1. EVOLUTION OF OCEAN FLOOR:
BIRTH AND DESTRUCTION

2. Ocean Floor from 2 MYBP to present - current scenario….

3. OCEAN FLOOR
¤Ocean floor is the bottom of the ocean.
¤Ocean floors have a common structure
created from tectonic movement and
sediment from various sources.
¤Relatively short lived features on the
planet.
¤No oceanic crust older than 180 Ma old
is known from the present oceans

4. Continent
al
Shelf
Continenta
l shelf
Continental
slope
Continental
slope
Seamoun
t
Volcanic
island
Continental
rise
Abyssal
plain
mid-ocean
ridge
Rift
valley
trenc
h

6. EVOLUTION OF OCEAN FLOOR
•An individual ocean basin grows from an
initial rift, reaches a maximum size, then
shrinks and ultimately closes.
•Wilson Cycle refers to the sequence of
events leading to the formation,
expansion, contracting and eventual
elimination of ocean basins.

7. The Wilson Cycle
Rift valley forms as
continent begins to split.
Example:
African Rift Lakes.
Sea-floor basalts begin
forming and continents
diverge.
Example: Red Sea.
Broad ocean basins widen,
trenches develop, subduction
begins. Example: Atlantic
Ocean.

8. Subduction eliminates much
of sea-floor and oceanic
ridge.
Example: Pacific Ocean.
Last of sea-floor is
eliminated, continents collide
forming mountain chain.
Example: Mediterranean
Sea.
Convergence of continental
plates and uplifting to form
mountain range. Example:
Himalayas.

9. Stage Examples Dominant motions Characteristic feature
1.Embryonic East
African rift
valleys
Crustal expansion
and uplift
Rift valleys
2.Young Red sea,
Gulf of
California
Subsidence and
spreading
Narrow seas with
parallel coasts and a
central depression
3.Mature Atlantic
ocean
Spreading Ocean basin with acti
mid-ocean ridge
4.Declining Pacific
ocean
Spreading and
shrinking
Ocean basis with acti
spreading axes; also
numerous island arcs
and adjacent trenche
around margins
5.Terminal Mediterra
nean sea
Shrinking and uplift Young mountains
6.Relict
scar/suture
Indus
suture in
the
Himalayas
Shrinking and uplift Young mountains

10. Formatio
n of
incipient
ocean
basin

11. 3-4
Juvenile Ocean Basin

12. DRIVING FORCES AND PROCESSES OF
EVOLUTION
•Sea floor spreading
•subduction

13. DRIVING FORCES AND PROCESSES OF
EVOLUTION
•Sea floor spreading
–New oceanic lithosphere is created by the
upwelling and partial melting of material from
the asthenosphere at the ocean ridges
•Subduction
–The process of consumption of a lithospheric
plate at convergent plate margins. Here one
part of the sea floor plunges below another
and down into the asthenosphere.

14. Sea-Floor
Spreading

15. Sea-Floor
Spreading
heat

16. Sea-Floor
Spreading
Deep
Sediment
layer
shallow
Sediment
layer

17. •Rift valleys along oceanic ridge crests
indicate tension, are bounded by
normal faults and are floored by
recently-erupted basaltic lava flows.
•Axis of the oceanic ridge is offset by
transform (strike-slip) faults which
produce lateral displacement.

18. •Rates of sea-floor spreading vary from 1
to 10 cm per year for each side of the
ridge and can be determined by dating
the sea floor and measuring its distance
from the ridge crest.
•Continents are moved by the expanding
sea floor.

19. Magnetic anomalies form parallel bands arrange
symmetrically about the axis of the oceanic ridge.

20. •As basaltic rocks crystallize, some minerals
align themselves with Earth’s magnetic
field, as it exists at that time, imparting a
permanent magnetic field, called
paleomagnetism, to the rock.
•Periodically Earth’s magnetic field polarity
(direction) reverses poles.

21.  Subduction is the process at a deep-sea
trench whereby one part of the sea floor
plunges below another and down into the
asthenosphere. Destruction of sea floor
occurs in subduction zones.

25. •Benioff Zone is an area of increasingly
deeper seismic activity, inclined from the
trench downward in the direction of the
island arc.

26. Movement of plates is caused by thermal
convection of the “plastic” rocks of the
asthenosphere which drag along the
overlying lithospheric plates, and gravity
which pulls submerged plate downward.

27. TWO MODELS OF PLATE MOTION — MANTLE DRAG AND
EDGE FORCE

28. MANTLE DRAG
•Plates are driven by
the viscous drag of
the asthenosphere
on their bases.
•Astenosphere is the
top of the
convection system.
•Cannot account the
movements of small
plates.
EDGE FORCE
•Plates are driven by
the forces applied to
their margins/edges.
•Oceanic lithosphere
represents the top
of the convection
system.
•explains the motion
of small plates
•Acceptable
thermodynamically
and much more
effective to transfer
heat from mantle.

29. CONCLUSION
¤Ocean floor is the bottom of the ocean.
¤Evolution of ocean floor is explained by
wilson cycle
¤ Ocean forms at the embryonic stage.
¤ Developes and widens in young and mature
stages.
¤ spreading continues and shrinkage starts at
declining stages.
¤ Shrinkage continues and uplifting begins at
terminal stage and finally become a relict.
¤Sea floor spreading and subduction are the
two major forces respnsible for the
evolution of plates.

30. REFERENCES
•Philip kearey, keith s klepeis and
Frederick j vine ,chapters 6,7 and 9,
Global Tectonics,3rd ed,wiley-blackwell
2009
•Butterworth-Heinemann, Ocean Basins
: Their Structure and Evolution (2nd
Edition),p 60
•Jones and Bartlett; Invitation to
oceanography; origin of ocean basins
•Wikipedia and Google for
images;en.wikipedia.org:sea floor.

31. THANKS