DECCAN TRAPSDECCAN TRAPS

CONTENTSCONTENTS• INTRODUCTION

• DISTRIBUTION

• THICKNESS

• STRATIGRAPHIC POSITION

• CLASSIFICATION

• STRUCTURE

• PETROLOGICAL CHARACTER

• AGE OF DECCAN TRAPS

• ECONOMIC IMPORTANCE

• CONCLUSION

• REFERENCE

INTRODUCTIONINTRODUCTION

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.

• Distribution of Deccan Traps in India

DISTRIBUTIONDISTRIBUTION

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.

THICKNESSTHICKNESS

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 around 20.

STRATIGRAPHIC POSITION AND STRATIGRAPHIC POSITION AND CLASSIFICATIONCLASSIFICATION

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.

CLASSIFICATIONCLASSIFICATION

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 Narmada.

The upper flows are well developed characteristically in Bombay, Kathaiwar and kutch. They are about 450m and contain numerous ash beds and intertrappean beds

STRUCTURESTRUCTURE The trap is characterised by flat topped hills and step like

terraces.

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.

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 residual deposits they are Laterite and Black cotton soil.

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.

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 traps – step like terraces

Columnar basaltColumnar basalt

• DECCAN TRAPS

CONCLUSIONCONCLUSION

• Deccan trap is one of the important formation in Indian stratigraphy.

• 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 of Basalt.

REFERENCESREFERENCES• Geology of India and Burma-M.S.Krishna,6 th

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 edition (1987) page no.(275-287)

• Deccan volcanisms-K.V.Subbarao and R.N.Sukeheswala editted.

• Fundamentals and historical geology and stratigraphy of India( 1982) 211-215

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