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