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Earth Chapter 15 Part 2 1 Limestone 2 3 Breccia 4 Shale 5 6 Oil Shale 7 Siltstone 8 9 Sandstone 10 Sandstone 11 Coal 12 Metamorphic rocks • Previously existing rocks changed by heat, pressure or hot solutions into distinctly different rock • Causes associated with geologic events – Movement of the crust – Heating and hot solutions from magma intrusion – Temperatures must be high enough to cause recrystallization, but not melting 13 Metamorphic rocks 14 Gneiss 15 Slate 16 17 Marble 18 Marble Colorado 19 Seismic Waves • Remember the earth is not solid rock • All rocks and rock materials can be made to flow – Behaves as semi-solid like wax or putty – Under extreme temperature & pressure – Moves slowly upward toward the surface • Earth’s internal heat and rock movement is related to what's happening on the surface • To get a look at the Earth’s interior – Study Earthquakes – These create Seismic Waves radiating outward through the solid and semi-solid interior 20 Seismic Waves Epicenter Hypocenter 21 Seismic Waves • P-wave – Longitudinal (compressional) – Fastest waves – Move through surface rocks and interior solid and liquid materials • S-wave – Transverse (shear) wave – Second fastest – Do not travel through liquids 22 Seismic Waves – Surface waves • Much like water waves • Slowest of the three – Occur where S- or P-waves reach the surface – Two types of surface waves • Love waves – horizontal S-waves – move side to side • Rayleigh waves – Like rolling water waves – More destructive 23 Seismic Waves 24 Seismic Waves 25 Theory of Plate Tectonics • Individual continents shift positions on Earth’s surface • Patterns between continental shapes can be fit together • “Pangaea” • Original concept: “Continental drift” 26 Pangaea 27 Theory of Plate Tectonics 28 Evidence from the Ocean • Oceanic ridges – Coincide with submarine earthquakes – Rift along crest – Large amount of heat escapes from crest – Mid-Atlantic Ridge • Oceanic trenches – Long, narrow, and deep troughs with steep sides – Always run parallel to continental edges 29 Seafloor Spreading Hypothesis • Hot, molten rock moves up from Earth’s interior emerging along a rift • Outflow in both directions creates new rocks • Drilling evidence – Thin sediment layers near ridge, becoming thicker toward continents – Older fossils and rocks near continents, becoming younger near rifts 30 Plates and Boundaries • Basis of Plate Tectonics theory • Lithosphere broken into fairly rigid plates • Plates move on asthenosphere 31 • Earthquakes, volcanoes and other rapid changes in Earth’s crust occur most often at plate edges • Three plate motions: – Divergent – Convergent – Transform 32 Divergent Boundaries • Occur between two plates moving away from each other • Molten material from mantle rises to fill fissures • New crust zone • Often accompanied by volcanic activity • Example: MidAtlantic Ridge 33 Convergent Boundaries • Occur when two plates move toward each other • Old crust destroyed in the process • Subduction zone – Belt with one crust subducting under another – Subducted material partially melts and joins mantle 34 Convergent Boundaries • Three possibilities 1. Converging continental and oceanic plates 2. Converging oceanic plates 3. Converging continental plates 35 Ocean-Continent Plate Convergence • Oceanic plate of denser basaltic material subducted under less dense granite-type continental shelf • Marked by oceanic trench, deep-seated earthquakes and volcanic mountains • Example: convergence of South American Plate with Nazca Plate 36 Ocean-Ocean Plate Convergence • Trench and underwater ridge created by Subduction • Associated with deep-seated volcanoes • Island arcs form where melted, subducted material rises up above sea level through the overriding plate 37 Continent-Continent Plate Convergence • Less dense, granitetype materials resist Subduction • Colliding plates pile up, producing a deformed and thicker crust of lighter materials • Example: Tibetan Plateau and Himalayan Mountains 38 Transform Boundaries • Occur when two plates slide by each other • Crust is neither created nor destroyed in the process • Irregularities in movement along boundary • Sudden jerks produce earthquakes • Example: San Andreas Fault along California coastline 39 Present-day Understandings • Major remaining question: What drives the plates? • Current working hypothesis: convective cells in asthenosphere – Hot fluid materials rise at diverging boundaries – Some escapes to form new crust – Remainder spreads beneath the lithosphere, dragging overlying plates with it – Problem: little supporting evidence 40