Kimberlites: A peep into the EarthEarths’s mantleWDC EDC Ka Cc 100 km Chennai SGT CG yf Bengal...

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