Concordant Plutonic bodies

1. Topic of the Seminar
CONCORDANT PLUTONS
Presented By :
ANUP UPADHYAYA,
3rd Sem., M.Sc., Applied Geology.

2. CONTENTS
 INTRODUCTION
 TYPES OF INTRUSIVE BODIES
 DISCORDANT
 CONCORDANT
1. SILLS
a) SINGLE SILL
b) COMPOSITE SILL
c) MULTIPLE SILL
d) DIFFERENTIATED SILL
2. LACCOLITHS
3. LOPOLITHS
4. PHACOLITHS
5. BYSMALITH
 CONCLUSIONS
 REFERENCES

3. INTRODUCTION
 A body of hot magma is less dense than the rock surrounding it, so it has a
tendency to move very slowly up toward the surface.
 It does so in a few different ways :
 including filling and widening existing cracks,
 melting the surrounding rock (called country rock)
 pushing the rock aside (where it is somewhat plastic),
 and breaking the rock.
• Some upward-moving magma reaches
the surface, resulting in volcanic
eruptions, but most cools within the
crust. The resulting body of rock is
known as a PLUTON.
• Plutons can have various different
shapes and relationships to the
surrounding country rock

4. TYPES OF INTRUSIVE BODIES
 There are two types of intrusive bodies
1. DISCORDANT
 A discordant igneous rock body cuts
across the pre-exiting rock bed.
 A dike is an example of discordant rock bodies.
2. CONCORDANT
 A concordant igneous rock body runs
parallel to the pre-existing bedrock.
 Laccoliths and sills are examples of concordant
igneous rock bodies.

5. INTRUSIVE IGNEOUS ROCK BODIES OR PLUTONS

6.  Sills are relatively thin tabular sheetlike body that
penetrates parallel to the bedding planes.
 Laterally it may extends for 100s of kms and upto 10
kms 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 and dolerites.
SILLS

7. Spreads parallel to the bedding planes of the
rocks, hence concordant in nature
limestone
sandstone
mudstone
Diagram of a SILL
SILL

8. TYPES OF SILLS
1. SINGLE SILL
 A simple sill is the product of a single intrusion.
2. MULTIPLE SILL
 A multiple sill is formed by two or more intrusions.
3. COMPOSITE SILL
 A composite sill is composed of more than one rock type
positioned between older layers of rock during more than
one intrusive episode.
4. DIFFERENTIATED SILL
 Exceptionally Large
 Sheet like injections of magma
 Segregation of minerals formed at various stages of
crystallization into separate layers or zones

9. CONCORDANT AND DISCORDANT IGNEOUS STRUCTRES

10. LACCOLITHS
 Laccoliths are concordant mushroom-shaped
bodies with
 a flat floor and
 a domed roof.
 A laccolith is sufficiently viscous (and silicic) to
limit magma flow along the horizontal plane and
shallow enough to physically lift the roof rocks.
 It causes folding of the overlying rock layers.
 Examples include :
 Gothic Mountain is a place where the flat floor of the laccolith is exposed.
 The Sleeping Ute Mountain of Utah.

11. DIAGRAMS OF LACCOLITHS

12. 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)
 Lopoliths typically consist of large layered intrusions that range in age
from Archean to Eocene.
 Lopoliths are usually mafic and they are characteristically much larger than Laccoliths.
 Examples include the Sudbury Igneous Complex of Ontario, the Bushveld
Igneous Complex of South Africa
LOPOLITH

13. PHACOLITHS
 A phacolith is a pluton of igneous rock parallel to the
bedding plane or foliation of folded country rock.
 These are concordant bodies that occurs along the crests
and troughs of the folded sedimentary strata.

14. 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.

15. CONCLUSIONS
 Most of the igneous activity on Earth is restricted to a narrow zone that is related
intimately with the motions of the lithospheric plates.
 All lavas contain dissolved volatiles upon eruption.
 The viscosity ,more so than the volatile content ,controls the violence of an eruption.
 Plutons can interact with the rocks into which they are intruded, sometimes leading to
partial melting of the country rock or to stopping and formation of xenoliths.

16. REFERENCES
Books Referred :
 Igneous and Metamorphic Petrology (Pearson) ; 2013 by J.D.Winter.
 Principles of igneous and metamorphic petrology (Freeman) ; 1990 by Anthony R
Philpotts.
 Igneous and Metamorphic Petrology (Wiley-Blackwell); 1982 by Myron G. Best.
Online Sources :
• https://www.slideshare.net/Sekhar9581/forms-of-igneous-rocks
• https://www.quora.com/What-is-the-difference-between-dykes-and-sills
• https://www.quora.com/What-are-%E2%80%9Concordant-
bodies%E2%80%9D