CONTINENTAL DRIFT: ABRAHAM ORTELIUS a Duchy map maker 1596 first proposed the
possibility of joining the continents such as America with Europe and Africa
ANTONIO PELLEGRINI drew the map showing the three continents together.
ALFRED WEGENER a German meteorologist put forth THE CONTINENTAL DRIFT THEORY.
According to him,
All continents formed a single continental mass called PANGAEA
All oceans formed a single universal ocean called PANTHALASSA
AROUND 200 mya THE PANGAEA BEGAN TO SPLIT INTO TWO LARGE MASSES CALLED LAURASIA
and GONDWANA LAND
By further splitting, Laurasia formed northern continents and Gondwana land formed southern
continents.
Evidence TO SUPPORT THE CONTINENTAL DRIFT
1. The matching of continents (jig-saw fit)
A. the shorelines of S. America and Africa have a remarkable match
B. a map was produced by Bullard in 1964 to show the jigsaw fit of these two continents.
C. it was fit around 1000 fathom line of the shoreline
2. ROCKS OF SAME AGE ACROSS THE OCEANS
A.the belt of ancient rocks of 2000 my from Brazil coast matches with those of Western Africa
B. Marine deposits of South America and Africa belong to the Jurassic age.
3.TILLITE
An A. sedimentary rock formed out of glacial deposits
B. sediments from India have similar counterparts on different continents of the south.
C.tillile indicates prolonged glaciations
D.The same glaciations are found in Africa, Falklands, Madagascar, Antarctica, and Australia
E. the glacial tillite indicates that unambiguous evidence of paleoclimates and drifting of
continents.
4.PLACER DEPOSITS
a. Formation of placer deposits of gold in Ghana coast has no source rock.
a. The gold-bearing veins of rocks are found in Brazil
5.DISTRIBUTION OF FOSSILS
Identical species of animals and plants are found along the coastal regions of the
different continents.
lemurs occur in India, Madagascar, and Africa.
The contiguous landmass was called LEMURIA
the fossils of megalosaurus were found in only South
Africa and Brazil.
MESOSAURUS
LEMURIA
DISTRIBUTION OF FOSSILS
Chapter-4 DISTRIBUTION OF OCEANS AND CONTINENTS
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FORCES FOR DRIFTING THE CONTINENTS
1. Wegner suggested that the movement responsible for the drifting of the
continents was caused by
A. POLAR FLEEING FORCE B. TIDAL FORCE
Possible driving forces for plate tectonics:
2. bottom lithosphere tractions by convection currents.
3. trench pull (covered earlier).
4. ridge push (sliding off a high, crust in compression).
5. trench suck (rollback).
6. global expanding or contracting forces.
7. membrane forces on spinning ellipsoid (e.g. variants of polar fleeing forces).
TIDAL FORCE
Wegener suggested that these two forces are
responsible for the movement of plates.
Most of the scholars consider that these forces are not
sufficient to move the plates.
POST DRIFT STUDIES
Information collected from the ocean
mapping is more useful to study the
continental drift
Convectional current theory
It was proposed by ARTHUR HOLMES IN 1930
Due to the difference in the temperature
currents are formed due to the disintegration of radioactive materials inside the earth.
These currents are found entire mantle portion
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MAPPING OCEAN FLOOR
1. Existence of ridges and deep trenches nearby continental margins
2. Mid oceanic ridge is the most active for volcanic eruptions
3. The ocean floor is much younger than the continents
4. Rocks of equal distance of the ridge have similar chemical composition and age
OCEAN FLOOR CONFIGURATION
OCEAN FLOOR CONFIGURATION
The ocean floor is segmented into three major divisions
Based on depth and configuration
1. Continental margins
a.Form transitional zone between continental shore and deep-sea basins
b.They include continental slope, shelf, continental rise, and deep oceanic trenches
ABYSSAL PLAINS
1. EXTENSIVE PLAINS
2.FOUND BETWEEN CONTINENTAL MARGIN AND MID OCEANIC RIDGE
3.CONTINENTAL SEDIMENTS GET DEPOSITED
MID OCEANIC RIDGES
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DISTRIBUTION OF VOLCANOES AND EARTHQUAKES
1.all volcanoes and earthquakes are parallel to the
coast
2.this line also coincides with the mid- Atlantic ridge
3.alpine Himalayan system
4.around the pacific ocean it is called a ring of fire
Mid oceanic ridges
1. Interconnected mountain system within the ocean
2. Longest mountain chain on the ocean floor
3. Consist of the central rift system at the crust
4. Intense volcanic activity is found
CONCEPT OF SEAFLOOR SPREADING
1.it was proposed by Hess in 1961
2.he believed that new lava pushes out the plates from the mid-oceanic ridge
3.palaeo magnetic studies of the ocean floor reveal that
A.along the mid-oceanic ridge, there is the intense volcanic eruption
B.huge amount of lava comes out along the mid atlanticn ridges
C.the equidistant rock formations have similar age and chemical compositions & magnetic
properties
7.rocks closer to the mid-oceanic ridges are young and normal polarity
8. The age of rocks increases as the distance increases from the mid-oceanic ridge
9. Oceanic crust is much younger( 200my) than continental crust (3200my)
10. The sediments of the ocean floor is very this
11.earth quakes are common along the deep-sea trenches
Positions of continents through geological past
PLATE TECTONICS
1. The theory of plate tectonics was introduced by McKenzie, parker, and Morgan in 1967
2. A tectonic plate is also called a lithosphere plate
3. It is a massive irregularly shaped slab of solid rock
4. Consists of an oceanic and continental sphere
5. Plates move horizontally over the Asthenosphere
6. Average thickness is 100 km of oceanic part and 200 km continental part
7. It may be oceanic or continental
8. Pacific plate is the largest oceanic plate whereas the Eurasian plate is the largest continental
plate
MAJOR PLATES OF THE EARTH CRUST
MAJOR PLATES
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MAJOR PLATES
1.Antarctica And Surrounding Oceanic
Plate 2. North American Plate
3. South American Plate Pacific Plate
India-Australia-New Zealand PLATE
6.African Plate Eurasian Plate
MINOR PLATES
1. Cocos
Plate 2. Nazca Plate 3. Arabian Plate 4.
Philippine Plate 5. Caroline Plate 6.Fuji
Plate
These plates are moving constantly
throughout geological time, not the
continent believed by Wegener
Pangaea was the convergent of all the
plates
Position of Indian subcontinent is traced
with the help of rocks analyzed from
Nagpur area
TYPES OF PLATE BOUNDARIES
I. DIVERGENT BOUNDARIES
1. New crust is generated 2. plates move away from each other
2. These are called spreading sites 3. Ex. Mid Atlantic Ridge
II.CONVERGENT BOUNDARY
1. Crust is destroyed 2. sinking of the plate is called „subduction zone‟
3. There are three ways in which subduction occurs
i. Ocean and continent ii. Ocean and ocean iii. continent and continent plates
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III TRANSFORM BOUNDARIES
1. Crust is neither produced nor destroyed
2. Plates slide horizontally
3. Perpendicular to the mid-oceanic ridges
4. Differential movement of a plate at the same time
5. Rotation of the earth has its effect on this movement
RATES OF PLATE MOVEMENT
1. The strips of normal and reverse magnetic field helped the scientists to study the rate of
plate movement
2. Arctic ridge has the slowest rate less than 2.5 cm /year east pacific rise has more than
3. 15 cm/year
FORCES OF THE PLATE MOVEMENT
1. Surface of the earth is dynamic
2. Interior is always mobile
3. Beneath the lithosphere there is always movement of magma horizontally
4. Heated material rises to the top and cooled material sinks down
5. This cycle is repeated over time and form convection cells
SOURCES OF HEAT
A. Residual heat b. Radioactive decay
6. It was first considered by Arthur Holmes in 1930
7. Later it also influenced Harry Hess
MOVEMENT OF INDIAN PLATE
1. Indian plate includes India and Australia
2. Northern boundary is along the Himalayas
3. It is the place of continental convergence
4. In the east it extends up to the Rakinyoma mountains of Myanmar
5. Eastern margin is spreading site
6. Western margin extends along Kirthar mountains, Makran coast red sea rift.
7. The boundary between India and Antarctica is called a divergent boundary
8. Till 225 m y an India was separated by Tethys sea
9. About 200 m, India started its journey towards the north
10. India collided with Asia about 40-50 m and caused the upliftment of the Himalayas
11. About 140 m at the position of the Indian plate is at 50°s latitude
12. During the movement of the Indian plate two events occurred in India
13. A. outpouring of lava and formation of Deccan plateau
B. Subsidence of west coast
14. The Himalayas started rising about 40 m.