UNIVERSITY OF SOUTH ALABAMA GY 111 Physical Geology Lecture 3 The Rock Cycle Last Time 1 Alfred Wegener and Drifting Continents 2 The Plate Tectonic Revolution 3 Plate Tectonics Mechanisms Wegener s hypothesis Continental Drift 300 million years ago the continents were all grouped together into a supercontinent he called Pangaea His supporting evidence Matching rock types and fossils types and ages And although Continental Drift was rejected Wegener got it right about Pangaea The Plate Tectonics Revolution Technological developments during the war increased our understanding of the world s oceans The Plate Tectonics Revolution Radar sonar and depth sounding revealed that the ocean bottoms were not flat planes The Plate Tectonics Revolution The single most important piece of evidence for plate tectonics was also discovered around the end of WWII was Paleomagnetism The Plate Tectonics Revolution Earth has a magnetic field and it isn t constant The Plate Tectonics Revolution Paleomagnetism shows that the ocean floor youngest near the ridges and oldest near the continents Paleomagnetism The Plate Tectonics Revolution The outer part of the Earth is broken up into several large tectonic plates The Plate Tectonics Revolution And where they rub against one another you get Earthquakes The Plate Tectonics Revolution Volcanoes active dormant and extinct The Plate Tectonics Revolution http shadow eas gatech edu anewman classes geodynamics misc Worldmap gif and mountain belts Internal guts of the Earth Four Major Geophysical Layers 1 The Crust 2 The Mantle 3 The Outer Core 4 The Inner Core 1270 km solid metal Heat exchange gives rise to Convection Currents The Plate Tectonics Mechanism Rising convection currents stress the rigid outer layer of the Earth Cooler Hotter The Plate Tectonics Mechanism Rising convection currents stress the rigid outer layer of the Earth This layer consists of the crust and the outer most mantle Geophysical layers Crust Cooler Mantle Hotter The Plate Tectonics Mechanism Collectively the rigid outer most part of the Earth about 100 km thick is called the Lithosphere Tectonic layers Geophysical layers Lithosphere Crust Cooler Athenosphere Mantle Hotter The Plate Tectonics Mechanism It is postulated that the convection currents can eventually break up the lithosphere into separate plates Tension Cooler Hotter The Plate Tectonics Mechanism Hence the term plate tectonics Asthenosphere The Plate Tectonics Mechanism Tectonic plates can interact in one of 3 ways The Plate Tectonics Mechanism Tectonic plates can interact in one of 3 ways 1 Move away from one another Divergent Plate Boundary The Plate Tectonics Mechanism Tectonic plates can interact in one of 3 ways 1 Move away from one another Divergent Plate Boundary 2 Move towards one another Convergent Plate Boundary The Plate Tectonics Mechanism Tectonic plates can interact in one of 3 ways 1 Move away from one another Divergent Plate Boundary 2 Move towards one another Convergent Plate Boundary 3 Slide past one another Transform Fault Plate Boundary The Plate Tectonics Mechanism Tectonic plates can interact in one of 3 ways 1 Move away from one another Divergent Plate Boundary 2 Move towards one another Convergent Plate Boundary 3 Slide past one another Transform Fault Plate Boundary Divergent Plate Boundaries Convergent Plate Boundaries San Andreas Fault Transform Fault Plate Boundaries Today s Agenda 1 Introduction to rocks 2 The Rock Cycle Web notes 3 Rocks Rocks are naturally occurring solids containing one or more minerals Rocks Rocks are naturally occurring solids containing one or more minerals They come in many many many different flavors Rocks Rocks are naturally occurring solids containing one or more minerals They come in many many many different flavors e g Granite Rocks Rocks are naturally occurring solids containing one or more minerals They come in many many many different flavors e g sandstone Rocks Rocks are naturally occurring solids containing one or more minerals They come in many many many different flavors e g gneiss Rocks We recognize 3 major rock groups Rocks We recognize 3 major rock groups 1 Igneous born of fire originally molten Rocks We recognize 3 major rock groups 1 Igneous born of fire originally molten 2 Sedimentary originally particulate material or produced from precipitation out of water Rocks We recognize 3 major rock groups 1 Igneous born of fire originally molten 2 Sedimentary originally particulate material or produced from precipitation out of water 3 Metamorphic pre existing rocks modified by pressure or temperature Igneous Rocks Can be either extrusive volcanic or intrusive plutonic Igneous Rocks Can be either extrusive volcanic or intrusive plutonic Extrusive volcanic rocks can be erupted as lava Igneous Rocks Can be either extrusive volcanic or intrusive plutonic Extrusive volcanic rocks can be erupted as lava or as pyroclastic material e g ash Sedimentary Rocks We recognize 4 major classes of sedimentary rocks Sedimentary Rocks We recognize 4 major classes of sedimentary rocks 1 Siliciclastic composed of broken bits of silicate minerals Alluvial fan Sedimentary Rocks We recognize 4 major classes of sedimentary rocks 1 Siliciclastic composed of broken bits of silicate minerals 2 Biochemical mostly composed of the remains of calcium carbonate secreting beasties reef Sedimentary Rocks We recognize 4 major classes of sedimentary rocks 1 Siliciclastic composed of broken bits of silicate minerals 2 Biochemical mostly composed of the remains of calcium carbonate secreting beasties 3 Chemical formed through chemical precipitation alteration Salt flat Sedimentary Rocks We recognize 4 major classes of sedimentary rocks 1 Siliciclastic composed of broken bits of silicate minerals 2 Biochemical mostly composed of the remains of calcium carbonate secreting beasties 3 Chemical formed through chemical precipitation alteration 4 Organic formed from plant material Peat bog Metamorphic Rocks We recognize 3 divisions of metamorphic rocks Metamorphic Rocks We recognize 3 divisions of metamorphic rocks 1 Foliated display a prominent layering schist Metamorphic Rocks We recognize 3 divisions of metamorphic rocks 1 Foliated display a prominent layering 2 Non foliated do not display layering marble Metamorphic Rocks We recognize 3 divisions of metamorphic rocks 1 Foliated display a prominent layering 2 Non foliated do not display layering 3 Cataclastic composed of broken up bits of rock mylonite