Lecture 7 Metamorphic Rocks

New Jersey granite gniess

Some of the oldest rock in the world located in New Jersey

Contact metamorphism

• occurs near molten magma/lava

• High temp

• Low pressure

Regional metamorphism

• high temp and high pressure

• Continental crust collision

• Subduction zones

• Volcanic arcs

Dynamic metamorphism

• Involves faulting and pressure

• Occurs over broad belts of crust

• Continental crust collisions

• Subduction zones

• Volcanic arcs

Shock metamorphism

Describes the effect of shockwave related deformation and heating during impact events

Hydrothermal metamorphism

Dissolved mineral-rich  water released from a magma chamber interacts with the surrounding rocks as it cools, changing both the chemistry of the water and the chemistry of the rocks.

Metasomatism

hydrothermal alteration that involves large amount of externally-derived fluid from magma flushed through the system at the high pressures and temperatures and substantially alters the chemical composition of the rock.

The approximate temperatures and pressures of metamorphic grades are illustrated below

Metamorphic isograd

An isograd is a plane of constant metamorphic grade in the field; it separates metamorphic zones of different metamorphic index minerals

Metamorphic Facies

A metamorphic facies is a set of metamorphic mineral assemblages that were formed under similar pressures and temperatures

Stress

A force applied to a surface and it varies with increasing temp and depth in the earth

Uniform stress

Applied equally from all directions

Foliation

Parallel fabric in regionally metamorphosed rocks

Metamorphic stress

Phyllite

Wavy, glossy sheen, with large mica flakes but similar to a slate

Migmatite

Mixed rock of Felsic composition and forms near large granite intrusions.

Represents transition between igneous and metamorphic rocks

My limits

Mixed rock formed during dynamic metamorphism

Marble

Metamorphosed limestone or dolostone

Skarn

Formed during the contact metamorphic zone of igneous intrusion

Quartzite

Metamorphosed sandstone

Hornfel

Contact metamorphic rock that has been baked and hardened by the heat of intrusive igneous masses

Amphibolite

Amphibolites are rocks composed mainly of amphibole and plagioclase feldspar, with little or no quartz

Serpentinite

A serpentinite is a hydrothermally metamorphosed mafic rock that is abundant on the ocean floor, but also occur in continental crust through interaction of mafic rocks with groundwater