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INTRUSIVE IGNEOUS
ROCKS
M.RAJASEKHAR
ASST.PROFESSOR
DEPARTMENT OF CIVIL
ENGINEERING
KUPPAM ENGINEERING COLLEGE, KUPPAM
FORMS OF INTRUSIVE IGNEOUS ROCKS
• Commonly observed forms of Plutonic (intrusive) rocks
observed in the field are: dykes,...
DYKES: Dykes and sills are the most common forms of the
intrusive igneous bodies.
• They are discordant
• Cut across the b...
• Quartz-Dolerite dykes of Midland valley of Scotland are
about 50-60 km long and upto 30m thick. Few places some
dykes ar...
eg. Lamprophyric rocks broadly represented by kimberlites.
Lamprophyre dykes are located close to the western and
eastern ...
SILLS: Sills are relatively thin tabular sheetlike body that
penetrates parallel to the bedding planes.
• Laterally it may...
mudstone
sandstone
limestone
Spreads parallel to the bedding
planes of the rocks, hence
concordant in nature.
Example Large Sill
LACCOLITHS: It is a concordant body, with flat bottom
and convex upward. It is dome shaped.
When viscous magma is
injecte...
Figure 4-26. Shapes of two concordant plutons.
a. Laccoliths with flat floor and arched roof.
b. Lopolith intruded into a ...
BYSMALITH: It is cylindrically shaped body.
• It is developed when highly viscous magma is injected,
because the lateral s...
• Their side sloping away from each other which makes them larger
and large downwards extending to greater depth
• It may ...
Stocks: Are smaller irregular
bodies with 10 km in maximum
dimension, and are associated
with batholiths.
PHACOLITHS: These are concordant bodies that occurs
along the crests and troughs of the folded
sedimentary strata.
LOPOLIT...
CHONOLITHS: This term is applied to all other intrusive
igneous bodies with irregular shape, i.e. the
body with no specifi...
VOLCANIC NECK or VOLCANIC PLUGS: It is
cylindrical conduit that fed magma upward to a volcanic
vent or it is a conduit of ...
TEXTURES OF IGNEOUS ROCKS
• Texture is defined as the overall appearance of a rock
based on size, shape and arrangement of...
PHANERIC TEXTURE
Is characterized by LARGE SIZE MINERALS which can be
easily seen by Naked eye (size at least 2mm or great...
Commonly associated with the INTRUSIVE (PLUTONIC)
IGNEOUS ROCKS, because magma in the crust cools at
slower rate and have ...
DIORITE
GABBRO
APHANITIC TEXTURE
Is characterized by FINE GRAINED MINERALS, which can
be seen under microscope (size < 1mm)
Commonly asso...
Basalt
Rhyolite
Obsidian
Based on crystalanity or definite shape:
• Crystals are bodies bounded by surfaces, having definite shape
by the internal ...
Based on Shape of the crystals
• The pattern or fabric of a rock depends on the shape as well as
relative size and arrange...
This happens when slow cooling is followed by rapid cooling.
Phenocrysts = larger crystals, matrix or groundmass = smaller...
ANDESITE PROPHYERY
Phenocrysts of Amphibole Ground mass mainly of
Plagioclase feldspar (Na/Ca)
Forms of igneous rocks
Forms of igneous rocks
Forms of igneous rocks
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Forms of igneous rocks

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Extrusive and Intrusive Forms of Igneous Rocks

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Forms of igneous rocks

  1. 1. INTRUSIVE IGNEOUS ROCKS M.RAJASEKHAR ASST.PROFESSOR DEPARTMENT OF CIVIL ENGINEERING KUPPAM ENGINEERING COLLEGE, KUPPAM
  2. 2. FORMS OF INTRUSIVE IGNEOUS ROCKS • Commonly observed forms of Plutonic (intrusive) rocks observed in the field are: dykes, sills, laccoliths, bysmaliths, phacoliths, lopolith, volcanic necks, batholiths and chonoliths. • Based on the attitudes of the associated country rocks the forms are called either as Concordant or Discordant.
  3. 3. DYKES: Dykes and sills are the most common forms of the intrusive igneous bodies. • They are discordant • Cut across the bedding of the rocks in which they intrude • Vertical to steeply inclined and sheetlike body (extensive in lateral dimension) • Thickness vary widely from an inch upto hundred of feet • Injected through fractures, joints, and weak planes
  4. 4. • Quartz-Dolerite dykes of Midland valley of Scotland are about 50-60 km long and upto 30m thick. Few places some dykes are very short upto few meters and as thin as few cm. Mafic dyke
  5. 5. eg. Lamprophyric rocks broadly represented by kimberlites. Lamprophyre dykes are located close to the western and eastern margins of the Cuddapah basin in the eastern Dharwar craton of India.
  6. 6. SILLS: Sills are relatively thin tabular sheetlike body that penetrates parallel to the bedding planes. • Laterally it may extends for 100s of km and upto 10 km in width. • Lateral extend mainly depends on the hydrostatic force, temperature, degree of fluidity or viscosity, weight of overlying sediment column. • Since basic magma are more fluid then acidic magma- mostly sills are made up of gabbros, dolerites and basalts
  7. 7. mudstone sandstone limestone Spreads parallel to the bedding planes of the rocks, hence concordant in nature.
  8. 8. Example Large Sill
  9. 9. LACCOLITHS: It is a concordant body, with flat bottom and convex upward. It is dome shaped. When viscous magma is injected rapidly along the bedding, as it cannot spreads it pushes up the overlying layers and keep on piling up. It causes folding of the overlying rock layers.
  10. 10. Figure 4-26. Shapes of two concordant plutons. a. Laccoliths with flat floor and arched roof. b. Lopolith intruded into a structural basin. The scale is not the same for these two plutons, a lopolith is generally much larger. Structures and Field Relationships
  11. 11. BYSMALITH: It is cylindrically shaped body. • It is developed when highly viscous magma is injected, because the lateral spreading along the bedding is less it acquires to move upwards and form cylindrical shape. • Causes breaking of overlying rock layers.
  12. 12. • Their side sloping away from each other which makes them larger and large downwards extending to greater depth • It may be occur discordant and concordant forms of igneous rocks • The irregular masses appears on the batholiths are called stocks and circulars masses are bosses • Their occurrence is commonly associated with the mountain- building process • These are either granites or granodiorites in composition BATHOLITHS: are the largest kind of plutons, irregular in shape and occupies large area.
  13. 13. Stocks: Are smaller irregular bodies with 10 km in maximum dimension, and are associated with batholiths.
  14. 14. PHACOLITHS: These are concordant bodies that occurs along the crests and troughs of the folded sedimentary strata. LOPOLITHS: These are basin or saucer-shaped concordant bodies with top nearly flat and convex bottom • They are very huge body with diameter upto 150 miles (app. 240 km) Lopolith
  15. 15. CHONOLITHS: This term is applied to all other intrusive igneous bodies with irregular shape, i.e. the body with no specific shape.
  16. 16. VOLCANIC NECK or VOLCANIC PLUGS: It is cylindrical conduit that fed magma upward to a volcanic vent or it is a conduit of the ancient volcano. Vary in diameter from a few 100s of m to a kilometer or more. These are filled up with crystalline rocks. Shape-circular, elliptical or irregular.
  17. 17. TEXTURES OF IGNEOUS ROCKS • Texture is defined as the overall appearance of a rock based on size, shape and arrangement of interlocking minerals • Texture depends on their • (a) Granularity (b) Crystalanity ( C) Shape of crystals • Based on granularity or grain size: Grain size depends on physical conditions that prevailed during the time of Crystallization of magma i.e. presence of volatiles, rate of cooling, pressure, temperature etc. Slow cooling = larger mineral grains Fast cooling = smaller mineral grains
  18. 18. PHANERIC TEXTURE Is characterized by LARGE SIZE MINERALS which can be easily seen by Naked eye (size at least 2mm or greater) Coarse-grained Phaneric - > 5mm Medium-grained Phaneric - 1 mm - 5mm Fine-grained Aphanitic <1 mm
  19. 19. Commonly associated with the INTRUSIVE (PLUTONIC) IGNEOUS ROCKS, because magma in the crust cools at slower rate and have enough time to result into large mineral grains. Eg. Granite; Pegmatite
  20. 20. DIORITE
  21. 21. GABBRO
  22. 22. APHANITIC TEXTURE Is characterized by FINE GRAINED MINERALS, which can be seen under microscope (size < 1mm) Commonly associated with the VOLCANIC (EXTRUSIVE) IGNEOUS ROCKS, because magma on the surface flows cools faster. Eg. Basalts; Rhyolite
  23. 23. Basalt Rhyolite
  24. 24. Obsidian
  25. 25. Based on crystalanity or definite shape: • Crystals are bodies bounded by surfaces, having definite shape by the internal arrangement of atoms i.e. Solidification of minerals from the gaseous or liquid states or from solutions Crystalanity grouped into three types based upon the shape of crystals formation they are Holo Crystalline : A rock composed of mostly crystals Hemi crystalline : A rock composed of partly crystals and glassy Holo hyaline : A rock composed of completely glassy matter
  26. 26. Based on Shape of the crystals • The pattern or fabric of a rock depends on the shape as well as relative size and arrangement of the minerals. The shape of the mineral grains in igneous rocks may be broadly grouped into three types Euhedral : Minerals are developed equally in size and shape and are completely bound with faces Sub hedral : Minerals are developed partially or to an intermediate state Anhedral Minerals are developed irregular shapes because their growth is controlled by neighboring materials
  27. 27. This happens when slow cooling is followed by rapid cooling. Phenocrysts = larger crystals, matrix or groundmass = smaller crystals ]PORPHYRITIC TEXTURE Is a distinctive mixture of large and fine grained mineral grains
  28. 28. ANDESITE PROPHYERY Phenocrysts of Amphibole Ground mass mainly of Plagioclase feldspar (Na/Ca)

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