Download 09_chapter 1

Chapter - I
INTRODUCTION
In the annals of Peninsular India, geologically a significant catastrophy
engulfed about 1/3rd of the land area at the end of cretaceous era. The so called
catastrophic event was manifested in the form of outpouring of enormous volume
of Basaltic lava that covered hundreds of square km. of the land through
spasmodic eruptions which gave rise to piles of lava flows. These piles carved the
Landscape of Deccan Plateau. The term Deccan Trap was first introduced by
W.H. Sykes in 1833 after Swedish word Trapp / Trappa meaning stair to describe
step like or terrace like formation (Fig.1.1). This is the second most extensive
geological formation after Igneous and Metamorphic complex of Archaean era in
Peninsular India (Fig. 1.2). It occupies a large tract between Bombay in the west,
Cutch in North West, Sarguja and Jashpur in the East, Belgum in the south, and as
far as Rajmahendri in South East, covering parts of states of, Maharashtra, Gujrat,
Madhya Pradesh and Karnataka. Major part of Deccan Plateau in Maharashtra
runs through Kelod, Nagpur and Pandharkawada in Vidarbha, East of Nanded,
Deglur, Udgir and Umarga in Marathwada and East of Akkalkot and Miraj in
Southern Maharashtra. In the West, Deccan Trap extends far beyond West Coast
up to Bombay high and even beyond that. In Ratnagiri off shore Deccan Trap has
been encountered in deep drill wells (Kalia 1988). Except Eastern part of Nagpur
district, whole of Bhandara, Chandrapur and Gadchiroli districts and southern part
of Sindhudurg district, all other districts of Maharashtra are occupied by Deccan
Trap. Thus Maharashtra can be considered as house of Deccan Trap.
Wadia (1967, p.292 p.301) and Krishnan (1968, p.407) have advocated
perfect horizontality of DeccanTrap Basalts.Crookshank (1936, p.277) has
mentioned deviation from horizontality near Morghat. However these cases are
not of Basalt to Basalt contact, but they represent the contact between Deccan trap
and Gondwana rocks.Wadia (1967, p.294) has attributed deviation from
horizontality at Rajpipala hills and other areas to the disturbances subsequent to
consolidation of flows.
(1)
Fig.1.1: Distant View of Deccan Trap Basalt Flows.
Fig. 1.2: Area covering Deccan Trap formation.
(2)
The Deccan Traps are made of layers of several lava flows with thickness
of individual flow ranging from few meters (7m) to as much as 40m maximum
and can be traced for a distance of 20 Km. (Karmarkar-1974, Gupte et.al.1974). In
Jawahar–Igatpuri section in Western Ghats about 700m thickness is reported to be
composed of 15 flows (Subbarao et.al 1988). On the western slope of Sahyadri
between Kasara and Kalsubai, 21 flows are exposed in vertical span of 1381 m.
From Poladpur to Mahabaleshwar within a vertical distance of 1200 m there are
47 flows. Compound flows of amygdaloidal basalts range in thickness from 30m
to 200 m.
The total thickness of Deccan Trap is also variable in different parts
because of undulating nature of ground over which the flows are overlying. The
trap cover is thickest near Bombay coast, where it is almost 3000 m.The section at
Matheran is about 850 m thick, at Mahabaleshwar it is 1700 m thick. The Lava
pile in Western Ghat is having combined thickness of 2500 m. In Melghat scarp,
north of Achalpur in Amravati District the flows have total thickness of 700 m. In
the Eastern part of Vidarbha total thickness varies from 70 m to 225 m. At
Hingana in neighborhood of Nagpur, in bore holes drilled for coal prospecting
thickness of traps has been found to vary between 50m to 70m.
The lava flows of two different types have been recognized. They are
pahoehoe or ropy lava and the aa or block lava. Pahoehoe is mobile, solidifies
with smooth and glazed surface have rope like wrinkles hence called as ropy
structure. The flows are also recognized as compound (Amygdaloidal) when
made of several smaller units. Karmarkar et.al. (1974), called such flow units as
Thin and Thicker irregular Amygdaloidal Basalt Flows, as each unit possesses
criteria of demarcation of flows with irregular top surface. Simple flows are
uniform over large area and made of single units. In general compound flows
show Pahoehoe characters, whereas simple flows show characteristics of Block or
aa flows. The former predominate in western Maharashtra between Dhule,
Buldhana, Aurangabad, Pune and Nasik whereas in the rest of the region of
Maharashtra Simple flows are predominant (Fig. 1.3).
(3)
The Compact Basalt flows are Thick extensive and free from vesicles,
amygdales, except for small portions at the top and bottom of the flows. The
major portion of these flows is jointed. The undulated Basalt flows having
vesicles are called as Vesicular Basalts (Compound Flows). However these
vesicles rarely remain empty but are generally filled with secondary minerals like
varieties of silica, calcite, zeolites and these vesicular Basalts containing infilling
of the secondary minerals are called as Amygdaloidal Basalts. In nature therefore
Vesicular Basalts are rare in occurrence and Amygdaloidal Basalts are more. As
mentioned earlier many of the amygdaloidal flows may be made of several
smaller units forming compound flows.
Kulkarni P.S. (1985) demarcated various flows in different ghat sections
of NE and Central part of Maharashtra, e.g. Buldhana Ghat section-10 flows,
Mhaismal Ghat section-17 Flows, and Nagapur Ghat section-18 Flows, etc.
Tejankar (2002) studied the basalt flows along Toranmal section of Western
Satpura region and concluded that Toranmal section exposes maximum thickness
of Deccan Basalt in the Western part of Satpura range comprising 50 Basalt flows
within a vertical pile of 787 m, lying between 348 m and 1135 m above MSL.
These flows represent Quartz and Olivine normative Tholeiite
Deccan Trap flows have horizontal attitude which can be observed along
Western ghats and in the areas of Khandesh to Solapur and throughout Vidarbha
region (Fig. 1.4). However in the regions like Mumbai and Salsette islands and in
the hills between Thane and Kalyan and west of panvel the flows show dip
varying between 8° and 12° towards west. In some areas very low dip between 2°
to 5° is observed which may be due to slope of original land surface on which
lava is outpoured.
A study of Land-Sat imagery carried out by Rajurkar et.al. (1990) has
revealed several lineaments traversing Maharashtra Plateau (Fig. 1.5). This study
is summarized in Table No. 1.1.
(4)
Fig. 1.3 : Regional Distribution of Basalt Flows
Fig. 1.4 : Panoramic View of Basalt Flows exposed in
Chikhaldara Ghat section
(5)
Lineament
Sahyadri
Chiplun
Warna
Ghod
Upper
Godavari
Kaddam
Lineament
Tapi
Purna
Sr.
No.
1
2
3
4
5
6
7
8
200 Km. long from south of
Amravati up to Jalgaon in west
where it joins Tapi lineament
1200 Km. long extending from
vicinity of Jalgaon in west to
Dhanbad in Bihar in the East
280 Km. long
West of Nasik up to
neighborhood of Parbhani
280 Km. long
225 Km. long
100km length
Mumbai to Ratnagiri
50 Km. wide
Extent
(6)
WNW-ESE
Northern border of
Maharashtra
(Course of Tapi River)
Course of Kaddam
River
WNW-ESE
NW-SE
(Course of Ghod River)
NW-SE (Course of
Warna River)
NNW-SSE
Parallel to west coast
Direction
Remarks
Towards east it possibly continues up to
south east of Nagpur and further east to
join Balaghat lineament
It represents Achalpur fault which is along
the southern foot of Gawilgad hills. The
fault was recorded by Blanford in 1869.
In Yavatmal district Basalt flows show dips
towards north along this line which has
been considered due to faulting.
Shows evidence of Quaternary Tectonic
movements.
Set of fractures observed in the Basalts of
this region. In North West part faulting is
suspected along this lineament.
Represents fault in Achaean basement
below and was reactivated in post Deccan
Trap period
Marked by presence of hot springs
The lineament is mainly represented by
fractures and dykes. No evidence of
faulting
Table No. 1.1: Lineaments Traversing Maharashtra Plateau
These lineaments throw some light on the nature of tectonic activity in the
region. The Tapi lineament, which form southern margin of Satpura horst
represents a zone of weakness along which there has been recurrent activity
during different geologic periods, as is evidenced from the inliers of Achaeans
and Gondwana rocks in the Deccan Trap and thick alluvial deposits of quaternary
age in the Tapi and Purna valleys. The crustal block, south of Tapi Purna
lineaments comprising the Maharashtra plateau appears to be tectonically a stable
block forming basement for Pakhal, Sullavai, Penganga and Gondwana
sedimentary sequences and thick Deccan Trap lava pile. The Godavari lineament
of Pranhita Godavari valley has controlled formation of these basins and their
sedimentation. The faulted margins of these basins indicate that some of the
lineaments are fault lineaments which had recurrent activity during different
geological periods. Over the Maharashtra plateau, in addition to NNW to NW
trending Godavari lineaments, there are dominantly ENE-NE trending lineaments
which represent cooling joints and fractures in the lava flows with no tectonic
significance. The Godavari lineament occurring in the trap flows appear to be
manifestations of the basement lineaments, the activation of which in post Deccan
Trap period is observed in Warna and Kaddam. Although some evidences of
recurrent activity have been observed in the case of some fault lineaments in the
Maharashtra crustal block south of Tapi-Purna lineaments, the block as a whole
appears to be tectonically stable.
(7)
(8)
Fig. 1.5 : Major Lineaments of Maharashtra (Source CGWB Nagpur)
Literature Survey:Deccan trap is major geological formation occurring in peninsular India,
covering an area of about 516000 Sq. Km. in western and central part of India
(Fig.1.2), about 82% of Maharashtra state (Fig.1.3). After independence
observations which have been made during geological investigations by experts
for engineering sites in various parts of Deccan trap area and for ground water
exploration in drought prone areas have revealed that there is considerable
variation in its field characters which have not been mentioned by earlier workers.
These observations have initiated the government organizations like GSI, ONGC
and a few Geology Departments at University and College levels in Maharashtra
state to undertake further studies which were mainly confined to Geochemical
studies of Basalts.
The literature survey shows that the earliest work on Deccan trap was of
Capt. Danger field (1824), who prepared geological map showing outcrops of
basalts of Malwa plateau of Madhya Pradesh. Subsequently a valuable
contribution was made to the knowledge of Deccan Trap formation by Blandford
who studied Deccan trap formation of western India (1856), the geology of
Taptee and lower Narbada valley (1869), The Geology of Nagpur (1872) and
Geology of Mahabaleshwar (1921). Holland (1892, 1906, 1908-1909), Fermor
and Fox (1916) and Fermor (1926, 1934) have also made significant contribution
in the studies of Deccan Trap. It was for the first time Washington (1922) has
studied petrochemistry of the traps. Subsequently Mathur and Naidu (1932),
Mathur (1934), Vemban (1947), Auden (1949), Sukeshwala (1953), Sukeshwala
and Poldervaart (1958) and A.C. Chatterjee (1961) have published papers on
Deccan trap and associated formations. Agashe, L.V. (1956) studied dykes
between Pune and Khandala. Agashe L.V., Gupte R.B. and Deshpande M.G.
(1964) studied volcanic vents of Alandi and Charholi and published in College of
Engineering Poona Magazine. Beane, J.E. and Hooper P.R. (1988) published a
note on picrite Basalts of Western Ghats, Deccan traps, India, in Deccan Flood
Basalts, Mem. Geol. Soc. of India, No.10 pp. 117-134. Beane J.E., Turner C.A.,
Hooper P.R., Subbarao K.V. and Walsh J.N. (1986) published a paper on
Stratigraphy, Composition and form of Deccan Basalts, westrn ghats, India, in
Bulletin, Volcanologique, volume, 48 pp. 61-83. Bodas M.S, Khadri S.F.R. and
(9)
Subbarao K.V. (1988) studied stratigraphy of Jawahar and Igatpuri formations
and published in ‘Deccan Flood Basalts’ Geological Society of India, Mem.10,
pp. 235-252.
The paleomagnetic studies of Deccan trap basalt flows and dykes were
carried out by Sahasrabuddhe et.al. (1963), Athawale et.al. (1970), Pal and
Bhimsankaram (1971), Wensink and Klootwijk (1971) and Wensink (1973).
The work on tectonic aspects of Deccan trap was also carried out by
Krishna Brahmam and Negi (1973), Bakshi A.K. (1994) carried out
Geochronological studies on whole rock basalts, Deccan Traps; India. Mahoney
et.al. (1985) carried out an isotopic investigation of some alkalic and tholeiitic
basaltic lavas in the northern Deccan area along the Narmada River. These lavas
are essentially contemporaneous.
Mahoney et.al. determined that the alkali and tholeiitic lavas have similar
isotopic composition and are roughly equal in volume in that particular Narmada
section.
Although it has long been known that the Deccan Trap lavas are
predominantly tholeiitic, Mahoney et.al. justifiably wondered whether other
unexplored areas of the Deccan might be found, where alkalic basalts occur in
insignificant volumes. Devey C.W. and LightFoot P.C. (1986) worked on
volcanological and Tectonic control of stratigraphy and structure in western
Deccan Trap (Bull. Volcanology, v. 48, pp. 195-207). Duncan R.A. and Pyle D.G.
(1988) published paper on “Rapid eruption of Deccan Flood Basalts at the
cretaceous tertiary boundary in “Nature” (vol. 333, pp. 841-843). Ghosh Pradip K.
and Pal R.N. (1984) have given evidence of Fissure eruption observed in
Khargone and Dhar Districts (GSI spl. publ. No.14 pp. 108-110). Jeffery K.L.,
Henderson P., Subbarao K.V. and Walsh J.N. (1988) studied distribution of
Zeolites in Deccan Flood Basalts (Geol. Soc. of India, Mem.10. pp. 151-162).
Kalia K.L. (1988) mapped thickness of Deccan Trap basalt Flows in India from
DSS studies (‘Deccan Flood Basalts’ Geol.soc.of India Mem. 10, pp. 91-116).
Khadri S.F.R., Subbarao K.V., Hooper P.R. and Walsh J.N.(1988) worked out
Stratigraphy of Thakurwadi formation, in Western Deccan Basalt Province.
(“Deccan Flood Basalts”, Geol. Soc. of India Mem.10 pp. 281—304). Recent
(10)
investigations carried out by Raman and Subbarao (1994) have indicated rare
element partial melting model and its petrogenetic significance in Deccan Traps.
Subbarao et.al. (1994) have given stratigraphy and structure of Central Deccan
Basalt Province and proposed various eruptive models which appear to have been
originated due to iso-static adjustment. Khadri et.al (1996) have proposed
stratigraphy, form and structure of east Pune Basalts and reported the occurrence
of new pyrite basalt horizons in Wai sub groups.
On the basis of Geological and Geophysical evidences ,West (1959) stated
that the Deccan trap flows originate in those areas where dykes are found, namely
in Cutch, Saurashtra, North Konkan, The Tapi and Narmada valleys and the
Gondwana basins of Satpuras and further east and they travel long distance to
other parts of the outcrop. The first Paleomagnetic measurement on Deccan Traps
was carried out by Irving (1994). The next detailed work on Deccan Trap samples
from Khandala and Linga areas by a group of British Scientists (Clegg et.al.
1956). A group at Osmania University, Hyderabad carried out paleomagnetic
investigations on Deccan trap from a few different localities (Pal et.al. 1971).
Verma and Mittal (1972, 1974) studied Deccan Trap of mount Girnar and mount
Pavagarh areas with respect to paleomagnetic aspect. Normal-Reverse-Normal
paleomagnetic sequence was reported by Sreenivasa Rao et.al. (1985) in the
Narmada region. While the above extensive studies of Deccan Traps were
completed or were in progress by overseas groups, Japan (Keno et.al. 1972) and
France (Courtillot et.al. 1986). Sano et.al. (2001) describes differentiation
processes of Deccan Trap Basalts based on Geochemical and Petrological studies.
He further stated that the Phenocryst assemblage and Chemical Trend of the least
contaminated basalts can be explained by fractional crystallization in shallow
chambers under Faylite–Magnetite-Quartz (FMQ) buffered conditions.Mudholkar
(2001) studied the magnetic evolution of the fresh Basalts from the ridge axis near
Egaria fracture zone, Central India ridge, on the basis of Geochemical and
Petrographic studies.
The origin of Deccan volcanic province has been much debated. The
debate concerns whether the magmas formed by melting a giant mantle plume,
Normal Plate tectonic processes or impact of large extra terrestrial bollide (e.g.
(11)
Mahoney 1988, Richard et.al. 1989, Chandrasekharam and Parthsarathy 1978,
Chatterjee and Rudra 1992, Sen 1995, Seth 2005 a, b). In the 1960 several authors
recognized the difficulties in explaining all volcanic phenomena on Earth with the
shallow mantle melting model required in the plate tectonic theory and proposed
the concept of hot spots (Wilson 1963). Wilson felt that the Hawaiian island
chain, which is located in the middle of large oceanic plate, could not be
explained by shallow mantle processes required by Plate Tectonics. Wilson model
for the Hawaiian volcanic chain called for generation of magmas from a spatially
fixed thermal plume rooted in the deep, non convecting mantle. Soon after
Wilson, Morgan (1972) presented concept of mantle plumes. Whereas hot spot
sensustrictorefers to a hot jet or thermal plume, Morgan’s plume would include
material transfer from deep to shallow mantle. In the subsequent years,
geochemists and geophysists have used the term “plume” at random to mean
different things; but in general, “Plumes are upwellings and downwellings that are
maintained either by thermal or chemical buoyancy or by both in concert”
(Anderson and Natland 2005). The Deccan Traps eruption is often used as a
spectacular example of mantle plume activity (Richard et.al. 1989; Duncon and
Richards 1991). The basic idea is that the Deccan magmas formed by melting a
giant “plume head” that rose from the core mantle boundary. This plume head
was anchored to the source by long tail that created the Chagos-Laccadive
volcanic chain. A jump of a ridge that is now the Central Indian Ridge about 40
million years ago broke up the chain and the original plume tail is now creating
volcanism on Reunion Island. There are several authors who have doubted the
plume theory as far as the origin of the Deccan Trap is concerned (e.g., Seth
2005a). Chandrasekharam and G. Sen and D. Chandrasekharam, Parthsarathy
(1978) noted that Deccan Basalts predominantly erupted through fissures in the
crust and proposed a model of shallow mantle melting in which pre existing rift
zones
were
reactivated
and
magma
simply
poured
out
of
fissures
(Chandrasekharam and Parthsarathy 1978).
An important argument in favor of the plume origin of the Deccan is that
too much lava came out in too short a time requiring some special melting
mechanism that does not fit the normal Plate Tectonic schemes (Sen, 1995).
(12)
Much finer age refinement with radioisotope dating of the lavas and a more
accurate estimate of the volume of the lavas are needed to have a stronger
constraint on the eruption rate of the Deccan. Without such refinement, the mean
eruption rate could have varied between 1 and 40 Km3 per year. A paleomagnetic
study by Chenet et.al. (2007) suggests that there were episodic bursts of lava
eruption with intermittent quiescence.
Considering the research of the earlier workers, in the present
investigation the attempt has been made to decipher the nature of volcanicity that
has produced basalt flows in time and space. Most of the workers attributed
Deccan Trap as the product of fissure type of volcanicity, but Agashe and Gupte
(1968, 1971) have shown that in addition to fissure type, central type of
volcanicity also existed in some part of Deccan Trap area of Western
Maharashtra. Subsequently on the basis of systematic studies of the field
characters of basalt flow exposed in road cuts and in railway cuts taken for ghat
sections from R.L. 40 m to R.L. 1220 m over a large area of Deccan Trap
formation Gupte et.al. (1971), Karmarkar (1974, 1978) Kulkarni S.R. (1975)
Marathe (1976, 1980), Kulkari P.S. (1984) and Tejankar A.V. (2002) have shown
that there is distinct variation in the nature of volcanicity at different times and
at different places in Western Maharashtra, Marathwada and Khandesh region of
Maharashtra state. Hence the present work is concentrated on these lines for
Vidarbha region of Maharashtra state.
Area of Present investigation:In the present investigation attempt has been made to determine nature of
volcanicity in the north-east part of Deccan Trap formation i.e. Vidarbha region of
Maharashtra. The area selected for the investigation is Ghat section known as
Chikhaldara Ghat in which basalt flows are clearly exposed in the approach road
to Chikhaldara Hill Station ( R.L. 1092 m) and hill ranges 77˚ 19' North 21˚ 24'
East.
The Chikhaldara ghat section is situated at a distance of 100 Km. North
West of Amravati. It is approachable by all weather road from Amravati (Fig.1.6).
There is Melghat Tiger Reserve forest on this hill station.
(13)
(14)
Fig No. 1.6 : Location Map of Chikhaldara
The Methodology of Investigation:A)
Study of field characters of Basalt flows:As shown by the earlier workers (Gupte 1974), Karmarkar (1974, 1978),
Kulkarni S.R. (1975) Marathe (1976, 1980) , Kulkarni P.S. (1984) and Tejankar
A.V. (2002), who gave more stress on the field studies of the Basalt flows which
can give clues to the nature of volcanicity. Therefore much stress has been given
to the studies of field characters of basalt flows exposed in the Chikhaldara Ghat
section (Fig. 1.7). For this purpose traverses were taken from the foot of the ghat
(R.L. 600 m) up to Chikhaldara hill station (R.L. 1092 m) during four summer
seasons between 2006 to 2011, when road cuts remain free from cover of
vegetation and moss. During the field work individual basalt flows were
demarcated and traced in the cuttings along the road to determine their extent,
thickness and field characters. The vertical variations from top to bottom of each
flow were critically studied. Wherever possible the vertical thicknesses of the
basalt flows were actually measured. On the basis of demarcation of the basalt
flows their chronological sequence in the vertical stretch of 492 m is depicted.
B)
Petrographic studies:To determine mineralogical and textural variation in basalt flows a large
number of specimens from the basalt flows were collected and their thin sections
examined under petrological microscope. Critical observations of about 150 thin
sections were carried out to determine mineralogical and textural characters of the
flows (Fig. 1.9).
The relative proportion of different minerals by volume in basalt flows
was determined by Dalesse-Rosiwaal method.
Anorthite content of plagioclase phenocrysts was determined by Michael
Levy method.
C)
Chemical studies:Suitable specimens from the flows have been chemically analyzed. The
major element-oxides content, Trace elements and also rare earth elements of
sixteen basalt flows were obtained by utilizing facilities available at National
Institute of Oceanography Goa. The results of these analyses are utilized to
(15)
determine chemical variations in the basalt flows occurring in the area studied.
Attempt is also made to determine nature of the magma. These results are
compared with the chemical characters of basalt flows occurring in other parts of
Maharashtra state.
Fig. 1.7 : Basalt Flows of Chikhaldara
(16)
Previous work:In the area of Chikhaldara Ghat Section very little work in this problem
has been carried out. However the work on the similar lines has been carried out
in different parts of Deccan plateau.
Preliminary petrographic and paleomagnetic studies of lava flows around
Boral region Chikhaldara plateau, Amravati district MS, carried out by Dr. S. F.
R. Khadri (SGB Amravati University Journal Vol: 3(1), 2008). Rock magnetic
and palaeomagnetic investigations of lava flows around Chikhaldara plateau
Amravati Dist. (MS Journal Geological society of India). A brief reference of the
Geology of the district is made by Blanford (1869), pertaining to the Geology of
the Taptee and Narmada valleys and some adjoining districts, wherein salient
features of the southern parts of the Gawilgarh range and the Purna plain are
outlined.
The main aspect of this thesis is to decipher nature of volcanicity that has
produced basalt flows and has been discussed at length. Marathe S.S. (1976)
studied petrology and structural peculiarities of the Godavari valley Basalts near
Nasik. He had reported 27 dykes exposed in the vicinity of 2.5 to 3 Km. from
Right and Left bank of Gangapur Dam. He discussed their influence in
topographic expression. Karmarkar B.M. (1973) noticed 85 fractures in 20 Km.
stretch of Borghat section along Pune–Mumbai railway track and in Tunnels from
Khandala to Karjat. Basalt flows show closely spaced jointing pattern around
these fractures. Kulkarni P.S. (1985) studied different Ghat sections of Central
Maharashtra. He had correlated various flows exposed in these Ghat sections and
concluded that the sequence of flows in all these ghats are different. This means
that the flows building up one ghat have not reached the neighboring ghat, even
18 Km. away from each other. Chande D.G. (1986), on the basis of field and
laboratory studies showed that out of 28 dykes located in Gangapur–Vaijapur area
21 dykes are of Compact Basaltic nature while remaining seven dykes are of
Amygdaloidal Basalt. The dykes of Compact Basalt further show field evidences
of their feeder and hypabyssal nature. Out of 21 dykes of Compact Basalt, 13
(17)
dykes are showing their feeder nature and remaining 8 dykes are hypabyssal
injections. Anirudha De (1996) studied Deccan Trap lava flows in Satpura and
states that these are simple lava flows characterized by several zones of primary
volcanic structures. Subbarao (2000) studied the basalt flows with reference to
their rare earth elements and concluded that “Sr” isotopic ratio for the tholeitic
spilite flow and associated mineral phases which can provide direct evidence for
spilitic degradation of tholeiites and increase in rare earth elements from basalt to
spilite.
Ray and Bose (1996) concluded that the genesis of Deccan Basalt has
been considered to be a two step process involving major petrogenetic problems.
The primary state in the generation of magma type with distinct geochemical
characterization, where as the second stage involves contamination. Godbole
(1996) studied Geology and Chemical stratigraphy of the Basalt Flows of Akot
Harisal section from Satpura range of Amravati District. Deshmukh (1996)
carried out geochemical studies of Basalt Flows exposed at Chikhaldara and
Bairamghat area and on the basis of vertical variation in chemistry of basalt flows
the Lava pile is divided into five and four groups respectively. These groups are
separated by chemical marker flows. Flows present in these areas show chemical
affinity to Ambanali formation.Chatterjee (1996) carried out petrographic and
Geochemical studies of Narmada-Tapi-Satpura dykes system between 74° and
76° longitudes of Central India. Bulk of these dykes is of Basalt and dolerite with
intermediate and acidic dykes being scanty. Chawade (1996) studied the
petrology and Geochemistry of dykes in Deccan Basalts in parts of Lower
Narmada valley. Keshav (1998) reported the field Geology and Petrography of
greater than 40 Km. long East-West trending Dhule-Parola dyke of Southern Tapi
Rift. Sethna (1996) studied Petrology of the basic dolerite dykes around
Nandurbar area, south of Tapi River and observed that these dykes contain large
amount of Pigeonitic pyroxene, which is not so common among dolerites
encountered along the west coast part of the Deccan Volcanic Province.
Sengupta (1996) studied Petrology and Geochemistry of Deccan Trap
flows intersected in Salbardi drill hole near Salbardi hot spring in Amravati
(18)
District. The drill hole intersected 604 m thick basaltic lava pile comprising 26
flows. The Basalt sequence is underlained by Lameta sediments. The basaltic
flows of this area are of simple type and range in thickness from 4 m to 75 m.
They are Porphyritic in varying degree (5% to 22% phenocryst) set in ground
mass of plagioclase, clinopyroxene, opaque, glass etc. Further he also divided the
lava pile in to three stratigraphic units on the basis of vertical variation in
Chemical characteristics and shows the close compositional similarity of these
units with Ambanali and Mahabaleshwar formations of Western Deccan Basalts.
Venkata Rao (1996) carried out Paleomagnetic studies along five sections in the
Western Sempra region and showed that the Shahada–Toranmal section at
western edge has given R-N-R polarity pattern with the flows above 900 m height
showing random directions. The basalts along Eastern part of this sector along
Paratwada-Chikhaldara section, reveal transitional directions at lower elevations
and reverse polarity flows above. James Peter and Sing (2001) studied Satpura
basin and stated that Satpura basin could be considered in terms of Pre- rift, synrift, and post rift phases of Gondwana sedimentation.
(19)
(19)