1. No category

JOURNAL GEOLOGICAL SOCIETY OF INDIA
Vol.79, April 2012, pp.361-366
The Abundances of some Trace-elements in the First-ever
Reported Sample of Spinifex-Textured Komatiite
from Ghatti Hosahalli, Karnataka
M. RAMAKRISHNAN1, B. MAHABALESWAR2 and S. VISWANATHAN3
1
“Manipallavam”, 29, Balakrishna Road, Valmiki Nagar, Thiruvanmiyur, Chennai - 600 041
2
Department of Geology, Bangalore University, Bangalore - 560 056
3
Flat B-203, Block-B, United Avenue Apartments, South End, 7-1-29, Ameerpet, Hyderabad - 500 016
Email: [email protected]
Abstract: The paper reports wavelength-dispersive x-ray fluorescence spectrometric data on the abundances of
Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in the first-ever reported sample of spinifex-textured
komatiite from India at Ghatti Hosahalli in Karnataka. With some exceptions, these abundances are similar to those
reported for the spinifex-textured komatiite from the Barberton greenstone belt in South Africa. The values for some
alteration-resistant element ratios — Ti/Zr, Ti/Y, Ti/Sc, Ti/V, Zr/Y, Zr/Sc, Sc/Y, V/Zr, and V/Sc — for chondrite and for
spinifex-textured komatiites from Ghatti Hosahalli (India), Barberton (South Africa), Munro (Canada), and Yilgarn
(Australia) reveal that, except for the Ti/Zr ratio for the Ghatti Hosahalli komatiite, the other ratios from the four
terrains define a unique trend that is almost superimposed on the trend defined by these ratios for chondrite. This
suggests that the processes of formation of komatiitic lavas from the four far-separated terrains were similar, and
that, the source regions from which these lavas formed had a chondritic composition.
Keywords: Komatiite, Trace-elements, Ghatti Hosahalli, Karnataka, India, Barberton, Munro, Yilgarn.
INTRODUCTION
The first occurrence of a spinifex-textured komatiite in
India was discovered by Viswanatha (1977) and Viswanatha
et al. (1977) at Ghatti Hosahalli (Survey of India Topo
Sheet No. 57 C/5; Lat. 13°59'; Long. 76°17') in Karnataka.
Viswanatha et al. (1977) had described the geological setting
of this rock, its petrography, and given the major-element
composition of one sample.
This paper has four objectives: First, to report
wavelength-dispersive x-ray fluorescence spectrometric
data on the abundances of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr,
Y, Zr, Nb, Ba, Pb, and Th in the ‘original sample’ of the
Ghatti Hosahalli spinifex-textured komatiite. Secondly, to
compare some of these abundances with those reported for
V, Cr, Co, Ni, Cu, and Y by Narayana and Naqvi (1980) and
for V, Cr, Ni, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th reported
by Jayananda et al. (2008) for the Ghatti Hosahalli komatiite.
Thirdly, to compare these abundances with those reported
for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, and Ba, by
Smith and Erlank (1982) for the spinifex-textured komatiite
from the Barberton greenstone belt in South Africa. And
fourthly, to discuss the significance of some alteration-
resistant element ratios — Ti/Zr, Ti/Y, Ti/Sc, Ti/V, Zr/Y, Zr/
Sc, Sc/Y, V/Zr, and V/Sc — for spinifex-textured komatiites
from Ghatti Hosahalli (India), Barberton (South Africa),
Munro (Canada), and Yilgarn (Australia), in relation to the
values of these ratios in chondrite.
GEOLOGICAL SETTING AND AGE
The spinifex-textured komatiite occurs as a lensoid
serpentinite in the Ghatti Hosahalli belt, close to the western
margin of the Chitradurga greenstone belt in the Western
Dharwar Craton. The Ghatti Hosahalli belt, about 15 km
long and 300 m wide, represents a linear en echelon array
of enclaves of high-grade supracrustal rocks, consisting
mainly of fuchsite quartzites with subordinate serpentinites,
steatites, and amphibolites. The fuchsite quartzites are
locally rich in sillimanite, kyanite, staurolite, and chloritoid.
Bedded barite is interstratified with the fuchsite quartzites
(Radhakrishna and Sreenivasaiah, 1974; Chadwick et al.
1981; Devaraju et al. 1999).
The belt is broadly discordant to the main, low-grade
Chitradurga greenstone belt, which rests on Peninsular
0016-7622/2012-79-4-361/$ 1.00 © GEOL. SOC. INDIA
362
M. RAMAKRISHNAN AND OTHERS
Fig.1. A. Detailed map of contact between Dharwar Supergroup and older Peninsular Gneiss and Sargur Group, Ghatti Hosahalli.
d - dolerite dyke; Tc- Talya polymict conglomerate; 2 - phyllites with local basis schists and metadoleritic sills; q - quartzite;
1 - chlorite schists and basic metalavas; Nc - Neralekatte oligomict quartz-pebble conglomerates; p - pegmatite; gr1, gr2 granites; g - dark and pale biotite gneisses; t - ultramafic talc-actinolite schists including serpentinite; q - quartzite, commonly
- cleavage-schistosity, dip in
fuchsitic and locally with seams of barytes; —
—
— - amphibolite; — - bedding, dip in degrees; —
degrees; → - linear structure; - fold axis; o - cleavage-bedding intersection; - mineral lineation; - long axis of deformed
clast. B. Setting of Ghatti Hosahalli area on west side of Chitradurga belt of the Dharwar Supergroup Dh. PG - Peninsular Gneiss
+ enclaves of Sargur Group; C. Equal area projections of structural data; a - Dharwr Supergroup; b - Sargur Group; c - Peninsular
Gneiss; - long axis of clasts; - mineral lineation; - fold axes and cleavage bedding intersections; o - crenulation axis;
- pole to bedding; - pole to slaty cleavage; + pole to crenulation cleavage; - pole to schistose fabric in gneiss; - pole
to shear zone; - pole to chloritised fracture; x - pole to close-spaced jointss (after Chadwick, 1981).
JOUR.GEOL.SOC.INDIA, VOL.79, APRIL 2012
SPINIFEX-TEXTURED KOMATIITE FROM GHATTI HOSAHALLI, KARNATAKA
Gneiss with a pronounced unconformity marked by a
basal oligomictic conglomerate at Narlakatte. The belt is
correlated with the Sargur Group, which is older than the
greenstone sequences of the Dharwar Supergroup in
Karnataka (Viswanatha and Ramakrishnan, 1976; Chadwick
et al 1981; Paranthaman, 2005). Sm-Nd whole-rock isochron
ages for komatiites from the Sargur Group greenstone
belts of the Western Dharwar Craton give an age of 3352±
110 Ma for the timing of eruption of the komatiite lavas
(Jayananda et al. 2008).
PETROGRAPHY
A lenticular serpentinite, about 150 m x 50 m, is exposed
in association with fuchsite quartzite on the hillock to the
east of the Jankal-Talya road, some 2 km south of
Kummanaghatta (Survey of India Topo Sheet No. 57 C/5;
Lat. 13°58', Long. 76°16'). Megascopically, the serpentinite
shows spinifex texture, with bladed crystals stacked
randomly and accentuated by thin stringers of magnetite
(Fig.2).
Fig.2. Outcrop of spinifex-textured komatiite at Ghatti Hosahalli,
Karnataka, India.
In thin sections, the rock is almost entirely composed of
serpentine minerals (mainly antigorite) with streaks of
magnetite. Within the fine-grained felt of serpentine,
elongated plates of antigorite are embedded, suggesting a
relict spinifex texture. Probably, the amphibolite facies
metamorphism and intense deformation have obliterated the
original mineralogy, but still retaining the blade-like
serpentine pseudomorphs.
363
dispersive x-ray fluorescence spectrometry (WDXRFS). The
instrument used for WDXRFS consisted of a Philips PW
1410 sequential x-ray spectrometer with a dual sample
changer, five-position analyzing crystal assembly, fine (150
µm) and coarse (550 µm) collimators, scintillation counter,
gas-flow proportional counter using P-10 gas (90% argon
and 10% methane), automatic discriminator and crystal
attenuator unit ( PW 1414), a PW 1140 x-ray generator (100
kV; 80 mA; 3 kW), and a PW 1370 electronic measuring
console comprising the PW 4620 h.v. supply-ratemeterchannel, PW 4625 h.v. supply, PW 4630 counter-timerprinter control, PW 1451 goniometer control unit and
stepping motor for selecting twentyfive pre-programmed
two-theta positions, and PM 8000 flat-bed chart recorder.
The Ghatti Hosahalli komatiite sample was ground to
minus 300 mesh using a hydraulic splitter, laboratory-type
jaw crusher, and disc mill. The powder was homogenized
in a mixer-mill. Smaller representative volumes of the
powder were obtained using two-way riffle pattern sample
dividers. Aliquots of 1g weighed from these splits were
transferred to cylindrical sample-dies, and with boric acid
as a backing, were palletized at a pressure of 2500 kg/cm2
in a hydraulic press to give pellets of 41 mm diameter.
The international rock standards, DTS-1 (dunite), PCC1 (peridotite), UB-N (serpentine), BCR-1, BR, and BHVO1 (basalts), W-1 (diabase), DR-N (diorite), and AGV-1
(andesite) were used as analytical standards. Powder-pellets
were made from 1 g aliquots of the analytical standards,
following the same procedure as for the samples.
Sc was determined using a gold x-ray tube, LiF 200
analysing crystal, vacuum path, coarse collimation, and a
gas-flow proportional counter. Zn was analysed using a gold
x-ray tube, LiF 200 analysing crystal, air path, fine
collimation, and a gas-flow proportional counter. V, Cr, Co,
and Ni were determined using a sliver x-ray tube, LiF 200
analysing crystal, air path, fine collimation, and a gas-flow
proportional counter. Cu was analysed using a silver x-ray
tube, LiF 200 analysing crystal, air path, fine collimation,
and a scintillation counter. Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th
were determined using a silver x-ray tube, LiF 220 analysing
crystal, air path, fine collimation, and scintillation counter.
For concentration-levels of less than 20 ppm, the
accuracy is within 10% and the precision within 5%. For
concentration-levels of more than 20 ppm, the accuracy and
precision are within 5%.
TRACE-ELEMENT DATA
ANALYTICAL METHODLOGY
Fifteen trace-elements were determined by wavelengthJOUR.GEOL.SOC.INDIA, VOL.79, APRIL 2012
Data on the abundances of Sc, V, Cr, Co, Ni, Cu, Zn,
Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in the first-ever reported
364
M. RAMAKRISHNAN AND OTHERS
Table 1. The abundances of some trace-elements in spinifex textured komatiites from Ghatti Hosahalli, Karnataka,
India and Barberton, South Africa (data in ppm)
Element
Sc
V
Cr
Co
Ni
Cu
Zn
Rb
Sr
Y
Zr
Nb
Ba
Rb
Th
This study
(n=1)
18
133
1967
71
520
87
75
9
67
6
22
4
15
<3
<2
Narayana and Naqvi (1980)
(n= 8)
Jayananda et al. (2008)
(n = 2)
Barberton
(n = 5)
x¯
s
C
x¯
s
C
x¯
s
C
ng
54
1186
116
1173
74
ng
ng
ng
10
ng
ng
ng
ng
ng
54
540
22
141
110
=
-
100
45.5
19
12
149
=
-
ng
81
1273
ng
3158
ng
53
7
15
3
14
0.53
10
1.83
0.06
5
115
23
17
3
1
3
0.38
9
0.1
0.06
6.2
9
0.7
32
43
6.7
21.4
71.7
90
5.5
100
19.2
113
3065
126
1521
121
72
1.1
36
7.9
24
1.7
8.2
ng
ng
17.6
441
7.3
299
66
6.4
1.1
3.1
1.6
7.2
0.6
3.9
-
15.6
14.4
5.8
19.7
54.5
8.9
100
8.6
20.3
30
35.3
47.6
-
x¯ = arthimetic mean; s = standard deviation; C = coefficient of variation in percent; n = number of samples; n for
V : Ghatti Hosahalli (Narayana and Naqvi, 1980) is 7 and for Y it is 1. n for Sc, Cu, Rb, Nb and Ba: Barberton :
Sc = 1 , Cu = 4, Rb = 4, Nb = 4 , Ba = 3. Source of data for Barberton: Smith and Erlank (1982); ng = not given
sample of spinifex-textured komatiite form Ghatti Hosahalli,
together with data on the abundances of V, Cr, Co, Ni, Cu,
and Y reported by Narayana and Naqvi (1980) and of
V, Cr, Ni, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th reported by
Jayananda et al. (2008) are given in Table 1. Data on the
abundances of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb,
and Ba for the spinifex-textured komatiite from the
Barberton greenstone belt of South Africa, reported by Smith
and Erlank (1982), are also given in Table 1. In Table 1, the
trace-elements are arranged in increasing order of their
atomic number (Z) from Sc (Z = 21) to Th (Z = 90).
Data on some alteration-resistant element ratios — Ti/
Zr, Ti/Y, Ti/Sc, Ti/V, Zr/Y, Zr/Sc, Sc/Y, V/Zr, and V/Sc —
for chondrite and for spinifex-textured komatiites from
Ghatti Hosahalli (India), Barberton (South Africa), Munro
(Canada), and Yilgarn (Australia) are given in Table 2.
DISCUSSION
As the Barberton greenstone belt in South Africa is the
type area for spinifex-textured komatiite (STK), it is essential
to compare the abundances of Sc, V, Cr, Co, Ni, Cu, Zn, Rb,
Sr, Y, Zr, Nb, Ba, Pb, and Th determined by us for the
Ghatti Hosahalli STK with the values reported by Smith
and Erlank (1982) for the Barberton STK. Likewise, it is
necessary to compare the abundances for V, Cr, Co, Ni, Cu,
and Y reported by Narayana and Naqvi (1980) and the
abundances of V, Cr, Ni, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and
Th reported by Jayananda et al., (2008) for the Ghatti
Hosahalli STK with the values for the Barberton STK. Such
a comparison is made in Fig.3. The x-axis in Fig.3 shows
the trace-elements arranged in increasing order of their
atomic number (Z) from Sc (Z = 21) to Th (Z = 90).
The trends of the three sets of data on the abundances of
trace-elements for the Ghatti Hosahalli STK follow the trend
of values for the Barberton STK. The notable exceptions
Table 2. Some alteration-resistant element ratios for chondrite and for
spinifex-textured komatiites from Ghatti Hosahalli (Karnataka,
India), Barberton (South Africa), Munro (Canada), and Yilgarn
(Australia)
Ratio
Ti/Zr
Ti/Y
Ti/Sc
Ti/V
Zr/Y
Zr/Sc
Sc/Y
V/Zr
V/Sc
No. of
Samples
Chondrite
Ghatti
Hosahalli
Barberton
Munro
Yilgarn
102
275
83
8.4
2.5
0.7
4.2
12
8
57
210
70
9.5
3.6
1.2
3
5.8
7.4
121
269
84
13
2.8
1.2
2.4
9.5
5.9
117
210
74
14
1.9
0.8
2.7
8.4
5.3
111
275
98
14
2.4
0.9
2.8
8
7
-
1
3
3
7
Source of data for chondrite Ti/Zr, Ti/Sc, Ti/V, Zr/Y, and V/Zr: Nesbitt
and Sun 1976 quoted by Smith and Erlank (1982). Ti/Y and V/Sc:
Nesbitt and Sun (1980) quoted by Arndt and Nesbitt (1982). Zr/Sc: Wanke
et al. (1974) quoted by Ludden and Gelinas (1982) . Sc/Y: Ahrens (1965,
p. 97). For Barberton: From Smith and Erlank (1982). For Munro: Ti/Zr,
Ti/Sc, Ti/V, Zr/Y, and V/Zr: From Smith and Erlank (1982). Ti/Y and
V/Sc: From Smith and Erlank (1982). Ti/Sc, Zr/Sc, Sc/Y, and V/Sc:
Computed by the authors.
JOUR.GEOL.SOC.INDIA, VOL.79, APRIL 2012
SPINIFEX-TEXTURED KOMATIITE FROM GHATTI HOSAHALLI, KARNATAKA
Fig.3. Comparison of trace element abundances in the Ghatti
Hosahalli spinifex-textured komatiite (STK) determined by
the authors with those reported by Narayana and Naqvi
(1980) and by Jayananda et al. (2008) and with those
reported by Smith and Erlank (1982) for the Barberton
STK. Ghatti Hosahalli STK: 1. Determined by the authors.
2. Narayana and Naqvi (1980). 3. Jayananda et al. (2008).
4. Smith and Erlank (1982).
are our values for Cr (1957 ppm), Ni (520 ppm), and Sr
(67 ppm) which differ from the values for the Barberton
STK (Cr = 3065 ppm; Ni = 1521 ppm; and Sr = 36 ppm).
The abundance reported by Narayana and Naqvi (1980) for
the Ghattihosahalli STK, Cr (1186 ppm) differs from the
values for the Barberton STK (Cr = 3065). The abundances
reported by Jayananda et al. (2008) for the Ghatti Hosahalli
STK for Cr (1273 ppm), Ni (3158 ppm), Sr (15 ppm), and
Zr (14 ppm) differ from the values for the Barberton
STK (Cr = 3065 ppm; Ni = 1521 ppm; Sr = 36 ppm; and Zr
= 24 ppm). Our values for Ni (520 ppm) differs from the
value of 1173 ppm reported by Narayana and Naqvi (1980)
and from the value of 3158 ppm reported by Jayananda
et al. (2008).
Such differences are only to be expected considering
the effects of alteration and metamorphism on the
JOUR.GEOL.SOC.INDIA, VOL.79, APRIL 2012
365
Fig.4. Trends of some alteration-resistant element ratios for
chondrite and for spinifex-textured komatiites from Ghatti
Hosahalli (India), Barberton (South Africa), Munro
(Canada), and Yilgran (Australia). GHH: Ghatti Hosahalli.
B: Barberton. M: Munro. Y: Yilgarn.
distribution of trace-elements like Rb, Sr, and Ba, the
different conditions (for example, varying degrees of mantlemelting and the pressure-temperature conditions of melting)
under which komatiitic lavas erupted during the early
Archaean in Ghatti Hosahalli, India, and in Barberton, South
Africa, and the compositional variations in the source
regions. What is important is the similarity in the trends of
the abundances of trace-elements in the Ghatti Hosahalli
and Barberton spinifex-textured komatiites (see Fig. 3).
Figure 4 shows some alteration-resistant element ratios
– Ti/Zr, Ti/Y, Ti/Sc, Ti/V, Zr/Y, Zr/Sc, Sc/Y, V/Zr, and
V/Sc – for chondrite and for spinifex-textured komatiites
(STKs) from Ghatti Hosahalli (India), Barberton (South
Africa), Munro (Canada), and Yilgarn (Australia). Except
for the Ti/Zr ratio for the Ghatti Hosahalli STK, the other
366
M. RAMAKRISHNAN AND OTHERS
ratios from the four terrains define a unique trend.
Interestingly, this trend is almost superimposed on the trend
defined by these ratios for chondrite. This suggests that,
from geochemical considerations, the processes of formation
of komatiitic lavas from the four far-separated terrains were
similar, and that, the source regions from which these lavas
formed had a chondritic composition.
CONCLUSIONS
With some exceptions, the abundances of Sc, V, Cr, Co,
Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in the firstever reported sample of spinifex-textured komatiite from
India at Ghatti Hosahalli in Karnataka, are similar to those
reported for the spinifex-texured komatiite from the
Barberton greenstone belt in South Africa. Some of the
observed differences are due to the effects of alteration and
metamorphism on the distribution of trace-elements like Rb,
Sr, and Ba, the different conditions (for example, varying
degrees of mantle-melting and the pressure-temperature
conditions of melting) under which komatiitic lavas erupted
during the early Archaean in Ghatti Hosahalli, India, and in
Barberton, South Africa, and the compositional variations
in the source regions. The values for some alteration-resistant
element ratios — Ti/Zr, Ti/Y, Ti/Sc, Ti/V, Zr/Y, Zr/Sc, Sc/Y,
V/Zr, and V/Sc — for chondrite and for spinifex-textured
komatiites from Ghatti Hosahalli (India), Barberton (South
Africa), Munro (Canada), and Yilgarn (Australia) reveal that,
except for the Ti/Zr ratio for the Ghatti Hosahalli komatiite,
the other ratios for the four terrains define a unique trend
that is almost superimposed on the trend defined by these
ratios for chondrite. This suggests that the processes of
formation of komatiitic lavas from the four far-separated
terrains were similar, and that, the source regions from which
these lavas formed had a chondritic composition.
Acknowledgements: We are indeed grateful to Dr. B. P.
Radhakrishna for encouragement, his interest in our work,
and for constantly urging us to publish the trace-element
data presented in this paper. We are also grateful to Mr.
S.C. Sehgal, Mr. T. Narsimha, and Mrs. G. Kalyani for
technical assistance.
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(Received: 15 May 2010; Revised form accepted: 28 February 2012)
JOUR.GEOL.SOC.INDIA, VOL.79, APRIL 2012