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

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Frequently-anticipated questions:


What does this data set describe?

Title:
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
Abstract:
40Ar/39Ar data from plutonic, dike, and alteration samples collected during geologic mapping of the eastern part of the Bonnifield mining district geologic map area in parts of Fairbanks A-1 and Fairbanks A-2 and Healy D-1 and Healy D-2 quadrangles yield results indicating the plutons, dikes, and a gold-bearing quartz vein in the Bonnifield Map area range from 85 to 95 m.y.
Supplemental_Information:
Attribute information for the three tables (entities) is included in this metadata file under the "Entity_and_Attribution_Information" section. The tables are hierarchical with the SampleLocationDescription table being the parent of of the SummaryAges table which is in turn the parent of StepHeatingData table. The the tables are connected by the SampleNumber and DatedMaterial columns. All tables comprise a single layer as follows:
ArgonGeochronologicData: SampleLocationDescription, SummaryAges, and StepHeatingData
  1. How should this data set be cited?

    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:

    Other_Citation_Details: 23 pp.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -147.8028
    East_Bounding_Coordinate: -147.1864
    North_Bounding_Coordinate: 64.0634
    South_Bounding_Coordinate: 62.9455

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date:
    Ending_Date:
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: tabular digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Point data set.

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 6
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -147
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000
      False_Northing: 0

      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.

  7. How does the data set describe geographic features?

    SampleLocationDescription.csv
    Location and description of rock samples collected for trace-element geochemical analyses in the eastern Bonnifield mining district, Fairbanks and Circle quadrangles, Alaska (Source: Alaska Division of Geological & Geophysical Surveys)

    SampleNumber
    Unique sample identifier (Source: Alaska Division of Geological & Geophysical Surveys)

    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.

    Latitude
    Latitude in decimal degrees, NAD 27 (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:63.8411
    Maximum:64.066
    Units:decimal degrees

    Longitude
    Longitude in decimal degrees, NAD 27 (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:-147.8358
    Maximum:-147.3248
    Units:decimal degrees

    UTME
    Easting (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:459098
    Maximum:484148
    Units:meters

    UTMN
    Northing (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:7079208
    Maximum:7104209
    Units:meters

    Zone
    UTM Zone (Source: Alaska Division of Geological & Geophysical Surveys)

    "6" indicates 06W NAD27 Alaska Projection

    Description1
    Brief rock description part 1 0f 3 (truncated to 255 characters) (Source: Alaska Division of Geological & Geophysical Surveys)

    Brief rock description

    Description2
    Brief rock description part 2 of 3 (for descriptions longer than 255 characters) (Source: Alaska Division of Geological & Geophysical Surveys)

    Brief rock description

    Description3
    Brief rock description part 2 of 3 (for descriptions longer than 510 characters) (Source: Alaska Division of Geological & Geophysical Surveys)

    Brief rock description

    SummaryAges.csv
    Summary of 40Ar/39Ar radiometric ages of samples in this report. Preferred interpreted ages are underlined in the Adobe Acrobat portable document version of the tables. (Source: Alaska Division of Geological & Geophysical Surveys)

    SampleNumber
    Unique sample identifier, corresponds to "SampleNumber" attribute in "SampleLocationDescription.csv (Source: Alaska Division of Geological & Geophysical Surveys)

    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.

    DatedMaterial
    Material used for age date (Source: Alaska Division of Geological & Geophysical Surveys)

    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.

    IntegratedAgeMa
    Integrated age and age error in million years (Ma). (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:84.3 +- 0.5
    Maximum:111.1 +- 1.3
    Units:Ma

    PlateauAgeMa
    Plateau age and age error in million years (Ma) for each sample. Preferred interpreted ages are underlined in the Adobe Acrobat portable document version of the tables. Null values indicate that the age could not be determined. (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:64.2 +- 1.0
    Maximum:102.5 +- 1.5
    Units:Ma

    PlateauInformation
    Describes the number of fractions, percent 39Ar released, and Mean Standard Weighted Deviation (MSWD) used for the plateau age. Null values indicate that the age could not be determined. (Source: Alaska Division of Geological & Geophysical Surveys)

    number of fractions, % 39Ar released, MSWD.

    IsochronOrOtherInformation
    Lists the isochron age and information of the isochron age if appropriate. Comments regarding some of the other age analyses are also listed in this column. (Source: Alaska Division of Geological & Geophysical Surveys)

    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".

    StepHeatingData.csv
    The Step heating data is the root 40Ar/39Ar analytical data associated with each recorded Power output level for each run of dated material from a sample in this report. (Source: Alaska Division of Geological & Geophysical Surveys)

    SampleNumber
    Sample number contains an identifier that along with the "DatedMaterial" column relates the Step Heating data to the "SummaryAges" entity. The "SampleNumber" attribute corresponds to the "SampleNumber' attribute inboth the "SampleLocationDescription" and "SummaryAges" entities. (Source: Alaska Division of Geological & Geophysical Surveys)

    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.

    DatedMaterial
    Dated Material contains a string describing the material used to for the analysis along with the "SampleNumber" attribute relates the "StepHeatingData" entity to the "SummaryAges" entity. The information in this attribute and corresponds to the "Dated Material" attributes in the "SummaryAges" entity respectively. (Source: Alaska Division of Geological & Geophysical Surveys)

    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.

    Laser_mW
    Laser output level in megawatts, or "integrated" of each heating step (Source: University of Alaska Department of Geosciences Geochronology Laboratory)

    ValueDefinition
    IntegratedIndicates row of data from entire step heating run

    Range of values
    Minimum:300
    Maximum:9000
    Units:Megawatts

    Cum39Ar
    Cumulative ratio of 39Argon released at this step. Null indicates that a cumulative value is not appropriate. (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:0.0022
    Maximum:1.0001

    Ratio40Ar39ArMeasured
    Measured 40Ar/39Ar ratio for each heating step, corrected for blank and 39Ar decay (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:-87.3886
    Maximum:887.4823

    Ratio40Ar39ArMeasuredError
    The one sigma error for each 40Ar/39Ar measurement. (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:0.0332
    Maximum:122.5255

    Ratio37Ar39ArMeasured
    The ratio of measured 37Ar to measured 39Ar for each heating interval for each sample corrected for blank and 37Ar and 39Ar decay (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:-0.4268
    Maximum:0.6338

    Ratio37Ar39ArMeasuredError
    The one sigma error for each 37Ar/39Ar measurement. (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:0.0001
    Maximum:2.7043

    Ratio36Ar39ArMeasured
    Ratio of measured 36Ar to measured 39Ar for each step interval for each sample corrected for blank and 39Ar decay (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:-0.0458
    Maximum:0.6338

    Ratio36Ar39ArMeasuredError
    The one sigma error for each 36Ar/39Ar measurement. (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:0.0000
    Maximum:0.7423

    PercentAtm40Ar
    Percent of 40Ar which is atmospheric in composition at each step level (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:-107.7808
    Maximum:1044.4022

    RatioCaK
    ratio of Calcium to Potassium as determined from 37Ar/39Ar (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:-0.0047
    Maximum:20.4314

    RatioCaKError
    The one sigma error for each Ca/K determination. (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:0.0001
    Maximum:4.9721

    RatioClK
    ratio of Chlorine to Potassium as determined from 38Ar/39Ar (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:-0.0002
    Maximum:0.1204

    RatioClKError
    The one sigma error for each Cl/K determination. (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:0.0000
    Maximum:0.0964

    Ratio40ArRad39ArK
    ratio of radiogenic 40Ar to 39Ar derived from potassium (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:5.592
    Maximum:783.8764

    Ratio40ArRad/39ArKError
    One sigma error for each 40ArRad/39ArK value (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:0.0403
    Maximum:147.7079

    AgeMa
    calculated age for each temperature step for each sample (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:35.9800
    Maximum:2418.7300
    Units:Millions of years

    AgeErrorMa
    one sigma error of the age determination of each heating step (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:0.2500
    Maximum:841.5300
    Units:Millions of years

    WeightedAverageOfJFromStandards
    one sigma error of the age determination of each heating step (Source: Alaska Division of Geological & Geophysical Surveys)

    J value, calculated from the weighted average of standards placed in various positions in the nuclear reactor


Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

    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

  3. To whom should users address questions about the data?

    State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys
    GIS Data Manager/Cartographer
    3354 College Road
    Fairbanks, AK 99709-3707

    (907) 451-5029 (voice)
    (907) 451-5050 (FAX)
    dggspubs@alaska.gov

    Contact_Instructions:
    You may view our web site at <http://www.dggs.alaska.gov/> for the latest information on available data.Please e-mail your questions and data requests when possible since our web site and e-mail address will remain current even if our phone number and mailing address change.


Why was the data set created?

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.


How was the data set created?

  1. From what previous works were the data drawn?

    Freeman and others, 2009a (source 1 of 9)
    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.

    Other_Citation_Details: 69 p.
    Type_of_Source_Media: paper and digital
    Source_Contribution:
    Provides chemical data for classification and description of samples

    Freeman and others, 2009b (source 2 of 9)
    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.

    Other_Citation_Details: (abstract), P. 282
    Type_of_Source_Media: paper
    Source_Contribution:
    Describes field work and initial geologic findings, reports preliminary ages

    Lanphere and Dalrymple, 2000 (source 3 of 9)
    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.

    Other_Citation_Details: 10 p.
    Type_of_Source_Media: paper
    Source_Contribution: Describes inter-calibration standards

    Samson and Alexander, 1987 (source 4 of 9)
    Samson, S.D., and Alexander, E.C., 1987, Calibration of the inter laboratory 40Ar/39Ar dating standard, MMhb-1: Chemical Geology v. 66.

    Other_Citation_Details: p. 27-34
    Type_of_Source_Media: paper
    Source_Contribution: Inter laboratory calibration data for age determination

    York, and others, 1981 (source 5 of 9)
    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.

    Other_Citation_Details: p. 1136-1138
    Type_of_Source_Media: paper
    Source_Contribution:
    Description of laser heating mass-spectrographic analysis method

    Layer and others, 1981 (source 6 of 9)
    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.

    Other_Citation_Details: p. 757-760
    Type_of_Source_Media: paper
    Source_Contribution:
    Description of laser step-heating mass-spectrographic analysis method

    Layer, 2000 (source 7 of 9)
    Layer, P.W., 2000, Argon-40/argon-39 age of the El'gygytgyn impact event, Chukotka, Russia: Meteoritics and Planetary Science v. 35.

    Other_Citation_Details: p. 591-599
    Type_of_Source_Media: paper
    Source_Contribution:
    Description of laser step-heating mass-spectrographic analysis method

    McDougall and others, 1999 (source 8 of 9)
    McDougall, I, and Harrison, T.M., 1999, Geochronology and Thermochronology by the 40Ar/39Ar method: Oxford University Press, Oxford.

    Other_Citation_Details: 269 pp.
    Type_of_Source_Media: paper
    Source_Contribution:
    Source reference for equations and corrections used in age calculation.

    Steiger and Jager, 1977 (source 9 of 9)
    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.

    Other_Citation_Details: p. 359-363
    Type_of_Source_Media: paper
    Source_Contribution: discussion of use of decay constants in age determination

  2. How were the data generated, processed, and modified?

    Date: Jul-2008 (process 1 of 5)
    Fieldwork - The eastern Bonnifield map area, including parts of the Fairbanks A-1, A-2, Healy D-1, and Healy D-2 quadrangles was mapped at 1:50,000 scale. As part of the mapping geologic, samples of igneous rocks and mineralized rocks with sericite were collected as potential samples for geochronology. Sample locations were determined using Garmin 12 XL GPS receivers. Field descriptions were recorded onto field note forms which were later transcribed into a MS Access database by a geological field assistant.

    Data sources used in this process:

    • Freeman and others, 2009b

    Date: Dec-2008 (process 2 of 5)
    Sample selection - A list of samples that were collected for radiometric ages was generated from th MS Access database and checked against available samples. Petrographic thin sections for the prospective samples were examined to eliminate samples that were altered. Sample locations were plotted in GIS along with the preliminary geologic map to determine which samples would provide the most geologically significant age information.

    Data sources used in this process:

    • Freeman and others, 2009b

    Date: Jan-2009 (process 3 of 5)
    Sample description - Sample descriptions were generated from field descriptions, petrographic descriptions, and major oxide geochemistry. The sample descriptions were also used in Freeman, and others, 2009

    Data sources used in this process:

    • Freeman and others, 2009a

    Date: Mar-2009 (process 4 of 5)
    Sample preparation - Mineral separates for 40Ar/39Ar dating were prepared to greater than 99.5 percent purity (determined by visual inspection) where they were crushed, sieved, washed, and hand-picked for mineral phases or small, phenocryst-free whole-rock chips. The monitor mineral MMhb-1 (Samson and Alexander, 1987) with an age of 513.9 Ma (Lanphere and Dalrymple, 2000) was used to monitor neutron flux (and calculate the irradiation parameter, J). The samples and standards were wrapped in aluminum foil and loaded into aluminum cans 2.5 cm in diameter and 6 cm in 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.

    Data sources used in this process:

    • Samson and Alexander, 1987
    • Lanphere and Dalrymple, 2000

    Date: May-2009 (process 5 of 5)
    Sample analysis - Upon their return from the reactor, the samples and monitors were loaded into 2-mm-diameter holes in a copper tray that was then loaded into an ultra-high-vacuum extraction line. The monitors were fused and samples heated using a 6-watt argon-ion laser following the technique described in York and others(1981), Layer and others (1987), and Layer (2000). Argon purification was achieved using a liquid nitrogen cold trap and an SAES Zr-Al getter at 400C. The samples were analyzed in a VG-3600 mass spectrometer at the Geophysical Institute, University of Alaska Fairbanks. The argon isotopes measured were corrected for system blank and mass discrimination, as well as calcium, potassium, and chlorine interference reactions following procedures outlined in McDougall and Harrison (1999). System blanks generally were 2x10e-16 mol 40Ar and 2x10e-18mol 36Ar, which are 10 to 50 times smaller than fraction volumes. Mass discrimination was monitored by running both calibrated air shots and a zero-age glass sample. These measurements were made on a weekly to monthly basis to check for changes in mass discrimination. A summary of all the 40Ar/39Ar results is given in table 2, with all ages quoted to the +-1 sigma level and calculated using the constants of Steiger and Jaeger (1977). The integrated age is the age given by the total gas measured and is equivalent to a potassium-argon (K-Ar) age. The spectrum provides a plateau age if three or more consecutive gas fractions represent at least 50 percent of the total gas release and are within two standard deviations of each other (Mean Square Weighted Deviation less than ~2.5). All samples were run three times to verify sample consistency.

    Data sources used in this process:

    • York, and others, 1981
    • Layer, and others, 1987
    • Layer, 2000
    • McDougall and Harrison, 1999
    • Steiger and Jaeger, 1977

  3. What similar or related data should the user be aware of?


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    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 aluminum 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.

  2. How accurate are the geographic locations?

    All field locations were determined by the geologists in the field using Garmin 12XL GPS receivers with no differential correction.

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    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.

  5. How consistent are the relationships among the observations, including topology?

    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.


How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints:
This report and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
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. 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.

  1. Who distributes the data set? (Distributor 1 of 1)

    State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    907-451-5020 (voice)
    907-451-5050 (FAX)
    dggspubs@alaska.gov

    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our web site (<http://www.dggs.alaska.gov>) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
  2. What's the catalog number I need to order this data set?

  3. What legal disclaimers am I supposed to read?

    The State of Alaska makes no express or implied warranties (including warranties of merchantability and fitness) with respect to the character, function, or capabilities of the electronic services 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, any failure thereof, or otherwise, and in no event will the State of Alaska's liability to the requester or anyone else exceed the fee paid for the electronic service or product.

  4. How can I download or order the data?

  5. Is there some other way to get the data?

    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.Turn around 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 a exact shipping ammount.


Who wrote the metadata?

Dates:
Last modified: 22-Jun-2011
Metadata author:
Metadata manager
State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys
Fairbanks, AK 99709-3707
USA

907-451-5020 (voice)

Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:


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