Chap 8
Mineral resources which are metamorphic rocks include marble and slate.
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Principal types of metamorphism -
Contact Dynamic Regional metamorphism
Contact metamorphism
Contact metamorphic rocks form under conditions of high temperature and low pressure. They are arrayed in aureoles, or metamorphosed zones, around plutons and other intrusive igneous bodies.
Differential pressure
Differential pressure is a non-uniform field of pressure; the pressure acting on a rock in some directions is stronger than it is in others. Many metamorphic rocks form under conditions of differential pressure, which influences the development of metamorphic structures and textures in significant ways.
Dynamic metamorphism
Dynamic metamorphism is associated with faults and areas where lots of pressure builds up in the crust, but the temperature is not very great, such as in the accretionary wedges at convergent plate boundaries.
How is an orogenic metamorphic belt exposed?
Erosion accompanied by uplift of mountain roots gradually exposes metamorphic rocks that may have originated many kilometers beneath the surface. Commonly, the highest grades of metamorphism are localized where the highest mountains occur-or where the highest mountains once existed because this corresponds to the area of greatest uplift and
What are metamorphic fluids and why are they important?
Fluids within sedimentary rocks or issuing from magmas can accelerate chemical changes which occur during metamorphism and can cause new minerals to form. How do you define fluid?
Foliated
Foliated texture is produced by the preferred orientation of platy minerals.
What is foliated texture, and what are some examples of foliated rocks?
Foliated texture is produced by the preferred orientation of platy minerals. Foliated metamorphic rocks form a graded series of grain size and/or development of foliation, from fine grained slate, to phyllite and coarser grained schist, to gneiss, with segregated bands of minerals. Amphibolite is another fairly common coarse grained foliated metamorphic rock.
What are the principal agents of metamorphism?
Intrusive magmas or deep burial provide heat which causes metamorphism. Pressure is produced by overlying rocks (lithostatic) or is differential pressure produced by various stresses.
What are lithostatic and differential pressures, and why are they important?
Lithostatic pressure is a uniform field of pressure experienced by most rocks beneath Earth's surface. Like the hydrostatic pressure experienced by divers underwater, the pressure acting on a rock embedded in the crust "feels" the same from all directions.
What is a metamorphic facies?
Metamorphic facies are characterized by particular minerals which reflect specific ranges of temperature and pressure.
What does metamorphism have to do with climate?
Metamorphic fluids can release greenhouse gases into the atmosphere. The Eocene was the warmest period in the Cenozoic. This was probably caused in part by a greenhouse effect created by enhanced atmospheric CO2 content, which has been estimated to have been between twice and six times the modern value. The correlation of Eocene global warming and the rise of the Himalayan mountains may be a good example of this phenomenon.
Plate Tectonics and Metamorphism
Metamorphic rocks formed near the surface and within an oceanic-continental convergent plate boundary zone result from low temperature and high pressure conditions. Higher temperatures and pressures existing at depth within such plate boundaries produce higher grades of metamorphism in a descending oceanic plate.
What are isograds and metamorphic zones?
Metamorphic rocks often can be arranged in metamorphic zones which reflect the pressure and temperature conditions of metamorphism
How do metamorphic zones and metamorphic facies differ?
Metamorphic zones show the gradational metamorphic charge within a single rock composition-for example, politic. Metamorphic facies are groups of many different rock compositions whose mineral contents all indicate common temperature and pressure conditions during metamorphism.
Why is metamorphism worth studying?
Metamorphism is an important process that is closely related to plate tectonics, the growth of continents, and even climate change. It is also responsible for producing a number of economically valuable materials. Though largely hidden from view, metamorphism is part of the world around you. The world would be a much different and less interesting place without it.
What are some economically valuable metamorphic minerals?
Mineral resources which are metamorphic minerals include graphite, talc, and asbestos.
Nonfoliated
Nonfoliated textures do not exhibit preferred orientation of minerals.
What is a common nonfoliated metamorphic texture, and what are some examples of nonfoliated metamorphic rocks?
Nonfoliated textures do not exhibit preferred orientation of minerals. Common nonfoliated metamorphic rocks are marble, quartzite, greenstone, and hornfels.
What is shock metamorphism?
Shock metamorphism is a type of dynamic (pressure-dominated) metamorphism associated with meteorite impacts. The pressure is extremely high relative to other natural processes that operate on Earth.
Why do rocks metamorphose?
The environment in which rocks exist changes as they are buried, subjected to intrusion, and deformed by tectonic forces. Minerals are no longer stable (no longer "in equilibrium") as conditions change. Minerals can react with one another to create more stable kinds of minerals (heterogeneous metamorphic reactions) or undergo rearrangements in their own atoms to reduce the strain that builds up within them (crystal lattice reorientation and polymorphic transformation).
What is metamorphism?
The transformation of rocks, usually beneath Earth's surface, as the result of heat, pressure, and/or fluid activity, produces metamorphic rocks
Regional metamorphism
is the most common type of metamorphism. As the name implies, regional metamorphism has a broad range. Temperature and pressure both act as driving forces for metamorphic reactions in regional metamorphism.
