Jones III, J.V. (ORCID: 0000-0002-6602-5935)
Benowitz, J.A. (ORCID: 0000-0003-2294-9172)
20200921
40Ar/39Ar Isotopic Data and Ages for Rocks from the Yukon-Tanana Upland of Eastern Alaska and the Northern Aleutian Range of South-Central Alaska
tabular digital data
Anchorage, Alaska
U.S. Geological Survey, Alaska Science Center
Suggested citation: Jones III, J.V., and Benowitz, J.A., 2020, 40Ar/39Ar isotopic data and ages for rocks from the Yukon-Tanana upland of eastern Alaska and the northern Aleutian Range of south-central Alaska: U.S. Geological Survey data release, https://doi.org/10.5066/P96762V3.
https://doi.org/10.5066/P96762V3
This data set contains 40Ar/39Ar isotopic data and ages for rocks from the Yukon-Tanana upland of eastern Alaska and the northern Aleutian Range of south-central Alaska. The entire sample suite was collected as part of geological mapping and supporting geochemical and geochronological analysis were conducted from 2013 to 2019 by the Mineral Resources Program of the U.S. Geological Survey (USGS). Legacy bedrock samples archived from earlier USGS field investigations were also analyzed in some cases. Hornblende, muscovite, and (or) biotite were extracted from bedrock samples of igneous and metamorphic rocks and analyzed at the University of Alaska Fairbanks Geochronology Laboratory in order to determine the 40Ar/39Ar age of each mineral phase. The data tables accompanying this data release report the resulting 40Ar/39Ar analytical data and interpreted ages for each mineral separated from a bulk rock sample.
40Ar/39Ar dates of hornblende, muscovite, and (or) biotite aid in the interpretation of the thermal history of the mineral and the rock that contains it. In this study, 40Ar/39Ar dates were determined for one or more minerals from igneous and metamorphic bedrock samples. The 40Ar/39Ar ages help to constrain the age of regional deformation, metamorphism, and cooling and provide key insights into the geological and metallogenic evolution of large regions of eastern and south-central Alaska. These data will be used in support of multiple geological maps, reports, and journal articles that describe the geological framework and mineral resource potential of Alaska.
2020
publication date
None planned
-153.5
-141.0
64.5
60.2
USGS Metadata Identifier
USGS:ASC311
ISO 19115 Topic Category
geoscientificInformation
USGS Thesaurus
geology
geochronology
potassium-argon analysis
GeoRef Thesaurus
Ar/Ar
NASA GCMD Earth Science Keywords Thesaurus
earth science
USGS Geographic Names Information System (GNIS)
Alaska
Divide Mountain
Taylor Mountain
Mount Harper
Ladue River
Fortymile River
Sixty Mile River
Aleutian Range
Lake Clark
Neacola River
Drift River
Blockade Lake
McArthur River
Tlikakila River
Chokotonk River
Tuxedni River
Chigmit Mountains
None
Yukon-Tanana upland
None
None. Users are advised to read the metadata thoroughly to understand appropriate use and data limitations.
U.S. Geological Survey
James V. Jones
Geologist
mailing and physical address
4210 University Drive
Anchorage
Alaska
99508-4626
U.S.A.
907-786-7000
ascweb@usgs.gov
Jones III, J.V. (ORCID: 0000-0002-6602-5935)
2015
Tectonic and metallogenic evolution of the eastern Yukon-Tanana upland, Alaska
web site
Science Portal
389
Anchorage, Alaska
U.S. Geological Survey, Alaska Science Center
This is a link to the broader USGS Alaska Science Center research project supported by these data. Users will find a description of the research project and links to associated reports, publications, and data products.
https://alaska.usgs.gov/portal/project.php?project_id=389
Jones III, J.V. (ORCID: 0000-0002-6602-5935)
2014
Metallogeny and tectonics of the Neacola Mountains and
Lake Clark region, south-central Alaska
web site
Science Portal
388
Anchorage, Alaska
U.S. Geological Survey, Alaska Science Center
This is a link to the broader USGS Alaska Science Center research project supported by these data. Users will find a description of the research project and links to associated reports, publications, and data products.
https://alaska.usgs.gov/portal/project.php?project_id=388
Mineral samples were irradiated with monitor mineral MMhb-1 with preferred age of 523.5 Ma (Renne et al, 1994). Samples and the monitors were step-heated or fused using a 6-watt argon-ion laser. Argon purification was achieved using a liquid nitrogen cold trap and SAES Zr-Al getter at 400 degrees C. The argon isotopes were measured and corrected for system blank and mass discrimination, as well as neutron induced reactions on calcium, potassium and chlorine. Typical full-system 8 min laser blank values (in moles) were generally 2e-16 mol 40Ar, 3e-18 mol 39Ar, 9e-18 mol 38Ar, and 2e-18 mol 37Ar, and 2e-18 mol 36Ar, which are 10-50 times smaller than the sample/standard volume fractions. Correction factors for nucleogenic interferences during irradiation were determined from irradiated CaF2 and K2SO4 and were: (39Ar/37Ar)Ca = 7.06e-4, (36Ar/37Ar)Ca = 2.79e-4, and (40Ar/39Ar)K = 0.0297. Mass discrimination was monitored by analyzing air shots with an assumed 40Ar/36Ar value of 295.5 (Nier, 1950). The mass discrimination during these experiments was 1.3% per mass unit. No significant variation in discrimination over the course of the analyses was measured and so a single value was used in data reduction. Ages with +/- 1 sigma error were calculated using the decay constants of Renne et al, 2010. The integrated age is the age given by the total gas measured and is equivalent to a potassium-argon (K-Ar) age. A plateau age is reported if three or more consecutive gas fractions representing at least 50 percent of the total gas released that are within two standard deviations of each other and with an overall Mean Square Weighted Deviation (MSWD) less than or equal to 2.5.
No unexpected values are found in these data. Blank cells in the data tables indicate values were either not provided, not measured, or not calculated.
This data set is complete; no data were omitted.
All samples collected since 2014 have horizontal positions measured using hand-held GPS units with positional accuracy of 3 meters. The location for samples collected in 1974 were obtained from 1:63,360 scale topographic field sheets.
Geochronology Laboratory at UAF
2019
UAF 40Ar39Ar Methods
Fairbanks, Alaska
Geochronology Laboratory at University of Alaska Fairbanks
This is a supplemental PDF document included in this data release. The file name is UAF_40Ar39Ar_methods.pdf.
pdf file
2019
publication date
UAF 40Ar/39Ar methods
Provides detailed description of laboratory methods for 40Ar/39Ar geochronology.
Nier, A.O.
1950
A redetermination of the relative abundances of the isotopes of carbon, nitrogen, oxygen, argon, and potassium
Physical Review
vol. 77, no. 6, p. 789
https://doi.org/10.1103/PhysRev.77.789
journal article
1950
publication date
Nier, 1950
Calculation of argon isotope abundance ratios
Renne, Paul R.
Deino, Alan L.
Walter, Robert C.
Turrin, Brent D.
Swisher, Carl C.
Becker, Tim A.
Curtis, Garniss H.
Sharp, Warren D.
Jaouni, Abdur-Rahim
1994
Intercalibration of astronomical and radioisotopic time
Geology
vol. 22, p. 783-786
https://doi.org/10.1130/0091-7613(1994)022<0783:IOAART>2.3.CO;2
journal article
1994
publication date
Renne et al, 1994
Data on monitor mineral MMhb-1
Renne, Paul R.
Mundil, Roland
Balco, Greg
Min, Kyoungwon
Ludwig, Kenneth R.
2010
Joint determination of 40K decay constants and 40Ar*/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology
Geochimica et Cosmochimica Acta
vol. 74, p. 5349-5367
https://doi.org/10.1016/j.gca.2010.06.017
journal article
2010
publication date
Renne et al, 2010
Decay constants
Mineral separation was done at the Geochronology Laboratory at the University of Alaska Fairbanks (UAF). For 40Ar/39Ar analysis, bulk rock samples were crushed, sieved, washed and hand-picked to obtain pure hornblende, biotite, and muscovite mineral separates. Samples and standards were wrapped in aluminum foil and loaded into aluminum cans of 2.5 cm diameter and 6 cm height. The samples were irradiated in position 5c of the uranium enriched research reactor of McMaster University in Hamilton, Ontario, Canada for 20 megawatt-hours. After irradiation, the samples and standards were returned to UAF and loaded into an ultra-high vacuum extraction line. The standards were fused, and the samples heated, using a 6-watt argon-ion laser. Argon purification was achieved using a liquid nitrogen cold trap and a SAES Zr-Al getter at 400 degrees C. The argon isotopes were analyzed in a VG-3600 mass spectrometer, fitted with a single Daly detector, and operated in peak mode.
2019
Point
0.0001
0.0001
Decimal degrees
North American Datum of 1983
GRS 1980
6378137
298.257222101
geology_40Ar39ArData_Alaska_Jones.csv
Table of 40Ar/39Ar isotopic data, including heating power levels, measurements, and calculated age for each heating step. There are 811 records in this table.
Author defined
Sample
Sample identifier as collected in the field; an internal USGS identifier. Descriptive and locational information about the sample is provided in table
geology_40Ar39ArSummary_Alaska_Jones.csv.
Author defined
Sample identifier; most labels consisting of the last two digits of the year collected, an abbreviation identifying the collector, and a number and possible suffix.
LabID
Sample name assigned by the laboratory corresponding to the USGS sample identifier and mineral analyzed.
Author defined
Alphanumeric code consisting of UAF and a hyphenated number.
Lab
Laboratory where analysis was conducted
Author defined
UAF
Geochronology Laboratory, University of Alaska Fairbanks
Author defined
Sample_material
Mineral analyzed
Author defined
The following values are used in this data set: biotite, hornblende, and muscovite.
Monitor_mineral
Reference mineral used to monitor neutron flux and calculate the irradiation parameter, J.
Author defined
MMhb-l
hornblende standard for 40Ar/39Ar
Samson, S.D., and Alexander, E.C., 1987, Calibration of the interlaboratory 40Ar/39Ar dating standard, MMhb1: Chemical Geology, v. 66, p. 27-34, https://doi.org/10.1016/0168-9622(87)90025-X. Renne, P.R., Deino, A.L., Walter, R.C., Turrin, B.D., Swisher, C.C., Becker, T.A., Curtis, G.H., Sharp, W.D., and Jaouni, A.R., 1994, Intercalibration of astronomical and radioisotope time: Geology, v. 22, p. 783-786, https://doi.org/10.1130/0091-7613(1994)022<0783:IOAART>2.3.CO;2.
Monitor_mineral_age
Published age of the monitor mineral
Author defined
The monitor mineral used for all analyses in this data set is MMhb-1 with age 523.5 Ma.
J_value
Measure of neutron fluence
Author defined
0.005069
0.005650
J_unc
Uncertainty (1-sigma) in measure of neutron fluence
Author defined
0.000017
0.000046
Laser_power_mW
Laser power setting, in milliwatt, for each heating step. Blank cells indicate an integrated analysis.
Author defined
500
12000
mW (milliwatt)
Integrated
Integrated analysis indicates that values were calculated by weighting individual heating steps by the fraction of 39Ar released. Blank cells designate a heating step fraction.
Author defined
The term 'Integrated' indicates the values were calculated by weighting the individual heating steps by the fraction of 39Ar released.
39Ar_cum
Cumulative 39Ar released at this step. Blank cells indicate an integrated analysis.
Author defined
0.00069
1.00000
percentage in decimal format
40Ar_mV
Abundance of 40Ar in millivolt
Author defined
4.9957
38363.1091
mV (millivolt)
40Ar_mV_unc
Uncertainty (1-sigma) in 40Ar in millivolt
Author defined
0.1100
1890.1793
mV (millivolt)
39Ar_mV
Abundance of 39Ar in millivolt
Author defined
0.1257
3461.2629
mV (millivolt)
39Ar_mV_unc
Uncertainty (1-sigma) in 39Ar in millivolt
Author defined
0.0163
1.9715
mV (millivolt)
38Ar_mV
Abundance of 38Ar in millivolt
Author defined
-0.0077
181.3537
mV (millivolt)
38Ar_mV_unc
Uncertainty (1-sigma) in 38Ar in millivolt
Author defined
0.0070
0.3693
mV (millivolt)
37Ar_mV
Abundance of 37Ar in millivolt
Author defined
-0.0013
2.6300
mV (millivolt)
37Ar_mV_unc
Uncertainty (1-sigma) in 37Ar in millivolt
Author defined
0.0180
9.9773
mV (millivolt)
36Ar_mV
Abundance of 36Ar in millivolt
Author defined
-1.4553
139.3879
mV (millivolt)
36Ar_mV_unc
Uncertainty (1-sigma) of 36Ar in millivolt
Author defined
0.0070
1.5371
mV (millivolt)
Perc_atm_40Ar
Percent atmospheric 40Ar in measurement
Author defined
-88.16
143.11
percent
Perc_atm_40Ar_unc
Uncertainty (1-sigma) in percent atmospheric 40Ar in measurement
Author defined
0.07
61.12
percent
Ca_K_ratio
Calcium to potassium ratio as determined from 37 argon derived from calcium and 39 argon derived from potassium; 37Ar(Ca)/39Ar(K).
Author defined
-0.42547
48.42797
Ca_K_ratio_unc
Uncertainty (1-sigma) in calcium to potassium ratio
Author defined
0.00025
4.48215
Cl_K_ratio
Chlorine to potassium ratio as determined from 38 argon derived from chlorine and 39 argon derived from potassium; 38Ar(Cl)/39Ar(K).
Author defined
-0.00413
0.25133
Cl_K_ratio_unc
Uncertainty (1-sigma) in chlorine to potassium ratio
Author defined
0.00002
0.03959
40Ar_39Ar_K
Ratio of radiogenic 40Ar to 39Ar derived from potassium
Author defined
-501.69492
205.36012
40Ar_39Ar_K_unc
Uncertainty (1-sigma) in ratio of radiogenic 40Ar to 39Ar
from potassium
Author defined
0.02432
92.36374
Age_Ma
Age calculated for each heating step from ratio of radiogenic 40Ar to 39Ar from potassium, in millions of years.
Author defined
-257083.62
1387.19
Ma
Age_Ma_unc
Uncertainty (1-sigma) in calculated age, in millions of years
Author defined
0.36
1108.12
Ma
geology_40Ar39ArSummary_Alaska_Jones.csv
Table with descriptive sample information, including location, rock description, and summary of geochronology analyses. This table contains 91 records and is presented in comma separated value (CSV) format.
Author defined
Sample
Sample identifier as collected in the field; an internal USGS identifier.
Author defined
Sample identifier; most labels consisting of the last two digits of the year collected, an abbreviation identifying the collector, and a number and possible suffix.
AK_Region
Region of Alaska where sample was collected
Author defined
Values in this data set include 'Eastern Alaska' and 'South-central Alaska'.
AK_Subregion
Geographic area where sample was collected
Author defined
Values in this data set include 'Lake Clark/Neacola Mountains' and 'Yukon-Tanana upland'.
Latitude
Latitude given in decimal degrees; datum NAD83
Author defined
60.2381
64.4066
decimal degree
Longitude
Longitude given in decimal degrees; datum NAD83
Author defined
-153.4093
-141.0140
decimal degree
Rock_Class
Basic rock classification of the sample
Author defined
Attributes in the data set are 'igneous' and 'metamorphic'
Rock_Type
Sample rock type
Author defined
General rock description
Rock_Comment
A more detailed rock description than Rock_Type
Author defined
A more descriptive rock description than Rock_Type
Analysis_Type
type of geochronologic analysis
Author defined
40Ar/39Ar
argon-argon radiometric dating
Author defined
Analysis_Lab
Laboratory where analysis was conducted
Author defined
UAF
Geochronology Laboratory, University of Alaska Fairbanks
Author defined
LabID
Sample name assigned by the laboratory corresponding to the USGS sample identifier and mineral analyzed.
Author defined
Alphanumeric code consisting of UAF and a hyphenated number
Sample_Material
Mineral analyzed
Author defined
The following values are used in this data set: biotite,
hornblende, and muscovite.
Preferred_40Ar_39Ar_Age
Preferred 40Ar_39Ar_Age of the sample material, in millions of years. Value -9999 indicates the analysis is not reliable and so no preferred age is reported.
Author defined
24.6
265.7
Ma
Preferred_40Ar_39Ar_Age_unc
Uncertainty (1-sigma) of the preferred 40Ar/39Ar age, in millions of years. Value -9999 indicates the analysis is not reliable.
Author defined
0.4
7.5
Ma
Preferred_40Ar_39Ar_Age_type
Method used to calculate Preferred_40Ar_39Ar_Age
Author defined
Values include variations of integrated age, isochron age, plateau age, weighted average, or no reliable age.
Preferred_40Ar_39Ar_Age_comment
Details on how Preferred_40Ar_39Ar_Age was calculated.
Author defined
Details on how Preferred_40Ar_39Ar_Age was calculated
Integrated_40Ar_39Ar_Age
Integrated 40Ar/39Ar age, in millions of years, calculated from total gas measured
Author defined
24.6
704.5
Ma
Integrated_40Ar_39Ar_Age_unc
Uncertainty (1-sigma) on the integrated 40Ar/39Ar age, in millions of years
Author defined
0.4
8.0
Ma
Plateau_40Ar_39Ar_Age
Plateau 40Ar/39Ar age, in millions of years, calculated from three or more consecutive gas fractions representing more than 50% of the total gas released that are within two standard deviations of each other and with an overall Mean Square Weighted Deviation (MSWD) less than or equal to 2.5. Value -9999 indicates data did not meet the criteria necessary to calculate a plateau age.
Author defined
24.6
265.7
Ma
Plateau_40Ar_39Ar_Age_unc
Uncertainty (1-sigma) on the plateau 40Ar/39Ar age, in millions of years. Value -9999 indicates data did not meet the criteria necessary to calculate a plateau age.
Author defined
0.4
7.5
Ma
Plateau_40Ar_39Ar_Age_MSWD
Mean square of weighted deviates (MSWD) on calculated plateau age. Value -9999 denotes no data.
Author defined
0.05
13.09
Plateau_40Ar_39Ar_Age_comment
Comments on the plateau age, including number of heating steps used and percentage of 39Ar released.
Author defined
Comments on the plateau age, including number of heating steps used and percentage of 39Ar released.
Isochron_40Ar_39Ar_Age
Isochron 40Ar/39Ar age in millions of years. Blank cells are present.
Author defined
33.4
125.1
Ma
Isochron_40Ar_39Ar_Age_unc
Uncertainty (1-sigma) on the isochron 40Ar/39Ar age, in millions of years. Blank cells are present.
Author defined
0.6
8.3
Ma
Isochron_40Ar_39Ar_Age_MSWD
Mean square of weighted deviates (MSWD) on calculated isochron age. Blank cells are present.
Author defined
0.52
2.00
Isochron_40Ar_39Ar_Age_comment
Comments on the isochron age; gives number of heating steps included in calculation. Blank cells are present.
Author defined
Comments on the isochron age; gives number of heating steps included in calculation.
40Ar_36Ar_initial
Initial 40Ar/36Ar calculated from isochron. Blank cells are present.
Author defined
280.7
317.4
40Ar_36Ar_initial_unc
Uncertainty (1-sigma) of initial 40Ar/36Ar calculated from isochron. Blank cells are present.
Author defined
3.9
28.7
geology_40Ar39ArDataDictionary_Alaska_Jones.csv
Table listing the name of all fields in each table, with a brief description of the field and the data units, if applicable.
Author defined
Table
Name of the data table the field is found in.
Author defined
The data tables in this data set include geology_40Ar39ArData_Alaska_Jones.csv and geology_40Ar39ArSummary_Alaska_Jones.csv.
Field
Field name found in data table listed in Table.
Author defined
The field names are single words or concatenated abbreviations that describe the contents of the field.
Description
Brief description of the contents of the field
Author defined
Brief description of the contents of the field
Units
The unit of measurement for applicable data fields
Author defined
%
percent
Author defined
Ma
mega-annum or million years
Author defined
mV
millivolt
Author defined
MW
megawatt
Author defined
n/a
not applicable
Author defined
U.S. Geological Survey, Alaska Science Center
mailing and physical address
4210 University Drive
Anchorage
Alaska
99508-4626
U.S.A.
907-786-7000
ascweb@usgs.gov
Authoritative source for this data.
Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty.
CSV
Data are distributed in a Zip package containing data in CSV format and FGDC metadata in XML and HTML formats.
Compression applied by the 7-Zip utility using default compression (5). The file can be decompressed and unpacked by open source or commercially available unzip tools.
0.40
https://doi.org/10.5066/P96762V3
None
20201125
20200904
U.S. Geological Survey, Alaska Science Center
mailing and physical address
4210 University Drive
Anchorage
Alaska
99508-4626
U.S.A.
907-786-7000
ascweb@usgs.gov
FGDC Content Standard for Digital Geospatial Metadata
FGDC-STD-001-1998