Welcome to the to the session of ah fluid
inclusions in minerals . In this module we
will be discussing about ah the principles
of microthermometry . And in the last class
we discussed about certain ah specifications
ah, requirements that these ah heating freezing
ah systems must ah met must must qualify for
the for carrying out the microthermometry
experiments on this fluid inclusions .
We discussed about ah their certain specification
in terms of there range of ah operation, the
thermal response is have operation changing
from ah freezing to heating mode , and ah
many of the other aspects which we ah discussed
in the last class.
ah Will quickly ah have a view of a these
ah microthermometric ah apparatus or which
are the microscopic heating freezing systems
which are mounted on microscopes .
There are ah many such commercially available
models ah which will find in any of the research
laboratories ah carrying out fluid inclusion
work anywhere . And ah without getting into
too much of the ah minor details about this
ah equipment which one can ah experience when
the when was starts working with them . So,
this one which is ah here in this ah figure
this picture it is ah this this is a heating
ah gas flow a heating compression system .
Originally designed by the united states ah
geological survey . And is adopted by ah the
fluid incorporated ah in Denver Colorado united
states of America . And ah the basic operation
of this ah heating freezing system is that
the freezing is done by a by by cold nitrogen
gas, the nitrogen gas is ah it comes from
a commercially available nitrogen gas cylinder
.
And this which is the container of liquid
nitrogen there liquid nitrogen dewar within
that there is a copper coil assembly and the
dry nitrogen gas is made to circulate through
this assembly and is controlled by the flow
meter over here .
Ah Which makes the nitrogen gas flow at a
specific ah rate , and ah by which the gas
nitrogen gas gets cooled and it can see ah
well insulated ah delivery tube; which is
connected to the ah heating freezing system
, which is your ceramic ah stage and within
which the sample hold assembly chamber is
is placed . Within that chamber the fluid
inclusion are the vapor the w for is thin
section in which we study study the fluid
inclusions is kept , and ah the heating is
done.
So, within this there is a ah heating element,
and the heating is done by passing comprised
air and by applying ah desired current, the
heating element gets heated up and the ah
sample is the sample chamber gets heated.
And the temperature is recorded by this device
which is a temperature indicator or say to
indicator . And ah so, this the system the
way it works that ah be the attachment for
heating and freezing the different .
So, once the freezing is done or freezing
is freezing work is completed , then the ah
this ah cold nitrogen gas delivery tube is
detached and is and the hot comprised air
tube is attached with and the heating is done
. And the temperature is temperature of any
phase ah change as as you can as we see through
the microscope or if this microscope is fitted
with a ah digital camera and on a computer
screen or on a display ah video display unit
, we can ah record the phase changes, and
record the temperature from reading out from
the value here .
And this systems ah need to be calibrated
with available standards . Ah The synthetic
fluid inclusion standards these there are
available which can be a pure water or a carbon
pure carbon dioxide or ah inclusion stapret
ah any different pressure temperature, conditions
or even there are certain ah other type of
metallic standards with known melting point
. Which can also be used to calibrate ah this
equipment and ah this kind of period calibration
is essential to ah record the fluid inclusion
thermometric ah observations .
Ah So, this ah is essentially known as the
ah gas flow heating compressing system and
this popularly known as the Renaults stage
ah.
Named on the by the by the person who has
fabricated this ah equipment .
The other one which is also quite popular
is the linkam THMS G 600 ah ah microscope
heating the hot and cold stage . So, this
particular ah Renault stage it works in the
range of minus 196 degree, Celsius that is
the temperature at which ah nitrogen boils
at ah atmospheric pressure say above 196-degree
centigrade ah centigrade or minus 76 kelvin
.
So, this ah and the depending on the specification
on the capacity of this heating element by
applying the ah current through this ah variable
transformer . The temperature range of operation
can go to minus 196 to plus 700 degree Celsius
. And there are ah there are devices which
can be ah used to avoid the condenses enough
moisture when the stage is cool to sub 0 ah
temperatures.
As well as to also ah protect the objective
when the temperature goes above 500-degree
Celsius ah temperature .
So, this particular stage also works more
or less in the similar manner, but the only
difference is that it does not need to be
the freezing and heating modes . Does not
need to be any change over or connection or
the disconnection of the ah ah tube.
And ah here we can see the the system in this
totality .
So, this is a temperature controller this
is a liquid nitrogen pump.
And this liquid nitrogen pump pumps slope
ah liquid nitrogen from this dewar at any
controlled rate as we desire . Depending on
the rate at which we would ah like to decrease
the temperature or freezing or during and
ah the system ah here .
Ah It actually ah the heating is done by applying
the by by the co temperature controller by
setting the ah limits of heating and also
the heating rate . And ah this is a ah silver
heating block, on which the sample holder
as you can see is roughly about even less
than about 2 centimeter in diameter . And
having a central aperture for central hole
for the ah light to pass through when it is
mounted on a transmitter light microscope
.
And ah this system also needs to be in it
is ah the the configuration in which the model
in which it is shown here . It also needs
to be ah the device for the anti-frosting;
that means, the ah avoid avoidance are condensation
a moisture on the glass windows are on the
objective which will abstract the optical
path for which the nitrogen gas is ah is allowed
to flow in the form of a jet ah so, that it
dries of the moisture.
And the temperature when it goes above 300
degree Celsius . It can be there would be
water circulation system which can be ah designed
or even sometimes there are better ah available
device from the manufacturer which will do
the water circulation . And ah so here we
can ah make a gas that the the size of the
ah vapor on which we could do the microthermometric
experiment would be limited ah.
Although, the initially when we carry out
the fluid inclusions study thunder a normal
microscope .
We can use a larger size ah vapor or the w
poly thin section that we discussed . And
ah while bringing it to the stage hot and
cold stage for taking the micro thermometric
run , they need to be broken down to smaller
ah pieces smaller sizes as we will see them
later on . So, ah there are other make other
models of this of this a heating freezing
system , and ah these there are many other
ah such makes which are of multipurpose uses
, like for material scientists and for biological
purpose.
And ah the stages that are used for the microthermometric
experiments for fluid inclusions are the once
which we just briefly discuss here ah.
So, there are ah this kind of systems here
the as as you can see here the sample chamber
here can be moved in the x and y direction
from the ah knobs which are shown here is
one and 3 , this ah sample chair can chamber
can be opened for ah inserting the sample
chamber or taking it out .
And this is the this is connected to a platinum
ah register which ah reads the temperature
. And the advantage of this ah particular
linkam stage is that the temperature at any
point of time can be held by the controller
at that exactly at that value ah whether it
is ah depending irrespective of whether it
is below 0 or above 0 .
And these are kind of stages are also can
be calibrated by using synthetic fluid inclusion
standards or any other ah standard material
whose melting points are known . And it works
on a 3-point calibration ah below below 0
degrees are below 0 degree Celsius at at 0
degree or anything any temperature higher
.
So, generally ah this kind of calibration
are stored in the temperature in the controller
and ah they can be periodically checked or
can be ah re reset for to ensure that whatever
data we are obtaining from this ah stages
are correct and also reproducible . So, with
this much of little bit of idea on the instrumentation
ah there are other makes like, high make ah
which is ah a French heating compression system
that is also used in many of the research
laboratories and ah .
So, with this and the basic idea about the
functioning of this equipment and the specifications
, and what are the features that we must this
we should look for while going for such kind
of stage ah heating freezing system is ah
as we discussed before . Well ah, with this
the brief introduction we will now get into
the proper topic of the ah fluid inclusion
the microthermometry, the basic principles
of microthermometry .
And let us first ah begin with the simple
cases, because as we discussed there could
be many ah many questions ah many many uncertainties
many questions and ah ah many of the areas
in which the ah fluid inclusion research is
actually progressing , but ah for a beginner
we can always start with this and going by
the very simple ah cases and avoid and the
assumptions , the very basic assumptions that
we made before ah getting into the topic of
fluid , above the fluid inclusions and ah
before going for any study further study of
this fluid inclusions .
Ah We have to ah we have to first consider
this very simple assumptions . And if we recall
the number one assumption is that the entrapment
is homogeneous means the the time the condition
during which their fluid is encapsulated in
the solid lattice of the host mineral the
fluid was homogeneous .
And then they fluid once trapped behaves as
a close system without any subtraction or
addition of material from with the surrounding;
that means, with the host mineral are ah anything
in the surrounding . And also it has followed
a constant composition constant density path
ah during it is ah it is for the revolution
after the entrapment of this fluid in fluid
in the the host mineral .
And then ah the other assumption is that that
we are actually ah that is basically the way
we are defining our problem, that we are actually
sampling the fluid depending on exactly the
way we are addressing the problem whether
it we are trying to study and over deposit
are a metamorphic craft and we think that
the fluid that we have we are sampling is
actually representative of the geological
condition um in that prevailed during the
formation of this main role .
Well so, we will go by the very simple cases
. So, the they this one is an aqueous biphase
inclusion which you have already described
. These are the most a common type of inclusions
that we find in minerals host, minerals like
aqueous and all other host minerals that we
discussed calcite fluoride appetite , metamorphic
minerals like garnet cordinite or even ore
minerals like cassiterite wolframite sphalerite
and so on .
So, this is ah inclusion which is an aqueous
biphase inclusion, where there is a vapor
bubble and a aqueous liquid and it is boundary
is quite distinct with respect to the ah solid
host mineral.
So, this is the liquid solid interface and
this is the liquid vapor interface .
And ah so these are the most common type ah
the simplest type where we know that it could
it is it is water . And this water the only
come only thing which you could possibly accommodate,
right now is that this water is not a pure
water . It has some dissolved electrolytes
in it . The other ah type of inclusions which
also a very common as we aqueous polyphase
inclusion . In this sense that they have liquid
plus vapor plus a solid host mineral which
is inside it .
And as per our assumption this host mineral
ah twisted the precipitated, after the after
the fluid was encapsulated in the host ah
mineral , and this ah this crystal precipitated
out of this liquid when it it attend it is
saturation concentration ah.
So, we call them they aqueous polyphase, liquid
plus vapor plus crystal , and the third most
a common type of inclusions are the mixed
water and gas or water and carbon dioxide
inclusion, where we have a liquid ah reach
ah this liquid aqueous liquid this is a carbonic
liquid and is a carbon dioxide vapor where
we see that the the meniscus the the interface
between the vapor carbon dioxide and the liquid
carbon dioxide is not that very dark it is
another pretty sharp and prominent .
So, these are the inclusions which are very
easy to identify when we see them in the ah
inclusion in the host mineral that we are
studying . So, ah we will try to understand
the principles of microthermometry by asking
this or by trying to understand that how this
possibly could have happened.
Means, what are the conditions in which we
can expect the fluid ah the crustal fluid
a fluid that is anywhere in the ah subsurface
ah could have been in what kind of a state
so that the mineral that will go from from
it and will encapsulate the fluid .
So, here this is a familiar ah so we can we
can attempt ah to understand the ah the situation
in which fluid inclusions could be interrupt
and in what condition.
So, as you see here this is the unary water
system , it go it could initially we could
think of it is a pure water at a on a pressure
temperature diagram.
Here is this is the this line is the with
a negative slope is we know that water ah
increases in this volume is it ah is it ah
sorry decreases in volume is it a solidify
. So, there is a ah negative dp by dt slope
and this is the solid liquid or the melting
line.
And this is a solid and vapor this is the
sublimation curve , and this is the curve
on which there is quite distance of liquid
and vapor .
So, if you look at this situation , the there
is a huge ah field in which the water is stable
is a one phase liquid . So, if if we imagine
that a that the condition in the in the crossed
anywhere in the below the surface , could
be ah even though we have not put the exact
values of the pressure, but we know that there
is a vast stability field of ah liquid water
; which is capable of existence in the liquid
form and can also deposit minerals depending
on when the particular mineral is attending
saturation ah with respect in the in the in
the liquid . This is the field of vapor.
So, the only condition which will give rise
to a inhomogeneous or heterogeneous condition
is on the locus of this ah curve which we
call is the boiling curve where the liquid
and vapor would coexist . So, let us try to
first ah see to well.
So, the factors that within this ah vast liquid
field or also for example, in the vapor field
ah.
Anywhere any point on this curve will represent
a certain percentage or certain volume percent
of a liquid and vapor . And will uniquely
define a value of density of that particular
ah fluid .
And this fluid in this region where it is
homogeneous liquid , and there will be points
on this pretty field which will be corresponding
to the densities exactly the similar density
values and we can join them ah with line . So,
this these lines actually a representing the
values of a consentience; the let us say this
could be a value ah of a say 0.9 , it could
be a value of ah say 0.9 this could be a value
corresponding to possibly, let us say 0.85
or this is 0.7, just for the sake of ah ah
value I am just putting here .
So, that means, this this diagram the this
ah this lines which are plotted here.
The did not there they represent , same value
of density and that density will be also the
same where the bulk ah density that is calculated
on the basis of the ratio of the liquid plus
vapor . So, as we move along this particular
line , the density will be less and less . And
what we observe here is that the slope of
this isodensity line will also become Shelwar
has not when the ah the density value will
keep on decreasing .
Now, so this ah from pure water, let us move
onto a water which will content some dissolved
sodium chloride in it.
And will be moving from the pure water to
a system where it is just water plus NaCl
. And the reason why you are considering NaCl
let me tell it at the beginning , the sodium
is the most ah common a most abundant of the
cationic species that we see in natural in
crustal fluid . And chloride is also the dominate
amongs the anions . And the crustal fluid
ah the the aqueous fluid which actually we
encounter the most most of the environments
will have sodium chloride exist dominant species
.
And it has been the system which is been very
extensively and widely studied ah adjust were
volumetric ah properties are concern . And
we still I represent the crustal fluid as
a fluid with ah in the belonging to the water
NaCl system . So, let us say that this ah
dotted lines represent a value say let us
say 5 weight percent NaCl in that particular
liquid . So, then by virtue of the ah concentration
of the electrolyte is density will be little
higher .
So, the isochore will become stripper as an
when we go from pure water which is represented
by this green line to the ah dotted line which
ah.
And still if we dissolve more of sodium chloride
unit let us say this is 10 percent sodium
chloride than the density will be still be
ah higher and the slope of the isochores will
be will become stripper.
So, this is a general ah rule.
So, in the context of the fluid inclusions
this understanding ah will play a important
role , because will be considering the inclusion
the inclusion fluid to have been entrapped
in the one phase liquid field . And will be
having some dissolved ah constituent which
can be expressed in in terms of the weight
percent.
So, on weight percent NaCl, and the isochore
the the density line because the inclusion
is going to evolve of the when when the pressure
and temperature changes the inclusion is going
to follow a that this isodensity line, because
of a basic assumption that that you have already
made .
And ah as we all know this is the critical
ah point of pure water at 374 degree Celsius
, and 218 bars corresponding to that.
So, this is this is 300 and ah this this correspond
to 374 degrees Celsius and 218 bars pressure
. And this 0.32 grams per cc among we express
ah density in in unit of grams per cc.
At this is the critical density that is a
0.32 grams per cc, and this is the this is
the a critical isochore .
So, the situation that we ah consider that
the fluid could have been entrapped by the
by the growing crystal could be anywhere here.
Could be a ah situation corresponding supercritical
state . Or could be ah similarly when we have
a vapor ah situation corresponding to the
the aqueous ah a liquid is actually that much
lower pressure weight high temperature situation
. There are ah such situations possible in
the subsurface conditions .
And then still it can be entrapped by a growing
ah crystal by some ah mechanism and the vapor
could be entrapped.
Similarly, the vapor will also have in the
in the vapor field it is also possible to
have such kind of ah the lines of ah isodensity
lines which will be intersecting the ah boiling
curve at different pressure temperature conditions
which will be which will see them ah later
The similar ah diagram can be explained on
the basis of the ah what we know is from the
fundamental so, P-V isotherm .
And these are the different pressure and this
is the critical temperature of water . And
this ah dotted curve here represents the situation
in which there will be coexistence . There
will be coexistence of ah liquid plus vapor
, and this region will correspond to correspond
to a supercritical fluid .
And ah as we all know that within this ah
the pressure ah which is below that if we
increase the pressure than the vapor will
be liquefied.
And it is not possible to further ah decrease
the volume in the after after we cross this
ah boundary; where it is say it is defined
by liquid plus vapor field ah separating from
a one phase supercritical fluid .
So, this is ah the previous diagram which
was ah a pressure temperature ah translation
of this kind of a ah P-V of the the temperature
pressure ah diagram in which we can .
The same same situation could be understood
in the ah in the situation which you ah we
discuss the boiling curve . And the this is
the critical ah point of water , and ah this
ah even though this is not exactly a ah temperature
composition diagram, but here the situation
is shown that from a pure vapor which ah to
a pure liquid or anywhere in between when
it could be a mixture of liquid plus vapor
as we move towards a right this will be the
vapor will be ah smaller and proportion.
And here it is a largely a vapor with a negligible
ah proportion of liquid . And ah this roughly
this dotted line will separate the 2 regions
where the little be a which will be corresponding
to the boiling curve that we showed on a pressure
temperature space in the first diagram .
And ah here the situation is that if you originally
ah think that this inclusion was trapped over
here . As a temperature will decrease the
phase separation that we see inside the inclusion
will be resulting in a dominantly at aqueous
liquid plus a vapor or every inclusion is
trapped here and the temperature is decreased,
then will have a dominantly a ah liquid with
a small proportion of vapor we will be discussing
a little bit detailed about ah the implications
of such a situation . And ah so will ah continue
our discussion on the principles of microthermometry
with the help of such a simple phase diagrams
ah will.
Thank you.
