Metamorphic Rocks and Rock Cycle Shmulik Marco

Three Basic Types of Rocks Igneous Rocks formed by solidification of molten rock (magma). Examples: basalt, granite. Sedimentary Rocks formed as layers of sediments accumulate. Examples: sandstone, limestone.

3. Metamorphic Rocks Lithostatic Pressure Differential Pressure Formed by transformation of preexisting rocks in the solid state under high pressures and temperatures Lithostatic Pressure Differential Pressure

Metamorphism: Processes of generating metamorphic rocks 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 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

No preferred orientation 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: The main metamorphic agent is heat.

Pressure & Temperature Regimes

Pressure & Temperature Regimes 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 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

t0 t5 t1 t4 t2 t3 PTt Path T P Original rock forms: t0 Burial, pressure and temperature increase, metamorphism, : t1 - t3 Exhumation: t4 - t5 T t0 t5 t1 t4 P t2 t3

Rock Cycle סלעים מגמתיים סלעים מטמורפיים סלעים סדימנטריים מטמורפוזה התכה התכה סלעים מטמורפיים אירוזיה אירוזיה מטמורפוזה סלעים סדימנטריים

Rock Cycle