Zircon U-Pb and 40Ar/39Ar results from dikes collected within the Bruin Bay fault zone, lower Cook Inlet

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Frequently anticipated questions:

What does this data set describe?

Title:
Zircon U-Pb and 40Ar/39Ar results from dikes collected within the Bruin Bay fault zone, lower Cook Inlet
Abstract:
This data release presents zircon U-Pb LA-ICP-MS geochronology from igneous rocks exposed in a coastal exposure at Ursus Head, Iliamna C-2 Quadrangle. Sills and dikes exposed in a coastal exposure at Ursus Head are deformed within the Bruin Bay fault zone. Common dikes intruding late Triassic Kamishak Formation strata composing the hanging-wall of the Bruin Bay fault are cut by numerous small-scale, low-angle, bedding-parallel, and high angle contractional faults. Sample 09MAW006A collected from one of many dikes deformed in the fault zone produced a uni-modal distribution of zircon ages of with a weighted mean of 206.92 +/-0.96 (2 sigma, n=47) and an MSWD of 1.1. Sample 09BG020C collected from a sill of more mafic composition yielded few zircons and produced only eight ages with a weighted mean of 212.49 +/-2.28 (2 sigma) and an MSWD of 3.42. The accompanying report also presents 40Ar/39Ar geochronology results from rocks collected roughly 7 km southwest of Contact Point, Iliamna B-3 Quadrangle.
Supplemental_Information: 
geochron-data: Geochronology lab files and applicable documentation. 
geochron-summary: Identification numbers, coordinates, sample descriptions, and summary ages of each sample.
  1. How should this data set be cited?

    Gillis, R.J., Benowitz, J.A., O'Sullivan, P.B., Layer, P.W., and Wartes, M.A., 2017, Zircon U-Pb and 40Ar/39Ar results from dikes collected within the Bruin Bay fault zone, lower Cook Inlet: Raw Data File RDF 2017-7, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 13 p.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -153.618730
    East_Bounding_Coordinate: -153.608320
    North_Bounding_Coordinate: 59.553710
    South_Bounding_Coordinate: 59.553160

  3. What does it look like?

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

    Beginning_Date: 2012
    Ending_Date: 2017
    Currentness_Reference: ground condition

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

    Geospatial_Data_Presentation_Form: report and 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 0.000001. Longitudes are given to the nearest 0.000001. 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 6378206.40000000037.
      The flattening of the ellipsoid used is 1/294.978698199999997.

  7. How does the data set describe geographic features?

    rdf2017-7-geochron-data
    Geochronology lab files and applicable documentation. (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))

    rdf2017-7-geochron-summary
    Identification numbers, coordinates, sample descriptions, and summary ages of each sample. (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))

    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= two digits of year, AAA=geologist's initials (one to three characters), 999=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.

    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))

    free text

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

    Range of values
    Minimum:59.55316
    Maximum:59.55371
    Units:decimal degrees

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

    Range of values
    Minimum:-153.61873
    Maximum:-153.60832
    Units:decimal degrees

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

    A brief sample and/or station description.

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

    Range of values
    Minimum:8
    Maximum:47

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

    Range of values
    Minimum:36
    Maximum:49

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

    Range of values
    Minimum:206.92
    Maximum:212.49
    Units:Ma

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

    Range of values
    Minimum:207.14
    Maximum:213.54
    Units:Ma

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

    Range of values
    Minimum:9.24
    Maximum:9.61

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

    Range of values
    Minimum:7.15
    Maximum:11.46

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

    Range of values
    Minimum:0.96
    Maximum:2.28

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

    Range of values
    Minimum:1.04
    Maximum:4.05

    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))

    Range of values
    Minimum:1.10
    Maximum:3.42

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

    Range of values
    Minimum:0.003261
    Maximum:1.000000

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

    Range of values
    Minimum:340.37
    Maximum:1157.97

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

    Range of values
    Minimum:257.01
    Maximum:518.99

    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))

    Range of values
    Minimum:1.324
    Maximum:2.231

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?

    Lower Cook Inlet field studies in 2009 and 2012 were funded by the State of Alaska. We appreciate Pathfinder Aviation and pilot Merlin (Spanky) Handley for the helicopter support, Jack Barber at Alaska Air Taxi and Jose de Creeft at Northwind Aviation for charter fixed wing services, James and Shelia Isaak at Alaska Homestead Lodge, and Ray and Linda Williams at their lodge at Pile Bay for accommodations while performing field work. Lastly, we wish to thank Bob Swenson for drawing our attention to these spectacular outcrops, and who spent many hours pondering their significance.

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

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

    (907)451-5039 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov

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

Why was the data set created?

The Energy Resources Group from the Alaska Division of Geological & Geophysical Surveys (DGGS) has conducted topical stratigraphic, structural, and geochronologic studies along the western margin of lower Cook Inlet basin since 2009 to improve knowledge of its Mesozoic geologic framework and help spur industry interest in this under-explored region of the petroleum basin. The publicly-available geological and geochronologic data augment state- and federally-funded geologic mapping along the basin margin performed since 2013. This report presents zircon U-Pb LA-ICP-MS and 40Ar/39Ar step-heating geochronology results for one mafic and two felsic dikes in the Iliamna B-3 and C-2 quadrangles at Ursus Head and near Contact Point, lower Cook Inlet.

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: 2012 (process 1 of 2)
    Fieldwork - Samples of igneous dikes from deformed outcrops were collected by DGGS field geologists based on their cross-cutting relationships with structural features.

    Date: 2012 (process 2 of 2)
    Data analysis - Zircon grains were isolated and prepared for Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) analysis using standard procedures combined with specific customized procedures described in: Donelick, R.A, O'Sullivan, P.B., and Ketcham, R.A., 2005, Apatite fission-track analysis: Reviews in Mineralogy and Geochemistry, Mineralogical Society of America, v. 58, p. 49-94. Significant additional discussion of analytical procedures can be found in the accompanying report.

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

    Betka, P.M., and Gillis, R.J., 2014, Preliminary characterization of brittle deformation on the Iniskin Peninsula: Implications for the kinematic history of the Bruin Bay fault system, lower Cook Inlet, Alaska: Preliminary Interpretive Report PIR 2014-5, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 14 p
    Betka, P.M., and Gillis, R.J., 2015, The superposition of strike-slip and reverse-slip faults in the Bruin Bay fault system, Ursus Head, lower Cook Inlet: Preliminary Interpretive Report PIR 2015-5-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: p. 5-8
    Betka, P.M., and Gillis, R.J., 2016, Observations on the Bruin Bay fault system between Chinitna and Tuxedni bays, Cook Inlet, Alaska: Preliminary Interpretive Report PIR 2016-1-10, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: p. 73-78
    Gillis, R.J., Wartes, M.A., and O'Sullivan, P.B., 2011, Preliminary findings from reconnaissance structural studies along the Bruin Bay fault system and adjacent areas, south-central Alaska: AAPG Pacific Section Meeting, Anchorage, Alaska, May 10, 2011: Poster and Presentation Gillis, R.J. and others, 2011, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet
    Gillis, R.J., Swenson, R.F., Wartes, M.A., and Frohman, R.A., 2013, Reconnaissance investigations of the Bruin Bay fault system along the western margin of lower Cook Inlet and upper Alaska Peninsula: Preliminary Interpretive Report PIR 2013-1G, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: p. 33-37

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

  1. How well have the observations been checked?

    This data set 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 formally reviewed for technical content or for conformity to the editorial standards of DGGS. Questions regarding the accuracy of the analytical values can be best answered by the originating lab.

  2. How accurate are the geographic locations?

    Sample location coordinates (in NAD27 datum) were obtained using Garmin eTrex GPS units, with typical reported accuracy of about 9 ft.

  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 99709-3707
    USA

    (907)451-5039 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov

    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
  2. What's the catalog number I need to order this data set?

    RDF 2017-7

  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: 30-Aug-2017
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Metadata Manager
3354 College Road
Fairbanks, AK 99709-3707
USA

(907)451-5039 (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 2.9.21 on Wed Aug 30 16:10:06 2017