Executive Summary : | Previous,petrography and petrogenesisoftheDeccan Trap tlowspenetrated by threeboreholesRtotal
thickness = 3,417 feet) in Dhandhuka,Botad and Wadhwan Junction in the eastern Saurastra and
Ahmedabad, Gujaratareasjresolved48 lavatlows,5bedsofagglomerateand 840feetofinterand infra-trappean
beds(W est,I958). Studiespertaining to geochemistry and geochronology (Alexander,1981)and Sr
isotopic compositions(Alexanderand Paul,1977)of190 m thick lava package (comprises of 10 lava
tlows)in Sagarareawereprimarilybased ondrillcoresampes. ecen 'F--drlllz-d-1Qmr a-Bme-Hol'eM -
(KBH-1), Iocated atRasati (Survey of India Topographic sheetNo.47 G/11 and 47 G/15 (scale
1:50,000)j near Koyna (-2.5 km SSW of Koyna Dam reservoir region) is unique of its kind and
representsto a deepestbore hole thatextendsup to the base ofthe Deccan Traps,however,such details
areyettobeascertained(Fig.1).
Physicalfeatures ofthe coresrecovered from the borehole indicated thatthe lava package com prises of
numberofIava tlows,often marked by avesicularand/oramygdaloidaltops(often brecciatealso)and
underlain by fine grained massive basalt.But,no infra-trappean beds were noticed atthe base.These
.
+ longestdrillcore samplesavailable provide unique opportunity to study sub-surface Iava tlow sequences
tlow by tlow.Therefore,such athick basaltic package isrequired to beconstrained in to a stratigraphic
fram ework.However,such studieshave notbeen carried outon K oyana dillcore sam ples. Asdrillcores
are leastaffected by alteration/weathering,they provide more accurate chem icalcompositions,therefore
these samples are ofgreatsigniGcance (whileconstruction ofstratigraphic framework and precise age
estimates).However,Iateralcontinuityoflavatlowsiscriticalforconstructingastratigraphicframework.
Systematic litho-logicallogging backed by detailed petrography ofcore specimenswould be undertaken
in therecognition ofphysically distinctlava tlowsand theirtlow boundaries.'Asmajorpartofthe> ,
DeccanTrapsoutcrop(Fig.2a)ishorizontalorgentlydippingandinsomeareaslavashavebeen
shown to have Iittle Iateralcompositionalvariation for distances of almost 100 km (e.g.,
Choubey,1973;Beaneetal.,1986;LightfootandHawkesworth,1988).Thethickpileofbasalt
in the M ahabaleshwer area of the southwestern Deccan is stratigraphically constrained and
geochemically wellcharacterized (e.g.,Najafietal.,1981;Mahoney etaI.,1982;Cox and
Hawkesworth l985;Beane etal.,1986;Subbarao etal.,1988b;Khadrietal.,1999a;Bodasetal.,
1988;M itchelland Cox,1988;Lightfootand Haw kesw orth,1988;Lightfootetal.,1990;Peng et
aI.,1994).lnthisregion,elevvn basaltformationswererecognized and grouped into threesub-
groups (Fig.2b)with a maximum totalstratigraphic thicknessof3.4 km (e.g.,Subbarao and
Hooper,1988),howeverbaseisnotexposedinthisregion.DrillingthroughtheDeccanTrapsnear
' çCJ
. Koynarevealeda-933m thick pileofbasaltictlows,underlain bygraniticbasementrocks(inproximity
to the 1967 M 6.3 Koyng earthquakesite(Fig.1)j,reached adepth of95lm on January 17,2013 aùd
furtherdrillingisinprogress(RoyetaI.,2013).Theorderofsuperposition inthissequencewouldretlect
thatthe oldertlowsoccuratthe base ofthe BoreHole;however,such assum ptionsneed to be exam ined.
Therefore,itis necessary to find outgeochem icaland isotopic characters ofthe -933 m thick pile of
KoyanabasaltIava tlowsand atthe sametime itisalso necessary to understand chem icalcorrespondence
o t ese ava ows wlih--that o -119--1-1 sou hw estern -eccan fôi-t-f-h-â-tlonrrM r 'e=sectionsr-'f-o
establish nature ofgeochemistry and Ar/Arages ofthe firstlava flow and the clay-stratigraphy ofthe
intervening intratrappen and bole sediments to find out possible level ùf the K/T boundary is also
required.To understand the Iateralcontinuity oflava flowsand to characterizethem into distinctchem ical
types,chemicalsignaturesofthe sampled tlowsare required to be exam ined.Presence ofdistinctive lava
flows in the -933 m thick lava package requires justification from the major and traie elemental
chemistry.Theintrazflow variationswould bestudied insomeofthe tlowsformostofthemajoroxides
and keytraceelements.Basedon major-oxides,theseIavatlowswouldbegroupedintodistinctchemical
types(e.g.high aluminaquartz normativetholeiite,high hypersthene normative tholeiite,diöpside andj . '
olivine norm ativetholeiite,olivine normativetholeiite,tholeiite,high olivine norm ative tholeiiteand high
diopside olivine normative tholeiite).Some of the objectives might be to unambiguously sortout
stratigraphic superposition, geochem ical evolution and ages of the Deccan province. Keeping these
objectives,presentprojectproposalintendstostudydrillcoresoftheentireDeccanvolcanicpile.ltseems.
drillcoresare the only'possible way to makesignificantprogress on furtherunderstanding ofthe Deccan
Traps and its possible relationship with the K/T boundary event.The proposed stratigraphic studies,
primarilybasedontlnetraceelementalabundances,theirratiosandisotopiccompositionsconstitutemajor
compolientandwouldbeundertakeninthisprojectproposal. |