Presentation on theme: "Pangaea Colliding Plates Objectives –Explain how plate tectonics accounts for the movement of continents –Compare and contrast divergent, convergent."— Presentation transcript:
Colliding Plates Objectives –Explain how plate tectonics accounts for the movement of continents –Compare and contrast divergent, convergent and transform plate boundaries. –Explain how convection currents inside Earth might be the cause of plate tectonics Key Terms – plate tectonics, lithosphere, divergent boundary –Convergent boundary, transform fault boundary
Plate Tectonics Tectonic plates –Think of the hypotheses of continental drift and sea-floor spreading as clues to a mystery. –How can the two hypotheses be explained? In the 1960’s, geologists developed a new theory to explain the apparent movement of the continents. The theory of plate tectonics suggests that Earth’s crust and upper mantle are broken into sections called plates (that move). But, what are they made of and how do they move??
We already know that the Earth’s crust is a layer of solid rock. The uppermost portion of the mantle is also solid –Together, these two areas are known as the lithosphere
We also know that there is an area in the mantle that is less solid. Here, the material acts more like a putty; it’s a solid that can flow. –This putty-like layer is called the asthenosphere
Plates Divergent Boundaries –The boundary between two tectonic plates that are moving away from each other Magma is forced upward between the two plates, creating a new crust, thus making…. Mid-ocean ridges are divergent boundaries
Learning Check The theory that suggests that Earth’s crust and upper mantle are broken into sections called plates (that move) is known as… –plate tectonics Together, the Earth’s crust is a layer of solid rock and the uppermost portion of the mantle is also solid are known as –Lithosphere The boundary between two tectonic plates that are moving away from each other is known as… –Divergent boundary
Convergent Boundaries –Crustal material can be destroyed where 2 plates meet head on. –This type of boundary is called a convergent boundary –What do you think happens when two plates containing continental crust collide? The two plates crumple forming mountain ranges! The Himalaya Mountains formed when the Indian Plate collided with the southern part of the Eurasia plate.
There are three styles of convergent plate boundaries –Continent-continent collision –Continent-oceanic crust collision –Ocean-ocean collision Convergent Boundaries
Transform Fault Boundaries –A third type of boundary that is formed when two plates slide past one another in opposite directions. Think about the San Andreas Fault in California – This is where the North America and the Pacific plate slide past one another! Along this boundary, the Pacific plate moves NW relative to the North American plate at an average rate of 2 cm per year.
Transform Fault Boundary
Transform Fault Bound. Cause Earthquakes!
Causes of Plate Tectonics –How does the theory of plate tectonics explain the cause of plate movements? The driving force behind this movement is HEAT! A material that is hot is less dense than the same material that is cold This is because the same mass takes up more volume (space) when the material is heated. This helps us explain the process of convection currents…
Convection Currents in the Earth
Convection Currents –C.C.’s within the Mantle cause the various plates in Earth’s lithosphere to move around. –As the plates bump into each other, boundaries form! –Plates move in different directions because there are many conv. cells within the Mantle!
Learning Check! A type of boundary that is formed when two plates slide past one another in opposite directions is known as –Transform Fault Boundary Boundary where crustal material can be destroyed where 2 plates meet head on is –Convergent Boundary Mountain Ranges –Convergent Earthquakes –Transform Fault
Forms mountains, e.g. European Alps, Himalayas Continent-Continent Collision
Called SUBDUCTION Continent-Oceanic Crust Collision
Oceanic lithosphere subducts underneath the continental lithosphere Oceanic lithosphere heats and dehydrates as it subsides The melt rises forming volcanism E.g. The Andes Subduction
When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches. –E.g. The Mariana Trench is 11 km deep! Ocean-Ocean Plate Collision