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Late Archaean High-Mg granitoidsin the Eastern Dharwar Craton in

Kolar district of Karnataka, India

R.P. Nagar

and

S.S. Nayak

Geological Survey of India,

Kumarswamy Layout,

Bangalore 560078



Regional geology� The Dharwar Craton in the Southern India

± is divided along the eastern boundary of the Chitradurga Schist belt

± into eastern and western sub-blocks (Swami Nath et al 1976; Guptaet al. 2003).

� The western Dharwar Craton (WDC)

± Dominated by old (>3.0 Ga) peninsular gneisses with

± Broad sediment-rich greenstone belts

� The eastern Dharwar Craton (EDC) comprises

± Younger TTG basement (2.70-2.56 Ga) with

± Small remnants of older (>3.0 Ga) TTGs and

± Volcanic-rich thin, elongated greenstone belts (Jayananda et al.,2009).

� The late Archaean 2.56-2.52 Ga granitoids are the most abundantlithology in EDC.

� The high-Mg granitoids occurs within these granitoids to the west of Kolar Schist belt in Srinivaspur area in Kolar district of Karnataka.



The late Archaean granitoids1. Mostly intra-crustal anatexis related K-rich granitoids (Moyen et al, 2003).

2. Minor (about 5 %) mantle-derived rocks known as sanukitoid suite of rocks(Stern et al., 1989, 1990; Stern and Hanson, 1990). These includes

� High-Mg monzodiorite and quartz-monzodiorite named as sanukitoids(Shirey and Hanson, 1984), These rocks are silica-oversaturated with high molar ratio of MgO/(MgO+FeOt) i.e. mg# (>0.60), high Ni, Cr, andLILE contents.

� High-Mg granodiorite-diorite, considered as derivatives of sanukitoids(Stern et al., 1989, 1990; Stern and Hanson, 1991).

3. Rocks of sanukitoid suite forms a continuous series with SiO2 contentsranging from 55 % to 73 % and are characterized by

� Relatively high mg# (molar ratio of FeO /FeO+MgO) of 0.43-0.62,

� High abundances of Cr (� 150 ppm), Sr (500-2000 ppm), Ba (1000-2500 ppm), P2O5 (�0.5), Al2O3 (15-17 wt. %), Na2O (4-5.5 wt. %), K2O(0.5-4 wt. %),

� Low Rb/Sr ratios (0.01-0.02), low K2O/Na2O ratio (�1) and

� Steeply fractionated, subparallel REE patterns (Cen= 65-170, Ybn = 3-6) without Eu anomalies (Stern and Hanson, 1991).



South Indian high-Mg granitoids

1. High-mg granitoids are recorded from many parts of the world.

2. However, only few occurrences of high-Mg granitoids are reportedfrom Eastern Dharwar Craton in South India.

� Dod-Dosa-Patna area, west of Kolar schist belt (Balakrishnanand Rajamani, 1987; Krogstad et al., 1995)

U±Pb zircon age of 2631±6 Ma for the Dod gneiss, 2610 10Ma for the Dosa gneiss and 2553 3 for the Patna granite

Krogstad et al., 1991

� Nalgonda-Kammam area (Sarvothaman, 1998, 2001)

� Kabbaldurga-Kamasandra area, Closepet granite to Kolar schistbelt (Jayananda et al. 2000)

Ages between 2530 2550 Ma

� In the present study,

Further occurrence of high-Mg granitoids in Srinivaspur area of Kolar district of Karnataka is recorded.

Preliminary results of its mode of occurrence, petrological and

geoch

emical ch

aracteristics discussed.



Simplified geological map of southern India

showing the location of reported Mg-rich granitoids

in Srinivaspur area in Eastern Dharwar Craton

Index:

6. Deccan Trap

5.Cuddapah

Supergroup;4.Closepet Granite;

3.Supracrustal

belts;

2.Gneiss and

granite (s.l.);1.Line separating

southern

granulite belt

and Dharwar

craton;



Mode of occurrence

1. As bands flanked by leucogranite within host biotite-granite.

2. As trains of centimeter to meter scale enclaves within host biotite-granite.

± A t hin rim of unusually felsic material around the enclaves,similar to that reported by Seaman and Ramsay (1992) in

magma mingling zone from Maine, is usually present.

± This felsic leucogranitic material often intrudes enclavesresulting into back-veining.

± Small microgranular enclaves are also commonly presentwithin the high-Mg granitoid enclave.



High-Mg granitoids enclave with surrounding

leucocratic granite within granite



Micro-granular mafic enclave (MMEs) with back

veining within High-Mg granite



Petrology� High-Mg granitoid

± Fine to coarse grained and mesocratic to melanocratic. ± Composed mainly of plagioclase, microcline, quartz, hornblende andbiotite with accessory opaque, epidote, acicular apatite sphene and zircon.

� Leucogranite

± Coarse grained and

± Composed mainly of microcline, plagioclase and quartz with minor biotiteand accessory epidote, apatite, sphene and zircon.

� Host granite

± Medium grained and mesocratic.

± It consists of plagioclase, microcline and quartz with minor hornblende and

biotite

� Microgranular enclaves within high-Mg granitoids

± Fine-grained and melanocratic

± Composed of hornblende, biotite and plagioclase



Hornblende, plagioclase and biotite in MMEs within

high-Mg granitoids



Acicular apatite bordering amphibole in high-Mg

granitoid



Geochemical characteristics: Types of

granitoids

High-Mg Granitoids Leucogranites Host granite

N 4 3 3

mg# High (0.38-0.50) Low (0.0-0.26) Moderate (0.30-

0.31)

Cr 62-109 ppm 17-76 ppm 46-77 ppm

Ni 135-167 ppm 127-147 ppm 146-147 ppmSiO2 Moderate (66.36-

70.41 %)

Very high (73.35-

76.19 %)

Moderate (60.62-

70.41 %)

Ba Low (241-476 ppm) High (478-572

ppm)

Ba (339-585 ppm)

�Preliminary geochemical study was carried out.

�Major oxides, Ba, Cr and Ni were determined by Philips 1410 XRFSpectrometry in PPOD laboratory of Geological survey of India,Bangalore.



Classification diagram: O¶Connor feldspar triangle 1965

( High-Mg granitoids, ¨ Host granite and + Leucogranite)



Classification Diagrams

High-Mg granitoids Leucogranite and host

biotite-granite

Feldspar triangle

diagram after

O¶Connor 1965).

Granite-

granodiorite

Granites

Shand (1943) Meta-aluminous to

slightly peraluminous

Peraluminous

Peccerillo and

Taylor (1976)

Calc-alkaline to high-K

calc-alkaline

HIGH-K calc-alkaline



+

++

++

+

¨¨

¨

¨ ¨

¨

Guo S S, Li S G. (2009) Petrochemical characteristics of leucogranite

and a case study of Bengbu leucogranites. Chinese Sci Bull, Vol. 54:

1923-1930, doi: 10.1007/ s11434-009-0355-4

Srinivaspur granitoids plotted on Guo and Li (2009)

discrimination diagrams of leucogranite



( High

-Mg granitoids, ¨ Host granite and + Leucogranite)

Harker variation

diagram



Harker Variation Diagrams

� Major oxide contents in the leucogranite, host graniteand high-Mg granitoids show a sub-linear to linear trends on Harker variation diagrams.

� K2O is positively correlated with SiO2 while other oxidesare negatively correlated.

� There is a gradual increase in SiO2 and K2O content

and

� Gradual decease in other oxides from high-Mggranitoids to leucogranite via host granite.



Sanukitoid suite Vs High-Mg granitoidsSanukitoid suite of Roaring

River Complex

Srinivaspura high-Mg

granitoids

SiO2 Continuous variation from 55to 73 % 60.62 to 70.41 %

Normative silica saturation Saturation to oversaturation Oversaturation

mg# Relatively high (0.43 to 0.59) 0.34 to 0.50

mg#s Vs MgO, Fe2O3, Al2O3, CaO, and TiO2Positively correlated Positively correlated

Ni High About 80 ppm 135 to 167 ppm

Cr High About 135 ppm 62 to 109 ppm

Na2O High (4.3 to 5.5 % %) 3.48 to 4.29 %

P2O5 0.69 % to 0.08 % 0.10 to 0.27 %K2O 0.76 to 4.1 % 1.87 to 3.34 %

LREE-enriched patterns Subparallel to Sanukitoids -

Ce 350 ppm to 52 ppm -

Eu anomalies Small or absent -

Sr 2032 ppm to 537 ppm -



Salient features: High-Mg granitoids

� Compared with Roaring River Complex sanukitoid suite, high-Mg

gragitoids from Srinivaspura are

± slightly more evolved and

± have relatively less mg#, Na2O, and K2O.

� They are not Closepet-like granitoids

± as all have K2O/Na2O ratio of <1.

�

Sr, REE including Ce and Eu not available.



Discussion� A linear trend in Harker diagram

± Suggestive of a genetic link in these three types of granitoids

± This variation can not be due largely to fractional crystallization asleucogranite spatially occurs in between other two granites instead of forming a continuous outcrop.

� The occurrence of leucogranite around high-Mg granitoids

± Suggestive of genetic link between high-Mg granitoid andleucogranite

± Leucogranite might have been produced due to in situ partial meltingof host granite by high-Mg granitoids (Seaman and Ramsay, 1992).

� The occurrences of microscopic features compatible with magmamingling and mixing in high-Mg granitoids (Hibbard, 1991)

± Acicular apatite

± Reversely zoned plagioclase

� Characteristic features of synplutonic dykes (Pitcher, 1997) present instudy area

± The necking of dyke along its length,

± Back-veining of leucocratic veins into the dyke

± Dismemberment of the dyke into trains of angular almost amoeboidenclaves and

± Cuspate margins convex towards the host



Conclusion

Origin of th

eh

igh

-Mg granitoids

� Derivatives of light rare earth elements-enriched monzodiorite of mantle origin (Stern and Hanson, 1991).

� Fractional crystallization of sanukitoidal magma (Sarvothaman,2001)

� Present investigations suggest that these can also be derived bymagma mixing and mingling.



Thank You



XRF analysis of granitoid samples, Kolar district, Karnataka

Sample No 1 2 3 5 6 8 9 10 11 12

Lithology

High-Mg

granitoid

Leuco-

granite

Granite High-Mg

granitoid

Leuco-

granite

High-Mg

granitoid

High-Mg

granitoid

Granite Granite Leuco-

granite

SiO2 66.36 75.62 72.77 70.41 76.19 60.62 68.09 73.15 69.66 73.35Al

2O

314.97 13.85 14.35 14.63 13.51 13.82 15.84 13.99 14.92 13.95

Fe2O

34.50 0.91 2.11 2.32 0.86 8.62 3.74 1.92 3.4 1.72

MnO 0.12 0.02 0.04 0.04 0.01 0.14 0.09 0.03 0.07 0.03

MgO 2.32 0.16 0.46 0.63 0.07 3.03 1.17 0.44 0.77 0

CaO 3.83 1.34 1.92 2.09 1.20 4.14 2.98 1.79 1.88 2.05

Na2O 3.89 2.85 3.40 4.29 3.09 3.48 3.93 2.97 3.80 2.69

K 2O 1.65 4.13 3.39 3.34 4.85 2.86 1.87 3.98 4.20 4.57

TiO2

0.46 0.10 0.18 0.29 0.05 1.01 0.47 0.26 0.40 0.11

P2O

50.23 0.03 0.06 0.10 0.02 0.27 0.15 0.07 0.16 0.04

LOI 0.18 0.17 0.64 0.39 0.43 0.20 0.90 0.40 0.59 0.41

Ba 406 478 585 476 648 277 241 339 708 572

Ni 166 142 149 167 127 147 135 147 146 147

Cr 109 60 77 62 76 92 87 46 46 17

mg# 0.50 0.26 0.3 0.34 0.14 0.41 0.38 0.31 0.31 0

K2O/Na2O 0.42 1.45 0.99 0.78 1.57 0.82 0.47 1.34 1.1 1.7



Sam No 1 2 3 5 6 8 9 10 11 12

Lithology

High-Mg

granitoid

Leuco-

granite Granite

High-Mg

granitoid

Leuco-

granite

High-Mg

granitoid

High-Mg

granitoid Granite Granite

Leuco-

granite

Q 26.40 40.21 35.39 27.54 37.04 17.91 30.37 36.35 26.76 35.86

C 0.37 2.33 1.74 0.40 1.04 0.00 2.29 1.71 1.09 0.95

Or 9.75 24.41 20.03 19.74 28.66 16.90 11.05 23.52 24.82 27.01

Ab 32.92 24.12 28.77 36.30 26.15 29.45 33.26 25.13 32.16 22.76

An 17.50 6.45 9.13 9.72 5.82 13.64 13.80 8.42 8.28 9.91

Di 0.00 0.00 0.00 0.00 0.00 1.69 0.00 0.00 0.00 0.00

Hy 5.78 0.40 1.15 1.57 0.17 6.77 2.91 1.10 1.92 0.13

Il 0.26 0.04 0.09 0.09 0.02 0.30 0.19 0.06 0.15 0.06

Hm 4.50 0.91 2.11 2.32 0.86 8.62 3.74 1.92 3.40 1.72

Tn 0.00 0.00 0.00 0.00 0.00 2.09 0.00 0.00 0.00 0.00

Ru 0.33 0.08 0.14 0.25 0.04 0.00 0.37 0.23 0.32 0.08

Ap 0.55 0.07 0.14 0.24 0.05 0.64 0.36 0.17 0.38 0.10

Sum 98.34 99.01 98.68 98.15 99.85 98.01 98.34 98.60 99.27 98.56

CIPW normative composition



Rock type/ Characteristics

Sanukitoids of Superior province

(Stern et al. 1989)

Mg#:>0.60

Ni and Cr: > 100

ppm

Cr: >200 ppm

Intermediate SiO2: 55-60 %

Strong enrichment in certain LILEs

Strongly enriched LREE (Cen = 80-250 X chondrites

Eu anomaly: Little or no

Sr and Ba: >500 ppm mostly ~1000 ppm

Rb/Sr ratio: <1

K2O: > 1 %

Primitive, high-Mg, intermediate-silica

rocks like Monzodiorites and

trachyandesite

Chemically evolved sanukitoids (Stern

et al. 1989)

Relatively high

mg#,

High abundances of Sr and Ba, steeply LREE-enriched patterns Chemical characteristics which are

consistent with their derivation from

sanukitoid parents

Average Sanukitoid (Stern et al. 1989) MgO:6.8 %, mg#:

0.63, Ni: 150 ppm,

Cr: 350 ppm,

SiO2: 56 %, Na2O: 3.9 %, K2O: 2.1%, Sr and Ba bot h: 1200 ppm,

Ce: 120Xchondrites, Rb/Sr ratio: 0.05

Sanukitoid siute (Shirey and Hanson

1984)

Primitive monzodiorites and their

derivative

Sanukitoids of Setouchi volcanic belt

of Japan (Koto 1916; Tatsumi

1981,1982; Tatsumi and Ishizaka1982a, 1982b)

Mg#:near 0.70

Ni : near 200 ppm

Olivine: Fo87-89

SiO2: 55-60 %

Sanukites (Weinschenk 11891) Glassy andesites with bronzite needles

Sanukitoid (Koto 1916) All textural modification of « sanukite «.

Sanukitoid (Tatsumi and Ishizaka

1982a, 1982b)

Relatively aphyric, plagioclsae-free

andesites and basalts

Sanukitoid suite of Roaring River Complex, southwestern Superior

province (Stern et al. 1989)

1)Continuous variation in SiO2 (from 55 to 73 %) and variation fromnear silica saturation to silica oversaturation on a normative basis

2) Relatively high and decreasing mg#s (from 0.59 to 0.43),

concurrent with decreasing MgO, Fe2O3, Al2O3, CaO, and TiO2

3) Ni contents of about 80 ppm and Cr about 135 in diorite to

monzodiorite

4) High and decreasing contents of Na2O (from 5.5 % to 4.3 %), Sr

(from 2032 ppm to 537 ppm), Ce (from 350 ppm to 52 ppm), and

P2O5 (from 0.69 % to 0.08 %)

5) High K2O (0.76-4.1 %) and

6) Subparallel, LREE-enriched patterns in which Eu anomalies are

small or absent



Guo S S, Li S G. (2009) Petrochemical characteristics of leucograniteand a case study of Bengbu leucogranites. Chinese Sci Bull, Vol. 54:

1923-1930, doi: 10.1007/ s11434-009-0355-4



References

� References

� BALAKRISHNAN, S. and RAJAMANI, V. (1987) Geochemistry and petrogenesis of granitoids around the Kolar schist belt, south India: Constraints for the evolution of the crust in the Kolar area. Jour. Geol., Vol. 95, pp. 219-240.

� CASTRO, A., MORENO-VENT AS, I. and DE LA ROSA, J.D. (1991) H-type (hybrid) granitoids: a proposed revision of the granite-type classification andnomenclature. Earth Science Reviews, Vol. 31, pp. 237-253.

� GUPT A S., RAI, S.S., PRAKASAM, K. S., SRINAGESH, D., BANSAL, B.K., CHADHA, R.K., PREISTLEY, K. and GAUR, V.K. (2003) The nature of crustin southern India: Implications for Precambrian crustal evolution. Geophy. Res. Lett., Vol. 30, pp. 1419. doi. 10.1029/2002GL016770

� HIBBARD, M.J. (1991) Textural anatomy of twelve magma-mixed granitoids systems in Enclave and granite petrology by Barbarin, B and Didier, J .

� JAYANANDA, M., MIYAZAKI, T., GIREESH, R.V. MAHESHA, N. and KANO, T. (2009) Synplutonic mafic dykes from Late Archaean granitoids in theEastern Dharwar Craton, Southern India. Jour. Geol. Soc. Vol. 73, pp. 117-130.

� KROGST AD, E.J., HANSON, G.N. and RAJAMANI, V. (1991) U-Pb ages of zircon and sphene for two gneiss terranes adjacent to the Kolar schist belt,south India: evidence for separate crustal evolution histories. Journal of Geology, Vol. 99, pp. 801-816.

� KROGST AD, E.J., HANSON, G.N. and RAJAMANI, V. (1995) Sources of continental magmatism adjacent to the late Archaean Kolar stuture zone,South India: distinct isotopic and elemental signatures of two late Archaean magmatic series. Contrib. Miner. Petrol. Vol. 122, pp. 159-173.

� MOYEN, J.F., MARTIN, H., JAYANANDA, M. and Auvray, B. (2003) Late Archaean granites: a typology based on the Dharwar Craton (India). Precamb.Res. Vol. 127, pp. 103-123.

� O'CONNOR J T (1965) A classification for Quartz-rich igneous rocks based on feldspar ratios. U.S. Geol. Survey Prof Paper 525-B: B79-B84

� PECCERILLO, A. and T AYLOR, S. R. (1976) Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey.Contributions to Mineralogy and Petrology, Vol. 58, pp. 63±81.

� PITCHER, W.S. (1997) The nature and origin of Granite, second edition, Chapman and Hall, 387p.

� SARVOTHAMAN, H. (1998) Archaean to Palaeozoic events in the formation of a continental segment of Gondwana: evidence from southern India.(Gondwana 10: Event Stratigraphy of Gondwana) Jour. African Ear. Sci. Vol. 27, No. 1A, pp. 168-169 (abs.).

� SARVOTHAMAN, H. (2001) Archaean High-Mg granitoids of mantle origin in the Eastern Dharwar Craton of Andhra Pradesh. Jour. Geol. Soc. Ind. Vol.58, pp. 261-268.

� SEAMAN, S.J., and RAMSAY, P.C. (1992) Effect of magma mingling in the granites of Mount Desert Islands, Maine. Jour. Geol., Vol. 100, pp. 395-409.

� SHAND, S. J. (1943) Eruptive Rocks. Their Genesis, Composition, Classification, and Their Relation to Ore-Deposits with a Chapter on Meteorite. New York: John Wiley & Sons.

� SHIREY, S.B. and HANSON, G.N. (1984) Mantle-derived Archaean monzodiorites and trachyandesites. Nature, Vol. 310, pp. 222-224.

� STERN, R.A. and HANSON, G.N. (1991) Archaean high-Mg granodiorite: A derivative of light rare earth element-enriched monzodiorite of mantle origin.Jour. Petrology, Vol. 32, pp. 201-238.

� STERN, R.A., HANSON, G.N. and SHIREY, S.B. (1989) Petrogenesis of mantle-derived, LILE-enriched Archaean monzodiorites and trachyandesite(sanukitoids) in southwestern Superior Province. Canad. Jour. Ear. Sci., Vol. 26, pp. 1688-1712.

� SWAMI NATH, J., RAMAKRISHNAN, M. and VISWANATHA, M.N. (1976) Dharwar stratigraphic model and Karnataka Craton evolution. Rec. Geol.Surv. Ind. Vol. 107, Part 2, pp. 149-175



Figure 2: Field and microphotograph of granitoids in Kolar district of Karnataka.

(a) High-Mg granitoids enclave with surrounding leucocratic granite within

granite (b) Micro-granular mafic enclave (MMEs) with back veining within High-

Mg granite (c) Acicular apatite bordering amphibole (d) Hornblende, plagioclase

and biotite in MMEs within high-Mg granitoids

high mg granitoid

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