ORIGINAL PAPER

Petrology and geochemistry of diamondiferous Mesoproterozoickimberlites from Wajrakarur kimberlite field, Eastern Dharwarcraton, southern India: genesis and constraints on mantle sourceregions

N. V. Chalapathi Rao Æ Rajesh K. Srivastava

Received: 17 April 2008 / Accepted: 24 July 2008 / Published online: 7 August 2008

� Springer-Verlag 2008

Abstract The petrology and geochemistry of some new

occurrences of Mesoproterozoic diamondiferous

hypabyssal-facies kimberlites from the Chigicherla,

Wajrakarur-Lattavaram and Kalyandurg clusters of the

Wajrakarur kimberlite field (WKF), Eastern Dharwar

craton (EDC), southern India, are reported. The kimber-

lites contain two generations of olivine, and multiple

groundmass phases including phlogopite, spinel, calcite,

dolomite, apatite, perovskite, apatite and rare titanite, and

xenocrysts of eclogitic garnet and picro-ilmenite. Since

many of the silicate minerals in these kimberlites have

been subjected to carbonisation and alteration, the com-

positions of the groundmass oxide minerals play a crucial

role in their characterisation and in understanding melt

compositions. While there is no evidence for significant

crustal contamination in these kimberlites, some limited

effects of ilmenite entrainment are evident in samples

from the Kalyandurg cluster. Geochemical studies reveal

that the WKF kimberlites are less differentiated and more

primitive than those from the Narayanpet kimberlite field

(NKF), Eastern Dharwar craton. Highly fractionated

(La/Yb = 108–145) chondrite-normalised distribution

patterns with La abundances of 500–1,000 9 chondrite

and low heavy rare earth elements (HREE) abundances of

5–10 9 chondrite are characteristic of these rocks.

Metasomatism by percolating melts from the convecting

mantle, rather than by subduction-related processes, is

inferred to have occurred in their source regions based on

incompatible element signatures. While the majority of

the Eastern Dharwar craton kimberlites are similar to the

Group I kimberlites of southern Africa in terms of

petrology, geochemistry and Sr–Nd isotope systematics,

others show the geochemical traits of Group II kimberlites

or an overlap between Group I and II kimberlites. Rare

earth element (REE)-based semi-quantitative forward

modelling of batch melting of southern African Group I

and II kimberlite source compositions involving a meta-

somatised garnet lherzolite and very low degrees of

partial melting demonstrate that (1) WKF and NKF

kimberlites display a relatively far greater range in the

degree of melting than those from the on-craton occur-

rences from southern Africa and are similar to that of

world-wide melilitites, (2) different degrees of partial

melting of a common source cannot account for the

genesis of all the EDC kimberlites, (3) multiple and

highly heterogeneous kimberlite sources involve in the

sub-continental lithospheric mantle (SCLM) in the East-

ern Dharwar craton and (4) WKF and NKF kimberlites

generation is a resultant of complex interplay between the

heterogeneous sources and their different degrees of par-

tial melting. These observations are consistent with the

recent results obtained from inversion modelling of REE

concentrations from EDC kimberlites in that both the

forward as wells as inverse melting models necessitate a

dominantly lithospheric, and not asthenospheric, mantle

source regions. The invading metasomatic (enriching)

melts percolating from the convecting (asthenosphere)

mantle impart an OIB-like isotopic signature to the final

melt products.

Keywords Petrology � Geochemistry � Kimberlite �Diamond � India

Communicated by T.L. Grove.

N. V. Chalapathi Rao (&) � R. K. Srivastava

Igneous Petrology Laboratory, Department of Geology,

Banaras Hindu University,

Varanasi 221005, India

e-mail: nvcr100@gmail.com

123

Contrib Mineral Petrol (2009) 157:245–265

DOI 10.1007/s00410-008-0332-y

Introduction

Kimberlites and related rocks are the focus of increasing

petrological and geochemical attention due to a variety of

reasons including (1) their derivation from deep parts of the

Earth’s mantle (e.g. Ringwood et al. 1992), (2) their

widespread spatial and temporal distribution, and signifi-

cance for understanding global geodynamic processes (e.g.

Heaman et al. 2004), (3) their relative immunity to crustal

contamination (e.g. Le Roex et al. 2003), (4) their role in

deciphering lithosphere versus asthenosphere interactions

(e.g. Nowell et al. 2004), (5) their ability to provide snap-

shots of compositional variation in the sub-continental

lithospheric mantle (SCLM) and clues regarding mantle

depletion and enrichment events (e.g. Carlson et al. 1996),

(6) their efficiency as agents of metasomatism (e.g. Foley

1992), (7) their role in providing ‘direct’ samples of the

Earth’s interior through mantle and lower crustal xenoliths

(e.g. Pearson et al. 2004) and (8) their economic potential

for diamonds and PGE (e.g. Rombouts 2003).

While Mesoproterozoic kimberlites with an age of about

1.1 Ga are well documented worldwide, across Africa,

Australia, North America, Australia and Greenland (see

Anil Kumar et al. 2007 for an overview), they are most

abundant (*100 examples) in the Eastern Dharwar craton

(EDC) of southern India. The EDC kimberlites offer an

excellent opportunity to study the tectono-magmatic pro-

cesses operating at the time of their emplacement, and to

understand the nature and evolution of the Precambrian

mantle.

In the last decade, there has been a spurt in the discovery

of new kimberlites in the EDC (e.g. Paul et al. 2006). Most

of these occurrences are well exposed and provide a rare

opportunity to investigate the nature and evolution of the

sub-continental or sub-lithospheric mantle in entirely new

geological domains of the Indian plate. They also consti-

tute promising prospects for refining the existing models

for the emplacement and evolution of the Indian kimber-

lites and in evaluating their genesis.

The objectives of this paper are to (1) document the

petrology and geochemistry of some newly discovered

kimberlites from three spatially separated clusters

(Wajrakarur-Lattavaram cluster, Kalyandurg cluster and

Chigicherla cluster) from the Wajrakarur kimberlite field,

southern India, and expand the available data set of such

occurrences from the Eastern Dharwar craton, (2) compare

the new data with those of the well established Group I and

II kimberlites of southern Africa to decipher their simi-

larities and differences, (3) evaluate the genesis of EDC

kimberlites in the light of recent petrogenetic models

developed for southern African and Indian kimberlites and

(4) address the possible reasons for the transitional char-

acters displayed by some of the EDC kimberlites.

Geological setting

The EDC of the southern Indian shield exposes a granite–

greenstone terrane composed predominantly of greenstone

belts, gneisses, granitoids, late- to post-tectonic intrusive

granites (the Closepet granite and its equivalents of

*2,500 Ma), platformal Proterozoic sedimentary basins

(the Cuddapah and Bhima basins) and widespread mafic

dyke swarms. A recent review of the geology of the EDC

has been provided by Naqvi (2005).

Kimberlites constitute some of the youngest intrusive

rocks of the EDC and occur in three fields (Fig. 1). The

nomenclature used by the Geological Survey of India (GSI)

is adopted throughout this study to avoid confusion. The

three kimberlite fields of the EDC are as follows: (1)

Narayanpet kimberlite field (NKF) with 60 kimberlites that

are non-diamondiferous (e.g. Paul et al. 2006), (2) Raichur

Kimberlite Field (RKF) comprising 15 kimberlites some of

which are reportedly diamondiferous (e.g. Lynn 2005) and

(3) Wajrakarur kimberlite field (WKF) consisting of

27 kimberlites with majority of them diamondiferous.

Kimberlites of WKF (Fig. 1) can be grouped into four spa-

tially distinct clusters: (1) northern Wajrakarur–Lattavaram

cluster (11 pipes), (2) south-eastern Chigicherla cluster

(5 pipes), (3) south-western Kalyandurg cluster (6 pipes) and

(4) southern Timmasamudram cluster (4 pipes). The present

study concerns kimberlites from this field.

Geology of the new kimberlite finds of Wajrakarur

kimberlite field

The present study pertains to the petrology and geochem-

istry of CC4 and CC5 kimberlites of the Chigicherla

cluster, KL-3 and KL-4 kimberlites of the Kalyandurg

cluster and P2A kimberlite from the Wajrakarur–Lattava-

ram (WL) cluster (Fig. 1). New geochemical data are also

presented for the P2 kimberlite of the WL cluster, and

compared to the available data for some of the same

occurrences from the published literature. The brief geo-

logy of each location is provided below:

CC4 kimberlite (14�3100000 N: 77�38000 E00), 1.75 km

west of Gollapalle. This is a circular body with outcrop

dimensions of 100 m 9 100 m, and is emplaced into

basement granitoids. The bulk of the body comprises a

hard melanocratic, greenish-black material, though a

weathered, carbonated and clay-rich variety is also

widespread. This unit is diamondiferous (Fareeduddin

2008).

CC5 kimberlite (14�5100000 N: 77�3800000 E), about 1 km

NE of Gollapalle. This is a narrow pear-shaped body of

dimensions 220 m 9 70 m, with an ENE–WSW trend,

emplaced into basement granitoid rocks. Crustal

246 Contrib Mineral Petrol (2009) 157:245–265

123

xenoliths (granitoid) are common. This body is charac-

terised by an abundance of kimberlite autoliths, which

gives the unit the appearance of a conglomerate.

Processing of bulk samples has revealed that it is

diamondiferous.

KL-3 kimberlite (14�3304000: 76�5704500), 0.5 km NNW

of Nagireddipalle. This is oval-shaped with dimensions

of 490 m 9 250 m, an ENE–WSW trend and is em-

placed into the Closepet granite. Country rock xenoliths

and eclogitic xenoliths are common. No diamonds

Fig. 1 Location map of the

Wajrakarur kimberlite field,

Eastern Dharwar craton,

southern India, showing the

distribution of four known

kimberlite clusters of

Wajrakarur–Lattavaram,

Timmasamudram, Kalyandurg

and Chigicherla (modified after

Nayak and Kudari 1999).

KL-1, 2, 3, 4, 5, 6 Kalyandurg

kimberlites; CC-1, 2, 3, 4, 5Chigicherla kimberlites;

P1–P12 Wajrakarur–

Lattavaram kimberlites;

TK-1 to TK-4 Timmasamudram

kimberlites. Inset map shows

the location of various

kimberlite and lamproite fields

in southern India

Contrib Mineral Petrol (2009) 157:245–265 247

123

have been recovered from this pipe (Nayak and Kudari

1999).

KL-4 kimberlite (14�3304100: 76�5906100), 2 km NE of

Nagireddipalle. It is blackish-green, hard and compact

hard banke rock with profusely altered yellow ground

and is mostly soil-covered. Eclogitic xenoliths are

present. Its dimensions are not available and is yet to

be tested for diamond.

P2A kimberlite (15�0104200: 77�2403500), located 100 m

south of Pipe-2 of Wajrakarur–Lattavaram cluster and

constitutes its satellite body. It was discovered by

Dhakate and Nayak (2002), and measures 500 m 9

120 m, with a NE–SW trend. This kimberlite is intensely

altered and carbonated and contains high proportion of

crustal xenoliths. It has been tentatively inferred to be

diamondiferous.

Age of kimberlite magmatism in the Eastern Dharwar

craton

The available data suggests that the kimberlites of WKF

(including those at Kalyandurg) and RKF were emplaced at

*1,100 Ma, whereas the kimberlites of NKF show a wider

age range from 1,100 to 1,400 Ma (e.g. Anil Kumar et al.

1993, 2001, 2007; Babu et al. 2005; Chalapathi Rao et al.

1996, 1999). High-precision isotope techniques such as

U–Pb dating on groundmass perovskite or titanite are fur-

ther required to refine the available age data.

Sample preparation and analytical techniques

As far as possible, the freshest outcrop samples were

chosen for study. Weathered surfaces were removed and

crustal and mantle xenoliths were manually hand-picked;

however, inherent alteration in the samples due to the

exposure of the kimberlites to tropical weathering for

millions of years could not be eliminated.

Carbon-coated thin sections were analysed by Electron

Probe Micro Analysis on a CAMECA SX-100 at the Indian

Bureau of Mines, Nagpur, India, with a beam current of

12 nA, an accelerating voltage of 15 kV and a beam

diameter of 1 lm. Standards supplied by BRGM, France,

were used to calibrate the instrument. On-line peak strip-

ping and corrections were performed using PEAKSIGHT

software supplied by CAMECA. After repeated analyses of

respective standards listed above along with the minerals of

interest, it was observed that the error on the elements was

not better than ±1%.

Whole rock major and trace element analyses were

carried out at the Activation Laboratories Ltd, Ancaster,

Ontario, Canada. ICP-OES (Model: Thermo-JarretAsh

ENVIRO II) was used to analyse major elements, whereas

ICP-MS (Model: PerkinElmer Sciex ELAN 6000) was

used to determine trace and rare earth element (REE)

concentrations. The precision is \5% for all analysed

elements when reported at 100 9 detection limit. Stan-

dards, including SY-3, W-2, DNC-1, BIR-1 and STM-1,

were run along with the samples to check accuracy and

precision. The analytical procedure is detailed by Gale

et al. (1999) and is also available in the Activation Labo-

ratories Ltd website (http://www.actlabs.com).

Petrography and mineral chemistry

The studied kimberlites have a typical inequigranular tex-

ture imparted by the two populations of olivine (rounded to

anhedral macrocrysts and subhedral to euhedral pheno-

crysts), which are almost totally altered to serpentine and

set in a fine grained groundmass of microphenocrystal

olivine, serpentine, phlogopite, spinel, ilmenite, perovskite,

carbonate and apatite. Sphene (in P2A) and xenocrysts/

megacrysts of garnet (in KL-3), and picro-ilemnite (in

KL-3 and CC4) are the other phases observed in these

kimberlites. As all the samples have undergone alteration

as exemplified by the high degree of serpentinisation as

well as, at times, carbonisation of ferromagnesian phases

viz., olivine and phlogopite, most of the petrological

information has to be extracted from the unaltered

groundmass oxide phases such as spinel and perovskite.

Backscattered electron (BSE) images depicting salient

petrographic aspects of the WKF kimberlites under study

are provided in Figs. 2 and 3.

Based on their textural characteristics, CC4, CC5, KL-3

and KL-4 kimberlites can be grouped as macrocrystal

hypabyssal serpentine calcite kimberlites, whereas P2A is

an altered macrocrystal hypabyssal serpentine kimberlite

(cf. Mitchell 1997). Hypabyssal kimberlites are considered

to be the best material to understand the character of a

kimberlite magma prior to the formation of diatreme and

pyroclastic portions of a kimberlite (Mitchell 2008). The

mineral chemistry data determined by Electron Probe

Micro Analyzer (EPMA) are presented in Tables 1, 2, 3, 4,

5, 6, 7, and 8 and are discussed below.

Olivine

Olivine, macrocrysts as well as phenocrysts, is an abundant

phase in all the kimberlites of this study (Figs. 2a–d, 3a)

and is extensively pseudomorphed by serpentine. Fresh

olivine macrocrysts (Fo91) are observed only in CC5

(Table 1). Serpentinised olivines from the various kim-

berlites of this study have compositions from Fo84 to Fo90.

These values are indistinguishable from the Fo84 to Fo92

248 Contrib Mineral Petrol (2009) 157:245–265

123

reported for fresh macrocrystal as well as for phenocrystal

olivines from other kimberlites of WKF (Chalapathi Rao

et al. 2004) and suggests that compositions of fresh and

serpentinised olivine are comparable.

Spinel

Spinel constitutes an important groundmass oxide phase

(Figs. 2a, b, 3a, b) in all the kimberlites of study. They

occur either as dispersed grains in the groundmass or as

aggregates (Fig. 2c). Atoll-shaped spinels are also common

due to resorption (Fig. 2a, b), while some exhibit marked

compositional zoning from Ti-poor core to Ti-rich rims.

Compositionally, the spinels of WKF show wide variation

(Table 2) and are relatively MgO-depleted compared to

those from the southern African kimberlites (Fig. 4a) and

are mostly confined to the field of Dharwar craton kim-

berlites. KL-3 spinels show some of the highest MgO

contents. Spinels from this study display both trends

(Trends 1 and 2) displayed by Group I and II kimberlites of

southern Africa (Fig. 4b; Mitchell 1986, 1995a). Such

extreme variation in the spinel composition was also

observed from the other Eastern Dharwar craton kimber-

lites and has been suggested to reflect variation in bulk

composition of their parental magmas (Chalapathi Rao

et al. 2004).

Phlogopite

Phlogopite is an essential mineral in all the studied

kimberlites and occurs as groundmass microphenocrysts

as well as rare macrocysts (Fig. 3a, e). However, the

Fig. 2 Backscattered electron

(BSE) images of various

minerals in CC4 and CC5

kimberlites. a Serpentinised

olivine (O) macrocrysts of up

to [1 mm dominating in CC4.

The groundmass is rich in

spinels and perovskite.

b Perovskite (P) forming

garlands around olivine in CC4.

Note the identical gray scale of

all the perovskites

demonstrating the lack of their

compositional variation.

c Clusters of groundmass spinel

(Sp) aggregates are a

conspicuous feature in CC4.

d Carbonate (Cb) in the

groundmass of the CC5. A

solitary barite (B) grain (bright)is also seen. e Groundmass

spinel (Sp) exhibiting extensive

compositional variation from an

iron-rich rim to iron-poor core

in CC5. f Acicular laths of

apatite prisms in CC5

Contrib Mineral Petrol (2009) 157:245–265 249

123

majority of phlogopite grains are highly altered, giving

low analytical totals (see Table 3 for data on P2A). Only

KL-3 has relatively pristine groundmass micas. Phlogo-

pites are all extremely poor in TiO2 (\0.6 wt%) and

highly aluminous (up to 13.73 wt%) typical of micas

characteristic of kimberlites (Mitchell 1995a). K2O con-

tents range between 8.56 and 10.07 wt%, close to the

pristine values.

Perovskite

Perovskite is a ubiquitous phase in the WKF and is par-

ticularly abundant in CC4 and CC5 kimberlites. It forms in

the final stages of magmatic crystallisation and occurs

either as discrete grains in the groundmass or as necklaces

surrounding earlier-formed olivine grains (Fig. 2a–c).

However, compositionally, they show little variation

(Table 4), with CaO ranging from 37.9 to 40.2 (wt %) and

TiO2 from 56.0 to 57.7 (wt%). Their FeOT contents range

from 0.96 to 1.34 wt%, indistinguishable from perovskites

from other WKF kimberlites (0.92–2.22 wt% FeOT;

Chalapathi Rao et al. 2004) and from archetypal kimber-

lites (1–2 wt%; Mitchell 1995a).

Sphene

Titanite is a relatively rare groundmass constituent in

kimberlites, but has been reported from Aries kimberlite of

Western Australia and inferred to be a late-magmatic to

hydrothermal constituent (Edwards et al. 1992). Sphene

occurs as a subordinate groundmass phase in P2A kim-

berlite (Fig. 3b, Table 5).

Fig. 3 Backscattered electron

(BSE) images of various

minerals in P2A and KL-3

kimberlites. a Highly altered

nature of the P2A. Note the

entirely serpentinised olivine

macrocryst (O; bigger) and the

groundmass olivine. Other

silicate phases such as

phlogopite (Ph) are also altered.

b Oxides such as titanite (Ti)and spinel (Sp) are much less

altered in P2A. c Xenocrystic

garnet grain in KL3. Note that

composition is almost uniform

except in the cracks where

alteration is seen. d Xenocrystic

picro-ilmenite grain in KL-3 is

continuously surrounded by a

rim that is calcium-rich.

e Phlogopite (Ph), spinel (Sp)

and carbonate (Cb) are

important groundmass phases

in KL-3. f Prismatic sprays of

apatite clusters in KL-3

250 Contrib Mineral Petrol (2009) 157:245–265

123

Apatite

It is a ubiquitous late-magmatic phase in all of the kim-

berlites of this study. It occurs as euhedral prisms or as

sprays of acicular crystals (Figs. 2f, 3f) in the mesostatis.

The latter are suggested to indicate relatively rapid cooling

(Mitchell 2008). Rarely, apatite is also found as inclusions

in phlogopite laths. Except for an altered grain in CC4 (see

Table 6), the analyses display a tight compositional range.

Carbonate

Carbonate occurs as an abundant primary and secondary

(deuteric) phase in the studied kimberlites, occuring mostly

as irregular patches in the mesostatis and also replacing

olivines (Figs. 2b, c, 3e, f). Calcite is the most abundant

carbonate, with minor dolomite in CC5.

Garnet

Garnets are observed only in KL-3 (Fig. 3c), where some

grains show kelyphitic reaction rims. EPMA studies

(Table 7) reveal that they are predominantly pyrope (54%)

with subordinate grossular (30%) and minor almandine

(16%). Their high Mg/(Mg + Fe) contents ([0.77) confirm

their mantle affinity (Schulze 2003), while low Cr2O3

contents (\0.32 wt%) and high Ca/(Ca + Mg + Fe) ratios

([0.29) demonstrate their eclogitic lineage and rule out

Table 1 Mineral chemistry of serpentinised olivine grains

Oxides (wt%) CC4 CC5 P2A KL-3

SiO2 43.57 41.320 46.84 39.76 44.71 42.53 43.07 39.87 39.32 39.16 37.62 36.63 39.00

TiO2 0.11 0.160 0.13 0.00 0.20 0.01 0.02 0.15 0.09 0.34 0.08 0.08 0.00

Al2O3 0.54 0.460 0.31 0.00 0.22 0.23 0.05 2.21 4.98 1.84 2.28 3.71 0.86

Cr2O3 0.03 0.030 0.04 0.00 0.08 0.13 0.05 0.12 0.31 0.26 0.09 0.03 0.07

FeO 5.47 7.060 6.02 8.82 6.37 5.60 6.03 5.19 4.68 7.55 8.95 6.77 6.89

MnO 0.14 0.030 0.12 0.12 0.10 0.03 0.1 0.15 0.05 0.06 0.14 0.06 0.00

MgO 36.06 35.930 36.69 51.50 36.97 36.52 33.73 38.23 35.31 36.39 37.27 36.59 37.61

CaO 0.22 0.260 0.15 0.00 0.20 0.31 0.31 0.43 0.42 0.33 0.18 0.16 0.06

Na2O 0.03 0.120 0.01 0.03 0.02 0.01 0.02 0.00 0.00 0.01 0.00 0.03 0.00

K2O 0.03 0.040 0.00 0.00 0.15 0.07 0.10 0.05 0.05 0.00 0.17 0.03 0.04

P2O5 0.00 0.02 0.00 0.00 0.07 0.00 0.06 0.02 0.01 0.02 0.00 0.00 0.01

Total 86.20 85.43 90.31 100.23 89.09 85.44 83.54 86.42 85.22 85.96 86.78 84.09 84.54

Fo 91.97 90.03 91.41 91.12 91.06 92.04 90.74 92.73 93.01 89.50 87.96 90.52 90.68

Fa 7.829 9.927 8.417 8.757 8.804 7.920 9.104 7.064 6.918 10.420 11.853 9.398 9.322

Table 2 Mineral chemistry of groundmass spinels

Oxides (wt%) CC4 CC5 P2A KL3

SiO2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

TiO2 10.21 12.44 13.44 6.17 12.01 30.31 15.85 16.74 0.13 18.09 17.03 10.26 10.82 10.46 18.79

Al2O3 10.10 1.13 7.66 10.09 1.85 0.16 6.66 3.42 37.08 5.12 5.82 7.38 1.13 7.31 11.45

Cr2O3 19.45 1.24 9.94 27.46 0.89 0.73 9.23 5.84 32.29 1.38 1.09 29.90 0.23 27.40 1.24

Fe2O3 24.80 42.97 30.57 23.95 43.21 10.70 26.24 28.58 0.00 32.48 32.99 19.63 46.97 22.03 26.14

FeO 21.11 36.41 25.63 20.21 38.19 53.09 31.41 39.31 13.34 30.78 32.74 15.04 36.27 15.86 24.58

MnO 0.68 0.97 0.67 0.47 1.44 2.70 1.01 1.53 0.21 0.96 0.97 0.62 0.77 0.57 2.28

MgO 13.88 3.20 12.13 11.89 1.65 1.78 9.43 4.05 15.51 10.98 9.01 16.87 2.16 16.97 15.01

CaO 0.14 0.00 0.07 0.06 0.14 0.12 0.10 0.05 0.02 0.07 0.24 0.19 0.47 0.11 0.44

Na2O 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

P2O5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Total 100.37 0.00 100.11 100.30 99.38 100.53 99.94 99.51 98.58 99.85 99.90 99.89 98.82 100.71 99.93

Fe+2/(Fe+2 + Mg) 0.46 0.86 0.54 0.49 0.93 0.94 0.65 0.84 0.33 0.61 0.67 0.33 0.90 0.34 0.48

Ti(Ti + Cr + Al) 0.22 0.80 0.37 0.12 0.76 0.97 0.44 0.59 0.63 0.66 0.62 0.19 0.84 0.21 0.49

Contrib Mineral Petrol (2009) 157:245–265 251

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their derivation either from peridotitic (Fig. 5a) or from a

Cr-poor megacrystic suite (Fig. 5b). Kelyphitic rims are

predominantly rich in CaO (up to 34.8 wt%) and FeO (up

to 21.65 wt%) (Table 7). Eclogitic xenoliths were reported

from the Kalyandurg pipes by Patel et al. (2006).

Picro-ilmenite

Xenocrysts of picro-ilmenite are common in CC4 and

KL-3 (Fig. 3d) with MgO contents of up to 6.78 (wt%)

(Table 8). Cr2O3 (up to 1 wt%) and Al2O3 (\0.14 wt%)

contents are low and strikingly similar to the low Cr2O3

picro-ilmenites from the Anuri kimberlite, Nuvavut,

Canada (Masun et al. 2004). Some of these grains also are

surrounded by Ca-rich kelyphitic reaction rims (Fig. 3d).

Table 3 Mineral chemistry of groundmass phlogopite

Oxides (wt%) P2A KL-3

SiO2 33.00 39.420 38.86 38.32 39.67

TiO2 0.61 0.590 0.36 0.44 0.55

Al2O3 12.73 11.340 12.85 9.65 13.73

Cr2O3 0.04 3.040 3.19 5.41 3.03

FeO 7.18 0.140 0.02 0.13 0.05

MnO 0.16 0.000 0.00 0.00 0.07

MgO 24.40 23.520 26.47 29.33 25.85

CaO 0.09 4.790 0.21 0.98 0.00

Na2O 0.06 0.050 0.06 0.00 0.03

K2O 9.39 8.560 10.07 9.78 9.94

P2O5 0.14 0.00 0.00 0.04 0.00

Total 87.80 91.45 92.09 94.08 92.92

Table 4 Mineral chemistry of perovskite

Oxides (wt%) CC4 CC5 KL-3

SiO2 0.00 0.13 0.00 0.00 0.00 0.00 0.00 0.00 0.46 0.00

TiO2 55.99 56.35 55.78 56.18 57.40 57.10 57.60 57.73 56.15 57.73

Al2O3 0.29 0.32 0.36 0.30 0.27 0.27 0.34 0.27 0.40 0.30

Cr2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.91

FeO 1.15 1.18 1.15 1.22 1.34 1.33 0.96 1.19 1.15 1.23

MnO 0.00 0.00 0.00 0.00 0.01 0.07 0.00 0.00 0.03 0.00

MgO 0.07 0.05 0.09 0.10 0.07 0.04 0.08 0.05 0.90 0.09

CaO 39.78 39.79 39.65 39.98 39.85 40.19 39.19 38.22 37.42 37.92

Na2O 0.25 0.27 0.33 0.26 0.24 0.23 0.23 0.47 0.58 0.42

K2O 0.02 0.01 0.03 0.02 0.03 0.00 0.04 0.00 0.03 0.02

P2O5 0.04 0.06 0.05 0.00 0.10 0.06 0.02 0.05 0.00 0.06

Total 97.59 98.16 97.44 98.06 99.31 99.29 98.46 97.98 97.12 98.68

Table 5 Mineral chemistry of apatite

Oxides (wt%) CC4 CC5 KL-3

SiO2 1.76 0.01 0.00 0.00 0.00 0.00

TiO2 0.00 0.00 0.00 0.00 0.00 0.00

Al2O3 0.38 0.02 0.00 0.00 0.02 0.00

Cr2O3 0.00 0.00 0.00 0.00 0.00 0.00

FeO 0.86 0.11 0.13 0.26 0.00 0.00

MnO 0.00 0.00 0.00 0.00 0.00 0.00

MgO 3.54 0.08 0.11 0.04 0.04 0.02

CaO 51.79 55.20 55.04 54.78 53.93 53.97

Na2O 0.62 0.12 0.20 0.01 0.02 0.04

K2O 0.09 0.02 0.00 0.00 0.00 0.00

P2O5 34.10 39.64 40.15 40.30 41.56 41.40

Total 93.14 95.20 95.63 95.39 95.57 95.43

252 Contrib Mineral Petrol (2009) 157:245–265

123

Geochemistry

Major element geochemistry

New major element data for the WKF kimberlites are

presented in Table 9. The contamination index (C.I.;

Clement 1982; Mitchell 1986; Taylor et al. 1994; Beard

et al. 2000) for most samples is\1.28 (Table 1), and thus,

they are minimally contaminated by crustal material. The

relatively high value (1.47) for CC4 is due to its carbonated

nature (LOI = 16.2 wt%), and reduced MgO content

(19.3 wt%). This sample shows the lowest SiO2 content

(24.4 wt%) of those measured (Table 9).

The ilmenite index (Ilm. I; Taylor et al. 1994) of the

WKF samples ranges from 0.35 to 0.79. High values (0.72

and 0.79) for P2A and CC4, respectively, are due to the

carbonation of the olivines, leading to lower MgO contents.

The remaining samples, especially those from Kalyandurg

cluster, show clear evidence of ilmenite-contamination by

their parent magmas, as also indicated by the presence of

ilmenite megacrysts.

WKF samples from this study are all silica-undersatu-

rated (\41%), with those from Kalyandurg cluster

displaying the highest undersaturation, and the widest

variation of CaO contents (7.91–17.6 wt%). They are

indistinguishable in this aspect with those from other EDC

kimberlites and Group I and II kimberlites of southern

Africa. Mg/Mg + FeT are high and range from 0.72 to 0.83

(Table 9) and highlight the mafic–ultramafic nature of the

samples. The K2O contents of P2 (WK–LT cluster) are

high (up to 2.20 wt%) due to high modal phlogopite. K2O/

Na2O ratios of all the samples is[1 thereby displaying the

potassic nature. With the increasing Mg/(Mg + FeT), the

samples of this study display a well-defined decrease of

TiO2 suggesting the fractionation of parent magma and plot

within the Group I kimberlite field of southern Africa

(Fig. 6).

Three inferences can be drawn from Fig. 6: (1) Some of

the EDC kimberlite magmas are less ‘primitive’ than those

from southern Africa; (2) WKF kimberlites show a wide

range in Mg#, and overlap with the Group II kimberlite

field and (3) non-diamondiferous NKF samples are the

most evolved of the kimberlites and occupy an entirely

different field. The peralkaline [molar (Na2O + K2O)/

Al2O3] and perpotassic (molar K2O/Al2O3) indices of the

Table 8 Mineral chemistry of picro-ilmenite from KL-3

Oxides (wt%) CC4 KL-3 KL-3 (rim)

SiO2 0.00 0.00 0.00

TiO2 49.88 49.69 40.73

Al2O3 0.02 0.14 0.71

Cr2O3 0.01 1.00 0.81

FeO 39.72 40.61 29.30

MnO 4.75 0.22 0.58

MgO 1.46 6.78 3.97

CaO 0.44 0.09 22.57

Na2O 0.00 0.06 0.38

K2O 0.00 0.05 0.04

P2O5 0.00 0.00 0.00

Total 96.28 98.64 99.09

Table 7 Mineral chemistry of garnet from KL-3

Oxides (wt%) KL-3 (kelyphite)

SiO2 40.60 39.290 38.27 40.96 30.13

TiO2 0.00 0.130 0.08 0.14 0.22

Al2O3 23.86 23.000 24.13 23.82 5.30

Cr2O3 0.25 0.220 0.32 0.20 0.19

FeO 8.32 8.480 8.10 8.27 21.65

MnO 0.29 0.220 0.21 0.27 0.00

MgO 15.60 15.820 15.75 14.64 0.26

CaO 11.65 11.440 11.59 11.77 34.84

Na2O 0.00 0.050 0.02 0.04 0.01

K2O 0.00 0.120 0.01 0.01 0.04

P2O5 0.02 0.03 0.00 0.00 0.01

Total 100.60 98.80 98.49 100.12 92.65

Mg/(Mg + Fe) 0.77 0.77 0.78 0.76 0.02

Ca/(Ca + Mg + Fe) 0.29 0.29 0.29 0.31 0.67

Py 54.16 54.70 54.80 52.49 0.69

Alm 16.20 16.45 15.81 16.63 32.43

Gro 29.07 28.42 28.98 30.33 66.87

Sp 0.57 0.43 0.42 0.55 0.00

Table 6 Mineral chemistry of xenocrystal (?) sphene

Oxides (wt%) P2A

SiO2 27.51 26.540 28.67

TiO2 37.91 36.970 36.07

Al2O3 0.13 0.160 0.20

Cr2O3 0.01 0.060 0.04

FeO 1.34 1.170 1.51

MnO 0.00 0.010 0.00

MgO 1.20 2.480 2.77

CaO 28.03 27.170 26.63

Na2O 0.00 0.000 0.00

K2O 0.00 0.000 0.01

P2O5 0.05 0.06 0.04

Total 96.18 94.62 95.94

Contrib Mineral Petrol (2009) 157:245–265 253

123

WKF kimberlites under study are essentially\1, similar to

those of archetypal kimberlites (B1; Mitchell 1995a).

Trace element (including rare earth elements)

and isotope geochemistry

New trace element data for the WKF kimberlites are pre-

sented in Table 10. The WKF kimberlites show large

variations in concentration of compatible trace elements

depending on the varying macrocryst/phenocryst matrix

ratio (Mitchell 1986). Excepting P2A, all the samples have

high V abundances (140–170 ppm) and are indistinguish-

able from other EDC kimberlites (75–355 ppm)

(Chalapathi Rao et al. 2004). Low V contents (39 ppm) in

P2A could be attributed to the high degree of alteration of

the pipe. Ni in kimberlites is principally hosted by olivine,

and hence, its abundance is directly proportional to the

macrocryst olivine content resulting in the variation of Ni

content in the samples (330–840 ppm). On the other hand,

the Cr (760–1,510 ppm) contents are much higher.

Zr and Nb are considered to be the least mobile

incompatible elements during hydrothermal alteration, and

are also relatively unaffected by small amounts of crustal

contamination (e.g. Price et al. 2000). On the Zr versus Nb

plot (Fig. 7), the WKF samples are unambiguously con-

fined to the Group I kimberlite field of southern Africa, and

are strikingly similar to the other EDC kimberlites.

Bivariate plots (Fig. 8a, b) involving Nb, a highly immo-

bile element, and more mobile elements such as Th and U

demonstrate that the samples of this study, and also those

of EDC, (1) are overwhelmingly confined to the Group I

kimberlite field of southern Africa and (2) show limited

crustal contamination.

WKF samples of this study show similar highly

fractionated (La/Yb = 108–145) chondrite-normalised

distribution patterns with La abundances being 500–

1,000 9 chondrite (Fig. 9a) and low HREE abundances of

Fig. 5 Variation in Cr2O3 (wt%) (a) and Ca/(Ca + Mg + Fe) (b) for

discriminating garnets derived from eclogites and peridotites (after

Schulze 2003). The black triangles are garnets from KL-4

Fig. 4 a MgO (wt%) versus Al2O3 (wt%) of spinels of this study.

The data for some Southern African kimberlite spinels are from Scott-

Smith and Skinner (1984) and that from other Dharwar craton

kimberlites are from Chalapathi Rao et al. (2004). b Fe2+/

(Fe2++Mg2+) versus Ti/(Ti + Cr + Al) (mol fraction) for ground-

mass kimberlite spinels projected onto the front face of the ‘reduced’

spinel prism. The trends exhibited by spinels are modified from

Mitchell (1986). CC Chigicherla pipes, KL3 Kalyandurg pipe-3, P2APipe-2A, Wajrakarur

254 Contrib Mineral Petrol (2009) 157:245–265

123

Ta

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yan

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yan

du

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yan

du

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yan

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aly

and

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ayak

and

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dar

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9)

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ata

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rav

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00

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.(2

00

7)

Contrib Mineral Petrol (2009) 157:245–265 255

123

5–10 9 chondrite. The steep slope of the REE patterns

coupled with low HREE suggests derivation from the

garnet-stability field (e.g. Gaffney et al. 2007). KL-4 dis-

plays the lowest HREE contents, which may reflect its

derivation from greater depths. Kimberlites of this study

are indistinguishable, in terms of REE patterns, from the

other WKF occurrences (Fig. 9a).

Normalised multi-element plots (Fig. 9B) demonstrate

that all the trace elements of the samples are highly enriched

over the primitive mantle and display sub-parallel incom-

patible trace element enrichment patterns. Samples show

strong negative troughs at K, Sr and P, and moderate rela-

tive depletion in Ti. Since these relative trace-element-

depletion patterns (troughs) are independent of Mg#, we

consider that fractional crystallisation could not have been

responsible for their origin, and we infer depletions to be

source-related. Likewise, the absence of Nb and Ta deple-

tions associated with the Ti troughs suggest that this feature

is not related to perovskite or ilmenite fractionation, but is

instead a feature of the primary magma. Fractional crys-

tallisation may, however, have contributed to the varying

extents of these depletions (see Le Roex et al. 2003).

Negative K, Sr and Ti anomalies (troughs) are known

from Group I kimberlites of Kimberley area, southern

Africa (e.g. Harris et al. 2004), and an almost ubiquitous

trough at K is seen in many mafic potassic rocks from Alto

Paranaiba Province, Brazil (Gibson et al. 1995). Le Roex

et al. (2003) interpret such potassium anomalies to be

primary features of kimberlite source regions. Sr depletion

can be accounted by the presence of clinopyroxene (e.g.

Smith et al. 1985) or calcite (Keshav et al. 2005) in the

source or even by an initial depletion due to melt extraction

(e.g. Chalapathi Rao et al. 2004). Depletion at P indicates a

residual phosphate-bearing phase such as apatite or pres-

ence of a complex K–Ba–P-rich metasomatic mineral

phase (Mitchell 1995b) in the source. Ilmenite or rutile in

the source can be a possible contributor for negative Ti

spikes. Negative anomalies at Nb and Ta are absent, sug-

gesting lack of subduction-related signatures experienced

by their source regions (Coe et al. 2008).

Three isotopically distinct kimberlite types are now

recognised, based primarily on studies from southern

African kimberlites (e.g. Smith et al. 1985; Becker and Le

Roex 2006), and from examples at Russia (e.g. Beard et al.

2000: Agashev et al. 2001), Venezuela (e.g. Kaminsky

et al. 2004) and India (e.g. Chalapathi Rao 2005). Pub-

lished eNd values for the WKF kimberlites (+0.7 to +2.5)

and NKF kimberlites (+4.5 to +5.2) are similar to the

isotope systematics of the Group I kimberlites of southern

Africa (see Chalapathi Rao et al. 2004, 2005). Strikingly

uniform and distinct initial 87Sr/86Sr compositions for NKF

(0.70312–0.70333) and WKF (0.70234–0.70251) kimber-

lites have been documented from groundmass perovskites

and are interpreted to represent the derivation of their

magmas from two distinct, yet internally homogeneous,

deeper (transition zone) mantle sources (Paton et al. 2007).

Discussion

Before constraining the source regions of the WKF samples

of this study from the available geochemical data, it is

important to assess their contamination from the crustal

and mantle material and also to infer the possible effects of

fractionation on the parent magma composition.

Contamination by the crustal and mantle xenoliths

and fractionation of the parent magma

The various contamination indices (C.I. and Ilm. I; see

above) have shown that, while crustal contamination in the

samples of this study is minimal, there is evidence for

entrainment of ilmenite in some of the Kalyandurg

kimberlites. Evidence against crustal contamination and for

a mantle derivation also comes from high Mg numbers

(Mg#) ([0.75) and high Ni contents (up to 840 ppm), which

are normally regarded as indicating the ‘primitive’ nature of

the magma. In addition, the major oxide compositions show

very low abundances of Al2O3 (\6.45 wt%) and Na2O

(\0.07 wt%) in all samples except P2 that would not be

expected if there was crustal contamination. Strongly LREE-

enriched REE patterns (500–1,000 9 chondrites), absence

of positive Eu anomalies, negative Nb and Zr depletions and

Fig. 6 Plot of Mg# versus TiO2 (wt%) for the kimberlites of this

study. Symbols are black diamond Chigicherla, black triangleKalyandurg, black square Wajrakarur-Lattavaram cluster (this work),

open circle Narayanpet kimberlite field, open square Wajrakarur-

Lattavaram cluster (previous work involving data for other pipes).

The published data for other pipes from WK–LT cluster and NKF are

also plotted for comparison and are from Chalapathi Rao et al. (2004).

Fields for South African Group I and II kimberlites are taken from

Eccles et al. (2004)

256 Contrib Mineral Petrol (2009) 157:245–265

123

the low HREE and Y contents provide further additional

evidence against significant crustal contamination.

Mantle contamination by peridotitic material could lead

to an increase in MgO, Ni and Cr contents in kimberlites,

but the abundances of REE and other incompatible trace

elements in mantle-derived xenoliths (peridotites and

eclogites) and xenocrysts such as ilmenite are negligible

when compared to those present in kimberlite magma and

hence their effects are minimal. At the most, entrainment

of peridotite-suite inclusions would only dilute REE

abundances to a limited extent (Harris et al. 2004). Fur-

thermore, eclogitic xenoliths are the more dominant

xenoliths in some of the pipes (e.g. Kalyandurg) in the

WKF and their LREE abundances (100 9 chondrite) are

several orders of magnitude lower than those of the host

kimberlites (Patel et al 2006).

Even though inevitable, fractional crystallisation is

considered not to play a major role in the evolution of

kimberlite magma (Mitchell 1995a). It was shown in the

preceding sections that the samples display some effects of

Table 10 Trace element (including rare earth element) content (in ppm) of samples under study

CC4 CC5 KL-3 KL-4 Pipe-2 Pipe-2a (3/PR2B) Pipe-2A CC4b CC5b

Trace elements (ppm)

Ba 1,751 2,138 1,394 1,317 3,108 3,368 193 1,376.5 1,326.9

Sr 1,630 2,037 861 737 903 1,167.3 358 589.1 715.4

Y 32 24 18 10 21 19.7 25 25.7 21.2

Sc 26 17 19 14 20 24.7 25 1.49 1.41

Zr 620 332 716 429 148 215.3 289 440.2 308.9

Cr 1,510 1,270 880 1,040 760 808.6 870 1,005.4 887.5

Ni 330 690 630 840 390 503.4 460 493.2 470.7

V 165 150 155 140 149 171.8 38 124.2 159.5

Ga 13 9 16 10 12 – 11 10.03 9.31

Rb 18 106 136 112 191 237.7 9 25.92 76.02

Nb 225 171 175 125 198 199 241 218.59 146.86

Hf 13.8 7.7 17.3 12.1 3.9 5.01 6.9 9.77 7.1

Ta 11.3 10.4 13.9 9.1 13.8 11 16.8 11.87 0.95

Th 22.9 20.1 14.2 12.2 21 19.43 25.1 46.71 44.55

U 5.2 4.1 3.3 2.6 3.8 3.56 5.2 6.03 4.55

REE (ppm)

La 225 175 119 103 155 132 190 202.9 173.2

Ce 406 329 223 189 272 233.3 334 392.9 324.9

Pr 43 34.8 24.9 19.8 28.4 24.7 33.8 39.2 31.7

Nd 150 123 88.4 66.6 98.6 87.67 115 142.9 115.7

Sm 21.5 17.2 13.3 9.4 14.4 13.27 16.7 21.48 17.75

Eu 6.6 5.3 4.1 2.8 4.5 3.48 5.3 5.51 4.76

Gd 15.3 11.2 9.1 6.2 10.1 18.2 11.6 18.2 15.2

Tb 1.9 1.4 1.1 0.7 1.3 1.2 1.4 1.52 1.28

Dy 7.7 6.1 4.8 3.1 5.6 5.09 6.4 6.33 5.37

Ho 1.3 0.9 0.8 0.5 0.9 0.83 1.1 0.83 0.70

Er 2.9 2.2 1.8 1.1 2.2 2.04 2.4 2.16 1.84

Tm 0.35 0.24 0.21 0.13 0.25 0.24 0.3 0.2 0.17

Yb 1.8 1.2 1.1 0.6 1.3 1.41 1.5 1.3 1.08

Lu 0.22 0.14 0.12 0.08 0.17 0.19 0.18 0.17 0.13

RREE 883.57 707.68 491.73 403.01 594.72 523.62 719.68 835.6 693.78

La/Yb 125.00 145.83 108.18 171.67 119.3 93.62 126.67 156.08 160.37

CC4 Chigicherla pipe-4, CC5 Chigicherla pipe-5, KL-3 Kalyandurg pipe-3, KL-4 Kalyandurg pipe-4, KL-5 Kalyandurg pipe-5, KL-6 Kalyandurg

pipe-6a Data from Chalapathi Rao et al. (2004)b Data from Paul et al. (2006)

Contrib Mineral Petrol (2009) 157:245–265 257

123

fractionation, but their Mg/Mg + FeT are sufficiently high

(0.72–0.83) to be considered typical of primitive magmas.

Models for origin of kimberlites

The origin of Group I kimberlites remains controversial,

with disagreements as to the nature and depth of their

source region, primary nature of their melts and the causes

of melting (plume vs. extension). At present, at least four

plausible sources have been inferred for Group I kimber-

lites viz., (1) Sub-continental lithospheric mantle (SCLM)

(e.g. Tainton and McKenzie 1994; Chalapathi Rao et al.

2004; Le Roex et al. 2003; Becker and Le Roex 2006) (2)

convecting (asthenospheric) mantle (e.g. Smith et al. 1985;

Price et al. 2000; Griffin et al. 2000; Mitchell 2008), (3)

deeper mantle products of ancient subducted oceanic crust

(transitional zone or lower, e.g., Ringwood et al. 1992;

Nowell et al 2004; Sumino et al. 2006; Gaffney et al. 2007;

Paton et al. 2007) and (4) the core–mantle boundary (e.g.

Haggerty 1994, 1999).

Nature of the mantle source region and mantle

metasomatism

High Ni (up to 840 ppm), Cr (up to 1,510 ppm) and Mg#

([0.75) and low Al2O3 contents (\6.45 wt%) of the WKF

samples suggests a highly refractory source similar to a

depleted harzburgite (e.g. Beard et al. 1998, 2000). High

abundances of incompatible elements, LILE as well as

HFSE, are characteristics of these magmas. For partial

melting of a primitive peridotite to produce such signa-

tures, the degree of melting has to be extremely low

(\0.1%, Arndt 2003). Even though it has been shown that

such small fractions of melts can be extracted from a

normal peridotite (e.g. Faul 2001), the involvement of a

highly enriched (metasomatised) mantle source is widely

invoked in the genesis of potassic–ultrapotassic alkaline

rocks to explain their extreme trace element enrichment

levels (e.g. Foley 1992). HREE depletion requires a source

that has experienced a previous depletion (melt extraction)

event (e.g. Tainton and McKenzie 1994; Chalapathi Rao

et al. 2004). This scenario of initial depletion and sub-

sequent enrichment is analogous to that experienced by

many continental lithospheric peridotite xenoliths

entrained in kimberlites (e.g.; Carlson et al. 1996; Carlson

and Irving 1998; Beard et al. 2007). Primary melts from an

upwelling plume mantle are unlikely to account the

observed major and trace element signatures in kimberlites.

Fig. 7 Zr (ppm) versus Nb (ppm) plot for the kimberlites of this

study. Symbols are the same as in Fig. 6. The field for Dharwar craton

kimberlites (WK–LT cluster and NKF) is from Chalapathi Rao et al.

(2004) and the other fields are from Caro et al. (2004)

Fig. 8 a Nb/Th and La/Th ratios for kimberlites under study. The

other fields (MORB, OIB, Karoo lavas and Group I kimberlites) and

primitive mantle (PM) and average crustal values are taken from

Harris et al. (2004). b Nb/U ratio for the kimberlites of this study.

Symbols are the same as in Fig. 6. The published data for other pipes

from WK–LT cluster and NKF are also plotted for comparison and

are from Chalapathi Rao et al. (2004). The other depicted fields are

taken from Le Roex et al. (2003)

258 Contrib Mineral Petrol (2009) 157:245–265

123

Mantle metasomatism can be attributed to two con-

trasting source enrichment processes: (1) Subduction-

derived melts (e.g. Murphy et al. 2002; Gaffney et al. 2007)

and (2) volatile and K-rich low viscosity melts derived

from convecting (asthenospheric) mantle that freeze in sub-

continental lithospheric mantle as veins and dykes (e.g.

McKenzie 1989; Foley 1992). Since there is no evidence of

any subduction-related signatures from our primitive

mantle normalised multi-element plots (above), we prefer

to place the source of the enriching melts in the convecting

mantle.

The compostional features revealed by incompatible

element patterns (Fig. 9b) suggest the presence of phlogo-

pite (±richterite), clinopyroxene, carbonate and apatite in a

garnet peridotite source. High CaO (up to 17.60 wt%)

contents also indicate a carbonate-bearing source (see

Girnis et al. 1995) for the WKF kimberlites. Experimental

studies reveal that kimberlite magma can originate from

low degrees of partial melting of carbonate-bearing garnet

lherzolite, which can account for high concentration of

incompatible elements, high LREE/HREE and low Al2O3

abundances (e.g. Dalton and Presnell 1998). Further evi-

dence for the carbonic metasomatism in the WKF domain

also comes from the recent report of sovitic carbonatite

occurring in association with a kimberlite near Wajrakarur

(Chatterjee 2005).

Depth and degree of partial melting

The highly fractionated REE patterns and the high Ni, low

Al2O3 and low HREE contents relative to typical MORB

indicates the involvement of garnet in the source region

Fig. 9 a Chondrite normalised

(values from Evensen et al.

1978) REE abundances for

kimberlites of this study. The

shaded area is the field of

kimberlites from the other

kimberlites of WK–LT cluster

and is taken from Chalapathi

Rao et al. (2004). b Primitive

mantle normalised (values from

Sun and McDonough 1989)

multi-element patterns for the

kimberlites of this study

Contrib Mineral Petrol (2009) 157:245–265 259

123

(Fig. 9a, b). The presence of diamonds and presence of

eclogitic xenoliths containing retrogressed majoritic garnet

inclusions in Kalyandurg kimberlites (Patel et al. 2006)

confirm that these kimberlite magmas were generated from

within the diamond stability field.

The degree of partial melting can be estimated, given

the SiO2 content of a melt and its Nb/Y ratio, since the

latter is not greatly affected by the metasomatic processes

(Rogers et al. 1992; Beard et al. 1998). Figure 10 dem-

onstrates that kimberlites of the WKF and NKF fields (1)

are the products of much smaller degrees of melting than

Ocean Island Basalts (OIB) and Mid Oceanic Ridge

Basalts (MORB) (Fig. 9a); (2) display a wide range of

degrees of partial melting compared to those of Group I

and II kimberlites of southern Africa, with the kimberlites

from the Kalyandurg cluster displaying the maximum

range and (3) the amount of partial melting undergone by

the WKF and NKF source regions is empirically inter-

mediate to that of Group I and II kimberlites, and similar

to that of world-wide melilitites. The latter observation is

consistent with experimental studies of near-solidus melts

produced at 30 kbar and at 30–70 kbar in carbonated

mantle peroditite which suggest that it is possible to

generate a continuous spectrum of melts ranging in

composition from kimberlite to melilitite (Gudffinsson and

Presnell 2005).

Petrogenetic modelling

Despite a plethora of geochemical data, the constitutional

make-up of a kimberlite parental melt is still unclear (e.g.

Kopylova et al. 2007). There is also paucity of crystal–

liquid distribution coefficients fully applicable to melts of

kimberlite composition. Nevertheless, diverse quantitative

and semi-quantitative petrogenetic models involving

inverse—as well as forward—modelling have been deve-

loped in recent years, based primarily on trace element

geochemical compositions, to constrain the petrogenetic

processes involved in the generation and evolution of

kimberlites.

Tainton and McKenzie (1994) developed a three-stage

inversion method to model observed REE-distribution

patterns of the Group I and II kimberlites and lamproites by

estimating the degree and depth of partial melting and the

modal mineralogy of the residue. They deduced that the

kimberlite component derived from a convecting mantle

(the precursor small fraction highly metasomatised melts)

was extracted from a depleted continental lithospheric

mantle. Similar results were obtained from the REE mod-

elling studies on fifteen Proterozoic kimberlites and three

lamproites from the Eastern Dharwar craton of southern

India, including those from the WKF and NKF (Chalapathi

Rao et al. 2004).

It has been suggested (e.g. Le Roex et al. 2003) that such

complex inversion modelling is not justified in view of the

magnitude of assumptions that are required in back-cal-

culating primary magma compositions. Becker and Le

Roex (2006) proposed a semi-quantitative forward mod-

elling of batch melting of southern African kimberlite

source compositions based on a source comprising a

metasomatised garnet lherzolite and very low degrees of

partial melting (F = 1%). To allow possible differences

between Group I and II kimberlite source regions, some of

the variables in modelling were restricted viz., (1) close to

primary magma compositions were used along with a fixed

degree of partial melting (F = 1%), (2) residual mineral-

ogy for Group I and II kimberlite source regions was fixed

based on varying modal proportions of clinopyroxene and

garnet and (3) partition coefficients of basalts (e.g. Schmidt

et al. 1999) were chosen for both Group I and II kimberlites

because of their availability as a coherent data set of

elements.

Studies by Becker and Le Roex (2006; Fig. 11) have

shown that Group I kimberlites were derived from sources

having higher Gd/Yb and lower La/Sm (relatively deeper

but less enriched regions), whereas the Group II kimber-

lites have a source with higher La/Sm but lower Gd/Yb

(relatively shallower but more enriched regions). Calcu-

lated melting trajectories (Fig. 11) of inferred Group I and

II kimberlite source regions demonstrate that increase or

decrease of partial melting cannot account for the differ-

ences between the two groups.

Mantle nodule data from the Eastern Dharwar craton is

relatively scarce compared to that from southern Africa.

However, both fertile- (sheared garnet lherzolite and

Fig. 10 Nb/Y versus SiO2 (wt%) plot illustrating the degree of partial

melting in the kimberlites of this study. The other fields are taken

from Beard et al. (1998). Symbols are the same as in Fig. 6

260 Contrib Mineral Petrol (2009) 157:245–265

123

wehrilite) and depleted-(granular garnet harzburgite and

lherzolite) garnet peridotite nodules, MARID suite of

xenoliths, glimmerites and bimineralic as well as polymi-

neralic eclogitic xenoliths have been reported and are not

different in petrography and composition to those of

southern African kimberlites (e.g. Ganguly and Bhatta-

charyya 1987; Nehru and Reddy 1989; Patel et al 2006).

Therefore, it is reasonable to assume similar kimberlite

source compositions, as adopted by Becker and Le Roex

(2006), for the EDC kimberlites. We have used the melting

trajectories of the inferred Group I and II kimberlite source

regions of Becker and Le Roex (2006) to model the

observed REE concentrations of WKF and NKF kimber-

lites to test whether the southern African model holds good

for the EDC kimberlite samples.

Results presented in Fig. 11 suggest that a simple

melting trajectory of assumed Group I kimberlite source

cannot account for the observed REE compositions of all

the kimberlites of the WKF and NKF. Some kimberlites are

confined to the melting trajectories of the inferred Group II

kimberlite source compositions. Furthermore, NKF and

WKF kimberlites display a relatively far greater range in

the degree of melting (4% to 0.1%) than those from the on-

craton occurrences from South Africa. The relatively

greater range of melting extent experienced by the WKF

and NKF source regions is also supported by the SiO2

versus Nb/Y plot (above). Note that the higher degrees of

partial melting (3–5%) experienced by some of the NKF

pipes was previously inferred from their Ce/Y versus Zr/Nb

ratios (Murthy and Dayal 2000). Interestingly, many of the

kimberlites from WKF (including CC4, CC5, KL-3, KL-4,

P2 and P2A) also plot in an inferred source region corre-

sponding to a hybrid composition between Group I and II

kimberlites (Fig. 11).

Different degrees of partial melting of the same mantle

source (either Group I or II) cannot explain the observed

variation of WKF and NKF samples (Fig. 11). Instead, a

complex interplay between Group I and II type kimberlite

sources in the generation of WKF and other EDC kim-

berlites is suggested, pointing to the involvement of

multiple and heterogeneous sources having the character-

istics of Group I and II kimberlites and mixtures. Such a

highly heterogeneous mantle source, not withstanding its

OIB-type isotopic signature, would be consistent with an

origin in sub-continental lithospheric mantle (SCLM) (e.g.

Schmidberger et al. 2001), but not in a convective

(asthenospheric) mantle, since mantle convection would

wipe out such geochemical heterogeneities over long time

scales. Haggerty and Birckett (2004) also attribute the

variations in EDC kimberlites to the varying degree of

partial melting and mixing of fertile, depleted and enriched

mantle rocks into proto-kimberlite melts.

While it is interesting to note that the basic premises

adopted and the results inferred from two contrasting

petrogenetic modelling techniques (inverse vs forward) as

applied to EDC kimberlites are quantitatively different, it

is significant that both of them culminate in the common

conclusion that the source regions of Group I (and Group

II) kimberlites lie within the SCLM. Experimental studies

involving mineral-melt partititioning of major and trace

elements between clinopyroxene and CO2-rich kimberlite

melts at a pressure of 6 GPa and at temperatures of 1,410

and 1,430�C reveal that Group I kimberlites of southern

Africa can be produced by *0.5% melting of a MORB-

type-depleted source that has been enriched by small

degree melts originating from a similar depleted source

and located at the lithosphere–asthenosphere transition

(Keshav et al. 2005). The interaction between the depleted

source (SCLM) and invading metasomatic (enriching)

melts percolating from the asthenosphere would have

given an OIB-like isotopic signature to Group I kimber-

lites (e.g. Le Roex et al. 2003; Khazan and Fialko 2005).

The isotopic differences between Group I and II kimber-

lites can thus be accounted by the variation due to their

metasomatic enrichment at different times in the SCLM,

but not by different processes (Tainton and McKenzie

1994, p. 796). Further constraints on the evolution of the

source regions of EDC kimberlites necessitates usage of

multi-element isotopic techniques, e.g., Pb–Pb, Lu–Hf,

Re–Os.

The homogeneity of the Sr-isotopic compositions of

perovskite and high pressure majoritic garnet inclusions in

some WKF samples led Paton et al. (2007) to place kim-

berlite sources in the transition zone (cf. Ringwood et al.

Fig. 11 La/Sm versus Gd/Yb for the kimberlites of study as well as

those for the other kimberlites from the WKF and NKF (data taken from

Chalapathi Rao et al. 2004). Illustrated curves (from Becker and Le

Roex 2006) represent melting trajectories of inferred Group I and II

kimberlite source regions having residual mineralogy as follows: Grp I,ol:opx:cpx:gt = 0.67:0.26:0.04:0.03; Grp II, ol:opx:cpx:gt = 0.67:

0.26:0.06:0.01. Numbers shown represent the degree of melting. Fields

for Kimberley (Grp I) and Swartrugens and Star (Grp II) kimberlites are

from Becker and Le Roex (2006). Symbols are the same as in Fig. 6

Contrib Mineral Petrol (2009) 157:245–265 261

123

1992), but the majoritic garnets may provide evidence that

they, rather than kimberlites, form in the transition zone

and could have been entrained by the convecting mantle

into the kimberlite source regions (Tainton and McKenzie.

1994). Furthermore, models such as those visualised by

Paton et al. (2007), Ringwood et al. (1992) and others,

listed above, predominantly involve domains composed of

subducted oceanic crust rising to the top of asthenosphere

before undergoing partial melting. However, we did not

find evidence of subduction signatures in any of the studied

samples of WKF. The model of Paton et al. 2007 also

contrasts with experimental studies, which invoke low

degree (0.7–0.9%) melting of a carbonated lherzolitic

mantle source at pressures and temperatures found in the

uppermost asthenosphere, far off from transition zone, for

Group I kimberlite genesis (Price et al. 2000).

Occurrence and distribution of Proterozoic kimberlite

clusters in the Eastern Dharwar craton

The Eastern Dharwar craton and its three distinct kimber-

lite fields constitute the world’s largest known repository of

Proterozoic kimberlites. A satisfactory unifying model to

account their occurrence and distribution is, so far, lacking.

The distribution of kimberlite fields (30–50 km) and clus-

ters (5–10 km) in southern Africa has recently been

explained (Gregorie et al. 2006) to represent the surface

envelope of dyke swarms generated inside a melt pocket,

and discharge of melt via dykes originating from sub-

regions of the pocket, respectively. The initiation of

swarms of kimberlite dykes has been considered inevitable

due to large excess pressure between melt and the sur-

rounding solid, which exceeds the hydraulic fracturing

limit of overlying rocks. This model requires an exten-

sional tectonic regime for the cratonic lithosphere to allow

the arrival of kimberlite dykes at the surface. Based on the

reconstructed Proterozoic geothermal gradient of the

southern Indian lithosphere during the mid-Proterozoic and

geodynamic modelling, Chalapathi Rao et al. (2004)

inferred that the EDC kimberlites were products of small

amounts of lithospheric extension without the need for a

mantle plume. This inference, in conjunction with the

extension-related mantle-mush compaction model (Grego-

rie et al. 2006), can account for the distribution of several

clusters and fields of kimberlites that erupted during the

Mesoproterozoic.

However, altogether, different proposals involving

impingement of a short-lived mantle plume at the base of

the Eastern Dharwar craton during Mesoproterozoic and/or

a major change and re-organisation of the mantle convec-

tion regime at this time have also recently been invoked

(Anil Kumar et al. 2007).

Relationship between different kimberlite clusters

in WKF and comparison with Southern African

occurrences

Samples from the Wajrakarur and Narayanpet kimberlite

fields display a wide-variation in the composition that can

be attributed to the varying degrees of partial melting of

highly heterogeneous lithospheric mantle sources. Crystal

fractionation and crustal/mantle contamination exercised

little impact on the primary magma composition. The

consistency of major and trace element characteristics of

the hypabyssal kimberlites of WKF, along with others from

the EDC, with the Group I and, at times, with Group II

kimberlites, demonstrates that the processes involved in

kimberlite source formation and magma generation are

repeatedly reproducible in time and space on a global scale

(cf. Mitchell 2008).

Haggerty and Birckett (2004) noted recently that there

are ‘neither archetypal kimberlites nor ideal lamproites’ in

India following their geochemical work on 57 samples

from 13 intrusions of Eastern Dharwar craton kimberlites.

On the other hand, Paul et al. (2006) noted that the Indian

samples show a general similarity to the established

and accepted kimberlites of southern Africa and lamproites

of Western Australia and suggest, based on the divergence

in geochemical characters, a transitional nature of the

Indian potassic, ultramafic rocks between kimberlites

and lamproites. However, a detailed assessment involv-

ing petrological and geochemical study of EDC kimberlites

of this study and also other recent works (see Chalapathi

Rao et al. 2004; Scott-Smith 2007) show remarkable sim-

ilarities with the southern African occurrences in many

aspects.

Kimberlite geochemistry versus diamond potential

The presently known EDC kimberlites are poorly dia-

mondiferous compared to their counterparts in cratonic

areas of southern Africa, Australia, Canada and Russia. A

multitude of reasons may account the non-diamondiferous

nature of the kimberlites viz., deep erosion, lack of dia-

mondiferous roots, rate of ascent of the magma, oxygen

fugacity, etc. However, an important observation of this

study is that the NKF kimberlites, which show the maxi-

mum extent of fractionation, are also non-diamondiferous

(Haggerty and Birckett 2004). An assessment of the extent

of evolution of kimberlite magma is significant in the

context of diamond exploration, since most primitive

kimberlites have been found to be diamondiferous, whereas

the more evolved pipes are commonly barren of diamond

as observed in the Late Cretaceous northern Alberta kim-

berlite province (Eccles et al. 2004).

262 Contrib Mineral Petrol (2009) 157:245–265

123

Acknowledgments Kimberlite samples were collected during a

field trip, jointly organised by the Geological Society of India and

Geological Survey of India, during November, 2005, to the

Wajrakarur kimberlite field. We offer our grateful thanks to the

officials of both these organisations for their excellent hospitality and

help. We also thank Geological Society of India for inviting us to

attend the ‘Group Discussion on Kimberlites and related rocks,’ of

which this field trip formed a part, and for extending financial support.

Helpful comments by Dave Pyle (Department of Earth Sciences,

Oxford), Ian Osborne (Department of Earth Sciences, The Open

University, Milton Keynes, UK) and two anonymous reviewers

together with editorial suggestions by Prof. T.L. Grove significantly

improved the presentation of this manuscript.

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