3A8 week 01 lecture 03 rocks and minerals 02

Metamorphic Rocks• The original rock is termed a protolith • The composition of the protolith and the conditions of metamorphism and deformation will largely determine the end structure

Geology for Engineers

Minerals and Rocks (II)

Metamorphic Rocks

• The original rock is termed a protolith

• The composition of the protolith and

the conditions of metamorphism and deformation will largely determine the end structure and composition of the metamorphic rock

Metamorphic Rocks

• Protoliths may be sedimentary, igneous

or even metamorphic

• Metamorphism may result from a

general increase (prograde), or

decrease (retrograde) of temperature

and pressure

Pressure-Temperature-Time

Metamorphic Rocks

Metamorphism may be:

• Dynamic (i.e some deformation

involved), e.g gneiss

• Static (i.e the end rock does not have a

preferred shape fabric) e.g hornfels

Gneiss

P-T fields of metamorphic grades

Index of Metamorphic Minerals

csmres.jmu.edu/

Index of Metamorphic Minerals

csmres.jmu.edu/

Isograd Map

Different Styles of Metamorphism

• Barrovian (regional) metamorphism

• Buchan (regional) metamorphism

• Contact metamorphism

• Shock metamorphism

• Dynamic metamorphism (e.g shearing)

into marble near

the contact with

the basalt.

Tectonic Settings of Metamorphism

Metamorphic Rocks

• Mudstone

(pelite)

Metamorphic Rocks

• Garnet Gneiss

Metamorphic Rocks

• This is an

eclogite You can

see the presence

of garnet (pink)

and pyroxene

(green)