USGS Home
Contact USGS
Search USGS

Interactive maps || Data download

K/Ar ages from the National Geochronological Data Base

Frequently-anticipated questions:

• What does this data set describe?
  1. How should this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  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?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How should this data set be cited?

   U.S. Geological Survey, 2002, K/Ar ages from the National Geochronological Data Base:.

   This is part of the following larger work.

   Zartman, Robert. E., Bush, Charles. A., and Carl, Abston, 1995, National geochronological and natural radioelement data bases: U.S. Geological Survey Digital Data Series DDS-14.

   Online Links:

   • <http://edc.usgs.gov/glis/hyper/guide/ngdb>

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: 177.5

   East_Bounding_Coordinate: -67.1

   North_Bounding_Coordinate: 71.0

   South_Bounding_Coordinate: 25.3

3. What does it look like?

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

   Calendar_Date: 1995

   Currentness_Reference: publication date

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 .002. Longitudes are given to the nearest .002. Latitude and longitude values are specified in Decimal degrees.

7. How does the data set describe geographic features?

   points

   Rock or mineral sample dated by K/Ar geochronology

   Recno (Record Number)

   Unique NGDB identifier for sample. Multiple analyses on a single sample have the same Record Number.

   Range of values
   Minimum:	3
   Maximum:	18332

   Rockname (Rock)

   Rock type from which the dating sample is from

   descriptive text of mixed case

   Mineral

   Mineral or phase dated

   descriptive text of mixed case

   Age

   Age of sample in millions of years (m.y.)

   Range of values
   Minimum:	-0.09
   Maximum:	6883
   Units:	m.y. (million years)

   Error

   Analytical error of calculated age

   Range of values
   Minimum:	0
   Maximum:	940
   Units:	m.y. (million years)

   Analysisty

   Method of K/Ar dating

   Value	Definition
   (no value)
   37Ar-41Ar total fusion
   39Ar-40Ar incremental (plateau)
   39Ar-40Ar total fusion
   40Ar-40K isochron
   40Ar/36Ar-40K/36Ar isochron
   Conventional K-Ar
   Conventional Rb-Sr (assumed initial 87Sr/86Sr)

   Agecomment

   Informative text about the estimated age or the material analyzed

   Value	Definition
   (no value)
   age meaning uncertain (analysis questionable)
   age meaning uncertain (geologic factors)
   age not evaluated
   age of intrusion
   age of later metamorphism
   age of metamorphic crystallization
   age of sedimentation
   age of uplift and cooling
   age of volcanism
   age reset by thermal event
   anomalous initial isotopic composition, age questionable
   initial age disturbed by later metamorphism
   initial age disturbed by weathering
   maximum age of intrusion
   maximum age of metamorphic crystallization
   maximum age of volcanism
   may denote delayed cooling
   minimum age of intrusion
   minimum age of metamorphic crystallization
   minimum age of mineralization
   minimum age of volcanism
   sample contains excess radiogenic argon, age is too old
   sample contains inherited material, age is too old

   K2Opct

   percent K20

   Range of values
   Minimum:	0
   Maximum:	64
   Units:	percent

   Ar40mol

   radiogenic 40Ar expressed as mol/gm scaled by 1.0E-10

   Range of values
   Minimum:	0.000000
   Maximum:	2453.000000
   Units:	mol/gm

   Arradpct (Arrad%)

   Percent radiogenic Ar

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	percent

   Deccon (Decay constant)

   Potassium decay contants used in age calculation

   text

   Latitude

   latitude in decimal degrees

   Range of values
   Minimum:	26.67
   Maximum:	71.0
   Units:	degree

   Latdir

   Direction of latitude

   Value	Definition
   N	North

   Longitude

   longitude in decimal degrees

   Range of values
   Minimum:	-67.1
   Maximum:	177.5
   Units:	degree

   Longdir

   Direction of Longitude

   Value	Definition
   E	East
   W	West

   St (State)

   Two letter abbreviation for State sample was collected from

   Formal codeset
   Codeset Name:	Two-letter abbreviations for US states
   Codeset Source:	USPS

   Precision

   Description of location precision

   descriptive text

   Refcode

   NGDB coded value linking radiometric date with published reference

   Reference

   Reference which is the source of the analytical information

   bibliographic citation

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 National Geochronological data base is maintained by the U.S. Geological Survey. It was published by Robert E. Zartman, Charles A. Bush, and Carl Abston in 1995. The K/Ar and Ar/Ar portion of the data base was prepared for by Nora Shew and Tom Kress.

3. To whom should users address questions about the data?
   U.S. Geological Survey
   c/o Nora Shew
   4200 University Drive
   Anchorage, AK 99508-4667
   U.S.A.
   

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

Why was the data set created?

This GIS representation of the data set facilitates the presentation and analysis of earth-science data.

How was the data set created?

1. From what previous works were the data drawn?

   DDS-14A (source 1 of 1)

   Zartman, Robert E., Bush, Charles A., and Abston, Carl, 1995, National Geochronological Data Base: U.S. Geological Survey Digital Data Series DDS-14A.

   Type_of_Source_Media: CD-ROM

   Source_Contribution: The entire data set was obtained from DDS-14A.

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

   Date: 2001 (process 1 of 1)

   The National Geochronologic data base (NGDB) is stored in a relational data base program. DDS-14A published the data as a relational data base and separate ASCII format. The comma seperated value files were imported into database software, Access, where the table relationships were re-built. It was necessary to edit some records in order for the data base to be re-built. The actual data values were not changed. Once the Access data base was completed, select fields were used to build a DBF file. Using ArcView a shapefile was produced called dds14_k_ar_age.shp

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?

   The radiometric ages are given in m.y., millions of years. The analytical error, also given in m.y., is listed for most ages. The numerical precision was not maintained during the data conversion and the user should be aware that more precision may be indicated than is real. Users should use this data set to learn about existing data, then research the original references to gain more information about the sample, analysis, and interpretation.

2. How accurate are the geographic locations?

   The precision of the latitude and longitude values was not maintained during the data conversion and the user should be aware that more precision may be indicated than is real. The text field 'Precision' describes the positional accuracy of each point.

3. How accurate are the heights or depths?

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

   This data set contains a subset of the National Geochronological data base, NGDB. Data for samples dated by a potassium-argon dating method and include location information are given here. The data set does not include the following dating methods: fission track, lead alpha, rubidium-strontium, samarium-neodymium, or uranium-thorium-lead. In addition, many fields associated with the K/Ar and Ar/Ar records were not included. Some of the missing fields are: analysis number, lab number, suite number, mineral code, county, quadrangle, scale, source, geo unit, petrographic code, lab code, and lexicon age.

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

   This is a point data set, where each point represents a published analytical age determination. If an age is published in multiple references, it is represented as a single point and only a single reference is cited.

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
   c/o Tom Kress
   12201 Sunrise Valley Drive MS954
   Reston, VA 20192
   USA
   

   703-648-6328 (voice)
   thkress@usgs.gov
   

2. What's the catalog number I need to order this data set?

   dds14k_ar_age.shp

3. What legal disclaimers am I supposed to read?

   The U.S. Geological Survey (USGS) provides this point data "as is." The USGS makes 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 been 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 distribuiton constitute or imply any such warranty.

4. How can I download or order the data?
   • Availability in digital form:

     Data format:	Sample locations and age information in format ESRI shapefile (version 1.0) Size: 1 megabyte
     Network links:	<http://tin.er.usgs.gov/karage/karage.zip>

   • Cost to order the data: none

Who wrote the metadata?

Dates:

Last modified: 23-Jan-2002
Last Reviewed: 03-Mar-2003

Metadata author:

U.S. Geological Survey
c/o Nora Shew
4200 University Drive
Anchorage, AK 99508-4667
USA

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

Metadata standard:

Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)