Zircon U-Pb age data, Alaska Highway Corridor, Tanacross and Nabesna quadrangles, Alaska

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Frequently anticipated questions:

What does this data set describe?

Title:
Zircon U-Pb age data, Alaska Highway Corridor, Tanacross and Nabesna quadrangles, Alaska
Abstract:
Twenty-two igneous and metamorphic rock samples were collected in a 20-km-long swath centered on the Alaska Highway between Tetlin Junction, Alaska, and the Canada border. Igneous and metamorphic rock samples were submitted to the Apatite to Zircon, Inc. laboratory (A2Z), where zircon U-Pb age analysis, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), was performed by Paul O'Sullivan. The 15 felsic plutonic rock samples and one gabbro sample yield Cretaceous zircon U-Pb weighted-mean ages ranging from 95.7 Ma to 106.2 Ma. Zircons from a metadiorite yield a Triassic weighted-mean age of about 241.9 Ma. Metamorphic zircons from two samples with felsic igneous protoliths yield Mississippian weighted-mean ages of 351.7 Ma and 354.6 Ma. Detrital zircons from two metaconglomerates yield individual grain ages from 100 Ma to 1,811 Ma, but are predominantly between 300 Ma and 345 Ma. Detrital zircons from a quartzite yield peaks at about 2,648 Ma, 1,946 Ma, and 1,807 Ma. Samples were analyzed for a variety of suites of major and trace elements depending on the sample type. The analytical data tables associated with this report are being released in digital format.
Supplemental_Information:
The DGGS metadata standard extends the FGDC standard to include elements that are required to facilitate our internal data management. These elements, referred to as "layers," group and describe files that have intrinsic logical or topological relationships and correspond to subdirectories within the data distribution package. The metadata layer provides an FGDC metadata file and may include other documentation files. Attribute information for each data layer is described in this metadata file under the "Entity_and_Attribute_Information" section. Data layer contents: >border: A polygon that encompasses the maximum geographic extent of the data observations >geochron-summary: Table containing sample descriptions, location coordinates, and summary ages of rock samples analyzed for zircon uranium/lead geochronology using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) >geochron-data: Data tables (.xlsx) that provide the detailed zircon U-Pb geochronology results. Note that this group of files also includes a documentation spreadsheet that explains how the data columns are named and organized.
  1. How should this data set be cited?

    Solie, D.N., O'Sullivan, P.B., Werdon, M.B., Freeman, L.K., Newberry, R.J., Szumigala, D.J., and Hubbard, T.D., 2014, Zircon U-Pb age data, Alaska Highway Corridor, Tanacross and Nabesna quadrangles, Alaska: Raw Data File RDF 2014-16, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 8 p.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -142.426900
    East_Bounding_Coordinate: -141.017100
    North_Bounding_Coordinate: 63.325100
    South_Bounding_Coordinate: 62.555500

  3. What does it look like?

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

    Beginning_Date: 2009
    Ending_Date: 2014
    Currentness_Reference: ground condition

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

    Geospatial_Data_Presentation_Form: digital-data, report

  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 0.0001. Longitudes are given to the nearest 0.0001. 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 1/294.9786982.

  7. How does the data set describe geographic features?

    rdf2014-16-border.shp
    A polygon that encompasses the maximum geographic extent of the data observations (Source: Alaska Division of Geological & Geophysical Surveys)

    rdf2014-16-geochron-summary.csv
    Table containing sample descriptions, location coordinates, and summary ages of rock samples analyzed for zircon uranium/lead geochronology using laser ablation-inductively coupled plasma-“mass spectrometry (LA-ICP-“MS) (Source: Alaska Division of Geological & Geophysical Surveys)

    SAMPLE
    Label assigned in the field to identify the sample. (Source: Alaska Division of Geological & Geophysical Surveys)

    Generic example of a sample identifier: YYAAA9999X: YY=last two digits of year, AAA=geologist's initials (one to three characters), 9999=unique station number, X= optional alpha character which indicates that multiple samples were collected at a given location or that multiple observations were recorded in the project database. The initials used by the geologists who collected samples for this project are: LF = Larry K. Freeman, MBW = Melanie B. Werdon, RN = Rainer J. Newberry, TDH = Trent D. Hubbard, Z = David J. Szumigala

    LAB_SAMPLE_NUMBER
    Label used by the lab to identify the sample. (Source: Alaska Division of Geological & Geophysical Surveys and Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the lab sample number is identical to the field sample number.

    The lab sample number is typically identical to the field sample number. However, in some cases, the sample number provided to the lab does differ from the number assigned in the field. We provide both numbers to document instances in which the sample numbers in the lab files differ from the field sample number.

    LATITUDE
    Latitude, NAD27 (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:62.5555
    Maximum:63.3251
    Units:decimal degrees

    LONGITUDE
    Longitude, NAD27 (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:-142.4269
    Maximum:-141.0171
    Units:decimal degrees

    ZIRCON_TYPE
    The type of zircon that was dated. (Source: Alaska Division of Geological & Geophysical Surveys)

    ValueDefinition
    zirconzircon crystal
    detrital zirconzircon grain

    ROCK_CLASSIFICATION
    The type of rock that was dated. (Source: Alaska Division of Geological & Geophysical Surveys)

    The rock we sampled were collected from: igneous, metaigneous, and metasedimentary units.

    DESCRIPTION
    Description of the sample (Source: Alaska Division of Geological & Geophysical Surveys)

    Characters 1 to 254 of a brief sample or station description.

    DESCRIP_2
    Extension of the sample or station description for descriptions which are greater than 254 characters in length (Source: Alaska Division of Geological & Geophysical Surveys)

    ValueDefinition
    NULLBlank (NULL) values indicate that the descriptive text is shorter than 254 characters.

    Characters greater than 254 of the sample or station description.

    NUM_MEASUREMENTS_USED
    Number of measurements used for calculating the age. (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; NUM_MEASUREMENTS_USED is not applicable.

    Range of values
    Minimum:7
    Maximum:49

    TOTAL_MEASUREMENTS
    Total number of measurements (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; TOTAL_MEASUREMENTS is not applicable.

    Range of values
    Minimum:38
    Maximum:50

    WMEAN_AGE_MA
    Weighted mean age, in millions of years (Ma). (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; WMEAN_AGE_MA is not applicable.

    Range of values
    Minimum:95.74
    Maximum:354.57
    Units:Ma

    MEAN_AGE_MA
    Mean age, in millions of years (Ma). (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; MEAN_AGE_MA is not applicable.

    Range of values
    Minimum:95.82
    Maximum:355.4
    Units:Ma

    S2_FFER
    2-sigma error + fractionation-factor error (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; S2_FFER is not applicable.

    Range of values
    Minimum:2.53
    Maximum:13.46

    S2_STDEV_FFER
    2-sigma standard deviation on the 2-sigma error + fractionation-factor error (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; S2_STDEV_FFER is not applicable.

    Range of values
    Minimum:2.92
    Maximum:90.81

    S2
    2-sigma error (not including fractionation factor error) (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; S2 is not applicable.

    Range of values
    Minimum:0.37
    Maximum:13.46

    S2_STDEV
    2-sigma standard deviation on the 2-sigma error (not including fractionation factor error) (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; S2_STDEV is not applicable.

    Range of values
    Minimum:0.42
    Maximum:20.31

    MSWDW
    Mean Square of Weighted Deviates. Lower value indicates decreasing scatter in the data. This is, roughly, a measure of the ratio of the observed scatter of the points (from the best-fit line) to the expected scatter (from the assigned errors and error correlations). The MSWD parameter cannot be compared to the classical R2 parameter, and is not a measure of how highly correlated the X- and Y-values are. If the assigned errors are the only cause of scatter, the MSWD will tend to be near unity. MSWD values much greater than unity generally indicate either underestimated analytical errors, or the presence of non-analytical scatter. MSWD values much less than unity generally indicate either overestimated analytical errors or unrecognized error-correlations. (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; MSWDW is not applicable.

    Range of values
    Minimum:1.04
    Maximum:4.27

    P_MSWDW
    Statistical scatter in the MSWD - values range between 1 (good) and 0 (poor) (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; P_MSWDW is not applicable.

    Range of values
    Minimum:0
    Maximum:1

    MIN_CONCORDANT_SCANS_IN_CALCULATION
    Value represents the minimum number of concordant scans required for a successful analysis. (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; MIN_CONCORDANT_SCANS_IN_CALCULATION is not applicable. Note: A2Z did not provide a MIN_CONCORDANT_SCANS_IN_CALCULATION value for sample: 09LF206A

    Range of values
    Minimum:5
    Maximum:5

    MEAN_U_PPM
    Mean concentration of uranium (U), in parts per million (ppm). (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; MEAN_U_PPM is not applicable.

    Range of values
    Minimum:5.49
    Maximum:2588.14
    Units:ppm

    MEAN_TH_PPM
    Mean concentration of thorium (Th), in parts per million (ppm). (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; MEAN_TH_PPM is not applicable.

    Range of values
    Minimum:2.51
    Maximum:804.53
    Units:ppm

    MEAN_U_TH_RATIO_PPM
    Mean concentration of uranium (U) divided by the mean concentration of thorium (Th); in parts per million (ppm). (Source: Apatite to Zircon, Inc. (A2Z))

    ValueDefinition
    NULLBlank (NULL) values indicate that the sample was a detrital zircon; MEAN_U_TH_RATIO_PPM is not applicable.

    Range of values
    Minimum:1.372
    Maximum:4.83
    Units:ppm

    rdf2014-16-geochron-data
    Data tables (.xlsx) that provide the detailed zircon U-Pb geochronology results. Note that this group of files also includes a documentation spreadsheet that explains how the data columns are named and organized. (Source: Alaska Division of Geological & Geophysical Surveys)

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 was supported by Alaska State Capital Improvement Project funds. Samples used in this report were collected by Larry Freeman, Melanie Werdon, David Szumigala, and Trent Hubbard of DGGS; and Rainer Newberry of the University of Alaska Fairbanks Department of Geology and Geophysics. Margaret Donelick and Jim McMillan (A2Z) provided technical assistance with sample preparation; Charles Knaack (Washington State University) provided technical assistance with LA-ICP-MS data collection; Paul O'Sullivan and Ray Donelick (A2Z) provided valuable assistance with LA-ICP-MS data interpretation.

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

    Alaska Division of Geological & Geophysical Surveys
    GIS Manager
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907)451-5020 (voice)
    dggsgis@alaska.gov

    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays

Why was the data set created?

The Alaska Division of Geological & Geophysical Surveys (DGGS) conducted a multi-year project (from 2006 through 2010) studying the geology and geologic hazards along the Alaska Highway corridor. As part of the bedrock geologic mapping, samples were collected for geochronologic analyses using 40Ar/39Ar, fission-track, and U-Pb dating techniques. Summaries of analytical results appear on bedrock-geologic maps that are being published in three segments. This report supplies the supporting data for the zircon U-Pb age results from the easternmost segment of the project, in the Tanacross and Nabesna quadrangles.

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: 2009 (process 1 of 2)
    Sample collection - DGGS field geologists collected rock samples from the surface or within 0.5 m of the surface. Care was taken to collect fresh, unweathered samples representative of rock types in the map area. Locations were recorded using hand-held GPS units with an estimated horizontal accuracy of approximately 10 m.

    Date: 2011 (process 2 of 2)
    U-Pb-geochron-data - DGGS submitted selected rock samples to Apatite to Zircon, Inc. in 2011. Paul O'Sullivan directed the processing and analyses of the samples in the A2Z laboratory. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses were performed at the Geoanalytical Laboratory, Washington State University, Pullman, Washington, U.S.A. Detailed discussion of laboratory techniques is provided in appendices to the accompanying report

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

    Solie, D.N., Layer, P.W., Werdon, M.B., Newberry, R.J., Freeman, L.K., and Lessard, R.R., 2013, 40Ar/39Ar data, Alaska Highway corridor from Delta Junction to Canada border, parts of Mount Hayes, Tanacross, and Nabesna quadrangles, Alaska: Raw Data File RDF 2013-8, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 35 p
    Solie, D.N., O'Sullivan, P.B., Werdon, M.B., and Lessard, R.R., 2013, Apatite fission track data, Alaska Highway corridor, Mount Hayes Quadrangle, Alaska: Raw Data File RDF 2013-9, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 17 p
    Solie, D.N., Werdon, M.B., Newberry, R.J., Freeman, L.K., and Lessard, R.R., 2008, Major-oxide, minor-oxide, trace-element and geochemical data from rocks collected in the Alaska Highway corridor Mount Hayes Quadrangle, Alaska in 2006 and 2007: Raw Data File RDF 2008-2 v. 1.0.1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 23 p
    Werdon, M.B., Freeman, L.K., Szumigala, D.J., Newberry, R.J., Andrew, J.E., Speeter, G.G., Solie, D.N., Hubbard, T.D., Griesel, G.A., and Elliott, B.A., 2014, Major-oxide, minor-oxide, and trace-element geochemical data from rocks collected in the Alaska Highway corridor, Mount Hayes, Tanacross, and Nabesna quadrangles, Alaska, in 2006, 2008, 2009, and 2010: Raw Data File RDF 2014-4, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p

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

  1. How well have the observations been checked?

    This data is being released in the DGGS Raw-Data File series. The information has been examined by several geologists familiar with the study area but the data and accompanying report have not been reviewed for technical content or for conformity to the editorial standards of DGGS. Questions regarding the accuracy of information in the the A2Z data files can be best answered by the originating lab.

  2. How accurate are the geographic locations?

    Locations were recorded using hand-held GPS units with an estimated horizontal accuracy of approximately 10 m.

  3. How accurate are the heights or depths?

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

    The original data files provided to us by A2Z included macros and proprietary calculations. The tabulated results presented in this data release are in the publication format specified by the lab.

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

    not applicable

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, 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).
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. 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.

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

    Alaska 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 website (<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?

    RDF 2014-16

  3. What legal disclaimers am I supposed to read?

    The State of Alaska makes no expressed 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.

  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 21-Jul-2014
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Metadata Manager
3354 College Road
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:

Generated by mp version 2.9.21 on Mon Jul 21 12:04:52 2014