Large eliptical orangeite sills (bleachedwhite) intruding Barakar Formation coal.

Ramnagar Colliery, Raniganj BasinEastern Damodar Valley

Small cylindrical sills of orangeite someexposed in longitudinal section, intrudingBarakar Formation coal and sandstone.

Kustore Colliery, Jharia BasinCentral Damodar Valley

Largeorangeite sillemplaced intoPermianBarakar For-mation coalseams.

Cylindrical sills of orangeite cutting PermianBarakar Formation coal and sandstone.

Ramnagar Colliery, Raniganj BasinEastern Damodar Valley

Orangeitedykes cuttingPermian sedi-ments.

Orangeite cylinder with small dyke-likeapophyses intruding sandstone and coal.

0 25

24°N

23°

N

86° 87 E

DamodarV alley fault

❢Asansol

❢

Bokaro

Jharia Dhanb

ad

0 25

❢ City , town, village

Alluvium

Cretaceous Basalts

Gondwana sediments

Archaean-Proterozoicbasement rocks

dK,T Dyke (Cret., T ertiary)

Bengal

Basin

88°

Rajmahal Hills

0 50km

86°E

❢

25°N

90°

Tura❢

Shillong

Sylhet

❢

Sylhet Traps

24°

23°

N

ChotanagpurPlateau

dK

❢ Rajmahal

dKdK

dTdK

dK

Shillong Plateau

❢

Mica Belt

92°

dT

Koderma

Fig. 2

Damodar Valley

❢Ranchi

Area ofmain map

INDIA

km

KHH-1KLA-1

ChasnalaBhowrah

RLA-1Asansol

°

Map of easternIndia showing locations ofthe Damodar Valley,Jharkhand, West Bengal.Location of the main sedi-mentary basins in the val-ley and sample locales.

Raniganj

Rationale for study Orangeite (Group II Kimberlite)magma is generated from garnet-bearing mantle at depths in excess of 150 km, and maytransport diamond to the surface. The petrogenesis of orangeite magma is not well under-stood, but it appears that orangeites are hybrid rocks consisting of variable proportions ofxenocrysts (principally olivine macrocrysts derived from disaggregated peridotite) plusphenocrysts and interstitial phases, representing extensive crystal fractionation from amafic alkalic melt.

We have collected Hf and Os isotope data for orangeite samples from the Damodar Valleyof eastern India. These data complement our major element, trace element and Sr-Nd-Pbisotopic studies. We propose to use these data to place constraints on the nature of the man-tle source(s) of orangeite, which has been the subject of recent debate.

Petrogenesis of Group II Kimberlites

Os Isotope Results

0.10

0.12

0.14

0.22

0.24

0.26

0.28

0 5 10 15 20 25

Chasnala

Bhowrah

0.16

0.18

0.20

RLA-1

KHH-1

KLA-1

AsansolIncreasing Os concentration

0.00

0.06

0.12

0.18

0 1 2 3

Asansol0.0

0.1

0.2

0.3

0 2 4 6 8

Chasnala

(1/Os)*1000 (ppt-1)

187Os/188Os

Measured 187Os/188Os vs. 1/[Os]*1000 (ppt.-1)

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0 10 20 30 40 50

0.00

0.04

0.08

0.12

0.16

0 5 10 15

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 5 10 15

Chasnala

Bhowrah

RLA-1

KHH-1

KLA-1 Asansol

AsansolChasnala

187Os/188Os vs. 187Re/188Os187Os/188Os

187Re/188Os

γOs(T) = 0

-60

-20

20

60

100

140

0 500 1000 1500

Chasnala

Bhowrah

RLA-1

KHH-1

KLA-1

Asansol

Os (ppt)

γOs(T)

γOs(T) vs. Os ppt

Damodar Valley orangeites Os isotopic data. After numerous attempts to obtain reproducible data, we also tried some procedural adjustments:reproducibility was not improved. Therefore, we suggest that these orangeite samples are extremely heterogeneous and small phases (<30µm)probably host the high Os concentrations.

8

12

16

Amp, ilmCpx

4

6

Phl

Amp

0

2

4

6

5 10 15 20 25 30

Ap

6

8

10

Phl

P2O

5K

2OF

e 2O

3*A

l 2O

3

MgO

4

6

8

Phl

Rut

35

40

45

50

55

Loss-on-ignition<10 wt.%>10 wt.%

Ol

0.2

0.6

1.0

Amp

5 10 15 20 25 302

4

6

8

Cpx

Perov

CaO

Na 2

OT

iO2

SiO

2

MgO

Major Element Variation in Damodar Valley Orangeites

Effects of crystal fractionation - primarily olivine (ol) and phlogopite (Phl),but also clinopyroxene (Cpx), rutile (Rut). Alteration (carbonation) is exten-sive in some samples (>10% LOI).

0.700 0.705 0.710 0.715 0.720 0.725

Damodar Valley Orangeites

Kimberlites

Orangeites (South Africa)

Lamproites

MORB OIB

Post-magmatic alteration

87Sr / 86SrT

Bul

kE

arth

εNd(T) vs. 87Sr/86SrT in Orangeites and other Mafic Rocks

Data references available on request.

Damodar Valley orangeites compared to kimberlites, lamproites, South Africanorangeites, mid-ocean ridge basalts (MORB) and ocean island basalts (OIB).

-40

-30

-20

-10

0

10

εε Nd(T

)

Pb Ba U Ta La Sr Nd Zr Ti Yb ScRb Th K Nb Ce P Hf Sm Y Lu V

0.1

1

10

100

1000

Wh

ole

Ro

ck/P

rim

itiv

eM

antl

e

KLA-3

KHH-1

Chasnala

Bhowrah

Evolved orangeites

Primitive mantle values ofSun & McDonough, 1989

Pb Ba U Ta La Sr Nd Zr Ti Yb ScRb Th K Nb Ce P Hf Sm Y Lu V

0.1

1

10

100

1000

Wh

ole

Ro

ck/P

rim

itiv

eM

antl

e

KLA-1

KLA-2

Asansol

Unevolved orangeites

Primitive mantle values ofSun & McDonough, 1989

Trace Element Variation inDamodar Valley Orangeites

The Damodar Valley orangeites can be subdivid-ed into two groups based on the mineralogy /trace elements (after Mitchell, 1995): Unevolvedand Evolved orangeites.

KLA-1

Ti-richphlogopite

Olivine

Apatite

Rutile

Cross-polars photomicrograph (x100)

Australia

Antarctica

India

Mad

agas

car

Afr

ica

RajmahalTraps

ShillongPlateau

KerguelenPlateau

Elan Bank

KerguelenHotspotToday

KerguelenHotspotat 75 Ma

-20°

-30°

30°

-40°

20°

-50° 20°

30°

40°

50°

60°

70° 80°

90°

Plate Tectonic Reconstruction Indian Ocean

100°

Reconstruction from Kent et al. 2002, using mantle convection code derived by Steinberger& O’Connell, 1998. Relative southward motion of the Kerguelen hotspot is based on Antretter et al. 2002.

115 MaAt 115 Ma, eastern India was

near the inferred location of the Kerguelenhotspot (calculated back to 75 Ma). At present,the hotspot is near 49°S but has likely driftedsouthward over time. Damodar Valleyorangeites were emplaced just to the south ofthe Rajmahal Hills, where flood basalts werecontemporaneously emplaced. Rajmahalbasalts and Damodar Valley orangeites mayform two parts of the same magmatic episode,which might have coincided with early Ker-guelen plume activity. Below, we compare datafor these three volcanic events.

A Kerguelen Connection?The Kerguelen hotspot is linked in space and time with the eruption of east India orangeites.

Compositional similarities also exist, particularly in isotopes. Could they be connected?

EM I

EM II738

1137

1141-2KA 24-25 Ma

KA30-26 Ma

KA<10 Ma

1136

749

1138

1140

1139

747750

Indian MORB

37.0

37.5

38.0

38.5

39.0

39.5

DMM

NHRL

17.0 17.5 18.0 18.5

RLAKHHKLAAsansolChasnalaBhowrah

Data references available on request.

Rajmahal TrapsBasalts

206Pb / 204Pb

208 P

b/20

4 Pb

Damodar Valley orangeites compared toRajmahal Traps lavas, Kerguelen hotspot lavas,Indian mid-ocean ridge basalts (MORB), and themantle ‘endmembers’. Also shown is the NorthernHemisphere Reference Line, a regression throughoceanic basalts north of the equator (in Pb plot).

IndianMORB

KA 24-25 Ma

KA 30-26 Ma

K.A.< 10 Ma

+5

-4 -2 0 +2 +4 +6 +8 +10- 5

+10

+15

Juvenile RockArray

+20

749

1140750

Broken Ridge1136, 1138

Data references available on request.

1137

RLAKHHKLAAsansolChasnalaBhowrah

747

RajmahalTrapsBasalts

(εH

f)T

(εNd)T

Isotopic compositions of Orangeitesand Kerguelen hotspot lavas

ConclusionsIndian orangeites (115 Ma) lie on or just below

the mantle array in Hf-Nd isotope space, com-

parable to some Rajmahal Traps and Kerguelen

basalts; similarities that are present in Pb iso-

topes too. These characteristics, when combined

with mineralogical and other geochemical data,

imply derivation of the orangeites from a gar-

net-bearing source. Subsequent interaction with

Indian lithosphere and/or lower crust is likely.

Plate tectonic reconstructions and isotopic over-

lap with Kerguelen hotspot-derived lavas permit

a contribution from the Kerguelen plume in the

orangeites.

-40°

-20°

0°

20°

-60°

80° 120°

60° 80° 100° 120°

RajmahalTraps

100°60°

ElanBank

KerguelenPlateau

BrokenRidge

NinetyeastRidge

Southeast Indian Ridge

Southern

CentralNorthern

1140

1137 750

749

738

747

1136

1138

1141-2

Present-day map of theIndian Ocean

Hafnium - Osmium Systematics of Cretaceous Group II Kimberl i tes from IndiaR .W. K e n t a , S . I n g l e b , N. M a t t i e l l i c , P. D . K e m p t o n d , A . S a u n d e r s e , K . S u z u k i f a

L o u g h b o r o u g h U n i v e r s i t y , U n i t e d K i n g d o mb To k y o I n s t i t u t e o f Te c h n o l o g y , J a p a nc U n i v e r s i t é L i b r e d e B r u x e l l e s , B e l g i u md N E R C , S w i n d o n , U n i t e d K i n g d o me U n i v e r s i t y o f L e i c e s t e r , U n i t e d K i n g d o mf I F R E E - J A M S T E C , Yo k o s u k a , J a p a n