What is metamorphosed basalt?

Answer 1

Metamorphism is when a rock of any particular composition get heated and put under pressure such that it partially melts and the chemical elements that make up the minerals rearrange to form new, usually high temperature and pressure versions of the original minerals since the composition is the same.

The pressure is provided usually over a long period of burial or tectonic movement and the heat is either on a regional or local scale (contact metamorphism) where the rocks being metamorphosed have a magma intruded next to them.

Basalt is an igneous rock (erupted from volcano) and is fine grained, ie. they cool quickly. Depending on the particular temperature and pressure it undergoes its minerals will change into particular other minerals. Metamorphic rocks of particular composition have been put into what are called 'facies'.

Read more at:

http://en.wikipedia.org/wiki/Basalt#Metamorphism

and

http://en.wikipedia.org/wiki/Blueschist

for a decent start.

Metamorphosed basalts are also important hosts for a variety of hydrothermal ore deposits, including gold deposits, copper deposits, volcanogenic massive sulfide ore deposits and a few others. (Wiki)

Answer 2

Metamorphosed basalt is a type of rock formed from the metamorphism of basalt, which is an igneous rock. Through heat and pressure, the mineral composition and texture of the basaltic rock change, resulting in the formation of metamorphosed basalt. This process typically occurs deep within the Earth's crust.