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Are plutons fine grained?
Plutonic rocks are coarse-grained as they are formed slowly that allows the formation of large crystals before the magma solidifies into a rock.
What type of rock is coarse-grained?
igneous rocks
Coarse grain varieties (with mineral grains large enough to see without a magnifying glass) are called phaneritic. Granite and gabbro are examples of phaneritic igneous rocks. Fine grained rocks, where the individual grains are too small to see, are called aphanitic. Basalt is an example.
How are plutons classified?
A plutonic rock may be classified mineralogically based on the actual proportion of the various minerals of which it is composed (called the mode).
What is the definition of plutons?
Definition of pluton : a typically large body of intrusive igneous rock.
Are plutons intrusive?
pluton, body of intrusive igneous rock the size, composition, shape, or exact type of which is in doubt; when such characteristics are known, more limiting terms can be used. Thus, plutons include dikes, laccoliths, batholiths, sills, and other forms of intrusions.
What is a coarse grained texture?
Coarse-grained textures generally indicate magmas that slowly cooled deep underground. Slow cooling gives crystals enough time to grow to easily seen sizes (i.e., larger than 1 mm). Thus, you can often figure out the relative order in which the minerals crystallized from the magma.
Are plutons extrusive structures?
Plutons or plutonic bodies are masses of intrusive igneous rock that have solidified underground, as opposed to volcanic (extrusive) rocks that solidify only after erupting onto the surface.
What are three characteristics used to classify plutons?
How are plutons classified? Plutons are classified by their shape, size, and relationship to the surrounding rock layers.
What is the composition of plutons?
Most plutons intruded into the upper crust are of granitic composition. That is, they are comprised mainly of the light-coloured minerals, the feldspars and quartz—a composition often referred to as ‘felsic’. Although dark minerals such as biotite and hornblende are usually present, giving the rock a speckled appearance, they are never abundant.
Why do plutons crystallize so quickly?
Rather than being a problem for rapid cooling, the crystals point to rapid crystallization. The Tatoosh pluton in Washington State is an example of a shallow granite pluton that crystallized quickly after rapid reduction in vapour pressure due to a sudden loss of volatiles.
What rocks are formed when cooling is more rapid than pluton?
Granitic dykes and pegmatites are well-known examples of granitic rocks that formed when cooling was more rapid than the cooling of a pluton. Also, large fine-grained rhyolite bodies show that coarse-grained texture does not necessarily form when cooling is slow within them.
What is an example of a shallow pluton?
The Tatoosh pluton in Washington State is an example of a shallow granite pluton that crystallized quickly after rapid reduction in vapour pressure due to a sudden loss of volatiles. This is exactly the opposite of the conventional ideas on which the sceptic’s claims are made.