1. Review of Deccan Trap in Malwa Region
Priyanka Sahu
&
Mohammad Rizwan
School of Studies in Earth Science,
Vikram University, Ujjain (M.P.)

2. CONTENT Introduction Geology of Deccan trap Petrology of Deccan trap
Geochemistry of Deccan trap
Age controversy
Economic Importance
Conclusion

3. Introduction
The Deccan trap are large Igneous Province located on the Deccan plateau of west Central India. (Between 170 – 240 N and 730 – 740 E)
The term “Deccan Trap” was coined by W.H. Sykes in 1833 and it is derived from a Sanskrit word Dakshin meaning “South” or “Southern” and a Swedish word Trapp/Trappa meaning “Stair”. The term was aimed to describe the step like or terrace like topography peculiar to this terrain.
They consist of multiple layers of solidified flood basalt that together are more than 3000m thick and cover an area of 500,000 km2.
Based on the area of occurrence, the Deccan lavas have been further classified into four viz. Malwa Traps: occurring in Malwa region of M.P.; Mandla Traps: occurring in Mandla region of M.P.; Saurashtra Traps: occurring in Saurashtra region of Gujarat and Main Deccan plateau: occurring in state of Maharashtra, Karnataka and A.P.

4. The Malwa constituting the Deccan Trap volcanic province (Upper Cretaceous –Eocene). The Malwa region occupies a plateau in Western M.P and South-Eastern Rajasthan (between 21010’ N and E ) with Gujarat in the West . The region include the M.P district of Agar, Dewas, Dhar, Indore, Jhabua, Mandsaur, Neemuch, Rajgarh, Ratlam, Shajapur, Ujjain parts of Guna and Sehore and the Rajasthan district of Jhalawar and parts of Banswara and Pratapgarh. It is covered an area of 81,767 sq. km. and elevation of 500m.Ujjain region constituting the Malwa region. Ujjain District is situated in Madhya Pradesh and lies between longitude ’ to ’ and latitude ’ to 230 5’ and area lies the toposheet No. 45M/16 and 46M/12.

5. LOCATION MAP OF UJJAIN IN MALWA REGION

6. Stratigraphy of the Deccan Trap after blanford and medlicott (1879)
Nummulitics of Surat and Baroch; Eocene of Kutch laterite UNC Upper traps Bombay region and Saurashtra. Lava flows with numerous (450m) ash beds; Sedimentary inter-Trappean beds of Bombay with large no. of fossils Vertebrata & Molluscan shells. Middle traps Malwa & Central India. Lavas & ash bed forming the (1200m) thickest part of the series. No fossiliferrous Inter-trappean bed. Lower traps M.P., Narmada, Berar etc, lavas with few ash bed. (150m) Fossiliferrous inter-Trappean UNC Lameta or Infra-Trappean series; Bagh bed; Jabalpur beds and Older rocks.

7. Cross section of deccan plateau

8. Petrology of Deccan trap
“The Petrography and Petrogenesis of forty-eight flow of Deccan trap”, West (1958) has made a valuable contribution by proposing for the first time that parental magma of the whole Deccan Trap region was tholeiitic in composition. Chatterjee (1961, 1964) suggested that there was an association of alkali olivine -basalt parental magma along with the tholeiitic parental magma. In Petrological composition the Deccan basalt are singularly uniform. In lava sequence consists of individual flow which are distinguish textures - Aphyrics, Microphyrics and Porphyrictic (by phenocryst, plagioclase, pyroxene, Oligoclase) and by geomorphic expression (cuestas; hogbags; cliffs; deep valley etc). The most common rocks is a normal augite-basalt of mean sp.gr the rock persist, quite undifferentiated in composition, form one extremity of the Trap area to the other.

9. The only variation is in the color and texture of the rocks; the most prevalent color is a grayish – green tint, but a perfectly black color or lighter shades are not uncommon.
The texture varies from a homogeneous, cryptocrystalline, almost vitreous basalt, through all gradation of coarseness, to a coarsely crystalline dolerite.
Petrography of the Ujjain flows, There are six flow renowned:-
6th flow: Medium grained porphyritic flow.
5th flow: Glass rich medium grained porphyritic flow .
4th flow: Coarse grained porphyritic flow.
3rd flow: Fine grained opaque rich porphyritic flow.
2nd flow: Fine grained porphyritic texture .
1st flow: Medium grained opaque.

10. GEOLOGICAL MAP OF UJJAIN SHOWING DIFFERENT FLOWS
Source:Hari,K.R.1986

11. Figure Showing
Inter-Trapean bed, Dharambadla,Ujjain

12. Different flows showing different structure,Ujjain area
Fractural red boles spheroidal weathering in basalt
Columnar joint in basalt pentagonal structures in basalt

13. Geochemistry of Deccan Trap
In the Deccan traps, collected from widely scattered localities, have been chemically analyzed in the detail by H.S. Washington The most striking feature of these analysis is the uniformity of composition the majority of the basalt, with variation in silica from 48.6 to52 percent. This chemical constitution of the traps, expressed in terms of standard normative minerals calculated from the composition, gives the following result as the norm of the Deccan Traps.
Quartz
4.14
Orthoclase
4.45
Albite
22.01
Anorthite
23.07
Diopside
17.41
Hypersthene
17.78
Olivine --
Magnatite
4.64
Ilmenite
3.65
Apatite
1.01

14. On the basis of geochemisrty; the elements in the Deccan Trap are divided into –
Major elements
Trace elements
Rare Earth elements
Major elements (Sukheswala et al, 1958)
Trace elements
Rare Earth elements (Alexander, 1979)
SiO2 Sc Y
TiO2 V La
Al2O3 Cr Ce
Fe2O3 Co Pr
FeO Ni Nd
MnO Cu Sm
MgO Zn Eu
CaO Ba Gd
Na2O Sr Tb
K2O Zr Dy
P2O5 Nb Ho
Cr2O3 Er

15. Age controversy of Deccan Trap
The age of Deccan Trap formation have a considerable range in geological time scale
Different views expressed from time to time. The age of Deccan Trap are as follows on the basis of –
Formation lying under the Trap ( indirect method)
Invertebrate fossil assemblage
Evidence by vertebrate fossils
Evidence by plant fossil
Radiometric Dating

16. Radiometric Dating : Beside the early work of V. S. Dubey and P. N
Radiometric Dating : Beside the early work of V.S. Dubey and P.N. Sukeswala recently specimen of basalt and Rhyolite from Bombay and pavagarh where studied by Rama Rao by K and Ar method. The age range from m.y. and m.y. respectively. But very recently Dr. W Wellmon and M.W. Medthunon (1970) of the Geophysical department of Canberra in Australia made measurment of specimens from Hyderabad, pavagarh and Madagascar and they found that the major age range from 59 m.y. to 64 m.y. Summing up it may be stated that the available evidence shows that a good part of the Traps may have been erupted in early Eocene.
Area
Age
Rajahmundry
Cretaceous to Paleocene
M.P.
Upper Cretaceous
Narmada Valley
Middle Cretaceous to upper Cretaceous
Cutch
Jurassic to Cretaceous
Borhill in Sind
Near Hyderabad in Sind
Uppermost Cretaceous

17. Economics importance (1)The Deccan Traps rocks are used extensively as building stone . (2) Basalt rock used as road metal. (3) As aggregate in cement concrete. (4) Store house of gems stone.(agate, amethyst, quartz, carnelian, onyx and other varieties of chalcedony which are used as semi-precious stones). (5) The Black soil formed over the Deccan trap is a rich soil particularly suitable for raising cotton. (6) The Traps are often capped by ferruginous and aluminous laterite. (7) It is rich enough in alumina to be high grade bauxite. Bauxite is useful in Petroleum filtration and in the manufacture of aluminium and alumina cements. (8) The vesicular parts of bedded lavas make good aquifers and yield fair supplies of underground water.

18. Thank You