Chapter 2 Flashcards
Tectonic
Tectonic
(tekton - “builder”) large scale processes affecting the structure of the Earth’s crust.
Continental Drift
Large-scale movements of continents across Earth’s surface driven by the plate tectonic system. The gradual movement of the continents across the earth’s surface through geological time.
Alfred Wegener 1915
Wrote a book on the break up and driftof continents, he laid out the similarity of geologic features on opposite sides of Atlantic. Pangaea - he named.
Pangaea
Supercontinent that coalesced in the late Paleozoic era and comprised all present continents. It began to break up in the Mesozoic era.
Seafloor Spreading
The mechanism by which new oceanic crust is formed at a spreading center on the crest of a mid-ocean ridge. as two plates move apart, magma wells up into the rift between them to form new crust, which spreads laterally away from the rift and is replaced continually by newer crust (convection).
Plate tectonics
Theory that describes and explains the creation and destruction of Earth’s lithospheric plates and there movement over Earth’s surface.
13 Major Plates
1 - Eurasian Plate 2 - North American Plate 3 - African Plate 4 - Indian Plate 5 - Arabian Plate 6 - Philippine Plate 7 - Pacific Plate 8 - Cocos Plate 9 - Caribbean Plate 10 - Australian Plate 11 - Nazca Plate 12 - South American Plate 13 - Antarctic Plate
Divergent Plate Boundary
Plates that move apart and new lithosphere is created (plate area increases - convection).
Convergent Plate Boundary
Plates come together and one plate is recycled into the mantle (Plate area decreases). Collides into each other with one going under.
Transform Faults
Plates slide horizontally past each other (plates do not change). Slide horizontally past each other and lithosphere is neither created nor destroyed.
Continental Crust
1 - Continental Crust is not as easily recycled back into the mantle as oceanic crust
2 - Continental Crust is weaker. Plate boundaries that involve continental crust tend to be more spread out and more complicated than those involving oceanic crust.
Mid-ocean Ridge
An under sea mountain chain at a divergent boundary, characterized by earthquakes, volcanism, and rifting. All caused by the tensional forces of mantle convection that are pulling the two plates apart.
Continental Rifting
Is the belt or zone of the continental lithosphere where the extensional deformation (rifting) is occurring. These zones have important consequences and geological features, and if the rifting is successful, lead to the formation of new ocean basins.
Subduction
A geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced to sink due to gravity into the mantle. Regions where this process occurs are known as subduction zones
Island Arc
Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone.
Magnetic Anomaly
A pattern of long narrow bands of high or low magnetic intensity on the seafloor that are parallel to and almost symmetrical with respect to the crest of a mid-ocean ridge.
Themoremanent Magnetization
When iron-rich lava cools, they become slightly but permanently magnetized in the direction of Earth’s magnetic field (of the time). The cold lava “remembers” the magnetization long after the magnetic field has changed.
Magnetic Time Scale
The detailed history of Earth’s magnetic field reversals as determined by measuring the themoremanent magnetization of sample rocks whose are are known.
Magnetic Chrons
(Greek: time) Major periods where the field is normal or reversed. Lasts about 1/2 a million years.
Magnetic Subchrons
Short lived reversals of fields that last anytime from several thousand years to 200 000 years.
Seafloor Spreading
Is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
18 mm/year (North American plate and Eurasian Plate
Relative Plate Velocity
The velocity at which one lithospheric plate moves relative to another.
Global Positioning System - GPS
Earth-orbiting satellites are used to make the same type of measurements as geodesy. The satellite constellation serves as an outside frame of referance. The satellites emit high-frequency Radio waves keyed to precise atomic clocks on board. Geologists use GPS to measure plate movements on a regular basis.
Isochron
A contour that connects rocks of equal age. Isochron tell us the time that has elapsed since the rocks were injected as magma into a spreading zone. Therefore the amount of spreading that has occurred since they formed.
Development of the Continents
1.1 billion years ago
Rodinia formed
Development of the Continents
750 million years
Late Proterozoic - Rodinia starts breaking up
Development of the Continents
237 million years
Early Triassic - Pangea assembled, Thetis ocean, Panthanlassic Ocean
Development of the Continents
195 million years
Early Jurassic - Pangea break up, Laurasia, Gondwana, Pacific Ocean
Development of the Continents
150 million years
Late Jurassic - Australia, India, Antarctic - breaking off from Africa
Development of the Continents
66 million years
Late Cretaceous - Atlantic ocean widens
Mantle Convention
Theory of mantle convention provides an example of why plates move. Mantle convection is the “engine” that drive large scale tectonic processes operating on Earth’s surface.
Whole Mantle Convention
The material from the plate circulates all the way through the mantle. Down as far as the core-mantle boundary.
Stratified Convention
Mantle is divided into two layers: Plate recycling of the lithosphere is confined to the upper mantle. A lower mantle is the portion moves slower then the upper mantle. The separation is maintained because the upper system is lighter than the lower system.
