How Himalayas are formed. My second PPT. :)

1. Origin of Himalayas
Lavanya Topa
IX-A

2. The Himalayas
Himalayas are one of the complex mountain systems of the
world. They represent great variety of rock systems dating
back from Cambrian to Eocene periods and from granites
and gneisses to sandstones, limestone's, boulder
conglomerates and shale. At several places rocks have been
highly metamorphosed.
Intense folding has led to the formation of recumbent folds,
overturned folds and even napes. It is because of this
complex situation that scholars have given divergent
views regarding the origin of these mountains.

3. Origin of Himalayas
These views may be grouped under three categories:
(a) geosynclinals evolution
(b) plate tectonics
(c) vertical movements

4. Geosynclinals Evolution
Exponents of this opinion mainly base their deduction on the
sedimentary nature of the Himalayan rocks majority of which
have evidence of marine origin and contain fossils of marine
organisms. Even the enormous thickness of the Himalayan rocks
allows them to associate their deposition under the bed of sea
whose floor underwent sinking with the increasing weight of
the deposits.
The geosynclinals origin of the Himalayas has obtained maximum
approval from the scholars. The theories of Suess, Argand,
Kober etc. all belong to this category. According to geologists
the disintegration of Pangaea led to the formation of a long
Mediterranean sea (called Tethys) between the two land masses
of Angaral and (north) and Gondwanaland (south).

5. This sea was occupying the region of the Himalayas during the
Mesozoic era (180 my.) During the end of the Paleozoic era
and beginning of the Mesozoic era the Tethys almost
engirdled the whole earth running from Europe in the west
to China in the east. Eroded material from the two land
masses were deposited in the Tethys and could assume
considerable thickness due to the sinking nature of the bed
of the sea. During Cretaceous period the bed of the sea
started rising which led to the folding of three successive
ranges of the Himalayas.

6. The first upheaval, which led to the formation of the Greater
Himalaya, took place during Eocene period. Similarly second
upheaval during Miocene period folded the Lesser
Himalayas and third starting in Pliocene period ended with
the birth of the Siwalik Hills.

7. Tectonic Plates
According to the plate tectonics the rise of the Himalayas is
viewed as the outcome of the collision of the Indian plate with
its Asian counterpart. This has resulted into the seduction of the
northern margin of the Indian plate, crustal shortening, folding
of the upper silica material, pilling up of nappes and isostatic
recovery.
Following features of the Himalayas lend support to these views:
(i) Flysch occurs along the Indus-Tsangpo and Shyok-Kailash
zones,
(ii) (ii) The low angle MCT (Main Central Thrust) separates the
central crystal lines from the meta- sedimentaries which occur
below the thrust and are pre-Cambrian to lower Paleozoic in
age.

8. Then Tethyan marine sediments occur over the central crystallines,
(iii) the klippen and windows were also taken to support large-scale
thrusting,
(iv) The MBT (Main Boundary Thrust) separates the Pre-
Cambrian Mesozoic metamorphics and sediments from the
Tertiary deposits. Above facts suggest crustal shortening in the
Himalayas which followed crustal consumption at the edges
and the intercontinental collision along the Indus-Suture zone.

9. Vertical Movements
Those who advocate vertical movements responsible for the
upliftment of the Himalayas take support from the fact that
the gravitational force, the main force among the various
bodies in space, can act only radially inhibiting enormous
horizontal translocation implicit in plate tectonics.

10. Views on origin of Himalayas
Edward Suess: According to Suess the folding of the Himalayas has
been caused by the com- pressional forces which have worked from the
north and led to the folding of the detritus deposited in the bed of the
Tethys. In this process the land mass of Angara land lying north of the
Tethys acted as backland whereas Gondwanaland along the southern
margin of the Tethys behaved as foreland and remained stationary. Due
to the southward movement of Angaraland the Tethyan sediment was
compressed against the Peninsular mass yielding place to three
successive are like ranges from west to east owing to two extended
horns of the Peninsula (the Aravallis and Delhi ridge in the west and
Meghalaya plateau in the east).
The southward bend in the Himalayan ranges is cited as a strong
argument in support of this theory which has almost lost its tenability
in the light of recent studies on global plate tectonics.

11. Emile Argand-the Swiss geologist E. Argand expressed his views on
the origin of the land mass of Asia in a paper entitled 'La Tectonique
de 1 Asia' before the International Geological Congress at Brussels in
1922. According to this theory the northward movement of southern
ancient rigid masses (consisting of Indian Peninsula and Arabian
Peninsula) folded the Tethyn sediments against the northern rigid
masses (consisting of Angaraland, Chinese Massif, Sardian Massif
and Russian Platform) which gave birth to the Himalayas. The
theory, which was earlier vehemently criticized by the scholars, has
got new lease of life through plate tectonics.

12. Kober-Famous German geologist Kober has presented a detailed
and systematic description of the surface features of the earth in
his book 'Der Bau der Erde' in which he has tried to establish a
relationship between ancient rigid masses and orogen (mobile
zones or geosynclines).
Thus he has tried to explain the origin of mountains on the basis of
his geosynclinals theory. According to this theory Tethys
geosyneline occupied the present-day place of the Himalayas and
was bordered by Angaraland in the north and Gondwanaland in
the south both of which acted as foreland.
During the Eocene period both these rigid masses (kratogens)
started converging as a result of which folds were formed along
the northern and southern borders of the Tethys sediments
giving birth to the Kunlun mountains in the north and
Himalayas in the south.

13. Tibetan plateau as median mass between these two mountains
remained unaffected by the folding, although it was slightly
raised due to the intense nature of the compressional forces.
During the upheaval of the Himalayas a fore deep was formed
whose infilling led to the formation of the Ganga Plain.
Although Kober's views seem to be more logical but majority
of scholars believe in one sided movement.

14. S.G. Burrard- Burrard put forth his contraction theory regarding
the origin of the Himalayas in 1912. According to this theory
below the earth's surface there is layer which is cooling at a
slower rate. After cooling this layer contracts and is broken
apart.
This promotes contraction in the surface layer also and folding of
the Himalayas. The drifting of the broken parts produces
vacuum which is filled up by the fresh arrival of deposits by the
rivers.
The folding of one such deposit is responsible for the upheaval of
the Siwalik. Because this theory creates many difficulties in
respect of isostasy it has not received adequate approval from
the scholars.

15. Fox and Weddel-According to Fox and Weddle the rise of the
Himalayas is the outcome of two different processes. In one such
process the compression from the hinterland area of the Tibetan plateau
produces wrinkles along its southern border which denotes the position
of present Himalayas.
Under the second process agents of erosion start eroding these folds and
removal of huge quantity of eroded material produces deep valleys and
gorges. Thus in order to maintain is static balance erstwhile folds are
further uplifted giving present gigantic height to the peaks of the
Himalayas.
So according to this theory the main cause of towering height of the
Himalayan peaks are the deep valleys and gorges carved out by the
Himalayan Rivers. Fox and Weddel have cited the terraced valley of
the Zakar Chu River which is a tributary of the Arun River.

16. Heim-According to Heim gradual rise in the Himalayan region
is causing subsidence in the neighboring Ganga Plain. This
is the main cause of occurrence of earthquakes in these
areas.
E.H. Pascoe-Pascoe raises the question in relation to the
Himalayas that it is not clear whether folding caused uplift
or uplift caused folding. There is an apparent difficulty
brought to light by gravity surveys in India according to
which maximum density is found along the belt extending
through Orissa, Jabalpur and Sindh called 'Hidden Range'
which is not the lowest topographic belt in the country.

17. In 1932 Glennie tried to explain this apparent anomaly by crustal
upward. "The gradual rise of the Hidden Range would have
brought die tachylite nearer and nearer to the surface, until die
rigidity of die overlying granitic layer broke down the result
being die outpouring of die Deccan Trap. While die Hidden
Range was being formed, the Himalayan region was occupied by
the broad, shallow depression of the Tethys geosynclines.
The continued and excessive sinking of these geosynclines is
presumed to have caused crustal weakness and a rapid
depending and narrowing of dies trough. The sediments are
imagined to have been folded as result of this narrowing, and
the surplus sedimentary matter to have folded up above the
trough to produce dies Himalayan Chain." (E.H. Pascoe, 1964,
pp. 2107-2112.

18. Wager's suggestion that die uplift to the Himalayas may be
regarded as consequence of the erosion of the southern margin of
the Tibetan highland falls under is stays. This appears to be
proved by greater uplift in the east where the valleys and gorges
are cut deeper dean in die west.
In a recent study of is stays in the Himalayas Chugh and
Bhattacharji have found that "is ostasy is generally in existence
in the Himalayas." They noted the order of under compensation
in die Outer Himalayas as 10% and that of overcompensation in
the Ganga Plain as 40% which proves that erosion in die
mountains and deposition in the plains" tend to maintain is
static equilibrium in the region as a whole."

19. A. Holmes-the upheaval of the Himalayas may also be explained
by Holmes' Convection Current Theory. According to this theory
the final stage in sub-crustal thermal convection currents is a
period of waning currents by gradual uplift until is static
balance is achieved in the zone. This zone is marked by
sedimentation-subsidence in die initial stage.
This is followed by a relatively short duration of orogenic
compression and root formation. Uplift in this second stage is
prevented by the down-dragging power of subsiding currents.
Folding associated in later phase's wittier metamorphism causes
uplift and die formation of mountain belts.

20. "One of die most astonishing facts is that, while the original
cover is being removed by erosion or gravity sliding, die
granitic heart or core of a mountain range may continue to
rise until it is exposed in the flanking valleys, and
eventually at the summit itself.
Everest and some of the Himalayan neighbours are celebrated
examples of this culminating feature of mountain building".
Also the uplift precedes napes and giant napes with granite
and magmatic cores are related to gravitational exogenesis
(A. Holmes, 1965).