-
Metamorphism is a __________________ that involves no melt phase.
solid-state recrystallization
-
The protolith of a metamorphic rock is the
parent
-
Fabric refers to the way ____________ in a rock are arranged.
minerals
-
Foliation is defined by the _______________arrangement of minerals.
plane or planar
-
Typical platy minerals (sheet silicates) defining a foliation include
chlorite,muscovite & biotite
-
Directed pressure during metamorphism produces a _________________.
foliation
-
If elements do not enter or leave a rock during recrystallization, then the rock system is
described as ___________ or __________________.
closed, isochemical
-
Marble is a metamorphic rock composed of coarse-grained
calcite
-
Quartzite is a metamorphic rock composed of a dense network of interlocking
quartz
-
Basalts when metamorphosed at temperatures of ~500oC or higher are transformed into
__________________________.
amphibolite
-
Slates are characterized by a tendency to break into even-parallel sheets due to the parallel
alignment of the flat crystal faces of
chlorite and muscovite
-
The foliation in a slate is called slaty
cleavage
-
Assuming a mudstone protolith, the transformation to a slate occurs at ~________ oC.
300
-
Phyllites are _________________ grained than slates, and when held up to the sunlight exhibit
a marked ____________, as rays of light reflect off the aligned crystals of ______________
and _________________.
coarser, sheen, chlorite, muscovite
-
Assuming a mudstone protolith, the transformation to schist occurs at temperatures between
about _______ and ______ oC. The resulting foliation is called ___________________.
400, 500, schisosity
-
Schist derived from a mudstone at temperatures between about 500 oC and 650 oC will consist
of quartz, feldspar, muscovite, biotite, garnet, and _____________. Such a rock would be
___________________ grained than a phyllite.
staurolite, coarser
-
The coarsest grained metamorphic rock is a
gneiss
-
A foliation in gneiss would be called ___________________. It forms as ions migrate over
microscopic distances at temperatures above ______ to ______ oC.
gneissosity, 600, 650
-
Metamorphic grade refers to the broad pressure conditions of metamorphism. True or false
- False, metamorphic grade refers to the relative temperature conditions under which rocks were
- metamorphosed
-
In general, metamorphic grade is dependent upon the
geotherm
-
Given a specific geotherm, low metamorphic grade rocks occur in the ___________________
part of the crust while higher grade rocks will occur at _________ levels.
upper, deeper
-
Given a mudstone protolith, and a geothermal gradient typical of arc-continent collisions, at
temperatures over 700 oC, the stable metamorphic mineral assemblage will consist of quartz,
feldspar, and ______________.
sillimanite
-
Isotherms are curves or surfaces of equal
temperature
-
Isotherms bend downward within
subduction zone settings
-
In volcanic arc settings, isotherms bend downward due to the introduction of hot magma. True
or false
False
-
An envelope of recrystallized rock surrounding a pluton is called a
contact metamorphic aureole
-
Non-foliated rocks found in contact metamorphic aureoles are called
hornfels
-
Phase diagrams depict the PT conditions under which various minerals are stable. True or false
True
-
Is andalusite a low or high pressure phase relative to kyanite?
low pressure
-
Is sillimanite a low or high temperature phase relative to andalusite?
high temperature
-
Which of the following metamorphic facies represent rocks that were metamorphosed under the
lowest PT conditions recognized by geologists?
zeolite facies
-
Which of the following metamorphic facies represent rocks that were metamorphosed under the
highest pressure conditions recognized by geologists?
eclogite
-
The hornfels facies forms during ____________________ metamorphism.
contact
-
In subduction zone settings the geotherm is _________.
10oC/km
-
The geotherm in collisional zones and active regions of continents is about __________.
25o - 35oC/km
-
The geotherm in island arcs is about _________.
50oC/km
-
Why do isotherms bow upward in island arcs and mid-ocean ridges?
- Isotherms bow upward in island arcs and mid-ocean ridges because hot magma is introduced in
- these regions.
-
Why do isotherms bend downward in subduction zone settings?
-
Isotherms bend downward in subduction zone settings because the cold subducting lithospheric
- plate descends at a rate faster than it can equilibrate (warm up) to the temperatures of the over
- ridging plate.
-
How would describe the distribution of metamorphic facies within a zone of collision between
an island arc and a passive continental margin?
- Zeolite and prehnite-pumpellyite facies would occur along the flanks. Moving progressively
- toward the interior of the zone of collision, you would encounter greenschist, amphibolite, and
- granulite facies.
-
What would happen to a mudstone if it were metamorphosed at temperatures in excess of
700oC under wet conditions?
The mudstone probably would melt.
-
Using the illustration shown below, please answer the following questions.
(a) What minerals would be stable at temperatures around 400oC, 600oC and 710oC?
(b) What is the relationship between textural type of metamorphic rock and metamorphic
grade?
(c) What is the relationship between metamorphic grade and facies development?
(d) What is the average temperature for the onset of metamorphism?
(e) If a mudstone undergoes metamorphism under wet conditions at temperatures above
~700oC, then what will happen?
- (a) @ 400oC chlorite, muscovite, and biotite would be stable
- @ 600oC quartz, feldspar, muscovite, biotite, garnet, and staurolite would be stable
- @ 710oC quartz, feldspar, biotite, sillimanite, and possibly muscovite would be stable
- (b) Low grade rocks are going to be composed largely of slates, phyllites, and schists while
- intermediate grade rocks are going to be schists and gneisses. High grade rocks are going to
- consist primarily of gneisses.
- (c) Greenschist facies rocks will be composed primarily of slates, phyllites, and schists.
- Amphibolite facies rocks will be mostly schists and gneisses, while high grade metamorphic
- rocks will be dominated by gneisses.
- (d) ~300oC
- (e) It will melt
-
In the illustration shown below, the continental geotherm is broadly representative of
collisional and other active regions of the crust. Please answer the following questions.
(a) What is the metamorphic facies series for a geotherm typical of subduction zone settings?
(b) What is the metamorphic facies series for a geotherm typical of continental regions?
(c) What is the metamorphic facies associated with geotherms around cooling magma?
- (a) Zeolite, blueschist, ecologite facies
- (b) Zeolite, prehnite-pumpellyite, greenschist, amphibolite, and granulite facies
- (c) Contact
-
In the following illustration what do the fields labeled A, B, and C represent?
A = kyanite. B = sillimanite. C = andalusite.
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