What is the chemical composition of blueschist?
Glaucophane/ferroglaucophane provide the blue colour characteristic of blueschists and are typically found with a combination of the following minerals: lawsonite, chlorite, garnet, albite, zoisite, phengite and paragonite mica.
What type of metamorphism makes blueschist?
Mafic Rocks
Very Low- to Low-Grade Metamorphism of Mafic Rocks at Medium-High Pressure—Blueschist. At very low to low-temperature (250–500 °C) and medium-high pressure (> 8 kbar), mafic rocks are generally metamorphosed to form blueschist, which contains the blue Na-rich amphibole—glaucophane.
What is blueschist rock?
Blueschist is a regional metamorphic rock formed under high-pressure (HP) low-temperature (LT) conditions.
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.
Under what conditions does Blueschist facies metamorphism form?
Abstract. 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.
How do you identify a blueschist?
Blueschist. Glaucophane is an azure-blue, lavender-blue or bluish-black mineral; giving the rock its name, and color. Typically the prismatic glaucophane crystals line up resulting in a distinct schistose foliation.
How does blueschist get to the surface?
Blueschists and other high-pressure subduction zone rocks are thought to be exhumed rapidly by flow and/or faulting in accretionary wedges or the upper parts of subducted crust, or may return to the Earth’s surface in part owing to buoyancy if the metabasaltic rocks are associated with low-density continental crust ( …
Why is blueschist found in subduction zones?
THE high-pressure, low-temperature metamorphic rocks known as blueschists have long been considered to form in subduction zones, where the descent of a relatively cold slab leads to the occurrence of unusually low temperatures at mantle pressures.
What texture is eclogite?
coarse grained
Epidote is composed relatively homo- genously and has a high clinozoisite component. The eclogites are coarse grained.
What is the difference between blueschist and greenschist facies?
As nouns the difference between blueschist and greenschist is that blueschist is (geology) a metamorphic rock containing glaucophane while greenschist is a metamorphic rock formed at low temperature and pressure, often with an abundance of green minerals such as chlorite, serpentine, and epidote.