EG - Vocab - Plate margins

Definitions

Types of plate margins - 1) divergent, 2) convergent and 3) transform

Take the plate margin tour.

A plate margin is just the edge of a tectonic plate.

A "continental" margin is not the same thing as a "plate" margin. A continental margin is the edge of a continent rather than the edge of a plate. Continents and plates are not the same thing.

Since each plate moves as a single unit, like an individual car moving slowly on a grid-locked freeway, when a plate collides with another, it's mostly the margins that "interact" with adjacent (immediately neighboring) plates. The outside is damaged and distorted more than the interior.

At plate margins, adjacent plates not only collide, but they can move away from each other (diverge) or slide horizontally past each other instead.

Depending on how the plates move relative to each other where they touch, plate margins are classified as one of three types - divergent, convergent and transform. A single plate is usually rimmed by more than one type of plate margin.

Different kinds of plate margins are more or less likely to be associated with particular geologic hazards such as earthquakes and volcanoes, and certain kinds of rocks.

Divergent margins: Where two adjacent (neighboring) plates move apart. All midocean ridges are divergent margins. A divergent margin can also occur on a continent as a new ocean basin forms. The East African Rift may be such an area. Instead of leaving a gap between two plates that move apart, that area is always filled with new igneous rock that attaches itself to become part of each diverging plate. New areas are added to ocean basins at divergent margins.
Convergent margins: Where two adjacent (neighboring) plates move towards each other and one plate either dives under the other (subduction zone) or the two plates crumple where they collide. All subduction zones and the Himalayas, a crumple zone, are examples of convergent margins. Areas of the Earth are lost into the interior or squashed horizontally to fit into a smaller area at convergent margins.
Transform margins: Where two adjacent plates slide horizontally past one another (like cars that pass each other on opposite sides of a road). The many short offsets (jogs) between adjacent segments of midocean ridges are the transformn margins. The San Andreas Fault is an unusual case of a transform margin that cuts through land. No new area of continenta or ocean is added or lost at transform margins.

Don't plates slide past one another at convergent margins too? Yes, but only in subduction where one plate dives under the other. The sliding is in the vertical direction and the net result is loss of real estate. In transform margins, the sliding by is in the horizontal direction and no loss of real estate occurs.

Look at the North American plate. What kinds of plate margins are around its rim?
Plates slide past one another at subduction zones and transforms such as the San Andreas Fault Zone. What is the difference that makes the motion at a subduction zone be considered "convergent" as opposed to "transform"?
Do you live within 200 miles of a plate margin?
What kind of plate margin is near San Diego? What kind of geologic hazards occur? What doesn't?
What kind of plate margin is near Chile? What kind of geologic hazards occur? What doesn't?
What kind of plate margin is near Washington, D.C.? What kind of geologic hazards occur? What doesn't?



	Definitions Back Home Types of plate margins - 1) divergent, 2) convergent and 3) transform Take the plate margin tour. A plate margin is just the edge of a tectonic plate. A "continental" margin is not the same thing as a "plate" margin. A continental margin is the edge of a continent rather than the edge of a plate. Continents and plates are not the same thing. Since each plate moves as a single unit, like an individual car moving slowly on a grid-locked freeway, when a plate collides with another, it's mostly the margins that "interact" with adjacent (immediately neighboring) plates. The outside is damaged and distorted more than the interior. At plate margins, adjacent plates not only collide, but they can move away from each other (diverge) or slide horizontally past each other instead. Depending on how the plates move relative to each other where they touch, plate margins are classified as one of three types - divergent, convergent and transform. A single plate is usually rimmed by more than one type of plate margin. Different kinds of plate margins are more or less likely to be associated with particular geologic hazards such as earthquakes and volcanoes, and certain kinds of rocks. Divergent margins Where two adjacent (neighboring) plates move apart. All midocean ridges are divergent margins. A divergent margin can also occur on a continent as a new ocean basin forms. The East African Rift may be such an area. Instead of leaving a gap between two plates that move apart, that area is always filled with new igneous rock that attaches itself to become part of each diverging plate. New areas are added to ocean basins at divergent margins. Convergent margins Where two adjacent (neighboring) plates move towards each other and one plate either dives under the other (subduction zone) or the two plates crumple where they collide. All subduction zones and the Himalayas, a crumple zone, are examples of convergent margins. Areas of the Earth are lost into the interior or squashed horizontally to fit into a smaller area at convergent margins. Transform margins Where two adjacent plates slide horizontally past one another (like cars that pass each other on opposite sides of a road). The many short offsets (jogs) between adjacent segments of midocean ridges are the transformn margins. The San Andreas Fault is an unusual case of a transform margin that cuts through land. No new area of continenta or ocean is added or lost at transform margins. Don't plates slide past one another at convergent margins too? Yes, but only in subduction where one plate dives under the other. The sliding is in the vertical direction and the net result is loss of real estate. In transform margins, the sliding by is in the horizontal direction and no loss of real estate occurs. Questions for thought Look at the North American plate. What kinds of plate margins are around its rim? Plates slide past one another at subduction zones and transforms such as the San Andreas Fault Zone. What is the difference that makes the motion at a subduction zone be considered "convergent" as opposed to "transform"? Do you live within 200 miles of a plate margin? What kind of plate margin is near San Diego? What kind of geologic hazards occur? What doesn't? What kind of plate margin is near Chile? What kind of geologic hazards occur? What doesn't? What kind of plate margin is near Washington, D.C.? What kind of geologic hazards occur? What doesn't? Related resources Periodic Table of the Elements Plate reconstructions including movies and maps. Los Alamos National Laboratory, Operated by the University of California for the U.S. Department of Energy Web Elements Plate reconstructions including movies and maps. Mark Winter, University of Sheffield, England