Page 1
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi
Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
SUPPLEMENTARY DATA 1
SUBSIDENCE ANALYSIS
Sediment Accumulation Curves (SACs):
The logic followed for the construction of the SACs is based on the Cant’s equation (1989) to relate the
thickness of sediments deposited (Δ Sed) within a fixed time interval, eustatic sea-level changes (Δ E),
subsidence (Δ Sub), to changes in water depth above the depositional interface (Δ D) :
Δ Sub + Δ E - Δ Sed = Δ D......................................................(1)
Cant’s equation is the simplistic version of general equation developed by Steckler and Watts (1978) for
the modern sedimentary basins. From Cant’s equation the net relative subsidence (i.e. effective change of
the depositional interfaces or relative sea-level) termed here as ΔDI (which includes the combined effects
of eustatic changes in the sea-level and crustal subsidence) is derived and is represented by the following
equation:
Δ DI = Δ D + Δ Sed. .......................................................................(2)
Δ DI = Δ Sub + Δ E. .......................................................................(3).
Compaction factors were derived using the published compaction curves of Sclater and Christie (1980),
depending upon the petrographic characters of the sediments and a rough estimate of their porosity. These
compaction factors do not account for diagenetic alterations or recrystallisation, but provide a generic
understanding of the amount of compaction suffered by the lithology in question. The following values
were used in the analysis of the Kaladgi sediments:
Highly compacted & recrystallized sandstones (quartzites) : 0.76
Well indurated, cemented sandstones : 0.86
Siltstones : 0.53
Mudstones & Shales : 0.41
Carbonates (without significant recrystallisation) : 0.75
Carbonates (recrystallized) : 0.69
In these “paleontologically barren” sediments, the estimates of palaeowater depths on the basis of
biofacies are not possible. Therefore, the depositional depths of the concerned horizons were estimated
based on their sedimentological characters with lesser precision). On an average, the following
paleobathymetric depths are assumed in the ensuing computation:
Limestones (unaffected by influence of surface waves in the water column) : -7
Limestones and Dolomites (deposited within wave-influence depths) : -5
Tidal muds and silts (=shales) : -3
Supratidal and beach sandstones : +3
Conglomerates : +7
Chertbreccias (reworked intraformational tectonically generated debris) : 0
Page 2
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi
Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
In absence of finer time controls (sediments being of Proterozoic age and devoid of diagnostic fossils) it
has been assumed that, each sequence (the Bagalkot and Badami Groups) represents a continuous
succession, uninterrupted by depositional breaks of significant magnitudes. Therefore, the total duration
of time required for the accumulation of each group is taken as 100 %. For determining the relative time
taken for a sequence (in a measured section), the aggregate stratigraphic thickness, using the maximum
exposed thickness in that particular section of each constituent Member (not the average thickness given
in Fig. 2- stratigraphic column in main paper) was used as the optimum time of accumulation. Based on
this, the time required for the sediments in each column was calculated as the % of the time required for
its accumulation. This value of time (in a relative proportion of the total maximum time which each
Group may have required) is used in the plotting of the curves, where the aggregate measured thickness of
the horizon (Member) in the particular section (T) was used for computing the relative time taken by it for
its accumulation as a percentile of the total time required by the host Group.
%T = T / a x 100 .......................................................................(4).
where a = 13717 m for Bagalkot Group and 1846 for Badami Group.
Methodology:
There is very little geophysical and no drilling data available that gives the vertical thicknesses of
individual sections / traverses in the Kaladgi basin. The only published geophysical data is limited to
Ramakrishna and Chayanulu (1987) who reviewed the erstwhile knowledge in various Purana basins,
including the Kaladgi Basin. Recently Mallik et al (2012) have included the geophysical depth-to-
basement based on 3-D gravity modelling. The discrepancies between geophysical estimates of
thicknesses and the stratigraphic thicknesses across the Purana basins were pointed out by Kale (1991).
No major addition to that knowledge is available in published literature. We therefore adopted the time-
tested methodology of backward computations from field data of stratigraphic and structural sections.
More than 30 stratigraphic sections and structural cross-sections were measured (Patil Pillai, 2004) across
the Kaladgi Basin. They were subjected to due fault-corrections to account for the dislocations suffered
across the faults. Fig. S1 below gives an example of how these corrections were applied.
Based on such structurally corrected sections, 17 vertical logs were measured in the exposures (with due
corrections for dip) with each lithological horizon (= stratigraphic Member) being assumed to be a
continuous deposit without internal break in sedimentation. Where significant breaks were observed, they
were duly noted. Stratal continuity was established in the field where continuous exposures could be
observed, while in other cases, they were extrapolated using the corrections shown in Figs. S1 & S2.
Page 3
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi
Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
Figure S1 : An example of fault-corrections applied to the Saundatti Quartzite for a N-S cross-section across
the Kaladgi Basin plotted along the longitude 75°45’E, based on the Survey of India (1:50000)
toposheets. This was also used in computing the folding-related shortening index of the strata
across the basin.
Page 4
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi
Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
Figure S2 : Sediment thickness measurements using fault-corrected N-S cross-sections across 4 sectors of
the basin. The correction methodology for section across 75°45’E is as shown in Fig. SD#1.1. The
red continuous line running across all the sections above is the trace of the Shirur Shear used to
position the sections along a common structural reference plane in the basin for comparison of
changes from west to east (top to bottom respectively).
Page 5
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
Table S1: DATA FOR CONSTRUCTION OF SEDIMENT ACCUMULATION CURVES (SAC)
Abbreviations used: T = Thickness; DF = Decompaction factor; DT = Decompacted Thickness; D.MSL = Depth from mean sea level;
∆D = Change in water depth; ∆ DI = Change in depositional interface; %CT = Cumulative Thickness; CDI = Cumulative DI.
Table S1a: Data of section measured along the Southern Limb of the Bagalkot Anticline
Sr. No
Lithology T in m DF DT m. D. MSL
(m) Δ D (m) Δ DI (m) % T % CT CDI
Bagalkot Group
1 CHIK. LST. 1607.14 1.45 2330.4 -7 0 2330.4 11.71 11.71 2330.4
2 CHITRA. DOL. 607.14 1.45 880.4 -5 2 882.4 4.43 16.14 3212.7
3 MAHA. CHBR. 571.43 1.00 158.0 0 0 158.0 4.16 20.30 3370.7
4 MAN. F. SHL. 178.57 2.47 441.1 -3 2 443.1 1.30 21.61 3813.8
5 ALM. QTZT. 642.86 1.32 848.6 3 6 854.6 4.69 26.29 4668.3
6 SAL. CGL. 71.43 1.32 94.3 7 4 98.3 0.52 26.81 4766.6
SUM= 3678.57 4752.6 4766.6 26.81
0.00729
Table S1b: Data of section measured along the Kendur-Konkankoppa Traverse
Sr. No
Lithounit T in (m) DF DT (m). D. MSL
(m) Δ D (m) Δ DI (m) % T % CT CDI
Badami Group
1 KONK. LST 96.2 1.33 127.9 -7 0 127.88 5.21 5.21 127.88
2 HALK. SHL 673.1 1.90 1278.9 -3 4 1282.85 36.46 41.67 1410.73
3 KEND. SST 519.2 1.17 607.5 5 8 615.50 28.12 69.79 2026.23
4 TORG. CGL 57.7 1.17 67.5 7 2 69.50 3.12 72.92 2095.73
SUM= 1346.2 2081.7 2095.73 72.92
0.05417
Bagalkot Group
1 MAN. F. SHL. 230.8 2.47 570.0 -3 0 570.00 1.68 1.68 570.00
2 ALM. QTZT. 326.9 1.32 431.5 3 6 437.53 2.38 4.07 1007.54
3 SAL. CGL. 19.2 1.32 25.4 7 4 29.38 0.14 4.21 1036.92
SUM= 576.9 1026.9 1036.92 4.21
0.00729
Page 6
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
Table S1c: Data of section measured along the Chitrabhanukot-Lokapur Traverse
Sr. No
Lithology T in (m) DF DT (m). D. MSL
(m) Δ D (m) Δ DI (m) % T % CT CDI.
1 CHITRA. DOL. 1939.39 1.45 2812.12 -5 0 2812.12 14.14 14.14 2812.12
2 CHIK. LST. 454.55 1.45 659.09 -7 2 661.09 3.31 17.45 3473.21
3 YAR. C. SHL. 121.21 1.96 237.58 -3 4 241.58 0.88 18.33 3714.79
4 JAL. PHYL. 30.30 2.47 74.85 -5 2 76.85 0.22 18.55 3791.64
5 MAN. F. SHL. 45.45 2.47 112.27 -3 2 114.27 0.33 18.88 3905.91
6 YAR. C. SHL. 60.61 1.96 118.79 -3 0 118.79 0.44 19.33 4024.70
7 CHIK. LST. 590.91 1.45 856.82 -7 4 860.82 4.31 23.63 4885.52
8 YAR. C. SHL. 75.76 1.96 148.48 -3 4 152.48 0.55 24.18 5038.00
9 JAL. PHYL. 30.30 2.47 74.85 -5 2 76.85 0.22 24.41 5114.85
10 YAR. C. SHL. 348.48 1.96 683.03 -3 2 685.03 2.54 26.95 5799.88
SUM= 3696.97 5777.88 5799.88 26.95
0.00729
Table S1d: Data of section measured along the Ramdurg-Mullur Traverse
Sr. No
Lithounit T in (m) DF DT (m). D. MSL
(m) ΔD (m) ΔDI (m) % T % CT CDI
Badami Group
1 GOK. SST. 500.00 1.17 585.00 5 0 585.00 27.08 27.08 585.00
2 TORG. CGL. 32.26 1.17 37.74 7 2 39.74 1.75 28.83 624.74
SUM= 532.26 622.74 624.74 28.83
0.05417
Bagalkot Group
1 CHITRA.DOL. 225.81 1.45 327.4245 -5 0 327.42 1.65 1.65 327.42
2 TIM. QTZT. 346.77 1.32 457.74 3 8 465.74 2.53 4.17 793.16
3 CHITRA. DOL. 274.19 1.45 397.58 -5 8 405.58 2.00 6.17 1198.74
4 YAR. C. SHL. 32.26 1.96 63.23 -3 2 65.23 0.24 6.41 1263.97
5 MAN. F. SHL. 48.39 2.47 119.52 -3 0 119.52 0.35 6.76 1383.49
6 ALM. QTZT. 403.23 1.32 532.26 5 8 540.26 2.94 9.70 1923.75
7 SAL. CGL. 16.13 1.32 21.29 7 2 23.29 0.12 9.82 1947.04
SUM= 1346.78 1919.04 1947.04 9.82
0.00729
Page 7
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi
Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
SUPPLEMENTARY DATA 2
PETROGRAPHY
Chemical Analysis
Samples Used:
Exposures of the Mallapur Intrusives were sampled at multiple locations in the field. Obtaining fresh (=
unweathered) samples was difficult (except in canal / well cuttings) since the terrain is deeply weathered.
Sufficiently large volumes of samples were collected to ensure that the same sample could be shared for
multiple analyses. The samples collected from locations 1, 2 and 3 (marked in Fig. 4 of the main text) and
their powders used in the chemical and other analyses were designated as D1, K1 and D5 respectively. D1
is a sample that is more metamorphically altered than the other two which have retained their igneous
mineralogy and texture as evident from the normative composition and XRD mineralogy given below as
well.
Methodology:
Fresh, ultrasonically cleaned chips of the rock samples were powdered to a grain size of 75 µm using a
Retsch PM-100 planetary ball mill and stainless steel grinding balls. 0.25 g of this sample powder was
mixed with 0.75 g lithium metaborate (LiBO2) and 0.50 g of lithium tetraborate (LiB4O7) in a platinum
crucible, and fused in a muffle furnace at 1050 °C for 10 minutes. After cooling, the crucible was
carefully immersed in 80 ml of 1N HCl in a 150-ml glass beaker and then magnetically stirred for 1 hour
until the fusion bead had dissolved completely. The sample volume was made up to 100 ml in a
volumetric flask. For major elements, 10 ml of this mother solution diluted ten times with distilled water,
and for trace elements, the mother solution itself, were analyzed by inductively coupled plasma atomic
emission spectrometry (ICP-AES, instrument: Jobin Yvon Ultima-2). USGS rock standards (QLO-1,
BHVO-2, AGV-2, BIR-1 and GSP-2) were similarly dissolved simultaneous with the samples and used
for calibrating the instrument and estimating the accuracy. The standard QLO-1 was used as unknown to
check the results. Weight loss on ignition (LOI) values were determined by igniting rock powders at
950°C, after drying them overnight at 110°C.
The results of the representative chemical compositions of samples of the Mallapur Intrusive are given in
Table 1 (of the main paper text). They are reproduced here (Table S2) only for ease of access.
Norm Calculations:
The major and trace element data was used to determine the normative mineral composition and their
normative weight % of the rock samples using the CIPW norm calculations. The norm calculations were
done using the program in MS Excel format written by Kurt Hollocher, Union College, NY. The
normative composition of the rock (assuming its igneous nature) is given in Table S3.
Page 8
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi
Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
Table S2: Representative Major oxide and Trace element (limited) compositions of the samples from
Mallapur Intrusives [also given as Table 1 in main text of the paper].
Major
Oxides
Wt % Trace Elements
In PPM
D1 K1 D5 D1 K1 D5
SiO2 49.32 50.98 47.80 Ba 932.55 326.09 347.13
TiO2 2.38 2.21 2.54 Cr 6.21 124.24 88.93
Al2O3 12.06 12.30 13.50 Ni 0.00 71.71 87.2
Fe2O3 2.93 2.79 2.93 Cu 50.77 ND ND
FeO 11.72 11.16 11.73 Sc ND 39.87 33.69
MnO 0.21 0.20 0.22 Sr 227.16 202.29 182.49
MgO 3.27 4.41 4.31 Y 55.30 52.05 58.74
CaO 7.96 9.32 8.98 Zn 220.68 180.57 251.99
Na2O 2.37 2.35 2.57 V 119.04 304.64 304.64
K2O 0.35 1.18 1.23 Zr 283.30 224.29 214.94
P2O5 0.37 0.31 0.47 Nb 59.53 ND ND
Total 92.93 97.21 96.29 Hf 6.92 ND ND
LOI 5.44 1.53 1.04 Ta 43.77 ND ND
Th 9.59 ND ND
U 28.79 ND ND
Table S3: Normative minerals and normative wt % of these minerals derived from CIPW norm
calculations of samples given in SD#2 Table 1.
Normative Minerals
Normative Wt % Computed Index D1 K1 D5
D1 K1 D5
Quartz 11.29 7.46 2.99 Fe3+/(Total Fe) in rock 30.00 30.01 29.99
Plagioclase 40.93 39.27 43.27
Orthoclase 2.79 7.26 7.56 Mg/(Mg+Total Fe) in rock
28.87 36.51 34.84 Diopside 13.61 20.56 16.56
Hypersthene 12.29 11.34 13.27 Mg/(Mg+Fe2+) in rock 36.71 45.10 43.30
Ilmenite 4.52 4.20 4.82 Mg/(Mg+Fe2+) in silicates
49.41 57.82 56.78 Magnetite 6.95 6.61 6.95
Apatite 0.86 0.72 1.09 Ca/(Ca+Na) in rock 64.99 68.67 65.88
Zircon 0.06 0.04 0.04 Ca/(Ca+Na) in plagioclase
49.52 47.88 48.26 Chromite 0.00 0.03 0.01
Total 93.3 97.49 96.56 Differentiation Index 55.01 53.99 53.82
Page 9
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
Fig. S3: XRD Graph of Sample # D1
Page 10
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
Fig. S4: XRD Graph of Sample # K1
Position [°2θ] (Copper (Cu))
10 20 30 40 50 60 70
Counts
0
1000
2000
An
nit
e-s
ide
rop
hy
llit
e
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i)
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i)
Acti
no
lite A
no
rth
ite
, so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
An
ort
hit
e,
so
dia
n;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i)A
no
rth
ite
, so
dia
n;
Acti
no
lite
An
ort
hit
e,
so
dia
nA
no
rth
ite
, so
dia
n;
Ap
ati
te-(
La
,Mg
,Si)
An
ort
hit
e,
so
dia
nA
no
rth
ite
, so
dia
nA
no
rth
ite
, so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
An
ort
hit
e,
so
dia
n;
Ap
ati
te-(
La
,Mg
,Si)
; C
lin
op
yro
xe
ne
Acti
no
lite
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
Ap
ati
te-(
La
,Mg
,Si)
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Ap
ati
te-(
La
,Mg
,Si)
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
Acti
no
lite
An
ort
hit
e,
so
dia
n;
Cli
no
py
roxe
ne
An
ort
hit
e,
so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
Ap
ati
te-(
La
,Mg
,Si)
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
ort
hit
e,
so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i)A
no
rth
ite
, so
dia
n;
Acti
no
lite
An
ort
hit
e,
so
dia
n;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
ort
hit
e,
so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
ort
hit
e,
so
dia
n;
Acti
no
lite
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
An
ort
hit
e,
so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
Ap
ati
te-(
La
,Mg
,Si)
; C
lin
op
yro
xe
ne
An
ort
hit
e,
so
dia
n;
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
ort
hit
e,
so
dia
n;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i)
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; C
lin
op
yro
xe
ne
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
An
nit
e-s
ide
rop
hy
llit
e;
Acti
no
lite
; A
pa
tite
-(L
a,M
g,S
i);
Cli
no
py
roxe
ne
K-1
Inte
nsi
ty C
oun
ts
Quartz
Anorthite
Clinopyroxene
Actinolite
Annite-siderophyllite
Apatite
Page 11
Implications of new 40
Ar/39
Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi Basin, Dharwar Craton, India
Shilpa Patil Pillai, Kanchan Pande & Vivek S. Kale
Fig. S5: XRD Graph of Sample # D5.
Inte
nsi
ty C
oun
ts
Page 12
XRD Analysis
Mineral assemblages:
The hand specimen and thin section petrology is described and discussed in the main text. To validate the
minerals identified in thin sections, representative XRD analysis (Figs. 1, 2 and 3) was carried out using
the powdered samples. They were run on PANalytical EMPYREAN Diffractometer system facility at IIT
Bombay, Mumbai using the X’Pert Data Collector, X’Pert Viewer and X’Pert HighScore Plus softwares.
The XRD-identified mineral assemblage for each sample is as follows:
1. Sample # D1: quartz - albite - clinochlore - aegerine - ilmenite – magnesioriebeckite. (Fig. S3).
2. Sample # K1: quartz - anorthite - clinopyroxene - actinolite – annite - siderophyllite - apatite.
(Fig. S4).
3. Sample # D5: quartz - albite - clinochlore - augite - ilmenite - actinolite - annite-siderophyllite
(Fig. S5).
Implications:
This shows that the pyroxene in the original gabbroic rock was altered (under low grade greenschist
metamorphic conditions) to amphiboles. The amphiboles are essentially the fibrous variety, indicating
predominance of stress metamorphism over thermal metamorphism. The albitic composition of the
plagioclase also reaffirms the low grade of metamorphism. The presence of anorthite detected in sample
no K1 suggests that it is perhaps the least altered and has a more pristine composition. The presence of
quartz (in thin sections, normative computations as well as the XRD analysis) indicates again the release
of free silica and its recrystallisation as quartz during the low grade metamorphic alteration. The quartz
crystals in thin sections show strain shadows and occur with the fibrous amphiboles or the sericitic mica
grains.
The variations in the mineralogy also indicates that the degree of metamorphic alteration imprinted on
different samples from different parts of the mafic body is variable.
Conclusions
It is significant that albitisation of slates has been earlier noted by Govinda Rajulu and Chadrasekhar
Gowda (1972) in the Kaladgi sediments north of Lokapur. This study therefore reaffirms this observation
and confirms that the Bagalkot Group has undergone low grade greenschist facies metamorphism.
The presence of magnesio-reibeckite (detected in the XRD analysis of sample D1 – which incidentally
also shows the maximum alteration and loss of original igneous texture in thin sections) is not repeated in
the other samples (i.e. # K1 & D5) that show the presence of fibrous amphibole variety actinolite.
Magnesio-reibeckite is known from glaucophane schists in different parts of the world (see: Phemister et
al., 1950; Miyashiro and Banno, 1958; Deer et al., 1963; De Roever et al., 1976; Berry et al., 2004),
including India (Narayanan Kutty et al., 1973) and is generally considered indicative of a low grade of an
incipient high pressure metamorphism.
In that sense, its presence in the studied sample establishes beyond doubt that the rock has suffered a low
grade of metamorphism, dominated by pressure over temperature changes. It may also be interpreted to
Page 13
be a localized imprint of shearing related stress that is not present in other parts of the Mallapur
Intrusives, given the proximity of sample D1 (collected near Loc #1 in Fig. 4) to a cross-fault in the
Lokapur syncline. The temperatures at which such changes occur do not exceed 150° – 200° C.
It is indicated therefore that the rock was originally a gabbroic mafic body emplaced along the axial trace
of the Lokapur fold. During the low grade metamorphism (dominated by stress over temperature) of the
Bagalkot Group, it was altered to an epidiorite with the uralitization of the pyroxene, albilisation of the
plagioclase and development of white mica – quartz in association with the fibrous amphiboles. The
degree of stress varied across the body, yielding small but significant changes in the resulting alteration
products.
REFERENCES [excluding those in the main text]
Allen P A and Allen J R 2013 Basin Analysis - Principles and Applications (3rd edition); Wiley-Blackwell, 549 p,
ISBN: 978-0-470-67377-5.
Berry L G, Mason B and Dietrich RV 2004 Mineralogy: Concepts, Descriptions, Determinations. CBS Publishers &
Distributers, New Delhi, 553p.
Best M G 1986 Igneous and Metamorphic petrology. CBS Publishers & Distributers, New Delhi, 423p.
Bond G C and Kominz M A 1984 Construction of tectonic subsidence curves for the early Palaeozoic miogeocline,
Southern Canadian Rocky mountains: Implications for subsidence mechanisms, age of breakup, and crustal
thinning; Geol. Soc. America Bull., 95; 155-173.
Cant D.J 1989 Simple equations of sedimentation: applications to sequence stratigraphy; Basin Res., 2(2); 73 – 81.
Cox K G, Bell J D and Pankhurst R J 1979 The Interpretation of Igneous Rocks. George Allen & Unwin, 445p.
Deer W A, Howie R A and Zussman J 1963 Rock-forming Minerals : Chain Silicates (Longmans), v. 2, 333-351.
Gallagher K and Lambeck K 1989 Subsidence, sedimentation and sea-level changes in the Eromanga Basin,
Australia. Basin Res., 2(2); 115-131
Geological Survey of India (1981) Geological and Mineral Map of Karnataka and Goa on 1:0.5 million scale. , GSI.,
Kolkatta.
Hollochar K Norm Calculations (Dept Geology, Union College, Schenectady, NY) http:// minerva. union.edu/
hollochk/c_petrology/other_files/norm_calculation.pdf.
Kale V S 1991 Constraints on the evolution of the Purana Basins of Peninsular India; J. Geol. Soc. India, v. 38,
231 -252.
Middlemost E A K 1985 Naming materials in the magma/igneous rock system. Earth Sci. Reviews, 37, 215–224.
Miyashiro A and Banno S 1958 Nature of glaucophanitic metamorphism; American J. Sci., 256, 97-110.
Narayanan Kutty T, Anantha Iyer G V and Ramakrishnan M 1973 Coexisting aegerine and magnesioriebeckite
from Bababudhan Hills Mysore state; Current Sci., 43 (1), 1-3.
Phemister J, Harvey C O and Sabine P A 1950 The riebeckite-bearing dikes of Shetland. Mineral. Mag. 29, 359 –
373.
Phillips W R and Griffen D T 1981 Optical mineralogy: the non-opaque minerals. CBS Publishers & Distributers,
New Delhi.
Sclater J G and Christie P A F 1980 Continental stretching : an explanation of the post-Mid Cretaceous subsidence
of the central North Sea Basin. J. of Geophys. Res., 85B7, 3711-3739.
Wilson M 1989 Igneous Petrogenesis. Springer, Netherlands, 466 p, doi 10.1007/978-94-010-9388-0.
Page 14
SUPPLEMENTARY DATA 3
GEOCHRONOLOGICAL DATA OF MALLAPUR INTRUSIVE
Table S4a: Argon isotopic composition (corrected for blank, mass discrimination and interference), Apparent
Age and percentage of nucleogenic and radiogenic argon for sample KB-1A. Errors on age are without
and (with) error on J respectively. Errors quoted are 2σ. J=0.0025961±0.000013
Temp.°C 36
Ar/39
Ar (±2σ)
40Ar/
39Ar
(±2σ) App. Age(Ma)
(±2σ) 39
Ar% 40
Ar*%
37Ar/
39Ar
(±2σ)
40Ar/
36Ar
(±2σ)
650 0.01936 70.421 280.61 8.48 91.98 0.8852 3682.7
0.00024 0.522 2.11 (2.49)
0.0086 66.2
700 0.01992 88.531 351.21 8.96 93.43 0.8920 4497.5
0.00020 0.780 3.02 (3.43)
0.0077 92.5
750 0.01743 111.657 441.01 9.87 95.45 0.8922 6496.7
0.00019 0.558 2.06 (2.86)
0.0077 85.2
800 0.01606 140.987 547.61 8.92 96.73 1.6474 9025.7
0.00008 0.705 2.44 (3.42)
0.0036 81.2
850 0.01689 209.589 774.68 11.42 97.86 6.3042 13790.4
0.00011 1.171 3.60 (4.81)
0.0332 180.7
900 0.01706 344.814 1154.92 14.62 98.81 11.7689 24799.2
0.00009 1.724 4.32 (6.11)
0.0264 219.7
950 0.01309 343.377 1154.66 15.40 99.15 12.1010 34884.1
0.00006 1.717 4.30 (6.10)
0.0242 305.9
1000 0.01599 346.270 1154.99 7.48 98.82 8.2034 25115.3
0.00016 1.731 4.32 (6.11)
0.0164 320.1
1050 0.02687 343.092 1154.74 5.21 98.17 21.0819 16165.9
0.00020 1.715 4.35 (6.13)
0.0422 178.1
1100 0.03763 339.996 1154.86 3.24 97.52 34.0071 11923.5
0.00022 1.700 4.38 (6.16)
0.0866 120.1
1200 0.04790 343.471 1154.7 3.24 96.64 32.9756 8793.7
0.00027 1.717 4.42 (6.18)
0.0660 79.8
1350 0.12849 373.099 1154.76 3.16 90.27 21.1355 3037.6
0.00054 1.866 4.74 (6.42)
0.0910 28.2
TOTAL 0.02254 243.364 873.88 100.00 97.57 9.3395 12143.0
0.00005 0.448 1.31 (3.75)
0.0086 45.8
Page 15
Table S4b: Argon isotopic composition (corrected for blank, mass discrimination and interference),
Apparent Age and percentage of nucleogenic and radiogenic argon for sample KB-1B. Errors on age
are without and (with) error on J respectively. Errors quoted are 2σ. J=0.0025961±0.000013
Temp.°C 36
Ar/39
Ar
(±2σ)
40Ar/
39Ar
(±2σ)
App. Age(Ma)
(±2σ) 39
Ar% 40
Ar*%
37Ar/
39Ar
(±2σ)
40Ar/
36Ar
(±2σ)
650 0.01979 66.855 265.83 8.51 91.38 1.0525 3427.0
0.00021 0.491 2.00 (2.36)
0.0044 52.8
700 0.02290 69.557 273.04 10.54 90.39 1.0573 3076.0
0.00025 0.367 1.51 (1.98)
0.0052 43.1
750 0.02050 98.900 390.2 9.61 93.95 0.9839 4887.4
0.00012 0.599 2.26 (2.88)
0.0035 59.3
800 0.01637 139.971 543.72 9.37 96.63 1.5846 8776.4
0.00016 0.702 2.44 (3.41)
0.0032 103.0
850 0.01856 209.478 772.44 8.06 97.61 5.9185 12344.4
0.00013 1.049 3.23 (4.54)
0.0118 117.5
900 0.02327 345.256 1153.31 15.64 98.31 13.3060 17521.2
0.00009 1.727 4.33 (6.12)
0.0266 132.5
950 0.01652 343.168 1153.76 15.86 98.90 13.8657 26793.0
0.00009 1.716 4.31 (6.11)
0.0277 244.1
1000 0.01814 345.596 1153.38 8.01 98.67 9.5626 22189.7
0.00016 1.729 4.32 (6.11)
0.0210 271.3
1050 0.03532 343.978 1153.77 5.09 97.51 23.5959 11861.0
0.00029 1.722 4.38 (6.16)
0.0473 137.7
1100 0.04890 342.762 1153.36 3.21 96.57 33.9698 8612.0
0.00027 1.720 4.43 (6.19)
0.0680 77.8
1200 0.06426 346.103 1153.5 3.20 95.35 36.5339 6354.2
0.00039 1.737 4.50 (6.24)
0.0732 59.5
1350 0.17460 383.436 1153.64 2.89 87.10 26.9600 2290.9
0.00057 1.917 4.91 (6.54)
0.0540 15.4
TOTAL 0.02746 240.458 862.16 100.00 96.97 10.3231 9739.6
0.00005 0.450 1.32 (3.72)
0.0078 31.8