RESEARCH ARTICLE

Geochemistry of the Palitana flood basalt sequenceand the Eastern Saurashtra dykes, Deccan Traps: cluesto petrogenesis, dyke–flow relationships, and regional lavastratigraphy

Hetu C. Sheth & Georg F. Zellmer & Pooja V. Kshirsagar &

Ciro Cucciniello

Received: 3 October 2012 /Accepted: 20 February 2013# Springer-Verlag Berlin Heidelberg 2013

Abstract Recent studies of large mafic dyke swarms in theDeccan Traps flood basalt province, India, indicate that someof the correlative lava flows reached several hundred kilome-ters in length. Here we present field, petrographic, mineralchemical, and whole-rock geochemical (including Sr-Nd iso-topic) data on the Palitana lava sequence and nearby dykes inthe Saurashtra region of the northwestern Deccan Traps.These rocks are moderately evolved, many with low-Ti-Nbcharacteristics. We infer that most dykes are notably (andsystematically) less contaminated by ancient continental crustthan the Palitana flows, but four dykes are equally or signif-icantly more contaminated, with some of the most extreme Sr-Nd isotopic compositions seen in the entire Deccan Traps(initial εNd is as low as −18.0). A Bhimashankar-type and aPoladpur-type dyke are present several hundred kilometers

from the type section of these magma types in the WesternGhats escarpment. We find no geochemical correlations be-tween the Palitana sequence and three subsurface sequences inNE Saurashtra containing abundant picritic rocks, surfacelavas previously studied from Saurashtra, or the WesternGhats sequence. Intriguingly, the Eastern Saurashtra dykescannot have been feeders to any of these lava sequences.Feeder dykes of these sequences may be located in southwest-ern or central Saurashtra, or in the Dhule-Nandurbar-Dediapada areas across the Gulf of Cambay, 200–300 km eastof Palitana. Our results indicate polycentric flood basalt erup-tions not only on the scale of the Deccan Traps province, butalso within the Saurashtra region itself.

Keywords Volcanism .DeccanTraps . Flood basalt . India .

Saurashtra . Palitana

Introduction

The Deccan Traps form a vast Late Cretaceous to Palaeocenecontinental flood basalt (CFB) province in India (Fig. 1a). Theflood basalts are best developed in the Western Ghats escarp-ment in the southwestern part of the province (Fig. 1a), wherethey have been divided into three subgroups and 11 forma-tions with a total stratigraphic thickness of ∼3.4 km over a∼500 km region (e.g., Najafi et al. 1981; Cox andHawkesworth 1985; Beane et al. 1986; Khadri et al. 1988;Lightfoot et al. 1990; Online Resource 1). Several stratigraph-ic sections in areas far from the Western Ghats contain lavapackages correlatable with the Western Ghats type section(e.g., Peng et al. 1998; Mahoney et al. 2000), whereas othersare stratigraphically and petrogenetically unrelated (e.g.,

Editorial responsibility: D.W. Peate

Electronic supplementary material The online version of this article(doi:10.1007/s00445-013-0701-x) contains supplementary material,which is available to authorized users.

H. C. Sheth (*) : P. V. KshirsagarDepartment of Earth Sciences,Indian Institute of Technology Bombay (IITB), Powai,Mumbai 400076, Indiae-mail: hcsheth@iitb.ac.in

G. F. ZellmerInstitute of Earth Sciences, Academia Sinica, 128 Academia Road,Nankang,Taipei 11529, Taiwan

C. CuccinielloDipartimento di Scienze della Terra,Università di Napoli Federico II, via Mezzocannone 8,80134 Napoli, Italy

Bull Volcanol (2013) 75:701DOI 10.1007/s00445-013-0701-x

Gundala

Tana

ESD10

ESD13

VaralESD12

Thorali

Jalia

Chok

501

431

401

187

GhetiPalitana

Samadhiala

242

Kadambagiri

Hastagiri

Shatrunjay

Shihor

182

Songadh

145

151

192

H I L L

R

A N G E

Vadal

Todach

Shetrunji River

5 km

H I L L S

Kobadi

Bhadi

Bhandaria

301

Nagdhaniba

To G

hogh

a 3

km

Budhel

VartejKhodiyartemple

Devgana

Agiali

Nesvad

ESD9

Karmadia

ESD16 Sartanpur

VavdiESD14

ESD3

ESD6

ESD8Nathugarh

ESD15

ESD7

Bhawanipura

Tansa

MUDFLA

TS

181

272

172

235

H I

L L

R

A N

G E

7 km2 km

Rabarika

Dihor

ESD5Bhadraval

Samadhiala

Talaja

Pavthi

To Mahuva36 km

119

Trapaj

Trapaj Bungalow RS

Dihor RS

ESD1

ESD2

Garibpura

Alang

Kukad

ESD4

To Palitana28 km

Shetrunji River

MUDFLATS

GULF OFCAMBAY

(KHAMBHAT)

Goriali

ESD17

71o 55'

Hathasani

Trambak

Gulf of C

ambay

To Bhavnagar

50 km

Gulf ofKachchh

ARABIAN SEA

Rajkot

Chogat-Chamardi

Girnar

Osham

Barda

Alech

CA

MB

AY

RIF

T

Mesozoic

Deccan Traps

Tertiary & Quaternary

Diu

Rajula

Shihor

JunagadhDECCANTRAPS

INDIA

Mumbai

ARABIANSEA

Western G

hats

Nandurbar

Dediapada

200 km

Pachmarhi

Dhule

Bhuj

Botad

NasikUmbergaon

SAURASHTRA

KACHCHH

Palitanastudy area

Dhandhuka

Wadhwan

Cambay

a b

c

ESD11Ramgadh

Rohisala

72o 00' 72o 05' 72o 10' 72o 15'71o 50'71o 45'

71o 55' 72o 00' 72o 05' 72o 10' 72o 15'71o 50'71o 45'

21o

20'

21o

25'

21o

30'

21o

35'

21o

40'

21o

45'

21o

20'

21o

25'

21o

30'

23

24

21o

45' To Chogat-Chamardi (5 km) and Valbhipur

0o15o

45o

60o

75o

90o

30o

105o

180o

345o

Palitana Dhadgaon NTDS

CD

S

46 C/2

46 C/3

41 O/14

41 O/15

Jasdan

Amreli

Babra

JabalpurPavagadh

RAJASTHAN

Valespur

72o

21o

70o

22o S A U R A S H T R APorbandar

NPDS

Pune

Dahanu

701, Page 2 of 23 Bull Volcanol (2013) 75:701

Sheth and Melluso 2008), suggesting that the Deccan lavaeruptions were polycentric.

CFBs are produced by large-scale basaltic fissure erup-tions, arguably fed by dyke swarms (e.g., Swanson et al.1975). The Deccan province has three major dyke swarms(Fig. 1a; e.g., Auden 1949; Deshmukh and Sehgal 1988;Vanderkluysen et al. 2011). One is the ∼ENE-WSW-trendingNarmada-Tapi dyke swarm, containing both tholeiitic andalkalic dykes (e.g., Bhattacharji et al. 1996; Melluso et al.1999; Ray et al. 2007). The second is the ∼N-S-trendingCoastal swarm, also with tholeiitic and alkalic dykes, on theKonkan plain between the Arabian Sea and theWestern Ghatsescarpment (e.g., Viswanathan and Chandrasekharam 1976;Widdowson et al. 2000; Hooper et al. 2010). The third is thetholeiitic Nasik-Pune swarm, outcropping in the WesternGhats northeast of Mumbai and partly on the Konkan plain,and with only a weak NNE-SSW preferred orientation (Beaneet al. 1986; Bondre et al. 2006; Vanderkluysen et al. 2011).Whereas the Narmada-Tapi dyke swarm may have fed someof the lower- and middle-level stratigraphic formations of theWestern Ghats sequence, the Coastal and Nasik-Pune swarmscontain many feeders to the middle and upper formations ofthe Western Ghats sequence (Bondre et al. 2006; Widdowsonet al. 2000; Hooper et al. 2010; Vanderkluysen et al. 2011).These results, and those based on plausible long-distance lavaflow correlation (e.g., Self et al. 2008), indicate that some ofthe Deccan lava flows travelled several hundred kilometersfrom their source areas.

The northwestern Deccan Traps (the Saurashtra, Kachchh,and Rajasthan regions, Fig. 1a) are much less studied andunderstood in comparison to the southwestern Deccan(Western Ghats), the central Deccan (the Dhule area), andthe northern and northeastern Deccan regions. Here we pres-ent extensive field, petrographic, mineral chemical, andwhole-rock geochemical (major and trace element and Sr-Ndisotopic) data on the Deccan flood basalt sequence at Palitana,in eastern Saurashtra, and on dykes outcropping betweenPalitana and the Gulf of Cambay (Fig. 1b, c). Using these

varied data sets we discuss the petrogenesis of the lavas andthe dykes, and also evaluate potential genetic relationshipsamong the Palitana lava sequence, the dykes, and previouslystudied mafic lava suites of Saurashtra, as well as more distantpotential correlatives outside Saurashtra. The results elucidatethe regional stratigraphic development and eruptive areas ofthe Deccan flood basalts.

Field geology

Deccan geology of Saurashtra

The Saurashtra peninsula is separated from the main Deccanoutcrop by the Arabian Sea and the Gulf of Cambay, thelatter developed along the Cambay rift (Fig. 1a, b).Geophysical studies and drilling for oil indicate ∼4 km thickbasalts in the Cambay rift buried under younger sediments(Ramanathan 1981), as well as a thinned crust (32–33 km)under the rift and under eastern Saurashtra (Rao and Tewari2005). Saurashtra, covered by the Deccan Traps in largepart, is topographically mostly flat and low lying (50–100 m above sea level); thick vertical sections through thelavas are therefore rare. The coastal fringes of Saurashtraexpose Tertiary and Quaternary calcareous sediments oralluvium. In northern Saurashtra, sub-Deccan Mesozoicsedimentary rocks crop out, and no pre-Mesozoic rocksare known from outcrops, borings, or xenoliths.

The Deccan geology of Saurashtra has special features thatcontrast with much of the Deccan Traps. These include severalvolcano-plutonic complexes, and a great range of rock typesfrom picrites through lamprophyres to rhyolites (e.g., Fedden1884; Krishnan 1926; Mathur et al. 1926; Chatterjee 1932;Subba Rao 1971; Bose 1973; Paul et al. 1977; Melluso et al.1995; Chatterjee and Bhattacharji 2001, 2004; Sheth et al.2011a, 2012; Kshirsagar et al. 2012). Mafic dykes are abun-dant (Auden 1949; Krishnamacharlu 1972; Misra 1999). Wellsdrilled for groundwater at Dhandhuka,Wadhwan, andBotad inNE Saurashtra (Fig. 1b) encountered intercalated basaltic andpicritic flows andminor pyroclastic rocks with a total thicknessof ∼400 m, and the picrites have been interpreted as primitiveliquids with 15–16 wt.% MgO (West 1958; Krishnamurthyand Cox 1977; Peng and Mahoney 1995; Melluso et al. 1995,2006, 2010; Krishnamurthy et al. 2000).

Melluso et al. (1995) sampled mafic lavas (as well asdifferentiated rocks) over a large area of Saurashtra (roughlybounded by the towns of Rajkot, Junagadh, Rajula, Amreli,and Shihor, Fig. 1b) and discussed their mantle sources andmagmatic evolution. Chatterjee and Bhattacharji (2001)studied mafic and silicic rocks from the Shihor-Palitana-Rajula area of eastern Saurashtra, and inferred that therhyolitic rocks had been derived by crustal melting. Theseauthors, and Sethna and Ravivarma (2005), reported major

Fig. 1 Geological maps of the Deccan Traps (a) and of Saurashtra (b),with important features and localities mentioned in the text marked inboth. Elliptical area in (a) is the northwestern Deccan region, withgreat compositional diversity and many igneous complexes (Sheth et al.2011a, 2012). NTDS is the Narmada-Tapi dyke swarm, CDS the Coastaldyke swarm, and NPDS the Nasik-Pune swarm (Vanderkluysen et al.2011 and references therein). Also shown in (b) are drillhole lava se-quences in NE Saurashtra located at Wadhwan, Dhandhuka, and Botad,and igneous complexes of Saurashtra (white stars). c Map of the area ofthe present study, showing the major topographic and geological features,including the Eastern Saurashtra dykes (black lines). The broad topo-graphic forms of Mount Shatrunjay (501 m) at Palitana and Hastagiri Hill(431 m) are shown by the grey contour lines. Filled circles are towns andvillages, and open circleswith the prefix ESD are dyke samples collected.Numbers next to open triangles are elevations in meters above mean sealevel.Numbers within grey ellipses are the 1:50,000 scale Survey of Indiatoposheet numbers, and grey crossesmark the boundaries of four adjacenttoposheets. The inset figure in (c) shows a rose diagram of the dyke trends

�

Bull Volcanol (2013) 75:701 Page 3 of 23, 701

and trace element analyses on some Palitana basalt flows,and several of their analyzed samples show low MgO, TiO2,and Nb contents. Chatterjee and Bhattacharji (2001) alsodated a few Palitana flow samples by the K-Ar method andobtained ages between 64 and 67 Ma.

Field observations and samples

The Palitana flood basalt sequence (∼450 m) is the thickestsequence in all of eastern Saurashtra, forming MountShatrunjay (501 m above mean sea level, Fig. 1c and OnlineResource 2). We sampled the lava flows along a staircasepilgrim route from the town of Palitana to the Jain templecomplex at the summit of Shatrunjay. Due to topographicreasons and the construction, exposures are not found contin-uously along the route, which exposes an essentially flat-lyingmafic lava sequence with at least 14 distinct flows (flow PL1at 490 m through flow PL14 at 90 m). Most flows are of thecompound pahoehoe type and are quite weathered. No dykeswere encountered. Two additional flows (PL15 and PL16)were sampled near a ravine in the south face of Shatrunjaybetween Palitana town and Hastagiri Hill (431 m). From theiraltitudes, we consider these flows as stratigraphically belowthe flows PL1 to PL14 in the Shantrunjay section.

Many ∼ENE-WSW-trending dykes are present in the areabetween Palitana and the Gulf of Cambay. Here termed theEastern Saurashtra dykes, these represent the westward ex-tension of the Narmada-Tapi dyke swarm into Saurashtraacross the Cambay rift (e.g., Auden 1949). They form lowlinear ridges over cultivated, nearly sea-level plains of high-ly weathered basalt flows (Fig. 1c and Online Resource 2),except for dyke ESD16 sampled at 250 m elevation in thehill range west of the Bhavnagar-Talaja Highway. Dykelengths vary from a few kilometers to >14 km (ESD10).Field notes and sample descriptions are provided in OnlineResource 3. The dykes are all mafic, except for a highlyweathered, ∼N-S-trending rhyolite dyke (ESD9) at Devganavillage, and a granophyre (ESD17) of unclear trend on thenorth side of the Palitana–Hastagiri road. Given the objectivesof this study we do not discuss the silicic dykes in any detail.The general ENE-WSW trend of the Eastern Saurashtra maficdykes (Fig. 1c and inset) shows the regional minimum com-pressive stress (σ3) direction to have been oriented NNW-SSEduring dyke emplacement (e.g., Pollard 1987; Gudmundssonand Marinoni 2002; Ray et al. 2007).

Petrography and mineral chemistry

The Palitana lava flows (PL- samples) and the EasternSaurashtra dykes (ESD- samples) are all basalts and doler-ites. Textural features of the freshest lava and dyke samples areillustrated in Fig. 2. Several contain clinopyroxene phenocrysts

or microphenocrysts (Fig. 2a–d), and dyke ESD7 contains raresmall clusters of clinopyroxene grains. The rocks also oftencontain plagioclase phenocrysts, rarely with well-developedzoning. Olivine (generally altered to serpentine or iddingsite)is minor, and flow PL8 and dyke ESD12 are olivine-free.Dykes ESD6 and ESD7 can be called three-phenocryst basalts,with phenocrysts of olivine, clinopyroxene, and plagioclase(Fig. 2b, c). They are of interest because three-phenocrystbasalt lavas have been described from the NE Saurashtradrillhole sequences (West 1958; Krishnamurthy and Cox1977). Most flows and dykes are considerably weathered, asshown by zeolite and calcite infillings, strongly serpentinizedolivine grains in dyke ESD7 (Fig. 2c), and highly alteredplagioclase in dyke ESD12 (Fig. 2d).

Mineral compositions of the lava flow PL8 and threeEastern Saurashtra dykes (ESD6, 7, and 12) were deter-mined using an Oxford Instruments Microanalysis Unitequipped with an INCA X-act detector and a JEOL JSM-5310 microscope at the CISAG (Centro InterdipartimentaleStrumentazioni per Analisi Geomineralogiche), Universityof Napoli. Analyses were performed with an acceleratingvoltage of 15 kV, a filament current of 50–100 μA, andcalibrated with natural and synthetic standards. The elementused for optimization was cobalt. Measuring times were of50 s. Microprobe standards used by Guarino et al. (2012)were used in this study. Relative analytical uncertainty is∼1 % for major elements and 3–5 % for minor elements.

Representative clinopyroxene analyses are presented inOnline Resource 4 and plotted in Fig. 3a. The subhedral toanhedral clinopyroxene phenocrysts and microphenocrysts inthe flow and dyke samples are commonly zoned and range incomposition between En48Fs12Wo40 and En32Fs33Wo35. Afew clinopyroxene crystals in the basaltic andesite PL8 haverims of diopside (En26Fs24Wo50). The phenocrysts show Feenrichment and Ca depletion from core to rim. Compositionsof groundmass clinopyroxenes are similar to those of thephenocrysts and range between En46Fs16Wo39 andEn36Fs29Wo35. Limited Ti enrichment is observed in allclinopyroxenes (up to 1.6 wt.% TiO2). The clinopyroxenesin the analyzed samples have lower Mg numbers (Mg#) of80–49 (where Mg#=Mg×100/[Mg+Fe+Mn]) and CaO thanthe clinopyroxenes of the more primitive NE Saurashtradrillhole lavas (Mg#=91–73; West 1958; Krishnamurthyand Cox 1977; Krishnamurthy et al. 2000; Fig. 3a). The latterclinopyroxenes fall in the diopside/salite field close to thediopside-augite boundary, whereas the clinopyroxenes ofthe rocks analyzed in this study lie within the field definedby the pyroxenes of all other Deccan Traps rocks (Fig. 3a).The different clinopyroxene compositions of the drillholelavas and the rocks of this study indicate different parentalmagmas. De (1981) also noted that optic axial angles of theclinopyroxenes of the drillhole lavas were quite distinct fromthose of clinopyroxenes of the main Deccan tholeiites.

701, Page 4 of 23 Bull Volcanol (2013) 75:701

Plagioclase phenocrysts in the flow and dyke samplesshow a wide range in composition from bytownite (An72) tolabradorite (An54), whereas groundmass plagioclase grainsextend the range towards more albite-rich compositions(Online Resource 4; Fig. 3b). The iron content (as FeOt)ranges from 0.1 to 1.2 wt.%. K-feldspar is rare and occurs inthe groundmass (Fig. 3b). The compositional range of theplagioclase phenocrysts in the rocks of this study partiallyoverlaps the field defined by plagioclase grains of thedrillhole lavas (Fig. 3b).

Opaque oxides analyzed in the flow and dyke samples areilmenite and Ti-magnetite (Online Resource 4). Ti-magnetiteshows a large range in ulvöspinel content (6–72 mol%),whereas ilmenite has a more restricted range (ilm92 to ilm88).Ilmenites have low Al2O3 (<0.5 wt.%) and MgO (<0.7 wt.%)

contents. Coexisting Fe-Ti oxides showed a wide range ofequilibration temperatures (1,130–793 °C) and oxygen fugac-ities (−9 to −14 log fO2 units), calculated using the program ofLepage (2003). Only the ESD12 data (temperature values of1,100–1,200 °C on the QFM buffer) can represent magmaticconditions, the others indicating late-stage subsolidus re-equilibration and alteration.

Whole-rock geochemistry

Analytical methods

Small chips of 16 Palitana flow samples and 17 EasternSaurashtra dyke samples were cleaned in an ultrasonic bath

Fig. 2 Main petrographic features of the Palitana lavas and the EasternSaurashtra dykes. Only the freshest samples are represented. Mineralnames are abbreviated as cpx (clinopyroxene), ol (olivine), and pl(plagioclase). Small black grains are Fe-Ti oxides. a PL8, basalticandesite flow: a cluster of clinopyroxene phenocrysts set in a fine-grained groundmass composed of clinopyroxene, plagioclase, and Fe-Ti oxides. b ESD6, subalkalic basalt dyke: altered olivine, plagioclase,and clinopyroxene phenocrysts in a groundmass of plagioclase,

clinopyroxene, and Fe-Ti oxides. c ESD7, basaltic andesite dyke:olivine (completely serpentinized), clinopyroxene, and plagioclasephenocrysts set in a groundmass composed of clinopyroxene, plagioclase,and Fe-Ti oxides. d ESD12, basaltic andesite dyke: clinopyroxene andplagioclase phenocrysts in a groundmass composed of clinopyroxene,plagioclase, and Fe-Ti oxides. All views are between crossed polars and atthe same scale

Bull Volcanol (2013) 75:701 Page 5 of 23, 701

and ground to powders of <75 μm grain size using a RetschPM-100 planetary ball mill and stainless steel grinding balls,at IIT Bombay. Then, 0.25 g of sample powder was mixedwith 0.75 g lithium metaborate (LiBO2) and 0.50 g oflithium tetraborate (LiB4O7) in a platinum crucible, andfused in a muffle furnace at 1,050 °C for 10 min. Aftercooling, the crucible was carefully immersed in 80 ml of 1 NHCl in a 150-ml glass beaker and then magnetically stirredfor 1 h until the fusion bead had dissolved completely. Thesample volume was made up to 100 ml in a volumetric flask.Ten milliliters of this solution diluted to 100 ml with dis-tilled water was analyzed by inductively coupled plasmaatomic emission spectrometry (ICP-AES) at theDepartment of Earth Sciences, IIT Bombay (instrument:Jobin Yvon Ultima-2). Several USGS rock standards weredissolved along with the samples. The standards DTS-2b,BIR-1, and BCR-2 were used for calibrating the instrument,and the standard BHVO-2 was analyzed along with thesamples to estimate the analytical accuracy. Loss on ignition(LOI) values were determined at IIT Bombay by heating therock powders at 1,000 °C in platinum crucibles, after

overnight drying in an oven at 110 °C to drive awayadsorbed moisture (H2O

−). The major oxide and LOI valuesare presented in Table 1.

A large suite of trace elements including the rare earthelements (REE) was analyzed at National Taiwan Universityon dissolutions of the samples by inductively coupled plas-ma mass spectrometry (ICP-MS), using an Agilent 7500cxspectrometer. Sample powders were dissolved in a HF-HNO3 (3:1) mixture in capped Savilex beakers at ca.100 °C, followed by evaporation to dryness, refluxing in 7 NHNO3, followed by evaporation to dryness and final dissolu-tion of the sample cake in 2 % HNO3. The solution wasdiluted with 2 % HNO3 and an internal standard solutionof 10 ppb Rh and Bi to a sample/solution weight ratioof 1:4,000. The internal standard was used for monitor-ing signal shift during ICP-MS measurements. The an-alytical precision for trace elements is better than ±5 %(2σ). Also run as an unknown was a solution of theBHVO-2 standard, measurements on which agreed wellwith the recommended values. The trace element data arereported in Tables 2 and 3.

diopside hedenbergite

enstatite ferrosilite

augite

pigeonite

feldspars in NE Saurashtra drillhole lavas

feldspars in all other Deccan Traps rocks

Anorthite

Albite Orthoclase

PL8

ESD7ESD6

ESD12

sanidineanorthoclase

olig

ocla

sean

desi

nela

brad

orite

byto

wni

te

CaMgSi2O6 CaFeSi2O6

Mg2Si2O6 Fe2Si2O6

pyroxenes in NE Saurashtra drillhole lavas

pyroxenes in all other Deccan Traps rocks

b

a

Fig. 3 a Pyroxenecompositions projected in theCa-Mg-Fe diagram for thePalitana lava PL8 and theEastern Saurashtra dykesESD6, ESD7, and ESD12.Compositional fields are shownfor pyroxenes in the NESaurashtra drillhole lavas(Krishnamurthy and Cox 1977)and in all other Deccan Traprocks (Melluso and Sethna2011 and references therein;Sheth et al. 2011a, 2012; L.Melluso, unpublished data). bFeldspar compositions in thesame samples. Feldsparcompositions in the DeccanTraps rocks including the NESaurashtra drillhole lavas areshown for comparison. Datasources are as in (a)

701, Page 6 of 23 Bull Volcanol (2013) 75:701

Tab

le1

Major

oxidecompo

sitio

ns(inwt.%

)of

thePalitana

lavas(PL-)andtheEastern

Saurashtrady

kes(ESD-)

Elev.

480m

471m

469m

465m

455m

450m

380m

370m

355m

335m

310m

250m

150m

90m

∼60m

∼50m

Sam

ple

PL1

PL2

PL3

PL4

PL5

PL6

PL7

PL8

PL9

PL10

PL11

PL12

PL13

PL14

PL15

PL16

BHVO-2

BHVO-2

Com

pBA

TB,p

TB,p

B,sa

B,sa

B,sa

B,sa

BA

BA

BA

B,sa

B,sa

BA

B,sa

BA

BA

Ref.

Meas.

SiO

252

.54

51.14

51.35

51.86

51.05

51.52

51.07

52.00

52.94

52.48

50.75

49.41

52.02

51.32

53.49

52.50

49.9

50.22

TiO

22.86

2.24

2.30

1.39

1.26

1.23

1.64

1.64

1.62

2.64

1.87

1.25

1.14

1.21

1.11

1.07

2.73

2.71

Al 2O3

12.60

14.46

14.23

15.09

15.02

14.77

14.23

13.38

13.91

12.65

13.87

14.37

14.53

15.53

12.73

14.13

13.5

13.23

FeO

11.39

10.40

9.89

9.52

9.22

9.27

9.14

8.30

8.06

10.87

10.74

10.62

8.33

8.86

8.23

7.76

Fe 2O3

3.42

3.12

2.97

1.90

1.85

1.85

1.83

2.49

2.42

3.26

2.15

2.12

2.50

1.77

2.47

2.33

12.3

12.60

MnO

0.21

0.17

0.20

0.18

0.20

0.15

0.17

0.16

0.16

0.20

0.21

0.20

0.17

0.16

0.17

0.17

0.166

0.17

MgO

4.12

4.82

5.09

6.13

6.67

6.39

6.92

7.25

6.12

4.26

5.62

7.74

6.57

5.76

6.44

6.29

7.23

7.26

CaO

8.74

8.27

8.44

10.83

11.24

11.73

9.90

11.61

11.10

10.12

10.52

12.15

11.92

13.03

12.16

12.46

11.4

11.55

Na 2O

2.18

2.44

2.98

2.27

2.45

2.01

2.99

2.25

2.59

1.72

2.90

1.68

1.98

1.90

1.72

2.03

2.22

2.05

K2O

1.84

2.83

2.44

0.74

0.95

0.85

1.77

0.72

0.90

1.62

1.22

0.31

0.75

0.21

1.27

0.90

0.52

0.42

P2O5

0.10

0.09

0.11

0.09

0.09

0.22

0.32

0.21

0.20

0.19

0.16

0.14

0.11

0.25

0.21

0.35

0.27

0.28

Mg#

39.2

45.3

47.9

53.4

56.3

55.1

57.4

60.9

57.5

41.1

48.3

56.5

58.4

53.7

58.3

59.1

(LOI)

1.63

4.02

4.45

5.63

5.52

5.20

4.70

5.40

4.84

3.82

7.00

6.20

6.00

4.40

5.20

5.30

Trend

N80

°N75

°N80

°N88

°N65

°N10

0°N88

°N88

°N70

°N80

°N80

°N60

°N90

°N85

°N70

°N35

5°?

Sam

ple

ESD1

ESD2

ESD3

ESD4

ESD5

ESD6

ESD7

ESD8

ESD10

ESD11

ESD12

ESD13

ESD14

ESD15

ESD16

ESD9

ESD17

Com

pB,sa

AA

BA

AB,sa

BA

B,sa

BA

B,sa

BA

B,sa

BA

BA

B,sa

Rhy.

Gran.

SiO

251

.74

59.36

59.55

52.28

61.17

51.30

56.17

51.24

55.62

50.83

52.05

51.18

52.59

52.65

51.44

88.46

75.20

TiO

22.58

1.46

1.29

1.92

1.26

2.95

1.36

2.35

2.79

2.55

2.63

1.07

1.78

2.30

2.27

0.34

0.51

Al 2O3

13.65

13.71

14.03

12.78

13.68

13.43

15.91

12.32

12.14

13.72

14.83

14.32

13.28

12.95

12.96

9.14

12.08

FeO

10.39

7.58

7.00

8.41

6.62

10.25

7.14

9.97

9.48

10.56

9.06

10.09

9.93

9.39

10.63

0.53

1.19

Fe 2O3

2.08

2.65

2.45

2.52

2.32

2.05

2.14

1.99

2.84

2.11

2.72

2.02

2.98

2.82

2.13

1.07

2.39

MnO

0.19

0.13

0.13

0.17

0.13

0.19

0.13

0.18

0.18

0.20

0.17

0.19

0.20

0.17

0.19

0.01

0.03

MgO

6.47

3.61

4.05

7.46

3.53

5.92

4.32

8.10

4.53

6.41

5.30

6.71

6.21

6.97

6.73

0.13

0.74

CaO

9.42

6.38

5.96

11.05

5.44

11.07

9.00

10.68

8.33

10.60

10.01

12.17

10.78

9.20

11.52

0.13

1.50

Na 2O

2.30

2.77

2.43

2.34

2.63

1.96

1.84

2.78

2.28

2.45

2.29

1.78

1.90

3.06

1.65

0.00

1.84

K2O

0.90

2.09

2.91

0.91

3.12

0.62

1.79

0.20

1.64

0.36

0.74

0.35

0.24

0.30

0.30

0.15

4.37

P2O5

0.28

0.26

0.21

0.16

0.11

0.27

0.19

0.20

0.18

0.20

0.19

0.12

0.13

0.19

0.17

0.05

0.13

Mg#

52.6

45.9

50.8

61.3

48.7

50.7

51.9

59.2

46.0

52.0

51.0

54.2

52.7

56.9

53.0

17.4

35.7

(LOI)

3.83

1.73

1.47

4.27

1.40

3.75

2.45

4.83

5.25

4.50

4.36

5.16

1.05

0.68

4.56

5.25

3.91

The

resolutio

nof

thealtim

eterwas

10m,sorepo

rted

elevations

ofsuccessive

flow

sthatare<10

mdifferentsay

nomorethan

theirorderof

superposition

.“Com

p.”indicatescompo

sitio

n(rocktype)

asdeterm

ined

bytheSIN

CLASprog

ram

(Vermaet

al.20

02)basedon

LOI-free

recalculated

data

andthetotalalkali–silica

diagram

ofLeBas

etal.(198

6).The

LOIvalues

arealso

prov

ided,

however,andprov

idean

idea

abou

tthedegree

ofalteratio

n,especially

inthemafic

rocks.Reference

values

andmeasuredvalues

ontheUSGSstandard

BHVO-2

(Wilson

,20

00)prov

idean

idea

abou

tanalytical

accuracy.ItsFe 2O3values

representtotaliron

measuredas

Fe 2O3

B,sasubalkalicbasalt,

BAbasalticandesite,A

andesite,T

B,p

potassictrachy

basalt,

ESD

9isarhyo

litedy

ke,w

ithvery

high

silicaow

ingto

considerablesilicification,

ESD

17isgranop

hyre

dyke

ofrhyo

litecompo

sitio

n,Mg#

100Mg2

+/(Mg2

++Fe2

+),atom

ic

Bull Volcanol (2013) 75:701 Page 7 of 23, 701

Tab

le2

Trace

elem

entdata

(inpp

m)forthePalitana

lavas

Sam

ple

PL1

PL2

PL3

PL4

PL5

PL6

PL7

PL8

PL9

PL10

PL11

PL12

PL13

PL14

PL15

PL16

BHVO-2

meas.

BHVO-2

recom.

P1,267

1,025

1,041

469

635

614

725

693

684

1,367

718

374

402

457

410

389

1,137

1,200

Sc

28.1

28.6

28.9

41.6

31.4

37.7

29.2

30.0

28.6

29.0

37.8

46.9

42.4

40.0

45.1

43.8

31.4

32

Ti

15,470

12,580

13,160

8,120

7,352

7,392

9,521

9,522

9,798

15,160

11,030

7,569

6,583

7,406

6,886

6,379

16,475

16,300

V338

315

303

263

239

249

292

303

294

361

311

292

252

267

297

255

321

317

Cr

127

97.6

101

264

174

190

297

375

281

139

134

247

195

245

234

210

288

280

Mn

1,465

1,230

1,413

1,237

1,433

1,077

1,185

1,154

1,139

1,301

1,468

1,413

1,199

1,170

1,245

1,212

1,312

1,290

Co

38.3

39.9

40.8

41.3

43.3

44.2

40.8

40.2

38.0

40.2

40.6

51.2

41.3

39.5

40.2

39.1

44.2

45

Ni

38.4

47.3

36.4

87.2

116

103

68.2

68.2

53.2

50.3

45.6

98.0

89.0

85.8

83.2

72.8

120

119

Cu

1,506

1,356

491

1,240

2,854

673

647

392

195

2,756

295

925

2,212

915

1,913

494

137

127

Zn

917

806

337

733

1,634

434

449

295

175

1,621

233

566

1,263

541

1,073

307

103

103

Ga

23.7

20.8

20.8

17.2

18.3

18.9

21.5

19.7

21.5

25.5

20.7

18.4

16.4

18.3

17.0

16.0

21.9

21.7

Rb

40.5

74.0

66.9

17.5

22.8

22.1

55.0

21.5

26.6

47.2

48.7

5.95

21.7

3.58

38.5

28.8

9.40

9.8

Sr

251

331

277

241

261

296

306

331

264

304

159

160

317

230

221

288

392

389

Y37.8

28.9

29.8

25.9

24.5

25.3

23.9

23.4

22.7

36.6

28.0

24.0

22.9

21.5

24.0

22.3

26.9

26

Zr

236

173

178

90.5

113

114

129

127

127

208

140

75.4

83.0

75.8

77.1

79.5

172

172

Nb

22.8

17.1

17.9

5.05

7.62

7.68

7.53

7.54

6.90

14.7

9.32

3.63

4.67

4.38

4.74

4.51

18.6

18

Cs

0.799

0.252

0.251

0.464

0.293

0.243

0.293

0.371

0.134

0.276

0.262

0.244

0.278

0.088

0.194

0.174

0.094

0.1

Ba

362

423

398

221

323

242

305

181

170

349

248

127

219

94.8

283

234

145

130

La

27.6

22.9

23.6

11.7

15.8

15.9

16.4

16.1

16.3

23.2

16.6

7.94

11.1

8.01

11.4

10.8

14.9

15

Ce

63.1

51.4

53.9

25.2

33.7

34.5

36.6

35.9

35.9

52.9

36.9

18.5

24.0

19.2

24.4

23.4

37.6

38

Pr

8.14

6.51

6.78

3.12

4.07

4.14

4.59

4.52

4.49

6.82

4.62

2.31

2.94

2.40

3.03

2.87

5.27

5.29

Nd

34.1

26.9

28.0

13.4

16.7

16.9

19.3

19.0

18.9

29.1

19.7

10.4

12.4

10.9

12.6

12.1

24.3

25

Sm

7.72

6.08

6.35

3.51

3.91

4.01

4.65

4.59

4.52

7.14

5.04

2.96

3.16

2.95

3.24

3.10

6.19

6.2

Eu

2.24

1.91

2.00

1.18

1.27

1.29

1.47

1.44

1.42

2.07

1.60

1.09

1.02

1.11

1.08

1.03

2.05

2.07

Gd

7.81

6.07

6.33

4.10

4.25

4.31

4.80

4.73

4.64

7.32

5.39

3.71

3.65

3.54

3.76

3.61

6.21

6.3

Tb

1.19

0.918

0.963

0.672

0.671

0.681

0.736

0.727

0.713

1.13

0.836

0.616

0.600

0.580

0.613

0.589

0.929

0.9

Dy

6.99

5.35

5.58

4.34

4.15

4.25

4.35

4.31

4.20

6.65

5.01

4.08

3.86

3.75

3.97

3.80

5.30

5.31

Ho

1.40

1.08

1.12

0.931

0.864

0.902

0.873

0.86

0.845

1.34

1.02

0.878

0.826

0.798

0.851

0.814

1.01

1.04

Er

3.69

2.81

2.93

2.54

2.37

2.43

2.27

2.26

2.21

3.52

2.66

2.43

2.27

2.18

2.32

2.24

2.53

2.54

Tm

0.525

0.395

0.414

0.372

0.343

0.352

0.317

0.317

0.307

0.490

0.376

0.357

0.335

0.322

0.345

0.333

0.34

0.34

Yb

3.26

2.47

2.55

2.36

2.18

2.25

1.96

1.96

1.92

3.07

2.35

2.29

2.14

2.02

2.16

2.14

2.055

2

Lu

0.469

0.352

0.367

0.347

0.322

0.330

0.279

0.281

0.270

0.438

0.337

0.331

0.318

0.296

0.314

0.312

0.2865

0.28

Hf

5.93

4.25

4.43

2.25

2.63

2.67

3.18

3.23

3.21

5.13

3.59

2.00

2.11

1.94

2.03

2.07

4.23

4.1

Ta

1.53

1.13

1.18

0.332

0.474

0.479

0.524

0.523

0.488

0.983

0.645

0.254

0.357

0.295

0.363

0.354

1.175

1.4

W0.446

0.353

0.285

0.166

0.157

0.194

0.141

0.122

0.195

0.279

0.157

0.112

0.203

0.133

0.248

0.169

0.208

0.27

Tl

0.169

0.284

0.249

0.082

0.148

0.110

0.206

0.094

0.086

0.218

0.169

0.036

0.146

0.026

0.212

0.163

0.020

0.059

Pb

107

77.8

35.7

77.4

177

53.7

35.9

29.4

15.6

161

23.0

56.7

128

59.0

105

45.4

1.28

2.2

Th

5.92

3.85

3.97

2.52

3.90

3.88

3.91

3.86

4.10

5.64

4.87

1.29

3.22

1.11

3.26

3.15

1.24

1.2

U1.38

0.897

0.920

0.483

0.581

0.673

0.799

0.801

0.930

1.29

1.06

0.287

0.940

0.239

0.969

0.885

0.421

0.42

701, Page 8 of 23 Bull Volcanol (2013) 75:701

Tab

le3

Trace

elem

entdata

(inpp

m)fortheEastern

Saurashtramafic

andsilicicady

kes

Sam

ple

ESD1

ESD2

ESD3

ESD4

ESD5

ESD6

ESD7

ESD8

ESD9a

ESD10

ESD11

ESD12

ESD13

ESD14

ESD15

ESD16

ESD17

a

P1,315

1,134

751

635

731

946

628

676

218

849

832

843

519

639

863

812

593

Sc

25.0

26.3

19.9

26.7

16.9

26.7

28.0

32.7

6.31

27.8

27.4

25.7

46.3

39.2

27.5

29.6

8.24

Ti

14,200

8,259

7,697

10,250

7,000

16,110

7,993

13,010

1,989

15,880

14,230

14,910

6,632

11,300

13,490

13,880

3,188

V322

250

176

279

146

361

225

379

41.7

311

347

341

344

371

345

374

16.5

Cr

259

176

248

468

344

161

243

380

506

218

214

197

454

440

299

308

304

Mn

1,374

973

979

1,225

891

1,387

930

1,253

38.1

1,268

1,449

1,250

1,526

1,495

1,283

1,480

220

Co

44.3

26.6

26.9

39.4

23.9

42.1

29.7

45.1

3.54

37.1

43.8

39.3

49.0

46.4

46.6

51.0

3.45

Ni

96.2

31.2

66.9

57.3

102

81.1

35.5

127

25.1

89.5

88.5

88.6

104

96.6

121

130

21.6

Cu

3,008

1,038

918

1,005

4,742

588

336

516

824

2,468

680

1,194

1,480

1,427

1,479

2,262

1,311

Zn

1,784

682

611

653

2,774

388

265

301

474

1,365

391

683

819

794

862

1,282

760

Ga

25.4

21.7

22.5

18.5

22.1

24.8

20.8

20.7

15.5

18.1

21.2

23.2

17.4

21.4

22.0

22.7

20.9

Rb

27.0

64.7

85.0

24.8

114

9.78

62.9

6.99

25.6

24.7

14.0

20.9

14.6

10.7

16.8

15.6

167

Sr

269

176

134

356

129

299

194

187

8.64

261

281

296

148

205

243

263

75.3

Y30.1

33.7

44.0

25.3

45.6

30.6

30.4

24.0

53.5

31.7

29.0

28.6

26.0

29.6

25.3

27.0

51.6

Zr

83.3

222

300

83.4

326

188

191

121

278

168

120

147

72.1

120

142

145

203

Nb

16.3

12.9

18.3

13.8

19.5

18.5

13.7

9.93

26.6

14.2

11.9

12.0

9.63

7.71

12.6

11.7

23.0

Cs

0.420

0.383

0.515

0.586

0.759

0.180

0.465

0.168

0.460

0.198

0.193

0.375

0.210

0.264

0.472

0.415

1.03

Ba

195

477

534

247

562

192

378

87.0

67.0

467

141

119

136

98.0

132

116

797

La

18.4

33.2

42.3

16.7

45.2

17.6

28.5

9.89

46.2

14.9

14.5

14.6

7.43

10.1

14.8

13.1

72.6

Ce

43.6

71.1

88.8

40.2

96.4

43.0

61.7

25.1

103

35.8

35.1

35.6

17.8

24.7

35.5

32.8

153

Pr

5.81

8.49

10.7

5.31

11.5

5.89

7.37

3.65

11.6

5.02

4.87

4.96

2.19

3.46

4.81

4.51

16.5

Nd

25.1

32.6

40.4

22.7

43.1

26.1

29.0

17.3

42.6

23.1

22.3

22.8

9.78

16.3

21.5

20.8

61.6

Sm

6.08

6.72

8.32

5.33

8.73

6.47

6.18

4.74

8.41

6.12

5.82

6.03

2.81

4.62

5.49

5.49

11.6

Eu

1.84

1.79

1.92

1.64

1.87

2.04

1.65

1.60

1.68

1.99

1.90

1.99

1.03

1.61

1.75

1.80

1.65

Gd

6.26

6.57

8.18

5.33

8.46

6.62

6.02

5.12

7.93

6.59

6.21

6.37

3.74

5.38

5.57

5.77

10.1

Tb

0.955

1.01

1.28

0.803

1.32

1.00

0.911

0.790

1.29

1.02

0.952

0.971

0.639

0.859

0.846

0.876

1.55

Dy

5.62

5.95

7.68

4.70

7.85

5.85

5.40

4.68

8.44

5.98

5.60

5.67

4.33

5.39

4.91

5.17

9.01

Ho

1.11

1.23

1.59

0.930

1.62

1.14

1.10

0.913

1.88

1.18

1.10

1.10

0.951

1.11

0.953

1.01

1.85

Er

2.87

3.31

4.32

2.38

4.42

2.92

2.98

2.33

5.43

3.01

2.82

2.78

2.64

2.92

2.43

2.58

5.09

Tm

0.400

0.479

0.633

0.333

0.642

0.402

0.427

0.317

0.822

0.418

0.386

0.376

0.394

0.416

0.330

0.351

0.751

Yb

2.43

3.02

4.04

2.05

4.09

2.46

2.69

1.91

5.31

2.53

2.32

2.28

2.49

2.58

1.99

2.15

4.74

Lu

0.334

0.438

0.587

0.285

0.593

0.345

0.394

0.263

0.771

0.352

0.322

0.314

0.363

0.368

0.278

0.302

0.680

Hf

2.58

5.36

7.26

2.66

7.72

4.71

4.81

3.14

7.23

4.25

3.20

3.69

1.81

3.08

3.48

3.63

5.66

Ta

1.15

0.851

1.24

0.927

1.29

1.29

0.933

0.688

1.77

0.960

0.827

0.832

0.647

0.520

0.887

0.803

1.83

W0.381

0.463

0.780

0.264

0.832

0.328

0.586

0.130

0.720

0.205

0.214

0.192

0.289

0.300

0.336

0.314

1.29

Tl

0.178

0.312

0.354

0.100

0.588

0.060

0.211

0.034

0.123

0.218

0.091

0.106

0.055

0.069

0.087

0.095

0.734

Pb

223

97.1

89.4

88.6

347

47.4

46.7

35.4

62.3

162

44.6

80.7

114

106

105

150

108

Th

4.50

11.8

16.9

2.47

18.7

3.81

10.0

1.36

22.2

2.31

2.27

2.23

0.952

1.55

2.82

2.04

31.9

U1.17

2.00

3.22

0.484

3.52

1.01

1.68

0.330

3.58

0.362

0.469

0.470

0.247

0.388

0.704

0.529

6.86

Bull Volcanol (2013) 75:701 Page 9 of 23, 701

A large subset of the samples (nine of the 16 flows andeight of the 15 mafic dykes, chosen so as to cover the rangeof the elemental variations) was analyzed for strontium andneodymium isotopic ratios at the Institute of Earth Sciences(IES), Academia Sinica, Taipei. Approximately 75–100 mgof whole rock powder was dissolved in a mixture of HF-HNO3 (3:1). Strontium and the REE were separated on quartzglass columns with a 2.5-ml resin bed of AG 50 W-X8, 100–200 mesh. Strontium was further purified by passing througha 0.15-ml column of Eichrom Sr-resin (100–150 μm).Neodymium was isolated from other REEs on 1-ml columnsusing Eichrom Ln resin (100–150 μm) as a cation exchangemedium.

Strontium was loaded on a single tungsten filament withH3PO4 for analysis using a Finnigan MAT-262 thermalionization mass spectrometer (TIMS) at the IES. 87Sr/86Srratios were normalized to 86Sr/88Sr=0.1194. NBS 987 wasused as a standard reference material and reproduced withina mean 87Sr/86Sr value of 0.710246±0.000020 (2 SE, long-term running average). The 2σ uncertainties of the 87Sr/86Srisotopic ratios are less than ±0.000015 for all samples exceptone.

Neodymium was analyzed as a 0.5 N HNO3 solutionusing a Nu Instruments multi-collector inductively coupledplasma mass spectrometer (MC-ICP-MS) at the IES.143Nd/144Nd ratios were normalized to 146Nd/144Nd=0.7219. We employed the JMC Nd standard in a sample-standard bracketing procedure, and normalized all samplesto a value of 0.511833 for this standard. The 2σ uncertaintiesof the 143Nd/144Nd isotopic ratios are less than ±0.000013 forall samples. Repeat analyses of the La Jolla Nd standardyielded 143Nd/144Nd=0.511842±0.000015 (2 SE, n=6). TheSr-Nd isotopic data are presented in Table 4.

Alteration

Though material as fresh as possible was collected in thefield, petrographic observations and LOI values indicateconsiderable alteration. LOI values range from 1.63 wt.%to as much as 7.00 wt.% for the flows, with 15 of the 16samples having values >3.82 wt.%. LOI values are 0.68–5.25 wt.% for the dykes, with 10 of the 15 dykes havingvalues >2 wt.% (Table 1). This alteration may have resultedin the loss (or gain) of the more mobile elements such as K,Na, Rb, Ba, Sr, and Pb (e.g., Peate et al. 2012). In fact,compared to the common 2–5 ppm Pb concentrations in theWestern Ghats and other Deccan lavas, as well as maficdykes (e.g., Peng et al. 1994, 1998; Vanderkluysen et al.2011), the Palitana flows have Pb concentrations rangingfrom 15.6 ppm (PL9) to as much as 177 ppm (PL5). Thedykes have still higher Pb concentrations from 44.6 ppm(ESD10) to as high as 347 ppm (ESD5). Pb contents do notcorrelate well with LOI values, but there are excellent

positive correlations (R2=0.98) between Pb and Cu, andbetween Pb and Zn for the samples (Online Resource 5),suggesting that hydrothermal fluids with high Pb-Cu-Znmay have affected the rocks. A similar alteration phenome-non has been reported from late-stage Deccan alkali basaltin the Mumbai area (Zellmer et al. 2012). Given the strongweathering, we treat the concentrations of the mobile ele-ments with caution, and use only the alteration-resistantelements (Ti, Zr, Nb, Y, Th, and the REE) and their ratios, aswell as isotopic ratios (particularly of Nd) for geochemistry-based interpretations.

Major and trace element variations

MgO contents of the flows range from 7.74 wt.% (PL12) to4.12 wt.% (PL1), and Mg# values from 60.9 to 39.2. MgOcontents of the dykes range from 8.10 wt.% (ESD8) to3.53 wt.% (ESD5), and Mg# values from 61.3 to 45.9(Table 1). Most flow and dyke samples have Mg# between45 and 55, suggesting that the rocks are moderately evolved.Our stratigraphically controlled samples from the Palitanalava sequence provide an opportunity to observe the mag-matic evolution with time. Figure 4 shows the concentra-tions and ratios of key alteration-resistant trace elements (Ti,Zr, Nb, Y, Th, and the REE) in the Palitana sequence plottedagainst the heights of the samples. Plots like this, for scoresof measured sections in the Western Ghats, have been usedto see magmatic evolutionary trends and, together with fielddata, to define stratigraphic formations (e.g., Najafi et al.1981; Cox and Hawkesworth 1984, 1985; Beane et al. 1986;Devey and Lightfoot 1986; Lightfoot and Hawkesworth1988; Lightfoot et al. 1990).

Based on combined shifts in the values of ratios ofalteration-resistant incompatible elements in Fig. 4, we di-vide the Palitana sequence into four intervals. The fourintervals (flows PL1–PL3, PL4–PL6, PL7–PL11, andPL12–PL16) are particularly well distinguished in thepanels of Ti/Y, La/Nb, Dy/Yb, and Zr/Nb vs. elevation.For example, flows PL1–PL3 have distinctly lower La/Nband Zr/Nb ratios, and distinctly higher Dy/Yb and Ti/Yratios, than flows PL4–PL6. Within these main intervals,there may be slight differences between flows. Thus flowsPL10–11 have distinctly lower La/Nb and Zr/Nb than theoverlying flows PL7–9. The ratio Zr/Nb is little changedeven during extreme alteration, is insensitive to fractionalcrystallization of minerals common in basaltic magmas, andis therefore one of the more useful in petrogenetic interpre-tations and geochemical comparisons of altered Deccanbasalts (e.g., Mitchell and Widdowson 1991). The signifi-cant variations in immobile incompatible trace element ra-tios within the Palitana lavas indicate that they are notrelated by simple crystal fractionation processes, and requiredifferent sources, degrees of melting, or assimilation of

701, Page 10 of 23 Bull Volcanol (2013) 75:701

Tab

le4

Isotop

icdata

forselected

Palitana

lavasandEastern

Saurashtramafic

dykes

Sam

ple

Rb/Sr

87Rb/

86Sr

(87Sr/86Sr)p

±2σ

(87Sr/86Sr)t

Sm/Nd

147Sm/144Nd

(143Nd/

144Nd)

p±2

σ(143Nd/

144Nd)

tεN

d t

PL1

0.16

10.46

70.71

0934

0.00

0013

0.71

0503

0.22

640.13

690.51

2202

0.00

0007

0.51

2144

−8.0

PL3

0.24

20.69

90.71

0937

0.00

0008

0.71

0292

0.22

680.13

710.51

2214

0.00

0007

0.51

2156

−7.8

PL7

0.18

00.52

00.7117

560.00

0013

0.7112

760.24

090.14

570.51

2014

0.00

0010

0.5119

52−11.7

PL9

0.10

10.29

20.7115

790.00

0013

0.7113

100.23

920.14

460.51

2017

0.00

0008

0.5119

56−11.7

PL10

0.15

50.44

90.71

2092

0.00

0008

0.7116

770.24

540.14

830.51

2247

0.00

0007

0.51

2184

−7.2

PL11

0.30

60.88

60.71

4743

0.00

0009

0.71

3925

0.25

580.15

470.51

2295

0.00

0008

0.51

2229

−6.3

PL12

0.03

70.10

80.7110

040.00

0009

0.71

0905

0.28

460.17

210.51

2221

0.00

0010

0.51

2148

−7.9

PL13

0.06

80.19

80.71

2770

0.00

0014

0.71

2587

0.25

480.15

410.5119

470.00

0009

0.5118

81−13

.1

PL16

0.10

00.28

90.71

3445

0.00

0008

0.71

3178

0.25

620.15

490.5119

260.00

0010

0.5118

60−13

.5

ESD3a

0.63

41.83

50.73

0250

0.00

0026

0.72

8555

0.20

590.12

450.5117

140.00

0012

0.5116

61−17

.4

ESD4

0.07

00.20

20.70

9768

0.00

0009

0.70

9582

0.23

480.14

200.51

2346

0.00

0007

0.51

2286

−5.2

ESD5

0.88

42.55

70.73

1951

0.00

0011

0.72

9590

0.20

260.12

250.5116

820.00

0006

0.5116

30−18

.0

ESD10

a0.09

50.27

40.70

7849

0.00

0009

0.70

7596

0.26

490.16

020.51

2678

0.00

0010

0.51

2610

+1.1

ESD11

0.05

00.14

40.70

8019

0.00

0009

0.70

7886

0.26

100.15

780.51

2590

0.00

0008

0.51

2523

−0.6

ESD14

0.05

20.15

10.70

6489

0.00

0008

0.70

6350

0.28

340.17

140.51

2666

0.00

0007

0.51

2593

+0.8

ESD15

0.06

90.20

00.70

8365

0.00

0013

0.70

8180

0.25

530.15

440.51

2583

0.00

0006

0.51

2517

−0.7

ESD16

0.05

90.17

20.70

7150

0.00

0013

0.70

6992

0.26

390.15

960.51

2663

0.00

0007

0.51

2595

+0.8

aTworepeatNdisotop

icmeasurementson

ESD3yielded

143Nd/

144Nd=0.5117

12±0.00

0008

(2σ)and0.5117

07±0.00

0009

(2σ),giving

ε Nd(t)values

of−1

7.5and−1

7.6,

respectiv

ely.One

repeat

Ndisotop

icmeasurementon

ESD10

yielded

143Nd/

144Nd=0.51

2670

±0.00

0007

(2σ),giving

ε Nd(t)valueof

+0.9.

All

143Nd/

144Ndvalues

areno

rmalized

toaJM

CNdvalueof

0.5118

33.

Reprodu

cibilityas

determ

ined

byrepeatmeasurementsof

theLaJolla

standard

is±0

.3epsilonun

its(2

SE).Notethesign

ificantly

greater2σ

erroron

theSrisotop

icratio

ofdy

keESD3comparedto

allothers.T

heSrisotop

icmeasurementswereon

unleachedsamples.S

ubscripts“p”and“t”on

SrandNdisotop

icratio

sandεN

ddataindicatepresent-dayandinitial(age-corrected

to65

million

years)

values,respectiv

ely

Bull Volcanol (2013) 75:701 Page 11 of 23, 701

lithospheric materials (which should raise La/Nb and Zr/Nbratios and lower Ti/Y ratios in the magmas).

Chemical classifications of the Mesozoic Gondwananflood basalt provinces (e.g., Erlank et al. 1984; Hergt et al.1991; Peate et al. 1992) have employed their combined TiO2

and Nb contents and Zr/Y and Ti/Y ratios. Using theseparameters, Melluso et al. (1995) classified the Deccanrocks of Saurashtra into low-Ti, high-Ti, and intermediate-Ti types, with 1.8 wt.% TiO2 as the upper limit for the low-Ti type (Fig. 5a–d). The low-Ti rocks have Nb <10–12 ppm(mostly <9 ppm), even when highly evolved, and low Zr/Y(average 3.7) and low Ti/Y (average 281) ratios. Based ontheir scheme, Palitana flows PL1, PL2, and PL3 are high-Tiflows, and flows PL10 and PL11 are intermediate-Ti flows.The remaining eleven (constituting ∼350 m of the section,see Fig. 4) are low-Ti flows. Thus the Palitana sequencecombines all three Ti types while low-Ti flows dominate.The Ti-based divisions of the Palitana flows nicely matchthe intervals of the Palitana lava pile based on otheralteration-resistant element ratios in Fig. 4. The EasternSaurashtra dykes can be similarly classified, though inFig. 5b–d data for several dykes are located outside or nearthe various fields rather than within. Dykes ESD13 (TiO2=1.07 wt.%, Nb=9.63 ppm) and ESD14 (TiO2=1.78 wt.%,Nb=7.71 ppm) are low-Ti by all plots, whereas dyke ESD6is high-Ti and dykes ESD12, ESD15, and ESD16 areintermediate-Ti by all plots.

Petrogenesis

The Ambenali Formation magmas are considered the parentalmagma type of the Western Ghats sequence, as they show theleast continental lithospheric influence and transitionalMORB-like chemical characteristics with εNd(t) values up to+8 (e.g., Mahoney et al. 1982; Macdougall 1986). MostWestern Ghats formations, with the exception of theAmbenali and Mahabaleshwar, contain lavas highly contam-inated by continental crust. In particular, the high SiO2, largeion lithophile element (LILE)/high field strength element(HFSE) ratios and 87Sr/86Sr ratios, and very low εNd valuesof the Bushe Formation lavas have been attributed to ∼20 %bulk assimilation of Precambrian crust (e.g., Lightfoot andHawkesworth 1988; Lightfoot et al. 1990; Peng et al. 1994).

Based on the same parameters, the Bhimashankar,Khandala, and Poladpur Formation lavas (Online Resource1) have also incorporated significant amounts of ancient crust.Primitive mantle-normalized multielement patterns of thePalitana flows and the Eastern Saurashtra dykes, which matchthose of the above Western Ghats formations, are shown inFig. 6. Normalized Pb values range from a few hundred to∼5,000 for the Palitana flows and the Eastern Saurashtradykes; these Pb values cannot be primary and are not plotted.However, the broad to close matches between the Saurashtrarocks and the Western Ghats formations suggest comparabledegrees of crustal incorporation in the former.

La/Sm

2 1 2 3 8 12 2016 250 5004 1.50

100

200

300

400

500

150

250

350

450

50

Ele

vatio

n (m

)

La/Nb Dy/Yb Zr/Nb Ti/Y

PL1-3

PL4-6

int-Ti

low-Ti

low-Ti

hi-Ti

2.52.0

low-TiPL7-9

PL10-11

PL12-16

3

Fig. 4 Geochemical stratigraphyof the Palitana lava sequence,with key alteration-resistantelement ratios of the lava samplesplotted against their elevationabove mean sea level. TheTi-character of the lavasdetermined from the plots inFig. 5b, c, d is also indicated

701, Page 12 of 23 Bull Volcanol (2013) 75:701

A plot of Ti/Y vs. Zr/Nb (Fig. 7) shows that the Palitanalavas as a group have much lower Ti/Y ratios and higherZr/Nb ratios than the Eastern Saurashtra dykes, with theexception of dykes ESD2, ESD3, ESD5, and ESD7. Thedata for the lavas overlap very well with the BusheFormation. We interpret the flows to be more contaminatedby crustal materials than most of the dykes. The sameconclusion is obtained from the Sr-Nd isotopic plot(Fig. 8a, b). Several Western Ghats stratigraphic formationsare well separated in Fig. 8a, particularly towards more“enriched” compositions (lower 143Nd/144Nd and higher87Sr/86Sr), and their elongated fields have been interpretedas mixing arrays between Ambenali magmas and continen-tal lithospheric materials of various types (e.g., Mahoney etal. 1982). All available Sr-Nd isotopic data on the Deccanrocks of Saurashtra are also shown in Fig. 8a, b. ThePalitana flow samples have highly negative εNd values of−6.3 to −13.5, whereas the Eastern Saurashtra dykes havevalues that are very highly negative to slightly positive(Table 4). Whereas most dykes have higher εNd values andlower 87Sr/86Sr values than the flows, and are thus lesscrustally contaminated, dykes ESD3 and ESD5 have themost “enriched” or continental-like isotopic ratios in the

suite, and in fact in nearly all Deccan Traps rocks, includingthe Bushe Formation lavas, the Boradi dolerite dyke fromthe central Deccan, as well as the Girnar silicic porphyriesand Chogat-Chamardi granophyres of Saurashtra (Fig. 8a).

It is known that none of the Deccan basalts of Saurashtrahad an Ambenali-like mantle source (Peng and Mahoney1995; Melluso et al. 1995, 2006): the high-Ti picrite basaltsof Saurashtra (and Pavagadh to the east), resembling oceanisland basalts, were derived from a clinopyroxene-rich,garnet-bearing source isotopically resembling that ofRéunion Island. On the other hand, the low-Ti picrite basaltsof Saurashtra originated in highly depleted, MORB-type,spinel-bearing mantle and assimilated considerable ancientcontinental crust. They thus acquired high ratios of the largeion lithophile elements to high field strength elements, highZr/Nb and 87Sr/86Sr, and low 143Nd/144Nd. Consistent withthis, Fig. 9a shows a very close match in multiple elementsbetween the Palitana low-Ti flows PL13 and PL16 and theBushe Chemical Type (Beane 1988), as well as a 80:20 bulkmixture of N-MORB magma and average Archaean felsiccrust.

Figure 9b is a plot of εNd vs. Zr/Y, illustrating variabledegrees of crustal contamination and source enrichment

Eastern Saurashtra dykesPalitana lavas

MgO (wt.%)10 15 2050

1.0

2.0

3.0

high-Tiint-Ti

PL1

PL2 PL3

PL10

ESD6

PL12

PL16

PL11

TiO2 (wt.%)

Nb

(ppm

)

10

20

30

40

50

60

70

00.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6

high-Ti

low-Ti

int-Ti

PL1

PL2

PL3

PL10

ESD6PL16

PL12

PL11

Zr/Nb

Y/N

b

10

8

6

4

2

00 5 10 15 20 25

int-Ti

high-Ti

PL1,2,3 PL10

ESD6

PL12PL16

PL11

low-Ti

low-Ti

30

dc

b

ESD14

ESD14

NE Saurashtra drillhole lavasa

50 km

low-Ti

int-Ti

high-Ti

Gul

f of C

amba

y

Arabian Sea

Shihor

Rajkot

PalitanaJunagadh

Amreli

Rajula

Dhandhuka

Botad

Wadhwan

Diu

Jasdan

BabraPorbandar

7270

22

21

Chotila

Pavagadh150 km

Talaja

Gulf of Kachchh

Fig. 5 a Map of Saurashtra showing the distribution of the high-Ti,intermediate-Ti, and high-Ti basalt surface outcrops (based on Mellusoet al. 1995). The drillhole lavas of Wadhwan, Dhandhuka, and Botadare also high-Ti, as are lavas of Pavagadh 150 km east of Wadhwan. b,c, d Classification of the Palitana flow and Eastern Saurashtra dyke

samples into the three Ti types, using the criteria and fields of Mellusoet al. (1995). Specific samples discussed in the text are indicated. Alsoplotted are data for the NE Saurashtra drillhole lavas (Krishnamurthyand Cox 1977). Note how, in (b), the Palitana lavas represent some ofthe most magmatically evolved of the low-Ti Saurashtra rocks

Bull Volcanol (2013) 75:701 Page 13 of 23, 701

inferred for various Western Ghats and Saurashtra lavas(Melluso et al. 2006), with data for the Palitana lavas andthe Eastern Saurashtra dykes plotted. The Saurashtra high-Tilavas with the highest Zr/Y ratios represent an enrichedsource, and the high-Ti drillhole lavas are more crustallycontaminated than the high-Ti surface lavas. Similarly, thePoladpur and Bushe Formation fields depict the significantcrustal contamination suffered by Ambenali-like magmaswith low Zr/Y, whereas the Neral Formation field enclosesstrongly crustally contaminated lavas starting with interme-diate Zr/Y ratios. The exact basement crust compositionunder Saurashtra being unknown, we have plotted bulkmixing curves between an Indian N-MORB magma (in-ferred by Melluso et al. 2006 to be parental to theSaurashtra low-Ti magmas) and average Archaean felsiccrust, as well as a Réunion-type magma and crust. Datafor all flow and dyke samples of this study are bounded bythe two curves. Again, the Palitana flow samples are locatedin the Bushe Formation field as in Fig. 7 (as well as theNeral Formation field). Samples PL13 and PL14 represent a

crustal input of 15 % in N-MORB magmas, and samplesPL7 and PL9 represent a similar crustal input in magmasthat blend N-MORB and Réunion type compositions. DykesESD3 and ESD5 would represent 30–35 % crustal assimi-lation by similar magmas, and this may have required con-current fractional crystallization (Bowen 1928; DePaolo1981), consistent with the fact that both these samples haveandesitic bulk compositions (Table 1).

Discussion: regional comparisons and correlations

Relationship of the Palitana lava sequence to the Saurashtraand Western Ghats lavas

The low-Ti-dominated Palitana sequence cannot be corre-lated with any of the NE Saurashtra drillhole sequences,which are all high-Ti, as well as relatively magnesian. Noplausible fractionation mechanisms can generate thePalitana lavas from the drillhole lavas, and clinopyroxene

2

10

100

200

RbBa Th U Ta Nb K La CePb Pr Sr P Nd Zr Hf SmEuGd Ti Tb DyHo Y Er TmYb Lu

2

10

100

RbBa Th U Ta Nb K La CePb Pr Sr P Nd Zr Hf SmEuGd Ti Tb DyHo Y Er TmYb Lu

2

10

100

RbBa Th U Ta Nb K La CePb Pr Sr P Nd Zr Hf SmEuGd Ti Tb DyHo Y Er TmYb Lu

2

10

100

RbBa Th U Ta Nb K La CePb Pr Sr P Nd Zr Hf SmEuGd Ti Tb DyHo Y Er TmYb Lu

rock

/prim

itive

man

tlero

ck/p

rimiti

ve m

antle

rock

/prim

itive

man

tlero

ck/p

rimiti

ve m

antle

2

10

100

RbBa Th U Ta Nb K La CePb Pr Sr P Nd Zr Hf SmEuGd Ti Tb DyHo Y Er TmYb Lu3

10

100

RbBa Th U Ta Nb K La CePb Pr Sr P Nd Zr Hf SmEuGd Ti Tb DyHo Y Er TmYb Lu

rock

/prim

itive

man

tle

rock

/prim

itive

man

tle 200

200 200

300

PL1PL2PL3Khandala MonkeyHill KOP21

PL10PL11

PL12PL14ESD14Poladpur avg.

PL7PL8PL9Khandala GiravliJEB128

ESD2ESD3ESD5Khandala MonkeyHill KOP21

ESD6ESD7

ESD10ESD11ESD12BhimashankarJEB366

ESD15ESD16

PL4PL5PL6Bushe CT

PL13PL15PL16

a b

c d

e f

Fig. 6 a to f Comparison of primitive mantle-normalized multielementpatterns of the Palitana lavas with those of selected Western Ghatslavas, members, or formation averages (main data sources are Beane et

al. 1986; Beane 1988; Vanderkluysen et al. 2011). The normalizingvalues are from Sun and McDonough (1989)

701, Page 14 of 23 Bull Volcanol (2013) 75:701

compositions (Fig. 2a) as well as Sr-Nd isotopic ratios(Fig. 8b) preclude genetic links, even for the youngest,high-Ti, Palitana flows (PL1, 2, and 3). In fact, thePalitana lavas are also different in isotopic ratios from thepicrite basalts sampled in surface outcrops in Saurashtra(Melluso et al. 2006; Fig. 8b).

From Fig. 6 we noted that most Palitana lavas can bebroadly to closely matched to particular Western Ghatslavas. This may merely imply similar petrogenetic evolutionrather than stratigraphic or genetic relationships with theWestern Ghats sequence, especially as the stratigraphic or-der of these chemical types observed in the Palitana se-quence does not conform to that in the Western Ghats(Online Resource 1). An important corollary of this is thatmajor chemical magma types of the Deccan are not chrono-stratigraphic, but instead must have erupted at differenttimes in different regions of the province. The same conclu-sion, that major magma types were diachronous, has beenreached for the Paraná province, for example (Peate 1997).

Also, Sr-Nd isotopic data for the Palitana flowschemically resembling particular Western Ghats forma-tions do not plot within the isotopic fields of thoseformations. Thus, while flows PL1 and PL3 werematched to the Khandala Formation by multielementpatterns (Fig. 6a), isotopic data locate them at the veryedge of the Khandala Formation field where it overlapsthe Poladpur and Thakurvadi fields (Fig. 8a). Thoughlow-Ti Palitana flows PL12 and PL14 resemble thePoladpur Formation lavas of the Western Ghats in theirmultielement patterns (Fig. 6d), the isotopic ratios ofPL12 locate it near, but not within, the PoladpurFormation field. Palitana low-Ti flows PL7, PL8, andPL9 and intermediate-Ti flows PL10 and PL11, stronglyresembling the Khandala Formation lavas in their

multielement patterns (Fig. 6b), are located well outsidethe Khandala Formation field in the isotopic plot(Fig. 8a).

The Ti/Yvs. Zr/Nb plot (Fig. 7) shows that the Saurashtramafic lavas and dykes are different from the Western Ghatslavas, with the exception that the low-Ti Saurashtra lavas(Melluso et al. 1995, 2004, 2006) as well as many Palitanalavas (this study) strongly resemble the Bushe Formationlavas in their very low HFSE abundances. Nevertheless, theSaurashtra low-Ti lavas are much poorer in the LILE thanthe Bushe basalts, precluding a perfect correspondence(Melluso et al. 1995).

Also, whereas many low-Ti Palitana flows (e.g., PL4,PL5, PL6, PL13, PL15, and PL16) are matched to theBushe Formation by multielement patterns and the Ti/Yvs. Zr/Nb plot (Figs. 6c and 7), none of the flows is matchedto the Bushe Formation by its isotopic ratios (Fig. 8a).Can this be due to alteration-caused lowering of the Srisotopic values? The flow and dyke data define a verygood anticorrelated array in Fig. 8a. A possible smallalteration effect in Sr isotopes exists for sample PL11,which is shifted a little to the right of the main array(and has the highest LOI value of all, 7.00 wt.%).Excepting this, from the well-anticorrelated array, weinfer that the Sr isotopic ratios of the Palitana flowsare not significantly affected by alteration.

Our results on the Palitana flow sequence are consis-tent with the observations of Melluso et al. (1995,2004) that the low-Ti Saurashtra basalts of Saurashtra,as well as the Dhule region, despite several elementalsimilarities to the Bushe lavas, are genetically andstratigraphically independent of the Bushe Formation.To summarize, the combined geochemical evidence sug-gests that there is no genetic or stratigraphic correlation

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Fig. 7 Plot of Ti/Y vs. Zr/Nbfor various Deccan mafic lavasas well as the Palitana lavas andthe Eastern Saurashtra dykes.Data sources are as follows:The Kalsubai and WaiSubgroups and the Khandalaand Bushe Formations of theLonavala subgroup (total624 samples): Beane 1988;Saurashtra high-Ti,intermediate-Ti, and low-Tilavas: Krishnamurthy and Cox1977; Melluso et al. 1995,2006; Peng and Mahoney 1995;Dhule area low-Ti flows:Melluso et al. 2004; Palitanalavas and the Eastern Saurashtradykes: this study. Samplenumbers are marked next tothese flow and dyke samples

Bull Volcanol (2013) 75:701 Page 15 of 23, 701

+5

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0.720 0.725 0.730

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(Nd data not available)

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Chogat-Chamardi mafic rocks (n = 4, S11a)

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701, Page 16 of 23 Bull Volcanol (2013) 75:701

between the Palitana sequence and the Western Ghatssequence.

Relationships of the Eastern Saurashtra dykes to the Palitanalavas

Geochemical correlations between the Eastern Saurashtradykes and the Palitana lava sequence should be evaluated, toexamine the dykes’ potential role as feeders to these lavas. Thedykes have exposed lengths of up to 14–15 km (e.g., ESD10)and reach within only 15 km of the Palitana sequence (Fig. 1c).Interestingly, the isotopic data for dykes ESD3 and ESD5along with their locations in Fig. 1c suggest theymay representa single dyke ∼20 km long, slightly arcuate in plan, andisotopically somewhat heterogeneous. This is comparable tothe internal chemical and isotopic variability known fromother individual Deccan mafic dykes (Chandrasekharamet al. 1999; Bondre et al. 2006; Ray et al. 2007; Vanderkluysenet al. 2011).

Despite the comparable degrees of magmatic evolution ofthe Palitana lavas and the Eastern Saurashtra dykes, theirdifferences in Ti and Nb suggest that they are geneticallyunrelated. Furthermore, the total and systematic Sr-Nd iso-topic separation between the flows and the dykes (Fig. 8a, b)rules out any genetic relationships between them. As for thePalitana flows, we believe that the Sr isotopic ratios of theEastern Saurashtra dykes have not been significantly affect-ed by alteration, because such alteration should have pro-duced at least partial overlap between the flow and the dykedata. Besides, Nd isotopic ratios, unaffected even duringsevere alteration and weathering (e.g., Faure 1986;DePaolo 1987; Mahoney et al. 2000; Sheth et al. 2011b),are completely different for the flows and the dykes. Giventhe large number of analyzed samples, we take the completeSr-Nd isotopic separation between the Palitana flows and

the Eastern Saurashtra dykes as a robust, primary feature,ruling out the dykes as feeders to the lavas.

To be further certain about this important result, wecompared the Palitana lavas and the Eastern Saurashtradykes on plots of initial εNd and the alteration-resistantincompatible trace element ratios Th/Nb, La/Nb, andZr/Nb (Fig. 10a–c). The three plots clearly show thatthe flows and the dykes define quite distinct fields.Contamination by ancient granitic crust should lead tohigh Th/Nb, La/Nb, and Zr/Nb in the magmas, alongwith low εNd values, and all the three plots show trendsconsistent with such contamination. The plots addition-ally show that is not only the dykes ESD3 and ESD5,analyzed for isotopic ratios, which are significantly mo-re contaminated than the Palitana flows (Fig. 10a), butalso the dykes ESD2 and ESD7, which are equally ormuch more contaminated than the Palitana flows(Fig. 10b, c). These four dykes, and the rest of theEastern Saurashtra dykes, enclose two very differentfields in Fig. 10a–c, with the field for the Palitana flowsin between, having little or no overlap, exactly as in theSr-Nd isotopic plots (Fig. 8a, b). This strongly corrob-orates our conclusion about the complete lack of geneticrelationships between the Palitana flows and the EasternSaurashtra dykes.

Relationships of the Eastern Saurashtra dykes to otherSaurashtra lavas

The fairly evolved Eastern Saurashtra dykes do not seemcorrelatable as a group to the NE Saurashtra drillhole lavas,many of which represent primitive picritic liquids (West1958; Krishnamurthy and Cox 1977; Krishnamurthy et al.2000). Clinopyroxene compositions (Fig. 2a) also requiredifferent parental magmas for both suites. Besides, only onedyke sample (ESD14) is located within the isotopic fields ofthe trends 1 and 2 drillhole flows (Fig. 8b). Potential corre-lations of the three-phenocryst basalt dykes ESD6, ESD7,and ESD12 with the drillhole three-phenocryst basaltswould be interesting to evaluate. Unfortunately, this cannotbe done for the isotopes, lacking data on the former,and full elemental and isotopic data are available onlyfor a single drillhole three-phenocryst basalt (sample D-3, Krishnamurthy and Cox 1977; Peng and Mahoney 1995).With these, the multielement patterns do not match well(overlap is for Sm and more compatible elements only, notshown). Thus, the Eastern Saurashtra dykes cannot be feedersof the NE Saurashtra drillhole lava sequences.

Could the Eastern Saurashtra dykes have fed anyother Saurashtra lavas, including those sampled fromsurface outcrops by Melluso et al. (1995, 2006)? Asearch for potential correlations between dyke and flowsamples with the same Ti character (e.g., the low-Ti

Fig. 8 a Sr-Nd isotopic plot for the Palitana lavas and the EasternSaurashtra dykes, with sample numbers indicated (without the PL- andESD- prefixes to avoid cluttering). Data are shown for the WesternGhats stratigraphic formations (Vanderkluysen et al. 2011). Data arealso shown for the central Deccan dolerite dyke SH49, the Saurashtralow-Ti and high-Ti picritic flows including the drillhole lavas, maficand silicic volcanic and subvolcanic rocks from the Chogat-Chamardicomplex and Osham Hill, and silicic porphyries from Mount Girnar(only Sr isotopic data available). Data sources are: P77, Paul et al.1977; PM95, Peng and Mahoney 1995; C99, Chandrasekharam et al.1999; M06, Melluso et al. 2006; S11a, Sheth et al. 2011a; S12, Sheth etal. 2012. All data are initial values for 65 Ma. b Sr-Nd isotopic plotwith data for various Saurashtra mafic rocks plotted. The rocks includethe Osham basaltic andesites and the Chogat-Chamardi gabbros andmafic dykes, the Saurashtra low-Ti picritic basalts, and the high-Tidrillhole lavas forming “Trend 1” and “Trend 2”. The two trends showsignificant overlap, but are well resolved on Nd-Pb and Sr-Pb isotopicplots. Two southern Saurashtra low-Ti lavas D57 and D60 (Melluso etal. 2006) discussed in the text are indicated. Fields for Indian N-MORB, Bhuj area mafic alkalic rocks, and Réunion lavas are alsoshown for comparison. Data sources are as for (a) above

�

Bull Volcanol (2013) 75:701 Page 17 of 23, 701

dyke ESD14 and the low-Ti picrite basalt D57 sampledbetween Amreli and Junagadh by Melluso et al. 2006)showed that elemental and isotopic data (e.g., MgO andNb contents as well as Sr-Nd isotopic ratios) completelypreclude genetic relationships. The Eastern Saurashtradykes cannot be feeders to any lavas yet analyzed fromSaurashtra. They may be arrested dykes that did notresult in eruptions, or feeders to flows below or abovethe studied lava sequences in Saurashtra.

Relationships of the Eastern Saurashtra dykes to the WesternGhats sequence

As regards correlations of the Eastern Saurashtra dykes todistant lava sequences, such as that of the Western Ghats,dyke ESD14 has a multielement pattern that very closelymatches that of the Poladpur Formation (Fig. 6d). DykesESD2, ESD3, and ESD5 to ESD7 are very similar to theKhandala Formation lavas (Fig. 6e), whereas dykes ESD10

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Fig. 9 a Primitive mantle-normalized multielement patterns forPalitana flows PL13 and PL16 (data of this study), compared to a80:20 bulk mixture of N-MORB (Sun and McDonough 1989) andArchaean felsic crust (Rudnick and Fountain 1995), and a lava flowrepresenting the Bushe Chemical Type (BSH02, Beane 1988). Nor-malizing values for primitive mantle are from Sun and McDonough(1989). b Plot of initial εNd vs. Zr/Y for various Western Ghatsformations, Saurashtra mafic lavas, as well as the Palitana lavas andEastern Saurashtra dykes with their sample numbers marked. Mixingcurves between N-MORB and Archaean felsic crust, and Réunionmagma and Archaean felsic crust, are shown (dashed lines) with theamount of crust indicated by numbers in percent. Heavy arrows

indicate the very different pathways of mantle source enrichment andcrustal contamination. Mixing end member compositions are as fol-lows: N-MORB: Nd=7.3 ppm, Zr=74 ppm, Y=28 ppm (Sun andMcDonough 1989), εNd=+8.7 at 65 Ma (Melluso et al. 2006), requir-ing 143Nd/144Nd=0.512998 (based on 143Nd/144Nd for chondritic av-erage=0.512638 today and 0.512553 at 65 Ma). Réunion magma: Nd=23.8 ppm, Zr=177 ppm, Y=25.8 ppm (Fisk et al. 1988), εNd=+4.0 at65 Ma (Melluso et al. 2006), requiring 143Nd/144Nd=0.512758. Ar-chaean felsic crust: Nd=43 ppm, Zr=229 ppm, Y=24 ppm (Rudnickand Fountain 1995), crust εNd=−35.0 at 65 Ma (Melluso et al. 2006),requiring 143Nd/144Nd=0.510759

701, Page 18 of 23 Bull Volcanol (2013) 75:701

to ESD12, ESD15, and ESD16 closely match the patterns ofthe Bhimashankar Formation lavas (Fig. 6f). Multielement(Figs. 6 and 7) and isotopic (Fig. 8) comparisons of indi-vidual dykes to the Western Ghats sequence mostly yielddifferent formation matches, ruling out genetic or strati-graphic relationships. There are however two notable ex-ceptions, the low-Ti dykes ESD14 and ESD11, closelymatched to the Poladpur and Bhimashankar Formations,respectively, by multielement patterns (Fig. 6d, f) as well

as Sr-Nd isotopic ratios (Fig. 8a). Another chemicallyBhimashankar-like dyke ESD15 (Fig. 6f) has isotopic ratiosthat locate it just outside the Bhimashankar Formation iso-topic field (Fig. 8a). We consider ESD14 and ESD11 asfully Poladpur- and Bhimashankar-type dykes far from thetype localities of these formations in the Western Ghatsseveral hundred kilometers away, and indicating similarmagmatic evolution and lithospheric contaminants.

Where are the feeder dykes of the Palitana and the drillholesequences?

The areal distribution of the high-Ti and low-Ti basalts andpicrite basalts of Saurashtra (Fig. 5a) may not be a guide totheir feeder dykes, given the potential for flood basalt flowsto travel far after eruption, palaeotopography permitting(e.g., Self et al. 2008). However, the distribution of thesetwo types seems systematic, in that high-Ti lavas onlyoutcrop north–northeast of a line connecting Rajkot toPalitana (Figs. 1b and 5a, Melluso et al. 1995), an observa-tion unchanged by the new data of this study. Also, theBotad, Wadhwan, and Dhandhuka drillhole successions, aswell as the thick Pavagadh section 150 km to the east(Melluso et al. 2006; Sheth and Melluso 2008) have onlyhigh-Ti basalts. The feeder dykes of the high-Ti basalts maybe located in the Cambay rift, on land (NE Saurashtra) or inthe Gulf of Cambay. Both possibilities are essentiallyuntestable, given the post-Deccan alluvial cover on landand the great amount of post-Deccan downfaulting withinthe rift, but the data suggest the presence of enriched, ocean-island-type mantle (the source of high-Ti magmas asdiscussed by Melluso et al. 1995, 2006) under the Cambayrift circa 65 million years ago.

There are other potential source areas in Saurashtra.Barring the dyke-free Amreli area west of Palitana(Figs. 1b and 5a), mafic dykes are abundant in Saurashtra(Auden 1949; Misra 1999; Sheth’s field data 2006–2011). Thearea south–southwest of Palitana, and up to Rajula, containsprofuse dykes of diverse compositions from picrites andankaramites through dolerites to rhyolites and pitchstones(Krishnamacharlu 1972; Chatterjee and Bhattacharji 2001,2004; Kshirsagar et al. 2012), which are yet to be analyzedfor isotopic ratios. Mafic dykes running ENE-WSW (theNarmada–Tapi trend) are also well-developed in centralSaurashtra around Jasdan and Babra (Figs. 1b and 5a), ofwhich the Sardhar dyke near Jasdan is >50 km long (Auden1949; Sethna et al. 2001). A systematic and comprehensivegeochemical study of these dykes is lacking, but if some ofthese dykes are feeders to the Palitana sequence, surfacetransport distances for the Palitana flows of a few tens ofkilometers to as much as 100–150 km are called for.

Alternatively, the search for the feeder dykes of the Palitanasuccession should consider the Deccan “mainland” region,

crusta

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Fig. 10 Plots of a initial εNd vs. Th/Nb, b La/Nb vs. Zr/Nb, and c Th/Nb vs. Zr/Nb for the Palitana flows and the Eastern Saurashtra dykes.The trends expected from crustal contamination are indicated by thearrows

Bull Volcanol (2013) 75:701 Page 19 of 23, 701

including the Umbergaon-Dahanu area on the western Indiancoast (Fig. 1a), relatively near eastern Saurashtra (<200 km).Nd-Sr-Pb isotopic ratios are available on only one of thesedominantly N-S-trending coastal dykes (dyke UDD9), andwith a 87Sr/86Sr of 0.71691 (Vanderkluysen et al. 2011) thedyke cannot be a feeder to the Palitana sequence. Besides, theUmbergaon-Dahanu dykes have exposed lengths ≤10 km (Ray2009).

Melluso et al. (1999, 2004) and Vanderkluysen et al. (2011)have reported low-Ti flows and dykes around Dhule,Nandurbar, Dhadgaon, and Dediapada areas (Fig. 1a), wherethe Narmada-Tapi dyke swarm achieves its most profusedevelopment (Krishnamacharlu 1971; Ray et al. 2007; Ray2009). These dykes include many low-Ti and high-Ti ones(Melluso et al. 1999), and whereas an extensive major andtrace element data set on over 80 of these dykes is published(Vanderkluysen et al. 2011), comparatively few (14) havebeen analyzed for Sr-Nd-Pb isotopic ratios. Most of thesehave Sr isotopic ratios too low to be feeders of the Palitanasequence, and similar to those of the Eastern Saurashtra dykes.

A multielement comparison between some Palitana lavasand some of the Nandurbar-Dhule-Dediapada dykes (data ofVanderkluysen et al. 2011) is shown in Fig. 11. Patterns of thePalitana high-Ti flows PL1, PL2, and PL3 closely match thepatterns of the high-Ti Nandurbar dyke NBD10 (TiO2=2.53 wt.%, Nb=13 ppm, Zr=137 ppm, Y=31 ppm) in manyelements (Fig. 11a). 87Sr/86Sr isotopic ratios for flows PL1 andPL3 and dyke NBD10 are, respectively, 0.71050, 0.71029,and 0.71093, and are thus different. The essentially identical

εNd values of the flows PL1 and PL3 (−8.0 and −7.8) aredifferent from that of the dyke NBD10 (−5.1). All four sam-ples however chemically match the Sakri-Dhule-Parola dykeSDPD1 (TiO2=3.13 wt.%, Nb=17 ppm, Zr=208 ppm, Y=42 ppm). This dyke has not been analyzed for isotopic ratios.Note that whereas dyke NBD10 is only a few kilometers long,SDPD1 is the longest known dyke in the Deccan Traps, at79 km (Ray et al. 2007).

Figure 11b shows that the low-Ti Palitana lavas PL4,PL5, and PL6 very closely match the low-Ti Nandurbardyke NBD1, and the low-Ti Dediapada dyke DD15 in manyelements (Vanderkluysen et al. 2011). We do not haveisotopic data on these Palitana flow samples, but NBD1has 87Sr/86Sr=0.71495 (and εNd=−14.7) which somewhatexceeds the entire isotopic range of the analyzed Palitanaflow samples (0.71029–0.71392, εNd from −6.3 to −13.5).Notably, this dyke is one of the longest in the Deccan, at54 km (Ray et al. 2007). Dediapada dyke DD15 has87Sr/86Sr=0.71064 and εNd=−6.5, well within the range ofthe Palitana lavas. Though a sample-to-sample correlation isnot possible with the Palitana samples we have analyzed (cf.Bondre et al. 2006), the isotopic differences are smallenough for this to be a highly potential source area of feederdykes. If the Palitana sequence was fed by dykes in theDediapada-Nandurbar-Dhule areas, lateral transport over200–300 km would be necessary, and is possible, notingthat (1) individual flows in the Columbia River provincereached lengths of over 500 km (Tolan et al. 1989), (2)dyke–flow correlations in the Deccan Traps have indicated

RbBa Th U Ta Nb K La CePb Pr Sr P Nd Zr Hf SmEuGd Ti Tb Dy Ho Y Er TmYb Lu

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b200

300Fig. 11 Comparison ofprimitive-mantle-normalizedmultielement patterns of ahigh-Ti Palitana flows totwo high-Ti dykes from theNandurbar-Dhule area, andb low-Ti Palitana flows totwo low-Ti dykes from theNandurbar and Dediapada area.The normalizing values arefrom Sun and McDonough(1989)

701, Page 20 of 23 Bull Volcanol (2013) 75:701

150–500 km, and in some cases up to 700 km, of lateraltransport for several flows (Bondre et al. 2006; Sheth et al.2009; Vanderkluysen et al. 2011), and (3) several of thedykes mentioned themselves reach considerable lengths.

Conclusions

We find that the 450-m thick Palitana lava sequence in theeastern part of the Saurashtra peninsula, northwesternDeccan Traps, is unrelated to surface lavas and subsurfacesequences previously studied from Saurashtra, as well as tothe Western Ghats sequence several hundred kilometers tothe southeast. We also find that the Eastern Saurashtradykes, outcropping between Palitana and the Gulf ofCambay, cannot represent the feeder dykes of the Palitanaor the other lava sequences. The Palitana lavas and theEastern Saurashtra dykes are crustally contaminated, thelavas generally much more so than the dykes. Four of thedykes are however equally or significantly more contami-nated than the Palitana flows, two of them analyzed for Sr-Nd isotopic ratios showing some of the most “enriched” Sr-Nd isotopic compositions in the entire Deccan Traps. Theresults show that several eruptive centers for the Deccanflood basalts are required within the Saurashtra region itself.The feeder dykes of the Palitana (and the drillhole) se-quences may exist within the Cambay rift, buried underseveral kilometers of post-Deccan sediments. Or, the feederdykes may outcrop 100–150 km from Palitana, in central orsouthwestern Saurashtra, where dykes abound but remainpoorly studied. Alternatively, the Palitana sequence may bederived from dykes in the Dediapada-Nandurbar-Dhuleareas, 200–300 km to the east across the Gulf of Cambay.An extensive elemental dataset on these dykes is available(Vanderkluysen et al. 2011), but more isotopic data arerequired before a meaningful correlation of these well-exposed dykes with the Palitana and other Saurashtra lavascan be attempted.

Acknowledgments This work was supported by the Industrial Re-search and Consultancy Centre (IRCC), IIT Bombay Grant 09YIA001,and a Department of Science and Technology (Govt. of India) GrantSR/FTP/ES-19/2007, to Sheth. Zellmer acknowledges support by theNational Science Council of Taiwan (NSC 99-2116-M-001-010).Kshirsagar was supported by a Ph.D. fellowship from IIT Bombay.Funds for EPMA analyses by Cucciniello were provided by ItalianMIUR (PRIN Grants 2008 to Leone Melluso). We thank BadrealamShaikh and Dipak Gosain for assistance in the field, Poonam Mohiteand Trupti Gurav for assistance with sample preparation and ICP-AESanalyses, Rong-Yi Yan and I-Jhen Lin for assistance with sampledissolution and ICP-MS analyses, Kanchan Pande and George Mathewfor helpful discussions, and Leone Melluso for his unpublished Deccanmineral analyses. The manuscript was greatly improved by extensive,in-depth reviews of several versions by Godfrey Fitton, Fred Jourdan,Leone Melluso, Loÿc Vanderkluysen, and two anonymous reviewers,as well as the Associate Editor David Peate.

We dedicate this work to John J. Mahoney for his massive contri-butions to the subject of flood basalts including the Deccan, and for hisparticular interest over the past several years in identifying the feederdykes of the Deccan flood basalts. John passed away on 23rd Novem-ber 2012 at Honolulu, and his enthusiasm, encouragement, and friend-ship will be greatly missed.

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