Top Banner

of 34

L6 Metamorphic Rocks

Jun 02, 2018

Download

Documents

Hemant Dhaked
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
  • 8/11/2019 L6 Metamorphic Rocks

    1/34

  • 8/11/2019 L6 Metamorphic Rocks

    2/34

  • 8/11/2019 L6 Metamorphic Rocks

    3/34

    What is Metamorphism?

    Metamorphism is a change in form thathappens in Earths crustal rocks inresponse to changes in temperature

    and pressure.

  • 8/11/2019 L6 Metamorphic Rocks

    4/34

  • 8/11/2019 L6 Metamorphic Rocks

    5/34

  • 8/11/2019 L6 Metamorphic Rocks

    6/34

    Factors controlling Metamorphism

    Simplest way to understand metamorphism is to remember cookingeffects

    What you cook ?

    Same is in the metamorphism process the end product will dependupon the initial composition and then the pressure/temperature

    Factors that controls or influence metamorphism:

    Chemical composition of the initial rock Intergranular fluids Temperature and pressure Time

  • 8/11/2019 L6 Metamorphic Rocks

    7/34

    Type of Metamorphism Metamorphic changes thatoccur while temperature andpressure are rising (withabundant inter-granular fluid)

    are termed progrademetamorphism

    Metamorphic changes thatoccur as temperature andpressure are declining (withless inter-granular fluid) arecalled retrograde metamorphiceffects.

    The intergranular fluid are not pure and plays important role inprocess of metamorphism (fluids mainly includes small amount ofgases, salts and mineral constituents dissolved from the host rock

    If the fluids are absent or available in very less quantity the processof metamorphism is very slow and few changes in mineral

    composition occurs

  • 8/11/2019 L6 Metamorphic Rocks

    8/34

    The source of temperature is either from magma or dueto the depth factor

    Metamorphism usually result into change in mineralcomposition and texture of rocks (Igneous andSedimentary Rocks) which are subjected to temp. >100 0 C and pr essu re >1000 s Mp a.

    Low-grade metamorphism:Occ urs at abou t 100 0 C to 500 0 C

    High-grade metamorphism:Occurs at > 500 0 C

    Temperature

  • 8/11/2019 L6 Metamorphic Rocks

    9/34

  • 8/11/2019 L6 Metamorphic Rocks

    10/34

    Uniform Stress Differential Stress

    min

    inter

    max

    Pressure

    Pressure (stress) result into change in texture of the originalrocks

    Rock are solid, which can be squeezed more strongly in onedirection

    Texture in metamorphic rocks are the result of differentialstress

    Whereas, the texture resulted from uniform stress arecommonly seen in igneous rocks, because igneous rockscrystallize from Liquid magma.

  • 8/11/2019 L6 Metamorphic Rocks

    11/34

    Development of differenttextures in rocks of the samecomposition different stresses

    Granite Granite-Gneiss

    Granite, consisting of quartz,feldspar, and mica (the darkmineral) will crystallized undera uniform stress and micagrains will be randomlyoriented.

    Whereas, under adifferential stress. Majoras well as Mica grains willbe oriented parallel to themaximum stress direction,giving the rock a distinctfoliation

  • 8/11/2019 L6 Metamorphic Rocks

    12/34

    Granite

  • 8/11/2019 L6 Metamorphic Rocks

    13/34

    Gneiss

  • 8/11/2019 L6 Metamorphic Rocks

    14/34

  • 8/11/2019 L6 Metamorphic Rocks

    15/34

    Type of MetamorphicRocks classified based on

    Textures

    Foliated Non-foliated

  • 8/11/2019 L6 Metamorphic Rocks

    16/34

  • 8/11/2019 L6 Metamorphic Rocks

    17/34

    Foliated Rocks Foliation: when platy , lamellar or f laky minerals

    (e.g., sheet silicate minerals the micas: biotite,muscovite, chlorite etc.), occurring in rock orientthemselves paral le l to one another (i.e.,

    perpendicular to the direction of maximum pressure orstress).

    Randomorientationof minerals

    Preferredorientationof minerals

  • 8/11/2019 L6 Metamorphic Rocks

    18/34

  • 8/11/2019 L6 Metamorphic Rocks

    19/34

    Slate: fine grained foliated metamorphic rock formed under low-grade metamorphism (from mudstone, shales or claystones)

  • 8/11/2019 L6 Metamorphic Rocks

    20/34

    Further deformation

    Slate when metamorphosed further will give rise to morefoliated rock known as Phyllite

    It is characterized by wavy texture/foliation Formed under low-grade metamorphism

  • 8/11/2019 L6 Metamorphic Rocks

    21/34

    Foliation under microscope (mica and quartz

    [darker grains])

  • 8/11/2019 L6 Metamorphic Rocks

    22/34

    Phyllite to- Schist

    Schist: is formed underintermediate to high grademetamorphism fromPhyllites

  • 8/11/2019 L6 Metamorphic Rocks

    23/34

    Gneiss: parallel foliation; medium to coarse grained; quartz-feldspars

    marked by lighter layers and darker are the ferromagnesian minerals

  • 8/11/2019 L6 Metamorphic Rocks

    24/34

    Non foliated rocks These rocks lack foliation Common e.g., are Quartzite and Marble

  • 8/11/2019 L6 Metamorphic Rocks

    25/34

    Quartzites

    Medium to coarse grainedmade up of fused quartzgrains

    Has sandy texture, alsotermed as Granulose texture.

  • 8/11/2019 L6 Metamorphic Rocks

    26/34

    Marble

    Metamorphosed from limestone Medium to coarse grained Crystalline texture Shows tight interlocking of calcite grains Formed under intermediate to high grade

    metamorphism

  • 8/11/2019 L6 Metamorphic Rocks

    27/34

  • 8/11/2019 L6 Metamorphic Rocks

    28/34

  • 8/11/2019 L6 Metamorphic Rocks

    29/34

  • 8/11/2019 L6 Metamorphic Rocks

    30/34

    Other examples of use of MakranaMarble from India

    Birla Mandir, Jaipur

    Victoria Memorial, Calcutta

    Sheikh Zayed Grand Mosque, Abu Dhabi

  • 8/11/2019 L6 Metamorphic Rocks

    31/34

  • 8/11/2019 L6 Metamorphic Rocks

    32/34

    Importance of Metamorphic rocks -SLATESFine grained impermeable, cleavable and softIncompetent; cannot withstand great loadsBut since they are impermeable and split easily; thin large sized slabs ofuniform thickness can be extracted for roofing purpose.Economic importance: Since they are bad conductor of electricity used in

    electrical industries for switch board base

    GNEISSGneissic rocks are rich in SILICA i.e. predominantly Quartz and Feldsparsalong with garnet, pyroxene, Hornblende etc.

    Non-porous and impermeable nature increases the strength of the rockFoliated character to some extend improves workabilityLoad perpendicular to foliated planes gives more stronger foundation

  • 8/11/2019 L6 Metamorphic Rocks

    33/34

    If mineral assemblage is more or less similar to Granite (with less % maficminerals) then:

    It is used as building stone

    As aggregate for making concreteAs road metals etc.

    SCHISTMainly composed of prismatic or platy minerals, which contributes indevelopment of Schistose Structure. Eg. Hornblende, tourmaline, sillimaniteetc (prismatic); chlorite, muscovite, biotite, talc, kyanite etc. (platy)Cleavable nature of Schists is the main reason for their weakness; they areincompetent

  • 8/11/2019 L6 Metamorphic Rocks

    34/34

    QUARTZITESANDSTONE (composed of quartz/feldspars/feldspathoid minerals) whenunder go metamorphism result into Quartzite.Granulose texture/structure (Granoblastic) makes them most competent rockamongst all other metamorphic rocks.Because metamorphism of Sst. Result disappearance of cementing material,

    bedding planes, fossil content etc.

    Quartzites are compact, hard and strong; very less porous and less permeablethan the parent Sst.Predominance of Quartz makes the rock very hard and suitable for roadmetal; can be used as concrete aggregate etc.Acts as strong foundation for any CE structure.