Oceanic and

Continental Crust

Oceanic crust

The rocks of the oceanic crust are very young, not older than 200 million years, compared with the

rocks of the continental crust 3.6 billion years old. The decompression

occurs beneath rifts in the crust, such as those found at the mid-ocean ridges, and it is through these rifts that lava is extruded onto the surface to create new ocean crust.

Oceanic crustOceanic crust is continuously being created at

mid-ocean ridges. At these ridges, magma rises into the upper mantle and crust, as the plates diverge. As it moves away from the ridge, the lithosphere becomes cooler and denser, and sediment gradually builds on top of it.

The youngest oceanic lithosphere is at the oceanic ridges, and is progressively older away from the ridges.

Continental crustThe continents include a wide range of rock

types, including granitic igneous rocks, sedimentary rocks, and the metamorphic rocks formed by the alterations of both. They contain a lot of quartz, a mineral absent in oceanic crust.

This core foundation is often referred to as a shield or basement rock. Rocks found in the shields were formed during the Precambrian and are some of the oldest rocks found on the Earth.

Continental crustThe first continental rocks were the result of

repeated melting, cooling, and remixing of oceanic crust, driven by volcanic activity above mantle convection cells, which were much more numerous and vigorous than today’s.

Geologists believe that the major continental cores were formed by the early solidification of the lighter components of magma between 3.9 and 3.8 billion years ago.

Continental crustThe continental shields are generally covered

by younger sedimentary deposits. These sedimentary rocks constitute the interior platforms of the continents

Evaluation Question

The two types of crust are __________ and ________ crust.

The crust that is found on the continents and at the beginning of the oceans (the continental shelf) is ________________.

Continental CrustContinental Crust

__________ is continuously being

created at mid-ocean ridges.

Oceanic Oceanic CrustCrust

Deformation

Stress is the amount of force per unit area on a given material

The process by which the shape of a rock changes because of stress is called deformation

Deformation

Two types of deformation can occur to rocks under stress

Layers can bend when stress is applied to them

When too much stress is applied, they can reach their elastic limit and break

Compression & Tension

Compression is the type of stress that occurs when an object is squeezed

Tension is stress that occurs when forces act to stretch an object such

Folding

Folding is the bending of rock layers because of stress in the Earth’s crust

Scientists assume that all rock layers start off horizontal

So when scientists see a fold, they know deformation has occurred

Types of Folds

There are two main types of foldsAnticlines, upward, arching fold

Synclines, downward, trough-like folds

Faulting

Some rock layers break when too much stress is applied to them.

The surface along which a rocks break and slide past each other is called a fault

Faulting

The two sides of a fault are known as the hanging wall and the footwall

The type of fault that forms is dependent on where the hanging and footwall are located

Types of Faulting

There are three types of faults that occurNormal FaultsReverse FaultsStrike-Slip Faults

Normal Faults

When rocks are pulled apart because of tension, normal faults often form

When a normal fault moves, it causes the hanging wall to move down relative to the footwall

Reverse Fault

When rocks are pushed together by compression, reverse faults often form

When a reverse fault moves, it causes the hanging wall to move up relative to the footwall

Special type of reverse fault occurs when the hanging walls continues to be pushed over top of footwall called a “thrust fault”

Strike-Slip Fault

Forms when opposing forces cause rock to break and move horizontally

If you were standing on one side of the fault when it moved, the ground on the other side would appear to move to your left or right

Thrust Fault

Plate Tectonics & Mountain Building

When tectonic plates collide, land features that start as folds and faults, can eventually become large mountain ranges

When tectonic plates undergo compression and tension, they can form mountains in several ways

Folded Mountains

Form when rock layers are squeezed together and pushed upward

These mountains form at convergent plate boundaries

Appalachian Mountains 390 million years ago

Fault-Block Mountains

When tectonic forces put enough tension on the Earth’s crust, a large number of normal faults can occur

Fault-Block mountains form when tension causes large blocks of the Earth’s crust to drop down relative to other blocks

Often leaves sharp, jagged peaks

Volcanic Mountains

Located at convergent plate boundaries where oceanic crust sinks into the asthenosphere at subduction zones

The rock that is melted at subduction zones forms magma which rises to the surface and erupts

Volcanic Mountains

Sometimes these mountains can rise above the sea and become islands

A majority of the tectonically active volcanic mountains have formed around the Pacific Plate which is known as the Ring of Fire

Uplift and Subsidence

Uplift is the rising of regions of Earth’s crust to higher elevations

Subsidence is known as the sinking of Earth’s crust to lower regions

Uplifting of Depressed Rock

One way areas rise without deforming is a process known as rebound

Rebound occurs when the crust slowly springs back to its previous elevation

Rebound happens when a weight is removed from a region ( glacial melting)

Tectonic Letdown

Subsidence can occur when the lithosphere becomes stretched

A rift zone is a set of deep cracks that forms at a divergent plate boundary

As the plates move apart, the rift zone begins to subside between the plates

Question 1

What are two types of deformation?

Answer

Layers of rock can bend when stress is applied to them and if too much pressure is applied then the layers can break

Question 2

What type of fold has an upward, arching fold that looks like the letter ‘A’?

A. SynclineB. MonoclineC. Anticline

Answer

The answer is C. An anticline has an upward, arching fold

Question 3

What type of fault forms when opposing forces cause rock to break and move horizontally?

A. Normal FaultB. Reverse FaultC. Strike-Slip Fault

Answer

The answer is C. A strike-slip fault is formed when opposing forces cause the rock to break and move horizontally.

GAMES

C V B C Z ONR OCN R S E HC R UUOB B U S GE Y J S NF MF S L A J G G SO A S R T NS V G FL G U F O I C Z G ND MS L L C F D UGC A B UT E S X A J

•MAGMA•OCEANIC•FAULT•FOLD•CRUST

CROSS WORD

And that’s all thank you