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