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PLATE-TECTONICS-COT.pptx
- 1. Lesson Objectives: 1. Define folds, faults, stress, strain 2. Explain how the movement of plates leads to the formation of folds and faults
- 3. In 1912 German meteorologist Alfred Wegener proposed that in the beginning, the Earth has only one giant landmass called Pangaea, which means "all land." This is known as the Continental drift theory. How the Continents Formed?
- 5. The Earth’s crust is divided into plates, known as tectonic plates, and these plates move due to the convection currents in the Earth’s interior.
- 6. In 1919, Sir Arthur Holmes, an English geologist, proposed the presence of convection cells in the Earth’s mantle. When the rocks in the Earth’s interior are heated by radioactivity, they become less dense, and they rise toward the surface of the Earth. When they cool down, they become denser and sink. How the Continents Formed?
- 10. In a convergent boundary, the plates move or collide to each other. When the plates move away from each other, they are in a divergent boundary. Finally, when plates slide past each other, they are in a transform boundary. CONVERGENT TRANSFORM DIVERGENT
- 14. Plate Boundaries (Convergence) A.Oceanic – Continental Convergence B.Oceanic – Oceanic Convergence C.Continental – Continental Convergence
- 15. Triple Junction -a place where 3 lithospheric plates meet
- 16. Formation of Folds and Faults
- 17. What causes folding and faulting? STRESS AND STRAIN Stress- refers to the force applied to an object.
- 18. Compression Force acting perpendicular to and towards a surface. It happens when rocks squeezes together, causing rocks to fold or fracture to break.
- 19. Tension - a force perpendicular to and away from a surface When rocks are pulled apart, they are under tension . Rocks under tension lengthen or break apart.
- 20. Shear a force acting parallel to a surface When forces are parallel but moving in opposite direction.
- 21. Since the pressure and temperature are low at the Earth’s surface, rocks tend to break or fracture when subjected to compressional and tensional stresses. Fractures can either be a fault or a joint. A fault is a break in the rock where there is considerable movement on the fracture surface while a joint is a break where there is no considerable movement. Fracture Strain a change in a solid’ s shape caused by application of stress
- 22. FRACTURE
- 23. GEOLOGIC FOLD AND FAULT
- 24. defined as a bend in rock due to compressional forces. FOLD
- 25. Types of Fold
- 26. Types of Fold 1.Monocline- simple bend in the rock layer so that they are no longer horizontal
- 27. 2. Anticline- a fold that arches upward. The rocks dip away from the center of the fold.
- 28. 3. Syncline- a fold that bends downward
- 29. FAULTS a fracture or zone of fractures between two blocks of rocks
- 30. 3 Types of Faults 1. Normal Fault- occurs when the crust is being pulled apart in which the overlying (hanging-wall) blocks move down with respect to the lower (foot wall) block. (tensional stress)
- 31. 2. Reverse fault- occurs when the crust is being compressed in which the hanging-wall block moves up over the footwall block. (compressional stress)
- 32. 3. Strike-slip Fault- a dip-slip fault in which the dip of the plane is vertical . Strike-slip result from shear stresses.
- 34. In 1960, the American geophysicist, Harry Hess, explained how the convection currents in the Earth’s interior make the seafloor spread. Convection currents carry heat from the molten materials in the mantle and core towards the lithosphere. These currents ensure that the materials formed in the lithosphere are “recycled” back into the mantle. In this “recycling” process, which was later named as seafloor spreading, the molten materials flow out to form mid-oceanic ridges, spread sideways to form seafloor, and disappear into the ocean trenches. Seafloor Spreading
- 36. Oceanic ridges are formed at divergent boundaries, where plates move away from each other; while trenches are formed at subduction zones where plates collide with each other or at convergent boundaries. Seafloor Spreading
Editor's Notes
- When the molten materials rise, they slowly spread sideways. This motion makes the seafloor above it to be pulled apart, creating a break or an opening called mid-oceanic ridge, where the molten materials go out. New oceanic crust is formed from the outpouring of the molten materials, and as the process continues, oceanic ridges or underwater mountain ranges are built. Oceanic ridges are composed of volcanic rocks. As the molten materials continuously flow out from the ridges, the seafloor also keeps on spreading forming a central valley, or a rift valley, at the summit of the oceanic ridges. The molten materials push the seafloor away from the ridges and towards the trenches. Trenches are depressions on the ocean floor. When the molten materials are brought near the trenches, they start to cool, become denser and sink back down into the Earth where it is heated and melted again. The spreading of the seafloor continues as a “recycling” process. As new seafloor is created, it continues the process until it disappears back into the deep ocean trenches. Records show that the oldest seafloor is relatively younger (about 170 million years old) than the oldest rocks (about 3 billion years old) found on land. This shows that the seafloor is constantly recycled. As new oceanic crust is formed at the oceanic ridge, it pushes away the older materials. This means that the nearer the ocean floor to the oceanic ridge, the younger it is compared to the ones farther from the ridge.
- When the molten materials rise, they slowly spread sideways. This motion makes the seafloor above it to be pulled apart, creating a break or an opening called mid-oceanic ridge, where the molten materials go out. New oceanic crust is formed from the outpouring of the molten materials, and as the process continues, oceanic ridges or underwater mountain ranges are built. Oceanic ridges are composed of volcanic rocks. As the molten materials continuously flow out from the ridges, the seafloor also keeps on spreading forming a central valley, or a rift valley, at the summit of the oceanic ridges. The molten materials push the seafloor away from the ridges and towards the trenches. Trenches are depressions on the ocean floor. When the molten materials are brought near the trenches, they start to cool, become denser and sink back down into the Earth where it is heated and melted again. The spreading of the seafloor continues as a “recycling” process. As new seafloor is created, it continues the process until it disappears back into the deep ocean trenches. Records show that the oldest seafloor is relatively younger (about 170 million years old) than the oldest rocks (about 3 billion years old) found on land. This shows that the seafloor is constantly recycled. As new oceanic crust is formed at the oceanic ridge, it pushes away the older materials. This means that the nearer the ocean floor to the oceanic ridge, the younger it is compared to the ones farther from the ridge.