Table 2. ⁴⁰Ar/³⁹Ar results from Santa Isabel Wash

Group

Map Unit

Location in UTM coordinates (north, east)

Sample

Mineral3

Bulk4 Ca/K

J-Factor5

# of aliquots  included in calculation  over total #

Inverse Isochron Age (Ma) (± 2sSD)

40Ar/39Ar  (± 1s SD)

40Ar/36Ar  (± 1s SD)

MSWD

95% critical MSWD range (Mahon [1996])

7

Tmrcan

3367803mN 0709909mE

CAN-95-11

Oligoclase

4.0

0.00080202

17/18

6.0 ± 0.4

4.15 ± 0.12

268 ± 15

1.21

0.42-1.83

7

Tmrcan

3367705mN 0709305mE

CAN-95-12

Oligoclase

4.9

0.00080402

6/7

5.9 ± 0.8

4.07 ± 0.28

287 ± 9

1.89

0.12-2.78

6

Tmrec

3366006mN 0704401mE

LCR-94-110

Oligoclase

2.1

0.00080872

6/9

6.1 ± 0.5

4.20 ± 0.15

286 ± 4

0.45

0.12-2.78

6

Tmrao

3362808mN 0701203mE

INF-94-75

Anorthoclase

0.52

0.00041781

10/13

6.4 ± 0.3

8.45 ± 0.04

287 ± 1

7.77

0.27-2.19

6

Tmrsiw

3362507mN 0703502mE

INF-94-47

Oligoclase

3.9

0.00041911

9/9

6.5 ± 0.3

8.59 ± 0.12

293 ± 5

1.94

0.24-2.29

6

Tmrsiw

3365004mN 0698608mE

INF-94-33

Oligoclase

4.5

0.00041841

8/8

6.6 ± 0.5

8.81 ± 0.29

289 ± 1

0.56

0.21-2.40

6

Tmrsiw

3365307mN 0700800mE

CHO-94-45

Oligoclase

4.5

0.00041791

8/8

6.7 ± 0.3

8.94 ± 0.09

281 ± 4

0.98

0.21-2.40

6

Tmrsiw

3365501mN 0699403mE

SUN-94-30

Oligoclase

5.2

0.00080842

16/18

5.7 ± 0.4

3.92 ± 0.12

285 ± 2

2.39

0.40-1.86

5

Tmatoro

3362507mN 0703008mE

INF-94-68

Labradorite

43

0.00042081

13/13

9.3 ± 0.8

12.24 ± 0.50

288 ± 5

4.29

0.35-1.99

4

Tmrsf

3365807mN 0697809mE

LCS-94-72

Anorthoclase

0.17

0.00081022

8/8

12.7 ± 0.5

8.69 ± 0.07

285 ± 11

0.45

0.21-2.40

3

Tmdtomb

3362807mN 0703509mE

DIN-94-46

Andesine

14

0.00042181

8/8

15.5 ± 0.7

20.48 ± 0.25

287 ± 3

2.92

0.21-2.40

3

Tmdtomb

3363300mN 0701506mE

INF-94-52

Andesine

5.7

0.00042021

12/12

15.9 ± 0.7

21.09 ± 0.15

286 ± 2

1.24

0.33-2.05

3

Tmdtomb

3364403mN 0698208mE

INN-94-73

Andesine

17

0.00042111

8/8

15.9 ± 1.2

21.03 ± 0.64

289 ± 3

1.01

0.21-2.40

3

Tmdtomb

3365004mN 0699204mE

WIN-94-32

Andesine

14

0.00042201

8/8

16.1 ± 0.8

21.30 ± 0.28

280 ± 4

0.74

0.21-2.40

3

Tmdtomb

3367102mN 0702305mE

PHO-94-10

Andesine

13

0.00042181

8/8

16.2 ± 0.8

21.32 ± 0.25

267 ± 11

5.02

0.21-2.40

3

Tmdtomb

3365305mN 0703704mE

LCR-95-08

Andesine

29

0.00082982

5/5

16.7 ± 1.0

11.21 ± 0.25

277 ± 12

0.64

0.07-3.12

3

Tmdtomb

3366607mN 0702108mE

PHO-94-86

Andesine

19

0.00082982

13/13

16.4 ± 1.4

11.02 ± 0.42

271 ± 8

1.36

0.35-1.99

3

Tmblol

3361806mN 0702004mE

INF-95-24

Andesine

15

0.00081202

14/15

16.3 ± 1.0

11.18 ± 0.28

298 ± 7

1.96

0.37-1.94

3

Tmbkc

3362309mN 0699204mE

KC-95-19

Andesine

14

0.00081022

15/18

17.1 ± 2.2

11.77 ± 0.73

273 ± 7

2.11

0.39-1.90

2

Tmrbio

3362004mN 0698503mE

KC-95-17

Andesine

16

0.00082032

13/13

17.1 ± 2.4

11.63 ± 0.79

287 ± 2

1.18

0.35-1.99

  ¹ Irradiation UofM#75² Irradiation UofM#81³ Based on representative electron microprobe analysis⁴ Estimated from ⁴⁰Ar/³⁹Ar analysis⁵ Calculated assuming 27.8 Ma for Fish Canyon sanidine