Physical Geology Introduction


Metamorphism refers to a set of processes 
that result in changes in mineralogy and 
texture accompanying changes in 
temperature and pressure.

As noted previously, the boundary between 
diagenesis (sedimentary) and the onset of 
metamorphism is truly fuzzy.

Metamorphic Types	

Contact Metamorphism - nearby heat source - 
an intrusive igneous body is injected into a 
colder, older rock - heat flows from the 
intrusive body into the country rock

Regional Metamorphism - no obvious heat 
source - increasing depth of burial plus 
deformation results in an increase in 
temperature and pressure

Dynamic Metamorphism - variable pressure 
at relatively low temperatures - often 
associated with fault zones
n High Pressure - Low Temperature 
Metamorphism - associated with subduction 

Effects of Metamorphism

Increasing Grain Size

Increasing Temperature and Pressure may 
aid in the RECRYSTALLIZATION of minerals 
in the rock

Small grains become larger - oriented with 
respect to direction of applied pressure(s) - 

Clay minerals are often enlarged with 
increasing metamorphism

Growth of New Minerals

New minerals may grow during 

CaCO3 + SiO2 = CaSiO3 + CO2

The presence of wollastonite can be used as 
an indicator of the Degree of Metamorphism

ISOGRAD - a line on a map connecting 
points of equal degree of metamorphism


Is the rock banded? - each band is often a 
single mineral - GNEISS

Does the rock exhibit foliation - parallelism 
of the cleavage of micas?

	Schist - coarse

	Phyllite - fine - barely visible

	Slate - very fine

If the rock is neither foliated nor banded it is 
called a granofels if it is coarse grained or a 
hornfels if it is fine grained

Marble - a metamorphosed limestone

Quartzite - a metamorphsed quartz arenite

Degree of Metamorphism	

A function of the composition of the parent 
rock - the PROTOLITH

		Marble - had a parent rich in carbonate

		Quartzite - quartz sandstone parent

		Slate, Schist, Gneiss - clay mineral rich 

Metamorphic Facies - attempts to deduce 
degree of metamorphism

Plate Tectonics and Metamorphism

Divergent Boundaries - contact 
metamorphism : basaltic lavas in contact 
with sediments

Convergent Boundaries : Subduction Zones : 
high pressure/low temperature 

Convergent Boundaries : 
Continent/Continent collision - regional