Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
25 Cards in this Set
- Front
- Back
|
Rifting |
Rifting is the process by which continental lithosphere undergoes extension. It may ultimately lead to the development of ‘spreading’ which is where the extension and vertical thinning become so great that magmatism is triggered and new (oceanic) crust is formed at the axis of extension (i.e. the spreading center. |
|
|
Earth structure |
defined by seismic discontinuities; concentric shells of rock or liquid with contrasting chemical and physical properties |
|
|
Core Mantle Crust |
Core: iron alloy Mantle: ultramafic Crust: mafic to felsic |
|
|
Moho Discontinuity |
Boundary between mantle & crust, defined seismically and petrologically. |
|
|
Where does the oceanic crust form? What is its composition? How thick is it? How old is it? |
- Forms at mid-ocean ridges by partial melting of the mantle. - Basaltic in composition. - 5-10 km thick. - No older than 200 Ma. - Igneous extrusion and intrusion. |
|
|
Why isn't oceanic crust no older than 200 Ma? |
The subduction process consumes older oceanic lithosphere. |
|
|
How thick is the continental crust? When did the majority of continental crust form? Is continental crust homogeneous or heterogeneous? What is the general composition of the upper crust? Lower? |
- 40 km on average. - During the precambrian. - Heterogeneous. - Upper crust is granitic, lower crust is mafic. |
|
|
Where does most of the continental surface lie? Where does most of the ocean floor lie? What are most plates made up of? |
- Continental surface lies within 1 km of sea level. - Ocean floor lies at 4 km below sea level. - Most plates are made up of both oceanic and continental crust. |
|
|
Lithosphere How thick is it in the ocean? The continental? |
It exhibits a component of elastic strength. Includes crust and uppermost mantle. Varies in thickness. Moves as a plate - exceptions are orogens. - 70-100 km thick for oceans - 200-225 km for continental |
|
|
Asthenosphere |
Weak, solid, but behaves as a viscous fluid (convective flow). |
|
|
Buoyancy |
Plates float atop the mantle, displacing a mass of mantle equal to the mass of the plate, this is known as isostasy. |
|
|
Describe how plates have lateral rigidity |
When a load is placed on a plate, it may flex like a diving board as the plate under and surrounding the mass is depressed into the mantle. |
|
|
What are the major tectonic plates? (7) |
- Pacific Plate - North American Plate - Eurasian Plate - African Plate - Antarctic Plate - Indo-Austrailian Plate - South American Plate |
|
|
What are the minor tectonic plates? (9) |
- Nazca Plate - Philippine Sea Plate - Arabian Plate - Caribbean Plate - Cocos Plate - Caroline Plate - Scotia Plate - Burma Plate - New Hebrides Plate |
|
|
Aulocogen |
A failed rift. |
|
|
How do we know that plates move? |
Earthquakes localized along plate boundaries. |
|
|
What are the boundaries between plates? |
Divergent (MORs), convergent (island arcs), and transform. |
|
|
Oceanic transform faults |
Spreading occurs perpendicular to the ridge axis and any curvature is taken up by transform faults. Different rates of spreading. |
|
|
What compensates for spreading at MORs? |
Subduction. |
|
|
Where is magma generated? What drives magmatism & how? |
- At subduction zones. - Water in the mantle, it reduces the temperature of the surrounding rocks. |
|
|
What are the three mechanisms that drive subduction? |
1) Convection 2) Ridge push: push from the spreading center 3) Slab pull: Increasing density and age coolness of the oceanic lithosphere. |
|
|
Example of a transform plate boundary? |
San Andreas |
|
|
How is plate movement described? |
By a rotation at a specified angular velocity around an imaginary axis (Euler pole). |
|
|
How do oceanic plates move in relation to ridges and transform faults? |
Perpendicular to ridges and parallel to transform faults. |
|
|
How can Euler poles be determined for oceanic plates? |
By drawing lines perpendicular to transform faults and fracture zones. |
