Metamorphic Zones

Introduction

  • Metamorphic zones are the area where the metamorphic minerals are stable under certain temperature and pressure.
  • There are different metamorphic zones found in different lithologies over a terrain.
  • The sequential arrangement of metamorphic zones is called metamorphic facies series.
  • Barrovian series of zones: Both temperature and pressure increases gradually along the metamorphic gradient.
  • The major factor responsible for barrovian metamorphism is crustal thickening and regional metamorphism in the orogeny.
  • The following zones can easily be recognize in pelitic rocks.

Chlorite zone

  • The zone is characterized by the appearance of clayey minerals such as muscovite and chlorite.
  • The zone is take place at low temperature and pressure where low grade metamorphic rocks are formed such as Phyllites and slates.

Biotite zone

  • The zone is indicated by the transformation of muscovite or chlorite to brown biotite.
  • Biotite schist rock found in this zone.

Garnet zone

  • Almandite Garnet is the diagnostic mineral of this zone.
  • The zone takes place at medium grade metamorphism.
  • Rock found in this zone is garnetiferous mica-schist.

Staurolite zone

  • The zone is found in medium to high grade metamorphism with the presence of mineral staurolite.
  • Staurolite is mainly found in iron rich argillaceous rocks.

Kyanite zone

  • Kyanite is present in the argillaceous rocks.
  • Mineral assemblage consists of muscovite and quartz also.

Sillimanite zone

  • The zone is present in high grade metamorphism where temperature ad pressure is high.
  • Metamorphic rock such as gneiss is found here which consists of biotite, garnet and sillimanite along with potash feldspar.

BARROVIAN ZONES