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A new 40Ar/39Ar eruption age for the Mount Widderin volcano, Newer Volcanic Province, Australia, with implications for eruption frequency in the region

04 May 2016-Australian Journal of Earth Sciences (Taylor & Francis)-Vol. 63, Iss: 2, pp 175-186

AbstractThe Mount Widderin shield volcano is located near Skipton, western Victoria, in the Western Plains subprovince of the monogenetic Pliocene–Holocene Newer Volcanic Province (NVP). Radiometric ages for lavas in the Hamilton–Skipton–Derrinallum area are few, owing to limited suitable outcrop for K–Ar or 40Ar/39Ar geochronology studies. Existing age constraints for flows in this area have been inferred from Regolith Landform Units (RLUs), complemented by a small number of K–Ar studies on ≥1 Ma flows. Although the RLU approach provides a valuable overview of relative eruption ages across the NVP, it is of limited use in eruption frequency studies. Additional radio-isotopic ages are required to refine age ranges for individual RLUs, and to validate previous assignment of individual flows to specific RLUs. We report a new, high-precision 40Ar/39Ar age of 389 ± 8 ka (2σ) for a Mount Widderin basalt sample. Based on this age and geomorphic observations, we propose that both the Widderin and Elephant lava f...

Topics: Lava (55%), Volcano (55%), Shield volcano (52%)

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Summary

  • Ar laser step-heating analytical results for NVP26 groundmass.
  • Table A2. 40Ar/39Ar ARGUSVI data and blank values for laser step-heating analysis of sample NVP26 excluding interference corrections.
  • Ar age spectra and inverse isochron diagrams for individual NVP26 groundmass aliquants.
  • Grey symbols are excluded from age calculation results.
  • In inverse isochron diagrams, solid lines represent preferred isochron results and dashed lines indicate position of inverse isochrons constructed from all data points.

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A new
40
Ar/
39
Ar eruption age for the Mount Widderin volcano,
Newer Volcanic Province, Australia, with implications for eruption
frequency in the region.
E. L. MATCHAN, E. B. JOYCE, AND D. PHILLIPS
School of Earth Sciences, The University of Melbourne, VIC 3010, Australia.
*Corresponding author: ematchan@unimelb.edu.au
SUPPLEMENTARY PAPERS
Australian Journal of Earth Sciences (2016) 63,
http://dx.doi.org/10.1080/08120099.2016.1156576
----------------------------------------------------------------------------------------------------------------
Copies of Supplementary Papers may be obtained from the Geological Society of
Australia's website (www.gsa.org.au), the Australian Journal of Earth Sciences
website (www.ajes.com.au) or from the National Library of Australia's Pandora
archive (http://nla.gov.au/nla.arc-25194).
----------------------------------------------------------------------------------------------------------------
SUPPLEMENTARY PAPERS
Table A1. ARGUSVI
40
Ar/
39
Ar laser step-heating analytical results for NVP26
groundmass.
Table A2.
40
Ar/
39
Ar ARGUSVI data and blank values for laser step-heating analysis
of sample NVP26 excluding interference corrections.
Figure A1.
40
Ar/
39
Ar age spectra and inverse isochron diagrams for individual NVP26
groundmass aliquants. Errors symbols are 1σ. Grey symbols are excluded from
age calculation results. In inverse isochron diagrams, solid lines represent
preferred isochron results and dashed lines indicate position of inverse
isochrons constructed from all data points. Step numbers are indicated.
Appendix B Supplementary information related to the contact between lava flows
from Mount Widderin and Mount Elephant.
Matchan et al. 2016 Australian Journal of Earth Sciences 63/2 Supplementary Papers http://dx.doi.org/10.1080/08120099.2016.1156576
1

Table A1. ARGUSVI
40
Ar/
39
Ar laser step-heating analytical results for NVP26 groundmass.
a,b,c,d
Sample
Step Laser
40
Ar ±1σ
39
Ar ±1σ
38
Ar ±1σ
37
Ar ±1σ
36
Ar ±1σ
39
Ar Cum.% Apparent
ID
No Power (x10
-14 39
Ar Age (ka)
mol)
d
NVP26-1 101.3 mg
NVP26-1a 1 4% 345.50 0.08 63.788 0.045 0.1344 0.0006 99.1 2.9 0.7128 0.0031 0.2264 2.719 0.081 38.41 2.080 0.015 17.98 401.604 2.8 0.7
NVP26-1b 2 6% 501.14 0.22 105.177 0.043 0.1812 0.0008 132.7 3.0 0.9615 0.0043 0.3734 2.208 0.050 42.72 2.035 0.012 47.63 392.884 2.4 0.6
NVP26-1c 3 9% 530.49 0.13 104.603 0.076 0.2008 0.0006 138.7 4.1 1.0655 0.0029 0.3713 2.320 0.068 40.03 2.030 0.009 77.12 391.926 1.7 0.4
NVP26-1d 4 12% 316.81 0.07 52.986 0.037 0.1329 0.0004 88.9 3.1 0.7050 0.0022 0.1881 2.937 0.104 33.56 2.007 0.013 92.06 387.339 2.4 0.6
NVP26-1e 5 18% 279.59 0.07 28.168 0.046 0.1422 0.0003 110.9 1.8 0.7542 0.0016 0.1000 6.888 0.110 19.46 1.932 0.017 100.00 372.937 3.4 0.9
Total gas age: 391.8 ± 4.7 (2σ)
NVP26-2 71.5 mg
NVP26-2a 1 4% 645.08 0.34 106.061 0.078 0.2676 0.0006 173.3 2.5 1.4197 0.0031 0.3765 2.859 0.041 34.29 2.086 0.009 18.78 402.608 1.8 0.5
NVP26-2b 2 6% 702.98 0.29 144.297 0.108 0.2572 0.0004 191.8 2.0 1.3645 0.0023 0.5123 2.327 0.025 42.05 2.049 0.005 44.33 395.444 1.0 0.3
NVP26-2c 3 8% 563.02 0.16 117.904 0.060 0.2037 0.0006 142.5 2.3 1.0804 0.0031 0.4186 2.115 0.034 42.71 2.039 0.008 65.20 393.696 1.6 0.4
NVP26-2d 4 10% 450.09 0.10 86.882 0.030 0.1731 0.0006 113.1 4.0 0.9182 0.0032 0.3084 2.278 0.081 39.09 2.025 0.011 80.59 390.944 2.2 0.6
NVP26-2e 5 14% 447.18 0.12 65.464 0.035 0.1992 0.0004 133.7 2.3 1.0570 0.0021 0.2324 3.575 0.061 29.43 2.010 0.010 92.18 388.052 1.9 0.5
NVP26-2f 6 20% 341.33 0.09 30.637 0.042 0.1757 0.0005 139.1 2.6 0.9319 0.0027 0.1088 7.948 0.146 18.49 2.060 0.026 97.60 397.680 5.1 1.3
NVP26-2g 7 30% 199.01 0.06 13.555 0.032 0.1060 0.0004 99.1 2.3 0.5625 0.0019 0.0481 12.794 0.302 15.61 2.292 0.043 100.00 442.346 8.3 1.9
Total gas age: 396.1 ± 4.0 (2σ)
NVP26-3 76.0 mg
NVP26-3a 1 4% 399.93 0.13 68.267 0.040 0.1644 0.0004 101.9 2.4 0.8724 0.0021 0.2423 2.613 0.063 34.87 2.043 0.009 16.45 394.387 1.8 0.5
NVP26-3b 2 6% 516.57 0.33 103.661 0.042 0.1942 0.0005 136.2 2.1 1.0303 0.0025 0.3680 2.299 0.036 40.45 2.016 0.008 41.42 389.151 1.5 0.4
NVP26-3c 3 8% 430.47 0.18 89.732 0.060 0.1588 0.0005 109.2 2.2 0.8426 0.0027 0.3185 2.130 0.044 41.56 1.994 0.009 63.04 384.867 1.8 0.5
NVP26-3d 4 10% 325.98 0.08 64.475 0.052 0.1243 0.0004 85.5 2.0 0.6592 0.0019 0.2289 2.322 0.054 39.62 2.003 0.009 78.57 386.710 1.7 0.4
NVP26-3e 5 14% 340.29 0.08 52.219 0.043 0.1488 0.0005 100.8 3.2 0.7895 0.0028 0.1854 3.377 0.108 30.73 2.002 0.016 91.15 386.548 3.1 0.8
NVP26-3f 6 30% 445.42 0.07 36.739 0.068 0.2361 0.0005 185.6 2.7 1.2523 0.0028 0.1304 8.842 0.128 16.06 1.947 0.023 100.00 375.808 4.5 1.2
Total gas age: 387.2 ± 4.3 (2σ)
NVP26-4
101.1 mg
NVP26-4a 1 4% 632.41 0.24 108.707 0.046 0.2586 0.0008 172.1 2.5 1.3720 0.0043 0.3859 2.771 0.040 35.23 2.050 0.012 19.72 395.637 2.3 0.6
NVP26-4b 2 6% 723.03 0.30 152.589 0.092 0.2607 0.0005 197.1 1.6 1.3828 0.0028 0.5417 2.260 0.019 42.90 2.033 0.006 47.40 392.419 1.1 0.3
NVP26-4c 3 8% 571.53 0.17 122.726 0.065 0.2054 0.0006 143.8 2.1 1.0895 0.0031 0.4357 2.051 0.030 43.09 2.007 0.008 69.67 387.349 1.5 0.4
NVP26-4d 4 10% 398.11 0.12 76.565 0.041 0.1559 0.0005 92.6 3.0 0.8271 0.0025 0.2718 2.116 0.070 37.97 1.974 0.010 83.56 381.126 1.9 0.5
NVP26-4e 5 14% 427.80 0.09 58.687 0.036 0.1977 0.0004 129.7 2.8 1.0487 0.0021 0.2083 3.868 0.084 26.82 1.955 0.011 94.21 377.346 2.1 0.6
NVP26-4f 6 30% 486.47 0.19 31.927 0.036 0.2690 0.0008 215.2 2.3 1.4270 0.0041 0.1133 11.798 0.128 12.42 1.892 0.039 100.00 365.248 7.5 2.0
Total gas age: 387.2 ± 4.1 (2σ)
NVP26-5
101.0 mg
NVP26-5a 1 4% 740.37 0.26 128.485 0.073 0.3001 0.0007 208.2 3.1 1.5920 0.0037 0.4561 2.836 0.042 35.80 2.063 0.009 22.89 398.219 1.7 0.4
NVP26-5b 2 6% 783.34 0.27 168.031 0.077 0.2798 0.0007 206.6 1.3 1.4843 0.0035 0.5965 2.152 0.013 43.43 2.025 0.007 52.83 390.826 1.3 0.3
NVP26-5c 3 8% 575.39 0.10 121.589 0.051 0.2090 0.0005 141.9 2.6 1.1088 0.0025 0.4316 2.043 0.037 42.47 2.010 0.006 74.50 387.942 1.2 0.3
NVP26-5d 4 10% 391.34 0.08 71.175 0.049 0.1575 0.0006 102.9 4.8 0.8358 0.0029 0.2527 2.529 0.118 36.24 1.992 0.012 87.18 384.597 2.4 0.6
NVP26-5e 5 14% 408.08 0.10 47.829 0.035 0.1968 0.0006 135.1 2.7 1.0439 0.0031 0.1698 4.944 0.098 23.63 2.016 0.019 95.70 389.134 3.7 1.0
NVP26-5f 6 30% 414.33 0.13 24.106 0.043 0.2322 0.0004 187.5 3.7 1.2321 0.0024 0.0856 13.612 0.270 11.22 1.928 0.030 100.00 372.221 5.8 1.6
Total gas age: 390.2 ± 3.8 (2σ)
b
Interference corrections: (
36
Ar/
37
Ar)
Ca
= (2.5713 ± 0.0023) x 10
-4
; (
39
Ar/
37
Ar)
Ca
= (6.6200 ± 0.0801) x 10
-4
; (
40
Ar/
39
Ar)
K
= (1.00 ± 0.05) x 10
-10
; (
38
Ar/
39
Ar)
K
= (1.2136 ± 0.0016) x 10
-2
c
J-value is 0.0001070135 ± 0.0000000648 ( 0.061%;1σ), based on an age of 1.1811 ± 0.0006 Ma (1σ) for AC sanidine (Phillips et al., submitted)
d
Sensitivity = 3.55 x 10
-17
mol/fA
(fA)
(fA)
b
(fA)
(fA)
b
a
Data are corrected for mass spectrometer backgrounds, discrimination, radioactive decay and interference corrections (see Table A.2 for values excluding the interference correction). Errors are
one sigma uncertainties and exclude uncertainty in the J-value.
(fA)
Matchan et al. 2016 Australian Journal of Earth Sciences 63/2 Supplementary Papers http://dx.doi.org/10.1080/08120099.2016.1156576
2

Table A1. ARGUSVI
40
Ar/
39
Ar laser step-heating analytical results for NVP26 groundmass.
a,b,c,d
Sample
Step
ID
No
NVP26-1
101.3 mg
NVP26-1a 1
NVP26-1b 2
NVP26-1c 3
NVP26-1d 4
NVP26-1e 5
NVP26-2
NVP26-2a 1
NVP26-2b 2
NVP26-2c 3
NVP26-2d 4
NVP26-2e 5
NVP26-2f 6
NVP26-2g 7
NVP26-3
NVP26-3a 1
NVP26-3b 2
NVP26-3c 3
NVP26-3d 4
NVP26-3e 5
NVP26-3f 6
NVP26-4
NVP26-4a 1
NVP26-4b 2
NVP26-4c 3
NVP26-4d 4
NVP26-4e 5
NVP26-4f 6
NVP26-5
NVP26-5a 1
NVP26-5b 2
NVP26-5c 3
NVP26-5d 4
NVP26-5e 5
NVP26-5f 6
Background correction
Blank no.
40
Ar ±1σ
39
Ar ±1σ
38
Ar ±1σ
37
Ar ±1σ
36
Ar ±1σ
EXB#74 7.276 0.011 0.085 0.019 -0.121 0.043 0.020 0.027 0.03095 0.00053
EXB#75 7.787 0.024 0.056 0.017 -0.055 0.030 -0.002 0.032 0.03330 0.00021
EXB#75 7.787 0.024 0.056 0.017 -0.055 0.030 -0.002 0.032 0.03330 0.00021
EXB#76 7.792 0.013 0.086 0.022 -0.062 0.020 0.025 0.011 0.03381 0.00035
EXB#76 7.792 0.013 0.086 0.022 -0.062 0.020 0.025 0.011 0.03381 0.00035
EXB#82 3.336 0.016 0.060 0.018 -0.008 0.021 -0.014 0.015 0.01726 0.00011
EXB#82 3.336 0.016 0.060 0.018 -0.008 0.021 -0.014 0.015 0.01726 0.00011
EXB#83 3.393 0.019 0.092 0.017 -0.003 0.020 -0.009 0.015 0.01881 0.00014
EXB#83 3.393 0.019 0.092 0.017 -0.003 0.020 -0.009 0.015 0.01881 0.00014
EXB#83 3.393 0.019 0.092 0.017 -0.003 0.020 -0.009 0.015 0.01881 0.00014
EXB#84 3.429 0.010 0.102 0.022 -0.044 0.022 0.020 0.014 0.01812 0.00036
EXB#84 3.429 0.010 0.102 0.022 -0.044 0.022 0.020 0.014 0.01812 0.00036
EXB#89 2.515 0.025 0.081 0.008 -0.083 0.017 0.035 0.014 0.01532 0.00035
EXB#89 2.515 0.025 0.081 0.008 -0.083 0.017 0.035 0.014 0.01532 0.00035
EXB#89 2.515 0.025 0.081 0.008 -0.083 0.017 0.035 0.014 0.01532 0.00035
EXB#90 2.707 0.029 0.092 0.023 -0.093 0.012 0.012 0.012 0.01736 0.00047
EXB#90 2.707 0.029 0.092 0.023 -0.093 0.012 0.012 0.012 0.01736 0.00047
EXB#90 2.707 0.029 0.092 0.023 -0.093 0.012 0.012 0.012 0.01736 0.00047
EXB#91 3.219 0.017 0.088 0.022 -0.079 0.036 -0.012 0.013 0.01936 0.00012
EXB#91 3.219 0.017 0.088 0.022 -0.079 0.036 -0.012 0.013 0.01936 0.00012
EXB#91 3.219 0.017 0.088 0.022 -0.079 0.036 -0.012 0.013 0.01936 0.00012
EXB#92 3.523 0.014 0.081 0.004 -0.067 0.026 0.051 0.019 0.02015 0.00044
EXB#92 3.523 0.014 0.081 0.004 -0.067 0.026 0.051 0.019 0.02015 0.00044
EXB#92 3.523 0.014 0.081 0.004 -0.067 0.026 0.051 0.019 0.02015 0.00044
EXB#94 2.449 0.015 0.036 0.017 -0.051 0.013 -0.023 0.007 0.01431 0.00031
EXB#94 2.449 0.015 0.036 0.017 -0.051 0.013 -0.023 0.007 0.01431 0.00031
EXB#94 2.449 0.015 0.036 0.017 -0.051 0.013 -0.023 0.007 0.01431 0.00031
EXB#95 2.554 0.027 0.081 0.010 -0.040 0.011 0.018 0.020 0.01585 0.00021
EXB#95 2.554 0.027 0.081 0.010 -0.040 0.011 0.018 0.020 0.01585 0.00021
EXB#95 2.554 0.027 0.081 0.010 -0.040 0.011 0.018 0.020 0.01585 0.00021
(fA)
(fA)
(fA)
(fA)
(fA)
Matchan et al. 2016 Australian Journal of Earth Sciences 63/2 Supplementary Papers http://dx.doi.org/10.1080/08120099.2016.1156576
3

Table A2.
40
Ar/
39
Ar ARGUSVI data and blank values for laser step-heating analysis of sample NVP26 excluding interference corrections
a
Background correction
Sample Step Laser
40
Ar ±1σ
39
Ar ±1σ
38
Ar ±1σ
37
Ar ±1σ
36
Ar ±1σ
Blank no.
40
Ar ±1σ
39
Ar ±1σ
38
Ar ±1σ
37
Ar ±1σ
36
Ar ±1σ H1/Ax H1/L1 H1/L2 AX L1 L2 H1/CDD ±1σ
ID No
Power
[40] [40] [40] (1amu) (1amu) (1amu) (%)
NVP26-1 101.3 mg
NVP26-1a 1 4% 345.50 0.08 63.853 0.045 0.970 0.052 99.1 2.9 0.7383 0.0030
EXB#74
7.276 0.011 0.085 0.019 -0.121 0.043 0.020 0.027 0.03095 0.00053 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.402846 0.095942
NVP26-1b 2 6% 501.14 0.22 105.265 0.043 1.435 0.036 132.7 3.0 0.9957 0.0042
EXB#75
7.787 0.024 0.056 0.017 -0.055 0.030 -0.002 0.032 0.03330 0.00021 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.402846 0.095942
NVP26-1c 3 9% 530.49 0.13 104.695 0.076 1.491 0.035 138.7 4.1 1.1012 0.0027
EXB#75
7.787 0.024 0.056 0.017 -0.055 0.030 -0.002 0.032 0.03330 0.00021 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.402846 0.095942
NVP26-1d 4 12% 316.81 0.07 53.045 0.037 0.776 0.025 88.9 3.1 0.7279 0.0021
EXB#76
7.792 0.013 0.086 0.022 -0.062 0.020 0.025 0.011 0.03381 0.00035 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.402846 0.095942
NVP26-1e 5 18% 279.59 0.07 28.241 0.046 0.511 0.027 110. 9 1.8 0.7827 0.0015
EXB#76
7.792 0.013 0.086 0.022 -0.062 0.020 0.025 0.011 0.03381 0.00035 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.402846 0.095942
NVP26-2 71.5 mg
NVP26-2a 1 4% 645.08 0.34 106.176 0.078 1.561 0.029 173.3 2.5 1.4643 0.0030
EXB#82
3.336 0.016 0.060 0.018 -0.008 0.021 -0.014 0.015 0.01726 0.00011 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-2b 2 6% 702.98 0.29 144.424 0.108 2.006 0.032 191.8 2.0 1.4138 0.0022
EXB#82
3.336 0.016 0.060 0.018 -0.008 0.021 -0.014 0.015 0.01726 0.00011 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-2c 3 8% 563.02 0.16 117.998 0.060 1.653 0.030 142.5 2.3 1.1170 0.0031
EXB#83
3.393 0.019 0.092 0.017 -0.003 0.020 -0.009 0.015 0.01881 0.00014 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-2d 4 10% 450.09 0.10 86.957 0.030 1.186 0.023 113. 1 4.0 0.9472 0.0031
EXB#83
3.393 0.019 0.092 0.017 -0.003 0.020 -0.009 0.015 0.01881 0.00014 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-2e 5 14% 447.18 0.12 65.553 0.035 0.989 0.028 133.7 2.3 1.0914 0.0020
EXB#83
3.393 0.019 0.092 0.017 -0.003 0.020 -0.009 0.015 0.01881 0.00014 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-2f 6 20% 341.33 0.09 30.729 0.042 0.597 0.024 139.1 2.6 0.9677 0.0026
EXB#84
3.429 0.010 0.102 0.022 -0.044 0.022 0.020 0.014 0.01812 0.00036 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-2g 7 30% 199.01 0.06 13.620 0.032 0.299 0.027 99.1 2.3 0.5880 0.0018
EXB#84
3.429 0.010 0.102 0.022 -0.044 0.022 0.020 0.014 0.01812 0.00036 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-3 76.0 mg
NVP26-3a 1 4% 399.93 0.13 68.334 0.040 1.009 0.037 101.9 2.4 0.8986 0.0020
EXB#89
2.515 0.025 0.081 0.008 -0.083 0.017 0.035 0.014 0.01532 0.00035 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-3b 2 6% 516.57 0.33 103.752 0.042 1.533 0.024 136.2 2.1 1.0653 0.0024
EXB#89
2.515 0.025 0.081 0.008 -0.083 0.017 0.035 0.014 0.01532 0.00035 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-3c 3 8% 430.47 0.18 89.804 0.060 1.288 0.032 109.2 2.2 0.8707 0.0027
EXB#89
2.515 0.025 0.081 0.008 -0.083 0.017 0.035 0.014 0.01532 0.00035 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-3d 4 10% 325.98 0.08 64.531 0.052 1.037 0.016 85.5 2.0 0.6813 0.0018
EXB#90
2.707 0.029 0.092 0.023 -0.093 0.012 0.012 0.012 0.01736 0.00047 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-3e 5 14% 340.29 0.08 52.286 0.043 0.840 0.032 100.8 3.2 0.8155 0.0027
EXB#90
2.707 0.029 0.092 0.023 -0.093 0.012 0.012 0.012 0.01736 0.00047 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-3f 6 30% 445.42 0.07 36.862 0.068 0.778 0.028 185.6 2.7 1.3001 0.0027
EXB#90
2.707 0.029 0.092 0.023 -0.093 0.012 0.012 0.012 0.01736 0.00047 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-4 101.1 mg
NVP26-4a 1 4% 632.41 0.24 108.820 0.046 1.572 0.039 172.1 2.5 1.4162 0.0043
EXB#91
3.219 0.017 0.088 0.022 -0.079 0.036 -0.012 0.013 0.01936 0.00012 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-4b 2 6% 723.03 0.30 152.719 0.092 2.127 0.040 197.1 1.6 1.4335 0.0027
EXB#91
3.219 0.017 0.088 0.022 -0.079 0.036 -0.012 0.013 0.01936 0.00012 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-4c 3 8% 571.53 0.17 122.821 0.065 1.721 0.043 143.8 2.1 1.1265 0.0031
EXB#91
3.219 0.017 0.088 0.022 -0.079 0.036 -0.012 0.013 0.01936 0.00012 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-4d 4 10% 398.11 0.12 76.626 0.041 1.129 0.037 92.6 3.0 0.8510 0.0023
EXB#92
3.523 0.014 0.081 0.004 -0.067 0.026 0.051 0.019 0.02015 0.00044 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-4e 5 14% 427.80 0.09 58.773 0.036 0.971 0.026 129.7 2.8 1.0820 0.0020
EXB#92
3.523 0.014 0.081 0.004 -0.067 0.026 0.051 0.019 0.02015 0.00044 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-4f 6 30% 486.47 0.19 32.069 0.036 0.672 0.042 215.2 2.3 1.4824 0.0040
EXB#92
3.523 0.014 0.081 0.004 -0.067 0.026 0.051 0.019 0.02015 0.00044 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-5 101.0 mg
NVP26-5a 1 4% 740.37 0.26 128.622 0.073 1.943 0.075 208.2 3.1 1.6456 0.0036
EXB#94
2.449 0.015 0.036 0.017 -0.051 0.013 -0.023 0.007 0.01431 0.00031 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-5b 2 6% 783.34 0.27 168.168 0.077 2.360 0.016 206.6 1.3 1.5374 0.0035
EXB#94
2.449 0.015 0.036 0.017 -0.051 0.013 -0.023 0.007 0.01431 0.00031 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-5c 3 8% 575.39 0.10 121.683 0.051 1.692 0.021 141.9 2.6 1.1453 0.0024
EXB#94
2.449 0.015 0.036 0.017 -0.051 0.013 -0.023 0.007 0.01431 0.00031 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-5d 4 10% 391.34 0.08 71.243 0.049 0.999 0.043 102.9 4.8 0.8622 0.0027
EXB#95
2.554 0.027 0.081 0.010 -0.040 0.011 0.018 0.020 0.01585 0.00021 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-5e 5 14% 408.08 0.10 47.918 0.035 0.849 0.032 135.1 2.7 1.0787 0.0030
EXB#95
2.554 0.027 0.081 0.010 -0.040 0.011 0.018 0.020 0.01585 0.00021 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
NVP26-5f 6 30% 414.33 0.13 24.230 0.043 0.566 0.024 187.5 3.7 1.2803 0.0022
EXB#95
2.554 0.027 0.081 0.010 -0.040 0.011 0.018 0.020 0.01585 0.00021 1.001217 0.998905 0.993785 0.992794 0.990793 0.993521 320.505939 0.150435
(fA)
(fA)
(fA)
(fA)
(fA)
a
Data are corrected for mass spectrometer backgrounds, discrimination and radioactive decay.
Argus Sensitivity and Discrimination Corrections
(fA)
(fA)
(fA)
(fA)
(fA)
Matchan et al. 2016 Australian Journal of Earth Sciences 63/2 Supplementary Papers http://dx.doi.org/10.1080/08120099.2016.1156576
4

Figure'A1.'
40
Ar/
39
Ar(age(spectra(and(inverse(isochron(diagrams(for(individual(NVP26(groundmass(aliquants.(Errors(symbols(
are(1σ.(Grey(symbols(are(excluded(from(age(calculaHon(results.(In(inverse(isochron(diagrams,(solid(lines(represent(preferred(
isochron(results(and(dashed(lines(indicate(posiHon(of(inverse(isochrons(constructed(from(all(data(points.(Step(numbers(are(
indicated.(
300
320
340
360
380
400
420
440
460
480
500
Age (ka)
300
320
340
360
380
400
420
440
460
480
500
Age (ka)
Plateau steps are dark grey error symbols are 1σ
300
320
340
360
380
400
420
440
460
480
500
Age (ka)
300
320
340
360
380
400
420
440
460
480
500
0 20 40 60 80 100
Age (ka)
NVP26-1
Plateau age =391.1 ± 2.4 ka (2σ)
MSWD=1.6, p=0.2
Includes 74.1% of the
39
Ar
a
b
c
d
e
NVP26-2
Plateau age =394.4 ± 1.7 ka (2σ)
MSWD=1.9, p=0.2
Includes 61.8% of the
39
Ar
NVP26-3
Plateau age =387.1 ± 1.9 ka (2σ)
MSWD=1.1, p=0.3
Includes 74.7% of the
39
Ar
NVP26-4
f
g
h
1
2
3
4
5
0.0018
0.0020
0.0022
0.0024
0.0026
0.0028
0.0030
36
Ar/
40
Ar
39
Ar/
40
Ar
1
2
3
4
5
6
7
0.0018
0.0020
0.0022
0.0024
0.0026
0.0028
0.0030
1
2
3
4
5
6
0.0018
0.0020
0.0022
0.0024
0.0026
0.0028
0.0030
1
2
3
4
5
6
0.0018
0.0020
0.0022
0.0024
0.0026
0.0028
0.0030
0.04 0.08 0.12 0.16 0.20
error symbols are 1σ
36
Ar/
40
Ar
36
Ar/
40
Ar
36
Ar/
40
Ar
Cumulative %
39
Ar
NVP26-1
age = 403.3 ± 5.6 ka (2σ)
40
Ar/
36
Ar
i
= 292.7 ± 2.1 (2σ)
MSWD = 0.1
n = 4 of 5
NVP26-2
age = 393 ± 17 ka (95% CI)
40
Ar/
36
Ar
i
= 298.6 ± 5.2 (95% CI)
MSWD = 4
n = 5 of 7
NVP26-3
age = 391.6 ± 4.4 ka (2σ)
40
Ar/
36
Ar
i
= 296.3 ± 1.8 (2σ)
MSWD = 1.4
n = 5 of 6
NVP26-4
age = 395 ± 15 ka (95% CI)
40
Ar/
36
Ar
i
= 294.6 ± 5.9 (95% CI)
MSWD = 8.7
n =5 of 6
Matchan et al. 2016 Australian Journal of Earth Sciences 63/2 Supplementary Papers http://dx.doi.org/10.1080/08120099.2016.1156576
5

Citations
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Journal ArticleDOI
Abstract: Abstract The Newer Volcanics Province of SE Australia is a very large continental basaltic province, with an area of >23 000 km2, a dense rock equivalent volume of <900 km3 and >400 monogenetic volcanoes; it has been active since c. 8 Ma. Lava fields, shields, scoria cones are common, and there are >40 maars and volcanic complexes. Maars occur dominantly in the south where magmas erupted through Tertiary sedimentary aquifers, whereas in the north, over Palaeozoic crust, there are few. Complex interactions of the magma volatile content, magma ascent rates, conduit characteristics and the availability and depth of aquifers caused diverse eruption styles. Volcanoes commonly occur close to major crustal faults, which acted as magma conduits. There is no simple age pattern of volcanism across the province. Volcanism was probably triggered by transtensional decompression in the crust where fault sets intersect, affecting hot, hydrated mantle that had welled up through edge-driven convection where the base of the lithosphere thins abruptly at the edge of the continent. Rock compositions range from picritic to basaltic andesitic. Some volcanoes are polymagmatic. Regional geophysical datasets have clarified the regional characteristics of the province, whereas detailed ground magnetic and gravity surveys resulted in new insights into the subsurface structure of maar-diatremes.

25 citations


Cites background from "A new 40Ar/39Ar eruption age for th..."

  • ...…(McDougall et al. 1966; Aziz-ur-Rahman & McDougall 1972; Gray & McDougall 2009; Gouramanis et al. 2010; Matchan & Phillips 2011; Ismail et al. 2013; Matchan et al. 2016), and possibly as early as 7.8 Ma (Edwards et al. 2004), to about 5 ka (McDougall & Gill 1975; Blackburn 1966; Blackburn et al.…...

    [...]


Journal ArticleDOI
Abstract: Here we present 40Ar/39Ar ages of volcanic features in the Cenozoic intraplate Newer Volcanic Province in southeast Australia. The <5 Ma volcanic products in the Newer Volcanic Province can be subdivided into tholeiitic, valley-filling Newer Plains basalts, and alkaline scoria cones, lava shields, and maars of the Newer Cones series. Plateau ages range from 3.76 ± 0.01 to 4.32 ± 0.03 Ma (2σ; all sources of uncertainties included) for the Newer Plains series, with production rates of volcanism decreasing post 4 Ma. We suggest that magmatism is related to the complex interplay of magma upwelling due to edge-driven convection and the Cosgrove track mantle plume located in the northeast of the province at 6.5–5 Ma. Plateau ages range from 1290 ± 20 to 41.1 ± 2.2 ka (2σ) for the Newer Cones series, with a diffuse age progression in the onset of volcanism for these features from east to west. Analyses of the distribution and geomorphology of these volcanic features indicates a strong control of basement faults on volcanism, reflected in alignment of volcanic features along Paleozoic north-south oriented basement faults in the east and Cretaceous northwest-southeast oriented extensional features in the west. This age progression can be explained by a westerly migration of stress derived from the left-lateral strike-slip Tasman Fracture Zone. This suggests that the general mechanism of volcanism changed from upwelling due to plume-assisted edge-driven convection prior to ∼4 Ma to stress-dependent upwelling at around 1.3 Ma.

18 citations


Journal ArticleDOI
Abstract: Intraplate continental basaltic volcanic provinces (ICBVPs) occur on all continents and represent some of the most enigmatic volcanic systems. Constraints on the origin(s) and evolution of ICBVPs are predicated on detailed knowledge of eruption histories, which are often poorly quantified. Although the 40Ar/39Ar geochronology method has been applied successfully to lava flows, age determinations on scoria cones and maars are more challenging. In this study, we test the potential of entrained anorthoclase megacrysts to yield accurate 40Ar/39Ar ages for scoria cones and maars from the Pliocene-Holocene Newer Volcanic Province (NVP) of south-eastern Australia. The NVP is an ICBVP containing >400 eruption centres with ages spanning 4.6 Ma – 5 ka. K-Ar and 40Ar/39Ar age data exist for a large number of lava flows, but age constraints for scoria cones and maars that lack associated lavas are rare. High-precision 40Ar/39Ar step-heating data were measured on anorthoclase megacrysts from five eruption centres in the NVP. From youngest to oldest, anorthoclase xenocrysts from Mount Noorat (n = 3), Mount Leura (n = 2), Mount Shadwell (n = 3), and The Anakies East Cone (n = 2) yielded reproducible mean inverse isochron ages of 101.75 ± 0.96 ka (2σ), 165.4 ± 1.6 ka (2σ), 353.8 ± 1.9 ka (95% CI), and 2.178 ± 0.005 Ma (95% CI), respectively. In contrast, Lake Keilambete anorthoclase (n = 2) produced discordant age spectra and incongruous isochron/mini-isochron ages of 433.5 ± 7.2 ka (2σ) and 413.4 ± 4.5 ka (2σ). A single anorthoclase megacryst from Mount Franklin gave an age of 126.3 ± 7.2 ka (95% CI). By directly comparing megacryst age results with recently published, high-precision (

10 citations


Journal ArticleDOI
Abstract: Intraplate basaltic volcanism is one of the most common, yet poorly understood, types of volcanism. Intraplate continental basaltic volcanic provinces (ICBVPs) typically comprise tens to hundreds of usually monogenetic, small-volume eruption centres, often cumulatively producing significant volumes of mainly primitive basaltic magmas. A wide range of mechanisms have been invoked to account for ICBVP melt generation, ranging from deep mantle plumes to local tectonic perturbations of the lithospheric mantle. The key to understanding the cause(s) of intraplate volcanism is understanding the geochemical evolution of magmatism within a regional tectonic framework. Unfortunately, many ICBVPs contain complex arrays of overlying lava flows, with uncertain eruption sources and a lack of precise age constraints. The Newer Volcanic Province (NVP) in south-eastern Australia is a young (~4.6 Ma–5 ka), geochemically and volcanologically diverse ICBVP, comprising ≥416 volcanic centres covering an area of ~23,000 km2. As with other ICBVPs, elucidating the underlying controls on magmatism has proved contentious, with recent studies favouring edge-driven convection, but divided as to the changing nature of volcanism. At the eastern boundary of the NVP, in the Melbourne area, previous work has indicated a complex network of lava flows representing almost the entire age and geochemical range of the NVP, making this an ideal microcosm for studying the evolution of the NVP. In this study, a holistic approach to lava flow mapping is utilised to unravel the complex network, incorporating diagnostic petrography, geochemistry and precise 40Ar/39Ar geochronology. This work reveals seven major lava flows, here named the Tullamarine, Redstone Hill, Aitken Hill, Mount Kororoit, Fenton Hill, Tulloch Hill and Mount Fraser flows, along with eight smaller-volume flows, here named the Pretty Sally, Green Hill, Bald Hill, Mount Cooper, Mount Ridley, Crowe Hill, Springs Hill and Summerhill Road flows. 40Ar/39Ar ages for eleven lava flows and eruption centres span an age range of 7.9–0.8 Ma. These new data reveal that alkalic, small-volume eruptions in the Melbourne area occurred exclusively between ~8 and 3.8 Ma. Post ~3.8 Ma, large-volume, tholeiitic eruptions dominated. A local progression from alkalic to tholeiitic volcanism is contrary to a province-wide progression from tholeiitic to alkalic volcanism inferred by previous studies. The earliest four eruptions (ca. 8 Ma) were aligned with the Cosgrove hotspot track and are probably unrelated to the broader NVP. The ages and geochemical variations of the younger flows are consistent with melt generation due to edge-driven convection. Magma composition might have been controlled by local perturbations within the convective cell, with tholeiitic magmas generated during high-degree melting in regions of more intense upwelling, and alkalic melts reflecting lower-degree melting and less-intense upwelling. The episodic nature of volcanism is likely due to restricted magma transport to the surface, which was only possible during brief periods of favourable tectonic conditions.

1 citations


References
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Journal ArticleDOI
Abstract: On August 24, 1976 the IUGS Subcommission on Geochronology (FOOTNOTE 4) met in Sydney, Australia, during the 25th International Geological Congress. They unanimously agreed to recommend the adoption of a standard set of decay constants and isotopic abundances in isotope geology. Values have been selected, based on current information and usage, to provide for uniform international use in published communications. The Subcommission urges that all isotopic data be reported using the recommended values (see appendix). The recommendation represents a convention for the sole purpose of achieving interlaboratory standardization. The Subcommission does not intend to endorse specific methods of investigation or to specifically select the works of individual authors, institutions, or publications. All selected values are open to and should be the subjects of continuing critical scrutinizing and laboratory investigation. Recommendations will be reviewed by the Subcommission from time to time to bring the adopted conventional values in line with significant new research data.

9,109 citations


"A new 40Ar/39Ar eruption age for th..." refers methods in this paper

  • ...…sample NVP26 [0.0001070135 § 0.0000000648 (0.061%; 1s)] was calculated based on an age of 1.1811 § 0.0011 Ma (2s) for AC sanidine (Phillips et al. 2016) using the decay constants of Steiger and J€ager (1977) and the Lee et al. (2006) atmospheric argon composition [40Ar/36Ar D 298.56 § 0.62 (2s)]....

    [...]


01 Jan 2003

7,828 citations


"A new 40Ar/39Ar eruption age for th..." refers methods in this paper

  • ...Step-heating spectra and isochron plots were generated using ISOPLOT/ Ex v.3.75 (Ludwig, 2012)....

    [...]


Journal ArticleDOI
Abstract: Since the development of SIMS and LA-ICP-MS technologies in the 1980s and 1990s, single grain U–Pb dating of detrital zircon has quickly become the most popular technique for sedimentary provenance studies. Currently by far the most widespread method for visualising detrital age distributions is the so-called Probability Density Plot (PDP), which is calculated by summing a number of Gaussian distributions whose means and standard deviations correspond to the individual ages and their respective analytical uncertainties. Unfortunately, the PDP lacks a firm theoretical basis and can produce counter-intuitive results when data quantity (number of analyses) and/or quality (precision) is high. As a more robust alternative to the PDP, this paper proposes a standard statistical technique called Kernel Density Estimation (KDE), which also involves summing a set of Gaussian distributions, but does not explicitly take into account the analytical uncertainties. The Java-based DensityPlotter program ( http://densityplotter.london-geochron.com ) was developed with the aim to facilitate the adoption of KDE plots in the context of detrital geochronology.

915 citations


"A new 40Ar/39Ar eruption age for th..." refers background or methods in this paper

  • ...We suggest that a more meaningful approach may involve consideration of kernel density estimation (KDE, e.g. Vermeesch, 2012) in conjunction with a corresponding probability density plot (PDP)....

    [...]

  • ...A KDE gives essentially the same frequency summary information as a histogram, but is continuous and thus avoids the under-smoothing issues inherent to histograms (Vermeesch, 2012)....

    [...]


Journal ArticleDOI
Abstract: Atmospheric argon measured on a dynamically operated mass spectrometer with an ion source magnet, indicated systematically larger 40 Ar/ 36 Ar ratios compared to the generally accepted value of Nier [Nier A.O., 1950. A redetermination of the relative abundances of the isotopes of carbon, nitrogen, oxygen, argon, and potassium. Phys. Rev . 77 , 789–793], 295.5 ± 0.5, which has served as the standard for all isotopic measurements in geochemistry and cosmochemistry. Gravimetrically prepared mixtures of highly enriched 36 Ar and 40 Ar were utilized to redetermine the isotopic abundances of atmospheric Ar, using a dynamically operated isotope ratio mass spectrometer with minor modifications and special gas handling techniques to avoid fractionation. A new ratio 40 Ar/ 36 Ar = 298.56 ± 0.31 was obtained with a precision of 0.1%, approximately 1% higher than the previously accepted value. Combined with the 38 Ar/ 36 Ar (0.1885 ± 0.0003) measured with a VG5400 noble gas mass spectrometer in static operation, the percent abundances of 36 Ar, 38 Ar, and 40 Ar were determined to be 0.3336 ± 0.0004, 0.0629 ± 0.0001, and 99.6035 ± 0.0004, respectively. We calculate an atomic mass of Ar of 39.9478 ± 0.0002. Accurate Ar isotopic abundances are relevant in numerous applications, as the calibration of the mass spectrometer discrimination.

782 citations


"A new 40Ar/39Ar eruption age for th..." refers methods in this paper

  • ...…sample NVP26 [0.0001070135 § 0.0000000648 (0.061%; 1s)] was calculated based on an age of 1.1811 § 0.0011 Ma (2s) for AC sanidine (Phillips et al. 2016) using the decay constants of Steiger and J€ager (1977) and the Lee et al. (2006) atmospheric argon composition [40Ar/36Ar D 298.56 § 0.62 (2s)]....

    [...]

  • ...2016) using the decay constants of Steiger and J€ager (1977) and the Lee et al. (2006) atmospheric argon composition [(40)Ar/(36)Ar D 298....

    [...]


Book
01 Jan 1988
Abstract: 1. Historical introduction 2. Basis of the 40AR/39AR dating method 3. Technical aspects 4. 40AR/39AR data presentation and interpretation App.4.1 Isochron analysis 5. Diffusion theory and measurements: App.5.1 Derivation ofthe diffusion equation App.5.2 Separation of the variables solution for a plane sheet App.5.3 Translation to spherical coordinates App.5.4 Sample diffusion calculation 6. 40Ar/39Ar thermochronology App.6.1 Closure temperature of first-order loss 7. Application and case histories References

764 citations


"A new 40Ar/39Ar eruption age for th..." refers background in this paper

  • ...Plateau ages are defined as including >50% of the total 39Ar, from at least three contiguous steps, with 40Ar /39Ar ratios within error of the mean at the 95% confidence level (e.g. McDougall & Harrison, 1999)....

    [...]