Lecture 8: Metamorphism

Metamorphism

Transformation of the mineralogy, texture, and sometimes chemical composition of a parent rock (protolith).

Protolith

Parent rock from which metamorphic rock is derived; can be igneous, sedimentary, or metamorphic.

Diagenesis

The process of sedimentary alteration, representing the lower limit of metamorphism.

Melting

An igneous process representing the upper limit of metamorphism.

Aureole

oval shaped fsp

Contact metamorphism

Type of metamorphism caused by the heat of magma invading pre-existing rock.

Recrystallization

Formation of new or enlarged crystals at the expense of pre-existing mineral grains.

Lithostatic pressure

Pressure from overburden that applies equal stress from all directions.

Isochemical metamorphism

Metamorphism where no new elements are introduced, maintaining the concentration of existing elements.

Allochemical metamorphism

Metamorphism involving the integration of elements introduced during the reaction process.

Dynamic metamorphism

Metamorphism dominated by pressure and stress, causing rocks to be subjected to shear forces.

Foliation

Planar arrangement of mineral grains formed from directed compression that causes reorientation and compositional banding.

Porphyroclast

Large relic grains from the protolith that have experienced deformation but retained their original composition.

Impact metamorphism

Result of very high pressure and temperature in a short time, producing impactites.

Metamorphic grade

Describes the relative temperature and pressure conditions under which metamorphic rocks form.

Index minerals

Minerals used to distinguish different zones of regional metamorphism.

Hydrothermal metamorphism

Metamorphism dominated by chemically active fluids interacting with rocks.

Metamorphic facies

Set of rocks representing various chemistries within limited metamorphic conditions.

Burial metamorphism

Metamorphism induced by a significant accumulation of materials in a subsiding basin.

Granoblastic texture

Texture characterized by coarse-grained, equidimensional crystals with boundaries intersecting at 120°.