1.1 What is the Plate tectonic theory

Question 1

General plate tectonic theory

Answer 1

• Earth has a three-layered structure.
• The Earth’s lithosphere is broken up into tectonic plates.
• Tectonic plates are constantly moving.
• Plate movements result in the formation of major landforms we find on the Earth’s surface, such as volcanoes, fold mountain ranges, and oceanic trenches. It also explains the occurrence of certain phenomena, such as earthquakes and tsunamis

Question 2

Layers of the earth

Answer 2

1. Core
2. Mantle
3. Crust

Question 3

Core

Answer 3

• innermost layer
• hottest layer : 4400 to 6000ºC
• thickest layer of 3300km

Question 4

Mantle

Answer 4

• lies above the core
• 1000 to 3700ºC
• about 2900km thick

Question 5

Crust

Answer 5

• outermost layer
• thinnest layer, 6 to 70 km

Question 6

Parts of layers of earth

Answer 6

Mantle is made up of the:
1. uppermost mantle
2. Asthenosphere
3. lowermost mantle

Lithosphere (solid parts of earth) is made up of the:
1. Crust
2. Uppermost mantle

Question 7

Lithosphere

Answer 7

Types of lithosphere:
1. Continental crust (continental lithosphere)
2. Oceanic crust (oceanic lithosphere)

Oceanic crust is denser than continental crust
Lithosphere is divided into tectonic plates

Question 8

Continental Crust (CC)

Answer 8

• layer of granitic, sedimentary and metamorphic rocks, which forms the continents and areas of shallow seabed close to the shores
• thicker CC covers 40% of earth’s surface, while the thinner OC covers the rest
• comprises of mainly lighter granitic rocks

Question 9

Oceanic Crust (OC)

Answer 9

• extends 5-10km beneath ocean floor
• composed of diff types of basalts
• comprises of mainly heavier granitic rocks

Question 10

Global plate movement

Answer 10

• plates lie on top of semi-solid mantle
• plates move relative to each other at constant motion
• landforms such as mountains and volcanoes are created

Question 11

Plate boundaries

Answer 11

1. Divergent plate boundaries (plates are moving away from each other)
2. Convergent plate boundaries (plates are moving towards each other)
3. Transform plate boundaries (plates are sliding horizontally past each other)

Question 12

What drives tectonic plate movement

Answer 12

• convention currents
• slab-pull force

Question 13

Convention Driven Plate Movement

Answer 13

• main driving force of plate movement
• heat from the Earth’s core causes the material in the mantle to become less dense and rise towards the surface.
• Since hotter, less dense material rises while colder, denser material sinks.
• The rising material in the mantle spreads horizontal under the more rigid crust, exerting a driving force on the overlying plates and dragging them apart causing divergent plate movement
• The material in the mantle then loses heat, becoming denser and sinking towards the core
• Convergent plate movement occurs where convention currents collide
• Mental moving to core then gets heated up again and the process repeats.
• This rising and sinking of the mantle material form a current known as convection currents

Question 14

Slab-pull force

Answer 14

• gravity-controlled subduction of denser OC
• subduction along drag the rest of the plate along with it, causing plates to move

Question 15

Tectonic subduction

Answer 15

• occurs mostly at suduction zones where OC subduct under CC
• when two plates converge/move towards each other, the denser oceanic crust is pulled down by gravity as it subduct beneath the less dense crust.
• The denser oceanic crust sinks deeper into the mantle under its own weight, pulling the rest of the plate with it. This results in further convergence.
• in situations where subducted part of the plate gets detached from the plate, sinking into the mantle w/o exerting much slab-pull force
• instead, detached part induces convention in mantle that creates a suction forces that drives plate movements

Question 16

Case Study: Mid-Atlantic Ridge (NEA)

Answer 16

• movement of North American plate towards west and Eurasian plate towards the east is caused by gravity pulling denser rocks away from Mid-Atlantic Ridge in both directions
• as rocks near elevated ridge cools, they become denser, and dragged downwards under its own weight, away from the ridge
• allows magma to well up from mantle, wedging plates further apart

Question 16

Case Study: Western Pacific Ocean

Answer 16

• being denser, Pacific plate dives under other CP like Eurasian plate
• under influence of gravity, less dense part of the plate descends into less dense underlaying mantle and drags rest of plate along
• convention in mantle plats a smaller role as compared to slab-pull force