Thanks a lot for this valuable discussion.
My honest gratitude to all.
Regards,
Trisrota
On 10/14/12, Bruce Yardley <[log in to unmask]> wrote:
> Dear Trisrota
>
> In a word, yes. No possible protolith has the Ca:Mg ratio of tremolite, so
> monomineralic tremolite rocks must be a) metasomatic and b) have undergone
> metasomatism at the time that the tremolite grew.
>
> If the ultimate precursor was igneous you would hope to find a little Fe
> left and also low mobility "igneous" elements like Cr, whereas if it was
> originally dolomite it could be very pure tremolite.
>
> Bruce
>
>
> Professor Bruce Yardley
> School of Earth and Environment
> University of Leeds
> Leeds LS2 9JT
> UK
> Tel. +44 (0)113 343 5227
>
>
> ________________________________
> From: Metamorphic Studies Group [[log in to unmask]] On Behalf
> Of Trisrota Chaudhuri [[log in to unmask]]
> Sent: 13 October 2012 12:48
> To: [log in to unmask]
> Subject: [geo-metamorphism]
>
>
> Dear all,
> Kindly forgive me for questioning again.
> So can I take it as granted that sent percent tremolite bearing rock is
> unlikely to be a product of close system equilibrium assemblage except the
> cases of skerns? Because fortunately or unfortunately I didn't get any
> calcite and/or dolomite. So, I have to discard this possibility. And about
> the possible protolith even if we consider even it was
> pyroxenite/diopsidite, at least water has to be added to the system (?).
> Diopside, reacting to H2O and CO2 can produce Tremolite and calcite. If I'm
> not getting calcite/dolomite, again this extra Ca theoritically has to leave
> the system (open system process again?).
>
> On Oct 9, 2012 1:47 PM, "Axel Liebscher"
> <[log in to unmask]<mailto:[log in to unmask]>> wrote:
> Dear all,
>
> just a short addition to what Bruce mentioned:
>
> The infiltrated rock will act as a chromatographic column. That is, not only
> the rockīs composition will change (eventually giving raise to pure albite
> in Bruceīs case) but also the fluid, by traveling through the rock and
> reacting with the mineral assemblage, will change its composition. Depending
> on mass ratio, fluidīs composition will evolve towards the composition
> defined by the rockīs mineral assemblage (in the case given by Bruce the
> composition at the triple point). Once the fluid composition is adjusted to
> the triple point it may move through rock without leaving any further
> chemical fingerprint. On the other hand, any new fluid pulse will first
> enter a rock that has already been albitized and thus will pass this part of
> the rock without any change in composition of neither the rock nor the fluid
> itself.
>
> Best regards
>
> Axel
>
>
> Am 09.10.2012 09:53, schrieb Bruce Yardley:
> Dear Trisrota and all
>
> As far as I am aware the rules of thermodynamics have not changed since
> Sumit and I were young, and the Korzhinsky phase rule still stands. We ought
> to be able to make more of it nowadays because we understand a lot more
> about which elements can reach high concentrations in solution, but it has
> been largely forgotten. Put very simply, the argument is that the larger the
> fluid flux through a rock the fewer the minerals that will be present. If
> the mineral that is present is a solid solution, it will not show the
> chemical variation you might expect.
>
> A simple way of thinking about it is to imagine an activity diagram for a
> quartz-saturated system with axes that are, for example, log (aK+/aH+) and
> log (aNa+/aH+). There will be fields for the stability of K-feldspar, albite
> and muscovite (among others) and they will meet at a triple point. If a rock
> contains those 3 minerals and a small amount of fluid, then the fluid
> composition will be adjusted to that point. However if fluid is introduced
> from a different rock type, or even from the same lithology at a different
> temperature, it will have a different composition which will lie within the
> stability field of one of the minerals. Suppose the incoming fluid is higher
> in Na and has a higher pH than the fluid at the triple point; it will gain
> protons by converting muscovite to feldspar, and swap Na for K by albitising
> K-feldspar. Eventually, if enough fluid comes through, the rock will be
> composed only of albite, perhaps also with quartz. This reflects the
> relatively low mobility of Al and Si compared to Na and K.
>
> Personally, when I read accounts of rocks that have supposedly experienced
> large fluid fluxes but still have low variance assemblages, I am supicious
> of their veracity. If I can be forgiven some advertising, Springer are about
> to produce a book dealing with aspects of metasomatism, edited by Dan Harlov
> and Hakon Austreheim and in my chapter I have tried to remind readers of
> Korzhinsk's contributions.
>
> Bruce
>
> Professor Bruce Yardley
> School of Earth and Environment
> University of Leeds
> Leeds LS2 9JT
> UK
> Tel. +44 (0)113 343 5227
>
> ________________________________________
> From: Sumit Chakraborty
> [[log in to unmask]<mailto:[log in to unmask]>]
> Sent: 07 October 2012 12:28
> To: Metamorphic Studies Group; Bruce Yardley
> Subject: Re: [geo-metamorphism]
>
> Dear Trisrota and others,
>
> As Bruce points out, pure tremolite rocks are most likely derived from
> marble, and they are white....beautiful samples come from Romania, for
> example....should be very easy to check if your hand specimens are like
> this.
>
> This brings me, however, to another question that I have been thinking
> about for a while. When I was a student, admittedly quite some time
> back, we were taught that a monomineralic rock was a tell tale sign of
> open system behavior.
>
> This was used as a simple example of the use of the phase rule.....the
> general idea being (very loosely paraphrasing Korzhinskii, Thompson et
> al.) that there are obviously many elements in natural rocks and fluids,
> and so no matter how you define things, you tend to end up with many
> "components" (in the phase rule sense). Therefore, to get only one
> phase, one would have to fix several intensive variables in addition to
> P and T, and this was most readily accomplished by fixing / defining /
> constraining some chemical potentials by contact with an external
> reservoir ("fluid bath"). I am staying away here from using the somewhat
> more loaded term - "buffering", and from using the names of the variety
> of "components" that have been used in the literature (e.g. K-component
> etc.). That general thinking seemed like sound logic to me, and was used
> to explain all kinds of things from quartz veins in crustal metamorphic
> rocks to dunites in mantle rocks. "Tremolite rock" reminded me of this
> because these Rumanian samples always seemed to me to be a prime
> illustration of this - with all these elements available (Ca, Mg, Si,
> H,....), one can think of many minerals with simple structures that
> could have formed....instead, nature chose to make a monomineralic rock
> with one, single mineral with a relatively complex structure....because,
> several chemical potentials were constrained?
>
> Now we deal a lot more with fluid fluxes and open system behavior, but
> that line of reasoning appears to have disappeared, and I often find
> that people are not even aware of this kind of reasoning using the phase
> rule. Newer textbooks / notes do not deal with this either. I am
> wondering if there is a reason for this, and if some of you who have
> been more continuously involved with the evolution of the field have
> some insights about why / how thinking has evolved in this regard? I
> have followed the evolution only sporadically myself, more for teaching
> than for my own research.
>
> Sumit
>
>
>
>
> On 07.10.2012 12:26, Bruce Yardley wrote:
> Dear Trisrota
>
> Are you sure it is tremolite? Pure tremolite rocks are normally derived from
> dolomitic marble, which seems unlikely with greywackes. In particular I
> think you need to have some idea of the Al-content, but just as important is
> a clear picture of the field relationships and whether there are veins or
> any metasomatic effects in other units nearby.
>
> Bruce Yardley
>
> Professor Bruce Yardley
> School of Earth and Environment
> University of Leeds
> Leeds LS2 9JT
> UK
> Tel. +44 (0)113 343 5227
>
>
> ________________________________
> From: Metamorphic Studies Group
> [[log in to unmask]<mailto:[log in to unmask]>] On
> Behalf Of Trisrota Chaudhuri
> [[log in to unmask]<mailto:[log in to unmask]>]
> Sent: 07 October 2012 06:46
> To: [log in to unmask]<mailto:[log in to unmask]>
> Subject: [geo-metamorphism]
>
> Dear all,
> I've found some Archean, sheet like basic dykes which, when observed under
> thin section, is seen that they consist of 100% tremolite. They are
> associated with grewacke. Is there aby possibility that these mafics could
> be a part of metasomatized (rodingitized?) oceanic crust? Please enlighten
> me that how to explain the formation of such 100% tremolite bearing rocks.
>
> --
> Trisrota Chaudhuri,
> JRF of Indian Statistical Institute and Jadavpur University,
> Kolkata, India.
>
> --
>
>
> ***************** Sumit Chakraborty
> ****************************************
> http://www.gmg.ruhr-uni-bochum.de/petrologie
>
> Institut fuer Geologie, Mineralogie und Geophysik;
> Ruhr-Universitaet Bochum;
> D-44780 Bochum; Germany
>
> Email: [log in to unmask]
> Tel: +49-(0)234-322 -4395 / -8521 / -8155
> Fax: +49-(0)234-321 4433
>
> ****************************************************************************
>
>
> --
> Dr. Axel Liebscher
> Head of Centre for CO2 Storage
> Phone: +49 (0)331/288-1553
> FAX: +49 (0)331/288-1529
> Email: [log in to unmask]<mailto:[log in to unmask]>
>
> Helmholtz Centre Potsdam
> GFZ German Research Centre For Geosciences
> Public Law Foundation State of Brandenburg
> Telegrafenberg, 14473 Potsdam
>
--
Trisrota Chaudhuri,
JRF of Indian Statistical Institute and Jadavpur University,
Kolkata, India.
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