UNIVERSITY OF SOUTH ALABAMA Last Time GY 111 Physical Geology Lecture 25 Agents of Metamorphism Seismic Waves Earthquakes A Seismic waves and the Earth s interior B Earthquake intensity and magnitude C Seismographs and locating earthquake epicenters on maps D Case Studies Seismic Waves As P and S waves travel through the Earth they speed up and slow down according to the density of the materials they pass through This results in wave refraction Three major types of seismic waves are distinguished 1 P waves Primary travel by compression 2 S waves Secondary travel by shear 3 Surface waves Long waves travel along the surface Seismic Waves If an earthquake is powerful enough seismic waves can make it around the world Propagation of P waves Locating Epicenters on maps You need at least 3 seismograph stations But wave refraction results in the formation of shadow zones where P or S waves do not occur The S wave shadow zone is wider than the P wave shadow zone P wave shadow zones 1 Seismicity of Australia Indonesia and New Zealand 1990 2000 Today s Agenda Metamorphism 1 A Agents of Metamorphism B Types of metamorphism C Hydrothermal fluids webnotes only Web notes 25 Source http earthquake usgs gov Metamorphism Metamorphism Metamorphism a solid state change recrystallization of a parent rock by physical agents using operating deep within the interior of the Earth 1 Agents of Metamorphism Heat 25 C to 800 C up to the point of melting Geothermal Gradient the increase in ambient temperature with depth 15 to 30 C km under stable continental rocks 200 C km under mid oceanic ridges Shale Parent Rock Slate Metamorphic Rock http www geo umn edu courses 1001 Summer Session MeltingVsDepth jpg Metamorphism 1 Agents of Metamorphism Heat 25 C to 800 C up to the Metamorphism 1 point of melting 2 Agents of Metamorphism Heat 25 C to 800 C up to the point of melting Pressure 1 bar to 12 kbars 2 3 Pressure 1 bar to 12 kbars Chemically active fluids AKA hot water 1 bar 1 atmosphere 12 kbar 12 000 atmospheres http news service stanford edu news 2005 http www geol ucsb edu faculty hacker geo102C lectures hydrostat jpg 2 Types of Metamorphism Types of Metamorphism zRegional heat and pressure zRegional heat and pressure Associated with convergent plate boundaries Isobars versus isograds http www indiana edu geol105 images gaia chapter 5 regmeta jpg Types of Metamorphism z Contact heat only Types of Metamorphism z Contact heat only Metamorphic aureole Metamorphic aureoles Metamorphic aureoles Types of Metamorphism z Cataclastic pressure only Types of Metamorphism z Cataclastic pressure only Mylonites Shear zones http www cliffshade com colorado homestake hsz01 jpg http instruct uwo ca earth sci 200a 001 03dymet gif 3 Today s Homework 2 1 Assignment number 4 due Tuesday Rock mineral assignment due 2 weeks from today Next Time 1 Regional metamorphism 4
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