Theory Of Plate Tectonics Flashcards
What is the Theory of Plate Tectonics?
The theory dealing with the dynamics of Earth’s outer shell, the lithosphere, which revolutionized Earth sciences by providing a uniform context for understanding mountain-building processes, volcanoes, and earthquakes.
When was the concept of plate tectonics formulated?
The concept of plate tectonics was formulated in the 1960s.
What is the lithosphere?
The rigid outer layer of Earth, typically about 100 km (60 miles) thick, that overlies a plastic layer called the asthenosphere.
What types of plates are in the lithosphere?
The lithosphere is broken up into seven very large plates, six or seven medium-sized regional plates, and several small ones.
Divergent
Convergent
Collision
Construction
Destructive
Conservative
How do tectonic plates move?
Tectonic plates move relative to each other at rates of 5 to 10 cm (2 to 4 inches) per year by convection currents
What interactions occur at plate boundaries?
Plates interact along their boundaries by converging, diverging, or slipping past one another.
What geological features result from plate motions?
Mountains rise where plates converge, and continents fracture and oceans form where plates diverge.
What are the two types of crust?
The two types of crust are denser oceanic crust, primarily composed of basalt, and less dense continental crust, primarily composed of granite.
Why does continental crust float on the mantle?
The low density of the thick continental crust allows it to ‘float’ high on the much higher density mantle below.
What is the temperature gradient in the Earth’s mantle?
The Earth’s mantle has a temperature gradient where the highest temperatures occur at the contact with heat-producing core, increasing with depth.
What are the characteristics of rocks in the upper mantle?
Rocks in the upper mantle are cool and brittle, capable of breaking under stress and producing earthquakes.
What are the characteristics of rocks in the lower mantle?
Rocks in the lower mantle are hot and plastic, flowing when subjected to forces instead of breaking.
What is the boundary between the upper and lower mantle?
The lower limit of brittle behavior is the boundary between the upper and lower mantle.
What is palaeomagnetism?
Palaeomagnetism results from the zone of magma ‘locking in’ the Earth’s magnetic polarity when it cools.
How do scientists use palaeomagnetism?
Scientists use palaeomagnetism to determine historic magnetic activity during periods of large-scale tectonic activity through the reconstruction of relative plate motions.
What is mantle convection?
Convection currents occur in the mantle due to heat radiating outwards from the inner core.
What is the composition of the mantle?
The mantle material is mostly peridotite and behaves like a viscous liquid when heated.
What scientific theory supports mantle convection?
The Rayleigh-Benard theory supports the concept of mantle convection.
What is known about the internal structure of the Earth?
The internal structure is known from calculations based on how different seismic waves travel through solid and liquid layers.
What minerals are included in the Earth’s composition?
The mineral composition includes olivine and Helium-3, known from the study of lavas and scientific calculations.
How do convection cells in the mantle affect tectonic plates?
Convection cells in the mantle move the plates by frictional drag when they make contact with the base of the crust.
What is slab pull?
Slab pull is a force where denser oceanic plates are subducted, creating a suction force.
How does the Pacific Plate move?
The Pacific Plate moves faster than most other plates due to significant subduction around its edge.
What are mantle plumes?
Mantle plumes are large-scale buoyant forces that push the crust up.
