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FIELD REPORT FOR GEOLOGICAL EXCURSION TO

DECCAN TRAPS, PUNE,

INDIA

PURUSHOTTAM GUPTA

INT .MSC . EARTH SCIENCE

6 SEMESTER

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ACKNOWLEDGEMENTS

I would like to thank Prof. M.Jayananda & Prof. G.V.R. Prasad

for giving us the opportunity to work on Deccan Basalts during

this field trip.

I would also like to thank Dr.Raymond Duraiswami & all the

faculty of Geology Department,Pune University for guiding us

in the field .

I would also like to thank our classmates for their valuable

contribution and help in preparing this report.

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INTRODUCTION

Global distribution of large igneous provinces (shown in black)

The beginning and the end of the Cretaceous period in India witnessed

voluminous outpouring of lavas and stupendous volcanic explosions. In the early

Lower Cretaceous (114-118 Ma), nearly 20,000 km² area of eastern India

embracing the Rajmahal Hills in Jharkhand and the Sylhat region in Meghalaya

was affected by volcanism. Towards the close of the Cretaceous (61 to 69 Ma),

more than 500,000 km² land in western and central India was inundated by

extensive floods of lavas. The eastern theatre of volcanism is known as the

Rajmahal Volcanic Province and the western domain as the Deccan Volcanic

Province . The Deccan Volcanism was preceded by eruption of lavas 91-95 Ma ago

in offshore north-western Karnataka, giving rise to the Saint Mary's Islands. In the

Rajmahal Volcanic Province the lava pile was nearly 244 m thick, while the lava

succession is more than 2,500 m in the Nasik district in Maharashtra in the Deccan

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Volcanic Province.

The Deccan lavas are believed to have flowed 100-300 km from their sources

along the Western Ghats and in the Narmada Valley, before they froze to form

stepped plateaus. Evidently, the lavas must have been very mobile and, therefore,

spread far and wide, overcoming topographic impediments, filling depressions

and valleys, damming rivers and streams, and burying forests and grasslands. The

result of the lava floods was the evolution of flat-topped plateaus, with step-like

landform called the Deccan Traps. The Deccan Volcanic Province covers

Maharashtra and adjoining regions in Gujarat, Madhya Pradesh, Andhra Pradesh,

and Karnataka.

One among the most remarkable volcanic provinces on earth, the Deccan

Volcanic Province (DVP) is a very prominent terrane of the Indian subcontinent.

The name Deccan Traps was given by E. Vrendenburg, 1908. Outcrops of the DVP

in distant Rajahmundry in Andhra Pradesh and in Kachchh and Saurashtra in

Gujarat indicate that the extent of the DVP was much larger in the past. Offshore

drilling west of the Konkan Coast revealed subsurface extension of the Deccan

lavas in the Arabian Sea. In some places the top of the larva lie nearly 1,500 m

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below the sea level, pointing to the foundering by faulting of the western part of

the DVP.

Nature of Deccan Lavas

The bulk of the Deccan lavas are tholeiite basalts of simple type. In addition to

basalts, the other rock types of the DVP are alkali basalts (basanite and picrite).

nephelinites, carbonatites and rhyolites. occuring in minor amounts in the rifted

western margin of the domain and in the Narmada Valley. In the Sahyadri Range

the lava buildup comprises dominant pahoehoe flow fields. These are aggregates

of many flow lobes, each of which grew by thickening through injection of melt

under solidified crust .

Thin irregular flows with ropy surfaces dipping in different directions, and piled up

into chaotic masses, are quite common in western Maharashtra .The Bor Ghat

section along the Pune-Mumbai tract provides a portrait of the variable

morphology, structure and texture — thick extensive flows of compact basalt,

tabular flows of amygdaloidal basalt, thin irregular flows of amygdaloidal basalts,

and thin irregular flows of vesicular basalt .It seems that in the early stage, viscous

lavas erupted in small quantities, and later there was fissure eruption in the

Mumbai-Pune region. East of Pune near Daund, a hummocky flow with toes,

lobes toccatas and lava tubes characterize are terminal part of the Thakurvadi

Formation. (Valdiya,2010}

Lavas of CFB

• Lithosphere is below continents

• Continents have refractory roots

• In super plume events,continents fragment.Thus,CFB can be formed by plume impacts or

astroroid impact.

• DVP lavas are enriched .Higher incompatible elements.

• Higher LREE & Lower HREE indicated it is not depleted.

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Lithostratigraphy — Magnetostratigraphy

On the basis of detailed studies in the Mahabaleshwar-Nasik region in

Maharashtra, involving interpretation of measured sections,

palaeomagnetism, analyses of major and trace elements in rocks, and

determination of isotopic ratios of rare earths and strontium, a

standard stratigraphy of the DVP has been established .The DVP lava

succession is divisible into four subgroups comprising fifteen

formations, each distinctive in its chemical types. The younger

formations have wider spread - the Poladpur Formation lavas extending

800 km northwestwards to Gujarat and northwards to Madhya

Pradesh, and the Mahabaleshwar lavas reaching as far south as Belgam

in Karnataka. It may be stressed that the lava flows are not continuous -

there is pinching and swelling along their spread. There is also

southward overstepping of successive units such as the Bushe

Formation tapering out near Lonilind, and the Khandala Formation

resting directly under the Poladpur. The upper Wai Subgroup makes up

the entire southern part of the DPV, overstepping all older formation

southwards, the Mahabaleshwar Formation overstepping the

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Precambrian rocks of Belgam, and so on.{Valdiya,2010}

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COMMON TERMS & TERMINOLOGIES

Simplified definition of lava types and their morphology. Note that all the sketches are along the

longitudinal section

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Distribution of predominantly pahoehoe /compound and a`a/ simple flows in the Deccan Volcanic

Province

Compound lava flows, defined as those lavas which are divisible into flow. units,

commonly have a shield-like form and are thought to develop when the rate of extrusion

of lava is relatively low.

Simple lava flows, defined as those lavas which are not divisible into flow-units, are

thought to form when the rate of extrusion of lava is relatively high.

• All information in points is from field notes.

• All information in paragraphs & sketches are from various research journals.

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THE FIELD

Our field trip was mostly centered around the city of Pune within a radius of 100 km .The weather was

sunny ,clear & comparatively hot with temperatures reaching upto 30°C from 12 December 2012 to 15

December 2012

Day 1

Diveghat

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Compound pahoehoe flow with predominant vesicles (left bottom) .Field sketch of compound pahoehoe flow unit

(right top) . Sketch of part of a flow lobe at DiveGhat (right bottom). A,B, C, and D refer to the crust, zone of elongated

vesicles, jointed core, and segregation veins respectively.

• Zeolite minerals like Stilbite & green earth also found. Horizontal vesicle banding seen

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A few metre away a dike was recorded.

Chilled margin (left) & dike offshoot (above)

Dike is easily identifiable from difference in colour &

differential jointing pattern from rest of the rock body.

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Diveghat Site 2

Bushe formation. Hummocky flows

• Exposed Bushe Fm show hummocks & spheroidal weathering.Flow direction is towards NWW

Photograph & Field sketch of flow lobes exposed along the road cut in Diveghat Note the termination of lobe 2 against lobe 4. Only the upper crust of lobe 4 is exposed, while the basal crust, crudely jointed and spheroidally weathered core, and part of upper crust of lobe 1 are exposed.

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Diveghat Site-3

Columnar jointing seen(not very prominent).Poladpur Fm.Typical colonnade/ entablature

structures seen.Simple flows have lots of columns.Some plumose jointing also seen.

Simple flows in the DVP generally can exhibit well-developed jointing patterns. These patterns are

generally persistent laterally and are referred to as colonnade and entablature .Entablature refers to

0.30- to 0.50-m- thick, irregular columns that occur in the upper portions of flows. They commonly

deviate from a perpendicular orientation and may form radiating patterns. In certain flows, two or

more levels of entablature are seen, usually separated by platy joints .Well-developed colonnade

structures are usually seen in the lower portions of most simple flows. Columns are commonly

perpendicular to the base of the flow and their width ranges from 0.50 to 2.0 m. An upper

colonnadezone is also present in some flows. The entablature is often glassy and sometimes shows

horizontal vesicular zones. In other flows, no clear distinction between the colonnade and

entablature can be made, and the entire flow shows highly irregular jointing and a fine texture. Good

examples of entablature and colonnade structures are seen at southern parts of the Western

Ghats(Katraj Ghat, Dive Ghat, Mahabaleshwar, etc.)(Bondre et al,2004)

Photograph & Field sketch of a simple flow exposed in

Dive Ghat .A refers to the entablature, a zone of

randomly oriented jointing that imparts a chaotic

appearance to the zone.

B refers to the colonnade, characterized by more regular

columnar joints.

Entablature is probably the result of cooling caused by

fresh lava being covered by water. The flood basalts

probably damned rivers. When the rivers returned the

water seeped down the cracks in the cooling lava and

caused rapid cooling from the surface downward. The

division of colonnade and entablature is the result of

slow cooling from the base upward and rapid cooling

from the top downward.

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Diveghat

Site-4(site-3 + 200m)

Flow top breccias of compound flow seen.Bunline & crust also seen (red)

Sketch of small, bun-shaped pahoehoe lobes exposed along road cut

Angular rubble blocks occurring near the upper surface of

a typical a`a flow exposed in Diveghat area, Pune district

Photo courtesy-G.S.I.

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Purandar Fort

Site-5

Purandar is about 40kms south-east of Pune.

Perched on a gigantic mountain mass, its

height above sea-level is 1398 metres and

about 700 metres above the plain at its foot.

To an unaided eye, the lava flow is usually light to dark grey, fine to medium grained rock with aphyric

(without identifiable minerals) to phyric (with identifiable minerals/phenocrysts) texture. Sometimes the

rock contains crystals (mainly plagioclase feldspar-an aluminosilicate) as large as 2cm or even more and

is called a "megacrystic basalt" or "Giant Plagioclase Basalt (GPB)".

The lowest sub-group, the Kalsubai, contains a number of horizons of lavas with abundant, large tabular plagioclase crystals termed megacrysts: these are the GPBs . Individual GPB flows are 5^10m thick and occur at distinct horizons within the eruptive sequence. GPB flows were mostly sampled in road cuts and quarries, where the flows are relatively well exposed .At these locations it is clear that the GPBs are not homogeneous, but are composed of at least two magmatic components.one aphyric or sparsely phyric and another rich in plagioclase megacrysts The GPB lavas consist of plagioclase megacrysts in a finegrained matrix. The plagioclase megacrysts are 2-50mm long.( Higgins & chandrasekharam,2007)

(Clockwise from above left)Variations in the

plagioclase megacryst content within a single

GPB flow. The field of view is 40 cm.Field

photographs.Photomicrograph of the GPB flow

showing plagioclase laths.

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Model for the formation of Giant Plagioclase Basalt flows, Deccan.(Higgins & chandrashekharam,2007)

A possible history is as follows. (1) Plagioclase megacrysts crystallize in a convecting magma chamber just below the

lava pile. (2) Currents sweep the crystals to the top of the chamber, where they accumulate as a result of their

buoyancy.The crystals coarsen in response to the continuous supply of hot magma.(3) New magma sweeps through

the plagioclase mush, mingles and mixes, then erupts to form the GPBs.

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• GPB of deccan are used as Lithostratigraphy markers between bushe & poladpur

fm.(Kalsubai(U) & Wai(L) supergroup)

• 4 places in Deccan GPb are foundM1-Jowar,M2-bhimashankar,M3-Lonavala,M4-Purandar

manchar fm.Thus they are an indication of four times magma chamber replenishment.

SITE-6 (EN RO UT E PUR AN DA R) Columnar Jointing

Columnar jointing results when basalt or (other igneous rocks) cools from the outside in causing shrinkage and the development hexagonal joint structure.

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Day 2 (13.12.12)

SITE-1 SUS ROAD 1 8 .3 2 N ,7 3 .4 6 E • Mid point between Wai & Kalsubai Fm.

• Lava toe-endogenous lava growth

• No new visco-elastic thrust

• Toe inflates to lobe

• Lobes coalace to form larger lobes(sheet lobes)

• Both hummocky & sheet pahoehoe seen.

(Clockwise from top)Road cut section.

Generalized sketch of flow lobes.

Sketch of a lobe exposed

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• Massive flow has dixitaxitic texture & fine gas cavity.

• Vesicles merge at the central crack

• Lots of Zeolite minerals seen as last phase in hydrothermal activity mainly

okenite,stilbite,scolocite

A large vesicle hosting a

variety of secondary/ cavity

minerals

Blue cavenzite and heulandite,Green apophylite & stilbite. Photo courtesy-G.S.I.

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SITE-2 KATRAJ GHAT 1 8 .2 6 N ,7 3 .5 1 E • Edge of shield (volcano)

• End of Bushe Fm.

• Dyke seen.Age is 59±5 My Ar/Ar

• Younger than Bushe

• No direct feeder relation

• N5° strike.Parallel to west coast.

• Sharp,jointed ,crenulated margin

• In magmatic plumbing system,if outflow is not continous ,lava falls back as seen here.

(Clockwise from above)Margin offset & lava falling back seen.

Dyke intruding(dolerite) the previous flow.(In Magnification) Chilled,sharp & jointed margin.

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SITE-3 AMBEGAON 18 .2 5N,73.50 E (+26 Km. site2)

• Flood lava fills depression.Lava is stagnated in pool & ponded

• Convective current cause recling of the crust.

• Based on analogy of Hawaiian lava lakes.

• Features formed due to the sinking of the flow-top breccias crusts into these flows’ molten

interiors

Thick flood basalt lava flows cool conductively inward from their tops and bases, usually developing

columnar jointing. Although relatively rapid cooling in such flows due to meteoric water circulation has

been previously demonstrated, mixing of the surface crust with the interior – as observed in active lava

lakes – has not been shown. The breccia-cored rosettes described are restricted to the “simple” flows from

this province, which tend to be single cooling units of greater spatial dimensions than typical pahoehoe

lobes constituting the compound pahoehoe flows . Several simple flows are characterized as rubbly

pahoehoe i.e.,flows with extensively brecciated flow-top crusts.(Sheth et al,2011)

• Differential shear lead to platy joint like structure

Differential shear Cooling columns

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SITE-4 LONAVALA 18 .4 1N,73 .2 3E

We are

looking

here.

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SITE-5

• Transitional flowtop breccias

• Flow banding seen.Kinkery type

• Tooth paste lava(A transitional type of lava that develops within flow fields when

the lava has cooled sufficiently to have a high viscosity and when the flow is

advancing slowly.)

• Anisotropy of magnetic susceptibility

Toothpaste lava, an important basalt structural type which illustrates the transition from

pahoehoe to aa,. Its transitional features stem from a viscosity higher than that of

pahoehoe and a rate of flow slower than that of aa. Viscosity can be quantified by the

limited settling of olivine phenocrysts and rate of flow by field observations related to the

low-angle slope on which the lava flowed.(Rowland & walker ,1987)

Characteristic features of

toothpaste lava. Direction of flow

is left to right. Arrows

approximately I, 0.5, and 0.01 m

long in a, b, and c, respectively. a

Toothpaste tongue issuing from

curved bocca. S I-S2, lateral shear

zone evidenced by imbricate

shearing and clinker. Note how

longitudinal lineations maintain

same spacing along length of

tongue. b Cut-away view showing

pulse buckles (Pb) and pulse flaps

(PjJ, features of discontinuous

extrusion. Note how vesicles

deformed because crust was

retarded relative to underlying

lava. c Close up showing spines

pointing back toward

bocca.(Top)Field image.

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In Hawaii, this transitional morphological type is found at greater distance from the vent and has a rough,

hackly crust that deforms into broken plates or ropy folds. In case of toothpaste lava, the ‘ridges’ are

formed perpendicular to the flow direction and the surface grooves and striations on the surface are

parallel to the flow direction.. Moreover, it is not clear as to how an extremely viscous lava type like

toothpaste lava (viscosity: 6000–12,000 Pas) could be generated locally in a predominantly pahoehoe

flow.(Duraiswami,2009)

DAY-3 (14.12.12)

SITE-1 BHADGAON TO SUPE 1 8.25N ,7 4.1 9E

(120 KM FROM PUNE)

• Eastern Bushe(terminal)

• Pahoehoe to aa conversion

• Pipe vesicles along with breccias seen.

• Chemically the fm. is Bushebut physically transformed

• Flow correlation after 120km

• Rubbly pahoehoe

• Hulendite zone(Ca,Mg Zeolite)

The pahoehoe flow exposed in the Morgaon area probably represents the terminal parts of a larger flow

field belonging to the Bushe Formation16. It is envisaged that the lavas belonging to the Bushe Formation

could have erupted close to the crest line of the Western Ghats near Lonavala and the lavas could have

travelled eastwards to the extent of >140 km through a complex network of interconnected lobes

constituting distinct flow-fields. The earlier extent of the Bushe Formation was mapped as ending a short

distance east of Pune city.However, the present investigation and presence of pahoehoe east of Daund and

near Indapur, could indicate that the Bushe Formation could be more extensive than previously mapped.

The presence of evidence of a lava lobe preserving the evidence of pulsed inflation in the terminal parts of

the hummocky flow is significant. Based on this evidence it can be concluded that pulsed inflation could

be a phenomenon common in the terminal parts of some of the hummocky pahoehoe flows from the

Deccan Trap and can account for some of the intriguing geometry in the pahoehoe

flows.(Duraiswami,2009)

• Museum quality mineral samples found

here.

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SITE-2 KUKDI RIVER

SECTION 1 8 .1 6 N ,7 4 .1 8 E

• Ash beds from Java(Toba

caldera)

• Highly reworked by local

people

Rhyolitic tephra predating late

Pleistocene (26,000–12,000 yr B.P.)

alluvium was recognized in

Quaternary sediments of the Son

Valley, north-central India in and later

identified as having been derived from

Toba, northern Sumatra The Toba ash

occurs extensively in the Indian subcontinent and marks a ca. 74,000-yr-old event. In the Bay of

Bengal and Indian Ocean it is about 10 cm thick, whereas in several alluvial basins, it is usually

1-3 m thick. The latter occurs in a partly reworked state but as nearly chemically pure first-cycle

sediments, The ash has a broad northwesterly dispersal pattern. Samples of ash from the Indian

subcontinent compare closely with the Youngest (74,000 yr B.P.) Toba Tuff and the deep-sea

Toba ash in bulk chemical composition, REE signature, and bubble-wall shard morphology.

However, a more proximally located and thicker (2-5 m) ash-bed, from the alluvial basins in the

gneissic area and close to east coast, has a lower magnitude negative Eu anomaly, possibly

because of minor contamination by feldspathic silt. Quarternary sediments in the central

Narmada and middle Son basins contain rich late and middle Pleistocene mammalian and

cultural records. Based on the presence of the ash layer marker and stratigraphic relations, late

Pleistocene sediments within the subcontinent can be correlated with those from central India

and the deep sea. (Acharyya and Basu,1993)

Middle Palaeolithic archaeological assemblages at Jwalapuram in Kurnool district, Andhra

Pradesh, associated with 2.55 in thick layer of volcanic ash with glass shards representing the 74

ka BP Youngest Toba Tuff, indicate that humans were present in the Indian continent . The

Stone Age people must have braved the rains of volcanic dust that fell in Maharashtra, adjoining

Andhra Pradesh and in the Narmada and Son valleys in Madhya Pradesh.(Valdiya,2010)

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SITE-3 JEJURI 1 8 .1 6 N,7 4 .0 8 E

• Debris flow of alluvial formed under

gravity

• Unconformity b/w Deccan &

Quaternary.

• Metrionic diagenesis

• Nodular & concretionary calcrete

• Cementation by percolation

• Near source

SITE-4 • 16,500±500 yr bp

• Upper Pleistocene

• Mud flow overlain by

water deposit.

• Sheet flood deposit

Gastropod shells

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DAY-4 (15.12.12)

SITE-1 SHIRVAL 1 8 .0 5 N,7 3 .3 9 E

• Ambenali flow

• 1-2 metre thick flow top breccias seen with massive

core.

• Crust occurs as enclaves within cores.

• Rosette pattern seen

• Flow bottom breccias also seen

• No time gap.

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general road cut section

SITE-2 MAHABALESHWAR 1 7 .5 8 N ,7 3 .3 8 E

ARTHUR SEAT • Savitri river section

• Poladpur to ambenali transition 600m

• Ambenali to mahabaleshwar transition 800m

• Only place in the world showing triangular facets with flat topped mountain together.

Flow top breccia

Flow bottom

breccia

Rosette

cooling

pattern

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Triangular peaks to the left & flat topped mountains to the right.

• Formed due to post collisional stress buildup.

SITE-3 LATERITE DEPOSITS • Residual deposits formed in hot,

humid, climate containing lots of

vegetation, high temperature &

precipitation.

• Chemical alterarion of basalts.

• The decay of plant products

producec weak acids,which

cause alteration of primary

minerals.

• Alkalis are first to move in

solution

• Iron,TiO2 is left

• Reworked laterite is duricrust

• Oldest laterite is of Jurassic age

in India.

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Typical textbook illustration of a laterite profile . Rock structure is usually preserved in the pallid and mottled zones indicating that these zones consist of weathered rock in situ with no volume alteration.

In the Deccan region of western India ferricrete duricrusts, usually described as laterites, cap some basalt summits east of the Western Ghats escarpment, basalts of the low-lying Konkan Plain to its west, as well as some sizeable isolated basalt plateaus rising from the Plain. The duricrusts are iron-cemented saprolite with vermiform hollows, but apart from that have

little in common with the common descriptions of laterite. The classical laterite profile is not present. In particular there are no pisolitic concretions, no or minimal development of concretionary crust, and the pallid zone, commonly assumed to be typical of laterites, is absent. A relatively thin, non-indurated saprolite usually lies between the duricrust and fresh basalt. The duricrust resembles the classical laterite of Angadippuram in Kerala (southwestern India), but is much harder. The High Deccan duricrusts capping the basalt summits in the Western Ghats have been interpreted as residuals from a continuous (but now largely destroyed) laterite blanket that represents in situ transformation of the uppermost lavas, and thereby as marking

the original top of the lava pile.(Ollier and Sheth,2008)

• In India ,near sea-level laterites have age of 20 my & far from sea have age of 30-40 my

• Help in drainage pattern origin.

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REFERENCES 1. Acharyya, S. K., and Basu, P. K. (1993). Toba ash on the Indian subcontinent and its implications

for correlation of late Pleistocene alluvium.Quaternary Research , 10–19.

2. Bondre N R, Duraiswami R A and Dole G 2004 Morphology and emplacement of flows from the

Deccan volcanic province, India; Bull. Volcanol.

3. Bondre N R, Duraiswami R A, Dole G, Phadnis V M and Kale V S 2000 Inflated pahoehoe lavas

from the Sangamner area of the western Deccan volcanic province; Curr. Sci.1004-1007

4. Bondre N R, Duraiswami R A and Dole G 2004a Morphology and emplacement of flows from

the Deccan volcanic province, India; Bull. Volcanol. 29-45

5. Bondre N R, Duraiswami R A and Dole G 2004b A brief comparison of lava flows from the

Deccan volcanic province and the Columbia-Oregon Plateau flood basalts: Implications for

models of flood basalt emplacement. In: Magmatism in India through Time (eds) H C Sheth and

K Pande; Proc. Ind. Acad. Sci. (Earth Planet. Sci.) 113 pp 809-817

6. Duraiswami R A, Dole G and Bondre N R 2003 Slabby pahoehoe from the western Deccan

volcanic province: Evidence for incipient pahoehoe-aa transitions; J. Volcanol. Geotherm. Res.

121 195-217

7. Duraiswami R A ,2009 Pulsed inflation in the hummocky lava flow near Morgaon,

western Deccan Volcanic Province and its significance Curr Sci.

8. Higgins MD, Chandrasekharam D (2007) Nature of Sub-volcanic magma chambers, Deccan

Province, India: evidence from quantitative textural analysis of plagioclase megacrysts in the

giant plagioclase Basalts. J Petrol 48:885–900

9. Ghosh Biswajit, 2011Giant Plagioclase Basalt from Northern Part of Jhabua District, Madhya

Pradesh,Central India. Topics in Igneous Petrology: A Tribute to Professor Mihir K. Bose.

10. Sheth, H. C., Ray, J. S., Senthil Kumar, P., Duraiswami, R. A.,Chatterjee, R. N., Gurav, T., 2011

Recycling of flow-top breccia crusts into molten interiors of flood basalt lava flows: Field and

geochemical evidence from the Deccan Traps. In: Ray, J., Sen, G., Ghosh, B. (Editors), Topics in

Igneous Petrology, pp.161-180. Springer.

11. Valdiya,K.S.,2010,Making of India: A Geodyanamical Evolution

12. http://www.portal.gsi.gov.in/portal/page?_pageid=127,689645&_dad=portal&_schema=PORTAL

13. Rowland SK, Walker GPL (1987) Toothpaste lava: characteristics and origin of a lava

structural type transtional between pahoehoe and aa. Bull Vocanol 49:631–641

14. Ollier C D, Sheth H C 2008The High Deccan duricrusts of India and their significance for

the ‘laterite’ issue