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Rocks
There are three main types of Rocks
A. Igneous Rocks
B. Sedimentary Rocks
C. Metamorphic Rocks
Each type of rock is formed in different locations
and tell us a lot about the processes that have
happened in the past.
Rock formation occurs in the
lithosphere.
Different rocks form in
different locations
A rock on the surface may have
once been 20 km underground.
The Rock Cycle
All rocks on earth are a part of a large process called the Rock Cycle.
In this cycle, rocks are created and changed by different processes.
The Rock Cycle
It is a useful summary of the relationships between rocks.
Any type of rock can be transformed in any other type of rock and
has probably happened many times in the rocks history.
Several key processes change rocks
•Weathering:
the physical and chemical breakdown of rock.
•Transportation:
the transportation of from the weathering site
•Deposition:
the deposition of sediments after transportation
•Lithification:
sediments turning into rock by the processes of
compaction and cementation
•Melting:
The heating of solid rock till it melts
•Metamorphism:
The changing of rock by heat, pressure &
chemically active fluids
•Crystallization:
The growth of crystals from a cooling
magma
•Uplift and exposure: The movement of rock to the surface by
weathering & erosion, faulting etc
Igneous Rocks
• result from the crystallization of magma
•occur in a wide variety of forms of different shapes and sizes
•major subdivision is into the extrusive or volcanic rocks and the
intrusive or plutonic rocks.
Intrusive Igneous
•Formed under ground
•Usually medium to coarse grained texture due to slow cooling.
•Typically light colored.
Extrusive Igneous
•Formed on surface
•glassy or fine-grained due to rapid cooling
•May have voids due to degassing of the magma
•Typically dark colored.
Extrusive (volcanic)
Intrusive (plutonic)
Extrusive rocks
•occur as lava flows and pyroclastic ash or debris that is
ejected into the air during eruptions.
•often occur in characteristic volcanic cones
•submarine lava flows form characteristic pods called
pillow lava.
Intrusive rocks
•also occur in a variety of forms.
•vertical sheets of igneous rock are called dykes
•horizontal sheets, parallel or near parallel to layering are
known as sills. Fatter pods of crystalline rock are called
laccoliths. Very large crystalline bodies are called
batholiths.
Sedimentary Rocks
•formed by the lithification of unconsolidated sediments.
•lithification is a process of compaction and cementation
The weight of overlying sediments causes sediments to
be reduced in volume by 40%
There is also an increase press and temp
The heat causes some minerals to melt,
like silica and calcite
these go into solution and fill spaces between remaining
grains.
They then harden to form a glue or cement: cementation
Metamorphic Rocks
•generated by recrystallization of either igneous or sedimentary
rocks by the action of any or all of the following:
Pressure
Temperature
Pore Fluids
The lower limit of metamorphic temperatures is 150 °C.
The upper limit is the melting temperature when magma forms.
The type of metamorphic rock is determined by the parent rock,
and the P/T conditions.
In general, metamorphism causes:
Growth of new minerals
Deformation and rotation of mineral grains
Recrystallization of minerals as larger grains
Production of strong brittle rocks
Metamorphic rocks are divided into several groups on the basis of
the P/T conditions of formation:
Burial Metamorphic Rocks: are formed under the base of
immensely thick layers of sediments
Regional Metamorphic Rocks: generated mainly by pressure in
the roots of mountain belts. Colliding continental plates push up
the mountains and alter the rock.
Contact Metamorphic Rocks: occur where a mass of magma
invades and bakes the rock around it.
Dynamic Metamorphic Rocks: are formed along transform fault
zones.
Contact Metamorphic Rocks
generated mainly by temperature at the margins of igneous
intrusions. Sometimes called thermal metamorphic rocks.
a-sedimentary rocks b-contact metamorphic c-burial metamorphic
d-regional metamorphic
e-igneous rock
Metamorphic rocks are also subdivided on the basis of there
texture:
Non-foliated Rocks: recrystallized texture but no preferred
mineral orientation.
Foliated Rocks: with strong mineral orientation and/or
mineral banding or layering
Homework:
1. Start reading Chapter 3: Rocks
2. Complete worksheet on the rock cycle
3. Complete Rock Cycle Diagram
Depositional Environments for Sediments
Where sediments accumulate:
a- alluvial fans
j- continental shelf
b- Glaciers
k-continental slope
c- rivers
l-abyss
d- dunes
m-reefs
e- lakes
f- lagoons
g- esturies
h-deltas
i- tidal flats