ArgonGeochronologicData: SampleLocationDescription, SummaryAges, and StepHeatingData
Layer, P.W., Benowitz, J.A., and Freeman, L.K., 2011, 40AR/39AR Ages from the East Bonnifield geologic map area, Fairbanks A-1, Fairbanks A-2, Healy D-1, and Healy D-2 quadrangles, Alaska: Raw Data File RDF 2011-2, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys, Fairbanks, Alaska - USA.Online Links:
This is a Point data set.
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 1
Ordinates (y-coordinates) are specified to the nearest 1
Planar coordinates are specified in meters
The horizontal datum used is North American Datum of 1927.
The ellipsoid used is Clarke 1866.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.25722210088.
Generic example of unique sample identifier: 20YYAAA9999X: YY=last two digits of year, AAA=geologist's initials (one to three characters), 9999=unique station number, X=unique alpha character designating a sample was taken at the field station. Geologists' initials represent the following: 'JOE' = Joe Andrew; 'LF' = Larry Freeman; 'MBW' = Melanie Werdon; 'RN' = Rainer Newberry; 'Z' = David Szumigala.
| Range of values | |
|---|---|
| Minimum: | 63.8411 |
| Maximum: | 64.066 |
| Units: | decimal degrees |
| Range of values | |
|---|---|
| Minimum: | -147.8358 |
| Maximum: | -147.3248 |
| Units: | decimal degrees |
| Range of values | |
|---|---|
| Minimum: | 459098 |
| Maximum: | 484148 |
| Units: | meters |
| Range of values | |
|---|---|
| Minimum: | 7079208 |
| Maximum: | 7104209 |
| Units: | meters |
"6" indicates 06W NAD27 Alaska Projection
Brief rock description
Brief rock description
Brief rock description
Generic example of unique sample identifier: 20YYAAA9999X; Where: YY=last two digits of year, AAA=geologist's initials (one to three characters), 9999=unique station number, X=unique alpha character designating a sample was taken at the field station. Geologists' initials represent the following: 'JOE' = Joe Andrew; 'LF' = Larry Freeman; 'MBW' = Melanie Werdon; 'RN' = Rainer Newberry; 'Z' = David Szumigala.
Identifies material that was used to for the age analysis includes either mineral name for mineral seperates or "Whole Rock" for samples of fine-grained or aphanitic groundmass. Some samples were run as duplicates.
| Range of values | |
|---|---|
| Minimum: | 84.3 +- 0.5 |
| Maximum: | 111.1 +- 1.3 |
| Units: | Ma |
| Range of values | |
|---|---|
| Minimum: | 64.2 +- 1.0 |
| Maximum: | 102.5 +- 1.5 |
| Units: | Ma |
number of fractions, % 39Ar released, MSWD.
If an isochron age is listed the column contains the age and age error in Ma, the initial ratio and error of 40Ar to 36 Ar (40Ar/36Ari), number (N) of fractions, and the Mean Standard Weighted Deviation (MSWD). Other values include "Loss Spectrum", "Reset, and "Reset/Loss".
Generic example of unique sample identifier: 20YYAAA9999X; Where: YY=last two digits of year, AAA=geologist's initials (one to three characters), 9999=unique station number, X=unique alpha character designating a sample was taken at the field station. Geologists' initials represent the following: 'JOE' = Joe Andrew; 'LF' = Larry Freeman; 'MBW' = Melanie Werdon; 'RN' = Rainer Newberry; 'Z' = David Szumigala.
Identifies material that was used to for the age analysis includes either mineral name for mineral seperates or "Whole Rock" for samples of fine-grained or aphanitic groundmass. Some samples were run as duplicates.
| Value | Definition |
|---|---|
| Integrated | Indicates row of data from entire step heating run |
| Range of values | |
|---|---|
| Minimum: | 300 |
| Maximum: | 9000 |
| Units: | Megawatts |
| Range of values | |
|---|---|
| Minimum: | 0.0022 |
| Maximum: | 1.0001 |
| Range of values | |
|---|---|
| Minimum: | -87.3886 |
| Maximum: | 887.4823 |
| Range of values | |
|---|---|
| Minimum: | 0.0332 |
| Maximum: | 122.5255 |
| Range of values | |
|---|---|
| Minimum: | -0.4268 |
| Maximum: | 0.6338 |
| Range of values | |
|---|---|
| Minimum: | 0.0001 |
| Maximum: | 2.7043 |
| Range of values | |
|---|---|
| Minimum: | -0.0458 |
| Maximum: | 0.6338 |
| Range of values | |
|---|---|
| Minimum: | 0.0000 |
| Maximum: | 0.7423 |
| Range of values | |
|---|---|
| Minimum: | -107.7808 |
| Maximum: | 1044.4022 |
| Range of values | |
|---|---|
| Minimum: | -0.0047 |
| Maximum: | 20.4314 |
| Range of values | |
|---|---|
| Minimum: | 0.0001 |
| Maximum: | 4.9721 |
| Range of values | |
|---|---|
| Minimum: | -0.0002 |
| Maximum: | 0.1204 |
| Range of values | |
|---|---|
| Minimum: | 0.0000 |
| Maximum: | 0.0964 |
| Range of values | |
|---|---|
| Minimum: | 5.592 |
| Maximum: | 783.8764 |
| Range of values | |
|---|---|
| Minimum: | 0.0403 |
| Maximum: | 147.7079 |
| Range of values | |
|---|---|
| Minimum: | 35.9800 |
| Maximum: | 2418.7300 |
| Units: | Millions of years |
| Range of values | |
|---|---|
| Minimum: | 0.2500 |
| Maximum: | 841.5300 |
| Units: | Millions of years |
J value, calculated from the weighted average of standards placed in various positions in the nuclear reactor
This project is part of the Alaska Airborne Geophysical/Geological Mineral Inventory Program funded by the Alaska State Legislature and managed by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. Partial funding for the geologic mapping and 39Ar/40Ar geochronology was also provided through the State of Alaska General Fund and the U.S. Geological Survey STATEMAP Program under award number 08HQAG0051. Samples were collected as part of the geologic mapping program during 2008 by J.E. Andrew, M.B. Werdon, D.J. Szumigala, and L.K Freeman of DGGS and by R.J. Newberry of the Department of Geology & Geophysics, University of Alaska Fairbanks
(907)451-5020 (voice)
dggsgis@alaska.gov
In 2008, the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted a geologic mapping project in parts of the Fairbanks A-1, Fairbanks A-2, Healy D-1, and Healy D-6quadrangles. Our purpose was to map the bedrock geology at a scale of 1:50,000 as part of the Alaska Geophysical/Geological Mineral Inventory (AGGMI) program investigations in the Bonnifield mining district. DGGS published geochemical data resulting from the 2008 work in 2009 (Freeman and others, 2009a). A brief discussion of the results was given in Freeman and others (2009b) and Freeman and others (2010). The purpose of this DGGS Raw Data File is to present the 40Ar/39Ar results and make them available for use to the public that are interested in the area.
Freeman, L.K., Werdon, M.B., Szumigala, D.A., Andrew, J.A., Newberry, R.J., and Athey, J.A., 2009, Geochemical, major-oxide, minor-oxide, trace-element and carbon data from rocks collected in 2008 in the eastern Bonnifield mining district, Fairbanks and Healy quadrangles, Alaska: Alaska Division of Geological & Geophysical Surveys Raw Data File RDF 2009-1.
Freeman, L.K., Newberry, R.J., Andrew, J.A., Werdon, M.B., Szumigala, D.A., Athey, J.A., and Burns, L.E., 2009, Recent geologic mapping in the eastern Bonnifield mining district, Alaska: Geological Society of America Abstracts with Programs v. 41, no. 7.
Lanphere, M.A., and Dalrymple, G.B., 2000, First-principles calibration of 38Ar tracers: Implications for the ages of 40Ar/39Ar fluence monitors: U.S. Geological Survey Professional Paper 1621.
Samson, S.D., and Alexander, E.C., 1987, Calibration of the inter laboratory 40Ar/39Ar dating standard, MMhb-1: Chemical Geology v. 66.
York, D., Hall, C.M., Yanase, Y., and Kenyon, W.J., 1981, 40Ar/39Ar dating of terrestrial minerals with a continuous laser: Geophysical Research Letter v. 8.
Layer, P.W., Hall, C.M., and York, D., 1987, The derivation of 40Ar/39Ar age spectra of single grains of hornblende and biotite by laser step heating: Geophysical Research Letter v. 14.
Layer, P.W., 2000, Argon-40/argon-39 age of the El'gygytgyn impact event, Chukotka, Russia: Meteoritics and Planetary Science v. 35.
McDougall, I, and Harrison, T.M., 1999, Geochronology and Thermochronology by the 40Ar/39Ar method: Oxford University Press, Oxford.
Steiger, R.H., and Jager, E., 1977, Sub-commission on geochronology: convention on the use of decay constants in geo- and cosmochronology: Earth and Planetary Science Letters v.36.
Data sources used in this process:
Data sources used in this process:
Data sources used in this process:
Data sources used in this process:
Data sources used in this process:
Coordinates of sample locations were determined by the geologists in the field using Garmin 12XL GPS receivers with no differential correction. The coordinates were recorded in field notes along with hand sample descriptions and other locality information. The coordinates were up-loaded into an MS Access database and were checked against recorded coordinates in geologists field notes. DGGS submitted eight rock samples to the UAF Geochronology Laboratory for 40Ar/39Ar dating. Separates for 40Ar/39Ar dating were prepared to >99.5% purity (visual inspection) using standard heavy liquid and magnetic separation techniques followed by hand-picking under a binocular microscope.Thin section examination of the samples prior to crushing indicated that the chosen minerals were free from alteration and sufficiently coarse-grained for mechanical separation.For all minerals, grains in the size range of 250 - 500 microns were used.For each sample, ~50-80 mg of biotite or 250-350 mg of hornblende or whole rock (phenocryst-free groundmass) was packaged in an aluminium foil tube and irradiated in position 5C at the McMaster University nuclear reactor, in Hamilton, Ontario.Approximately 20 samples were irradiated at a time.Six packages containing ~20 mg of the standard mineral mmhb-1 (Samson and Alexander, 1987) with an age of 513.9 Ma (Lanphere and others, 1990) were also irradiated with the samples to determine the irradiation parameter (J) and the flux gradient in the reactor.Samples and standards were analyzed 45 to 90 days after irradiation. The irradiated samples were step-heated on-line in a Modifications Ltd. low-blank furnace.Temperature control was better than 5 degrees and a maximum temperature in excess of 1600o C was achievable to ensure complete sample fusion.The extracted argon was purified in a two-stage process using a liquid nitrogen cold finger and two SAES Zr-Al getters.Prior to measurement of the Ar, the gas was collected on an activated charcoal finger.The purified Ar gas was measured using a Nuclide 6-60-SGA 15 cm mass spectrometer.The sensitivity of the spectrometer is 6.5 x 10-15 mol/mV and system noise is generally around 0.02 mV.System blanks are generally better than 1 X 10-14 mol for 40Ar.Argon isotopic measurements for both samples and standards were corrected for the system blanks, for decay of37Ar and 39Ar, and for reactor-induced isotopic interferences.Ages were calculated using the equations and corrections from McDougall and Harrison (1999) and the constants from Steiger and Jaeger (1977) and are shown in Table 2 (age summary) and Table 3 (analytical data).All errors on analyses are reported at the 1-sigma level. For each mass spectrometer analysis, five Ar isotope abundances are measured.36Ar is used to determine the amount of atmospheric or initial Ar in the sample, 37Ar provides an estimation of the Ca content in the mineral, 38Ar provides an estimation of the Cl content, 39Ar reflects the K content and 40Ar is a mixture of initial and radiogenic Ar.The age of the sample is proportional to the ratio of the amount of radiogenic 40Ar to the amount of 39Ar produced by neutron bombardment from 40K.
All field locations were determined by the geologists in the field using Garmin 12XL GPS receivers with no differential correction. Estimated position errors as calculated by the Garmin 12XL receivers were recorded in the field and range from 3 to 6 meters for the samples used in this data.
This dataset includes all of the samples submitted for 40Ar/39Ar age date analyses from the Healy and Fairbanks quadrangle that were collected by DGGS during the summer of 2008.
No topologic relationships are present in the data. Sample numbers in the each of the three tables were recorded by geologists in the field, recorded on sample bags and on field note sheets. The sample numbers were transcribed into an Access database by a field assistant. Table 1 was generated from the database and was cross checked against the sample numbers recorded on the bags for consistency. Sample numbers in tables 2 and 3 were generated by the UAF geochronology lab from the a list provided by DGGS and cross checked with sample numbers on the bags. We are certain that the sample numbers in the table are logically correct.
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- Access_Constraints:
- This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
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- Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
(907)451-5020 (voice)
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dggspubs@alaska.gov
RDF 2011-2
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DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media by mail, phone, fax, or email from the DGGS Fairbanks office. To purchase this or other printed reports and maps, contact DGGS by phone (907-451-5020), e-mail (dggspubs@alaska.gov), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard. Turnaround time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for the exact shipping amount.
| Data format: | PDF (version 1.6) |
|---|---|
| Network links: |
<http://dx.doi.org/10.14509/22482> |
| Data format: | CSV |
|---|---|
| Network links: |
<http://www.dggs.alaska.gov/pubs/id/22482> |
DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media over the counter, by mail, phone, fax, or email from the DGGS Fairbanks office. Turnaround time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for exact shipping amount.
(907)451-5020 (voice)