide and one is subducted. Volcanic island arcs are produced (Example-Aleutian Islands, Alaska). Continental-Continental Convergence Two continental plates collide Himalayas in India Starts with oceanic-continental convergence until all the seafloor is consumed Continental plates do not subduct so instead are thrust upward to form mountains Transform Boundaries Plates slide past one another No new crust is created and no new crust is destroyed Transform faults ae large faults Most join two segments an oceanic ridge Aid the movement of oceanic crustal material Earthquake and Volcanic Patterns Volcanoes-occurs along convergent boundaries Earthquakes occur along all plate boundaries Earthquakes-Earthquakes occur at 3 depths Shallow-0-70 below the surface Intermediate-70-350 below the surface Deep-350-670 below the surface Intermediate and deep earthquakes only occur along oceanic-oceanic and oceanic-continental convergent boundaries
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