metamorphic rock

                             - METAMORPHIC ROCK -

                  It is defined as recrystallisation of pre-existing rock due to change in temperature, pressure, chemical fluids. Due to which physical as well chemical equilibrium of mineral present in the pre-existing rock is disturb and hence to establish equilibrium. The rock formed by metamorphism is called metamorphic rocks. And process is called Metamorphism.

         AGENTS OF METAMORPHISM:-

    a) Heat (temperature).

    b) Pressure.

    c) Chemical active fluid.

a) TEMPERATURE: - It is more effective than pressure temperature with depth and hence it is more at greater depth. The temperature may be supplied by magma chamber and radioactive minerals. Due to increase in temperature the minerals becomes unstable.  b) PRESSURE: - The pressure may be due to earth movement or due to load of above     laying rocks. Two kinds of pressure have to be recognized while considering pressure as metamorphic agent.

Directed pressure                          OR            Non-uniform pressure	Hydrostatic pressure                             OR                         Uniform pressure
1] It is present at shallow depth.                      2] It is act only on solid.                                   3] It is not equal in all sides. 4] Due to this elongation of minerals       takes place.                                                  5] Banded structure are produced.	1] It is present at greater depth. 2] It is act solid as well as liquid. 3] It is equal from all sides. 4] Due to this equidimensional volume       decrease, density increase.  5] Equidimensional structure may        produce.

  

C] Chemical Active Fluid: - Gases and liquid released from magma and G.W. changed with chemically active substance. Chemical fluids play only a secondary and passive role.

KINDS OF METAMORPHISM :-

              Different kinds of metamorphism are thus due to various combination of        heat, directed pressure, uniform pressure. The following types:-

1]  Heat is Predominant :-(Thermal Metamorphism)  

                      Temperature is main active agent as compared with pressure.

a) Clay rock              heat                Hornfelspar, and alusite, sillimanite, with                      

                                                         Quartz, mica.

b) Limestone

       Pure (CaCo3)           heat            Marble (white) (CaCo3) (Calcite mineral)

    Impure limestone                                                                                                                        Dolomite (CaMgCo3)      heat          Serpentine marble, Tremolite marble.

c) Arenaceous rock (sand stone)         heat           Quartzite vitreous lustre

                                                                                 (Hard, compact).

2] Directed pressure is predominant: - (Cotaclastic metamorphism)

   It is effective only at shallow depth. Due to directed pressure only rock get crushed.

a) Rudaceous Rock                     directed               crushed conglomerate

    Conglomerate, Breccia          pressure               crushed breccia.

b) Porphyritic Granite                                      Augen gneiss.

c) Clay Rock                                             slate (slaty cleavage).

3] Directed pressure and Heat is predominant :- (Dynamothermal metamorphism)

                 Due to this process producing typical metamorphic rocks Gneiss and  schists . And structure shows gneissose and schistose. 

   a) Argillaceous Rock                                       

 shale     pressure       slate   heat        phyllite   more   heat    mica schist with quartz

if excess Al2O3                         kyanite schist

if excess Fe Mg Al2O3                             Garnel schist

if excess Carbonaceuos                     Graphic schist

b) Quartzo Felspar rock                     (Quartz schist ) or Schistose Quartzite

     Quartzite  granite                        granite gneiss.

c) Basic Igneous Rock                 Epidiorite plagioclase and hornblende.

       Basalt

   Step 1) ( plagioclase + Augite)

  Step 2) Epidiorite                       Hornblende schist ( Amphibolites ).

  Diorite                            Hornblende gneiss.

   Syenite                          Biotite gneiss.

d) Plutonic Metamorphism:- (Heat and uniform pressure predominant )

                   Granulose structure may produced.

 Granite                               Granulites and charno ckite  .