COMAGMAT-NET 3.3 (1997)
Vernadsky Institute, Moscow, Russia
Moscow State University, Moscow, Russia
Access to COMAGMAT-NET .............................
3.1
4. WORKING WITH COMAGMAT-NT
Starting the Program ............................. 4.1
Main Petrological Functions ................... 4.2
Data INPUT .........................................
4.3
Define Conditions ..................................
4.4
Calculations .........................................
4.5
5. GRAPHICS MANAGER
Basic Plot Procedure .....................................
5.1
Additional graphics ......................................
5.2
6. OUTPUT FILES
Basic Format .........................................
6.1
Getting Files ..........................................
6.2
7. TROUBLESHOOTING
8. REFERENCES
1. INTRODUCTION
Welcome to Comagmat-NET 3.3 (1997) program! This is a network version of
COMAGMAT-3.0 (1992-1995), a popular package of phase equilibria models
widely distributed among igneous petrologists and geochemists (Ariskin
et al., 1993; Ariskin and Nielsen, 1993). The
COMAGMAT programs have been constrained in the Vernadsky Institute (Moscow,
Russia) by over 20 years of field works, petrography, geochemistry and
computer simulating the formation process of differentiated sills and volcanic
series occurred in Eastern Siberia, Karelia, Kamchatka, and Mid-Ocean Ridge
systems (Ariskin et al., 1988-1995; Barmina
et al., 1989,1992; Frenkel et al., 1989). This
program is designed to be simple and intelligible at every stage of petrological
calculations with the input and output files organized to be user friendly.
The COMAGMAT programs operate in a sophisticated environment and provide
a graphics support making it useful for beginners and dabblers.
1.1. Petrological Significance
The COMAGMAT model is a series of linked programs developed to calculate
phase equilibria for dry and hydrous natural magmas crystallizing in the
range of pressures from 1 atm to 10-12 kbar and including both open (12
oxygen buffers) and closed system fractionation with respect to oxygen.
The modeling process may be calculated for systems ranging from basalts
to dacites, with modeled major elements including Si - Ti - Al - Fe(tot)
- Mg - Ca - Na -K and P, where Fe(tot) is assumed to be divided to Fe2+
and Fe3+ species (Nikolaev et al., 1996). Moreover,
COMAGMAT allows the user to simulate behaviour of 20 trace elements, including
Mn, Ni, Co, Cr, V, Sc, Sr, Ba, Rb, Cu, and REE. The modeled minerals include
olivine (Fo-Fa solution), plagioclase (An-Ab), 3 pyroxenes (augite, pigeonite,
and ortho- pyroxene: En-Fs-Wo plus Al and Ti), ilmenite (Ilm-Hem), and
magnetite (Mt- Ulv). The results of the program are in the form of calculated
liquid lines of descent, plus the equilibrium mineral proportions and compositions.
The phase equilibria calculations form the core of a model that allows
the user to simulate processes ranging from simple isobaric crystallization
to polybaric fractionation.
THERMODYNAMIC BACKGROUND
2.1. Mineral-melt geothermometers
The building blocks of COMAGMAT are a set of empirically calibrated expressions
that are used to calculate equilibrium temperatures and phase relations.
These expressions describe mineral-melt equilibria for major and trace
elements in terms of pressure, temperature, oxygen fugacity and liquid
composition (Ariskin et al., 1987, 1993; Ariskin
and Barmina, 1990). These mineral-melt geothermometers have been calibrated
using an earlier version of the INFOREX database which now includes information
on over 11,000 melting experiments published in 235 works (Ariskin
et al., 1992, 1996, Meshalkin and Ariskin,
1996, 1997). Applying these geothermometers to the initial database liquid
compositions, one can invert these calculations to estimate mineral-melt
equilibria temperatures: comparison of the calculated and experimental
temperatures indicate an accuracy of 10-15oC (Ariskin
et al., 1987,1993). Similar comparisons of the calculated and experimental
mineral compositions indicate that Fo, An, En and Wo contents can be predicted
within 1-3 mol%. Note, that the best fit with experimental data can be
obtained if apply the COMAGMAT mineral-melt expressions to tholeiitic and
transitional systems ranging from magnesium basalts to dacites.
2.2. Trace element partitioning
One of the major advantages of COMAGMAT is the linkage between the major
and trace element systematics. Calculation of the major element mineral-melt
equilibria controlled parameters, such as temperature and fractionating
mineral proportions, allows us to constrain the trace element systematics
based on the values of the single component distribution coefficients:
such an approach is used to calculate the behaviour of 20 trace elements
- Mn, Ni, Co, Cr, V, Sc, Sr, Ba, Rb, Cu plus REE (Barmina
et al., 1989,1992).
2.3. Solving Equilibrium Problem
The problem of the calculation of mineral-melt equilibrium at a given set
of independent parameters of state is equivalent to the search for an extreme
of one of the thermodynamic potentials. To address the problem we take
advantage of numerical solutions of nonlinear empirical equations that
describe mineral-melt equilibria and mass action law, combined with the
mass balance constraints for a whole system composition (Frenkel
and Ariskin, 1984). This approach combines the basic empirical and
thermodynamic considerations into a hybrid algorithm allowing one to simulate
the differentiation of multiply saturated magmas step by step, as the total
percent crystallized is increased (Ariskin et al.,
1993).
3. SYSTEM REQUIREMENTS
3.1. Access to COMAGMAT-NET
The COMAGMAT-3.3 programs operate under any UNIX SVR4. It uses the Perl
interface to FORTRAN-based core and SQL-database (Postgres-95) for data
manipulation. For access to Comagmat-net is required a any frame-capable
Web Browser (Netscape-2.x or later, MSIE-3.0 or later). All users data
is contained in SQL-database and user can edit his database records. Each
record is protected by users computer IP-address. For access to Comagmat-net
interface user can click
here or load the "http://www.geo.web.ru/users/comagmat/frames.html"
page in his WWW-browser.
4. WORKING WITH COMAGMAT-NET
4.1. Starting the Program
For first start of Comagmat software, click
here and follow the instructions. Each screen contains some input fields
and submit buttons. You could use only navigation buttons in the document
body ("Get Values", "Yes", "No" etc.). Don't
use "Back" or "Forward" buttons on the Browser panel.
If you have the last visited record, you can choose the record by the comment
from this table.
Define Conditions ?................................. 4.3
Data INPUT ? ....................................... 4.4
Calculations ? ..................................... 4.5
4.2. Main Petrological Functions.
There are 3 main modes in COMAGMAT-NET that may be used in solving more
general petrological problems. They are given in the first active box and
can be selected. We remove the "Layered intrusion" petrological
option from network version,
because in this version we can use only one data record simultaneously.
* Thermometry of Mineral-Melt Equilibria allows one to calculate mineral-melt
equilibria temperatures for the melt (inclusion) compositions that are
supposed to be saturated with a mineral. That solid phase may be selected
directly from the screen. Now is supported Olivine, Plagioclase, Augite,
LowPyroxene, Ilmenite and Magnetite mineral-melt equilibria.
The next 2 routine have common peculiarities in specifying the model
calculations:
* Simulating Equilibrium Crystallization
* Simulating Fractional Crystallization
Next request is regarding a possibility to change a species of low-Ca pyroxene
to be simulated (this version of COMAGMAT enables to calculate simultaneously
only one high-Ca and one low-Ca pyroxene). To do that move highlighted
field to Opx or Pigeonite. Note, that for tholeiitic and related systems
you should select Pig while for the calc-alkaline melts Opx is more reliable
phase. This option is not actual for Mineral-Melt Equilibrium calculation.
After definition of required fields user should press "Get Values"
button.
4.3 Data INPUT
The next step is filling of the start melt composition request. The fill-in
form contains 10 petrochemical input fields. User should enter the start
melt composition to this form and click to the "Get Values" button.
If any field is not filled, the program accept it as "0.00".
The last variable parameter in this screen is H2O content in the initial
melt. Really it only a first very primitive attempt to account for water
presence as a factor decreasing mineral-melt equilibria temperature in
a different degree for different minerals.
Note, that the COMAGMAT program includes a special subroutine to simulate
water solubility as a function of temperature, pressure and SiO2 content
(see "Subroutine Solub" in Program Listing of Ariskin
et al., 1992b). The simulating process will be ceased if a current
H2O content in the liquid is more than the model calculated solubility.
After that, user should enter the comment, reference, his name and his
mail. It is optional fill-in form, but the time-to-live of the record without
this attributes is 24 hours and if you fill this form, the time-to-live
of the record is one year. Next time, you can edit or recalculate this
record.
Then, user should enter the trace elements composition. By default, all
trace element content is 1. It is convinient for trace component trends
research.
4.4. Define Conditions
The next screen involves both pressure and redox routines that should be
specified with definition of the values of main variables peculiar to those
conditions. First of all, it is necessary to select what kind of the effect
of pressure (isobaric or polybaric) on phase equilibria you wish simulate
in the calculations. Move highlighted field to a pressure routine.
It is obvious that the first routine is not need in a special comment (you
should only define the total pressure from the screen), but polybaric mode
deserves a notice. The most reliable results the high pressure model gives
in the range as much as 10-12 kbar, while more elevated pressures also
can be modelled. The main problem here is correct parameters to simulate
low-Ca pyroxenes precipitation and absence in the COMAGMAT model of the
high-temperature Spinel crystallization. New geothermometers for the mineral-melt
equilibria are now in development. The Decompression (Polybaric) Crystallization
is modelled in COMAGMAT system by means of monotonous decreasing the total
pressure from an initially given P to a final value PminP-YP with a constant
pressure increment YP per each 1% of the system crystallized. It results
in specific liquid line of descent that are principally different from
the isobaric ones but may be more corresponded to the natural petrochemical
trends observed in basaltic series (Ariskin, Barmina,
1992).
After defining the pressure parameters the user must specify the model
redox conditions. The COMAGMAT program allows us to simulate crystallizing
systems that are either closed or open with respect to oxygen. The first
case is peculiar for the systems where fO2 is controlled internally by
mineral-melt equilibria and reactions in the liquid phase, first of all
the Fe2+/Fe3+ relations. The latter is supposed to be the main factor controlling
the oxygen fugacity in a closed system. So, one should specify the initial
Fe2+/FeO(tot) ratio in the melt to simulate the closed respect to O2 crystallization.
To model the open to O2 system crystallization, the user should
select an oxygen buffer. A special table including 12 different oxygen
buffers will appear on the screen, so that one can select the redox conditions
by movement of highlighted field:
IW : Myers,Eugster,1983
WM : Myers,Eugster,1983
IM : Huebner J.S.,1971
MH : Myers,Eugster,1983
QFM : Myers,Eugster,1983
IQF : Myers,Eugster,1983
NNO : Huebner J.S.,1971
CCO : Myers,Gunter,1979
COC>5kb: Woermann et al.,1977
COC<5kb: French B.H., 1966
GRA : Ulmer, Luth, 1991
ARB : Arbitrary buffer
The Menu Manager allows to make changes not only in petrological parameters
but also in precision of calculations. The default values of calculating
temperature and phase compositions can be changed in the "Advanced
Options" screen:
Temperature accuracy,C 1.0
Phase compositions, mol.% 0.1
set of trace elements 1
crystal increment,% 1
break point of calculation,% 50
Of course, it is no real absolute accuracy of simulation, but only precision
of the convergence for the main computation iteration loops. Nevertheless,
in same cases if you faced a trouble in modeling any compositions for a
given conditions a slight modifications in the precision parameters may
help to calculate more evolved liquid line of descent. However, we don't
recommend to use the operation often.
4.5. Calculations
Just after starting the program reads Data input and runs the simulation
subroutine that is corresponded to one of the main routines selected. During
the modeling process the equilibrium state information is accumulating
in the output file. I
One can track each step of the calculations (corresponding to a given crystal
increment) on the screen while the calculations are accumulating in the
computer memory. It is taken 0.3-0.5 sec to simulate crystallization for
a one initial composition to a bulk crystallinity of 70-80%. The fractionation
process is simulating markedly fast than the equilibrium crystallization.
In some cases (especially if you gave an extremely high extent of equilibrium
crystallization or try to model advanced precipitation of magnetite) the
simulating process may be ceased earlier than you were indicated in the
calculation options. Usually, it is due to a of the scheme used in the
algorithm. Corresponding diagnostics will be appeared on the screen. In
that case, try to change slightly input parameters (e.g., to decrease the
crystallization increment or alter initial composition as for a component
in the scale of 0.05-0.10 wt.%). If it does not help to advance the simulation
you should stop the calculations.
5. GRAPHICS MANAGER
A system of graphics support of the COMAGMAT calculations has been developed
independently on the and "comagmat" program. It involves the
Graphics Manager that permits ..............
5.1. Basic Plot Procedure
..........................................
5.2. Additional graphics
..........................................
6. OUTPUT FILES
6.1. Basic Format
..........................................
6.2. Getting Files ?
..........................................
7. TROUBLESHOOTING
The main reasons hat can result in troubleshouting the program is connected
with the fact that the program has a lot of different modes and can operate
in a wide range of natural compositions, so that we simply could not forsee
all possible nonstandard situations. Nevertheless a special system of diagnostic
with comments is present (see Section 3.5). We would be also grateful if
you were fixed the troubleshouting parameters and sent the information
to us.
8. REFERENCES
Al'meev R.R., Ariskin A.A. (1996) Mineral-melt equilibria
in a hydrous basaltic system: computer modelling. Geochem. Intern., 34
(7): 563-573.
Ariskin A.A., Barmina G.S., Frenkel M.Ya. (1987)
Computer simulation of basalt magma crystallization at a fixed oxygen fugacity.
Geochem. Intern., 24 (6): 85-98.
Ariskin A.A., Barmina G.S., Frenkel M.Ya., Yaroshevsky A.A. (1988) Simulating
low-pressure tholeiite-magma fractional crystallization. Geochem. Intern.,
25 (4): 21-37.
Ariskin A.A., Barmina G.S. (1990) Equilibria thermometry between plagioclases
and basalt or andesite magmas. Geochem. Intern., 27 (10):129-134.
Ariskin A.A., Frenkel M.Ya., Tsekhonya T.I. (1990). High-pressure fractional
crystallization of tholeiitic magmas. Geochem. Intern., 27 (9): 10-20.
Ariskin A.A., Bouadze K.V., Meshalkin S.S., Tsekhonya T.I. (1992) Inforex:
A database on experimental studies of phase relations in silicate systems.
Amer. Miner., 77 (5/6): 668-669.
Ariskin A.A., Frenkel M.Ya., Barmina G.S., Nielsen R.L. (1993) COMAGMAT:
a Fortran program to model magma differentiation processes. Computers and
Geosciences, 19: 1155-1170.
Ariskin A.A., Nielsen R.L. (1993) Application of computer simulation of
magmatic processes to the teaching of petrology. Journal of Geol. Education,
41: 438-441.
Ariskin A.A., Barmina G.S., Ozerov A.Yu., Nielsen R.L. (1995) Genesis of
high-alumina basalts from Klyuchevskoi Volcano. Petrology, 3 (5): 449-472.
Ariskin A.A., Barmina G.S., Meshalkin S.S., Nikolaev G.S., Almeev R.R.
(1996) INFOREX-3.0: A database on experimental phase equilibria in igneous
rocks and synthetic systems.II.Data description and petrological applications.
Computers and geosciences, 22 (10): 1073-1082.
Barmina G.S., Ariskin A.A., Frenkel M.Ya. (1989)
Petrochemical types and crystallization conditions of the Kronotsky Peninsula
plagiodolerite (Eastern Kamchatka). Geochem. Intern., 26 (9): 24-37.
Barmina G.S., Ariskin A.A., Kolesiov G.M. (1992) Simulating the REE spectra
of hypabyssal rocks in the Kronotsky series, Eastern Kamchatka. Geochem.
Intern., 29(3): 45-54.
Frenkel M.Ya., Yaroshevsky A.A., Ariskin A.A., Barmina
G.S., Koptev-Dvornikov E.V., Kireev B.S. (1989) Convective-cumulative model
simulating the formation process for stratified intrusions In: Magma-crust
interactions and evolution. Theophrastus Publications, S.A., Athens-Greece,
p. 3-88.
Frenkel M.Ya., Ariskin A.A. (1984) A computer algorithm for equilibration
in a crystallizing basalt magma. Geochem. Intern., 21 (5): 63-73.
Meshalkin S.S., Ariskin A.A. (1996) INFOREX-3.0:
A database on experimental phase equilibria in igneous rocks and synthetic
systems. I. Datafile and management system structure. Computers and Geosciences,
22 (10): 1061-1071.
Nikolaev G.S., Borisov A.A., Ariskin A.A. (1996)
Calculation of the ferric-ferrous ratio in magmatic melts: testing and
additional calibration of empirical equations for various magmatic series.
Geochem. Intern., 34 (8): 641-649.
