Metamorphic Rocks and Rock Cycle

1
Metamorphic RocksandRock Cycle

• Shmulik Marco

2
Three Basic Types of Rocks

1. Igneous Rocks formed by solidification of molten
   rock (magma). Examples basalt, granite.
2. Sedimentary Rocks formed as layers of sediments
   accumulate. Examples sandstone, limestone.

3
3. Metamorphic Rocks
Formed by transformation of preexisting rocks in
the solid state under high pressures and
temperatures
Lithostatic Pressure
Differential Pressure
4
Metamorphism Processes of generating
metamorphic rocks. Rocks undergo mineralogical
and physical changes in solid state
5
Metamorphic Textures

• Foliation
• set of flat or wavy parallel surfaces produced by
  deformation
• define a preferred orientation, usually
  perpendicular to directed pressure and parallel
  to shear
• often expressed in orientation of platy
  minerals such as micas

6
Schist Preferred OrientationFoliation
7
Foliated Rock Schist
10 cm
8
Metamorphic TexturesFoliation and Cleavage

• Foliation
• set of flat or wavy parallel surfaces produced by
  deformation
• define a preferred orientation, usually
  perpendicular to directed pressure and parallel
  to shear
• often expressed in orientation of platy
  minerals such as micas and chlorite

9
Granite Equidimensional Crystals, No Preferred
Orientation
10
Gneiss with Lineation
11
Gneiss Preferred OrientationLineation
12
Metamorphic Textures
Lineation
13
Ductile Deformation Folds
14
Quartzite No preferred orientation
15
(No Transcript)
16
Metamorphic Minerals Grow in rocks only during
metamorphism (solid state!) Indicative of
pressure and temperature Do not form from cooling
magma
17
Contact Metamorphism
Contact Metamorphism The main metamorphic agent
is heat.
18
Pressure Temperature Regimes
19
Pressure Temperature Regimes

• Pressure
• Increases with depth at about 1/3 kilobar per
  kilometer
• Does not vary much with geographic position or
  plate-tectonic setting

20
Pressure Temperature Regimes

• Temperature Increases with depth at a rate that
  varies substantially with plate-tectonic setting
• 20ºC per kilometer in stable continental crust
• 40ºC per kilometer in orogenic belts
• 60ºC per kilometer in volcanic regions

21
Pressure Temperature Regimes

• Deformation stress
• Direction varies substantially with
  plate-tectonic setting
• Magnitude limited by strength of rocks to be less
  than 1 kilobar

22
Metamorphic Grade

• Geologists determine pressure and temperature
  from mineral assemblages
• geothermometers
• geobarometers

23
Types of Metamorphism

• Regional metamorphism
• caused by large-scale lithospheric movements
• Contact metamorphism
• caused by high temperatures near magmatic
  intrusions
• Deformation metamorphism
• caused by faulting, tight folding, and shearing
• Hydrothermal metamorphism
• caused by circulation of hot fluids
• Burial metamorphism
• caused by subsidence and burial of sediments

24
PTt Path

1. Original rock forms t0
2. Burial, pressure and temperature increase,
   metamorphism, t1 - t3
3. Exhumation t4 - t5

T
t0
t5
t1
t4
P
t2
t3
25
Rock Cycle
????? ???????
?????????
????
????
????? ?????????
???????
???????
?????????
????? ??????????
26
Rock Cycle