subsidence analysis sediment accumulation curves (sacs) · subsidence analysis sediment...

Implications of new 40

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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


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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.


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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.


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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).


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Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi Basin, Dharwar Craton, India


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


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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


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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.


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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


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Fig. S3: XRD Graph of Sample # D1


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Fig. S4: XRD Graph of Sample # K1

Position [°2θ] (Copper (Cu))

10 20 30 40 50 60 70

Counts

0

1000

2000

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K-1

Inte

nsi

ty C

oun

ts

Quartz

Anorthite

Clinopyroxene

Actinolite

Annite-siderophyllite

Apatite


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Fig. S5: XRD Graph of Sample # D5.

Inte

nsi

ty C

oun

ts

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

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.


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

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

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