Alaska Radiometric Ages

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Frequently anticipated questions:


What does this data set describe?

Title: Alaska Radiometric Ages
Abstract:
The Alaska Radiometric Age file is a database of radiometric ages of rocks or minerals sampled from Alaska. The data was collected from professional publications and/or received from researchers and used by permission.
Supplemental_Information:
The radiometric dates in this data set were collected from published sources through 1990(approximately). The dates were compiled over many years and published as a map in the series Decade of North American Geology, by the Geological Society of America.
  1. How might this data set be cited?
    U.S. Geological Survey, 1999, Alaska Radiometric Ages.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: 172.0
    East_Bounding_Coordinate: -130.0
    North_Bounding_Coordinate: 72.0
    South_Bounding_Coordinate: 54.0
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 1999
    Currentness_Reference:
    Date on which data provided online was extracted from the database
  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?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.002. Longitudes are given to the nearest 0.002. Latitude and longitude values are specified in Decimal degrees. 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 6378206.4.
      The flattening of the ellipsoid used is 1/294.98.
  7. How does the data set describe geographic features?
    points
    Characteristics of points in shape table.
    Quad
    Name of 1:250,000 scale quadrangle (Source: USGS Geographic Names Information System) Name of 1:250,000 scale quadrangle.
    Latdeg
    Degree of latitude
    Range of values
    Minimum:50
    Maximum:70
    Units:degrees
    Resolution:1.
    Latmin
    Minute of latitude
    Range of values
    Minimum:0.0
    Maximum:59.9
    Units:minutes
    Resolution:0.1
    Latdir
    Direction of latitude
    ValueDefinition
    NNorth
    Londeg
    Degree of longitude
    Range of values
    Minimum:126
    Maximum:179
    Units:degrees
    Resolution:1.
    Lonmin
    Minute of longitude
    Range of values
    Minimum:0.0
    Maximum:59.9
    Units:minutes
    Resolution:0.1
    londir
    Direction of longitude
    ValueDefinition
    EEast
    WWest
    Sample
    Sample ID from published source. If none was given in the cited source, then a sample id was created for this database. free text
    Rock
    Rock name or type
    ValueDefinition
    ADAMadamellite
    AGNSaugen gneiss
    ALSKalaskite
    ALTaltered
    AMPHamphibolite
    ANDandesite
    APLaplite
    ASHash
    BASbasalt
    BIOTbiotitite
    BENTbentonite
    BSCHblueschist
    BRECbreccia
    CGconglomerate
    DACdacite
    DIdiorite
    DIAdiabase
    ECLGeclogite
    FELSfelsite
    GABgabbro
    GDIgranodiorite
    GLASSglass
    GNLTgranulite
    GNSgneiss
    GNSTgreenstone
    GRgranite
    GRTDgranitoid
    GSCHgreenschist
    HBDThornblendite
    HFLShornfels
    INTRintrusive
    LAMPlamprophyre
    LATlatite
    LBASleucobasalt
    LGABleucogabbro
    MAFmafic
    MARmarble
    METAmetamorphic
    METBmetabasite
    METPmetapelite
    METVmetavolcanic
    METWmetawacke
    MIGmigmatite
    MONmonzonite
    MONDImonzodiorite
    MYLTmylonite
    OTHERother (rock identified in comments field)
    PEGpegmatite
    PHYLphyllite
    PORPHporphyry
    PYRXpyroxenite
    Q DIquartz diorite
    QMDquartz monzodiorite
    QMONquartz monzonite
    QSquartz sericite
    QTZTquartzite
    RHYrhyolite
    SBRECsedimentary breccia
    SCHschist
    SERPserpentinite
    SKARNskarn
    SSsandstone
    SYsyenite
    TONtonalite
    TRCHtrachyte
    TRONDtrondjemite
    TUFFtuff
    UMAFultramafic
    VOLvolcanic
    UNIDunidentified
    XENOxenolith
    Method
    Isotopic dating method
    ValueDefinition
    APb-alpha
    FFission track
    KK-Ar
    PPb methods
    RRb-Sr
    SSm-Nd
    Mineral
    Mineral or phase dated from sample; or denotes that date is calculated from an isochron.
    ValueDefinition
    ACactinolite
    AMamphibole
    APapatite
    AWanorthoclase
    BIbiotite
    CHchlorite
    FDfeldspar
    GLglass
    GPglaucophane
    HOhornblende
    ICisochron
    KFK-feldspar
    MImica
    MUmuscovite
    OTother (mineral identified in comments field)
    PAparagonite
    PHphengnite
    PLplagioclase
    PPphologopite
    PYpyroxene
    RIriebeckite
    SAsanidine
    SEsericite
    SPsphene
    TRtremolite
    UNunknown
    WRwhole rock
    ZIzircon
    Age m.y.
    Age of sample in millions of years positive number
    Comment
    Field for free text. free text
    Ref
    Reference of data sample. free text

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Geological Survey
  2. Who also contributed to the data set?
    The radiometric age data base has been maintained since the mid-1970's. Compilers include: F.H. Wilson, Nora Shew, G.D. DuBois, and Shawn Dadisman.
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Nora Shew
    4200 University Drive
    Anchorage, AK
    U.S.A.

    907-561-1181 (voice)
    nshew@usgs.gov

Why was the data set created?

Database of radiometric ages is designed to aid in the research of geochronologic information of Alaska rocks and minerals. Users should always review the cited publications for more complete descriptions of the samples, analyses, and geologic interpretation.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 1999 (process 1 of 1)
    The Alaska radiometric age file is a compilation of published and other released radiometric dates on rocks and minerals of Alaska. The precision of the analyses and the locations of the samples vary widely from the various sources. This compilation has not attempted to interpret the data. Users of this data should always refer to the published sources of the information.

    This database contains for each record: location, dating method, rock type, mineral/phase dated, age (in millions of years), comments, and references. The data was imported into Microsoft Access, brought into ArcView3.1 as an event theme, and then converted into a shape file. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Nora Shew
    4200 University Drive
    Anchorage, AK
    USA

    907-561-1181 (voice)
    nshew@usgs.gov
  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?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    The radiometric age database does not include the analytical information which is often found in the published sources. Also, the database records do not contain the geologic interpretation of the analysis. Users of this database should always /refer to the publications listed in the 'Reference' field for detailed information about each analysis.
  5. How consistent are the relationships among the observations, including topology?
    Generally, the radiometric ages in the database are as published. Some potassium-argon ages have been recalculated using the decay constants recommended by the IUGS Subcommission on Geochronology in 1976. Dates that have been recalculated are noted in the 'Comments' field.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
Use_Constraints:
The U.S. Geological Survey makes no warranties related to the accuracy of the data and users are required to determine the usability for any particular purpose.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey
    Attn: Tom Kress
    12201 Sunrise Valley Drive MS954
    Reston, VA
    USA

    703-648-6328 (voice)
    thkress@usgs.gov
  2. What's the catalog number I need to order this data set? akages.shp
  3. What legal disclaimers am I supposed to read?
    The U.S. Geological Survey (USGS) provides this point data "as is." The USGS make no guarantee or warranty concerning the accuracy of information contained in the dataset. Further, the USGS makes no warranties, either expressed or implied, as to any other matter whatsoever, including, without limitation, the condition of the product, or its fitness for any particular purpose. The burden for determining fitness for use lies entirely with the user. Although this data has bee processed successfully on computers at the USGS, no warranty, express or implied, is made by the USGS regarding the use of this data on any other system, nor does the fact of distribution constitute or imply any such warranty.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 07-Dec-2016
Metadata author:
U.S. Geological Survey
Attn: Nora Shew
4200 University Drive
Anchorage, AK
USA

907-561-1181 (voice)
nshew@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://mrdata.usgs.gov/metadata/akages.faq.html>
Generated by mp version 2.9.47 on Mon Mar 26 17:20:46 2018