GEOLOGY

Detailed explanation-1: -Regional metamorphism, under extreme high temperature and uniform pressure over large areas of continental crust forms high-grade metamorphic rocks like slate, phyllite, amphibolites, varieties of schists, para-and ortho-gneisses, quartzite, and marble.

Detailed explanation-2: -Metamorphism occurs because some minerals are stable only under certain conditions of pressure and temperature. When pressure and temperature change, chemical reactions occur to cause the minerals in the rock to change to an assemblage that is stable at the new pressure and temperature conditions.

Detailed explanation-3: -Since gneisses form at the highest temperatures and pressures, some partial melting may occur. This partially melted rock is a transition between metamorphic and igneous rocks called a migmatite. Migmatites appear as dark and light banded gneiss that may be swirled or twisted some since some minerals started to melt.

Detailed explanation-4: -During metamorphism, rocks may fold, fracture, or even partially melt to a viscous state and flow before reforming into a new rock. Metamorphic rocks change in appearance, mineralogy, and sometimes even chemical composition from their parent rock source.