2455 Ridge Road, Berkeley CA 94709
kludwig@bgc.org
User's Manual for
A Geochronological Toolkit for Microsoft Excel
Berkeley Geochronology Center
Special Publication No. 4
rev. August 26, 2008
Kenneth R. Ludwig
Isoplot 3.00 28 August, 2008 2
Table of Contents
INTRODUCTION........................................................................................................................................ 5
ISOPLOT 3 REQUIREMENTS .......................................................................................................................... 5
DEFAULT FOLDERS FOR EXCEL ADD-INS..................................................................................................... 6
PROBLEMS WITH EXCEL VERSIONS FOR THE MACINTOSH ............................................................................ 6
INSTALLING AND INVOKING ISOPLOT............................................................................................... 6
Memory Settings for Macintosh Computers running OS-9 or earlier.................................................... 7
Problems................................................................................................................................................. 7
THE INPUT DATA-RANGE...................................................................................................................... 8
HEADER ROWS ............................................................................................................................................ 8
DATA IN A SINGLE, CONTIGUOUS RANGE.................................................................................................... 8
DATA IN DISCONTINUOUS ROWS................................................................................................................. 9
DATA IN DISCONTINUOUS COLUMNS .......................................................................................................... 9
EXCLUDING DATA WITH FONTS IN STRIKETHROUGH................................................................................... 9
USING BOLDED FONTS TO SPECIFY ADDED EMPHASIS TO PLOT-SYMBOLS ................................................. 9
SPECIFYING SYMBOL COLORS WITH FONT COLORS..................................................................................... 9
EARLY VERSUS LATE DATA SELECTION ....................................................................................................... 9
NUMERIC OUTPUT FROM ISOPLOT................................................................................................... 9
ISOPLOT CHARTS ................................................................................................................................... 10
HIDDEN WORKSHEETS CREATED BY ISOPLOT ........................................................................................... 10
ADDING NEW DATA TO AN EXISTING CHART............................................................................................ 10
MODIFYING CHARTS ................................................................................................................................. 11
Selecting and modifying simple data-point symbols and outline error-symbols.................................. 11
Adding Data-Point Labels.................................................................................................................... 11
Embedding charts into the data-worksheet .......................................................................................... 11
Embedding images of charts into the data-worksheet.......................................................................... 12
Superimposing charts ........................................................................................................................... 12
USING FILLED ERROR-ELLIPSES AND ERROR-BOXES .................................................................................. 12
COLOR-SCALING OF FILLED SYMBOLS ....................................................................................................... 14
EXPORTING CHARTS TO OTHER PROGRAMS................................................................................................ 14
THE MAIN ISOPLOT DIALOG BOX.................................................................................................... 15
ISOPLOT PREFERENCES....................................................................................................................... 19
NUMERIC PREFERENCES............................................................................................................................ 19
GRAPHICS PREFERENCES........................................................................................................................... 20
CLASSICAL ERROR-WEIGHTED X-Y REGRESSIONS AND ISOCHRONS ................................ 22
REGRESSION MODELS ............................................................................................................................... 22
Model 1................................................................................................................................................. 22
Model 2................................................................................................................................................. 22
Model 3................................................................................................................................................. 23
A WORD ABOUT 3-POINT ISOCHRONS ...................................................................................................... 23
COMMENTS ON REGRESSIONS WITH LOW PROBABILITIES-OF-FIT ............................................................. 23
EXAMINING RESIDUALS OF REGRESSIONS.................................................................................. 24
ROBUST REGRESSIONS........................................................................................................................ 25
Isoplot 3.00 28 August, 2008 3
U-PB CONCORDIA PLOTS .................................................................................................................... 26
CONVENTIONAL VERSUS TERA-WASSERBURG CONCORDIA REPRESENTATIONS ....................................... 26
Asymmetric ........................................................................................................................................... 27
Monte Carlo ......................................................................................................................................... 28
SHOWING DECAY-CONSTANT ERRORS IN THE CONCORDIA CURVE........................................................... 29
SPECIFYING THE STYLE OF THE CONCORDIA-CURVE AGE TICKS .............................................................. 29
THE “CONCORDIA” AGE............................................................................................................................ 30
Calculating a Concordia Age............................................................................................................... 30
Calculating a Concordia Age............................................................................................................... 31
Concordia Age MSWD’s ...................................................................................................................... 31
Concordia Age Errors .......................................................................................................................... 31
Effect of Decay-Constant Errors on Concordia Ages and Errors........................................................ 32
THREE-DIMENSIONAL REGRESSIONS FOR U-PB CONCORDIA..................................................................... 32
Planar Regressions............................................................................................................................... 32
Linear, Concordia-Constrained 3-D Regressions (The Total Pb/U Isochron) .................................... 33
EXTRACTING RELIABLE AGES FROM SUITES OF SINGLE-ZIRCON
238
U/
206
PB DATES ..... 35
PB-PB ISOCHRONS AND GROWTH CURVES................................................................................... 37
THE
230
TH-
234
U-
238
U SYSTEM ................................................................................................................. 38
230
TH/U ISOCHRONS WITH VARIABLE
234
U/
238
U ........................................................................................ 38
230
TH/U ISOCHRONS WITH SECULAR EQUILIBRIUM
234
U/
238
U .................................................................... 41
SINGLE-ANALYSIS
230
TH/U AGES.............................................................................................................. 41
WEIGHTED AVERAGES OF A SINGLE VARIABLE........................................................................ 42
ARGON-ARGON AGE SPECTRA AND PLATEAU AGES................................................................ 43
USER-SPECIFIED PLATEAU STEPS.............................................................................................................. 44
CONNECTING LINES FOR ERROR BOXES .................................................................................................... 44
THE ARGON-ARGON PLATEAU-ISOCHRON .................................................................................. 44
CUMULATIVE PROBABILITY PLOTS AND HISTOGRAMS ......................................................... 47
PROBABILITY PLOTS............................................................................................................................ 48
ADDING AN ALGEBRAICALLY-DEFINED CURVE TO AN EXISTING PLOT........................... 49
ADDING AN ALGEBRAICALLY-DEFINED CURVE TO AN EXISTING PLOT........................... 49
AGE LIMITS FOR A SERIES OF DATED, STRATIGRAPHICALLY-ORDERED UNITS........... 50
STRATIGRAPHICALLY-CONSTRAINED DATES WITH CLOSE TO GAUSSIAN UNCERTAINTIES......................... 50
STRATIGRAPHICALLY-CONSTRAINED DATES FROM
230
TH/U ANALYSES.................................................... 51
DECONVOLUTION OF MULTIPLE AGE COMPONENTS USING THE SAMBRIDGE-
COMPSTON ALGORITHM.................................................................................................................... 52
YOUNGEST ZIRCON IN A SUITE OF DETRITAL ZIRCONS......................................................... 53
UTILITY FUNCTIONS FOR ISOTOPIC DATA .................................................................................. 54
ACCESSING ISOPLOT’S USER FUNCTIONS .................................................................................................. 54
URANIUM-LEAD FUNCTIONS..................................................................................................................... 56
URANIUM SERIES FUNCTIONS ................................................................................................................... 59
Isoplot 3.00 28 August, 2008 4
O
THER RADIOGENIC-ISOTOPE FUNCTIONS ................................................................................................ 60
STATISTICAL FUNCTIONS .......................................................................................................................... 60
ROUNDING FUNCTIONS ............................................................................................................................. 63
ACKNOWLEDGMENTS.......................................................................................................................... 63
REFERENCES........................................................................................................................................... 64
APPENDIX I: TIPS ON MINIMIZING PLOT-CONSTRUCTION TIME......................................... 66
APPENDIX II: TOOLBAR-ONLY FUNCTIONS.................................................................................. 67
APPENDIX III – ERROR CORRELATIONS........................................................................................ 71
HOW TO CALCULATE AN ERROR CORRELATION........................................................................................ 71
By differentiation.................................................................................................................................. 71
By observation...................................................................................................................................... 72
INDEX......................................................................................................................................................... 74
Isoplot 3.00 28 August, 2008 5
Introduction
Isoplot (an “Add-In” program than runs under Microsoft Excel) is a flexible tool for the interpretation of
radiogenic-isotope data. In addition to the plotting and calculation of the usual (Rb/Sr, Sm/Nd…) iso-
chrons, Isoplot can:
• Construct U-Pb concordia plots and calculate ages using conventional concordia intercepts, the
“Concordia Age” algorithm, 3-D planar concordia intercepts, or 3-D linear (“Total U/Pb”) iso-
chrons;
• Calculate uranium-series isochron ages using 3-D or 2-D isochrons and construct
230
Th/
238
U-
234
U/
238
U evolution curves and isochrons;
• Construct single-stage growth-curves for plots of common-Pb data;
• Construct cumulative-probability+histogram plots and linearized-probability diagrams;
• Calculate and construct plots for either error-weighted or robust (nonparametric) averages of a sin-
gle variable;
• Calculate both conventional (analytical-error weighted) and robust (nonparametric) x-y regressions
for “classical” and Pb-Pb isochrons;
• Plot Ar-Ar step-heating diagrams and find the statistically-best plateau steps and age;
• Combine Ar-Ar isochron with Ar-Ar step-heating diagrams to obtain the logically optimum combi-
nation of both;
• Plot curves for almost any function;
• Use simple Bayesian constraints Improve the estimates and error-assignments for a package of
stratigraphically-constrained radiometrically-dated units whose ages overlap within errors (with a
special variant for
230
Th/U ages);
• Deconvolute mixtures of components having Gaussian error-distributions using the Sambridge-
Compston approach;
• Provide Monte Carlo errors as well as asymptotic (first-order) errors for most linear regressions,
isochrons, and concordia-intercept solutions;
• Extract reliable ages and errors from complex suites of Phanerozoic single-zircon dates;
• Expand the number of Excel functions by more than 50, including many functions for radiogenic-
isotopes (including 16 for U/Pb and 8 for
230
Th -
234
U-
238
U alone).
Isoplot is available without charge – contact Ken Ludwig directly (kludwig@bgc.org).
Isoplot 3 Requirements
For Windows computers, Isoplot requires an English-language version
1
of Excel 97, Excel 2000, Excel
2002 or Excel 2003. For Macintosh operating systems, you will need Excel 98, Excel 2001, Excel X, or
Excel 2004.
Isoplot 3 is not compatible with Excel 2007. If you absolutely must use Excel 2007, request a copy
Isoplot 4, which is recommended for Excel 2007 only. Isoplot 4 has no more functionality than Isoplot 3.7,
and somewhat less flexibility. Expect a speed penaly of about a factor of 10 when using Excel 2007.
1
For Windows systems, you must set the Control Panel's Regional and Language Options to English), and
also check the Use System Separators box in the International tab of Excel's Options or Preferences sheet.
