for a changing world

First-Principles Calibration of ^Ar Tracers: 

mplications for the Ages of 40Ar/39Ar 

Fluence Monitors

'rofessional Paper 1621

J.S. Department of the Interior 

J.S. Geological Survey
Availability of Publications of the U.S. Geological Survey

Order U.S. Geological Survey (USGS) publications from the 

offices listed below. Detailed ordering instructions, along with 

prices of the last offerings, are given in the current-year issues 

of the catalog "New Publications of the U.S. Geological 

Survey."

Books, Maps, and Other Publications 

By Mail

Books, maps, and other publications are available by mail 

from—

USGS Information Services 

Box 25286, Federal Center 

Denver, CO 80225

Publications include Professional Papers, Bulletins, WaterSupply Papers, Techniques of Water-Resources Investigations, 

Circulars, Fact Sheets, publications of general interest, single 

copies of permanent USGS catalogs, and topographic and 

thematic maps.

Over the Counter

Books, maps, and other publications of the U.S. Geological 

Survey are available over the counter at the following USGS 

Earth Science Information Centers (ESIC's), all of which are 

authorized agents of the Superintendent of Documents:

• Anchorage, Alaska—Rm. 101, 4230 University Dr.

• Denver, Colorado-Bldg. 810, Federal Center

• Menlo Park, California-Rm. 3128, Bldg. 3, 

345 Middlefield Rd.

• Reston, Virginia-Rm. 1C402, USGS National Center, 

12201 Sunrise Valley Dr.

• Salt Lake City, Utah-2222 West, 2300 South (books and 

maps available for inspection only)

• Spokane, Washington-Rm. 135, U.S. Post Office 

Building, 904 West Riverside Ave.

• Washington, D.C.-Rm. 2650, Main Interior Bldg., 

18th and CSts.,NW.

Maps only may be purchased over the counter at the following 

USGS office:

• Rolla, Missouri—1400 Independence Rd.

Electronically

Some USGS publications, including the catalog "New Publications of the U.S. Geological Survey" are also available electronically on the USGS's World Wide Web home page at 

http://www.usgs.gov

Preliminary Determination of Epicenters

Subscriptions to the periodical "Preliminary Determination of 

Epicenters" can be obtained only from the Superintendent of

Documents. Check or money order must be payable to the 

Superintendent of Documents. Order by mail from—

Superintendent of Documents 

Government Printing Office 

Washington, DC 20402

Information Periodicals

Many Information Periodicals products are available through 

the systems or formats listed below:

Printed Products

Printed copies of the Minerals Yearbook and the Mineral Commodity Summaries can be ordered from the Superintendent of 

Documents, Government Printing Office (addiess above). 

Printed copies of Metal Industry Indicators and Mineral Industry Surveys can be ordered from the Center for Disease Control 

and Prevention, National Institute for Occupational Safety and 

Health, Pittsburgh Research Center, P.O. Box 18070, Pittsburgh, PA 15236-0070.

Mines FaxBack: Return fax service

1. Use the touch-tone handset attached to your fax machine's 

telephone jack. (ISDN [digital] telephones cannot be used with 

fax machines.)

2. Dial (703) 648-4999.

3. Listen to the menu options and punch in the number of your 

selection, using the touch-tone telephone.

4. After completing your selection, press the start button on 

your fax machine.

CD-ROM

A disc containing chapters of the Minerals Yearbook (1993- 

95), the Mineral Commodity Summaries (1995-97), a statistical compendium (1970-90), and other publications is updated 

three times a year and sold by the Superintendent of Documents, Government Printing Office (address above).

World Wide Web

Minerals information is available electronically at 

http://minerals.er.usgs.gov/minerals/

Subscription to the catalog "New Publications of the U.S. 

Geological Survey"

Those wishing to be placed on a free subscription list for the 

catalog "New Publications of the U.S. Geological Survey" 

should write to—

U.S. Geological Survey 

903 National Center 

Reston, VA 20192
U.S. Department of the Interior 

U.S. Geological Survey

First-Principles Calibration of 38Ar Tracers 

Implications for the Ages of "Ar/^Ar 

Fluence Monitors

By Marvin A. Lanphere and G. Brent Dalrymple

Professional Paper 1621
U.S. Department of the Interior

Bruce Babbitt, Secretary

U.S. Geological Survey

Charles G. Groat, Director

Any use of trade, product, or firm names in this publication

is for descriptive purposes only and does not imply endorsement

by the U.S. Government.

United States Government Printing Office: 2000

For additional copies please contact:

USGS Information Services 

Box 25286 

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Text edited by George A. Havach

Layout and design by Stephen L Scott

Manuscript approved for publication, November 8,1999

Library of Congress Cataloging-in-Publication Data

Lanphere, Marvin A., 1933-

First-principles calibration of 38Ar tracers : implications for the ages of 40Ar/39Ar 

fluence monitors / by Marvin A. Lanphere and G. Brent Dalrymple.

p. cm. — (U.S. Geological Survey professional paper; 1621) 

Includes bibliographical references. 

1. Argon-argon dating—Standards. I. Dalrymple, G. Brent. II. Title. III. Series.

QE508 .L26 2000 

551.7'01-dc21

00-022524
CONTENTS

Page

Abstract———————————————————————————————————————————— 1

Introduction————————————————————————————————————————— 1

Analytical Procedure———————————————————————————————————— 2

Results———————————————————————————————————————————— 3

Discussion—————————————————————————————————————————— 5

Acknowledgments—————————————————————————————————————— 10

References Cited——————————————————————————————————————— 10

FIGURES Page

1. Flowchart showing procedures for calibrating 38Ar tracer systems and mineral standards————————————t— 1

2. Drawing of a McLeod gauge—————————————————————————————————————————————I— 3

3. Age-spectrum plot for biotite standard GA1550———————————————————————————————————-— 9

4. Isotope-correlation plot for biotite standard GA1550————————————————————————————————-— 9

TABLES

1. Volume measurement of the closed-capillary McLeod gauge——————————————————————————— •— 3

2. Pressure, volume, and temperature measurements for an aliquant of commercially purified Ar gas——————• — 4

3. Calculation of the Ar content in aliquant———————————————————————————————————————t— 4

4. Calibration of 38Ar tracers from bulb system A with splits of Ar gas———————————————————————-)— 4

5. Calibration of 38Ar tracers from bulb system A, using biotite standard 62ALe-l————————————————-— 5

6. History of calibration standards and tracer systems used in the U.S. Geological Survey

laboratory in Menlo Park, Calif.———————————————————————————————————————————-— 5

7. K and radiogenic-40Ar contents of biotite standard BS-1——————————————————————————————-— 6

8. K and radiogenic-40Ar contents of biotite standard SB-2—————————————————————————————— -— 6

9. K and radiogenic-40Ar contents of biotite standard SB-3—————————————————————————————— -— 6

10. Calibration of intralaboratory biotite standards used in the U.S. Geological Survey laboratory in

MenloPark, Calif.------------—————————————————————————————————^— 6

11. K contents of biotite standards BS-1 and SB-2 determined by isotope-dilution mass spectrometry——————i— 6

12. Ar analyses of the SORI biotite in different laboratories——————————————————————————————|— 7

13. K-Ar ages and analytical data for hornblende standard MMhb-1—————————————————————————\-— 8

14. 40Ar/39Ar total-fusion ages and analytical data for hornblende standard MMhb-1————————————————f— 8

15. 40Ar/39Ar total-fusion ages and analytical data for biotite standard GA1550—————————————-—————(-— 9

III

First-Principles Calibration of 38Ar Tracers: Implications for

Ages of ^Ar/^Ar Fluence Monitors

By Marvin A. Lanphere1 and G. Brent Dalrymple2

ABSTRACT

The accuracy of the ages of primary mineral standards used 

as fluence monitors is the limiting factor in calculating accurate 40Ar/ 39Ar ages. A primary mineral standard can be dated 

only by measuring its K and radiogenic-Ar contents, using 

calibrated 38Ar tracers. We describe the analytical procedure 

for first-principles calibrations of 38Ar tracers in the U.S. 

Geological Survey (USGS) laboratory in Menlo Park, Calif. 

Two laboratories in Japan that have made first-principles calibrations of 38Ar tracers report good agreement with the values 

obtained in the USGS laboratory for the radiogenic-40Ar content of the SORI biotite standard. The ages of fluence monitors 

determined in the USGS laboratory and those reported in the 

literature differ by nearly 2 percent. However, the radiogenic40Ar content of the primary mineral standard on which these 

ages are based has been measured by first-principles Ar calibration in only one laboratory, and that value has never been 

verified by first-principles measurement in other laboratories.

INTRODUCTION

The mineral standards used in geochronology must be calibrated by using first principles; that is, the contents of 

radioactive parent isotope and radiogenic daughter isotope in 

the mineral standard must be measured directly. Once this 

standard has been dated from its measured isotopic contents, 

it then can be used for second-order calibrations of isotopic 

tracers or other mineral standards (fig. 1).

The 40Ar/ 39Ar method is a relative dating technique that is 

a variant of the K-Ar method. The 40Ar/ 39Ar method depends 

on using a mineral standard (also known as a monitor mineral or fluence monitor) of known age to measure the effective 

fast-neutron dose that an unknown sample receives during

'U.S. Geological Survey, 345 Middlefield Rd., CA 94025. 

2Current affiliation of Oceanographic & Atmospheric Science, Oregon 

State University, Corvallis, OR 97331.

irradiation. The age of the unknown sample is then calculated relative to the age of the standard. At present, some 

disagreement exists about the ages of certain commonl y used 

mineral standards. Various authors have published papers 

that contain sets of data on the 40Ar/ 39Ar comparison of 

mineral standards (for example, Roddick, 1983; Hurford and

Hammerschmidt, 1985; Lanphere and others, 1990; 

and others, 1996; Lanphere and Baadsgaard, 1997,

Renne and others, 1998). Some of these papers are abstracts;

complete analytical data have not yet been published, 

of these studies, the principal source of uncertainty 

value adopted for the age of the primary mineral st£

Baksi 

1998;

In all 

is the 

ndard

against which all the others are compared. The precision of 

40Ar/ 39Ar ages is substantially better than their accuracy, and 

so the accuracy of the age of the primary mineral standard 

is the limiting factor in calculating accurate 40Ar/ 39Ar ages, 

although it does not affect the precision of ages deter: nined 

relative to that standard.

The straightforward first-principles way to date a primary 

mineral standard for the K-Ar dating method is to measure 

the K and radiogenic-Ar contents of the mineral. This primary mineral standard can then be used to calibrate secondary 

mineral standards by the process of intercalibration, wherein 

the age of a secondary mineral standard is calculated relative 

to the known age of the primary mineral standard. A l^boratory equipped to do only 40Ar/ 39Ar dating cannot makelK and 

Ar determinations and must depend on quantitative measure-

^Artracer 

system #2

mineral

standard #1

mineral 

standard #2

mineral 

standard #3

Figure 1.—Flowchart showing procedures for calibrating 38A r tracer 

systems and mineral standards.

1
FIRST-PRINCIPLES CALIBRATION OF 38Ar TRACERS: IMPLICATIONS FOR THE AGES OF 40Ar/38Ar FLUENCE MONITORS

ments made in a conventional K-Ar laboratory for the age 

of the primary mineral standard. In the 1950's and 1960's, 

many of the laboratories engaged in K-Ar dating made firstprinciples calibrations of 38Ar tracers; other laboratories 

depended on calibrating their 38Ar tracers by using mineral 

standards whose radiogenic-40Ar content had been measured 

in some other laboratory that had made first-principles calibrations.

Other ways have been suggested to calibrate fluence 

monitors for 40Ar/ 39Ar dating. Renne and others (1994) and 

Hilgen and others (1997) proposed the use of the astronomically calibrated geomagnetic-polarity time scale to date 

mineral standards for the 40Ar/ 39Ar method. Renne and others (1994) pointed out that this method is independent of 

absolute isotopic measurements. Rial (1999) showed that 

the climate system of the Earth responds nonlinearily to astronomical forcing by frequency-modulating variations in 

insolation; he used a simple model to explain the varying 

durations of the ice ages. Thus, the astronomical method is 

a model, not a first-principles calibration, that assumes perfect synchroneity between Milankovich forcing, climate 

change, geomagnetism, and their geologic records—a questionable presumption at the 1- to 2-percent-confidence level. 

Kunk and others (1994) described a proposal to have the 

U.S. National Institute of Standards and Technology determine the 38Ar content of an 38Ar tracer system by pressure 

measurements; this would be a first-principles calibration, 

but the work has not yet been done. Renne and others (1997) 

determined an 40Ar/ 39Ar isochron age of 1,925±94 yr on 

sanidine from the eruption of Mount Vesuvius in 79 C.E. 

This measurement would be a first-principles calibration, 

but the precision of only about 5 percent does not satisfy 

the requirement for a primary standard.

The art of first-principles 38Ar tracer calibration has 

largely been lost. In fact, most laboratories in operation 

today have never done such calibrations. Many of the laboratories that made first-principles calibrations during the 

1960's have been closed, and those still in existence, such 

as the U.S. Geological Survey (USGS) laboratory in Menlo 

Park, Calif., have not done them for many years. In addition, the calibration procedures were almost never described 

in detail. From 1964 to 1965, we made several first-principles calibrations of the USGS 38Ar tracer systems; all 

subsequent tracer systems and mineral standards are traced 

directly to those first-principles calibrations. We thought it 

would be useful to describe the calibration procedure we 

used and to discuss how first-principles calibrations of Ar 

tracers were done there.

First-principles calibrations of such elements as K, Rb, 

Sr, U, and Pb are relatively straightforward, though exacting, and rely primarily on weighing, which can be done easily 

with high precision and accuracy. A solution containing a 

carefully weighed amount of a standard reference material 

of known isotopic composition is mixed with a solution 

containing an isotopic tracer, also of known isotopic composition, to determine the concentration of a given isotope

in the tracer solution. A weighed amount of the tracer solution can then be added to a solution containing a dissolved 

rock or mineral of unknown age to determine, by comparison with the tracer, the concentrations of the isotopes used 

in the age calculations.

First-principles calibrations in the K-Ar method, however, 

are not so straightforward. The K content can be measured 

by isotope dilution in the same way as for Rb or U. However, 

measuring the Ar content is inherently more difficult because 

the Ar cannot be weighed but must be measured in gaseous 

form at low pressure. Using the various gas laws, we can derive the relationship n=PV/RT, where n is the Ar content (in 

moles), P is the pressure, V is the volume, T is the temperature (in kelvins), and R is the universal gas constant. There 

are two ways to measure the Ar content of an aliquant of 

gas. The first way is to isolate a volume of air, whose elemental composition is known, and then remove all the other 

gases. This way requires that the air be dry; that is, all water 

vapor must be removed. This step is required because the 

humidity of air varies widely and is difficult to measure accurately; the measured Ar content of air, 0.934±0.001 volume 

percent (Hodgman and others, 1969), is for dry samples. 

The second way is to use commercially purified Ar gas, 

which can be supplied with impurities of less than 10 ppm. 

This second way avoids the problem of variation in the humidity of air and does not require the removal of other gases. 

The Ar-isotopic composition can then be measured to confirm the absence of isotopic fractionation in its preparation. 

We chose the second way as being simpler and, in principle, 

more accurate.

ANALYTICAL PROCEDURE

The analytical procedure involves trapping an aliquant 

of commercially purified Ar gas in a McLeod gauge (Dushman, 1962) and measuring its pressure and volume; the temperature of the Ar gas is measured with an accurate Hg 

thermometer. Using these measurements and knowing the 

gas constant, R, we can calculate the Ar content of the 

aliquant. The McLeod gauge (fig. 2) consists of an open 

and a closed tube made of precision-bore capillary tubing 

of uniform cross section and a small reservoir, the volume 

of which must be accurately known. The aliquant is trapped 

in the closed tube, and so the volume of the closed tube 

must also be measured as accurately as possible. At the time 

of our measurements, McLeod gauges of sufficient precision and accuracy were unavailable commercially, and so 

we constructed one. We mapped the volume of the closed 

tube along its length by incrementally filling the capillary 

tube to various heights with Hg and weighing the Hg (table 

1). The height of the Hg column was measured to within 

±0.005 mm with a cathetometer. The capillary tubing must 

be clean, or else Hg sticking to the wall of the tubing can 

interfere with the meniscus at the top of the Hg columns. 

This condition was checked by raising the Hg columns with
RESULTS

Table 1.—Volume measurements with the closed-capillary McLeod 

gauge.

7TQ

Hg

vol/cm Avol/cm h(cm)

(g) (cm3)

24.25 

24.50

23.65

24.50

25.20 

25.55

1.4760 

2.3608

3.1380

4.2040

5.0395 

6.4143

0.10904 

.17442

.23180

.31060

.37237 

.47399

0.03410 

.03433

.03443

.03457

.03465 

.03456

} 0.03473

} .03475

} .03497

} .03500 

} .03424

3.2 

5.1

6.7

9.0

10.70 

13.70

the system under high vacuum and confirming that the Hg 

columns in both the closed and open tubes were at the same 

level.

In principle, the measurements are straightforward, but in 

practice they are not so easy. The goal is to obtain an aliquant 

of Ar gas similar in volume to an 38Ar tracer, but this procedure requires working near the low-pressure limit of a McLeod 

gauge. The commercially purified Ar gas was delivered in a

Hg

K-Hg

Figure 2.—McLeod gauge. Heavy lines, precision-bore capillary tubing. Right, entire gauge with Hg level (shaded) before trapping volume of Ar gas to be measured. Left, measurements made to determine pressure of volume of Ar gas trapped within gauge after Hg 

level is raised, h, distance between top of Hg column in closed tube 

and top of closed tube; Ah, distance between tops of two Hg columns.

1-L glass bulb with a breakseal. The manufacturer's sjpecifications are as follows:

Minimum purity—99.9995 percent |

CO2———————————max 1 ppm

H2————————————max 1 ppm

H2O———————————max 3 ppm

N2_.—————————-max 2 ppm

O2————————————max 2 ppm

Total hydrocarbons——max 0.5 ppm

The glass bulb of Ar gas was attached to the apparatus, and 

the Ar gas was expanded into a calibration system thit contained the McLeod gauge, reservoirs, and various gas pi 3ettes. 

The Ar gas in the glass bulb was at a pressure of 1 atm, and so 

a gas pipette consisting of two stopcocks connected with a 

length of Pyrex tubing was used to isolate a suitable volume 

of the Ar gas for measurement. After the Ar gas was ex] >anded 

into the calibration system, a column of vacuum-distilled Hg 

was raised to isolate the Ar gas in the closed tube of the 

tn was 

th the 

;d and 

cLeod

McLeod gauge. The Ar gas in the rest of the syste 

pumped away. Measurements were then made wi 

cathetometer of the top of the Hg columns in the clos 

open tubes relative to the top of the closed tube of the IV 

gauge. A rubber bulb was used to pressurize the Hg re .ervoir 

so that the Hg columns could be moved to different positions. The measurements on a typical aliquant of Ar jjas are 

listed in table 2; a typical calculation of the volume of Ar gas 

in the aliquant is listed in table 3. All errors cited in I his report are standard deviations, or la uncertainties.

After completing these measurements, the Hg column isolating the aliquant of Ar gas in the closed tube was lowered, 

and the entire aliquant was transferred into a reservoir, using 

activated charcoal cooled with liquid N2 . The reservor was a 

2-L Pyrex boiling flask whose volume was determined by

weighing it empty and full of water. A gas pipette con

of two 2-mm-bore mercury-seal stopcocks connected with a 

length of tubing of known volume was attached to the reservoir. The volume of the pipette was determined by weighing 

the pipette empty, filling the length of tubing with Eg, and

weighing the pipette again. The volumes of reservoir

pette are listed in table 3. Because the volumes of both the 

pipette and the reservoir were known, the depletion constant 

of the system, A,, could be calculated from the relation 

A=(volume of pipette)/(volume of pipette+volume oi reservoir). The reservoir-pipette system is similar to the Ar bulb 

tracer system described by Lanphere and Dalrymple (1966). 

Splits of Ar gas made with the gas pipette were mixed with 

38Ar tracers. The gas-tracer mixtures were analyzed

noble-gas mass spectrometer, and from these resu 

knowledge of the A value, the initial tracer quantity 

the 38Ar bulb-tracer system was calculated.

sisting

;md piwith a 

ts and

m of

RESULTS i

Five splits of Ar gas from aliquants 7 and 8 were used to 

calibrate 38Ar tracers from bulb system A. Aliquants 1 and 8
FIRST-PRINCIPLES CALIBRATION OF 38Ar TRACERS: IMPLICATIONS FOR THE AGES OF ""Ar/^Ar FLUENCE MONITORS

Table 2.—Pressure, volume, and temperature measurements for an 

aliquant of commercially purified Ar gas.

[h, distance between top of Hg column in closed tube and top of closed tube; 

Ah, distance between tops of two Hg columns; T, temperature; a, cross-sectional area of closed tube]

Set

1

2

3

4

5

6

7

8

h 

(cm)

6.860 

6.867

6.370 

6.362

6.092 

6.115

7.310 

7.318

8.092 

8.088

8.830 

8.835

6.978 

6.990

5.694 

5.712

Ah 

(cm)

6.638 

6.670

7.208 

7.190

7.542 

7.555

6.240 

6.250

5.612 

5.613

5.108 

5.107

6.598 

6.570

8.040 

8.072

T

26.2 

26.2

26.0 

26.1

26.1 

26.1

26.2 

25.6

25.5 

25.7

25.5 

25.5

25.6 

25.7

25.5 

25.6

hAh 

(mm2)

4,553.7 

4,580.3

4,591.5

4,574.3

4,594.6 

4,619.9

4,561.4 

4,573.8

4,541.2 

4,539.8

4,510.4 

4,512.0

4,604.1 

4,592.4

4,578.0 

4,610.7

a 

(mm2)

3.497 

3.497

3.475 

3.475

3.475 

3.475

3.497 

3.497

3.500 

3.500

3.500 

3.500

3.497 

3.497

3.475 

3.475

ahAh 

(mm4)

15,924 

16,017

15,955 

15,896

15,966 

16,054

15,951 

15,995

15,894 

15,889

15,786 

15,792

16,101 

16,060

15,909 

16,022

were separately prepared volumes of Ar gas. The performance 

of bulb system A over time was described by Lanphere and 

Dalrymple (1966). The 38Ar content, Tx, of any given tracer is 

calculated from the relation

where X=0.826xlO~3 for this tracer system. The data for the 

five calibrations are listed in table 4.

Similar calibrations had been made earlier by the first 

author at the California Institute of Technology (CIT), using commercially purified Ar gas in an apparatus similar to 

that described above. Aliquants of Ar gas were used to calibrate 38Ar tracers that, in turn, were used to measure the radiogenic-40 Ar content of an intralaboratory biotite mineral 

standard. This biotite standard, 62ALe-l, was separated from 

a Jurassic tonalite in the Alaska-Aleutian Range batholith of 

south-central Alaska. The sample was collected along the road 

between Pile Bay on Lake Iliamna and Iliamna Bay on the 

Pacific Ocean (Reed and Lanphere, 1969). The radiogenic-40 Ar 

content of biotite standard 62ALe-l is 2.157xlO~9 mol/g, 

based on the CIT measurements.

A total of 12 calibrations were made on 38Ar tracers from 

the USGS laboratorory's bulb system A, using the radiogenic40 Ar content of biotite standard 62ALe-l biotite measured at 

CIT (table 5). The difference between the mean value of these

Table 3.—Calculation of the Ar content in aliquant 9.

Given: Mean temperature = 25.8°C or 298.95K 

Mean ahAh = 15,951+83.3 mm4 

R = 62.364xl06 mm4/mol-K 

Volume of reservoir = 2,179.1 cm3 

Volume of pipette = 2.6204 cm3 

(Volume of pipette)/(volume of reservoir + volume of pipette) = 1.201xlO-3

Calculation: n = ahAh/RT = 0.85557X1Q-6 mol Ar gas

40 Ar = 0.996x0.85557x10-6 = 0.85215x10-6 mol

Table 4.—Calibration of 38Ar tracers from bulb system A with splits of Ar gas. 

[Tx, 38Ar content of tracer; T0, initial tracer quantity]

Aliquant

7-2

7-3

7-4

8-3

8-4

40 Ar content 

(10-n mol)

93.16

93.05

92.93

97.28

97.17

Tracer

A-26

A-53

A-9

A-48

A^9

(lO-n'mol)

33.340

32.688

33.383

31.624

31.445

Mean

a

°x

T

34.064

34.150

33.632

32.903

32.743

33.498

.65

.29
DISCUSSION

Table 5.—Calibration of 38Ar tracers from bulb system A, using biotite standard 62ALe-l.

[Radiogenic-40Ar content of biotite standard 62ALe-l was measured at the California Institute of Technology, using a tracer system calibrated with commercially purified Ar gas. Tx, 38Ar content of tracer; TO, initial tracer quantity]

Tracer

A-2

A-12

A-13

A-24

A-35

A-50

A-77

A-124

A-160

A-184

A-221

A-222

TX 

(10-11 mol)

33.424

33.136

33.149

33.081

32.884

32.356

31.915

30.680

29.352

28.785

28.041

27.855

Mean

a

<**

T

(10-ll0mol)

33.479

33.466

33.507

33.743

33.848

33.720

34.009

33.989

33.508

33.511

33.659

33.462

33.658

.20

.06

38Ar tracer calibrations and the mean value of the Ar gas calibrations of the USGS laboratory's bulb system A (table 4) is 

0.48 percent. Note that these two sets of calibrations are tied 

directly to independent first-principles calibrations made in 

two different laboratories.

A total of 16 different bulb-tracer systems and 1 batch tracer 

system have been used in the USGS laboratory since the 

1960's (table 6). These tracers have been used to calibrate 

three additional biotite standards, BS-1, SB-2, and SB-3 

(tables 7-9), which were separated from the same sample of 

tonalite that yielded biotite standard 62ALe-l. Each of these 

biotite standards was treated as an independent standard 

mineral, and their ages were measured, not assumed. The good 

agreement in the ages of these standard biotites (table 10) 

demonstrates that we have been able to fill and refill 38Ar 

tracer systems without propagating systematic errors. These 

tracers and standard biotites have been used for K-Ar and 

40'Ar/ 39Ar dating of other minerals that can potentially be used 

as fluence monitors. The age of a fluence monitor, not just its 

radiogenic-40Ar content, must be known. The K contents of 

biotite standards BS-1 and SB-2 were measured by isotopedilution mass spectrometry at the U.S. National Bureau 

of Standards (table 11). The difference between the flamephotometer and isotope-dilution K2O contents of biotite standard SB-2 is less than 0.05 weight percent. Intercomparisons 

of flame-photometer values of biotite standards BS-1, SB-2, 

and SB-3 were used to normalize the K content of biotite 

standard SB-3 to the isotope-dilution values of biotite 

standards BS-1 and SB-2.

Table 6.—History of calibration standards and tracer systems used 

in the U.S. Geological Survey laboratory in Menlo Park, Calif.

[Tracer systems A, C, D, and F had glass pipettes; all other tracer systems \ ad metal 

pipettes except tracer system OSA, which was a batch tracer]

Year Calibration standard Tracer system

1964 Commercially purified Ar gas 

Biotite1 62ALe-l

1965

1966

1967

1970

1970

1971

1971

1971

1977

1978

1978

1981

1981

1984

1985

1986

1986

Commercially purified Ar gas 

Biotite1 62ALe-l

Biotite1 62ALe-l 

Biotite BS-1

Biotite1 62ALe-l

Biotite BS-1

Biotite BS-1

Biotite BS-1 

Biotite SB-2

Biotite BS-1 

Biotite SB-2

Biotite BS-1

Biotite SB-2

Biotite SB-2 

Biotite SB-3

Biotite SB-2 

Biotite SB-3

Biotite SB-2 

Biotite SB-3

Biotite SB-3

Biotite SB-3

Biotite SB-3

Biotite SB-3

Biotite SB-3

C

D

F

G

H

J

K

OS

N

Is

P

C

A

ij

s)

Tf

I

w W

Radiogenic-40 Ar content measured at the California Institute of Technology, using 38Ar tracers calibrated with commercially purified Ar gas.

DISCUSSION

Other laboratories have made first-principles Ar 

tions and have produced data that provide comparisons 

those from the USGS laboratory in Menlo, Park Calif. 

(1968) calibrated an 38Ar batch-tracer system at the Geolo 

cal Survey of Japan, using commercially purified Ar gas 

a McLeod gauge. He then used the 38Ar tracers to ::

calibrawith

Shibata 

gland

neasure
FIRST-PRINCIPLES CALIBRATION OF 38Ar TRACERS: IMPLICATIONS FOR THE AGES OF *°ArPAr FLUENCE MONITORS

Table 7.—K and radiogenic-40Ar contents of biotite standard BS-1.

[Analysts: K2O, L.B. Schlocker; Ar, J.C. Von Essen]

Table 9.—K and radiogenic-40Ar contents of biotite 

standard SB-3.

[Analysts: K2O, M. Taylor; Ar, J.C. Von Essen]

K2O content 

(weight percent)

Radiogenic-40Ar content 

(10-9 mol/g)

K2O content 

(weight percent)

Radiogenic-40 Ar content 

(10-9 mol/g)

8.97

8.83

8.84

8.90

8.87

8.57

8.95

8.85

8.86

8.83

8.84

8.87

8.75

Mean = 8.841

a = 0.0984 

(1.1 percent)

Gx = 0.0273

(0.31 percent)

2.193

2.164

2.174

2.126

2.187

2.149

2.183

2.194

2.177

2.196

2.201

2.208

2.191

2.213

Mean = 2.183x10-9

a = 0.0233x10-9 

(1.08 percent)

(7^=0.0063x10-9 

(0.29 percent)

9.03

9.07

9.01

9.01

9.02

9.03

9.02

9.02

9.02

9.00

8.99

8.98

9.00

9.01

9.03

9.01

9.00

9.01

Mean = 9.014

a = 0.019

(0.21 percent)

ax = 0.0045

(0.05 percent)

2.221

2.209

2.200

2.243

2.207

2.211

2.205

2.219

2.204

2.210

2.218

Mean = 2.213x10-9

a = 0.0011xlO-9 

(0.51 percent)

a, = 0.0034x10-9 

(0.15 percent)

Table 8.—K and radiogenic-40Ar contents of biotite 

standard SB-2.

[Analysts: K2O, L.B. Schlocker; Ar, J.C. Von Essen]

Table 10.—Calibration of intralaboratory biotite standards used in 

the U.S. Geological Survey laboratory in Menlo Park, Calif.

Biotite standard Radiogenic-40Ar calibrations Age (Ma) 1

K2O content 

(weight percent)

Radiogenic-40 Ar content 

(10-9 mol/g)

BS-1

SB-2

6 with D bulb tracers 

8 with F bulb tracers

2 with OSA batch tracers

162.7+2.5

162.1±2.1

9.20

9.18

9.19

9.21

9.18

9.20

9.20

9.19

9.19

9.18

9.19

9.18

9.16

9.20

9.20

9.16

Mean = 9.188

a = 0.014

(0.15 percent)

cx = 0.0035

(0.038 percent)

2.225

2.194

2.214

2.260

2.215

2.224

2.286

2.262

2.260

2.256

2.264

2.277

Mean = 2.245X10"9

a = 0.029X10-9 

(1.29 percent)

ar = 0.0084xlO-9 

(0.37 percent)

SB-3

2 with D bulb tracers 

8 with K bulb tracers

8 with N bulb tracers 

3 with Q bulb tracers

162.9±0.9

-i, A,p=4.962xl(r10 yr1 , 40K/K=1.167xl(T* mol/mol.

Table 11.—K contents of biotite standards BS-1 and SB-2 determined by isotope-dilution mass spectrometry.

[Analysts: E.L. Garner and L.A. Machlan. Uncertainty is estimated error limit and includes an allowance for possible effects of trace impurities in measurement of 39K/ 41K 

ratio]

Biotite standard K content K2 O content

BS-1

SB-2

7.3942

7.3937

Mean = 7.3940±0.0185

7.6306

7.6311

Mean = 7.6308±0.0191

8.9069

8.9063

Mean = 8.9066±0.0223

9.1917

9.1923

Mean = 9.1920+0.0230
DISCUSSION

Table 12.—Ar analyses of the SORI biotite in different laboratories.

Laboratory Radiogenic-40Ar content 

(10-6 cm3/g)

Reference

Geological Survey of Japan 

Okayama University, Japan

U.S. Geological Survey, Menlo Park, Calif.

24.90+0.15

25.23±0.22 

25.05±0.35

24.98±0.13

Uchiumi and Shibata (1980).

Nagao and others (1984). 

Nagao and others (1996).

K. Uto (written commun., 1998)

the radiogenic-40Ar content of a biotite standard, separated 

from the SORI granodiorite in Gumma Prefecture, Japan; 

results of the analyses are listed in table 12 (Uchiumi and 

Shibata, 1980). Keisuke Nagao calibrated an 38Ar bulb-tracer 

system at Okayama University, Japan, using Ar gas separated 

from air, and used these tracers to measure the radiogenic40Ar content of the SORI biotite standard (table 12; Nagao 

and others, 1984, 1996). Finally, Kozo Uto of the Geological 

Survey of Japan analyzed the SORI biotite standard in the 

USGS laboratory in Menlo Park, Calif, using 38Ar tracers from 

bulb tracer-system U (table 12). The close agreement of the 

results on the SORI biotite standard from all three laboratories shows that the first-principles calibrations of 38Ar tracers, when done carefully, yield concordant results.

The ages of the fluence monitors used for 40Ar/ 39Ar dating in various laboratories differ by nearly 2 percent. Renne 

and others (1998) made a detailed intercalibration of six minerals used as neutron-fluence monitors. They adopted biotite 

standard GA1550 prepared at the Australian National 

University (ANU) as their primary neutron-fluence monitor, 

from which they determined the ages of the other fluence 

monitors. McDougall and Roksandic (1974) reported a K-Ar 

age of 97.9±0.9 Ma for biotite standard GA1550, based on a 

K content of 7.70±0.03 weight percent and a radiogenic-40Ar 

content of (3.01±0.01)xlO~5 cm3/g (at standard temperature 

and pressure). They stated that a set of 38Ar tracers were 

accurately calibrated against known amounts of atmospheric 

Ar gas, but no details of the calibration procedure were given. 

The K content of biotite standard GA1550 was determined 

by flame photometry. Wellman (1971) gave a slightly more 

detailed description of the ANU calibration procedure. 

Capillary tubes of known volume were filled with dry air and 

sealed with a blob of molten glass; how the air was dried was 

not specified. The amount of Ar in the tubes was calculated 

by using the temperature and pressure of the laboratory. The 

air samples were mixed with tracers on an extraction line, 

and, after purification, the composition of the Ar mixture was 

measured on a mass spectrometer. In 1970, we attempted 

tracer calibrations by using this procedure but obtained widely 

varying (scattered) results. Wellman noted that this tracer 

calibration gave ages 1 to 2.5 percent older than previously

published Australian Cenozoic K-Ar ages, but the ree son for 

the difference was unknown. Renne and others (1998) 

redetermined the K content of biotite standard GA 550 by 

isotope-dilution mass spectrometry and obtained a C value 

of 7.626±0.016 weight percent, about 1 weight percert lower 

than the flame-photometry value of McDougall and Ro csandic 

(1974). Renne and others (1998) did not measure the 

radiogenic-40Ar content of biotite standard GA1550, Using 

the new K content and the radiogenic-40Ar content of 

McDougall and Roksandic (1974), Renne and others (1998) 

calculated an age of 98.79±0.54 Ma for biotite standard 

GA1550.

Multigrain samples of hornblende standard MMhb -1 

used as fluence monitors in an intercalibration exp 

involving the USGS laboratories in Menlo Park, Ca 

Reston, Va.; this experiment included biotite standard ( 

and several other standards. Hornblende standard IV 

was developed as a dating standard by B.C. Alexander 

and G.M. Mickelson. The initial analyses of hor: 

standard MMhb-1 were made at the USGS labor; 

Menlo Park, Calif.: K by flame photometry, and Ar by 

dilution mass spectrometry. From these measuremer 

Ar age of 519.5±2.5 Ma was calculated (Alexander an 

1978). The Ar measurements were made on a newly de 

multiple-collector mass spectrometer (Stacey and 

1981). Only about 20 percent of a typical gas sam 

introduced into the mass spectrometer. An isotopic 

of Ar took only 5 to 10 minutes to complete, and s 

common to analyze two or three splits of Ar gas 

age the results. This procedure was followed for 

measurements of hornblende standard MMhb-1 rep 

Alexander and others (1978). Subsequently, we noti 

the isotopic compositions of second and third split 

did not agree with the composition of the first split as 

they should have. In addition, the iso 

second and later splits of gas changed in the direction of the 

composition of the sample analyzed previously, indicating a 

memory effect (Dalrymple and Lanphere, 1969) in the 

unbaked sample manifold of the mass spectrometer that 

affected analyses of the second and later splits of the current 

sample. If only the first splits of Ar gas are used in calculating

were 

riment 

if., and 

A1550 

Mhb-1 

Jr.,

blende 

tory in

otopets, a Kothers, 

reloped 

others, 

le was 

nalysis

it was 

averthe Ar 

rtedby 

ed that

of gas 

well as 

)topic composition of the

and
FIRST-PRINCIPLES CALIBRATION OF 38Ar TRACERS: IMPLICATIONS FOR THE AGES OF 40Ar/38Ar FLUENCE MONITORS

the K-Ar age of hornblende standard MMhb-1, the age 

changes from the 519.5±2.5 Ma reported by Alexander and 

others (1978) to 514.9±2.2 Ma. The original Ar analyses plus 

additional Ar analyses have yielded the currently accepted 

K-Ar age of 513.9±2.3 Ma for hornblende standard MMhb1 (table 13). A mean 40Ar/39Ar age of 513.8±2.6 Ma was 

determined on hornblende standard MMhb-1, using biotite 

standard SB-3 as the fluence monitor (table 14). During the 

late 1980's, while Scott Samson and E.G. Alexander, Jr., 

were compiling analytical data on hornblende standard 

MMhb-1, we informed them about the new data from the 

USGS laboratory in Menlo Park, Calif. However, they chose 

to include only the original data (Alexander and others, 1978) 

for hornblende MMhb-1 in their compilation (Samson and

Alexander, 1987). This choice has caused unnecessary 

confusion about the mean K-Ar age of 513.9±2.3 Ma 

determined in the USGS laboratory in Menlo Park, Calif.

40Ar/ 39Ar ages were measured on biotite standard GA1550 

as part of an intercomparison experiment between the USGS 

laboratories in Menlo Park, Calif., and Reston, Va. Three splits 

each of biotite standard GA1550 and several other mineral 

standards were irradiated, using hornblende standard MMhb1 as the fluence monitor. Total-fusion 40Ar/ 39Ar ages were 

determined on two splits of each mineral, and an incrementalheating experiment was made on the third split. The two totalfusion ages of biotite standard GA1550 were 97.49±0.62 and 

97.05±0.60 Ma (table 15). An incremental-heating experiment 

yielded a weighted-mean plateau age of 97.0010.31 Ma for

Table 13.—K-Ar ages and analytical data for hornblende standard MMhb-1.

[Analysts: K2O, S.T. Neil; Ar, J.C. Von Essen]

K2O content

(weight percent)

1.867

1.881

1.876

1.877

1.875

1.881

1.874

1.872

1.869

1.873

1.867

1.872

Radiogenic-40 Ar content

(10-9 mol/g)

1.611

_ __

1.599

_ _ _

1.613

_ _ _

1.604

_ __

1.594

_ _ _

_ _ _

_ _ _

(percent)

86.2

_ _ _

94.8

__ _

89.9

_ _ _

95.2

___

91.7

_ __

_ _ _

_ __

Calculated age

(Ma)

515.9±3.3

_ _ _

512.4±3.2

_ _ _

516.4±3.2

__ _

513.9±4.4

___

511.0±4.4

_ __

_ _ _

__ _

Mean= 1.874±0.005

Table 14.—40Ar/ 39Ar total-fusion ages and analytical data for hornblende standard MMhb 1.

[Analysts: J.Y. Saburomaru and J.C. Von Essen]

ratio

88.51

58.94

48.65

48.77

66.72

72.83

ratio

2.504

2.500

2.424

2.447

2.472

2.453

ratio

0.1321

.0297

.005584

.004590

.005584

.02657

Radiogenic

40Ar 

(pet)

56.1

85.4

97.0

97.6

97.8

89.5

39ArCa 

(pet)

0.2

.2

.2

.2

.2

.2

36ArCa 

(pet)

0.5

2.3

11.5

14.5

11.7

2.4

Age 

(Ma)

511.3±4.6

517.4±4.6

512.4±4.5

516.3±4.5

511.4±2.6

513.9±2.8
DISCUSSION

Table 15.—40Ar/ 39Ar total-fusion ages and analytical data for biotite standard GA1550.

[Analysts: J.Y. Saburomaru and J.C Von Essen]

40Ar/39Ar ^Ar^Ar 36Ar/39Ar Radiogenic 40^

ratio

19.01

19.22

ratio

0.01440

.01303

ratio

0.009403

.007571

(lO-10 mol)

1.966

2.0766

(pet)

85.4

88.3

39ArCa 

(pet)

<0.01

.01

36ArCa 

(pet)

0.04

.05

K/Ca 

ratio

34.0

37.6

39 Ar 

(pet)

100

100

A 

0

97.4

97.0

ge 

la)

)±0.62

5±0.60

l/AJ

00

< £ 10°

H 0

£ oo

gS3 80

i— i 

AH

K ———————————— 97.00 ± 0.31 ————————————— >

^800^ 875 925 975 1,050 ^^ 

750

i 1 i 1 i 1 i 1 i 1 i 1 i 1 i 1 i 1 i

10 20 30 40 50 60 70 80 90 

CUMULATIVE PERCENTAGE OF 39Ar RELEASED

100

Figure 3.—Age-spectrum diagram forbiotite standard GA1550. Vertical dimensions of boxes 

is estimated analytical precision of increment ages at+la. Numbers are temperatures (in degrees Celsius) at which Ar was extracted.

8,000

C 6,000

^o 

m

4,000

2,000

1,050.

H5Q 

500,

age = 96.80 ±0.53 Ma 

40Ar/ 36Ar ratio = 297.6 ± 5.7

SUMSAN-2) = 0.91

biotite standard GA1550 (fig. 3), an isochron age of ?6.80± 

0.53 Ma (fig. 4), and an isochron intercept of 297.6±5.7. The 

difference between our 40Ar/ 39Ar plateau age and the age for

biotite standard GA1550 adopted by Renne and other: (1998)

100 200 300 400

39Ar/ 36Ar RATIO

Figure 4.—Isotope-correlation diagram for biotite standard 

GA1550. Numbers are temperatures (in degrees Celsius) at 

which Ar was extracted. Circles, points used in isochron fit; 

plus sign, point not used in isochron fit.

is 1.85 percent.

Minerals from the Fish Canyon Tuff of Colorado ha /e been 

dated in several laboratories. Renne and others (1998) 

calculated an age of 28.02±0.16 Ma for sanidine from the 

Fish Canyon Tuff on the basis of their intercalibration with 

biotite standard GA1550. Lanphere and others 1990), 

Lanphere and Baadsgaard (1997,1998), and Kozo Uto (written 

commun., 1998) suggested an age of 27.5 Ma for s;inidine 

and biotite from the Fish Canyon Tuff. The difference between 

the ages of 28.02 and 27.5 Ma is 1.89 percent, consistent 

with the difference in age of biotite standard GA1550.

The 40Ar/39Ar ages suggested by Renne and others (1998) 

for six mineral standards depend completely on tr|e radiogenic-40 Ar content of biotite standard GA1550 measured at 

the ANU. That value has never been verified by first-pr nciples

measurements in any other laboratory, and so the \r/39Ar
10 FIRST-PRINCIPLES CALIBRATION OF 38Ar TRACERS: IMPLICATIONS FOR THE AGES OF 40Ar/38Ar FLUENCE MONITORS

ages suggested by Renne and others (1998) are of 

questionable accuracy, though highly precise. The age of any 

primary mineral standard must be measured by first-principles 

calibration of the radiogenic-40Ar content in more than one 

laboratory. Because the 40Ar/ 39Ar ages suggested by Renne 

and others (1998) fail this criterion, we consider it unwise to 

adopt them for general use.

ACKNOWLEDGMENTS

The manuscript was improved by constructive comments 

from Robert Fleck, John Obradovich, lan McDougall, and 

Paul Renne.

REFERENCES CITED

Alexander, E.G., Jr., Mickelson, G.M., and Lanphere, M.A., 1978, 

MMhb-1; a new 40Ar-39Ar dating standard, in International 

Conference on Geochronology, Cosmochronology, and Isotope 

Geology, 4th, Snowmass-at-Aspen, Colo., 1978, Short Papers: 

U.S. Geological Survey Open-File Report 78-701, p. 6-8.

Baksi, A.K., Archibald, D.A., and Farrar, E., 1996, Intercalibration 

of 40Ar/39Ar dating standards: Chemical Geology (Isotope Geoscience Section), v. 129, p. 307-324.

Dalrymple. G.B., and Lanphere, M.A., 1969, Potassium-argon dating: San Francisco, W.H. Freeman and Co., 258 p.

Dushman, Saul, 1962. Scientific foundations of vacuum technique 

(2d ed.): New York, John Wiley & Sons, 806 p.

Hilgen, F.J., Krijsman, W., and Wijbrans, J.R., 1997, Direct comparison of astronomical and 40Ar/ 39Ar ages of ash beds; potential implications for the age of mineral dating standards: Geophysical Research Letters, v. 24, p. 2043-2046.

Hodgman, C.D., Weast, R.C., Shankland, R.S., and Selby, S.M., 

compilers, 1969, Handbook of physics and chemistry (49th ed.): 

Cleveland, Ohio, Chemical Rubber Co.

Hurford, A.J., and Hammerschmidt, K., 1985, 40Ar/ 39Ar and K/Ar 

dating of the Bishop and Fish Canyon Tuffs; calibration ages 

for fission-track dating standards: Chemical Geology (Isotope 

Geoscience Section), v. 58, p. 23-32.

Kunk, M.J., Dalrymple, G.B., and Snee, L.W., 1994, Progress 

on the preparation of the proposed ^Ar/ 39Ar standard MMhb2, plans for its calibration, and interlaboratory calibration of 

argon facilities [abs.], in Lanphere, M.A., Dalrymple, G.B., and 

Turrin, B.D., eds., International Conference on Geochronology, Cosmochronology, and Isotope Geology, 8th, Berkeley, 

Calif., 1994, Abstracts: U.S. Geological Survey Circular 1107, 

p. 183.

Lanphere, M.A., and Baadsgaard, H., 1997, The Fish Canyon Tuff; 

a standard for geochronology [abs.]: Eos (American Geophysical Union Transactions), v. 78, p. S326.

————1998, The Fish Canyon Tuff—a standard for geochronology 

[abs.]: Quebec 1998, Geological Association of Canada/Mineralogical Association of Canada/Association Professionnelle

des Geologues et Geophysiciens du Quebec/International Association of Hydrogeologists/Canadian Geophysical Union, v. 

23, p. A102.

Lanphere, M.A., and Dalrymple, G.B., 1966, Simplified bulb tracer 

system for argon analyses: Nature, v. 209, p. 902-903.

Lanphere, M.A., Dalrymple, G.B., Fleck, R.J., and Pringle, M.S., 

1990, Intercalibration of mineral standards for K-Ar and 40Ar/ 

39Ar age measurements [abs.]: Eos (American Geophysical 

Union Transactions), v. 71, p. 1658.

McDougall, lan, and Roksandic, Z., 1974, Total fusion 40Ar/ 39Ar 

ages using HIFAR reactor: Geological Society of Australia 

Journal, v. 21, p. 81-89.

Nagao, K., Nishido, H., Itaya, T, and Ogata, K., 1984, An age determination by K-Ar method: Okayama University of Science, 

Hiruzen Research Institute Bulletin, v. 9, p. 19-38 [in Japanese, 

with English abstract].

Nagao, K., Ogata, A., Miura, Y.N., and Yamaguchi, K., 1996, Ar 

isotope analysis for K-Ar dating using two modified-VG5400 

mass spectrometers—I: Isotope dilution method: Mass Spectrometry Society of Japan Journal, v. 44, p. 39-61.

Reed, B.L., and Lanphere, M.A., 1969, Age and chemistry of Mesozoic and Tertiary plutonic rocks in south-central Alaska: 

Geological Society of America Bulletin, v. 80, p. 23^4.

Renne, P.R., Deino, A.L., Walter, R.C., Turrin, B.D., Swisher, C.C., 

III, Becker, T.A., Curtis, G.H., Sharp, W.D., and Jaouni, A-R, 

1994, Intercalibration of astronomical and radioisotopic time: 

Geology, v. 22, p. 783-786.

Renne, PR., Sharp, W.D., Deino, A.L., Orsi, G., and Civetta, L., 

1997, 40Ar/ 39Ar Dating into the historical realm; calibration 

against Pliny the Younger: Science, v. 277, p. 1279-1280.

Renne, PR., Swisher, C.C., Deino, A.L., Karner, D.B., Owens,T.L., 

and DePaolo, D.J., 1998, Intercalibration of standards, absolute ages and uncertainties in 40Ar/ 39Ar dating: Chemical Geology (Isotope Geoscience Section), v. 145, p. 117-152.

Rial, J.A., 1999, Pacemaking the ice ages by frequency modulation 

of Earth's orbital eccentricity: Science, v. 285, p. 564-568.

Roddick, J.C., 1983, High precision Intercalibration of 40Ar/ 39Ar standards: Geochimica et Cosmochimica Acta, v. 47, p. 887-898.

Samson, S.D., and Alexander, E.G., Jr., 1987, Calibration of the 

interlaboratory 40Ar-39Ar dating standard, MMhb-1: Chemical 

Geology (Isotope Geoscience Section), v. 66, p. 27-34.

Shibata, Ken, 1968, K-Ar age determinations on granitic and 

metamorphic rocks in Japan: Geological Survey of Japan Report 227, 71 p.

Stacey, J.S., Sherrill, N.D., Dalrymple, G.B., Lanphere, M.A., and 

Carpenter, N.V., 1981, A five-collector system for the simultaneous measurement of argon isotope ratios in a static mass 

spectrometer: International Journal of Mass Spectrometry & 

Ion Physics, v. 39, p. 167-180.

Uchiumi, S., and Shibata, Ken, 1980, Errors in K-Ar age determination: Geological Survey of Japan Bulletin, v. 31, p. 267-273 

[in Japanese, with English abstract].

Wellman, Peter, 1971, The age and paleomagnetism of the Australian Cenozoic volcanic rocks: Canberra, Australian National 

University, Ph.D. thesis, 388 p.

•&• U.S. GOVERNMENT PRINTING OFFICE: 2000 — 573-047 / 20187 Region No. 8


Selected Series of U.S. Geological Survey Publications

Books and Other Publications

Professional Papers report scientific data and interpretations 

of lasting scientific interest that cover all facets of USGS investigations and research.

Bulletins contain significant data and interpretations that are of 

lasting scientific interest but are generally more limited in 

scope or geographic coverage than Professional Papers.

Water-Supply Papers are comprehensive reports that present 

significant interpretive results of hydrologic investigations of 

wide interest to professional geologists, hydrologists, and engineers. The series covers investigations in all phases of hydrology, including hydrogeology, availability of water, quality of 

water, and use of water.

Circulars are reports of programmatic or scientific information 

of an ephemeral nature; many present important scientific 

information of wide popular interest. Circulars are distributed 

at no cost to the public.

Fact Sheets communicate a wide variety of timely information 

on USGS programs, projects, and research. They commonly 

address issues of public interest. Fact Sheets generally are two 

or four pages long and are distributed at no cost to the public.

Reports in the Digital Data Series (DOS) distribute large 

amounts of data through digital media, including compact discread-only memory (CD-ROM). They are high-quality, interpretive publications designed as self-contained packages for viewing and interpreting data and typically contain data sets, 

software to view the data, and explanatory text.

Water-Resources Investigations Reports are papers of an 

interpretive nature made available to the public outside the formal USGS publications series. Copies are produced on request 

(unlike formal USGS publications) and are also available for 

public inspection at depositories indicated in USGS catalogs.

Open-File Reports can consist of basic data, preliminary 

reports, and a wide range of scientific documents on USGS 

investigations. Open-File Reports are designed for fast release 

and are available for public consultation at depositories.

Maps

Geologic Quadrangle Maps (GQ's) are multicolor geologic 

maps on topographic bases in 7.5- or 15-minute quadrangle 

formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, 

surficial, or engineering geology. Maps generally include brief 

texts; some maps include structure and columnar sections only.

Geophysical Investigations Maps (GP's) are on topographic 

or planimetric bases at various scales. They show results of 

geophysical investigations using gravity, magnetic, seismic, or 

radioactivity surveys, which provide data on subsurface structures that are of economic or geologic significance.

Miscellaneous Investigations Series Maps or Geologic 

Investigations Series (I's) are on planimetric or topographic 

bases at various scales; they present a wide variety of format 

and subject matter. The series also incudes 7.5-minute quadrangle photogeologic maps on planimetric bases and planetary 

maps.

Information Periodicals

Metal Industry Indicators (Mil's) is a free monthly newsletter that analyzes and forecasts the economic health of five 

metal industries with composite leading and coincident 

indexes: primary metals, steel, copper, primary and secondary 

aluminum, and aluminum mill products.

Mineral Industry Surveys (MIS's) are free periodic statistical 

and economic reports designed to provide timely statistical data 

on production, distribution, stocks, and consumption of significant mineral commodities. The surveys are issued monthly, 

quarterly, annually, or at other regular intervals, depending on 

the need for current data. The MIS's are published by commodity as well as by State. A series of international MIS's is also 

available.

Published on an annual basis, Mineral Commodity Summaries is the earliest Government publication to furnish estimates 

covering nonfuel mineral industry data. Data sheets contain 

information on the domestic industry structure, Government 

programs, tariffs, and 5-year salient statistics for more than 90 

individual minerals and materials.

The Minerals Yearbook discusses the performance of the 

worldwide minerals and materials industry during a calendar 

year, and it provides background information to assist in interpreting that performance. The Minerals Yearbook consists of 

three volumes. Volume I, Metals and Minerals, contains chapters about virtually all metallic and industrial mineral commodities important to the U.S. economy. Volume II, Area Reports: 

Domestic, contains a chapter on the minerals industry of each 

of the 50 States and Puerto Rico and the Administered Islands. 

Volume III, Area Reports: International, is published as four 

separate reports. These reports collectively contain the latest 

available mineral data on more than 190 foreign countries and 

discuss the importance of minerals to the economies of these 

nations and the United States.

Permanent Catalogs

"Publications of the U.S. Geological Survey, 1879-1961" 

and "Publications of the U.S. Geological Survey, 1962- 

1970" are available in paperback book form and as a set of 

microfiche.

"Publications of the U.S. Geological Survey, 1971-1981" is

available in paperback book form (two volumes, publications 

listing and index) and as a set of microfiche.

Annual supplements for 1982, 1983, 1984, 1985, 1986, and 

subsequent years are available in paperback book form.