EARTH AND SCI

LESSON 4: Tectonic Processes and forces

Folding
Results from the compression of rock because of high temperature and pressure from the

interior of Earth.

A fold is defined as a bend in rock due to compressional forces.
Folding of rocks are due to converging plate boundaries.
Fold Hinge
The fold hinge is the line joining points of maximum curvature on a folded surface.
This line may be either straight or curved.
Types of Fold Hinge

An anticline occurs when a tectonic plate is compressed by movement of other plates
This causes the compressed plate to bend in an upwards motion.
Sometimes these older rocks become exposed, if its’ fairly round, it is called dome.
Example of Anticline: Blue Ridge Anticlinorium of Northern Virgnia

A simple bend in the rock layers so that they are no longer horizontal.
A steplike fold in rock strata consisting of a zone of steeper dip within an

otherwise horizontal or gently dipping sequence.

Happens when one fold is pushed over the other limb due to increasing pressure.
Example: Wasatch Mountains of USA

It is an extreme type of overturned fold in which the axial plane acquires an almost

horizontal altitude.

Example: Millook Haven - Cornwall of United Kingdom
Faulting
Is a fracture or zone of fractures between two blocks of rock
Associated with earthquake
Fault Line
a place where there is a long break in the rock that forms the surface of the earth and where earthquakes are more likely to happen.
Types:

occurs when the crust is being pulled apart in which the overlying (hanging wall) block

moves down with respect to the lower(foot wall) block

occurs when the crust is being compressed the hanging wall block moves up

over the footwall block

refers to a dip-slip fault in which the dip of the fault plane is vertical.
Strike-slip faults result from shear stresses.
Example:San Andreas Fault
Stress
Stress is refer to the force applied to an object
Types:

"extensional stress” a force acting perpendicular to and away form a surface.
It stretches the rock.
Example: Continents

is a force acting parallel to a surface
shearing can cause masses of rock to slip.
shear stress - when forces are parallel but moving in opposite directions
Example: San Andreas Fault, Alphine Fault of New Zealand
Layers of the earth
Crust
The Earth's crust is home to all known organic life, including human life.
The crust is the thinnest of the four layers on the planet, and is just 1% of the entire

Earth.

Oceanic - thin, denser and made out of basalt rock
Continental- thicker, less dense, primarily composed of rock
Major
Pacific Plate
North American Plate
Eurasian Plate
African Plate
Antarctic Plate
Indo-Australian Plate
South American Plate
Minor
Cocos Plate
Nazca Plate
Arabian Plate
Philippine Plate
Caroline Plate
Fuji Plate
Juan De Fuca Plate
Mantle
The mantle makes up 84 percent of the Earth’s volume, and consists of both solid and molten

rock known as magma.

The mantle is much thicker than the crust.
upper mantle- contains lithosphere and the asthenosphere.
Outer core
The outer core is the third layer of the Earth
Earth’s outer core is a fluid layer about 2,260 km (1,400 mi) thick, composed of mostly iron and nickel that lies above Earth’s solid inner core and below its mantle.
The outer core is responsible for Earth’s magnetic field.
As Earth spins on its axis, the iron inside the liquid outer core moves around.
Inner Core
Inner core is a solid metallic ball made mainly of iron.
Inner core generates the Earth's magnetic field.
Without the magnetic field, life on Earth would be impossible.