program thermobarometry

Spear and Kohn GTB program manual 1

Program Thermobarometry

Version 2.1 May, 1999

Frank S. SpearDepartment of Geology, Rensselaer Polytechnic Institute, Troy, New York 12180

[email protected]

and

Matthew J. KohnDepartment of Geology

University of South Carolina, Charlston, [email protected]

(Please report bugs and comments to F. Spear: [email protected])

Table of Contents

General Description of Program Thermobarometry.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2General Program Notes

Installation.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2The Macintosh Fortran interface.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Description of Files .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Configuration file (Thermobarometry 1.9.fig).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Input of mineral data .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Keyboard input .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Tab-delimited mineral data files (ASCII) .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63-line data files (old format) (ASCII) .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8Mineral selection using data files .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Running the program ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Starting the program ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Main menu options.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Read mineral file.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Set plotting parameters.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Plot Keq lines.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11PostScript menu ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12I/O switch .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Plot digitized reaction curves.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Thermobarometry exercises.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Exercise 1: Mt. Moosilauke, New Hampshire.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Exercise 2: Thermobarometry on granulite facies rocks .. . . . . . . . . . . . . . . . . . . . . . . . . 26Exercise 3: P-T paths from thermobarometry on inclusion suites .. . . . . . . . . . . . . . 32

Table listing thermobarmeter calibrations.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37References to thermobarometers.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Appendix 1. PostScript graphics files.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Appendix 2. Fortran and Macintosh error messages .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43


General Description of Program Thermobarometry

The purpose of program Thermobarometry is to perform and plot the results ofthermobarometry calculations. The program was written by Matthew J. Kohn atRensselaer Polytechnic Institute (now at U. South Carolina) and has been modified for theMacintosh by F. Spear. An attempt has been made to incorporate all reasonablecalibrations of thermobarometers for crustal rocks that have been published in the literature.New code is being added frequently.

This manual contains a description of program Thermobarometry and exercises onhow to run it. The theoretical background is discussed at length in a set of short coursenotes published by the American Geophysical Union and distributed at 28th InternationalGeological Congress, which was held in Washington, D.C. in July, 1989 (Spear, F.S. andPeacock, S.M. (1989) Metamorphic Pressure-Temperature-Time Paths, 102 p. AmericanGeophysical Union, Washington.) and is also discussed in my text book (Spear, F.S.(1993) Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths, 799 p.Mineralogical Society of America, Washington, D. C.) among other places.

General Program Notes

Program Thermobarometry is coded in FORTRAN 77 and has been compiled usingAbsoft's MacFortran II (MPW) compiler. The program requires 1.1 Mb and version 2.1requires a Power Macintosh to run.

Installation

The program requires no special installation. All necessary files are in a folder namedÒGTB2.1(compile date)Ó

GTB 2.0 manual (this document- PDF format)GTB2.1_ppc(compile date) (the executable program)Thermobarometry 1.9.fig (configuration file for program startup)MOOSE.Tab (Mt. Moosilauke data file, tab-delimited)STONGE3.tab (Data file from St. Onge in tab-delimited format)SC-160.Tab (Data file from Coolen, 1980, tab-delimited)Postscript.tmp (Temporary file containing Postscript output of

graphics window)Digitize data (Folder containing digitized P-T information on

experimental and calculated reaction curves ofpetrologic interest

Note that the executable program (GTB) and the configuration file (Thermobarom 1.9.fig)must be in the same folder for the program to run.

The Macintosh Fortran interface

An attempt has been made to make these programs as "user friendly" as possible, but Ihave chosen to use a more standard Fortran I/O in many cases where the Macintoshguidelines call for menus and dialog boxes.


Program Thermobarometry has a Command window, an Output window and aGraphics window. Here are some important considerations when running the programs

(1) Input of user responses can only take place in the Command window (or a dialogbox, if implemented). The Command window must be the front (active) window forkeyboard I/O to occur. The Command window can be made active in the standardMacintosh ways: clicking on the window, selecting it from the Windows menu, or usingthe command-key equivalent (see menu).

(2) Text output is directed to the Output window, which may be scrolled, highlighted,copied, pasted and saved (not printed directly from the program). For each P-T curve islisted the reaction, the calibration, the analyses used and a list of the calculated temperaturesand pressures.

(3) Graphics output is directed to the Graphics window, which can be viewed while theprogram is running. Graphics output is also directed to a temporary PostScript file(PostScript.tmp) in a format compatible with Abobe Illustrator (version 3.0 - 8.0compatible). The PostScript file can be permanently saved with a new name by selectingthe menu option Òsave Postscript fileÓ and opened in the Illustrator for enhancement andprinting. For users of Canvas: the PostScript files can be opened in Canvas, but only afterfirst opening in Illustrator and saving in Illustrator 1.0 or Illustrator Ô88 formats, which canthen be read by Canvas.

Graphics output can also be obtained by screen dumps. The Macintosh systemprovides a way to get a dump of the entire screen using the command:

ðshift 3 - capture entire screenðshift 4 - capture a user-specified rectangle (crosshair - select rectangle)Caps lock on + ðshift 4 - capture a user-specified window (bullet)

This command will generate a file in PICT format, which can be opened in TeachText orany program that will handle PICT files. The file will be on the root folder labeled Picture1, Picture 2 etc. and will appear in the root directory of the start-up volume.


Description of Files

Configuration file (Thermobarometry 1.9.fig)

The configuration file contains a number of parameters that may be altered tocustomize the start up of the program. The file contains the information:

Thermobarometry 1.7 configuration file0 10 350 450 620 350 Window1:upL Y,X lowR Y,X maxY,X20 20 360 460 620 350 Window2:upL Y,X lowR Y,X maxY,X30 30 370 470 592 500 Window3:upL Y,X lowR Y,X maxY,XThermobarometry 1.9 Title for plot in graphics windowT ûC X-axis label 70. 350.0 800.0 15.00 9 0 xor,xmin,xmax,xlen,nxtic,nxdecP kbar Y-axis label 50. .0 10.00 10.00 10 0 xor,xmin,xmax,xlen,nxtic,nxdec1 1 = Plot the Al2SiO5 triple point (0 = no)0 0 = input from data file, 1=keyboard1 List manager window size

The configuration file may be modified in any text editor. Also, if you choose ÒSavePreferencesÓ from the file menu when the program is running, the current configurationwill be saved as the new configuration file.

Description of items in the configuration file:(1) Title line - a header only(2) Lines 2,3 and 4. The coordinates for the three windows used by the program in screenpixels. The values of Ylow and Xlow are used for the upper left coordinates of eachwindow and the values of Yhigh and Xhigh are the lower right coordinates. A value of 0(zero) for Yhigh and Xhigh will force the program to fit the window to the maximumdimensions of the screen you are using. The values of Ymax and Xmax give upper limitsto the window size, regardless of the size of the screen.(3) Lines 5 - 10. Default plot specifications. The next 6 lines give information about thedefault plot limits. The values of xor,xmin,xmax,xlen,nxtic,nxdec are defined asxor, yor Location of upper left of plot on graphics window (from upper left) in

pixels. Usually this value is not changed.xmin, ymin Minimum values for X (T) and Y (P) axes (change if desired)xmax, ymax Maximum values for X (T) and Y (P) axes (change if desired)

Note that Y is in kbar and T in ûCXlen, Ylen Physical length (on the screen) of X and Y axes in cmnxtic, nytic Number of tics on X and Y axes. (Change if desired)nxdec,nydec Number of decimal points for labels of X and Y axes. Usually 0 is fine for

thermobarometry applications.

The plotting information can be changed from within the program by selection ofmain menu option 2 (Set Plotting Parameters), and then saved as a new preference file, orthe configuration file can be edited. If you do change the plotting parameters, here aresome helpful hints:

(a) If you change the lower and upper bounds for T and P (xmin, xmax, ymin, ymax),be sure to also change the number of X and Y tics (nxtic and nytic) so that you haveintegral tickmarks.


(b) You may find it very useful to use a constant ratio of DT to DP in my P-T plots, sothat the slopes on the paper are similar from plot to plot. This helps comparing sets ofdata. In my text I used 30ûC/kbar for most of the plots.

(4) Line 11. Default data input switch. 0 = input from file, 1 = input from keyboard (switchable from within the program also)

(5) Line 12 Default ListManager window size. The ListManager window comes in 4 sizes (1 = small, 2 = wide, 3 = tall, 4 = large). The best one to use depends on the size of your screen. This switch sets the default size to use on startup (also switchable in the program).

Note that all of these options can also be changed after the program starts, so if you areconfused, just ignore this file and proceed.

Input of mineral data

Mineral analyses may be input directly from the keyboard, or by a data file. Theprogram supports a generalized tab delimited data file format as described below. It isrecommended that your data be stored in this format.

Keyboard input

If keyboard input is selected (either by setting the switch in the configuration file orby choosing option 5 from the main menu), then a dialog box appears every time a mineralcomposition is required. The dialog box looks like this:


The name of the mineral requested is listed along with the elements to enter. Note that inthis example (garnet) the Si and Al contents are already specified. These values may notcorrespond to the actual analysis, but they are never used in calculations, so their values areirrelevent. They may be changed or left alone. Also note, that it is only necessary to enterthe values of cations that are used in the calculations. For example, the Ferry and Spear(1978) calibration of the garnet-biotite Fe-Mg thermometry uses only Fe and Mg, so it isnot necessary to enter Mn or Ca values. However, the Hodges and Spear (1982)calibration uses Fe, Mg and Ca so these values must all be entered. Other calibrations useMn as well, in which case Mn must also be specified. If in doubt, enter a full analysis.

Tab-delimited (ASCII) mineral data files

Tab-delimited files can readily be made using spreadsheets, and if you already haveyour mineral analyses in spreadsheet format, then making these files should be simple.Here are guidelines for this data file format.

(1) The data file should be ASCII and the columns should be tab-delimited. Actually, theimplementation of the FORTRAN compiler will also allow the data to be space, comma andslash delimited. This is both good and bad because it means that there must be no spacesor commas or slashes n the title or any other data field. That is, tabs, spaces, commas andslashes can only be used as field delimiters. (Dates sometimes are written with slashes.Slashes in dates must be changed to something else (dashes, underlines or backslashes).

(2) Rows of the data file are mineral analyses and there is one analysis per row.

(3) Columns of the data file (delimited by tabs, spaces or commas) represent specific datafields as defined by key words (described below).

Appearance of data file:

Line 1: An integer (free format) giving the number of data fieldsLine 2: Key words that define the identities of the columns of data (see list of keywordsbelow)Line 3: Data for analysis 1Line 4: Data for analysis 2etc.

Creation of tab-delimited data files

Tab-delimited data files can easily be created from most spreadsheet programs. Todo this you must first arrange your data so that each analysis occupies a single row in thespreadsheet. If your data are stored in columns, as most are, then you will have to use atranspose function to transpose the data into rows. Add lines 1 (number of fields) and 2(keywords). Then save your spreadsheet in TEXT format. In most spreadsheets (e.g.Microsoft EXCEL) this will tab-delimited. You can examine and edit the file in any ASCIIeditor or word processor such as MS WORD.


Key words recognized by the programs for tab-delimited data files:

Key word Comments

Sample Sample number: Defines the sample number (i.e. thin section number)Point Analysis number: Defines the analysis number for the sample or thin section, which

can be used for accessing the data record. Every analysis in a file must have aunique point number.

Min Mineral nameDate Date analysis was made (note this must not contain a slash Ô/ÕOxnorm Numer of oxygens for normalizationWt%tot Weight percent total: Defines the weight percent total for the analysisXpos X position: Defines the X coordinate for the analysis (e.g. for plotting traverses) in

mmYpos Y position: Defines the Y coordinate for the analysis in mmCSi Cations of SiCAl Cations of AlCFe3+ Cations of Fe3+

CFe2+ etc.CMgCTiCMnCZnCCrCCaCNaCKCFCClCNiCCO2CH2O Cations of H (as H2O)

CBa Cations of BaWSiO2 Weight percent of SiO2WAl2O3 Weight percent of Al2O3WFe2O3 Weight percent of Fe2O3WFeO etc.WMgOWTiO2WMnOWZnOWCr2O3WCaOWNa2OWK2OWFWClWNiOWCO2WH2O Weight percent of H2OWBaO Weight percent of BaO


Notes:(1) These are the only elements that the current version of the computer programs willrecognize. The letter ÒCÓ preceeding each element name signifies that it is molar units(cations) whereas ÒWÓ signifies it is weight percent of the oxide.

(2) Input for program THERMOBAROMETRY must be in cations. If yourdata are stored in weight percent, you must convert them before using in this program.Sorry.

(3) See the files named StOnge3.Tab, Moose.tab or SC-160.tab for examples of tab-delimited data files. You can use these as templates for creating your own input data file.

Mineral selection using data files

If you input data using mineral data files, then selection of the mineral from the datafile is done using a scrollable window and a dialog box:

The name of the mineral to pick is listed at the top. The numbers are the analysis numbersfrom the data file. The first 20 characters of the title are shown and the Wt% total is shown(there was no Wt% total in this file, so the word ÒNoneÓ is shown). Selection is done byhighlighting and clicking OK (or hiting return) or by double clicking on the desiredanalysis.

Note that the size of the display window can be changed by selecting theappropriate button. Selecting Òsave preferencesÓ from the file menu will cause this size tobe the default in the configuration file.


Running the Program

Start the program. You will see an initial citation.

The main menu of Thermobarometry looks like this:

Program Thermobarometry COMMAND LEVEL

0=EXIT 1=Read Mineral File 2=Make a new plot 3=Plot Keq Lines on P-T Diagram 4=Save Postscript file 5=I/O switch (file or keyboard) 6=Plot digitized reaction curves

Description of Main Options:

Option 1 -- Read Mineral File

The user is prompted to open a tab-delimited data file.

The program is dimensioned to accept up to 1000 analyses. If you have more than thisnumber of analyses in a file, either split it up or contact me and IÕll change the arraydimensions.

Option 2 -- Make a new plot

This option sets the scale on the plotting axis (plotter and screen) and draws the axes.When you choose option 2 the dialog box appears:


Adjust any items you choose, depending on how you want the plot to appear. Note thatthese are the default values from the configuration file. Hint: to make the tick marks fall onintegral numbers, be sure to have the correct number of ticks, depending on the differencebetween the maximum and minimum values of T and P.

If you choose OK the program will ask if you want to plot the Al2SiO5 triple point.After your response the plot will be drawn.

You will also be asked if you wish to save the old PostScript file. A newPostScript file will automatically be opened, but will over write the old one unless the oldone is saved here.

Option 3 -- Plot Keq Lines on P-T Diagram

This option performs the calculations. There are two submenus under this option,one for thermometers, and the other for barometers. Typing -1 toggles between the 2menus.


Thermometer menu CHOOSE 1 OF THE FOLLOWING REACTIONS 0=EXIT, -1=Next Menu************************************------------------------------------1=Grt-Bt (Fe-Mg) * 2=Grt-Chl (Fe-Mg)3=Grt-Hbl (Fe-Mg) * 4=Grt-Cpx (Fe-Mg)------------------------------------5=Grt-Phen (Fe-Mg) * 6=Grt-Ilm (Fe-Mn)7=Grt-Tur (Fe-Mg) * 8=Bt-Tur (Fe-Mg)------------------------------------9=Grt-Opx (Fe-Mg) * 10=Grt-Ol (Fe-Mg)------------------------------------11=Grt-Crd (Fe-Mg) * 12=Hb-Pl------------------------------------************************************

Barometer Menu CHOOSE 1 OF THE FOLLOWING REACTIONS 0=EXIT, -1=Next Menu*********************************************---------------------------------------------1=Grt-Pl-AlSi-Qtz * 2=Grt-Pl-Ms-Bt3=Grt-Pl-Ms-Qtz *---------------------------------------------4=Grt-Ms-Alsi-Qtz * 5=Grt-Bt-Ms-Alsi---------------------------------------------6=Grt-Pl-Cpx-Qtz * 7=Grt-Pl-Opx-Qtz8=Ab-Jd-Qtz * 9=Grt-Opx---------------------------------------------10=Grt-Pl-Hbl-Qtz * 11-Grt-Pl-Bt-Qtz---------------------------------------------12=GRIPS * 13=GRAIL14-GRAIP * 15=Grt-Crd-Sil-Qtz---------------------------------------------*********************************************

Each of these menu options has a number of different calibrations available, as is listed inthe accompanying table.

Option 4 -- Save PostScript file

This option promts the user for a file name to save the Postscript graphic. If you donot save the PostScript file, it will be erased (actually, it is stored in a temporary file namedPostScript.tmp, if you forget to save it, but it is better to rename the file with this option, orwhen you make a new plot).

Option 5 - I/O switch

This option permits toggling between input from a data file (option 1) or input fromthe keyboard. See discussion above about input of mineral data for details.

Option 6 - Plot digitized reaction curves


This option provides the capability of plotting on the P-T diagram the P-T locationsof curves that have been previously digitized and stored in data files. The program will plotgeneric files as well as data files generated by R. BermanÕs TWQ program.

When this option is selected, the Digit Plot menu options appear:

Open file nameDigit Plot Main Options Menu0 = Return to calling program1 = Read T-P digitized data file2 = Draw P-T curve3 = Plot entire fileYou must execute 1 before option 2

To open a new digitized data file, select option 1. Several files have been supplied withthis program:

There are 2 types of files supported by this option.

(1) Generic files look like this:

FSpear digitized data fileKyanite=sillimanite Helgeson 1978 1 491.3673 3751.613 2 771.9552 8825.807 0 0 0Sillimanite=andalusite Helgeson 1978 1 491.0406 3764.516 2 765.0957 -29.03226 0 0 0Kyanite=andalusite Helgeson 1978


1 491.6939 3729.032 2 204.2464 241.9355 0 0 0gross+2kyanite+qtz=3anorthite Helgeson 1978 1 900 19801 2 1246.766 28208.96 3 1497.513 34029.85 0 0 0

The first line is the header and must be included exactly as shown here:

FSpear digitized data file

The remaining sets of lines contain the digitized reaction curves.Line 1 Title of reaction curveLine 2 - n point number, T (C), P (bars)Line n+1 0 0 0 (signifies the end of a data stream)

These files were created by myself from plots in the literature using a digitizing pad and asmall basic program.

(2) R Berman (TWQ) data files look like this:

RBerman (TWQ) output fileTemperature (C)Pressure (bars) 100.000 1300.000 500.000 15000.000 20.000 20.000 0 0 2 15 0 0 0 01125.26618 15000.00 31071.06647 13815.83 2 964.20711 11399.17 2861.39553 8982.50 2 822.78298 8054.50 2 813.19527 7822.50 2810.80224 7764.50 2 810.19906 7750.00 2 809.60630 7735.50 2 807.21557 7677.50 2797.66775 7445.50 2 759.70646 6517.50 2 662.27918 4100.83 2565.34486 1684.17 2 517.69634 500.00 2 777.949 7459.018 0.3500000 87.6179 Ky 804.625 6566.701 0.3500000 87.6179 aQz + Co 2 19 0 0 0 0 967.71726 15000.00 3 940.50465 13815.83 2 885.68890 11399.17 2828.52020 8982.50 2 804.48786 8054.50 2 798.39995 7822.50 2796.87262 7764.50 2 796.49046 7750.00 2 796.10813 7735.50 2 794.57749 7677.50 2788.43244 7445.50 2 763.46094 6517.50 2 694.48316 4100.83 2656.53002 2892.50 2 613.54222 1684.17 2 587.32948 1080.00 2 570.67722 777.92 2560.13555 626.88 2 549.01292 500.00 2 768.415 7401.512 0.3500000 88.4903 Ms 795.417 6156.289 0.3500000 88.4903 W + Kfs + Co

Again, line 1 is a header and must be included exactly as shown. TWQ does not create thisline, so it must be added to the data file that is created by TWQ. The remaining lines arethose created by TWQ.

Note: These are the TWQ plot.dat files that the program creates. There have beenminor changes in the format of these files. I believe that the most recent version of TWQmay add 1 or 2 lines at the top of each plot.dat file. If you see these, then you must remove


them yourself before using in program Thermobarometry. Try and make your TWQ filelook exactly like the examples here.

To plot the curves, select option 2 or 3. If option 2 is selected, the user will beasked to select the specific reaction to be plotted and then asked what symbol to use forplotting points (0 for no symbol).

Note that the curves are NOT labeled, so you must keep track of what you haveplotted. A request has been made to add labeling, and this may be done in the future.


Thermobarometry exercises

There are three different exercises described for program Thermobarometry. Thepurpose of the first two exercises is to examine two important factors in thermobarometry:(1) The range of P-T calibrations for individual thermometers and barometers and (2) Theinternal consistency of selected sets of calibrations on a single, well equilibrated sample.Exercise 1 will examine these two factors using data from garnet + biotite + sillimanite +plagioclase + muscovite + quartz assemblages from Mt. Moosilauke, New Hampshire(Hodges and Spear, 1982). Exercise 2 will examine these two factors from a granulitefacies assemblage from the Furua complex of southern Tanzania (Coolen, 1980). Exercise3 reexamines a P-T path calculation of St-Onge (1987), using different calibrations of asingle thermometer and barometer.

Exercise 1: Thermobarometry on samples from Mt. Moosilauke, NewHampshire

Exercise 1, Part 1: Examine the range P-T results using garnet+biotite thermometry andGASP barometry.

The purpose of the first part of this exercise is to examine the differences betweendifferent calibrations of the garnet-biotite geothermometer and the garnet-plagioclase-Al2SiO5-quartz geobarometer. Both of these thermobarometers enjoy considerableapplication in rocks of the amphibolite facies and it is important to understand the rangeof results expected from different calibrations.

The data we will use for this comparison are those from Hodges and Spear(1982, Am. Mineral., v. 67, pp 1118-1134) from Mt. Moosilauke in northern NewHampshire. These rocks were thought to have crystallized at conditions near theAl2SiO5 triple point so the P-T conditions recorded by these rocks provide anindependent check of the accuracy of calibrations.

(1) Start program THERMOBAROMETRY by double clicking on theprogram icon. The following menu should appear:

Program Thermobarometry COMMAND LEVEL

0=EXIT 1=Read Mineral File 2=Make a new plot 3=Plot Keq Lines on P-T Diagram 4=Save Postscript file 5=I/O switch (file or keyboard) 6=Plot digitized reaction curves

(2) Select option 1, Select option 1 (again) and open the 1-line, tabdelimited ASCII file named MOOSE.tab.


This file contains data from pelitic schists from the Mt. Moosilauke, New Hampshireregion that were published by Hodges and Spear (1982, Am. Mineral., v. 67, pp 1118-1134). The list of analyses is:

1 78B Garnet Hodges and Spear (1982) Mt. Moosilauke 2 80D Garnet Hodges and Spear (1982) Mt. Moosilauke 3 90A Garnet Hodges and Spear (1982) Mt. Moosilauke 4 92D Garnet Hodges and Spear (1982) Mt. Moosilauke 5 145E Garnet Hodges and Spear (1982) Mt. Moosilauke 6 146B Garnet Hodges and Spear (1982) Mt. Moosilauke 7 146D Garnet Hodges and Spear (1982) Mt. Moosilauke 8 78B Staurolite Hodges and Spear (1982) Mt. Moosilauke 9 90A Staurolite Hodges and Spear (1982) Mt. Moosilauke10 92D Staurolite Hodges and Spear (1982) Mt. Moosilauke11 146B Staurolite Hodges and Spear (1982) Mt. Moosilauke12 78B Biotite Hodges and Spear (1982) Mt. Moosilauke13 80D Biotite Hodges and Spear (1982) Mt. Moosilauke14 90A Biotite Hodges and Spear (1982) Mt. Moosilauke15 92D Biotite Hodges and Spear (1982) Mt. Moosilauke16 145E Biotite Hodges and Spear (1982) Mt. Moosilauke17 146B Biotite Hodges and Spear (1982) Mt. Moosilauke18 146D Biotite Hodges and Spear (1982) Mt. Moosilauke19 78B Muscovite Hodges and Spear (1982) Mt. Moosilauke20 80D Muscovite Hodges and Spear (1982) Mt. Moosilauke21 90A Muscovite Hodges and Spear (1982) Mt. Moosilauke22 92D Muscovite Hodges and Spear (1982) Mt. Moosilauke23 145E Muscovite Hodges and Spear (1982) Mt. Moosilauke24 146B Muscovite Hodges and Spear (1982) Mt. Moosilauke25 146D Muscovite Hodges and Spear (1982) Mt. Moosilauke26 78B Plagioclase Hodges and Spear (1982) Mt. Moosilauke27 80D Plagioclase Hodges and Spear (1982) Mt. Moosilauke28 90A Plagioclase Hodges and Spear (1982) Mt. Moosilauke29 92D Plagioclase Hodges and Spear (1982) Mt. Moosilauke30 145E Plagioclase Hodges and Spear (1982) Mt. Moosilauke


31 146B Plagioclase Hodges and Spear (1982) Mt. Moosilauke32 146D Plagioclase Hodges and Spear (1982) Mt. Moosilauke33 Sillimanite (pure)

In this exercise we will use only one sample (90A), so the mineral numbers of interestare:

3 90A Garnet Hodges and Spear (1982) Mt. Moosilauke14 90A Biotite Hodges and Spear (1982) Mt. Moosilauke21 90A Muscovite Hodges and Spear (1982) Mt. Moosilauke28 90A Plagioclase Hodges and Spear (1982) Mt. Moosilauke

The garnet in this sample contains 6.08 wt % MnO (Xsps = 0.139) and 1.03 wt % CaO(Xgrs = 0.03). The plagioclase is An14. The interested thermobarometrist is encouragedto try this exercise with other samples from the suite.

Hit <Return> to return to the main menu, then

(3) The default plot should be plotted correctly for this exercise, unless the configurationfile has been changed. If you want to replot the axes (not necessary) go to menuoption 2 and check to make sure that the range on the axes is 350-800 ûC, 0-10 kbarand that the Al2SiO5 triple point is plotted:

(4) Select menu option 3 (Plot Keq lines on P-T diagram). This option performsand plots the geothermobarometric calculations. There are several sub-menus here, eachfor different thermobarometers and calibrations of those thermobarometers. The firstsub-menu to appear is the thermometer menu:


Thermometer menu CHOOSE 1 OF THE FOLLOWING REACTIONS 0=EXIT, -1=Next Menu************************************------------------------------------1=Grt-Bt (Fe-Mg) * 2=Grt-Chl (Fe-Mg)3=Grt-Hbl (Fe-Mg) * 4=Grt-Cpx (Fe-Mg)------------------------------------5=Grt-Phen (Fe-Mg) * 6=Grt-Ilm (Fe-Mn)7=Grt-Tur (Fe-Mg) * 8=Bt-Tur (Fe-Mg)------------------------------------9=Grt-Opx (Fe-Mg) * 10=Grt-Ol (Fe-Mg)------------------------------------11=Grt-Crd (Fe-Mg) *------------------------------------************************************

Choose number 1 (Grt-Bt thermometer). The following list of calibrations willappear:

Please choose which calibrationYou wish to apply0 = Return to Rxn menu1 = Ferry and Spear (1978)2 = Hodges and Spear (1982)3 = Ganguly and Saxena 1 (1984; sym)4 = Ganguly and Saxena 2 (1984; asym)5 = Perchuk and Lavrent''eva (1984)6 = Indares and Martignole (1985)7 = Ferry and Spear with Berman (1990) Grt8 = Patino Douce et al.

(6) Choose the Ferry and Spear calibration (option 1). Choose garnetanalysis 3:


and then biotite analysis 14. The Keq line plots on the graphics screen, and thetemperature and pressure conditions calculated for the plot are printed on the console.

Hit <Return> to return to the mineral selection query, and hit cancel to return to thecalibration menu.

(7) Choose the Hodges and Spear calibration (option 2). Again choosegarnet analysis 3 and biotite analysis 14. The resulting T is slightly higher(» 12ûC) than for the Ferry-Spear calibration. This is because Hodges-Spearincorporates a correction for Ca-Mg non ideal mixing in the garnet that the Ferry-Spearcalibration does not; as a rough rule of thumb, the Hodges and Spear correctioncontributes approximately 4 oC for each .01 increase in the mole fraction of grossular.The garnet in sample 90A has Xgrs of only 0.03, and so the increase in temperature isonly 3*4 degrees higher than the Ferry and Spear estimate. However, amphibolitegrade garnets with Xgrs = 0.15 - 0.25 are not uncommon in calcic metapelites andmetavolcanics, and in these bulk compositions, the difference in temperature inferredfrom the Ferry-Spear calibration versus the Hodges-Spear calibration may be 50-100ûC,with the Hodges-Spear calibration yielding the higher temperature.

(8) Hit cancel to return to the calibrations menu, and choose the Ganguly andSaxena 1 calibration (option 3). This is a symmetrical mixing model for garnet.Choose garnet analysis 3 and biotite analysis 14. You will then be asked tochoose a value for DWMn. Ganguly and Saxena suggested 3000 cal and Holdaway etal. (1988) suggested 2500 cal. Try both values and compare the results (noting that youdo not have to return to the calibration menu in order to do so). A value of 3000 cal forDWMn gives a temperature of 513ûC whereas the value of 2500 cal gives a T of 503ûC.


(9) Repeat number (8) using Ganguly and Saxena 2 calibration (option 4).This is an asymmetrical mixing model for garnet.

The difference between the Ganguly and Saxena calibration and the Hodges and Spearcalibration is in the way the garnet is modelled. Hodges and Spear assume the only nonzero terms in the garnet mixing model are those for Ca-Mg exchange. Ganguly andSaxena assume non zero terms for Ca-Mg, Ca-Fe, Mn-Mg and Fe-Mg. For the samplesfrom Mt. Moosilauke both mixing models give very similar results, but the resultsdiverge as the Mn content of the garnet increases.

It is certain from comparison of thermometric results with other estimates oftemperature as well as from experimental data that a correction for Ca-Mg mixing ingarnet is necessary. It is not clear, however, whether a correction for Mn or Fe-Mgexchange is necessary. For most typical pelitic schist assemblages, the quantities Xspsand Fe/(Fe+Mg) are highly (negatively) correlated (see, for example, Fig. 13A of ShortCourse notes). This is a simple consequence of the partitioning of Fe, Mg and Mnamong garnet, biotite, and other Fe-Mg-Mn silicates. As a result, it is not possibleusing natural data sets to separate the effect of Mn unambiguously from that of Fe/Mgon the mixing properties of garnet. The calibration of Ganguly and Saxena makes apositive adjustment to the temperature based on the Mn content and a negativeadjustment to temperature based on the Fe/Mg (actually, it is based on Fe minus Mg).Because of the strong correlation between these parameters, the corrections largely, butnot entirely, cancel. Experimental determinations will be needed to resolve theuncertainty in garnet mixing models.

(10) Repeat number (8) using the calibration of Perchuk and LavrentÕeva(option 5). Note that for this example this calibration gives a temperature of » 530ûC,approximately 20ûC higher than any of the others but this is not true for all samples.This calibration does not incorporate any explicit corrections for garnet non ideality, butis based on experiments conducted with natural garnet, so some measure of non idealityis implicit.

(11) Repeat number (8) using the calibration of Indares and Martingole(option 6). These authors give two different equations, and both are plotted here.(Note that you will have to hit return once to see the second model). Equation 1 givesresults very similar to the other calibrations whereas equation 2 gives a temperature of »457ûC. The difference between model 1 and model 2 is the garnet mixing model; model1 uses the Ganguly and Saxena mixing model whereas model 2 uses Hodges and Spear.

The Indares and Martingole calibration corrects for AlVI and Ti in biotite andgives temperatures lower than those that would be obtained without correction. In lowgrade rocks (with little AlVI or Ti in biotite) the correction is small. In high grade rocksthe correction can be as large as 100ûC.

Conclusion. The results of the comparative thermometry indicate that the Hodges andSpear (1982) and Ganguly and Saxena (1984) calibrations give similar temperatures.These two calibrations will also give results similar to the Ferry and Spear calibration ifthe Ca and Mn contents of the garnet are low. Corrections for AlVI and Ti in biotite areprobably necessary, but the magnitude of the correction is not certain.

(12) Return to Reaction menu by entering 0 from the calibration menu. Type -1(next menu) to get the barometer menu.


Barometer Menu CHOOSE 1 OF THE FOLLOWING REACTIONS 0=EXIT, -1=Next Menu*********************************************---------------------------------------------1=Grt-Pl-AlSi-Qtz * 2=Grt-Pl-Ms-Bt3=Grt-Pl-Ms-Qtz *---------------------------------------------4=Grt-Ms-Alsi-Qtz * 5=Grt-Bt-Ms-Alsi---------------------------------------------6=Grt-Pl-Cpx-Qtz * 7=Grt-Pl-Opx-Qtz8=Ab-Jd-Qtz * 9=Grt-Opx---------------------------------------------10=Grt-Pl-Hbl-Qtz * 11-Grt-Pl-Bt-Qtz---------------------------------------------12=GRIPS * 13=GRAIL14-GRAIP * 15=Grt-Crd-Sil-Qtz---------------------------------------------*********************************************

Select barometer reaction #1 (1=Grt-Pl-AlSi-Qtz). The following menu shouldappear:

Please choose which Reaction you wish to use:

0 = Return to main Rxn menu 1 = Garnet-Plag-Sill-Qtz 2 = Garnet-Plag-Anda-Qtz 3 = Garnet-Plag-Kyan-Qtz

Choose 1 because the assemblages contain sillimanite. The following menu willappear:

Please choose the Calibration you wish to apply

0 = Return to Alsi Menu 1 = Newton and Haselton (1981) 2 = Hodges and Spear (1982) 3 = Ganguly and Saxena (1984) 4 = Hodges and Crowley (1985) 5 = Koziol (1989)

Plot the Keq lines for sample 90A for each of the calibrations 1-5, usinggarnet #3 and plagioclase #28.

Examination of the results reveals that the pressures recorded by the Newton andHaselton, Hodges and Spear, and Hodges and Crowley calibrations are all very similar(3860-4140 bars) and cluster around the Holdaway (1971) triple point pressure. It isnot at all surprising that the Hodges and Spear (1982) and Hodges and Crowley (1985)calibrations reproduce the Holdaway triple point pressure inasmuch as the Mt.Moosilauke data were used in the calibration of these barometers. The pressure from the


Ganguly and Saxena calibration is lower by » 1 kbar and that from the Koziol

calibration higher by » 1 kbar.Which calibration is best? That is impossible to say. The Koziol calibration

uses the most recent, and best reversed, experimental data. At higher grossular contentsthe Koziol calibration tends to converge with that of Hodges and Spear, but at lowgrossular contents as in this example, they differ by » 1 kbar because of the differentvalues for the activity coefficient of grossular that are used. The Ganguly and Saxenacalibration gives lower pressures at low grossular contents because of the activitycoefficient of grossular in garnet; it converges with the others at higher grossularcontents. There are also systematic pressure differences introduced because of thedifferent sets of experimental data used in calculating the endmember reaction positionfor the calibrations.

Here is a summary of the plotted results:

Description of curves (all equilibria calculated with garnet #3, biotite #14 and plagioclase#28):

Thermometer calibrations in figure 1 = Ferry and Spear (1978) 2 = Hodges and Spear (1982) 3 = Ganguly and Saxena 1 (1984; sym) 4 = Ganguly and Saxena 2 (1984; asym) 5 = Perchuk and Lavrent''eva (1984) 6 = Indares and Martignole (1985) (Calibration One (G&S garnet model)) 7 = Indares and Martignole (1985) (Calibration Two (H&S garnet model))

Barometer calibrations in figure 8 = Newton and Haselton (1981)


9 = Hodges and Spear (1982)10 = Ganguly and Saxena (1984)11 = Hodges and Crowley (1985)12 = Koziol (1989)

Conclusion:If one were to assume that the above calibrations were completely independent

(which they most certainly are not) then the range of pressure-temperature conditionsshown in the plot would reflect the accuracy of the P-T estimates. Note that this range isDT = ± 35 ûC and DP = ± 1 kbar. This is a considerably larger error than the precision ofthe measurements.

Exercise 1, Part 2: Examination of internal consistency of thermobarometer calibrations

In this exercise we will examine whether sets of calibrations are internallyconsistent. (Clearly, they are not all consistent with one another). One of the reasonsfor checking for internal consistency is that it can be a very good test of how wellequilibrated the sample is. That is, if the sample has suffered various differentretrograde processes, then the compositions do not likely reflect those of the peakmetamorphic conditions. If this is the case then it is very unlikely that a set ofthermobarometers will give a very similar set of P-T conditions. Of course, to performthis exercise on a natural sample, one must have a consistent set of calibrations to startwith, and it is not always easy to tell if calibrations are mutually consistent. Berman(1988, 1990) and Powell and Holland (1988, 1990) have advocated this approach usingtheir respective data bases. As will be shown below, some of the publishedthermobarometer calibrations are also fairly consistent with one another because they usesimilar data sets for calibration, and can be used can be used to check for internalconsistency on natural samples as well.

(1) Start program Thermobarometry. Open the 1-line, tab-delimited datafile named Moose.tab. From the main menu, choose option 3 (plot Keq lines).

(2) Choose the Garnet-Biotite thermometer (#1) and the Hodges and Spearcalibration (#2). Plot the Keq line for garnet #3 and biotite #14.

(3) Go to the barometer menu and choose reaction 1 (GASP). Select thesillimanite reaction (#1), and plot the Keq line for the Hodges and Spearcalibration (#2) using garnet #3 and plagioclase #28.

(4) Return to the calibrations menu, and this time plot the Hodges andCrowley calibration (#4) for the same minerals. The result is very similar to thatobtained using the Hodges and Spear calibration because the calibration data sets arevery similar and the garnet solution model is the same.

(5) Return to the barometer menu and select reaction 2 (Grt-Pl-Ms-Bt).Choose the Hodges and Crowley calibration (# 2), and plot the Keq lineusing garnet #3, plagioclase #28, biotite #14 and muscovite #21.

(6) Return to the calibration menu, and choose calibration 3 (the Powell andHolland calibration with the Hodges and Spear garnet model). Plot the Keq lineusing garnet #3, plagioclase #28, biotite #14 and muscovite #21. Note thatthis reaction has a different slope, but it gives a similar pressure at 500 ûC.


(7) Return to the barometer menu, and select reaction 3 (Grt-Pl-Ms-Qtz).Choose the Hodges and Crowley calibration (#1). Plot the Keq line usinggarnet #3, plagioclase #28, and muscovite #21.

The plot you have generated should look something like this:

The reactions used in this plot are:

Thermometers1 = Garnet + biotite -- Hodges and Spear calibration

Barometers2 = Grt-Pl-AlSi-Qtz -- Hodges and Spear calibration3 = Grt-Pl-AlSi-Qtz -- Hodges and Crowley calibration4 = Grt-Pl-Ms-Bt -- Hodges and Crowley calibration5 = Grt-Pl-Ms-Bt -- Powell and Holland calibration with H&S garnet model6 = Grt-Pl-Ms-Qtz -- Hodges and Crowley calibration

Conclusion:The above set of thermometer calibrations gives a reasonably consistent set of P-

T conditions for different pelite equilibria. Note that many of the other calibrations arealso internally consistent (such as the Powell and Holland ones) and can be used toexamine the quality of data. Note, however, that just because a set of calibrations givesa well defined P-T point, it does not mean that that P-T point is correct because theremay be systematic errors in the calibrations and these may be quite large. Also, justbecause a set of calibrations gives a tight P-T cluster does not mean that the sample iswell equilibrated because there can be some factors that cancel. In summary, the abovetest is a necessary, but not sufficient, test of equilibration of a sample.


Exercise 2: Thermobarometry on granulite facies rocks

In this exercise we will examine the internal consistency of several differentthermobarometers on a mafic granulite sample from southern Tanzania studied byCoolen (1980).

(1) Start program Thermobarometry. Select menu option 1 and open the 1-line, tab-delimited file named SC-160.tab. The list of minerals in the file lookslike:

1 SC-160 OPX (Integrated)2 SC-160 CPX (Integrated)3 SC-160 Garnet4 SC-160 Hbl5 SC-160 PLAG6 SC-160 Ilmn (pure)

All analyses are of ÒmatrixÓ minerals and are believed to be representative of the peakmetamorphic conditions. Pyroxenes in retrogressed or slowly cooled granulites oftenexhibit exsolution textures, and in his study Coolen used an electron beam rastertechnique across pyroxene exsolution lamellae in order to obtain the integratedorthopyroxene and clinopyroxene compositions used in the data file. Unfortunately, hedid not probe all plagioclases, and the composition of the SC-160 plagioclase wasdetermined optically.

(2) Select menu option 2 ("Set plotting parameters") and adjust the temperaturerange to 450-900 and the pressure range to 5-15 kbar:


Select OK and answer 1 to plot the Al2SiO5 triple point. Note that with the above P-Taxes, you will only see the kyanite - sillimanite boundary plotted.

The thermobarometers that can be applied to this sample are:

(A) Garnet-clinopyroxene thermometry(B) Garnet-orthopyroxene thermometry(C) Garnet-hornblende thermometry(D) Garnet-plagioclase-clinopyroxene-quartz barometry(E) Garnet-plagioclase-orthopyroxene-quartz barometry(F) Garnet-plagioclase-hornblende-quartz barometry(G) Garnet-orthopyroxene barometry(H) GRIPS barometry

Examine the P-T conditions for mineral pairs for as many different calibrations of thesame equilibria as you care to test. Two possible problems to test are presented below.

Exercise 2, Part 1: Examine the range of P-T results using Grt-Cpx thermometry andGrt-Pl-Cpx-Qtz barometry: effects of ferric iron calculations and activity models.

(3) Go to the thermometer menu (option 3: plot Keq lines), and select thegarnet-clinopyroxene reaction (reaction 4).

(4) Select calibration #1 (Ellis and Green); first calculate the temperature without therecalculation for ferric iron (i.e. input a 0 for the ferric iron query). Input 3 forgarnet and 2 for clinopyroxene. The calculated temperature is about 880 oC at 7kbar.

(5) Return to the calibration menu, and select calibration 1 again. This time,however, input a 1 for the ferric iron query (i.e. do renormalize for ferric iron),and recalculate the temperature. After each phase is chosen, the ferric iron to totaliron ratio is printed on the screen while the program pauses. Note that the ratio for thepyroxene is much larger than for the garnet. The new temperature is about 740 oC.

Ferric iron is calculated using stoichiometric and charge balance constraints. Forexample, for the pyroxene, the number of cations is forced to be equal to 4 (e.g.CaMgSi2O6) while maintaining a charge of 12. Obviously, for phases that can containvacancies (e.g. mica, chlorite, and amphibole), there is no way of knowing beforehandwhat the number of cations is supposed to be; so, if you want to recalculate these phasesfor ferric iron, this recalculation must be done before the input file is read into theprogram.

The ferric iron recalculations indicate very little ferric iron in the garnet, but a lotof ferric iron in the pyroxene. This means that, relative to the uncorrected compositions,the Mg# of the garnet [Mg/(Fe+2+Mg)Grt] is not changed much, whereas the Mg# of thepyroxene is substantially increased (because some of the original Fe+2 has beenconverted to Fe+3). The more dissimilar the Mg#'s of the two phases involved in an Fe-Mg exchange equilibrium, the lower the temperature. Because pyroxene is the moremagnesian of the two phases, increasing its Mg# increases the disparity with the garnetMg#, and so the recalculated temperature becomes much lower than the non-recalculatedtemperature. Usually garnet has less ferric iron in it relative to other ferromagnesian


phases, so that ferric iron recalculations will tend to lower temperature estimates basedon Fe-Mg exchange equilibria involving garnet.

(6) Repeat steps 4 and 5 using calibration #2 (Powell, 1985), and compare withthe Ellis and Green temperatures. The Powell temperatures are about 865 and 730 oC at7 kbar; these results are not surprising because Powell used virtually the same data set asdid Ellis and Green for calibrating the thermometer. Typically, the results of the twocalibrations are quite similar.

(7) Repeat steps 4 and 5 with the Pattison and Newton calibration (#3).The temperatures are approximately 810 and 610 oC. The slope of the reaction is a bitless steep as well. The Pattison and Newton calibration is based on a more recent set ofexperimental data, and is generally more highly regarded because of the quality of theprocedure and materials used.

(8) Go to the geobarometer menu and select the Grt-Pl-Cpx-Qtz reaction(#6). Choose the Newton and Perkins calibration (#1). Do not renormalizefor ferric iron (enter 0), and calculate the pressure using mineral #'s 3 (Grt), 5(Plag), and 2 (Cpx). At a reference temperature of 750 oC, the pressure is about 9 kbar.

(9) Repeat step 8 using the Powell and Holland calibration (#2). Two Keqlines are plotted; the first uses the Hodges and Spear garnet activity model, and indicatesa pressure of about 8.3 kbar at 750 oC. The second line uses the Ganguly and Saxenaactivity model and indicates a pressure about 1.5 kbar higher. Most of the difference inpressure is due to the pyrope activity coefficient, which is substantially larger when theGanguly and Saxena model is used.

(10) Repeat step 8 using the Moecher et al. calibration (#4).

(11) Repeat step 8 using the Moecher et al. calibration (#5). Again, two linesare plotted that correspond to the Mg and Fe endmember reactions. The Mg reactionindicates pressures of about 10 kbar at 750 oC, while the Fe reaction suggests pressuresof 8.8 kbar. The Fe reaction also has a steeper slope; this is common in geobarometricreactions because the DS of reaction is often much larger for the Fe-endmember than forthe Mg-endmember, while the DV's are rather similar.

If you feel ambitious, you can try reestimating all the pressures with the ferric ironrenormalization. You will find that plagioclase is not recalculated, however, as this doesnot affect its anorthite content. These ferric iron recalculations affect the pressures for avariety of reasons, including (1) grossular contents are reduced because the ferric iron ingarnet is assigned as an andradite component, (2) the changes in the garnet compositionaffect the activity models, and (3) the composition of the pyroxene is significantlyaltered, raising the pressure for the Fe-endmember reaction and lowering it for the Mg-endmember.

Here is a summary of the plotted results, including ferric iron recalculations for allequilibria:


The calibrations plotted in this figure are:

Garnet-Clinopyroxene Thermometers: 1 Ellis and Green (1979) without Fe+3 recalculation. 2 Ellis and Green (1979) with Fe+3 recalculation. 3 Powell (1985) without Fe+3. 4 Powell (1985) with Fe+3. 5 Pattison and Newton (1989) without Fe+3. 6 Pattison and Newton (1989) with Fe+3.

Garnet-Plagioclase-Clinopyroxene-Quartz Barometers: 7 Newton and Perkins (1982) without Fe+3. 8 Powell and Holland (1988) with Hodges and Spear garnet, without Fe+3. 9 Powell and Holland (1988) with Ganguly and Saxena garnet, without Fe+3.10 Moecher et al. (1988); Mg endmember, without Fe+3.11 Moecher et al. (1988); Fe endmember, without Fe+3.12 Newton and Perkins (1982) with Fe+3.13 Powell and Holland (1988) with Hodges and Spear garnet, with Fe+3.14 Powell and Holland (1988) with Ganguly and Saxena garnet, with Fe+3.15 Moecher et al. (1988); Mg endmember, with Fe+3.16. Moecher et al. (1988); Fe endmember, with Fe+3.

Discussion


Using only garnet - plagioclase - clinopyroxene - quartz thermobarometry, theestimated temperatures range from nearly 600 to 900 oC, and the pressures from 6 to 12kbar. There are three primary causes of the range of P-T estimates, including (1)thermochemical data, (2) activity models, and (3) ferric iron calculations. It is worthnoting that ferric iron calculations are directly dependent on the quality of thecomposition data, and in the case of reintegrated pyroxenes may be highly suspect.Recently published internally consistent data bases (e.g. Powell and Holland, 1988,1990; Berman, 1988) often predict rather similar positions for endmember reactions, sothat much of the current disparity between and uncertainty in recent calibrations probablylies in activity models.

Exercise 2, Part 2: Examination of internal consistency of thermobarometer calibrations

For this exercise, because of the uncertainties inherent in ferric ironrecalculations, we will not recalculate any of the phases.

(1) Repeat steps 1 and 2 of the previous exercise, in order to redraw the P-Taxes.

(2) Go to the geothermometer menu and select the garnet-clinopyroxenereaction (#4). Choose the Pattison and Newton calibration, answer 0 tothe ferric iron query and calculate the temperature using the garnet (#3)and clinopyroxene (#2). As above, the temperature is approximately 810 oC at 8kbar, and 825 oC at 10 kbar.

(3) Return to the geothermometer menu and select the garnet-hornblendereaction (#3). Choose the Graham and Powell calibration (#1) andcalculate the temperature using the garnet (#3) and hornblende (#4). Thecalculated temperature is about 800 oC. In this calibration, ferric iron recalculations areexplicitly not to be made (Graham and Powell, 1984). Graham and Powell cross-calibrated the garnet-hornblende thermometer against the Ellis and Green garnet-clinopyroxene thermometer. Usually results are more similar, and the difference intemperature compared with the unrecalculated garnet-clinopyroxene temperature (880oC) could simply be a result of the uncertainty in the ferric iron content of theclinopyroxene.

(4) Return to the geothermometer menu and select reaction #9 (garnet-orthopyroxene). Select calibration #2 (Harley, 1985), input 0 for the ferriciron query (do not recalculate for ferric iron), and calculate the temperature usinggarnet #3 and orthopyroxene #1. This temperature is about ten degrees higher than thegarnet-clinopyroxene temperature.

(5) Go to the geobarometer menu and select reaction #6 (garnet-plagioclase-clinopyroxene-quartz). Choose the Newton and Perkins calibration, enter 0for the ferric iron query, and calculate the pressure.

(6) Return to the geobarometer menu and choose reaction #7 (garnet-plagioclase-orthopyroxene-quartz). Again choose the Newton and Perkinscalibration, enter 0 for the renormalization question (do not recalculate forferric iron), and calculate the pressure using minerals 3 (garnet), 5 (plagioclase),and 1 (orthopyroxene).


(7) Go back to the geobarometer menu and select reaction #10 (garnet-plagioclase-hornblende-quartz). Select calibration #5 (Kohn and Spear, 1990, withtschermakite reaction- Fe model). Kohn and Spear (1989) differs from Kohn and Spear(1990) in the amphibole activity models and in the geobarometric reaction (1989calibrations involve pargasite, whereas 1990 calibrations involve tschermakite). Enter0 so that ferric iron is not calculated, and select numbers 3 (garnet), 5(plagioclase), and 4 (hornblende). Repeat with calibration #6 (the Mgmodel). Two lines will be plotted for the Fe and Mg endmember reactions.

(8) Return to the geobarometer menu and select reaction #12 (GRIPS).Choose the Bohlen and Liotta calibration (#1), enter 0 to avoid ferric ironrenormalizations, and enter 3 (garnet), 6 (for pure ilmenite), and 5(plagioclase) (ilmenite + rutile are reported for this rock, but no analyses arepresented). The second calibration option is based on the original experimental work ofBohlen and Liotta (1986), but uses the Hodges and Spear garnet activity model insteadof the Ganguly and Saxena model preferred by Bohlen and Liotta.

Here is a summary of the results:

Thermometer calibrations in figure: 1 = Grt-Cpx --Pattison and Newton (1989) (parallel to 3) 2 = Grt-Hbl --Graham and Powell (1984) (vertical line) 3 = Grt Opx --Harley (1985)

Barometer calibrations in figure: 4 = Grt-Pl-Cpx-Qtz --Newton and Perkins (1982) 5 = Grt-Pl-Opx-Qtz --Newton and Perkins (1982) 6 = Grt-Pl-Hbl-Qtz --Kohn and Spear (1990); Fe-Endmember 7 = Grt-Pl-Hbl-Qtz --Kohn and Spear (1990); Mg-Endmember 8 = GRIPS --Bohlen and Liotta (1986)


DiscussionThese different thermobarometers all produce a reasonably consistent estimate of

the peak P-T conditions of about 10 + 1 kbar at 825 + 25oC. However, in light of theprevious exercise how confident are you about these results? Two reasons for theinternal consistency of the barometers are because Grt-Pl-Hbl-Qtz was cross-calibratedagainst calibrations 1-5 and 8, and because calibrations 4-7 all use the same garnetactivity model. It is worth noting that the GRIPS reaction is insensitive to the choice ofgarnet solution model because of the components involved in the reaction (almandineand grossular). Can you see why the presence or absence of an aluminosilicate ingranulite grade rocks is so important for thermobarometric studies?

Exercise 3: Calculation of P-T paths from thermobarometry on inclusion suites

For this exercise, we will reconstruct one of the P-T paths of St. Onge (1987, Jour.Petrology, v. 28, pp1-22). The samples examined in that study consisted of garnet +biotite + quartz + plagioclase + Al2SiO5 assemblages in which the garnets containednumerous inclusions of biotite and plagioclase. If it is assumed that the included biotite andplagioclase and host garnet have not changed composition since garnet growth, and it isfurther assumed that these compositions reflect equilibrium at the time of inclusion, thenthermobarometry may be applied to the inclusions to obtain a P-T path during garnetgrowth.

(1) Start program Thermobarometry. Open the 1-line, tab-delimited ASCIIdata file named STONGE3.tab. This file contains analyses for garnet, biotite andplagioclase for sample #3 of St. Onge (1987). The mineral analysis numbers in this fileare:

Garnet Biotite Plagioclase 1 Garnet #1 11 Biotite #1 21 Plagioclase #12 Garnet #2 12 Biotite #2 22 Plagioclase #23 Garnet #3 13 Biotite #3 23 Plagioclase #34 Garnet #4 14 Biotite #4 24 Plagioclase #45 Garnet #5 15 Biotite #5 25 Plagioclase #56 Garnet #6 16 Biotite #6 26 Plagioclase #67 Garnet #7 17 Biotite #7 27 Plagioclase #78 Garnet #8 18 Biotite #8 28 Plagioclase #89 Garnet #9 19 Biotite #9 29 Plagioclase #9

Each trio of analyses represents a particular radial position in the garnet. Garnet, biotiteand plagioclase #1 (analyses 1,11 and 21) are from the rim. Garnet, biotite and plagioclase#9 (analyses 9, 19, and 29) are from the core of the garnet.

The two thermobarometers that St. Onge (1987) applied to these rocks are thegarnet-biotite thermometer and the garnet-plagioclase-kyanite-quartz barometer. In hispaper, St. Onge apparently used a calibration very similar to that given by Hodges andSpear (1982).

(2) Choose menu option 2 and change the pressure scale to 0-10 kbar and thetemperature scale to 400-800 ûC. Draw axes and the Al2SiO5 triple point.

(3) Construct P-T curves for 3 of the 9 core-rim points. If you calculate the P-Tconditions for all 9 core-rim points you will find that interior points 3-8 cluster about the


same P-T conditions. Therefore we recommend that you use only the rim point (#1), aninterior point (#5) and the core point (#9).

It is an interesting exercise to use different calibrations of the thermometer andbarometer to see how this affects the P-T path that is calculated. First use the Hodgesand Spear calibration for each P and T estimate; then repeat the exerciseusing different calibrations for the thermometers and barometers. It is alsopossible to repeat the exercise using different equilibria as a barometer. For example, otherbarometers that can be applied to this rock are garnet-plagioclase-muscovite-biotite (reaction2), garnet-muscovite-AlSi-quartz (reaction 4) and garnet-biotite-muscovite-AlSi (reaction5). However, because St.-Onge did not present muscovite analyses, you will have toassume a pure muscovite composition (just enter a -5 for the muscovite analysis numberwhen prompted).

To calculate the path, go through the following steps:

(4) Choose main menu option 3.

(5) At the thermometer menu choose the garnet-biotite calibration. Select theHodges and Spear calibration.

(6) Plot the Keq line for garnet-biotite point 1 (i.e. garnet #1 and biotite #11).



(9) Go to the barometer menu, choose the reaction 1 (Grt-Pl-AlSi-Qtz = GASP),and then choose the reaction with kyanite (option 3). Select the Hodges andSpear calibration.

(10) Plot the Keq line for garnet-plagioclase point 1 (i.e. garnet #1 andplagioclase #21).



The screen should look like this (without the circles and arrow):


The curves are all garnet-biotite thermometry and garnet-plagioclase-kyanite-quartzbarometry using the Hodges and Spear calibrations.

1+4 -- Rim thermobarometry point (point 1: Grt #1, Bt #11, Pl #21)2+5 -- Intermediate point in the garnet (point 5: Grt #5, Bt #15, Pl#25)3+6 -- Core thermobarometry (point 9: Grt #9, Bt #19, Pl #29)

Discussion. The P-T path determined from the core-rim points showsdecompression with heating. It is a useful exercise to redo the P-T path using differentcalibrations of thermometers and barometers. If you do this you will find that the shape ofthe P-T path is fairly robust, but that the absolute P-T conditions shift somewhat (as muchas several kbar and tens of degrees). For example, using the Ganguly and Saxenacalibrations of the above two reactions (Grt-Bt calibration #3 with DWMn=3000 cals andGrt-Pl-Alsi-Qtz calibration #3) the results appear as:


The curves are all garnet-biotite thermometry and garnet-plagioclase-kyanite-quartzbarometry using the Ganguly and Saxena calibrations.

17+20 -- Rim thermobarometry point (point 1: Grt #1, Bt #11, Pl #21)18+21 -- Intermediate point in the garnet (point 5: Grt #5, Bt #15, Pl#25)19+22 -- Core thermobarometry (point 9: Grt #9, Bt #19, Pl #29)

Note that the dramatic decrease in pressure is still evident using these calibrations, but herethere is an implied decrease in temperature during garnet growth.

Whether the P-T paths are correct is another matter and requires that the initialassumptions are correct. Close examination of the petrology of these rocks using theGibbs method and diffusion calculations reveals some interesting paradoxes. (1) In theassemblage garnet + biotite + kyanite + muscovite + plagioclase + quartz garnet does notgrow over the calculated P-T path in a closed system but should be consumed, unless thesystem is open to garnet components. (2) The growth of garnet in the specifiedassemblage should result in the consumption of plagioclase and the remaining plagioclaseshould become more albitic. In these rocks the plagioclase becomes more anorthitic fromthe core to the rim. (3) The P-T conditions are such that diffusional modification of thegarnet is a distinct possibility. Note that the garnet is not strongly zoned, suggestingperhaps some diffusional reequilibration. On the other hand, diffusion halos around biotiteinclusions are not reported, suggesting little diffusion during cooling and perhaps a rapidcooling rate.

It is very difficult to assess the significance of these observations. It is certainlypossible that the P-T path is correct and these observations have some simple, if unknown,explanation. However, it is a truism that equilibrium is impossible to prove and to computea P-T path, one must assume a set of successive equilibrium states that have been preservedduring the entire post-garnet growth history. A process such as diffusionalhomogenization does not typically leave tell-tale tracks and it is impossible to evaluate the


magnitude of reequilibration due to diffusion without a degree of circularity. For example,the argument "the P-T conditions are sufficiently low so that diffusion is not likely to havebeen a major factor" is clearly circular because if diffusion has occurred, then the P-Tconditions are erroneous and cannot be used as a constraint. We feel that the best approachis to see if all of the petrologic observations can be fit into a coherent picture using allavailable phase equilibria and kinetic arguments.


Table listing thermometer and barometer calibrations in programThermobarometry

Geothermometer calibrations

(1) Garnet-biotite Fe-Mg exchange 1 = Ferry and Spear (1978) 2 = Hodges and Spear (1982) 3 = Ganguly and Saxena 1 (1984; symmetric Garnet solution model) 4 = Ganguly and Saxena 2 (1984; asymmetric Garnet solution model) 5 = Perchuk and Lavrent'eva (1984) 6 = Indares and Martignole (1985) 7 = Ferry and Spear w/ Berman (1990) Garnet solution model 8 = Patino Douce et al. (1993) 9 = Holdaway et al. (1997)10 = Gessmann et al. (1997)11 = Kleemann and Reinhardt (1994)

(2) Garnet-chlorite Fe-Mg exchange 1 = Dickenson + Hewitt (1986) Modified in Laird (1988)2 = Dickenson + Hewitt (1986) as in Laird (1988) w/Hodges + Spear

(1982) Grt3 = Dickenson + Hewitt (1986) as in Laird (1988) w/Ganguly + Saxena

(1984) Grt4 = Dickenson + Hewitt (1986) as in Laird (1988) w/Berman (1990) Grt

(3) Garnet-hornblende Fe-Mg exchange 1 = Graham and Powell (1984) 2 = Perchuk et al. (1985)

(4) Garnet-Clinopyroxene Fe-Mg exchange 1 = Ellis and Green (1979) 2 = Powell (1985) 3 = Pattison and Newton (1989) (XGrs>0.15)

(5) Garnet-phengite Fe-Mg exchange 1 = Krogh and Raheim (1978) 2 = Green and Hellman (1982) 3 = Hynes and Forest (1988)

(6) Garnet-ilmenite Fe-Mn exchange 1 = Pownceby et al. (1987) 2 = Pownceby et al. (1987) w/ Ganguly + Saxena (1984) Garnet

(7) Garnet-tourmaline Fe-Mg exchange 1 = Kohn: Colopietro + Friberg (1987) and Ferry + Spear (1978) garnet 2 = Kohn with Hodges and Spear (1982) garnet activity model 3 = Kohn with Ganguly and Saxena (1984) garnet activity model

(8) Biotite-tourmaline Fe-Mg exchange 1 = Colopietro and Friberg (1987) 2 = Colopietro and Friberg (1987) + Delta V of reaction

(9) Garnet-orthopyroxene Fe-Mg exchange 1 = Sen and Bhattacharya (1984)


2 = Harley (1985) 3 = Lee and Ganguly (1988) Eq'n 11.2 (w/Cp)

(10) Garnet-olivine Fe-Mg exchange 1 = O'Neil and Wood (1979)

(11) Garnet-cordierite Fe-Mg exchange 1 = Nochols, Berry and Green (1992)

(12) Hornblende - plagioclase 1 = Holland and Blundy (1994)

Geobarometer calibrations

(1) Garnet-plagioclase-Al2SiO5 (kyanite,sillimanite or andalusite)- quartz 1 = Newton and Haselton (1981) 2 = Hodges and Spear (1982) 3 = Ganguly and Saxena (1984) 4 = Hodges and Crowley (1985) 5 = Koziol (1989)

(2) Garnet-plagioclase-muscovite-biotite 1 = Ghent + Stout (1981) - Fe end member 2 = Ghent + Stout (1981) - Mg end member 3 = Hodges + Crowley (1985) 4 = Powell + Holland (1988) w/Hodges + Spear (1982) garnet 5 = Powell + Holland (1988) w/Ganguly + Saxena (1984) garnet 6 = Hoisch (1990) - Fe end member (R6) 7 = Hoisch (1990) - Mg end member (R5)

(3) Garnet-plagioclase-muscovite-quartz 1 = Hodges and Crowley (1985) (Fe) 2 = Hoisch (1990) Mg end member (R3)

(4) Garnet-muscovite-Al2SiO5 (sillimanite or kyanite)-quartz 1 = Hodges and Crowley (1985)

(5) Garnet-muscovite-biotite-Al2SiO5 (kyanite or sillimanite)-quartz 1 = Hodges and Crowley (1985) 2 = Holdaway et al. (1988)

(6) Garnet-plagioclase-clinopyroxene-quartz 1 = Newton and Perkins (1982) 2 = Powell and Holland (1988) 3 = Moecher et al. (1988)

(7) Garnet-plagioclase-orthopyroxene-quartz 1 = Newton and Perkins (1982) (Mg) 2 = Bohlen et al. (1983) (Fe) 3 = Perkins and Chipera (1985) (Mg+Fe) 4 = Powell and Holland (1987) (Mg) 5 = Moecher et al. (1988) (Fe)

(8) Albite-jadeite-quartz 1 = Holland (1980) 2 = Gasparik and Lindsley (1980)


(9) Garnet-orthopyroxene 1 = Harley and Green (1982) 2 = Harley (1984)

(10) Garnet-plagioclase-hornblende-quartz 1 = Kohn + Spear (1989) (Pargarsite-Fe Model I) 2 = Kohn + Spear (1989) (Pargarsite-Mg Model I) 3 = Kohn + Spear (1989) (Pargarsite-Fe Model II) 4 = Kohn + Spear (1989) (Pargarsite-Mg Model II) 5 = Kohn + Spear (1990) (Tschermakite-Fe Model) 6 = Kohn + Spear (1990) (Tschermakite-Mg Model)

(11) Garnet-plagioclase-biotite-quartz 1 = Hoisch (1990) Mg end member (R1) 2 = Hoisch (1990) Fe end member (R2)

(12) GRIPS 1 = Bohlen and Liotta (1986) 2 = Bohlen and Liotta with CaMg Grt interaction only

(13) GRAIL 1 = Bohlen et al. (1983) 2 = Bohlen et al. with CaMg Grt interaction only

(14) GRAIP 1 = Sum of Bohlen's work on GRIPS + GRAIL

(15) Garnet-cordierite-sillimanite-quartz 1 = Nichols, Berry and Green (1992) - Fe endmember 2 = Nichols, Berry and Green (1992) - Mg endmember


REFERENCES

Berman, R.G. (1990) Mixing properties of Ca-Mg-Fe-Mn garnets. American Mineralogist,75, 328-344.

Bohlen, S. R and Liotta, J. J. (1986) A barometer for garnet amphibolites and garnetgranulites. Journal of Petrology, v. 27, pp. 1025-1034.

Bohlen, S. R., Wall, V. J. and Boettcher, A. L. (1983a) Experimental investigation andapplication of garnet granulite equilibria. Contributions to Mineralogy and Petrology,v. 83, pp. 52-61.

Bohlen, S. R., Wall, V. J. and Boettcher, A. L. (1983b) Experimental investigations andgeological applications of equilibria in the system FeO-TiO2-Al2O3-SiO2-H2O.American Mineralogist, v. 68, pp. 1049-1058.

Colopietro, M. R. and Friberg, L. M. (1987) Tourmaline-biotite as a potentialgeothermometer for metapelites, Black Hills, South Dakota. Geological Society ofAmerica Abstracts with Programs, v. 19, p. 624.

Coolen, J. J. M. M. M. (1980) Chemical petrology of the Furua granulite complex,southern Tanzania. GUA Papers of Geology, Series 1, No. 13. 257 pages,Amsterdam. (Available from SUNY Stonybrook or UC Davis through interlibraryloan).

Dickenson, M. P. and Hewitt, D. (1986) A garnet-chlorite geothermometer. GeologicalSociety of America Abstracts with Programs, v. 18, p. 584.

Eckert, J.O.J., Newton, R.C., and Kleppa, O.J. (1991) The DH of reaction andrecalibration of garnet-pyroxene-plagioclase-quartz geobarometers in the CMAS systemby solution calorimetry. American Mineralogist, 76, 148-160.

Ellis, D. J., and Green, E. H. (1979) An experimental study of the effect of Ca upongarnet-clinopyroxene Fe - Mg exchange equilibria. Contributions to Mineralogy andPetrology, v. 71, pp. 13-22.

Ferry, J. M. and Spear, F. S. (1978) Experimental calibration of the partitioning of Fe andMg between biotite and garnet. Contributions to Mineralogy and Petrology, v. 66, pp.113-117.

Ganguly, J. and Saxena, S. K. (1984) Mixing properties of aluminosilicate garnets:constraints from natural and experimental data, and applications to geothermo-barometry. American Mineralogist, v. 69, pp. 88-97.

Ghent, E. D. (1976) Plagioclase-garnet-Al2O5 quartz: a potential geobarometer-geothermometer. American Mineralogist, v. 61, pp. 710-714.

Ghent, E. D., Robbins, D. B., and Stout, M. Z. (1979) Geothermometry, geobarometryand fluid compositions of metamorphosed calc-silicates and pelites, Mica Creek, BritishColumbia. American Mineralogist, v. 64, pp. 874-885.

Ghent, E. D. and Stout, M. Z. (1981) Geobarometry and geothermometry of plagioclase-biotite-garnet-muscovite assemblages. Contributions to Mineralogy and Petrology, v.76, pp. 92-97.

Graham, C. M., and Powell, R. (1984) A garnet-hornblende geothermometer: calibration,testing, and application to the Pelona Schist, Southern California. Journal ofMetamorphic Geology, v. 2, pp. 13-21

Green, T. H. and Hellman, P. L. (1982) Fe-Mg partitioning between coexisting garnet andphengite at high pressure, and comments on a garnet-phengite geothermometer.Lithos, v. 15, pp. 253-266.

Harley, S. L. (1984) An experimental study of the partitioning of Fe and Mg betweengarnet and orthopyroxene. Contributions to Mineralogy and Petrology, 86, 359-373.

Harley, S. L., and Green, D. H. (1982) Garnet-orthopyroxene barometry for granulitesand peridotites. Nature, v. 300, pp. 697-701.

Hodges, K. V. and Crowley, P. D. (1985) Error estimation and empiricalgeothermobarometry for pelitic systems. American Mineralogist, v. 70, pp. 702-709.


Hodges, K. V. and Spear, F. S. (1982) Geothermometry, geobarometry and the Al2SiO5triple point at Mt. Moosilauke, New Hampshire. American Mineralogist, v. 67, pp.1118-1134.

Hoisch, T. D. (1990) Empirical calibration of six geobarometers for the mineralassemblage quartz + muscovite + biotite + plagioclase + garnet. Contributions toMineralogy and Petrology, 104, 225-234

Holdaway, M. J. (1971) Stability of andalusite and the aluminum silicate phase diagram:American Journal of Science, V. 271, pp. 97-131.

Holdaway, M. J., Dutrow, B. L., and Hinton, R. W. (1988) Devonian and Carboniferousmetamorphism in west-central Maine: The muscovite-almandine geobarometer and thestaurolite problem revisited. American Mineralogist, v. 73, pp. 20-47.

Holland, T. J. B. (1980) The reaction albite = jadeite + quartz determined experimentally inthe range 600-1200 oC. American Mineralogist, v. 65, pp. 129-134.

Hynes, A. and Forest, R. C. (1988) Empirical garnet-muscovite geothermometry in low-grade metapelites, Selwyn Range (Canadian Rockies). Journal of MetamorphicGeology, v. 6, pp 297-309.

Indares, A. and Martignole, J. (1985) Biotite-garnet geothermometry in the granulite facies:the influence of Ti and Al in biotite. American Mineralogist, v. 70, pp. 272-278.

Kleeman, U., and Reinhardt, J. (1994) Garnet-biotite thermometry revisited: The effect ofAlVI and Ti in biotite. European Journal of Mineralogy, 6, 925-941.

Kohn, M. J., and Spear, F. S. (1989) Empirical calibration of geobarometers for theassemblage garnet - hornblende - plagioclase - quartz. American Mineralogist, 74, 77-84.

Kohn, M. J., and Spear, F. S. (1990) Two new barometers for garnet amphibolites withapplications to eastern Vermont. American Mineralogist, 75, 89-96.

Koziol, A. M. (1989) Recalibration of the garnet - plagioclase - Al2SiO5 - quartz (GASP)geobarometer and applications to natural parageneses. EOS, 70, 493.

Koziol, A. M. and Newton, R. C. (1988) Redetermination of the anorthite breakdownreaction and improvement of the plagioclase - garnet - Al2SiO5 - quartz barometer.American Mineralogist, 73, 216-223.

Krogh, E. J. and Raheim, A. (1978) Temperature and pressure dependence of Fe-Mgpartitioning between garnet and phengite, with particular reference to eclogites.Contributions to Mineralogy and Petrology, v. 66, pp. 75-80.

Laird, J. (1989) Chlorites: Metamorphic petrology. In Hydrous phyllosilicates (exclusiveof micas), MSA reviews in mineralogy, 19, 405-453.

Moecher D. P., Essene, E. J., and Anovitz, L. M. (1988) Calculation and application ofclinopyroxene - garnet - plagioclase - quartz geobarometers. Contributions toMineralogy and Petrology, 100, 92-106.

Newton, R. C. and Haselton, H. T. (1981) Thermodynamics of the garnet- plagioclase-Al2SiO5-quartz geobarometer. In R. C. Newton, et al. Eds., Thermodynamics ofMinerals and Melts, pp. 131-147, Springer-Verlag, New York.

Newton, R. C. and Perkins, D. III (1982) Thermodynamic calibration of geobarometersbased on the assemblages garnet - plagioclase - orthopyroxene (clinopyroxene) -quartz. American Mineralogist, v. 67, pp. 203-222.

Nichols, G.I., Berry, R.F., and Green, D.H. (1992) Internally consistent gahnitic spinel-cordierite-garnet equilibria in the FMASHZn system: geothermobarometry andapplications. Contributions to Mineralogy and Petrology, 111, 362-377.

O'Neill, H. St. C. (1980) An experimental study of Fe - Mg partitioning between garnetand olivine and its calibration as a geothermometer: corrections. Contributions toMineralogy and Petrology, 72, 337.

O'Neill, H. St. C., and Wood, B. J. (1979) An experimental study of Fe-Mg partitioningbetween garnet and olivine and its calibration as a geothermometer. Contributions toMineralogy and Petrology, v. 70, pp. 59-70.


Pati�o Douce, A.E., Johnston, A.D., and Rice, J.M. (1993) Octahedral excess mixingproperties in biotite: A working model with applications to geobarometry andgeothermometry. American Mineralogist, 78, 113-131.

Perchuk, L. L. and Lavrent'eva, I. V. (1981) Experimental investigation of exchangeequilibria in the system cordierite-garnet-biotite. In Saxena, S. K., ed. Kinetics andEquilibrium in Mineral Reactions. Springer Verlag, pp. 199-240.

Perchuk, L. L., Aranovich, L. Y., Podlesskii, K. K., Lavrant'eva, I. V., Gerasimov, V.Y., Fed'Kin, V. V., Kitsul, V. I., Karasakov, L. P., and Berdnikov, N. V. (1985)Precambrian granulites of the Aldan shield, eastern Siberia, USSR. Journal ofMetamorphic Geology, v. 3, pp. 265-310.

Perkins D. III and Chipera S. J. (1985) Garnet - orthopyroxene - plagioclase - quartzbarometry: refinement and application to the English River subprovince and theMinnesota River valley. Contributions to Mineralogy and Petrology, 89, 69-80.

Perkins D. III and Newton R. C. (1981) Charnockite geobarometers based on coexistinggarnet - plagioclase - pyroxene - quartz. Nature, 292, 144-146.

Powell, R. (1985) Regression diagnostics and robust regression ingeothermometer/geobarometer calibration: the garnet-clinopyroxene geothermometerrevisited. Journal of Metamorphic Geology, v. 3, pp 231-243.

Powell, R. and Holland, T. J. B. (1988) An internally consistent thermodynamic datasetwith uncertainties and correlations: 3. Applications to geobarometry, worked examplesand a computer program. Journal of Metamorphic Geology, v. 6, pp. 173-204.

Pownceby, M. I., Wall, V. J., and O'Neill, H. St. C., (1987) Fe-Mn partitioning betweengarnet and ilmenite: experimental calibration and applications. Contributions toMineralogy and Petrology, v. 97, pp. 116-126.

Sen, S. K., and Bhattacharya, A. (1984) An orthopyroxene-garnet thermometer and itsapplication to the Madras charnockites. Contributions to Mineralogy and Petrology, v.88, pp. 64-71.


42

Appendix 1: Notes on PostScript graphics files

A note about PostScript files:

PostScript files are ASCII and can be examined and edited using any text editor orword processor. Occasionally, errors are encountered in PostScript files so that the AdobeIllustrator will not open them. Illustrator v 3.0 is nice because it gives you the offendingcommand and the context so that you can edit the mistake out of your PostScript file.Illustrator v 5.0 is even better because it will go ahead and open the file up to the pointwhere the error is encountered.

I have found that the most common error occurs because the "end of a line"command (which is a small "s") is incorrectly placed. Here is a bit of PostScript code thatgenerates a line. If you find an error, you can try to edit the file so it looks more like thisone. If that still doesn't work, please let me know and I'll try to fix the bug.

Sample PostScript output to draw a few lines.Note that there should be only one m (move) command before the l (line) command andthat each group must be ended by one and only one "s" command...337.5054 470.0207 m (moves to a point)165.5054 606.0207 l (draws a line to next point)302.5054 737.0207 l (draws a line to next point)472.5054 622.0207 l (draws a line to next point)337.5054 470.0207 l (draws a line to next point)s (signals the end of the line)165.5054 606.0207 m (moves to a new point)472.5054 622.0207 l (draws a line to the next point)s (end of the line).A note to users of CANVAS

Our programs do not support output files that can be drafted in Canvas, but I havebeen told that it is possible to open Adobe Illustrator files in Canvas. If this is true (I havenever tried it) then it should be possible to create a PostScript file, open it in Illustrator,save it (the Illustrator program adds a lot of additional information that we do not put in thefile) and open the saved file in Canvas. Good luck.

program thermobarometry

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