Dive Ghat

LAVA FLOW MAPPING LOCAL FIELD WORK REPORT

Submitted by;

Yatindra Dutt

M.Sc. - I Sem.(Batch: 2009-2011)

Department of Geology

Submitted to;

Prof. N. K. karmalkar

Head,

Department of Geology

The student of science lives in a world of fragments. Nothing in that

vast array of visible things that we call Nature appears to our restricted

vision as a complete picture. True Artist that He is, the Creator never

reveals the whole of His design at once. Like a child with a jigsaw

puzzle we try to piece together the fragments of the picture…

Prof. Birbal Sahni, 1940

Certificate

This is to certify that Mr.. Yatindra Dutt has

participated and successfully completed the field

work at Diveghat on 7th October 2009 as a part

of syllabus of M.Sc.1stsem.,- led by the

Department of Geology, University of Pune, for

the academic year 2009-10.

Teachers in charge:-

Prof. N. R. Karmalkar

{1} Dr. Aditi Mookherjee Head,

Dept. Of. Geology,

{2}Dr. Milind.A.Herlekar University of Pune

CONTENTS

Certificate

Contents

1. Acknowledgment………………………………………………………….

2. Aim………………………………………………………………………..

3. Location……………………………………………………………………

4. Physiography of the Diveghat area………………………………………..

5. Field features of basaltic flows…………………………………………….

6. Regional stratigraphy………………………………………………………

a) Lithostratigraphy………………………………………………..

b) Chemostrtigraphy……………………………………………….

7. Deccan traps province of Western and Central India………………………

8. Map of the study area………………………………………………………

9. Previous Works……………………………………………………………

10. Description of traverse…………………………………………………….

11. Lithosection of Deccan Basaltic Flow in Diveghat ……………………….

12. Conclusion…………………………………………………………………

13. References…………………………………………………………………

ACKNOWLEDGEMENT

At the first instant I would like to acknowledge deep sense of gratitude to

the Ex-Head of Department, Prof. N. J. Pawar for his encouraging guidance &

suggestion for the field work and providing the requisite instrument facilities.

I would also like to thank the teaching faculty of the department, Dr. Aditi

Mookherjee, Dr. Milind Herlaker, for their company during field work as well as

valuable guidance in field and during writing this report.

I would like to specially thank all my classmates and senior students for

helping me in discussions as well as in making the report.

Name:

Class:

AIM

To know the basic procedures of orientation of toposheet in the field and to locate ones

position of field on the toposheet.

To identify and describe the different types of lava flow.

To record the readings of the features at different localities.

To observe the megascopic characteristics of rock samples.

To plot these observations on enlarged to toposheet and to prepare traverse geological

map.

To learn the use of Brounton compass and GPS instrument on the field.

LOCATION

Diveghat:-

Diveghat is located in the SSE direction of Pune city. It is accessible by the

Pune – Baramati road via Hadapasar. It is about 18 km from Pune city. It is included

in Survey of India toposheet no.47F/15 and 47 J/3, on the 1:25000 scale. It marks the

area between the latitude N 18° 24

’ 13

’’ and 18

° 24

’ 50

’’ and Longitude E 73

° 59

’ 22

’’

and 74° 00

’ 05

’’

PHYSIOGRAPHY OF DIVEGHAT AREA

It is part of a hill ranges which trends east-west. It has a maximum elevation

of 980 mts and minimum elevation of 640 mts. It is marked by a steep slope on its

Northern side, which also can be inferred from the closely spaced contours on

toposheet. While on its Small part it attains a plateau nature and hence shows

widening of contours. This hill range acts as a drainage divide between the drainage

basins of both the sides.

Drainage pattern on both sides is dominantly dendritic in nature. A water

body called Mastani Lake is present on the valley side of Diveghat, is one of the

historical sites in the study area.

FIELD FEATURES OF BASALTIC FLOWS

Terminology:

In field mapping of the Deccan Traps, several terminologies are in common

use. Lava flow refers to the product of a simple eruptive event. Lava flows are built of

flow units called lobes. Small lobes are called toes.

Lava flows are primarily of two types

1. AA

2. Pahoehoe

IDENTIFICATION OF TYPES OF FLOWS IN DECCAN TRAPS:

AA LAVA FLOWS:

This is a Hawaiian term meaning ‘stony with

rough lava’ or ‘to burn or blaze’. It is basaltic

lava, broken lava blocks called Clinkers. It

possesses an autobrecciated flow at the top and a

base. A loose broken shiny, sharp surface is

formed. This is due to the cooling of the upper

surface as the lava moves quickly. This clinkery

surface covers a massive dense core. The core is

the active part of the flow. As the lava moves

down slope the clinkers are carried along at

surface. At leading edges however these cooled

fragment tumble down the steep front and over

buried by the advanced flow. Thus, learning a

bottom and the top clinkery crust. Some crustal

clinker is seen to have entrained in the dense

core. The vesicularity of Aa flow is about 5-20% and they are angular in nature. This type of

flow may also show columnar joints and entablature structure. Necklace joints also

distinctive of the dense core of the Aa flow. Red boles or red horizons are most of the times

associated with such flows.

PAHOEHOE LAWAS:

Pahoehoe is also a Hawaiian term meaning ‘smooth or unbroken’. It is basaltic lava that

has a smooth, billowing, undulating or ropy surface. The ropy surface is due to movement of

very fluid lava under a congealing surface crust. It typically advances as a series of small

lobes and toes that continually break out from cooled crust.

In a section it shows a lower and an upper vesicular zone. The Lower vesicular

zone (LVZ) is considerably thinner than the upper. The base of this LVZ is characterized by

a chilled margin. This forms due to the burning effect of the top part of the cooled lower

flow by the overlying layer, which is in a molten state. The LVZ shows about 10 to 30%

vesicles. They are mostly rounded in shape.

Bole horizon

Top: Fragmentary breccia (Vesicle-rich)

Basal: clinkeryand vesicular

Middle: (Vesicle poor)

Columnerjointed

Aa flow

This part is followed by an area having minimum number of vesicles (about 0 to 5 %)

called as the dense core. It is the thickest part of the flow. This zone shows some internal

differential structures like the vesicle Cylinders, & Horizontal vesicle sheets.

Above this dense

core lies the Upper Vesicular Zone

(UVZ). It has about 15 – 20 %

vesicles. It may show pipe

amygdaloidal structure along with

ropy structures. Platy joints may

be seen on the top part. Along

with these inflection cleft fills or

squeeze ups are distinctively seen

only in pahoehoe flows. This

crust may be filled by lava of the

same lobe or its next overlying

lobes. In such a case they are

defined as Compound flow lobes.

Transformation of pahoehoe to aa flows is evidenced by slabby pahoehoe flows

(Duraiswami et al. 2003). Lava flows are classified as simple or compound flows. Simple

flows consist of a single lobe. They have joints perpendicular to the lower contact. Compound

flows may be as thick as 100m may be made of lobes 10cm-10m thick, consisting pahoehoe

or Aa lavas. Compound flows show a wide variation in petrography and are extremely

widespread in Deccan Traps. A lava sequence consists of individual flows which are

distinguished by textures (aphyric, microphyric, porphyritic etc.), by phenocrysts (plagioclase,

pyroxene,olivine etc.) and by geomorphic expression (cuestas, hogbacks, cliff, deep valleys,

etc.)

The emplacement of

flow is through the process of flow called

inflation (Bondre et al.2004) which causes

the thickening of the lobes by continued

injection of lava. The flow front advances

through break out as lava toes. The flow

becomes convex up. Rising fluid causes

vesicle banding. Stagnation causes vesicle

cylinder and jointing. The common inflation

features are called as tumuli, which are

whale- back shaped mounds with axial

cracks. The tumuli are usually 50-100m long

and 10-20m tall.

Their presence in Deccan lavas suggests comparison with Hawaiian lavas

where tumuli are widespread. Pillow lavas, pyroclastics and spiracles (steam injection

structures) suggestive of subaqueous origin are seen locally. Jointing types in lavas

are variously described as columnar, platy, hackly…among which the columnar joints

are most spectacular and wide spread. Sometimes genetic terms like colonnade and

entablature are used to describe the types of jointing. Lava flows develop preferred

pathways to deliver the lava from the vent to the flow front. These pathways occur in

the form of lava channels or lava tubes (Misra, 2002), forming an arterial system

around effusive centers. Pahoehoe flows are generally localized in tubes, whereas aa

flows prefer channels.

Giant Phenocryst Basalt (GPB) or megacrystic horizons are valuable

markers for mapping the lava stratigraphy. GPB are flow that contain unusually large

plagioclase phenocrysts (>30mm) which have an average compositional range of

An60-65.There is one view that GPB perhaps represent a dormant stage in the

fractionation process. Since the GPBs normally overlie red boles suggesting a pause

in volcanism, the dormancy view finds some support.

Bole beds are considered as marker horizons, which are valuable in

delineation of flows. They are commonly termed as red boles and green boles or

green earth. They are composed of pyroclasts of different shapes and sizes enclosed

within glass or fine ash particles (<10micrones). The pyroclasts having a thin

marginal crust and are often sintered. The glass may be devitrified. Red boles usually

contain nantronite, halloysite, iron oxide and silica .Green boles usually contain illite,

quartz and plagioclase. Bole beds are regarded as tuffs, the Red bole being a basic

composition and Green bole is of an acid to intermediate composition. After

eruptions of volcanic flows, pyroclasts are settled as ashes consolidated into bole

beds.

Zeolites occur as infillings in vugs, pipe amygdales and veins and they help

in the demarcation of flows. The distribution of Zeolites in to three zones was

proposed earlier as laumonite, scolecite, heulandite cutting across the basalt

stratigraphy, but later studies proved that it’s a random distribution. The common

Zeolite found in the Deccan basalts are heulandites, stilbite, mordenite and

apophyllite.

REGIONAL STRATIGRAPHY

The Deccan volcanic have erupted through the Precambrian crust of

Dharwar, Bastar, Aravalli and Bundelkhand cratons as well as the Satpura mobile

belt. At place they are undrerlain by Cretaceous sediments (eg, Bagh, Lameta,

Dharangadhara and Wadhavan sequences), which are commonly described as

Infratrappean sediments or merely as infra-trappeans. The lava pile has also many

intercalated sediments and ash beds (red bole, green bole, green earths.etc.) which are

commonly known as inter trappeans.

Deccan basalts are nearly horizontal over vast areas, except where they are

tectonically disturbed in the West Coast, Western Ghat, Khambhat graben and Son-

Narmada (SONATA) rift. The lavas are thinnest in the east and they progressively

thicken to about 2km in the west. This variation is attributed to pre Deccan-

topography as well as renewed faulting and scarp development.

The Deccan Volcanic is classified into three stratigraphic units, the lower,

middle and upper, on the basis of inter-trappean beds, bolesand fossil content. Later

they were classified in to lower and upper divisions based independently on

magnetic reversals and chemical criteria. Recent geological surveys by the GSI and

geochemical mapping by a multinational team with IIT, Mumbai as the nodal agency

have significantly enhanced our knowledge of the Deccan traps and brought out new

stratigraphic schemes. These studies have also shown that the stratigraphy youngs

from west to east, rather than in the reverse direction (E-W) as postulated earlier.

Lithostratigraphy of Deccan volcanic consists of formation and subgroups.

A sequence of flows with similar field, petrographic and gross chemical and isotopic

features has been termed as a formation. Formational boundaries are defined by the

recognizable breaks, presence of marker horizons and chemical shifts over wide area

.The formations are clubbed together in to subgroups based on the type of flows,

geochemical variation and marker horizons. The different sub groups are combined in

to a group called as Deccan Basalt Group or Sahyadri Group.

Lithostratigraphy has been worked out in detail for western Maharashtra

from Tapti river in the north to Belgam in the south, and from Aurangabad in the east

to the west coast covering an area of 1,50,000sq. Km, about one-third of the exposed

area of DVP. Stratigraphic correlation over such a vast area has limitations such as

monotonous similarity of lava flows lack of marker horizons on such a large scale and

complexity erosion and structural disturbances. However, regional gradient of the

undisturbed areas and marker horizons such as GPB are successfully used to erect a

regional stratigraphic column, which was extended on a reconnaissance scale to the

rest of DVP.

Recently, systematic geochemical mapping using similarities and

differences in chemical abundances and ratios as well as isotopic signatures have

been used to work out a chemo-stratigraphic column for the western DVP(Cox and

Hawkesworth,1985)especially in the well exposed sections in the Western Ghats

from Nashik to Mahabaleswar and from Pune to the west Coast for the length of the

Western Ghats of 500km and approximate area of30,000sqkms. The chemo-

stratigraphy was extended to the area in the South and the East by the reconnaissance

chemical mapping types, defined as one or more members having same chemical

composition.

Sub-provinces-:

DVP is broadly divided into 4 sub-provinces

Main Deccan plateau,

Malva plateau,

Mandla plateau,

Saurashtra plateau

Main Deccan plateau:

The best-studied area of Deccan basalts is the Western Deccan

Province covering mainly the Western Ghats. The type stratigraphy of the DVP is

extended to the central, Southern and South Eastern sections of the Main Deccan

Plateau on reconnaissance scale.

Lithostratigraphy:

The lithostratigraphic scheme praposed for western Maharashtra by

Godbole et al.(1996), suitably to confirm to stratigraphic coded is given below:

Group Subgroup Formation Thickness(m)

Sahyadri

Wai

Mahabaleshwar 600

Purandargad

900 Diveghat

Lonavala Karla

700 Indrayani

Kalsubai Ratangad

~1500 Salher

Chemical Stratigraphy:

The inter-university team (Subbarao et al. 2000) divided the Deccan Basalt Group

into twelve formations, which are combined into three subgroups.

Group subgroup Formation Magnetic polarity

Dec

can

basa

lt

Wai

(~500m)

Desur Normal(N)

Panhala N

Mahabaleshwar N

Ambenali Reverse(R)

Poladpur R

Lonavala

(525m)

Bushe R

Khandala R

Kalsubai

(2000m)

Bhimashankar R

Thakurwadi R

Neral R

Igatpuri R

Jawahar R

DECCAN TRAP PROVINCE OF WESTERN AND CENTRAL

INDIA

The Deccan Trap province occupies more than 5 lac Sq.Km. areas in

part of Western and Central India, in the state of Maharastra, Andhra Pradesh,

Gujarat, Karnataka, Madhypradesh. Maharashtra hosts the greatest aerial coverage of

these basaltic rocks. This is the third continental flood basalt province in terms of the

exposed area.

The Deccan trap provience is constituted dominantly of tholeiitic lava

flow stacked one above the other. A few units of giant phenocrysts bearing basaltic

lava and olivine basalt are recorded from this sequence. The basaltic flow have been

intruded by doloritice dykes (some of which are speculated to represent the feed dyke)

and occational alkaline intrusion (particularly along the western coastal trac and in

Narmada valley) Western part of the province, particularly in Gujarat & in the

Narmada Valley. Laterites & Quaternary alluvial cap the Deccan Trap flows in

Western & Southern Maharashtra.

Subbarao, et al., 2000 & many others classified the Deccan Traps based on

the combination of field mapping with petrochemical & isotopic studies. This is

known as the Chemostratigraphic classification.

Lithological classification of Deccan Trap Province is given by

Godbole at 1998 & Chemostratigraphic classification is given by cox & Hawkeswarth

1988, Subbara & Hooper 1988.

Lithostratigraphy

Chemical Stratigraphy

Super

Group

Group

Subgroup

Formation

Sub-group

Formation

D

E

C

C

A

N

T

R

A

P

S

A

H

Y

A

D

R

I

Wai

Mahabaleshwar

M4

Purandargad

Diveghat

Wai

Desur

Panhala

Mahabaleshar

Ambenali

Poladpur

Lonavala

Karla

Indrayani

-

M3

Lonalvala

Bushe

Khandala

Kalsubai

Upper Ratangad

M2

Lower

Ratangad

M1

Salher

Kalsubai

Bhimashankar

Thakurwadi

Neral

Igatpuri

Jawhar

Map of the Study Area

WADKI NALA

JADHAVWADI

Previous works

The early pioneer Geologists who laid the foundation for the study of

Deccan volcanic are T.J.Newbold, Blanford, P.N. Bose, L.L. Feror, C.S. Fox and

W.D.West. Multi-institutional international team co-ordinated by K.V. Subbaro

brought about a sea change, in our understanding of Deccan Traps. A large

volume of literature exists on the Deccan traps, the most important among them

being the edited volumes of Bulletin volcanogique, Subbarao (1988, 1994, 1999),

Project CRUAMSONATA (1995) AND Deshmukh and Nair (1996). Godbole

(1988), Hooper(1999), Walker(1999), Subbarao et.al. (2000), Nair and

Chandrasekharam (2003). Alkaline rocks of DVP are summarized by Gwalani

Krishnamurty (1988) and Srivastava and Hall (1995)

DESCRIPTION OF FIELD TRAVERSE

Location 1

Latitude- 18° 25’18” N

Longitude- 73° 58’ 59” E

Locality-Near green Kashmir hotel at turning point

Figure 1 -Dyke Figure 2-Phenocrysts present in the dyke

This is located at a left turn near wadaki nala on Hadapsar-Saswad road. One can

get a bird’s eye view and also estimate the overall physiography of the area. Exposure was not

in a position that one can specify that it is in which part of flow. It may be top or basal part of

the aa flow also. Abrupt change in the lithology indicates that it may be the presence of the

intrusive body. Weathering pattern also varies which indicates the presence of the discordant

body. On the basis of these factors this discordant is identified as dyke. At the point of contact

of the host rock and the dyke, chilled margins were observed. Color of the dyke material is

dark and can be called as melanocratic. At the margin of the dyke, rock showed very fine

grained aphanitic texture, formed due to the sudden cooling. In the middle area of the dyke

some phenocrysts are also seen in it, which are about 0.5 Cm-1Cm in length, the texture

changes from aphanitic to partially porphyritic. The dyke showed three sets of jointing, which

were formed by the cooling process. The vertical set of the joint is of 220-40, the horizontal is

of 280-100 and inclined set is of 305-125 and also the thickness of the dyke decreases with

increase in the elevation.

Location-2

Figure 3-Pipe amygdales (vesicle cylinder)

Figure 4-Chilled margin

Figure 5- Inflation Cleft

Latitude-18° 25’ 15” N

Longitude-73° 58’ 59” E

Elevation- 654m from MSL

The flow was identified as compound

pahoehoe flow with a number of sub units or

lobes. A lobe is a lava entity surrounded by its

own chilled margins. Upper part of lava lobe

shows red color chilled margin above this zone

there were a number of pipe amygdales and

vesicles found.

Inflation cleft makes the upper lobe

surrounded by its own chilled margin, show the

bun like feature, hence the flow become

convex up. Vesicle cylinder is also present

here. Hence this zone may be the basal zone,

which then followed above by the jointed lava

core which is nearly devoid of vesicles may be

the lava core. Vesicles again increase at the

upper portion indicates the lava crust;

subsequently increase in red color indicates the

change in flow.

Location-3

Figure 6-Purple color chilled margin

Figure 7-flow showing entablature

Latitude-18° 25’12” N

Longitude-73° 59’20” E

Elevation-682m from MSL

Locality-19.2km mile stone SH-64

New flow is separated from

lower pahoehoe flow irregularly spread

purple color chilled margin with

greenish amygdaloidal material. Above

this there is a closely space, jointed more

altered rock is present joints get widen

due to the deep rooted plants. Such

material get slumped down due to slope

instability and jointing called rock fall.

As we walked further we got the

colonnade and the entablature structure

formed due to the disturbance in the

isotherm because of the rain water at the

time of eruption surface temperature was

more, in such cases rain water drops the

temperature which produced the hackly

joints called colonnade. Hence the flow

identified as simple flow because we did

not get clinkery base. Core sample of

this flow contains porphyritic texture

and is of melanocratic nature. The

phenocryst present may be of

plagioclase.

Figure-8 Flow shows large vesicles which are filled with the secondary minerals.

Location-4


Longiude-73° 59’33” E


Locality-20.2km milestone

Clinkary base

Red bole

Fragmentary

top of Lower

flow

Figure-9 Red Bole horizon separates two different flows; also leaching of the Red Bole

material in to the top part of the lower flow is visible.

The flow can be identified as Aa flow as it has a fragmentary top. Flow started from

red bole horizon, of thickness ranging between 1 ft-3ft. Contact between second and third

flow is gradational. Pyroclastic material sinks in loosely packed fragment. These flows

possess amygdales in its lower portion. Massive core is devoid of vesicles.

Location-5




Figure-10 Figure-11

The flow can be identifid as Aa flow as it has clinkery base which posses melanocratic to

mesocratic with yellow colored plagioclase crystals showing vesicles. At the top of this flow

the presence of the autobrecciated fragments also noted,which confirms the flow type as Aa

flow. At the top slope wash is present-somekind of muchthicker deposit of recent origin.

Then the base of the flow is marked by red bole horizon.

Figure-12. These are some secondary minerals found in the cavities of the flows.

Location-6




Figure-13. AA flow, which is showing clinkery base and the Red Bole horizon.

This flow starts from 787m elevation as we again moved towards the Saswad.

Contact between fourth and fifth flow marked by the presence of the red bole horizon. It also

contains a clinkery base and the top consists of the fragmentary appearance. Core part shows

jointing pattern. He joints are of les thicker than core of previous flow. Hence we concluded

it as AA flow.

Location-7

Latitude-18° 24’91.5”N

Longiude-73° 59’98”E


Figure-14.

This contact with lower flow is marked by the brown color horizon which also can

be called as the brown Bole horizon. This Aa flow completely exposed at the curvature. It is

marked by the clinkery base containing vesicles. This zone is followed by the massive core

with fragmented top and necklace joints formed due to the contraction during cooling. At the

same location seventh flow is identified by the presence of red bole at the base but the top

cannot be clearly identified. Another important character present in this area is inter-

trappean beds just below the upper and lower flows.

Lithosection of Deccan Basaltic flow in Diveghat

Fig : Lithosection of lava flow mapped in Devighat

Dyke

Pipe amigdals of the BYZ

Core

Thin basal clinker

Core with columner jointing

Entablature

Basal clinker

Fragmentary top

Brown bole

Columner core with necklace jointing

Basal clinker zone

Clinkery top i.e., fregmentary

Core with small size jointing pattern

Basal clinker iter mixed with red bole

Fregmentary top surface

Core

Pahoehoe

Flow-1

Pahoehoe

flow-2

Aa

flow-1

Aa

flow-2

Aa

flow-3

Aa flow-4b

Aa flow-4a

Lobe with spheriodal weathering,

lower vesicular, dence core, chilled

margin, inflection cleft & jointing

pattern

CONCLUSION

Diveghat is a best place near the Pune city to study the types of lava flows, which

exsist in DVP. As here both types of flows are exposed in a very short distance of 3-4Kms

along the Pune – Baramati road .The flows in the Dive Ghat area, as the description says, are

of two types, Pahoehoe and Aa. The place near Wadki Nala, from where we started the field

work, contain an intrusive body and two Pahoehoe flows, which are exposed here at base of

the hill, in this locality , which is then followed by five AA type of flows, between the

elevation 682 MSL-802 MSL. At places these AA flows are separated from one another by

the presence of Red Bole. The base of seventh flow shows presence of Brown Bole. These

are identified by the particular characters which are described in the field features of basaltic

flow in the beginning.

References:-

G.G. Deshpande(1998). Geology of Maharastra, Geological Survey of India, pg.223

Godbole, S.M., Rana, R.S. and Natu, S.R. (1996), Lava stratigraphy of Deccan

Basalts of Western Maharashtra, Gond. Geol. Mag., Spl.Vol.2, pp.125-134.

Najafi, S.J., Cox, K.G. and Sukheswala, R.N. (1981). Geology and Geochemistry of

Basalt flows (Deccan Traps) of the Mahad-Mahabaleshwar Section, India, Geol. Soc

India.Vol-1, pg.113-116

Subbarao, K.V., Hooper, P.R. (1988). Reconnaissance map of the Western Deccan

Province, In Geol. Soc. India.Vol-2, pg.891-902

Dive Ghat

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