The close of the Mesozoic era was marked by the
outpouring of enormous lava flows which spread over vast
areas of Western, central and southern India. They issued
through long narrow fissures or cracks in the earths crust, from
a large magma basin and are therefore called fissure type
eruption. The rocks formed from the cooling of the lava are
called Deccan traps. The Deccan traps formation is the result
of tectonic disturbance connected with the formation of
Gondwanaland land. The lavas of Deccan traps has less
viscous and spread to form flat or terrace or plateau. Hence the
name Deccan traps. Deccan basalt appears massive, compact,
vesicular. The vesicles are formed as a result of the sudden
eruption on the surface due to the trapping of escaping gases.
The vesicles are later filled by secondary mineralizing
solutions and there by giving amygdaloidal basalt.
The area occupied by the Deccan traps is about 50000sq
kilometers including Bombay, Kathiawar, Kutch, Madya
Pradesh, Central India and parts of the Deccan. They are also
found in Belgaum in the South, Sirguja and Jashpur in the
North west. The present distribution shows that the traps may
have occupied some of the area intervening between the main
mass and the outlying patches, and that the original extent may
have been over 1.5 million sq kilometer including the segment
of unknown extent which has foundered in the Arabian sea to
the west of Bombay. The Deccan traps are thus the most
extensive geological formation of peninsular India. The lava
flows are occasionally as much as 15to 30m.
The maximum thickness attained by the Deccan traps, might
have been as much as 3000m along the coast of Bombay. The
thickness however rapidly become less further east and varies
much at different places. Towards the southern limit it is
between 600 to 800meter at Amarkantak, the eastern limit, the
thickness is 150meter while in Sind. In Kutch the traps are
about 800meter in thickness. The individual lava flows varies
from few feet to 36m. The bore hole at Bhusawal, 370m deep
revealed 29 flows. Although the flows enter generally
horizontal in their deposition, some are slightly inclined of
7. STRATIGRAPHIC POSITION ANDSTRATIGRAPHIC POSITION AND
Deccan traps overlies Archeans, Kalladgi group and Bhima
group unconformeambly along Southern margin. In Kutch
they overlies Jurassic rocks. In Narmada valley they overlie
the Bagh bed and near Jabalpur they overlie lameta bed. All
these rocks are called infratrappeans that is the rock live below
the traps. But this is more applicable to youngest among them
namely Bagh beds and lameta beds.
Upper trap(450m)-bombay and Kathiawar
Middle trap(1200m)-Central India and Malwa
Lower trap(150m)-central province and eastern areas.
The Deccan traps have been classified broadly into three
parts- upper, middle and lower with infratrappean beds or
lameta beds at their base.
The lower beds measuring of about 150m consist of number
of fossiliferous intertrappean layers of volcanic ash occur
rarely in association with lower flows.
The lower flows rests over lameta beds in M.P, bagh beds in
The upper flows are well developed characteristically in
Bombay, Kathaiwar and kutch. They are about 450m and
contain numerous ash beds and intertrappean beds
The trap is characterised by flat topped hills and step like
In amygdalular flows the top is usually highly vesicular, the
middle fairely compact and bottom showing cylindrical pipes
filled with secondary minerals.
Ash beds are seen in many parts of upper traps they are
brecciated structure, fragments of trap being found in a matrix
of fine grained material.
Columnar joints in the traps are seen in some places.
10. PETROLOGICAL CHARCTERPETROLOGICAL CHARCTER
First magma to erupt on a wider scale forming the
major part of the Deccan Traps was the Tholitic followed by
Rhyolit in fairly large proportion and the igneous activity
closed with the final eruptive phase of minor quantities of
the alkali olivine basalt magma. The common rock type is
basalt. Black or greenish black in colour, compact.
Sometimes exihibit vesicular or amygdaloidal structure. The
specific gravity varies from 2,9 to 3.1. It is generally
composed of Labrodorite Plagioclase Enstatite. Olivine and
titaniferous magnetite occur as accessory mineral. It
generally exihibit sub Ophilitic texture inter granular
texture is also noticed.
• Products of weathering
The Deccan Traps after weathering give rise to two
11. AGE OF DECCAN TRAPSAGE OF DECCAN TRAPS
The Deccan traps are volcanic in origin and therefore
entirely unfossiliferous. So the age of Deccan traps cannot be
accurately determined we have to determined intertrappeans
that is on the stratigraphic position. Luckily there is
fossiliferous intertrappean bed. So there is the problem of age
of Deccan trap. Generally the age is considered between upper
Cretaceous to Eocene. The age of Deccan trap is based on
stratigraphic and Palaeontological. Radiometric age of the
Deccan trap are also carried out by Washington(1964)on a few
specimens of Basalt flows from Bombay and Pavgada hills
gave 60-65MY and 42-45 respectively.
12. ECONOMIC IMPORTANCEECONOMIC IMPORTANCE
The basalt is widely used for building construction, rod
metals etc. The Gate way of India in Bombay harbours is
constructed with Trachytic rocks of Deccan traps. There are
several secondary minerals in the vesicles of Deccan basalt
such as Quartz, Amethyst, Augite, Chalcedony etc are used as
Gemstones. The cavities are store house of Zeolite minerals
which is used for ornamental purposes.
• Deccan trap is one of the important formation in Indian
• The lava erupted all along the fission crack in the surface of
the earth intermittently.
• It is the store house for many minerals like Zeolites, Augite,
Chalcedony, Amythyst,Quartz etc.
• The ore of Aluminium- Bauxite is formed by the weathering
• Geology of India and Burma-M.S.Krishna,6th
edition, (1982) page no.(405-421)
• Geology of India (volume1)-M.Ramakrishna
and R.Vaidyanathan.(2008) page no(80-96)
• Geology of India –D.N. Wadia 4th
(1987) page no.(275-287)
• Deccan volcanisms-K.V.Subbarao and
• Fundamentals and historical geology and
stratigraphy of India( 1982) 211-215