Transcript From Sediment to Rock: Rocks that form near the Earth’s

Metamorphic Rocks
and
Rock Cycle
Shmulik Marco
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. Metamorphic Rocks
Formed by transformation of preexisting
rocks in the solid state under high pressures
and temperatures
Differential Pressure
Lithostatic Pressure
Metamorphism: Processes of generating
metamorphic rocks. Rocks undergo mineralogical
and physical changes in solid state
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
Schist – Preferred Orientation
Foliation
Foliated Rock: Schist
5 cm
10 cm
Metamorphic Textures:
Foliation 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
Granite – Equidimensional Crystals,
No Preferred Orientation
Gneiss with Lineation
Gneiss – Preferred Orientation
Lineation
Metamorphic Textures
Lineation
Ductile Deformation: Folds
Quartzite
No preferred orientation
Metamorphic Minerals
Grow in rocks only during metamorphism (solid state!)
Indicative of pressure and temperature
Do not form from cooling magma
Contact Metamorphism
Contact Metamorphism:
The main metamorphic agent is heat.
Pressure & Temperature Regimes
Pressure & Temperature Regimes
•Pressure
– Increases with depth
at about 1/3 kilobar
per kilometer
– Does not vary much
with geographic
position or platetectonic setting
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
Pressure & Temperature Regimes
•Deformation stress
– Direction varies
substantially with
plate-tectonic
setting
– Magnitude limited
by strength of rocks
to be less than 1
kilobar
Metamorphic Grade
•Geologists
determine pressure
and temperature
from mineral
assemblages
–geothermometers
–geobarometers
60º/km
40º/km
20º/km
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
PTt Path
1. Original rock forms: t0
2. Burial, pressure and temperature
increase, metamorphism, : t1 - t3
3. Exhumation: t4 - t5
t0
t5
t1
P
t4
t2
t3
T
‫‪Rock Cycle‬‬
‫סלעים מגמתיים‬
‫התכה‬
‫אירוזיה‬
‫מטמורפוזה‬
‫התכה‬
‫סלעים מטמורפיים‬
‫אירוזיה‬
‫מטמורפוזה‬
‫סלעים סדימנטריים‬
Rock Cycle