Download Primary Structures in Metamorphic Rocks

Primary Structures in
Metamorphic Rocks
Engr. Sultan Ahmed Khoso
Metamorphic Rocks
 When the pre existing rocks buried deep below the Earth's surface, they modified by heat,
pressure and other chemical processes without melting. In result, pre existing rocks are
reformed into new rocks known as Metamorphic Rocks.
 Exposure to these extreme conditions has altered the mineralogy, texture, and chemical
composition of the rocks.
 This geological process is known as metamorphism, that occur in rocks due to the effects of
High temperature, High pressure, and Chemically active fluids.
 Any rock (igneous, sedimentary, or metamorphic) can become a metamorphic rock.
Types of Metamorphism
 Metamorphic rocks may be formed by two main geological processes namely:
 Contact Metamorphism occurs adjacent/around to the magma or lava intrusions.
 Contact metamorphism occurs when hot magma, or lava, heats pre-existing rock therefore changing the
crystallization.
 Therefore, pre existing rock are modified into metamorphic rocks only by high temperature and the pressure is
nearly to constant.
Types of Metamorphism
During contact metamorphism, mostly non foliated metamorphic rocks (the metamorphic rocks
having no any layered or banded appearance of minerals) are formed due to the absence of high
pressure.
Types of Metamorphism
 Regional metamorphism occurs when heat, pressure, and directed stress are all
simultaneously applied to a pre existing rock.
 Regional metamorphism is primarily due to the internal heat of the Earth, weight of the
overlying rock, and horizontal or tectonic forces that cause the rocks to deform.
 During regional metamorphism, mostly foliated metamorphic rocks are formed due to the
high pressure.
Types of Metamorphism
Primary Structures in Metamorphic Rocks
 Metamorphic rock structures are characterized by their textures.
 Therefore, on the basis of texture, structures of metamorphic rocks are broadly classified
either as foliated or non-foliated.
Foliated Metamorphic Rocks
 All metamorphic rocks that show the parallel layering or parallel alignment of mineral
grains or banding are called foliated metamorphic rocks.
 Foliated metamorphic rocks are formed within the Earth's interior under extremely high
pressures that are unequal, occurring when the pressure is greater in one direction than in
the others (directed pressure).
 This direct pressure causes the minerals in the original rock to reorient themselves with the
long and flat minerals aligning perpendicular to the greatest pressure direction.
Foliation in Metamorphic Rocks
Foliation Series
Foliated Metamorphic Rocks
Non Foliated Metamorphic Rocks
Non Foliated Metamorphic Rocks