Download Metamorphic Rocks - Geology

Metamorphic
Rocks
Standards
 Classify matter in a variety of ways
 Describe the composition and
structure of Earth’s materials,
including:
 the major rock types (i.e.,
sedimentary, igneous, metamorphic)
and their formation
Properties of
Metamorphic Rocks
• Metamorphic means change in form.
• Metamorphic rocks are formed when
existing rocks undergo changes.
• Sedimentary & igneous rocks can
change into metamorphic rocks, and
metamorphic rocks can change into
different metamorphic rocks.
Properties of Metamorphic Rocks
• During the process of metamorphism, rocks
and minerals change in response to changes in
temperature, pressure or other
environmental changes.
• The mineralogy, texture and/or chemical
composition of the rocks may alter during
metamorphism.
• Most metamorphic reactions (changes) occur
while the rocks are in a solid state (if the rock
becomes liquid, it is an igneous rock).
Texture Changes
• The average size of crystals in the rock
usually increases.
• The shape and arrangement of crystals in
the rock change
• Ex: limestone changes to marble: still
made of the mineral calcite, but it is now
dense and its texture is coarse with
irregularly shaped, interlocking grains.
Mineral Changes
• In general, if the original (parent) rock
contains one mineral, metamorphism
produces a rock of the same mineral.
Ex: limestone changes to marble, both are
made of calcite
• If multiple minerals are present in the parent
rock, the new metamorphic rock may have
different minerals.
Ex: shale contains clay minerals, quartz &
feldspar. During metamorphism, these
minerals change to chlorite.
Formation of
Metamorphic Rocks
• Metamorphic rocks are formed by
high temperature and/or pressure
Formation of
Metamorphic Rocks
1. Temperature induced changes
• Elevated temperatures cause
metamorphism:
 Lower temperatures cause slow
changes and produce less of a
change.
 Higher temperatures cause faster
changes and produce a greater
change
Formation of
Metamorphic Rocks
2. Pressure induced changes
• Chemical reactions are sensitive to
pressure (measured in kilobars).
• Greater amounts of pressure will
produce greater changes.
Formation of
Metamorphic Rocks
2. Pressure induced changes
• Deformation – change in the shape
of rocks or minerals in response to
mechanical forces
 Tectonic activity causes pressure
that creates foliation in
metamorphic rocks.
 Foliation is a set of flat or wavy
planes in a metamorphic rock
Formation of
Metamorphic Rocks
• Types of foliation:
 Slaty cleavage – rock splits into thin
sheets
 Schistosity – wavy, parallel
arrangements of minerals
 Gneissic – alternating layers, or
bands, of light and dark minerals
Types of Metamorphism
1. Regional metamorphism
2. Contact metamorphism
3. Metasomatism
Regional Metamorphism
• Caused by burial or strong tectonic
forces that impose high temperatures
and pressures on the rocks over a
large area.
• Pressure plays a greater role than
heat
• Most metamorphic rocks are of this
type.
• These rocks are foliated.
Regional Metamorphism
• Types of regional metamorphic rocks:
Rock Names
Parent Rock
• Slate………………..shale
• Phyllite……………..shale
• Schist………………shale
• Gneiss……………..shale, granite or
conglomerate
Slate
Schist
Phyllite
Gneiss
Contact Metamorphism
• Caused by heat and pressure produced by
a nearby igneous intrusion.
• Does not cover large areas like in regional
metamorphism.
• Heat plays a greater role than pressure.
• These rocks are called granoblastic and
are non-foliated.
Contact Metamorphism
• Types of contact metamorphic rocks:
Rock Names
Parent Rock
• Metaconglomerate……...conglomerate
• Quartzite…………………sandstone
• Marble……………………limestone
Metaconglomerate
Quartzite
Marble
Metasomatism
• Super-heated water enters pore
spaces or fractures in rocks and
creates metamorphic changes.
• Many deposits of valuable metal ores,
such as copper, zinc and lead, are
formed in this way.