Week 3 Plate Techtonics Flashcards
Ocean Spreading Center
Rifting and spreading along the mid-ocean ridge create new ocean lithosphere
Seafloor Spreading
At mid-ocean ridges, the release of pressure as the plates move apart allows hot magma from the asthenosphere to reach the ocean floor. There is cools and crystallized to form a new lithosphere. The system of mid-ocean ridges along divergent plate boundaries forms linear submarine mountain chains.
The ___ rocks are located close to the ocean ridges, while the rocks progressively ____ are further away from the ridge.
Younger
Older
The oldest recovered rocks from the seafloor are how old:
200 million years old
Continental Rift Zone
Rifting and spreading zones on continents are characterized by parallel rift valleys, volcanism, and earthquakes (called thermal plumes/mantle plums).
What happens when a plume nears the lithosphere with the overlying continent
A plume will spread laterally, doming the overlying plate and moving the rifted segments outwards from the central area. Uplift results in fractures that eventually can open to form narrow oceanic tracts.
Wilson Cycle
- Continental masses heat up and split
- Rift widens and the newly formed crust moves away from the ridge axis, the crust stretches, and fractures.
- Lava fills the lower elevations and the spaces between separating plates.
- As lava solidifies, it becomes a part of the trailing edge of a tectonic plate
- This rift may flood with water forming a new ocean
- The oceans begin to close and converge.
Ocean Continent Convergence
When the oceanic lithosphere meets the continental lithosphere, the ocean lithosphere is subducted, and a volcanic mountain belt is formed at the continental margin.
Subduction
The process by which the ocean lithosphere (heavier) is forced under the continental material (lighter). The subducted plate is heated, melted, and re-incorporated into the athenosphere. Volcanoes form where the melted material rises up through the overlying plate to the surface. Additionally, the continental crust is compressed, folded, and faulted forming mountains.
Ophiolite complexities
The byoant continents of the ocean floor are not subducted. These rocks are preserved on top of the crust.
Ocean-Ocean Convergent Boundaries
Where oceanic lithosphere meets oceanic lithosphere, one plate is subducted under the other, and a deep-sea trench and a volcanic island arc are formed.
Example: Mariana’s Trench
Continent-Continent Convergence Boundaries
Where two continents converge, the crust crumples and thickens, creating high mountains and a wide plateau.
Formation of mountain belts
Collision results in large zones of deformation where continental crust is involved in subduction.
Typically from high mountain ranges (orogens) with crustal thickening and crumbling (deformation).
Craton
the oldest part of a continent, formed and evolved and altered over a billion of years (stable).
Orogens
Bands of mountains. Younger along current active margins, ancient that are remnant mountains (just the roots), some welding cratons together.
Continental Shield
An assembly of ancient cratons and orogens.
Supercontinents
With continental collisions comes the assemblage of cratons into larger continental complexes (supercontinents).
Example: Rodinia (1.1 billion year old), Pangea (300 million year old and broke up 200 million years ago)
Isostasy
The property whereby the lithosphere maintains floatation balance. This mass is stable related to the asthenosphere and is not rising/sinking. Isostasy prevents it from being subducted.
Transform Boundaries
At a spreading ridge, the rift is not a long, continuous crack, but instead, it forms numerous short segments, whereby two opposite plates scrape past each other. These transform faults have a lot of stresses (leading to earthquakes)
Mid-ocean ridge transform fault
mid-ocean ridges are typically offset by transform faults
Continental Transform fault
At transform faults, plates slip horizontally past each other.
Hot Spots
Unusual volcanic eruptions happen when isolated plumes of magma rise from the asthenosphere to the surface. The plumes are fixed in the mantle so when the crust moves over it, there becomes a progressive trail of volcanoes at the Earth’s surface.
Types of Margins
DIvergent (spreading motion), convergent (subduction motion), transform (lateral sliding)
Divergent margin topography
Ridge/rift
