Open File Report OF-AR-30
New Mexico Bureau of Geology and Mineral Resources
A division of
New Mexico Institute of Mining and Technology
40
Ar/39Ar Data Repository for Pliocene
volcanic rocks of the Tschicoma
formation, east-central Jemez volcanic
field: chemistry petrography, and age
constraints.
Prepared By:
David Broxton1, Giday Woldegabriel1, Lisa Peters2, James Budahn3,
Gary Luedemann1
1
Los Alamos National Laboratory, MS T003, PO Box 1663, Los Alamos, NM 87544
2
New Mexico Bureau of Geology, Socorro, NM 87801
3
U.S. Geological Survey, PO Box 25046, Federal Center, MS 974, Lakewood, CO 80225
Data Repository for:
New Mexico Geological
Society Guidebook
Fall 2007
SOCORRO 2007
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
Peter A. Scholle, Director and State Geologist
a division of
NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY
Daniel H. López, President
BOARD OF REGENTS
Ex Officio
Bil l Rich ardson, Governor of New Mexico
Michael J. Davis, Superintendent of Public Instruction
Appointed
Ann Murphy Da ily, President, 1999–2004, Santa Fe
Randall E. Horn, Secretary/Treasurer, 1997–2003, Albuquerque
S idney M. Gutierrez, 2001–2007, Albuquerque
Anthony L. Montoya, Jr., 2001–2003, Socorro
Robert E. Taylor, 1997–2003, Silver City
NEW MEXICO GEOCHRONOLOGY RESEARCH LABORATORY STAFF
W ILLIAM M C I NTOS H , Geochronologist
M ATT HEIZ LER , Geochronologist
LISA PETER S , Argon Laboratory Technician
R IC H A R D E S SER , Argon Laboratory Technician
BUREAU STAFF
BRUCE D. A LLEN, Field Geologist
RUBEN ARCHULETA, Metallurgical Lab. Technician II
VALENTINA AVRAMIDI, Business Office Manager
ALBERT BACA , Lead Maintenance Carpenter
RASIMA BAKHTIYAROVA, Manager of Geologic Information Center &
Publication Sales Office
JAMES M. B ARKER, Associate Director for Operations,
Senior Industrial Minerals Geologist
PAUL W. BAUER , Associate Director for Operations,
Senior Geologist
DOUG BLAND, Special Projects Manager
RON BROADHEAD, Principal Senior Petroleum Geologist
RITA CASE, Administrative Secretary II (Alb. Office)
STEVEN M. CATHER, Senior Field Geologist
RICHARD C HAMBERLIN, Senior Field Geologist
SEAN D. C ONNELL, Albuquerque Office Manager, Field Geologist
RUBEN A. CRESPIN, Manager, Fleet/General Services
GINA D’A MBROSIO, Production Editor
KELLY DONAHUE, Senior Geological Lab Associate
NELIAW. DUNBAR, Assistant Director for Laboratories,
Analytical Geochemist
RICHARD ESSER , Geochronology Lab. Technician
ROBERT W. E VELETH, Senior Mining Engineer
BARBARA F AZIO, Executive Secretary
BRIGITTE F ELIX K LUDT, GIS Technician
BONNIE FREY, Chemistry Lab. Manager
LEO O. G ABALDON, Cartographer II
LEWIS G ILLARD, GIS Technician
NANCY S. GILSON, Editor
KATHRYN E. G LESENER , Senior Cartographer
IBRAHIM G UNDILER, Senior Extractive Metallurgist
LYNN H EIZLER , Senior Lab. Associate
MATT H EIZLER, Geochronologist
LYNNE H EMENWAY, Geologic Information Center Coordinator
GRETCHEN K. H OFFMAN, Senior Coal Geologist
PEGGY S. J OHNSON, Senior Hydrogeologist
GLEN E. J ONES, Assistant Director for Computer/Internet Services
THOMAS J. KAUS , Cartographer II
SHARI A. K ELLEY, Geologist, Information Specialist
DANIEL K ONING , Field Geologist
LYNNE K URILOVITCH, Geologic Lab Associate
PHILIP KYLE, Research Scientist
LEWIS A. L AND, Hydrogeologist
ANNABELLE LOPEZ , Petroleum Information Coordinator
DAVID W. L OVE, Principal Senior Environmental Geologist
JANE A. CALVERT L OVE, Managing Editor
VIRGIL W. LUETH, Mineralogist/Economic Geologist,
Curator of Mineral Museum
MARK MANSELL, GIS Specialist
DAVID MCCRAW, GIS Cartographer
WILLIAM C. MCI NTOSH, Senior Volcanologist/Geochronologist
CHRISTOPHER G. MC K EE, X-ray Facility Manager
VIRGINIA T. MCL EMORE, Minerals Outreach Liaison,
Senior Economic Geologist
LISA P ETERS, Senior Lab. Associate
L. GREER PRICE, Associate Director for Outreach,
Senior Geologist/Chief Editor
JAMES Q UARLES, Lab Associate
GEOFF RAWLING, Field Geologist
ADAM S. READ, Senior Geological Lab. Associate
MARSHALL A. REITER, Principal Senior Geophysicist
GREGORY SANCHEZ, Mechanic-Carpenter Helper
MIKE SMITH, GIS Technician
MIKE TIMMONS, Manager, Geologic Mapping
STACY TIMMONS , Senior Geological Research Associate
LORETTA T OBIN, Admin. Services Coordinator
AMY TRIVITT-KRACKE, Petroleum Computer Specialist
MANUEL J. V ASQUEZ , Mechanic II
PATRICK W ALSH, Subsurface Fluid Geologist
SUSAN J. W ELCH, Manager, Geologic Extension Service
JENNIFER WHITEIS, GIS Technician
MAUREEN WILKS, Geologic Librarian
EMERITUS
G EOR GE S. A USTI N , Emeritus Senior Industrial Minerals Geologist
L Y N N B R A NDVOLD , Emeritus Senior Chemist
C H A R LES E. C HAPI N , Emeritus Director/State Geologist
J O H N W. H A WLE Y , Emeritus Senior Environmental Geologist
J ACQUES R. RE NAULT, Emeritus Senior Geologist
S A MUEL T H OMPSO N III, Emeritus Senior Petroleum Geologist
RO BE R T H. WE BE R , Emeritus Senior Geologist
Plus research associates, graduate students, and undergraduate assistants.
Table 1. 40Ar/39Ar analytical data.
ID
Power
40
Ar/39Ar
37
Ar/39Ar
36
Ar/39Ar
-3
(°C/watts)
(x 10 )
39
(x 10
ArK
-15
K/Ca
n=3
MSWD=0.24
n=3
MSWD=0.09
12.3
16.4
22.0
-11.0
-2.0
464.552 0.923±1.240
463.0
39
Ar
Age
±1σ
(%)
(Ma)
(Ma)
50.3
92.3
98.3
99.2
100.0
2.01
2.37
2.50
-0.59
-0.28
2.15
0.60
0.51
0.38
0.26
0.61
1.08
98.3
2.36
0.54
58.8
91.7
98.3
99.3
99.8
100.0
2.41
2.52
2.52
2.07
0.73
4.50
2.45
0.22
0.18
0.19
0.25
0.27
0.83
0.41
98.3
2.49
0.23
Lab#=520-01
SHB-1-694, 94:6, L#532, groundmass concentrate, J=0.0001625±0.18%, D=1±0.01, NMUM-6,
B
700
24.70
0.3949
55.77
277.1
1.3
C
800
21.87
0.9862
45.10
154.8
0.52
D
900
22.66
3.074
48.36
31.1
0.17
X E
1000
24.60
6.876
61.21
4.7
0.074
X F
1200
17.05
6.066
50.89
2.4
0.084
X G
1400
62.46
41.73
171.7
1.0
0.012
Integrated age ± 2σ
n=6
471.1
0.54
Plateau ± 2σ steps B-D
Ar*
(%)
mol)
SHB-1-656, 95:6, #520, groundmass concentrate, J=0.000167±0.18%, D=1±0.01, nmum-6,
B
700
54.48
0.3777
161.8
237.9
1.4
C
800
48.02
0.9788
136.0
198.3
0.52
D
900
37.75
3.708
100.6
28.4
0.14
X E
1000
17.82
4.106
67.92
4.2
0.12
X F
1200
46.63
6.084
162.5
3.9
0.084
Integrated age ± 2σ
n=5
472.7
0.56
Plateau ± 2σ steps B-D
40
0.96 ±1.15
Lab#=532-01
33.4
39.4
37.9
28.6
14.5
23.9
6-22-83-9; Tray B-2, 18.90 mg groundmass concentrate, J=0.0014959±0.11%, D=1.00683±0.00186, NM-127, Lab#=51441-01
B
4
1.514
0.1224
1.483
17.1
4.2
71.7
5.0
2.93
C
7
1.250
0.1498
0.2917
134.8
3.4
94.1
44.8
3.17
D
10
1.745
0.2381
2.163
98.7
2.1
64.5
74.0
3.03
E
12
1.420
0.3645
1.259
36.2
1.4
75.9
84.6
2.91
F
15
1.842
0.5036
2.758
20.1
1.0
58.0
90.6
2.88
G
20
2.814
0.6956
6.280
14.7
0.73
36.1
94.9
2.74
H
25
4.972
0.8449
13.82
6.9
0.60
19.3
96.9
2.59
I
30
8.425
0.8905
25.15
3.8
0.57
12.7
98.1
2.88
J
40
10.72
0.9995
33.87
4.4
0.51
7.4
99.4
2.14
K
50
24.96
1.371
79.88
2.1
0.37
5.9
100.0
3.96
Integrated age ± 2σ
n=10
338.8
1.8
K2O=4.60% 3.03
0.07
0.01
0.03
0.03
0.06
0.12
0.18
0.31
0.35
0.89
0.05
Plateau ± 2σ steps B-K
0.08
n=10
MSWD=12.69 338.8
2.5 ±2.7
100.0
3.09
6-22-83-12; Tray B-4, 18.90 mg groundmass concentrate, J=0.001493±0.11%, D=1.00683±0.00186, NM-127, Lab#=51443-01
X A
2
113.9
0.3247
387.0
0.2
1.6
-0.4
0.1
-1.30
X B
4
2.009
0.2604
3.799
10.3
2.0
45.2
3.1
2.44
C
7
1.327
0.2355
0.8165
73.7
2.2
83.3
24.6
2.98
D
10
1.367
0.2326
1.004
106.1
2.2
79.7
55.6
2.93
E
12
1.880
0.2743
2.923
62.0
1.9
55.3
73.7
2.80
F
15
2.842
0.3508
6.033
39.5
1.5
38.3
85.3
2.93
G
20
5.403
0.4901
14.92
28.1
1.0
19.2
93.5
2.79
X H
25
16.04
0.7099
51.98
11.1
0.72
4.6
96.7
2.00
X I
30
35.39
0.9094
115.8
4.7
0.56
3.5
98.1
3.33
X J
40
45.57
1.372
151.2
4.3
0.37
2.2
99.4
2.68
X K
50
117.5
2.953
398.6
2.1
0.17
0.0
100.0
-0.06
Integrated age ± 2σ
n=11
342.2
1.5
K2O=4.66% 2.84
Plateau ± 2σ steps C-G
n=5
MSWD=5.74
309.4
1.9 ±1.0
90.4
2.93
5.65
0.10
0.02
0.02
0.03
0.06
0.13
0.39
0.83
1.10
2.94
0.14
0.06
ID
Power
40
Ar/39Ar
37
Ar/39Ar
36
Ar/39Ar
-3
(°C/watts)
(x 10 )
39
(x 10
ArK
-15
K/Ca
40
Ar*
(%)
mol)
39
Ar
(%)
Age
(Ma)
10-8-90-2a; Tray B-6, 18.30 mg groundmass concentrate, J=0.0014948±0.11%, D=1.00683±0.00186, NM-127, Lab#=51445-01
X A
2
42.19
0.1810
142.7
0.8
2.8
0.1
0.4
0.12
X B
4
2.502
0.1976
7.494
14.7
2.6
12.1
7.1
0.82
C
7
2.387
0.3705
6.451
51.8
1.4
21.4
31.0
1.38
D
10
4.127
0.5743
12.13
55.1
0.89
14.3
56.3
1.59
E
12
6.635
0.5967
20.33
35.7
0.86
10.2
72.8
1.83
F
15
8.843
0.6722
27.91
23.6
0.76
7.4
83.6
1.76
G
20
11.72
0.7786
37.80
16.5
0.66
5.2
91.2
1.66
H
25
20.39
0.8910
67.09
9.2
0.57
3.1
95.4
1.71
I
30
36.33
0.9618
122.5
4.5
0.53
0.6
97.5
0.58
X J
40
55.59
1.164
190.3
3.3
0.44
-1.0
99.0
-1.50
X K
50
86.71
1.470
290.6
2.1
0.35
1.1
100.0
2.55
Integrated age ± 2σ
n=11
217.3
0.90
K2O=3.05% 1.49
Plateau ± 2σ
steps C-I
n=7
MSWD=2.04
196.4
1.0 ±0.6
90.4
1.50
6-22-83-3; Tray H-4, 18.25 mg groundmass concentrate, J=0.0014841±0.11%, D=1.00683±0.00186, NM-127, Lab#=51509-01
X A
2
26.84
0.5853
93.65
0.3
0.87
-2.9
0.1
-2.09
B
4
1.648
0.2459
1.667
14.0
2.1
71.4
5.3
3.15
C
7
1.424
0.2527
0.9060
84.7
2.0
82.7
36.4
3.15
D
10
1.705
0.3157
2.147
80.5
1.6
64.3
66.0
2.93
E
12
2.922
0.4173
6.451
36.0
1.2
35.9
79.2
2.81
F
15
5.201
0.5006
13.99
21.9
1.0
21.3
87.3
2.97
X G
20
8.954
0.6373
27.70
18.0
0.80
9.2
93.9
2.20
X H
25
21.12
1.153
69.36
9.4
0.44
3.4
97.3
1.94
X I
30
54.25
1.300
185.8
3.3
0.39
-1.0
98.5
-1.48
X J
40
88.23
2.278
299.5
2.5
0.22
-0.1
99.5
-0.20
X K
50
158.1
2.755
537.1
1.5
0.19
-0.2 100.0
-1.05
Integrated age ± 2σ
n=11
272.1
1.2
K2O=3.86% 2.81
Plateau ± 2σ steps B-F
X
X
X
X
X
n=5
MSWD=15.38 237.2
1.7 ±0.9
6-22-83-5, D4:127, 18.29mg hornblende J=0.0014991±0.11%, D=1.00683±0.00186, NM-127,
A
2
371.3
2.216
1180.8
0.1
0.23
B
4
20.86
1.161
61.31
0.6
0.44
C
7
2.743
0.8869
4.336
2.9
0.58
D
10
2.265
0.8873
3.271
2.8
0.58
E
12
4.698
1.172
10.44
1.4
0.44
F
15
4.123
2.198
10.18
1.2
0.23
G
20
6.244
6.499
19.24
2.7
0.079
H
25
4.786
7.844
14.22
7.3
0.065
I
30
5.431
8.058
16.42
12.1
0.063
J
40
4.625
8.183
13.78
16.8
0.062
K
50
4.434
8.649
13.00
3.3
0.059
L
50
13.65
9.366
45.55
0.5
0.054
Integrated age ± 2σ
n=12
51.7
0.075
Plateau ± 2σ steps F-L
n=7
MSWD=0.34
43.9
87.2
±1σ
(Ma)
1.86
0.11
0.06
0.09
0.16
0.21
0.26
0.46
0.88
1.40
2.05
0.32
0.13
3.12
0.07
0.02
0.03
0.06
0.13
0.22
0.49
1.31
2.09
3.83
0.19
3.07
0.11
60.07
7.66
4.15
3.71
4.62
3.51
2.98
3.36
Horn
3.35
3.56
2.63
3.59
18.68
1.57
0.24
0.21
0.50
0.52
0.34
0.20
0.18
0.14
0.31
1.37
0.26
3.35
0.17
Lab#=51455-01
0.07 ±0.13
6.1
0.1
13.6
1.4
56.0
7.0
60.6
12.4
36.4
15.1
31.4
17.4
17.6
22.6
25.8
36.8
22.9
60.1
26.6
92.7
29.5
99.0
7.1
100.0
K2O=0.72%
84.9
ID
Power
40
Ar/39Ar
37
Ar/39Ar
Ar/39Ar
-3
(°C/watts)
X
X
X
X
36
(x 10 )
39
(x 10
ArK
-15
K/Ca
40
(%)
mol)
10-8-90-4, D6:127, 17.27mg hornblende, J=0.0014987±0.11%, D=1.00683±0.00186, NM-127,
A
2
386.4
2.983
1275.6
0.0
0.17
B
4
16.67
1.470
61.04
0.6
0.35
C
7
3.620
0.3685
9.812
2.3
1.4
D
10
3.954
0.3650
9.305
2.1
1.4
E
12
6.564
0.6204
16.54
1.0
0.82
F
15
10.52
2.014
28.38
0.7
0.25
G
20
5.384
7.967
14.89
2.8
0.064
H
25
5.075
8.683
13.59
4.9
0.059
I
30
4.869
9.255
12.90
5.9
0.055
J
40
2.979
9.715
7.203
22.6
0.053
K
50
7.847
10.76
23.87
5.4
0.047
L
50
50.35
13.63
169.8
0.3
0.037
Integrated age ± 2σ
n=12
48.6
0.061
Plateau ± 2σ steps E-L
n=8
MSWD=1.27
43.7
n=10
MSWD=2.71
183.4
39
Ar
(%)
Age
(Ma)
(Ma)
2.5
0.1
-7.5
1.3
20.7
6.0
31.2
10.2
26.3
12.3
21.9
13.8
30.5
19.5
35.0
29.6
37.4
41.8
55.5
88.2
21.5
99.3
2.6
100.0
K2O=0.72%
26.03
-3.37
2.03
3.33
4.67
6.23
4.47
4.83
4.96
4.51
4.59
3.60
4.38
22.34
1.49
0.36
0.33
0.65
1.01
0.35
0.20
0.17
0.10
0.29
3.30
0.25
89.8
4.66
0.17
1.79
2.93
3.34
3.12
3.25
3.19
2.73
2.86
2.72
2.72
2.91
1.29
0.12
0.10
0.11
0.14
0.16
0.14
0.17
0.19
0.28
0.33
3.06
0.15
Lab#=51454-01
2.7 ±0.7
1.0
5.2
19.3
16.2
28.9
26.9
25.5
36.5
22.2
45.7
17.4
54.4
14.2
65.0
14.3
78.5
11.4
91.9
8.1
100.0
K2O=3.85%
100.0
7-1-83-1; Tray B-3, 17.80 mg groundmass concentrate, J=0.0014943±0.11%, D=1.00683±0.00186, NM-127, Lab#=51442-01
X B
4
28.48
0.8003
88.33
2.8
0.64
8.6
1.3
6.58
C
7
5.825
0.7707
8.945
24.2
0.66
55.7
12.1
8.73
D
10
3.911
0.7791
2.443
53.6
0.65
83.2
36.1
8.76
E
12
3.944
0.6140
2.429
41.2
0.83
83.1
54.4
8.82
F
15
4.278
0.5803
3.877
33.9
0.88
74.3
69.6
8.56
G
20
4.982
0.6164
6.159
31.4
0.83
64.5
83.6
8.65
H
25
7.283
0.7187
14.07
16.2
0.71
43.7
90.9
8.57
I
30
10.75
0.8129
26.65
6.7
0.63
27.4
93.9
7.91
J
40
11.07
1.595
26.58
8.5
0.32
30.3
97.6
9.02
K
50
16.02
2.489
45.01
5.3
0.21
18.3 100.0
7.90
Integrated age ± 2σ
n=11
223.9
0.67
K2O=3.23% 8.57
Plateau ± 2σ steps C-K
n=9
MSWD=3.54
221.0
±1σ
Lab#=51457-01
0.07 ±0.54
8-21-88-1, D3:127, 12.19mg biotite, J=0.0014989±0.11%, D=1.00338±0.00158, NM-127,
A
10
69.13
0.2017
231.8
9.6
2.5
B
14
5.620
0.1919
15.40
20.1
2.7
C
18
4.283
0.1693
10.35
19.5
3.0
D
22
4.532
0.1825
11.48
17.7
2.8
E
26
5.425
0.1722
14.33
16.9
3.0
F
30
6.796
0.1800
19.05
15.8
2.8
G
35
7.120
0.1770
20.72
19.5
2.9
H
40
7.410
0.1763
21.54
24.8
2.9
I
45
8.819
0.2537
26.52
24.5
2.0
J
50
12.47
0.2501
38.87
14.9
2.0
Integrated age ± 2σ
n=10
183.4
2.6
Plateau ± 2σ steps A-J
Ar*
0.73 ±0.46
98.7
8.71
0.83
0.10
0.04
0.05
0.06
0.08
0.15
0.26
0.30
0.41
0.23
0.10
ID
Power
40
Ar/39Ar
37
Ar/39Ar
36
Ar/39Ar
-3
(°C/watts)
(x 10 )
39
(x 10
ArK
-15
K/Ca
40
Ar*
(%)
mol)
39
Ar
(%)
Age
(Ma)
R22 628-638, J2:144, 28.16 mg groundmass concentrate, J=0.0007448±0.10%, D=1.00535±0.00031, NM-144, Lab#=52725-01
X A
625
94.71
0.1484
317.3
1.6
3.4
1.0
2.9
1.30
X B
700
4.307
0.2259
10.42
17.1
2.3
28.9
34.0
1.67
X C
750
4.897
0.3439
11.08
13.5
1.5
33.7
58.6
2.22
D
800
5.358
0.6888
12.39
11.4
0.74
32.7
79.4
2.35
E
875
6.372
1.269
15.51
6.8
0.40
29.7
91.7
2.55
F
975
13.97
1.983
41.84
2.4
0.26
12.7
96.1
2.39
G
1075
17.80
2.016
52.97
0.6
0.25
13.0
97.2
3.11
H
1250
41.34
2.321
130.7
0.6
0.22
7.0
98.3
3.90
I
1700
28.68
7.923
93.48
0.9
0.064
6.0
100.0
2.32
Integrated age ± 2σ
n=9
55.0
0.70
K2O=1.01% 2.13
Plateau ± 2σ
steps D-I
CDV-15, J4:144, 28.04 mg groundmass concentrate, J=0.0007455±0.10%, D=1.00535±0.00031, NM-144, Lab#=52727-01
X A
625
4057.8
1.334
13711.6
0.8
0.38
0.2
0.4
8.29
X B
700
43.39
0.7601
139.1
10.0
0.67
5.4
5.9
3.16
C
750
11.57
0.5880
33.49
14.8
0.87
14.9
14.0
2.32
D
800
9.064
0.5538
24.63
28.6
0.92
20.2
29.6
2.46
E
875
13.07
0.4773
37.94
48.0
1.1
14.5
55.8
2.56
F
975
10.23
0.5320
28.40
45.2
0.96
18.4
80.5
2.54
G
1075
10.52
0.5570
29.03
17.8
0.92
18.9
90.2
2.68
X H
1250
22.38
5.004
71.83
10.2
0.10
7.0
95.7
2.11
X I
1700
29.93
10.83
100.1
7.8
0.047
4.2
100.0
1.69
Integrated age ± 2σ
n=9
183.3
0.41
K2O=3.37% 2.52
14.97
0.27
0.11
0.08
0.09
0.06
0.12
0.22
0.27
0.17
X
X
X
X
MSWD=1.49
22.8
154.5
0.53 ±0.46
0.97 ±0.15
5/25/83-1, D15:144, 26.95 mg hornblende, J=0.0007765±0.10%, D=1.00712±0.00131, NM-144,
A
800
309.4
1.962
1030.7
0.9
0.26
B
900
66.33
3.829
208.3
0.3
0.13
C
1000
51.33
4.320
167.1
0.4
0.12
D
1030
34.52
4.286
108.3
0.4
0.12
E
1060
14.48
6.887
40.31
1.0
0.074
F
1090
14.03
8.212
39.77
2.4
0.062
G
1120
10.93
8.271
30.48
5.8
0.062
H
1170
13.18
8.298
38.77
8.0
0.061
I
1200
5.717
9.310
11.29
3.7
0.055
J
1250
13.83
10.10
21.04
0.5
0.051
K
1300
97.51
23.16
204.5
0.0
0.022
L
1650
105.0
71.30
241.8
0.1
0.007
Integrated age ± 2σ
n=12
23.5
0.061
Plateau ± 2σ steps A-H
n=8
MSWD=2.06
19.1
41.4
0.66
0.04
0.05
0.06
0.09
0.20
0.56
0.76
0.52
0.07
0.12
n=5
MSWD=1.70
(Ma)
2.42
Plateau ± 2σ steps C-G
n=6
±1σ
84.3
2.51
0.09
6.91
7.16
3.24
4.04
4.42
4.16
3.67
3.39
4.44
11.88
54.68
57.31
4.46
2.85
1.96
1.25
0.99
0.42
0.28
0.18
0.15
0.13
0.68
10.45
3.97
0.40
3.67
0.29
Lab#=52692-01
0.075±0.134
1.6
3.8
7.7
4.9
4.5
6.8
8.3
8.7
21.7
12.8
21.1
23.0
23.9
47.6
18.3
81.5
55.1
97.1
61.1
99.4
40.0
99.5
37.6 100.0
K2O=0.43%
81.5
ID
Power
40
Ar/39Ar
37
Ar/39Ar
36
Ar/39Ar
-3
(°C/watts)
(x 10 )
39
(x 10
ArK
-15
K/Ca
40
Ar*
(%)
mol)
5-25-83-2, hornblende, J=0.0010539±0.10%, D=1.0063±0.001, NM-182L, Lab#=55193-01
X A
800
442.9
1.667
1493.3
0.331
0.31
X B
940
22.74
1.272
53.44
0.416
0.40
X C
1000
14.84
1.276
61.18
0.113
0.40
D
1120
10.07
4.455
30.94
1.53
0.11
E
1150
3.702
7.951
9.135
3.98
0.064
F
1180
3.930
8.083
10.33
3.37
0.063
G
1190
5.182
8.017
14.71
1.99
0.064
H
1220
4.058
8.310
10.50
2.50
0.061
I
1300
4.043
8.444
9.936
5.77
0.060
J
1650
109.4
9.243
366.1
0.317
0.055
Integrated age ± 2σ
n=10
20.3
0.07 ±0.04
39
Ar
(%)
(Ma)
±1σ
(Ma)
3.33
13.37
-5.97
2.46
3.17
2.95
2.86
3.14
3.45
3.71
3.21
5.46
1.28
3.59
0.34
0.15
0.16
0.26
0.17
0.11
2.01
0.29
95.8
3.18
0.20
CDV-16-3(i), Groundmass Concentrate, J=0.0010571±0.08%, D=1.0063±0.001, NM-182K, Lab#=55182-01
A
625
817.1
0.7261
2689.5
2.41
0.70
2.7
0.5
B
700
2.729
0.4691
4.330
35.5
1.1
54.5
7.7
C
750
1.925
0.4058
1.185
20.4
1.3
83.6
11.8
D
800
1.718
0.3968
0.6702
100.3
1.3
90.4
32.1
E
875
1.637
0.3715
0.5045
145.2
1.4
92.8
61.5
F
975
1.648
0.4700
0.6183
136.0
1.1
91.3
89.1
G
1075
2.163
0.9623
2.403
28.6
0.53
70.9
94.9
X H
1250
4.199
3.814
9.348
10.1
0.13
41.7
96.9
X I
1700
5.825
4.966
11.54
15.1
0.10
48.5 100.0
Integrated age ± 2σ
n=9
493.7
1.00 ±0.86
42.28
2.84
3.07
2.96
2.90
2.87
2.92
3.35
5.40
3.18
6.40
0.03
0.04
0.01
0.01
0.01
0.03
0.08
0.07
0.08
2.88
0.02
Plateau ± 2σ
steps D-J
n=7
MSWD=2.28
19.5
0.07 ±0.04
0.4
1.6
31.0
3.7
-21.1
4.2
12.8
11.8
44.9
31.4
39.4
47.9
28.9
57.7
40.5
70.0
44.7
98.4
1.8
100.0
K2O=0.40%
Age
X
X
X
X
Plateau ± 2σ steps E-G
n=3
MSWD=4.46
309.9
1.00 ±0.86
62.8
ID
Power
40
Ar/39Ar
37
Ar/39Ar
Ar/39Ar
-3
(°C/watts)
X
X
X
X
36
(x 10 )
39
(x 10
n=6
MSWD=0.81
Isochron±2σ
n=10
MSWD=2.3
steps A-I
40
Ar*
(%)
mol)
R8 95-951, plagioclase, J=0.0011782±0.08%, D=1.0063±0.001, NM-182K,
A
700
32.35
3.708
92.53
0.79
B
850
1.292
1.898
1.577
8.6
C
925
1.248
1.778
1.380
5.32
D
1000
1.053
1.777
0.9695
20.5
E
1100
1.012
1.761
0.6464
33.2
F
1175
1.085
1.662
0.7944
17.3
G
1250
0.9860
1.643
0.5864
11.1
H
1350
1.271
1.654
1.512
4.97
I
1450
1.449
1.734
2.148
15.6
J
1750
1.437
1.801
2.020
32.4
Integrated age ± 2σ
n=10
149.8
Plateau ± 2σ steps E-J
K/Ca
ArK
-15
39
Ar
(%)
Age
(Ma)
±1σ
(Ma)
Lab#=55180-01
0.14
0.27
0.29
0.29
0.29
0.31
0.31
0.31
0.29
0.28
0.30 ±0.02
114.6
40
16.4
0.5
76.1
6.3
79.1
9.8
86.8
23.5
95.5
45.7
91.0
57.2
96.2
64.7
75.6
68.0
66.1
78.4
68.8 100.0
K2O=0.71%
0.30 ±0.02
Ar/36Ar=339±15
76.5
11.29
2.09
2.10
1.94
2.06
2.10
2.02
2.04
2.04
2.10
2.05
0.85
0.07
0.11
0.03
0.02
0.04
0.05
0.13
0.05
0.03
0.04
2.07
0.03
1.99
0.05
Notes:
Isotopic ratios corrected for blank, radioactive decay, and mass discrimination, not corrected for interfering reactions.
Errors quoted for individual analyses include analytical error only, without interfering reaction or J uncertainties.
Integrated age calculated by summing isotopic measurements of all steps.
Integrated age error calculated by quadratically combining errors of isotopic measurements of all steps.
Plateau age is inverse-variance-weighted mean of selected steps.
Plateau age error is inverse-variance-weighted mean error (Taylor, 1982) times root MSWD where MSWD>1.
Plateau error is weighted error of Taylor (1982).
Decay constants and isotopic abundances after Steiger and Jäger (1977).
X symbol preceding sample ID denotes analyses excluded from plateau age calculations.
Weight percent K2O calculated from 39Ar signal, sample weight, and instrument sensitivity.
Ages calculated relative to FC-2 Fish Canyon Tuff sanidine interlaboratory standard at 28.02 Ma
Decay Constant (LambdaK (total)) = 5.543e-10/a
Table 2. 40Ar/39Ar analytical data.
ID
40
Ar/39Ar
37
Ar/39Ar
36
Ar/39Ar
-3
(x 10 )
X
X
X
X
X
39
(x 10
ArK
-15
K/Ca
mol)
40
Ar*
(%)
11-19-84-1, A13:144, single xtal san, J=0.0007667±0.10%, D=1.00535±0.00031, NM-144, Lab#=52642
05
3.718
0.0091
0.2720
15.765
56.2
97.9
06
3.746
0.0162
0.3371
15.038
31.5
97.4
04
4.025
0.0229
1.279
10.975
22.3
90.7
02
3.801
0.0132
0.5125
7.173
38.8
96.0
03
3.752
0.0199
0.1292
6.531
25.7
99.0
01
21.40
0.0327
7.524
0.109
15.6
89.6
Mean age ± 2σ
n=5
MSWD=1.80
34.9 ±26.9
Age
(Ma)
±1σ
(Ma)
5.03
5.04
5.04
5.04
5.13
26.33
5.04
0.02
0.02
0.03
0.04
0.04
2.31
0.03
DEB 10-91-7, D1 :127, single crystal sanidine, J=0.0014978±0.11%, D=1.00827±0.00148, NM-127, Lab#=51452
13
1.986
0.0066
0.1103
7.837
77.2
98.4
5.27
04
1.988
0.0067
0.0748
27.045
76.3
98.9
5.31
02
2.020
0.0075
0.1551
27.704
68.2
97.8
5.33
15
2.000
0.0077
0.0556
19.574
65.9
99.2
5.35
01
2.035
0.0070
0.1720
16.144
72.7
97.5
5.35
03
2.018
0.0104
0.1157
16.817
49.1
98.4
5.36
09
1.984
0.0070
-0.0040
22.925
73.4
100.1
5.36
05
1.986
0.0072
-0.0076
16.923
71.2
100.1
5.37
14
2.086
0.0071
0.3296
11.598
71.8
95.4
5.37
07
2.009
0.0064
0.0675
35.931
79.5
99.0
5.37
08
2.031
0.0071
0.0796
10.171
71.4
98.9
5.42
11
2.088
0.0071
0.2610
8.982
71.5
96.3
5.43
12
2.012
0.0064
-0.0004
12.352
80.1
100.0
5.43
10
2.007
0.0066
-0.0332
7.432
77.5
100.5
5.44
06
14.05
-0.0648
3.504
0.026
92.6
34.81
Mean age ± 2σ
n=15
MSWD=3.58
71.8 ±14.9
5.36
0.04
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.03
0.01
0.03
0.03
0.02
0.04
10.47
0.02
R25 1922-1923, sanidine, J=0.0011661±0.09%, D=1.0064±0.0005, NM-182L, Lab#=55188
04
2.680
1.328
4.940
0.207
0.38
06
2.417
0.0092
0.3124
1.861
55.2
05
2.419
0.0073
0.2349
1.980
69.5
14
2.478
0.0075
0.3412
3.518
68.1
07
2.419
0.0077
0.1238
7.099
66.6
08
2.601
0.0071
0.7172
2.648
71.7
02
2.438
0.0070
0.1538
4.404
73.3
09
2.405
0.0076
0.0237
3.829
67.6
03
2.402
0.0068
0.0141
6.754
75.3
15
2.409
0.0073
0.0080
4.921
70.0
13
2.450
0.0065
0.0359
2.008
78.8
12
2.174
1.254
-0.6888
0.192
0.41
10
2.456
0.0065
-0.5997
1.657
78.5
11
20.20
0.0673
56.88
0.022
7.6
Mean age ± 2σ
n=10
MSWD=0.69
69.6 ±12.6
0.83
0.10
0.10
0.05
0.03
0.07
0.04
0.05
0.03
0.04
0.08
0.85
0.11
7.87
0.03
49.6
96.2
97.2
96.0
98.5
91.9
98.2
99.7
99.8
99.9
99.6
114.1
107.2
16.8
2.80
4.89
4.94
5.00
5.01
5.02
5.03
5.04
5.04
5.06
5.13
5.22
5.53
7.13
5.03
ID
40
Ar/39Ar
37
Ar/39Ar
36
Ar/39Ar
-3
(x 10 )
39
(x 10
ArK
-15
mol)
K/Ca
40
Ar*
(%)
Age
(Ma)
±1σ
(Ma)
LAPC-98-13, A15:144, single crystal sanidine, J=0.0007666±0.10%, D=1.00535±0.00031, NM-144, Lab#=52644
07
3.950
0.0222
1.550
8.879
23.0
88.5
4.82
01
3.895
0.0088
1.302
37.202
58.3
90.1
4.85
14
4.804
0.0126
4.360
28.960
40.6
73.2
4.86
05
3.847
0.0087
1.093
30.949
58.9
91.6
4.87
06
3.834
0.0074
0.9560
37.015
69.1
92.7
4.91
02
4.230
0.0105
2.261
27.914
48.5
84.2
4.92
13
3.826
0.0082
0.8500
40.510
62.2
93.5
4.94
11
3.910
0.0067
1.001
35.555
76.0
92.5
4.99
15
3.886
0.0075
0.8930
44.149
67.9
93.2
5.00
04
3.764
0.0066
0.4530
51.828
77.4
96.5
5.01
03
4.344
0.0078
2.339
59.751
65.2
84.1
5.05
10
3.968
0.0118
0.9620
53.040
43.4
92.9
5.09
16
4.326
0.0092
2.110
20.782
55.8
85.6
5.11
12
3.971
0.0065
0.8910
50.279
78.6
93.4
5.12
Mean age ± 2σ
n=14
MSWD=7.33
58.9 ±31.6
4.98
Notes:
Isotopic ratios corrected for blank, radioactive decay, and mass discrimination, not corrected for interfering reactions.
Errors quoted for individual analyses include analytical error only, without interfering reaction or J uncertainties.
Mean age is weighted mean age of Taylor (1982). Mean age error is weighted error
of the mean (Taylor, 1982), multiplied by the root of the MSWD where MSWD>1, and also
incorporates uncertainty in J factors and irradiation correction uncertainties.
Decay constants and isotopic abundances after Steiger and Jäger (1977).
# symbol preceding sample ID denotes analyses excluded from mean age calculations.
Ages calculated relative to FC-2 Fish Canyon Tuff sanidine interlaboratory standard at 28.02 Ma
Decay Constant (LambdaK (total)) = 5.543e-10/a
0.18
0.03
0.07
0.03
0.03
0.04
0.04
0.05
0.04
0.02
0.02
0.03
0.05
0.03
0.05
% Radiogenic
SHB-1-656 Groundmass Concentrate
40
20
0
1.5
0.5
5
0
Apparent Age Ma
4
2.36 ± 0.54 Ma (MSWD = 0.24)
3
2
900
D
800
C
1
F
700
B
Integrated Age = 2.2 ± 1.1 Ma
0
0
10
20
30
40
50
60
70
80
90
0.07
0.08
0.09
Cumulative %39Ar Released
0.0040
E
0.0035
F
B
0.0030
C
D
36Ar/40Ar
0.0025
0.0020
0.0015
0.0010
0.0005
Isochron age = 3.21 ± 2.52 Ma
270 ± 60
MSWD = 0.07, n = 3
40Ar/36Ar Intercept =
0
0
0.01
0.02
0.03
0.04
0.05
39Ar/40Ar
0.06
100
K/Ca
1.0
% Radiogenic
SHB-1-694 Groundmass Concentrate
40
20
5
Apparent Age Ma
4
2.49 ± 0.23 Ma* (MSWD = 0.09)
3
G
2
800
C
700
B
900
D
F
E
1
2.45 ± 0.41 Ma*
0
0
10
20
30
40
50
60
70
80
0.07
0.08
90
100
Cumulative %39Ar Released
0.0040
0.0035
0.0030
F
G
36Ar/40Ar
0.0025
E
B
D
C
0.0020
0.0015
0.0010
0.0005
Isochron age = 3.01±2.24 Ma
40Ar/36Ar Intercept = 260 ± 160
MSWD = 0.016, n = 3
0
0
0.01
0.02
0.03
0.04
0.05
39Ar/40Ar
0.06
0.09
0.10
K/Ca
1.5
1.0
0.5
0
-0.5
0
% Radiogenic
6-22-83-9 Groundmass Concentrate
100
50
0
4
0
5
3.09 ± 0.08 Ma* (MSWD = 12.69)
Apparent Age Ma
4
3
7
C
4
B
10
D
12
E
15
F
20
G 2530
50
HIK
2
40
J
1
Integrated Age = 3.03 ± 0.06 Ma
0
0
10
20
30
40
50
60
70
80
90
100
Cumulative %39Ar Released
0.0040
0.0035
A
K
J
0.0030
I
H
36Ar/40Ar
0.0025
G
0.0020
0.0015
F
D
0.0010
B
E
0.0005
Isochron age = 3.12 ± 0.25 Ma
40Ar/36Ar Intercept = 285 ± 39
MSWD = 10, n = 10
C
0
0
0.1
0.2
0.3
0.4
0.5
39Ar/40Ar
0.6
0.7
0.8
0.9
K/Ca
2
% Radiogenic
6-22-83-12 Groundmass Concentrate
100
50
0
2.0
0
5
2.93 ± 0.06 Ma* (MSWD = 5.74)
Apparent Age Ma
4
3
7
C
10
D
15
F
12
E
20
G
4
B
2
30
I
25
H
1
40
J
Integrated Age = 2.84 ± 0.14 Ma
0
0
10
20
30
40
50
60
70
39
Cumulative % Ar Released
80
90
100
0.0040
0.0035
AK
J
I
H
0.0030
G
36Ar/40Ar
0.0025
F
0.0020
B
E
0.0015
0.0010
D
C
0.0005
Isochron age = 2.94 ± 0.08 Ma
40Ar/36Ar Intercept = 292 ±8.1
MSWD = 3.4, n = 9
0
0
0.1
0.2
0.3
0.4
0.5
39Ar/40Ar
0.6
0.7
0.8
0.9
K/Ca
1.0
10-8-90-2a Groundmass Concentrate
40
20
0
4
3
2
1
0
5
2
A
4
3
1.50 ± 0.13 Ma* (MSWD = 2.04)
30
I
2
1
4
B
0
12
E
10
D
7
C
15
F
20
G
25
H
Integrated Age = 1.49 ± 0.32 Ma
0
10
20
30
40
50
60
70
80
90
100
Cumulative %39Ar Released
0.0040
0.0035
J
K
A
I
HG
F
0.0030
E
D
B
C
0.0025
0.0020
0.0015
0.0010
0.0005
Isochron age = 1.48 ± 0.29 Ma
40Ar/36Ar Intercept = 296.2 ± 5.9
MSWD = 2.4, n = 9
0
0
0.2
0.4
0.6
0.8
1.0
39Ar/40Ar
1.2
1.4
1.6
1.8
% Radiogenic
6-22-83-3 Groundmass Concentrate
100
50
0
2.0
5
0
40
J
Apparent Age Ma
4
3.07 ± 0.11 Ma* (MSWD = 15.38)
3
7
C
4
B
10
D
12
E
15
F
2
20
G
1
25
H
Integrated Age = 2.81 ± 0.19 Ma
0
0
10
20
30
40
50
60
70
80
90
100
0.8
0.9
Cumulative %39Ar Released
0.0040
K I A
H
J
0.0035
G
0.0030
F
0.0025
36Ar/40Ar
E
0.0020
0.0015
D
0.0010
B
0.0005
C
Isochron age = 3.11 ± 0.19 Ma
40Ar/36Ar Intercept = 288 ± 14
MSWD = 5.8, n = 11
0
0
0.1
0.2
0.3
0.4
0.5
39Ar/40Ar
0.6
0.7
K/Ca
1.0
% Radiogenic
6-22-83-5 Hornblende
100
50
0
10
Apparent Age Ma
8
3.35 ± 0.17 Ma* (MSWD = 0.34)
6
4
B
4
7
C
12
E
10
D
2
40
J
30
I
25
H
15 20
F G
50
K
Integrated Age = 3.59 ± 0.26 Ma
0
0
10
20
30
40
50
60
70
80
90
100
Cumulative %39Ar Released
0.0040
0.0035
A
0.0030
L
B
G
I H
36Ar/40Ar
0.0025
JK
F
E
0.0020
0.0015
C
D
0.0010
0.0005
Isochron age = 3.36 ± 0.72 Ma
40Ar/36Ar Intercept = 301 ± 26
MSWD = 3.2, n = 12
0
0
0.1
0.2
0.3
0.4
39Ar/40Ar
0.5
0.6
0.7
0.8
K/Ca
0.8
0.6
0.4
0.2
0
% Radiogenic
10-8-90-4 Hornblende
80
40
1.5
1.0
0.5
0
-0.5
0
K/Ca
10
Apparent Age Ma
4.66 ± 0.17 Ma (MSWD = 1.27)
8
6
4
10
D
2
30
I
25
H
15
F 20
12
G
E
7
C
50
K
Integrated Age = 4.38 ± 0.25 Ma
0
0
40
J
10
20
30
40
50
60
70
80
90
100
Cumulative %39Ar Released
0.0040
B
0.0035
A L
0.0030
F
36Ar/40Ar
0.0025
K
C
E
G
H
D
I
0.0020
J
0.0015
0.0010
0.0005
Isochron age = 4.54 ± 0.32 Ma
40Ar/36Ar Intercept = 301 ± 10
MSWD = 1.2, n = 8
0
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
39Ar/40Ar
0.40
0.45
0.50
0.55
0.60
8-21-88-1 Biotite
40
20
0
3.5
3.0
2.5
5
10
A
2.0
1.5
3.06 ± 0.15 Ma* (MS WD = 2.71)
4
3
18
C
26
E
22
D
14
B
30
F
2
40
H
35
G
45
I
50
J
1
Integrated Age = 2.91 ± 0.33 Ma
0
0
10
20
30
40
50
60
70
39
Cumulative % Ar Released
80
90
100
0.0040
0.0035
A
J
I H
0.0030
F
G
B
E
0.0025
D
C
0.0020
0.0015
0.0010
Isochron age = 3.29 ± 0.33 Ma
40Ar/36Ar Intercept = 290.3 ± 6.6
0.0005
MSWD = 1.9, n = 10
0
0
0.1
0.2
0.3
0.4
0.5
39Ar/40Ar
0.6
0.7
0.8
% Radiogenic
7-1-83-1Groundmass Concentrate
100
50
0
0.8
0
10.0
8.71 ± 0.10 Ma* (MSWD = 3.54)
9.5
Apparent Age Ma
9.0
8.5
12
E
10
D
7
C
20
G
15
F
8.0
40
J
25
H
7.5
30
I
7.0
50
K
6.5
Integrated Age = 8.57 ± 0.23 Ma
6.0
0
10
20
30
40
50
60
70
39
Cumulative % Ar Released
80
90
100
0.0040
A
0.0035
B
0.0030
K
36Ar/40Ar
0.0025
I
J
0.0020
H
C
0.0015
G
0.0010
F
E
D
0.0005
Isochron age = 8.79 ± 0.14 Ma
40Ar/36Ar Intercept = 289.8 ± 6.9
MSWD = 2.5, n = 10
0
0
0.05
0.10
0.15
39Ar/40Ar
0.20
0.25
0.30
K/Ca
0.4
R22 628-638
40
20
0
3
1
-1
10
8
2.42 ± 0.12 Ma* (MSWD = 1.70)
6
4
625
A
2
10
975 G H
F
1700
I
Integrated Age = 2.13 ± 0.08 Ma
0
0
875
E
800
D
750
C
700
B
20
30
40
50
60
70
80
90
100
Cumulative %39Ar Released
0.0040
0.0035
A
I
H
0.0030
F
G
0.0025
E
B
D
C
0.0020
0.0015
0.0010
0.0005
Isochron age = 2.21 ± 0.09 Ma
40Ar/36Ar Intercept = 302 ± 4
MSWD = 2.3, n = 7
0
0
0.05 0.10
0.15
0.20
0.25 0.30 0.35 0.40 0.45
39Ar/40Ar
0.50
0.55 0.60
% Radiogenic
CDV-15 Groundmass Concentrate
80
40
0
1.5
0.5
5
0
4.5
4
Apparent Age Ma
3.5
2.51 ± 0.09 Ma*
MSWD = 1.44
3
2.5
B
700
2
F
975
E
875
D
800
C
750
G
1075
H
1250
1.5
1
I
1700
0.5
Integrated Age = 2.52 ± 0.17 Ma*
0
0
10
20
30
40
50
60
70
80
90
100
Cumulative %39Ar Released
0.00345
A
0.0034
0.00335
0.0033
I
0.00325
0.0032
B
36Ar/40Ar
0.00315
H
0.0031
0.00305
0.003
0.00295
E
0.0029
C
0.00285
0.0028
F
0.00275
G
Isochron age = 2.48 ± 0.11 Ma*
40Ar/36Ar Intercept = 296.2 ± 1.7*
MSWD = 2.4, n = 8
0.0027
0.00265
D
0.0026
0
0.01
0.02
0.03
0.04
0.05
0.06
39Ar/40Ar
0.07
0.08
0.09
0.1
0.11
0.12
K/Ca
1
% Radiogenic
5/25/83-1 Hornblende
80
40
0
3.67 ± 0.29 Ma* (MSWD = 2.06)
Apparent Age Ma
8
1000
C
6
4
1200
I
1060 1090
E
F
2
1120
G
1170
H
1030
D
800
A
Integrated Age = 4.46 ± 0.40 Ma
0
0
10
20
30
40
50
60
70
80
90
100
Cumulative %39Ar Released
0.0040
0.0035
A
C D
B
0.0030
H
FE
36Ar/40Ar
0.0025
G
L
K
0.0020
I
0.0015
J
0.0010
0.0005
Isochron age = 4.0 ± 1.0 Ma
40Ar/36Ar Intercept = 295 ± 17
MSWD = 5.1, n = 9
0
0
0.05
0.10
0.15
0.20
39Ar/40Ar
0.25
0.30
0.35
K/Ca
10
0.3
0.2
0.1
0
-0.1
% Radiogenic
5-25-83-2 Hornblende
100
50
0
0.6
0.2
0
14
Apparent Age Ma
12
10
1650
J
3.18 ± 0.20 Ma (MSWD = 2.28)
8
6
4
1170
E
2
1130
D
0
0
10
20
1315
I
1225
1180
1210
H
F
G
Integrated Age = 3.3 ± 0.3 Ma
30
40
50
60
70
80
90
100
39
Cumulative % Ar Released
0.0040
C
0.0035
J
A
0.0030
D
36Ar/40Ar
0.0025
G
B
H F
0.0020
I
E
0.0015
0.0010
Steps C-J
Isochron age = 3.20 ± 0.08 Ma
40
36
Ar/ Ar Intercept = 294 ± 3
MSWD = 2.7, n = 7
0.0005
0
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
39Ar/40Ar
0.40
0.45
0.50
0.55
0.60
K/Ca
0.4
% Radiogenic
CDV-16-3(i) Groundmass Concentrate
100
50
0
1.5
0.5
5
0
Apparent Age Ma
4
2.88 ± 0.02 Ma (MSWD = 4.45)
3
750
B
755
C
865
D
935
E
1250
1075 H
G
1010
F
2
1
Integrated Age = 3.18 ± 0.08 Ma
0
0
10
20
30
40
50
60
70
80
90
Cumulative %39Ar Released
0.0040
0.0035
A
0.0030
36Ar/40Ar
0.0025
0.0020
H
I
B
0.0015
G
0.0010
Steps B-G
Isochron age = 2.899 ± 0.06 Ma
40
36
Ar/ Ar Intercept = 295 ± 33
MSWD = 17, n = 6
0.0005
C
D
F
E
0
0
0.1
0.2
0.3
39Ar/40Ar
0.4
0.5
0.6
100
K/Ca
1.0
% Radiogenic
R8 95-951 Plagioclase
100
50
0
0.4
0.2
0.1
4.0
0
Apparent Age Ma
3.5
3.0
2.07 ± 0.03 Ma (MSWD = 0.81)
2.5
2.0
905
925
B C
1.5
1190
F
1120
E
1020
D
1750
J
1450
1250
I
G 1355
H
Integrated Age = 2.05 ± 0.04 Ma
1.0
0
10
20
30
40
50
60
70
80
90
100
Cumulative %39Ar Released
0.0040
0.0035
0.0030
A
36Ar/40Ar
0.0025
0.0020
0.0015
I
J
0.0010
B
0.0005
H
C
Steps A-I
Isochron age = 1.99 ± 0.05 Ma*
40Ar/36Ar Intercept = 339±15*
MSWD = 2.3, n = 10
D
F
G
E
0
0
0.1
0.2
0.3
0.4
0.5
0.6
39Ar/40Ar
0.7
0.8
0.9
1.0
1.1
K/Ca
0.3
11-19-84-1 Single Crystal Sanidine
0.2
Moles 39Ar
(x10-14)
0.3
% Radiogenic
0.1
100
80
60
60
20
0
Relative Probability
Weighted Mean Age = 5.04±0.03 Ma*
MSWD =1.8
3.6
4.
4.4
4.8
5.2
Age (Ma)
5.6
6.
6.4
K/Ca
40
DEB 10-91-7 single crystal sanidine
% Radiogenic
110
( x 10-14)
1
0.1
100
90
80
80
40
Relative Probability
Weighted Mean Age = 5.36±0.02 Ma
MSWD = 3.6**
4.0
4.5
5.0
5.5
Age (Ma)
6.0
6.5
7.0
K/Ca
60
Moles 39Ar
10
R25 1922-1923 Sanidine
0.001
150
50
100
40
-20
Weighted Mean Age = 5.03±0.03
Relative Probability
MSWD = 0.69
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
Age (Ma)
Age probability distribution diagram for R25 1922-1923 sanidine.
Points in gray not included in weighted mean.
K/Ca
% Radiogenic
0.1
Moles 39Ar
(x10-14)
10
LAPC-98-13 Sanidine
120
100
80
60
80
40
0
4.98 ± 0.05, MSWD = 7.33
3.6
4.0
4.4
4.8
Age (Ma)
5.2
5.6
6.0
6.4