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Metamorphic Rocksand
Rock Cycle
Shmulik Marco
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.
Three Basic Types of Rocks
3. Metamorphic RocksFormed by transformation of preexisting ormed by transformation of preexisting
rocks in the rocks in the solid statesolid state under high under high
pressures and temperaturespressures 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 OrientationFoliation
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 OrientationLineation
Metamorphic TexturesLineation
Ductile Deformation: Folds
QuartziteNo preferred orientation
Metamorphic MineralsGrow in rocks only during metamorphism (solid state!)Indicative of pressure and temperatureDo 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 plate-tectonic 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
60º/km40º/km
20º/km
•Geologists determine pressure and temperature from mineral assemblages–geothermometers–geobarometers
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 Path1. Original rock forms: t0
2. Burial, pressure and temperature increase, metamorphism, : t1 - t3
3. Exhumation: t4 - t5
P
T
t1
t2 t3
t0
t4
t5
Rock Cycle
סלעים מגמתיים
סלעים סדימנטריים
סלעים מטמורפיים
מטמורפוזההתכה
מטמורפוזה
התכה
אירוזיהאירוזיה
Rock Cycle
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