40Ar/39Ar geochronology data from the Ladue River-Mount Fairbanks area, eastern Alaska

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Frequently anticipated questions:


What does this data set describe?

Title:
40Ar/39Ar geochronology data from the Ladue River-Mount Fairbanks area, eastern Alaska
Abstract:
40Ar/39Ar geochronology data from the Ladue River-Mount Fairbanks area, eastern Alaska, Raw Data File 2024-32, provides 40Ar/39Ar geochronology results from rock samples collected in the Tanacross Quadrangle of eastern Alaska within the Ladue River drainage and the upper Dennison Fork of the Fortymile River drainage around Mount Fairplay. During the 2019 field season, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted geologic mapping and sampling in the Tanacross Quadrangle of eastern Alaska within the Ladue River drainage and the upper Dennison Fork of the Fortymile River drainage around Mount Fairplay. The area lies northeast of the Alaska Highway between Tok, Alaska, and the Canadian border. A recent geologic map of the area lies within the Yukon-Tanana Uplands, which DGGS and U.S. Geological Survey (USGS) identified as having the potential to host deposits of multiple critical minerals, as well as gold, copper, molybdenum, lead, zinc, and silver. Most known mineralization in the region is related to Cretaceous-Paleogene magmatism. These igneous rocks intrude metamorphic rocks of the North American continental margin and the structurally overlying allochthonous Yukon-Tanana Terrane, both of which are multiply deformed and juxtaposed along low-angle faults. Samples were collected for 40Ar/39Ar geochronology to further understand the crystallization ages of igneous rocks and the exhumation history of metamorphic rocks. This report's 18 40Ar/39Ar samples include one volcanic crystallization age, two pluton-alteration ages, and 15 metamorphic cooling ages. Differences in metamorphic cooling ages have been used to distinguish the allochthonous Yukon-Tanana Terrane from parautochthonous North America. The 15 metamorphic samples with cooling ages reported here were collected to aid in DGGS field mapping near this major terrane boundary. Allochthonous samples include eight samples from the Ladue River assemblage with muscovite cooling ages between ca. 105 and 235 Ma; a sample from the Klondike assemblage with a muscovite cooling age of ca. 147 Ma; a sample from the Fortymile River assemblage with a muscovite cooling age of ca. 186 Ma. Parautochthonous North America samples include a sample from the Jarvis assemblage with a muscovite cooling age of ca. 149 Ma and four samples from the Lake George assemblage with muscovite cooling ages of ca. 100 and 105 Ma and hornblende cooling ages of ca. 127 and 255 Ma. These data and report are available from the DGGS website: http://doi.org/10.14509/31454.
Supplemental_Information:
data:    Identification numbers, coordinates, sample descriptions, and summary ages of each sample; power output levels and resultant measurements from each sample run; and an index of the contents, format, and structure of the data.
  1. How might this data set be cited?
    Naibert, T.J., Heizler, M.T., Twelker, Evan, Newberry, R.J., and Wypych, Alicja, 2024, 40Ar/39Ar geochronology data from the Ladue River-Mount Fairbanks area, eastern Alaska: Raw Data File RDF 2024-32, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 16 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -142.489000
    East_Bounding_Coordinate: -141.006900
    North_Bounding_Coordinate: 63.687100
    South_Bounding_Coordinate: 62.805900
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 2019
    Ending_Date: 2024
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: csv
  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 0.0000001. Longitudes are given to the nearest 0.0000001. Latitude and longitude values are specified in decimal degrees. The horizontal datum used is WGS84.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    rdf2024_032-summary_data.csv, rdf2024_032-summary_data_dictionary.csv, rdf2024_032-step_heating_data.csv, rdf2024_032-step_heating_data_dictionary.csv
    Identification numbers, coordinates, sample descriptions, and summary ages of each sample; power output levels and resultant measurements from each sample run; and an index of the contents, format, and structure of the data. (Source: DGGS, see report for additional detail)

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?
    Sample collection and analyses for the Eastern Tanacross project was jointly funded by the State of Alaska and the U.S. Geological Survey's Earth Mapping Resources Initiative (EarthMRI) through cooperative agreement G19AC00262. We are grateful to have had access to Doyon Limited lands within the study area. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.
  3. To whom should users address questions about the data?
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    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 (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.

Why was the data set created?

The Eastern Tanacross project aimed to complete a 1:100,000 scale bedrock geologic map of a 1900 square mile area of the eastern Tanacross Quadrangle and part of the Nabsena Quadrangle. It is funded through the USGS Earth MRI program and targets an area of Alaska prospective for rare earth elements, other critical minerals, and conventional minerals including gold, copper, molybdenum, and silver.

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: 2019 (process 1 of 3)
    Sample collection and analysis - Fresh, unweathered samples from surface outcrops were collected by DGGS field geologists for dating. Sample location coordinates (in WGS84 datum) were obtained using GPS-enabled field tablets with a typical reported accuracy of +/- 10 meters. Samples were examined under a binocular microscope and/or in thin section to select unaltered mineral phases before sample preparation.
    Date: 2019 (process 2 of 3)
    Sample preparation - Twenty-four samples were submitted to the New Mexico Geochronological Research Laboratory (NMGRL) in Socorro, New Mexico. Nineteen samples yielded acceptable mineral separates for 40Ar/39Ar geochronology. Muscovite and/or hornblende were separated from rock samples using standard magnetic, heavy liquid, and hand-picking procedures. The samples were loaded into machined aluminum discs and irradiated for 16 hours at the USGS reactor in Denver, Colorado (NM-316), or for 14 hours at the Oregon State University reactor in Corvallis, Oregon (NM-312), along with the Fish Canyon Tuff sanidine standard (FC-2; assigned age-28.201 Ma; Kuiper and others, 2008) as a neutron flux monitor.
    Date: 2020 (process 3 of 3)
    Analytical methods - After irradiation, the samples and monitors were analyzed by step-heating with a 75W 810 nm diode laser. The samples were step-heated using between 12 and 16 increments. Reactive gases were removed by a 60-second reaction with a SAES GP-50 getter at 450 degrees C, and gas was also exposed to a cold finger at -140 degrees C. The samples were analyzed in a Thermo-Fisher Scientific Helix MC-plus mass spectrometer at NMGRL. Total system blanks were 3.5 x 10-17 mol 40Ar, 8 x 10-18 mol 39Ar, 5 x 10-19 mol 38Ar, 3 x 10-18 mol 37Ar, and 5 x 10-19 mol 36Ar. Isotopic ratios were corrected for blank, radioactive decay, and mass discrimination but were not corrected for interfering reactions.
  3. What similar or related data should the user be aware of?
    Naibert, T.J., Twelker, Evan, Wypych, Alicja, Athey, J.E., Newberry, R.J., Lopez, J.A., Regan, S.P., Sicard, K.R., Wildland, A.D., and Wyatt, W.C., 2020, Field station locations and magnetic susceptibility data collected in 2019 for the Eastern Tanacross Project, Tanacross and Nabesna quadrangles, Alaska: Raw Data File RDF 2019-9, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 p
    Newberry, R.J., 2020, The Mount Fairplay igneous complex: Preliminary Interpretive Report PIR 2020-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 32 p
    Twelker, Evan, and O'Sullivan, P.B., 2021, U-Pb detrital zircon geochronology of Cretaceous-Cenozoic sedimentary rocks in the Ladue River-Mount Fairplay area, Alaska: Preliminary Interpretive Report PIR 2021-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 16 p
    Twelker, Evan, 2021, Geologic investigation of the Ladue River-Mount Fairplay area, eastern Alaska: Report of Investigation RI 2021-5, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 86 p
    Wildland, A.D., Wypych, Alicja, Regan, S.P., and Holland, Mark, 2021, U-Pb zircon ages from bedrock samples collected in the Tanacross and Nabesna quadrangles, eastern Alaska: Preliminary Interpretive Report PIR 2021-4, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 47 p
    Wypych, Alicja, Twelker, Evan, Naibert, T.J., Athey, J.E., Newberry, R.J., Lopez, J.A., Regan, S.P., Sicard, K.R., Wildland, A.D., and Wyatt, W.C., 2019, Major-oxide and trace-element geochemical data from rocks collected in 2019 for the Eastern Tanacross project, Tanacross and part of Nabesna quadrangles, Alaska: Raw Data File RDF 2019-8, 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?
    The accompanying report provides a comprehensive discussion of processing methods. When applicable, errors are reported in the data tables. These data are being released in the DGGS Raw Data File series. Reports in this series present field data and analytical results with limited or no interpretation by DGGS staff or project collaborators. Analytical results may include interpretations by laboratories when an interpretive review of the analytical findings is necessary to develop usable output. The reports and accompanying data have been evaluated by project staff for general readability and logical consistency but have not undergone technical peer review.
  2. How accurate are the geographic locations?
    We recorded location information using GPS-enabled tablets running Esri ArcGIS Field Maps app, with a reported horizontal error of approximately 5 to 10 meters. Latitude and longitude are reported in the WGS84 coordinate system.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    This data release is complete.
  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
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    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 (https://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 2024-32
  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: 11-Dec-2024
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK
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
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.9.50 on Wed Dec 11 21:59:46 2024