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