KimberlitesKimberlites: A peep into the Earth’s: A peep into the Earth’sKimberlitesKimberlites: A peep into the Earth s : A peep into the Earth s mantlemantle
Anil KumarAnil KumarAnil KumarAnil Kumar
Isotope Geochemistry GroupIsotope Geochemistry GroupIsotope Geochemistry Group,Isotope Geochemistry Group,National Geophysical Research Institute, National Geophysical Research Institute,
HyderabadHyderabadHyderabadHyderabad
Distribution of kimberlites worldwide
Importance of Kimberlites
They are the only primary sources of diamonds and exotic mantle t i l i th f f d l hi h th t i f timaterial in the form of nodules which are the most informative
messengers from Earth’s mantle
KimberliteKimberlite
Diamond
M tMacrocrysts
Mantle rocks
Peridotite ‐ olivine, denstatite, garnet, and
clinopyroxene.
Eclogite ‐ garnet g gand clinopyroxene.
C conc. in mantle
100 ppm
1000‐3700 ppm
Pyroxene enters the garnetstructure at high pressure
1000 3700 ppm
A 400‐micron wideferropericlase inclusionferropericlase inclusion
Utility of kimberlites
• Composition of the deep mantle• Date the deep mantle perturbation eventsp p
Several natural radioisotopes have phalf lives suitable for geochronology
40K 40Ar (and 40Ca) 1 25 GaK Ar (and Ca) 1.25 Ga87Rb 87Sr 48.8 Ga238U 206Pb 4 47 GaU Pb 4.47 Ga235U 207Pb 704 Ma147Sm 143Nd 106 GaSm Nd 106 Ga
MORB OIBContinental crustContinental crust
Depleted mantle
?
TZ
Undepleted mantle
Cruust
DM
d /1
44Nd i
Sr /86Sr
i
C
BEBE14
3 N87Crust
DM
Time Time4.5 Ga 4.5 GaToday Today
Time Time
Narayanpet
DTDelhi
Ti
KoBh
Si16oCB
Ch
WajrakarurBombayHyderabad
Chennai
Calcutta
BuC
BC
SC
DC
La
Ra
14oGSB Z
a
Arabian
Chennai
Trivandrum
WDCEDC
KaCc
100 km ChennaiCG
sea Bay ofBengal
Bangalore
WDC
74o 12o
80oSGT
CG
LamproitesKimberlites
Historically famous diamondsy f
Great Mogul – 900 cts.Koh‐i‐Nor – 793 ctsKoh‐i‐Nor – 793 cts. Nizam – 440 cts. Regent – 410 cts.
l ffOrloff – 195 cts. Darya‐i‐Noor – 186 cts.Hope – 112 cts.pShah – 95 cts.
10
6
810
DM
246
Nd
DMCarbonatites
-2
02ε
CHUR
-6-42
60 200 400 600 800 1000 1200
Age in MaAge in Ma
MORB OIBContinental crust
D l t d tlDepleted mantle
TZ
Undepleted mantle
16o
Mu:1099+12Ma
Ko:1085+14Ma
NarayanpetCB
DT
Si:1094+ 8MaDelhi
Maj: 1067+ 31Ma
BuC
Ti
KoBh
Si
Mu:1091+56Ma
Si:1097+43Ma
Pipe 1:1091+20Ma
Pipe 5:1093+20Ma
Ch
Wajrakarur
Pipe 6:1102+23MaPipe 2:1092 +15Ma
BombayHyderabad
Chennai
CalcuttaBC
SC
DC
La
RaPipe 2:1124 +5‐3Ma
Si:1097+43Ma
14o
Pipe 7:1091+10Map
GSB Za
Arabiansea Bay of
Trivandrum
WDCEDC
KaCc
100 km Chennai
SGTCG
y fBengal
Bangalore
Ki b lit74o 12o
80oSGT
LamproitesKimberlites
Present day
EquatorEquator
1100 Ma
Reconstruction at 1100 Ma
Au
In
LaSi
Ka
SF
Co
Am
BaSF
WA
20
babi
lity 1160 Ma
10R
elat
ive
prob Alkaline
rocks
0400 600 800 1000 1200 1400 1600
Age in Ma
R
Umkondo igneous province1102 – 1112 Ma
Hanson et al. 2004. Science
Warakurna large igneous province Age : 1076 Ma
Thank Q