The granulite facies consists of very high grade metamorphic rocks like gneiss. The eclogite facies is an extremely high grade region of the plot and comprises metamorphic rocks that are a bit beyond our level in GY 111.
What is the parent rock of blueschist?
Blueschist
| Type | Metamorphic Rock |
|---|---|
| Metamorphic Type | Blueschist (subtype of Regional) |
| Metamorphic Grade | High P – Low T |
| Parent Rock | Basalt and Seafloor sediments |
| Metamorphic Environment | Along subduction zones at convergent plate boundaries |
Is shale The Protolith of gneiss?
The protoliths for gneiss can be any rock that contains more than one mineral, such as shale with its clay minerals and clay-sized quartz and feldspar, or an igneous rock with both dark-colored ferromagnesian minerals and light-colored non-ferromagnesian minerals (see Chapter 8 for review).
What does Blueschist facies indicate?
The blueschist metamorphic facies are characterized by the minerals jadeite, glaucophane, epidote, lawsonite, and garnet. They record metamorphism in the cool high-pressure/low-temperature thermal gradients at less than 7°C/km in subduction zones in the last 1 billion years.
What is the Protolith of gneiss?
The protolith of gneiss may be an igneous rock, in this case it is called an orthogneiss. It forms probably because of shear in vicous granitic magma. In this sense it is similar to igneous rocks like granite and gabbro and not similar to related metamorphic rocks like schist and phyllite which are foliated.
How do you find Protolith?
In low grade metamorphic rocks, original textures are often preserved allowing one to determine the likely protolith. As the grade of metamorphism increases, original textures are replaced with metamorphic textures and other clues, such as bulk chemical composition of the rock, are used to determine the protolith.
What is the Protolith of blueschist?
Characteristic mineral parageneses for various rock types under blueschist facies conditions are: Mafic protolith (basalt, andesite, gabbro, diorite): Alkali-amphibole (mostly glaucophane), lawsonite, epidote, jadeite, phengite, chlorite, garnet, quartz.
Where is blueschist facies formed?
subduction zones
See, blueschist facies rocks are generally formed in subduction zones where oceanic crust is being stuffed into a trench. That crust includes the basalts and other mafic and ultramafic rocks that will become true blueschist once they’re pressure-cooked.
What protolith is gneiss?
The protolith of gneiss may be an igneous rock, in this case it is called an orthogneiss. It forms probably because of shear in vicous granitic magma. Paragneiss is a variety with a sedimentary protolith. that metamorphosed first into slate, then became phyllite, schist, and finally gneiss.
What is the subclassification of gneiss?
Gneiss (Figure 10.17) forms at the highest pressures and temperatures, and has crystals large enough to see with the unaided eye. Gneiss features minerals that have separated into bands of different colours. Figure 10.17 Gneiss, a coarse-grained, high grade metamorphic rock, is characterized by colour bands.
What is the protolith of Blueschist?
What is the protolith of Migmatite?
Other migmatite hypotheses Such granites derived from sedimentary rock protoliths would be termed S-type granite, are typically potassic, sometimes containing leucite, and would be termed adamellite, granite and syenite.
What is blueschist facies?
Blueschist facies is a low temperature, high pressure prograde metamorphic path and is also known as the Franciscan facies series, after the west coast of the United States where these rocks are exposed.
Which rocks do not appear blue under blueschist conditions?
Felsic rocks and pelitic sediments which are subjected to blueschist facies conditions will form different mineral assemblages than metamorphosed basalt. Thereby, these rocks do not appear blue overall in color. Blueschist mineralogy varies by rock composition, but the classic equilibrium assemblages of blueschist facies are:
What are glaucophane schist-facies?
He advocated an independent “glaucophane schist-facies” to describe glaucophane-bearing schists and associated rocks with > 5% proportion of glaucophane. But the genetic and tectonic significance of this facies was not clear.
Why do we need to exhum rocks for blueschist facies analysis?
Thus in order for blueschist facies assemblages to be seen at the Earth’s surface, the rock must be exhumed swiftly enough to prevent total thermal equilibration of the rocks which are under blueschist facies conditions with the typical geothermal gradient.
