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The New Mexico Geochronological Database

Digital Database Series-Database: DDS DB1 (CD-ROM)
by: Maureen Wilks and Charles E. Chapin

1: Introduction

The New Mexico Geochronological Database is a compilation of published and unpublished radiometric ages of rocks in New Mexico. An earlier version of this database was published in 1975 as New Mexico Bureau of Geology and Mineral Resources Open-file Report 60 by C. E. Chapin, W. T. Siemers, and G. R. Osburn. Included in the updated compilation are dates determined by thermoluminescence and electron spin resonance methods. Over the past two decades data have been collected from original references.

The dataset contains over three thousand dates. Three hundred and fifty are Precambrian dates and represent the data reported in New Mexico Bureau of Geology and Mineral Resources Open-File Report 389 compiled by Paul Bauer and Terry Pollock in 1993. Most dates reported through 1999 have been included.

In researching this compilation, we have attempted to locate every published and unpublished age of rocks in New Mexico. Undoubtedly we have failed. However, this database is designed to be easily updated.

2: Acknowledgments

 The database has evolved over the past twenty-five years under the guidance and support of Dr. Charles E. Chapin. Numerous staff and graduate students have worked on this project over the years: W. T. Siemers, G. R. Osburn, L. L. Kedzie, and J. D. Boryta have contributed greatly to the Phanerozoic database. Dr. Paul Bauer and Terry Pollock are responsible for documenting Precambrian dates prior to 1993. M. Mansell, G. Jones, and F. Luo provided invaluable computer assistance in developing the database.

3: Method

AA=40/39 Argon-Argon
C14=Carbon 14
Cl36=Chlorine 36
ESR=Electron Spin Resonance
FT=Fission Track
KA=K/Ar Potassium-Argon
RS =Rb/Sr Rubidium-Strontium
PB=U/Pb Uranium-Lead
UT=U/Th Disequilibrium

4: Recalculated Ages

Dates prior to 1977 have been recalculated where possible using the decay constants reported by Steiger and Jager (1977).
1=K/Ar date recalculated using Table 2 in Dalrymple (1979)
2=After Steiger and Jager (1977)
3=Rb/Sr recalculated using t1/lambda1=t2/lambda2
4=Fission Track recalculated using ?=7.03 x10-17/yr.
5=Old U-Pb age reduce by 2%; 206Pb/238U reduce by 1.1%; 207Pb/235U reduce by 1%; 207Pb/206Pb unaffected by new decay constants.

5: Material

Material dated e.g. adularia, biotite, glass, sanidine etc.
Abbreviations used in the text are listed below.

biotite  bi
clinopyroxene cpx
concentrate conc.
feldspar  fsp
glass  gl
hornblende hbl
hypersthene hyp
langbeinite langb
magnetite mg
muscovite mu
nepheline ne
olivine  ol
orthoclase orth
plagioclase plag
sanidine  sand
whole rock wr

6: Formation

Where the formation name is known, it is listed. Where the formation name has been revised, the new name is given.
Abbreviations used in formation names are listed below.

Basaltic Bas
Formation Fm
Hornblende Hbl
Member Mbr
Mountain Mtn
Quartz Qtz

7: Region

Every date is linked to a region in New Mexico. The purpose of designating regions is to facilitate searches in the database. To date 350 regions have been identified. Regions include:

  • Mountain Ranges
  • Major Valleys
  • Basins
  • Plains
  • Rivers
  • Creeks
  • Hills
  • Buttes
  • Mesas
  • Towns
  • Mining Districts
  • Volcanic Fields

8: Location

The location is more specific than the region to help researchers locate a particular sample. It is often cited in the text, or determined from the latitude and longitude data using USGS 1:100,000-scale metric topographic maps.

We have tried to determine latitude and longitude for every recorded date. Over sixty percent of the dates had locations reported by latitude and longitude. Ten percent were reported by Section, Township, and Range. The remaining locations were determined from written descriptions and map locations, and in some cases estimated from the general region of the study area.

The accuracy of the location is keyed by the number assigned in the PositionAccuaracy field. See section 9.

9: Position Accuracy

The PostionAccuaracy# (1-9) indicates where the latitude and longitude coordinates were determined.

1=Original Data. Degrees and minutes.
2=Original Data. Recalculated from degrees only.
3=Original Data. Recalculated from degrees, minutes and seconds.
4=Original Data. Calculated from published Section, Township and Range
5=Determined from geographic location described in the text or from a map location.
6=General area given when no detailed description of the location is provided.
7=Not applicable as the date is a mean of numerous samples from different locations. In some cases individual    sample locations have been listed.
9=Original data. Recalculated from Universal Transverse Mercator Coordinates
10=Location of center of caldera given from which the volcanic rock is thought to have been erupted.

For dates with a PostionAccuracy# of 1-3, and 9 one should be able to accurately pinpoint the sample

For dates with a PostionAccuracy# of 4 one should be able to pinpoint the sample within a 1 sq. mile grid. In many cases only partial Section, Township, and Range data were reported.

For dates with a PostionAccuracy# of 5 the location is reasonably accurate based on published maps with latitude and longitude grids or from descriptions of the sample site.

For dates with a PostionAccuracy# of 6 the location is a rough estimate based only on the general region described in the text.

For dates with a PostionAccuracy# of 7, these dates represent an average of several samples from a wide area. The general area is given, but the precise location of the samples remains unknown, unless otherwise stated in the Comment Field

Universal Transverse Mercator coordinates were determined for all samples from latitude and longitiude using the program UTMS (Version 1.1) from the National Geodetic Information Center, except where the original data was already given in UTM coordinates.

10: Lab

A number is assigned to the laboratory where the date was determined. The laboratory codes are given below:

1 USGS, Denver
2 Univ. Arizona
3 Krueger Enterprises, Inc., Geochron Lab
5 Not given
6 USGS, Reston,
7 New Mexico Tech
8 USGS, Menlo Park
9 Univ. New Mexico
10 Teledyne
11 Oxford Univ., Great Britain
12 Canberra, Australia
13 Lawrence Livermore
14 Univ. Southern California
15 Case Western Reserve Univ.
18 Southern Methodist Univ.
19 Univ. Texas, Austin
20 Beta Analytic Laboratories
21 Los Alamos Nat. Lab.
22 Columbia Univ.
23 Brookhaven Nat. Lab.
24 Univ. Toronto
25 Univ. Pittsburgh
26 San Diego State Univ.
27 Geol. Surv. Israel
28 Yale
29 Univ. Georgia
30 Iowa State Univ.
31 Mobil
32 Continental Oil Company
33 Univ. British Columbia
34 Shell
35 FM Consultants, Great Britain
36 Univ. Kansas
37 Berkeley
38 Argonne Nat. Lab
39 Harwell, Great Britain
40 Florida State Univ.
41 Univ. Oslo, Norway
42 Geol. Surv. Japan
43 Miami Univ.
44 Carnegie Institute
45 Caltech
46 M.I.T.
47 Univ. Texas, Dallas
48 Univ. Calfornia, Santa Barbara
49 Washington Univ.
50 Kriti, Houston
51 Univ. North Carolina
53 Osaka Univ., Japan
54 Quaternary Isotope Lab, Seattle
55 Ohio State Univ.
56 Univ. of Michigan, Ann Arbor

11: Constants

1=IUGS constants, after Steiger and Jager, 1977
2=Pre-1977 IUGS constants
3=FT lambda after Steiger and Jager, 1977
5=Not given

12: Corrections & Additions

If you know of any ages that are not included in this work, or any corrections that need to be made please send the information to the attention of Maureen Wilks.

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