Research Projects

Previous,petrography and petrogenesisoftheDeccan Trap tlowspenetrated by threeboreholesRtotalthickness = 3,417 feet) in Dhandhuka,Botad and Wadhwan Junction in the eastern Saurastra andAhmedabad, Gujaratareasjresolved48 lavatlows,5bedsofagglomerateand 840feetofinterand infra-trappeanbeds(W est,I958). Studiespertaining to geochemistry and geochronology (Alexander,1981)and Srisotopic compositions(Alexanderand Paul,1977)of190 m thick lava package (comprises of 10 lavatlows)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 (scale1:50,000)j near Koyna (-2.5 km SSW of Koyna Dam reservoir region) is unique of its kind andrepresentsto a deepestbore hole thatextendsup to the base ofthe Deccan Traps,however,such detailsareyettobeascertained(Fig.1).Physicalfeatures ofthe coresrecovered from the borehole indicated thatthe lava package com prises ofnumberofIava tlows,often marked by avesicularand/oramygdaloidaltops(often brecciatealso)andunderlain 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 sequencestlow by tlow.Therefore,such athick basaltic package isrequired to beconstrained in to a stratigraphicfram ework.However,such studieshave notbeen carried outon K oyana dillcore sam ples. Asdrillcoresare leastaffected by alteration/weathering,they provide more accurate chem icalcompositions,thereforethese samples are ofgreatsigniGcance (whileconstruction ofstratigraphic framework and precise ageestimates).However,Iateralcontinuityoflavatlowsiscriticalforconstructingastratigraphicframework.Systematic litho-logicallogging backed by detailed petrography ofcore specimenswould be undertakenin therecognition ofphysically distinctlava tlowsand theirtlow boundaries.'Asmajorpartofthe> ,DeccanTrapsoutcrop(Fig.2a)ishorizontalorgentlydippingandinsomeareaslavashavebeenshown to have Iittle Iateralcompositionalvariation for distances of almost 100 km (e.g.,Choubey,1973;Beaneetal.,1986;LightfootandHawkesworth,1988).Thethickpileofbasaltin the M ahabaleshwer area of the southwestern Deccan is stratigraphically constrained andgeochemically wellcharacterized (e.g.,Najafietal.,1981;Mahoney etaI.,1982;Cox andHawkesworth l985;Beane etal.,1986;Subbarao etal.,1988b;Khadrietal.,1999a;Bodasetal.,1988;M itchelland Cox,1988;Lightfootand Haw kesw orth,1988;Lightfootetal.,1990;Peng etaI.,1994).lnthisregion,elevvn basaltformationswererecognized and grouped into threesub-groups (Fig.2b)with a maximum totalstratigraphic thicknessof3.4 km (e.g.,Subbarao andHooper,1988),howeverbaseisnotexposedinthisregion.DrillingthroughtheDeccanTrapsnear' çCJ. Koynarevealeda-933m thick pileofbasaltictlows,underlain bygraniticbasementrocks(inproximityto the 1967 M 6.3 Koyng earthquakesite(Fig.1)j,reached adepth of95lm on January 17,2013 aùdfurtherdrillingisinprogress(RoyetaI.,2013).Theorderofsuperposition inthissequencewouldretlectthatthe 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 ofKoyanabasaltIava tlowsand atthe sametime itisalso necessary to understand chem icalcorrespondenceo t ese ava ows wlih--that o -119--1-1 sou hw estern -eccan fôi-t-f-h-â-tlonrrM r 'e=sectionsr-'f-oestablish nature ofgeochemistry and Ar/Arages ofthe firstlava flow and the clay-stratigraphy oftheintervening intratrappen and bole sediments to find out possible level ùf the K/T boundary is alsorequired.To understand the Iateralcontinuity oflava flowsand to characterizethem into distinctchem icaltypes,chemicalsignaturesofthe sampled tlowsare required to be exam ined.Presence ofdistinctive lavaflows in the -933 m thick lava package requires justification from the major and traie elementalchemistry.Theintrazflow variationswould bestudied insomeofthe tlowsformostofthemajoroxidesand keytraceelements.Basedon major-oxides,theseIavatlowswouldbegroupedintodistinctchemicaltypes(e.g.high aluminaquartz normativetholeiite,high hypersthene normative tholeiite,diöpside andj . 'olivine norm ativetholeiite,olivine normativetholeiite,tholeiite,high olivine norm ative tholeiiteand highdiopside olivine normative tholeiite).Some of the objectives might be to unambiguously sortoutstratigraphic superposition, geochem ical evolution and ages of the Deccan province. Keeping theseobjectives,presentprojectproposalintendstostudydrillcoresoftheentireDeccanvolcanicpile.ltseems.drillcoresare the only'possible way to makesignificantprogress on furtherunderstanding ofthe DeccanTraps and its possible relationship with the K/T boundary event.The proposed stratigraphic studies,primarilybasedontlnetraceelementalabundances,theirratiosandisotopiccompositionsconstitutemajorcompolientandwouldbeundertakeninthisprojectproposal.