Week 3 Plate Techtonics

Question 1

Ocean Spreading Center

Answer 1

Rifting and spreading along the mid-ocean ridge create new ocean lithosphere

Question 2

Seafloor Spreading

Answer 2

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.

Question 3

The ___ rocks are located close to the ocean ridges, while the rocks progressively ____ are further away from the ridge.

Answer 3

Younger

Older

Question 4

The oldest recovered rocks from the seafloor are how old:

Answer 4

200 million years old

Question 5

Continental Rift Zone

Answer 5

Rifting and spreading zones on continents are characterized by parallel rift valleys, volcanism, and earthquakes (called thermal plumes/mantle plums).

Question 6

What happens when a plume nears the lithosphere with the overlying continent

Answer 6

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.

Question 7

Wilson Cycle

Answer 7

1. Continental masses heat up and split
2. Rift widens and the newly formed crust moves away from the ridge axis, the crust stretches, and fractures.
3. Lava fills the lower elevations and the spaces between separating plates.
4. As lava solidifies, it becomes a part of the trailing edge of a tectonic plate
5. This rift may flood with water forming a new ocean
6. The oceans begin to close and converge.

Question 8

Ocean Continent Convergence

Answer 8

When the oceanic lithosphere meets the continental lithosphere, the ocean lithosphere is subducted, and a volcanic mountain belt is formed at the continental margin.

Question 9

Subduction

Answer 9

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.

Question 10

Ophiolite complexities

Answer 10

The byoant continents of the ocean floor are not subducted. These rocks are preserved on top of the crust.

Question 11

Ocean-Ocean Convergent Boundaries

Answer 11

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

Question 12

Continent-Continent Convergence Boundaries

Answer 12

Where two continents converge, the crust crumples and thickens, creating high mountains and a wide plateau.

Question 13

Formation of mountain belts

Answer 13

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).

Question 14

Craton

Answer 14

the oldest part of a continent, formed and evolved and altered over a billion of years (stable).

Question 15

Orogens

Answer 15

Bands of mountains. Younger along current active margins, ancient that are remnant mountains (just the roots), some welding cratons together.

Question 16

Continental Shield

Answer 16

An assembly of ancient cratons and orogens.

Question 17

Supercontinents

Answer 17

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)

Question 18

Isostasy

Answer 18

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.

Question 19

Transform Boundaries

Answer 19

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)

Question 20

Mid-ocean ridge transform fault

Answer 20

mid-ocean ridges are typically offset by transform faults

Question 21

Continental Transform fault

Answer 21

At transform faults, plates slip horizontally past each other.

Question 22

Hot Spots

Answer 22

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.

Question 23

Types of Margins

Answer 23

DIvergent (spreading motion), convergent (subduction motion), transform (lateral sliding)

Question 24

Divergent margin topography

Answer 24

Ridge/rift

Question 25

Convergent Topography

Answer 25

Trench (in the ocean)