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Dear Researchers,
I am working on a petrographic analysis, and I have a thin-section database, referred to partially metamorphic rocks such as meta-basalt, meta-andesite, meta-gabbro and so on.
In the thin-section results, I have got the percentage of several main minerals such as Quartz, Epidote, Feldspar, Chlorite and some other minerals which are significantly varying among samples from one to another. For example, Quartz is fluctuating between 0 and 59 percent in various samples.
In my research, I need to categorize the mineral percentages in three ranges: Low range, Middle range and High range. For example, when we say that there is a high quantity of Quartz in a metamorphosed rock, what exact percent we are dealing with?
I would appreciate if you could share your ideas about this question.
Best,
Behzad
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That is a strange question. As Ioan Pintea suggested, 100% is a high quartz value for a quartzite, but 59% is a high value for your meta-basic rocks, but 59% might be a low value for a quartzite. The categories low, medium and high will be different for each different rock. You need to understand the purpose for making these categories. Is there any purpose? If not, why are you doing it?
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I'm working on an update to our previous global geochemical database. At the moment, it contains a little over one million geochemical analyses. It contains some basic geochronology data, crystallization dates for igneous rocks and depositional dates for sedimentary rocks. The database differs from GEOROC and EarthChem, in that it includes some interpretive metadata and estimates of geophysical properties derived from the bulk chemistry. I'd like to expand these capabilities going forward.
What would you like to see added or improved?
Here's a link to the previous version:
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A format that can be adopted by GIS!
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understanding research processes in igneous and metamorphic petrology.
Doing research in igneous petrology.
what are the tools and requirements for research starting before field observation and field observation and after field observation?
Igneous Petrology Scientific Research
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Hi Ayda,
A detailed literature check is fundamental. After having collected the samples, the first think you should do is to prepare a thin section. Too often geologists forget or consider as a secondary process the detailed petrographic description, but it is really the first activity to do, before analysing the rock.
To collect rocks a simple Eastwing hammer is not sufficient. You need a 3-5 kg sledgehammer. Eastwing comes after, to reduce the size and the weigth of the fresh rock chunk.
Good luck for your studies.
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I've used several thermometers and the results seem to contradict one another quite allot. Maybe someone can suggest a method, that's most reliable?
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Can anyone provide me thr spreadsheet for chlorite geothermometry calculation?
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During the melting of a metabasaltic rock at variable depths, the Ti budget in the anatectic granitic/intermediate melt is determined by the presence of Ti bearing minerals like Titanite, rutile, ilmenite etc. in the residual and/or fractionating assemblage. How the depth of melting/pressure of melting influences the stability of these minerals?
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Garnet The shales of Arghun Mountain have the mineral assemblages of quartz, feldspar, mica and garnet. The chemical composition of plagioclase, biotite, muscovite, chlorite and garnet shows that plagioclase is rich in albite, white mica is rich in the final members of muscovite, chlorite is more rich in the final members of amethyst and sedite, and phlogopite-anilite is basic. Garnets are rich in almandene and spesartine. In this study, the pressure and temperature of the upper limit and the lower limit of rock metamorphism were calculated using conventional geothermal-barometric methods. Using the Fe-Mg cation exchange thermometer between garnet and biotite, assuming a pressure of 4Kbar, the highest calculated temperature is 615 and the lowest calculated temperature is 429 ° C, and for 8 Kbar the highest calculated temperature is 644 and the lowest calculated temperature is 452 ° C. Using the multiple mineralogy equilibrium method, the calculated pressure and temperature for the upper and lower limits of metamorphism were about 801 ° C and 9kbar pressure, and 450 ° C and 7kbar pressure, respectively. This complex has been affected by two metamorphic and metamorphic phases of rocks. The second deformation in the region has been accompanied by the peak of metamorphism. A decrease in temperature of about 351 ° C in exchange for a decrease in pressure of about 2 kbar is observed in the metamorphic clay rocks of the study area.
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NASICON's and their common analogues use Na, K,Li or other alkali metals, Si, P and some other relatively common metals like Al, Ti, (Fe?) etc. NASICONs are with the formula Na1+xZr2SixP3-xO12with 0<x<3 . NA, Zr, Si are replaceable with isovalent elements and beyond. For example, LiTi2(PO4)3 is also considered a NASICON analogue, so is Li1+xAlxTi2-x(PO4)3. Both Sol-gel and Ball-milling then sintering techniques an be used for NASICONs.
While there are many common minerals like ZIrconia or Moissanite that shows fast ion conductivity, they act at quite high temperature. Silica is extremely common mineral, so is alumina, and apatites are quite common in sedimentary as well as some igneous environment. While complex silicates like Zeolites can exist in nature, why not NASICONs or their some sort of analogues? Does all of them react with moisture and Carbon dioxide relatively rapidly in geological scale? If they do exist, then what kind of geological environment would be conducive to their existence?
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I work as a mineralogist and I am not a specialist in NASICON phases, but the reason that these substances have not yet been found in nature will most likely be the strong hydrating ability and oxygen affinity of Ti and Zr. In even slightly hydrothermal environment there is anatase, resp. zircon (resp. hydrated zircon phases, gelzircon etc.) strongly stable. It is necessary to assess under what conditions, from which input components NASICON are synthesized and whether it is at least a little realistic for a similar synthesis to take place in nature. However, some Zr and Ti phases with PO4 or SiO2 have been found in nature. It is possible to use the search at: https://www.mindat.org/chemsearch.php
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I found quite huge idiomorphic apatite crystals (up to 0,5 mm) in the Anisian shallow water limestones and they look pretty much like porphyroblasts with pressure shadows. Limestones are highly recrystallized with mylonitic texture.
Whether an increase in temperature can cause the growth of apatites from phosphorus rich limestones?
What is the origin of phosphorus?
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Francolite synonymous with carbonate fluorapatite or
called collophane when microcrystalline
is the principal component of many sedimentary
phosphate rocks (“phosphorite”). Brushite (41.24 wt.% P2O5 ) and
monetite (52.16 wt.% P2O5) are only widespread in guano deposits,
where locally rather exotic phosphate minerals accommodating N, O
and H bridge the gap between organo-mineralic chemical compounds
and inorganic chemical compounds (coastal region in Chile). They can be the source of your apatite when recrystallized.
Marine upwelling along the shelf edge is responsible for the formation of carbonate-hosted phosphates and phosphorites. Some phosphorites accumulated within high energy — nearshore zones. Some formed in the outer shelf deposits. The common minerals besides francolite are smectite, illite, opal, sepiolite, clinoptilolite, quartz , siderite, smectite and palygorskite.
When they undergo physical-chemical alteration, e.g., an increase in T apatite may recrystallize and form XX of different X shape from elongated to stubby XX (pisms). You should investigate your apatite s.s.s. and determine how much carbon dioxide, F , Cl and OH is still in the XX. The OH- and CO3- anion complex should decrease along with increasing T. Also have a look at the minerals associated with the phosphate. The minerals mentioned above only occur in diagenetically overprinted phosphate-bearing limestones.
There are many phosphate deposits hosted by calcareous rocks.
See: DILL, H.G. and KANTOR, W. (1997) Depositional environment, chemical facies and a tentative classification of some selected phosphate accumulations.- Geologisches Jahrbuch, D 105: 3-43.
HGD
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I understand metasomatism as follows:-
1. It is a geological process which involves the transfer of fluid energy and materials to a new rock system.
2. It always involves contribution of new chemical materials to the intruded and interacted system.
3. It can changes the mineralogy, texture, geochemistry and isotopes of pre-existing rocks during its intrusion and interaction.
4. It is an igneous metasomatic process when the last remaining fluid portion of a crystallizing magma escapes and interacts with the earlier formed rocks.
5. It is a metamorphic metasomatic process when chemically active fluids are expelled out of pre-existing rocks through the rise of pressure-temperature conditions, and then which accumulates to interact with the rocks.
Thank you very much in advance.
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Metamorphism is an isochemical adjustment (be it contactmetamorphic, regional/dynamometamoprhic or burial metamorphic) to changing physical conditions pressure and temperature in the lithosphere. By definition the expulsion of carbon dioxide and water along with an increasing metamorphic grade is not involved in these processes. The lower limit called the very low-grade stage overlaps with the upper part of the diagenesis (around 200°C) and depends on the angle you look at this boundary using siliceous, organic or sulfidic matter. The upper limit is the onset of anatexis between 600 and 800°C which depends on the water content of the system. The metasomatism sensu stricto is a closed system.
Metasomatism is allochemical and an open system where in special zones at a certain P-T level a new mineral partly or wholly different in its chemical composition from the host mineral formed. These mineralizations may be caused by subcritical or supercritical solutions sparked by igneous bodies at different depth (contact -metasomatic / skarn) or in the course of burial or dynamometamorphic processes (see the isochemical analogues above). The replacement of preexisting rock-forming material occurs through chemically active liquids and gases from external sources.
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I have Raman spectra of carbonaceous materials from metasedimentary rocks and working on the estimation of their peak metamorphic temperatures. How can I deconvolute the spectra using the voigt function in Peakfit software for obtaining Raman peak values i.e. the G, D1, D2, D3 bands values as well as FWHM values; and other related parameters i.e. R1, R2? Suggestions and guidelines would be highly appreciated. Thank you.
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Hi Nasir,
in my view, the best way is to follow the approach by Lünsdorf et al. (2017): https://doi.org/10.1111/ggr.12178
There is a protocol which you can follow step wise. Fitting is done by using IFORS, that enables to reduce the operator bias (Lünsdorf & Lünsdorf, 2016).
Best,
Jan
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Hello Professors and colleagues
I am trying to draw a detailed Tectonic schematic cross section for a subducting slab focusing mainly on the transformation of shales and carbonates into greenschist facies schist and Thermal skarn overlying this slab .. ... i know that less is known about the 3D imagination of subduction zones and specially what happens to the sediments !
But what is the best schematic model i can follow from your opinion ?
Suggest references or attach your own images would enrich our discussion :)
Thanks in advance
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Dear Ahmed Morad: I understand perfectly what is your proposal. The best way to show how marine sediments get into a subduction zone is to draw a detail of the hinge zone where the oceanic plate bends when foundering inside the mantle. In this hinge zone stretching occurs, and some expansive graben structures are formed (normal faults parallel to the trench), which trap sediments and lead them to subduction. Then those sediments are metamorphosed under high P/T conditions and become phyllites and schists, usually white schists, and even metacherts and fine grained marbles. There is a quite accesible outcrop in a main freeway near the city of Puerto Cabello (north-central Venezuela) of eclogite knockers inside a relatively monotonous micaschist. A close look at thin sections of this schist shows the presence of kyanite, garnet, white mica, and Mg-glaucophane, these are usually called white schists, since the glaucophane is almost colorless and retrogradly altered to talc! Some have carbonate too, and in nearby localities of this same high P terrane there are also metacherts and marbles. So, there's no doubt that some marine sediments are indeed subducted and transformed to high P metamorphic rocks in the subduction complex. Regards, Sebastian.
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There are numerous databases for geochemical analyses for rocks like georoc and the National Geochemical Database of the USGS or purely mineralogical databases like mineralienatlas, mindat or webmineral. But is there a database for quantification of minerals in rocks?
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To sum up:
The recommendations of Guenter Grundmann , Harald G. Dill and Patricia Roeser provide the best results for my question.
The British Geological Survey shares its deposites data on their homepage:
If you want to search for the quantitative mineralogical composition of rock use the phrase "X-ray Diffraction" in the text search and the rock you search for.
In the pangaea-data warehouse the mineral composition of rocks are sourced from publications. The search for locations is also possible. The raw data can be downloaded or can be viewed as html.
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Dear all,
I am struggling to model a rock which contains the assemblage K-white mica + Na-white mica + chlorite + quartz + graphite + rutile. I have followed step by step the tutorial available on Perplex's website.
which suggests to model graphite-bearing rocks as an open system with respect to a binary H2O-CO2 fluid with buffered f(O2).
Following the tutorial, I have set a H2O-CO2 fluid in excess, modeled with equation 10 by Connolly & Cesare, 1993), buffered with X(O). Set SiO2 and O2 as excess components, then specified a sectioning value for X(O) of 0.33333333333333334 (1/3).
What I get from vertex is always the same error:
**error ver015* missing composant for O2.
I have tried everything. Changed equation, sectioning value, removed fluid/components in excess but it doesn't work.
Therefore, I was wondering if there is a better way to model a graphite-bearing rock.
Attached, you may find the DAT file for Perplex
Thank you very much.
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Dear Samuel,
There is a yahoo group which is dedicated for Perple_X. You can find the link of the group at the website of it. It is better to ask your question there and certainly you will get the solution of your problem.
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I've put a photo of mineral that I do not know.
This mineral generally occurred near the contacts of chromite lenses on the surface of serpentine foliation like sheet Silicates. The color shows copper or bronze and metallic luster but it is a very strange formation such a mineral in a sheeted form especially in serpentinized dunite!
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Some rocks with appreciable amount of felsic and mafic minerals have been crushed. In order to melt the rock at low temperature and/or to leach water-soluble cations, either boric acid (H3BO3) or mono-ammonium phosphate (NH6PO4) is mixed with the crushed rock and heated.
boric acid is commercial grade and mono-ammonium phosphate is fertiliser grade. Enough provision is made to vent out ammonia. Heating source is household gas cooking oven. Container is made of cast iron. The rocks are mixed, chiefly Granite and Gabbro. i.e. holocrystalline (pegmatite?) rocks with physically discernible grains. Rocks are crushed to about 2-5 mm size, heating period is below 3 hours on open deep bowl. The heated mixture is leached with rainwater to extract the soluble minerals.
My question is, which of these two chemicals would be able to form more water-soluble cation? Or which one would cause more melting temperature drop of the flux+ crushed rock mixture? Extraction of Na, and K cations are of first priority. Please also mention the ratio of rock vs flux as well.
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sorry,I don't understand your statement.
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Charnockite is an opx (usually hypersthene), quartz and feldspar bearing meta-igneous rock, mostly acidic in composition, and metamorphosed under granulite facies conditions. It is commonly found in Gondwana fragments such as in Sri Lanka and India. One of the key characteristic features of chranockite is that minerals of feldspar and quartz in the rock have a greenish appearance. Is there any scientific explanation for the cause of this colour?
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I just discovered this debate and was intrigued by your observation Craig, recalling that HCl treatment of Arendal charnockites caused them to turn grey (reported by the late Dennis Field in one of his papers). I think the green colour is related to deposits from a fluid along grain boundaries, being unrelated to the high grade assemblage. These rocks frequently form with beta-quartz, which upon cooling into alpha qz shrink a bit, making space for minor deposit, and I think some workers have shown that they are the cause of the ‘coloration malgachitique’. Perhaps it is possible to restore in some cases a sort of charnockite colour by chemical weathering where similar components are present? at least rational arguments should not overrule a good observation. In geology observation is always the first step!
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I am a materials science (and metallurgy) student and geology enthusiast. Comparing these two subjects side by side, I have found out some interesting pattern.
Ironmaking slag has 40-45% CaO, 30-40% SiO2 , 10-15% Al2O3 , about 5% MgO and 1-2% FeO. Steelmaking slag can have 40-60% CaO, 10-25% SiO2, 2-10% MgO, 5-35% FeO and 0-25% P2O5.
Ironmaking slag can have, among many other minerals, Akermanite, Monticellite, Gehlenite ,Anorthite, Pyroxene etc, along with some spinels. In my opinion , it matches with some feldspathoids with slightly mafic character. Steelmaking slag is more close to alkaline earth mafic rocks and peridotites. It has a good amount of spinels, monticellite, merwinite, silicocarnite, periclase etc.
Answers from metallurgists and Geologists are welcome
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Dear Mr. Bhowmick,
Slags are artificial products representing Fe ore which is made up of the Fe ore mineral and a wide range of gangue from carbonate to silicate minerals (rock) and the slag-producing additives e.g. limestone. The entire process in blast furnace takes place at low pressure and high temperatures. As a consequence of that the natural analogue is a combination of rocks forming at high T and low P which is the mafic volcanic clan (different types of basalt, see e.g. the major mineraloids in slags are Fe-enriched olivine s.s.s., pyroxenoids, wuestite and native elements plus Ca-Mg components). As far as the metamorphic part is concerned the natural equivalent well presenting these conditions is the so-called sanidinite hornfels facies (contact metamorphic reactions of carbonates at low pressure and very high temperature). These processes result in the formation of monticellite, akermanite, melilite, tilleyite, spurrite , rankinite , merwinite and larnite. The pressure conditions are below 1 kbar and the temperature greater than 700°C.
Kind regards
H.G.Dill
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Hello Professors and colleagues
I am studying Neoproterozoic meta-sediments can i apply the indices of alteration on it or it has to be on sedimentary rocks only ?
Thanks in advance
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Dear Mr. Morad,
Unless you have carried out a geological survey and studied the mineralogical association of your rocks the chemical studies and the use of any index based upon chemical data is meaningless. It is a repetive critics of mine.
It is good for riding the “paper-tiger” but in practice these figures are of no use. Because what it is all about, is the futile attempt to circumnavigate experience and knowledge in geology and mineralogy. To gather experience needs time and to pile up knowledge even more in combination with a series of physical and mental endowments.
We cannot delegate geosciences to the technicians in the chemical lab.
Sorry for this harsh critics which is a general statement rather a reference to your question.
Sincerely yours
Harald G. Dill
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Hello, everyone. I'm calculating the fO2 and fS2 for my chlorite whose temperature is around 300~350 ℃. Anyone can provide a software or spreedsheet to calculate those numbers by using solution model of Walshe (1986). Or, you can also recommend other easier calculating method! Thanks a lot!
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Mr, could find a way to calculate these parameters?
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Charoite is a rare alkali silicate that occurs in an attractively looking pink-purple rock in the Murun Massive, Sakha Republic, Yakutia, Siberia. This rock is a sort of skarn generated metasomatically at the contact between the Murun Syenite and the encasing limestone. I attach a photo of my sample. Does a similar rock occur elsewhere in the world?
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Dear Roberto:
Are you sure that hexagonal crystal in the charoite is reall quartz? Nepheline also forms sometimes perfect hexagonal prisms, and the alkaline nature of this rock suggests the possibility that it could be silica undersaturated, thus containing feldspathoids! I got a wonderful sample of charoite as a gift while assisting to the XXVIII International Geological Congress, in Moscow, on august 1984, in that country this colorful stone is used to make ornaments, ash trays, and the like. Among other things, including tourism and cultural activities (the Hermitage and Natural Science museums in Saint Petersburg), we made excursions all over the U.R.S.S. One 8 day-trip to Irkutsk, on Lake Baikal, sailing the western shore and going to the lapislazuli mines of the Czars (the phogopite books there were meter-sized, but I settled with a 20 cm and a 10 cm wide pseudo-hexagonal books), to the Primorsky Beach, where crops out a wonderful rapakivi granite so similar to the huge Parguaza rapakivi Granite outcropping in southern Venezuela..., to the outcrops of "grenvillian" high grade marbles, wih fresh forsterite, red spinel and phlogopite or scapolite, related with cordierite-sillimanite metapelitic gneiss ending with a famous nepheline syenite intrusion and skarn, with a dyke of alkali pegmatite, there the zircon and titanite crystals where visible at the naked eye!... Another excursion was to the Ukraine, where we visited the Korosten Anorthositic Complex and the Voilyn pegmatite field, there I got from the dumps a wonderful fist- sized microcline crystal, an 8 cm wide slice of bicolored topaz, and a graphic intergrowth of smoky quartz with cream-colored microcline, very showy. With regards, Sebastián.
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We have gabbro, pyroxenite, and serpentinized peridotite in a small area (5*5 km), adjacent to a greenschist-facies subduction melange (5 km far to the west). We also have "metamorphic sole" rocks including Pl-Amp migmatite within the pyroxenite.
All of those ultramafic-mafic rocks are depleted in HFSE and enriched in Pb and Sr.
The serpentinized peridotite is slightly depleted in LREE with no Eu anomalies. It is also depleted in Th, U, P, and HFSE.
The pyroxenite is significantly depleted in Th, U, P, HFSE, and LREE. However, the uralited pyroxenite is nearly flat in REE diagram and enriched in Th, U and P.
The gabbros are enriched in LREE and LILE with positive Eu anomalies.
The migmatite of the metamorphic sole has similar pattern with the pyroxenite.
In V vs. Ti diagram most of them plot in/near the IAT (& slab-proximal BABB and FAB) area.
They were possibly the SZ(subduction zone)-proximal ophiolite (SSZ type), however, they were also possibly the lower crust and mantle of an island arc.
So the question is: when we lost the upper crust, how to name those ultramafic-mafic rock complex, island arc or ophiolite? (answered)
A new question is:
How to interpret the LREE depletion of the ultramafic rocks, which "seems to be contradict with SSZ origin"?
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I recommend Cemal's answer
Best Regards
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Hello Everybody,
I am working with high grade metamorphosed manganese-rich pelitic rocks and i would like know if is possible to assess potencial primary or low grade mineralogy of these rocks using thermodynamic modelling (using pseudosection in THERMOCALC, for instance).
Cheers!
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Yes, redox matters especially if you deal with Paleoproterozoic ore – as you mention high-grade metamorphic ore, this is one of the possibilities. At the time, the ocean was weakly oxidized and stratified. This means that Mn4+ compounds formed in the oxic (upper) layer may be dissolved upon settling in reducing conditions, in the deeper layer. Initial minerals precipitated in the oxic layer are mostly Mn4+-oxides, subsequently (an possibly rapidly) converted into Mn2+-carbonates (as rhodochrosite) or Mn2+/Mn3+-silicates (as braunite, garnet, and much more). If you use a thermodynamic code/model, be careful to introduce initial conditions appropriate to the contemporaneous chemistry of the ocean, or of the layer of the ocean you’re concerned with. Cheers, Thierry
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Cooperation in igneous and metamorphic petrology and help in U/Pb dating.
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Dear Irakli,
What kind of cooperation you need? If it is theoretical, then feel free to contact me. For analytical support, you can contact University of Granada, Spain. Kindly check the following link: http://www.ugr.es/~ibersims/ibersims/Welcome.html
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Hello Profs and collages
i am asking if i can apply the relation
CIA = Al2O3/Al2O3+CaO+Na2O+K2O for meta pelitic rocks such as schists and phylites to indicate that chemical weathering affected the precursor of those metamorphic rocks ?
or metamorphism and subsequent hydrothermal alteration will result in a valueless results ?
thanks
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Dear Mr. Morad,
such chemical indices are attractive to those who do not know the side effects and cast aside other processes leading to similar datasets. The ratios pretend to be all-embracing if you ignore the "small print". In my opinion they should be used with a stark warning and always supported by other methods from different geoscientic disciplines such as geology, mineralogy and shallow geophysics.
Best regards
H.G.Dill
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Hello,
I deal with detrital heavy minerals. I found quite numerous topaz grains in several samples. I wonder if this is possible to distinguish between different source rocks (e.g., various pegmatites and skarns from the Bohemian Massif, Central Europe) using chemical composition of the topaz grains/crystals (major and minor elements using electron microprobe, and/or trace elements using laser ablation). This subject is completely new for me, I will be grateful for any tips.
Monika
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Considering the limited variability of topaz in terms of major elements, studying trace elements, both of your heavy minerals and suspected source areas, might be the most fruitful approach. Perhaps cathodoluminescence imaging may also give some information (e.g. Agangi et al., 2016. Relation between cathodoluminescence and trace-element distribution of magmatic topaz from the Ary-Bulak massif, Russia. Mineralogical Magazine, 80(5): 881-899.
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Points are two-combinations of n phase names. Lines are three-combinations of phase names. Point and line are incident upon one another if the two phase names comprising the point are part of the name of the line (e.g., point AB and line ABE are incident upon one another). In attached figures, lines of perspective are red, perspective triangles are green, and points of perspective of pairs of green triangles are connected with orange lines. Brute force counting of adjacencies is doable for Desargues configuration (n=5) , but impractical as system number of phases increases.
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It's been a while, but I've finally achieved an answer to my question. In the Euclidean plane, given points as two-combinations of n phase names and lines are three-combinations of the phase names there must be 1 point adjacent to 2n-4, 2 points adjacent to 2n-5, 3 points adjacent to 2n-6, ..., n-1 points adjacent to n-2.
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Hi,
I am in look out for literatures pertaining to allanite breakdown mehanisms in hybridized I-type meta-aluminous granite. The mafic differentiated source diorite (K2O-4-5%) and potash-rich (K2O 5-7%) granite are variably hybridized. A residual leucocratic micro-granite bearing (2-5%) modal allanite is emplaced along brittle-fractures during late stages of granite crystallization. 
I have analyzed 2-5% modal allanite in a late to post-kinematic leucogranite, showing alteration to britholite-(Ce) and parisite-(Ce). The EPMA data shows the transformation is partial; somewhere between allanite - parisite-(Ce) solid solution join. Few Calkinsite-(Ce) is also suspected. The breakdown product of allanite are thorite and clay.
Thanks in advance.
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Thanks Wentao Cao for taking time and listing the references. I appreciate your effort. 
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I mean can we use the Trace element data from chromites through LAICPMS  for petrogenesis and Tectonism? 
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you can read these papers
Pagé, P. and Barnes, S.J., 2009. Using Trace Elements in Chromites to Constrain the Origin of Podiform Chromitites in the Thetford Mines Ophiolite, Quebec, Canada. Economic Geology, 104: 997-1018.
Zhou, M. F., Robinson, P. T., Su, B. X., Gao, J. F., Li, J. W., & Yang, J. S., 2014. Compositions of chromite, associated minerals, and parental magmas of podiform chromite deposits: the role of slab contamination of asthenospheric melts in suprasubduction zone environments. Gondwana Research, 26, 262–283.
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Does a HREE depleted source explains HREE depletion itself?
HREE are commonly or exclusively garnet-controlled?
Which processes can cause different HREE content in a co genetic magma series? 
Can strongly positive Eu anomaly (at least 10 times higher)  be in any terms related to HREE depletion and  their concave upwards pattern in a REE chondrite normalized spidergram ?
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Zircon, xenotime and garnet can be responsible of HREE depletion in magmas. Of the three possible cases above you would expect, respectively: Ce, Hf, and Zr depletion and Eu anomaly decrease with differentiation (zircon fractionation);  a P depletion with differentiation (xenotime fractionation); and a LREE increase if garnet is fractionated.
I would expect Amphibole fractionation in a chondrite normalized REE 'spoon-shaped' pattern.
Different HREE contents in co-genetic magmas could be explained by accesory minerals fractionation
You can explore de different partition coefficients in this link:
Hope it helps.
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I have some grabbro samples, however, when I made EPMS analysis on the minerals in the rock slice, there are much more amphiboles than clinopyroxenes. Then I think the most clinopyroxenes should have altered to amphiboles. How could I distinguish between the two kinds of amphiboles?
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In igneous rocks, especially mafic igneous rocks, primary amphiboles tend to be pargasite or pargasitic hornblende. The problem arises in that at magmatic conditions, there are processes (hydration crystallization) that produce amphibole by reaction between pyroxene and melt. These amphiboles are usually pargasite or hornblende. However, reaction can continue subsolidus yielding low-Al hornblende, actinolite etc. that are generally construed as "deuteric" or metamorphic. Finally, if you have wholesale replacement of pyroxene by green or blue-green hornblende, it is probably metamorphic. The condition of the feldspar can also yield a clue in these situations. Is it altered? Is it more albitic than you would expect for the rock composition?
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It is usually seen that Pan-African granites are rich in LREE and U. Is it because Pan-African granites are anorogenic and highly differentiated, derived due to partial melting of metasomatised igneous crust?
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Dear Dr. Majumdar:
You are on the right track. There are two types of U deposits, one called intramagmatic bound to alaskites and another named U metasomatites.
The first group hosts davidite, uraninite, thorite, bedafite, eudyalite, and pyrochlore and is categorized as low grade-large tonnage (e.g. Roessing 300 ppm U3O8). They are mainly located  in southern Africa. The second one encompasses uranium mineralizations which occur in structurally-deformed rocks altered by metasomatic processes, and associated with the introduction of Na, K and Ca. Their mineralogy resembles the afore-mentioned ones (U-, Th-, P- and REE –bearing minerals). Their reference deposits are located in Brazil and Cameroon.
Partial melting of a granodioritic source rock produced a restite-bearing I-type monzogranite in the magmatic stage. The granite ascended synorogenically.
Residual late-magmatic melts are enriched in K or Na causing
different generations of albitization which led to the replacement of plagioclase by albite, and the formation of a Zr-Ce-La mineralization.
The hydrothermal phase gave rise to the uraninite mineralization
U-albitite deposits are normally in S- and A-type granites.
Best regards
H.G.Dill
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My rocks are amphibolite وamphibolized gabbro, gneiss (overprinted by amphibolite facies retrograde metamorphism) and schist. I dont know how can I determinethe source of protolith. As I know Pb and Rb/Sr ratio change during this grade of metamorphism. Can Sm/Nd be usefull? Separated mineral or whole rock or both of them? Thank you so much in advance.
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On gneiss and schist:
After you prove sedimentary nature of the gneisses and schists (e.g., based on relict textures), and that most elements are immobile during metamorphism, you can use a variety diagrams and indices.
Classification diagrams for meta-sedimentary rocks:
(a) SiO2/Al2O3–Fe2O3*/K2O diagram (after Herron 1988);
(b) SiO2/Al2O3–Na2O/K2O diagram (after Pettijohn et al. 1987);
(c) CIA–ICV (Chemical Index of Alteration vs. Index of Compositional Variability). Trends of fresh granites and fresh basalts are from (Lee 2002), subdivision on mature and immature, intense weathering and weak weathering sediments are from (Nesbitt and Young 1984; Cox et al. 1995).
(d) A–CN–K plot for meta-sedimentary rocks (after Fedo et al. 1995). Molar proportions: A-Al2O3, K-K2O, CN-CaO*+Na2O, CaO* = CaO-CO2-0.5xCO2-10/ 3xP2O5.
Indices for meta-sedimentary rocks:
The chemical index of alteration (CIA) (Nesbitt and Young 1984)
The CIW index (Harnois, 1988)
The PIA index (Plagioclase Index of Alteration) (Fedo et al. 1995).
The WIS (Weathering Intensity Scale) (Meunier at al., 2013)
References:
Cox, R., Lowe, D.R., and Cullers, R.L., 1995, The influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern United States: Geochimica et Cosmochimica Acta, v. 59, p. 2919–2940.
Fedo, C.M., Nesbitt, H.W., and Young, G.M., 1995, Unraveling the effects of potassium metasomatism in sedimentary rocks and paleosols, with implications for paleoweathering conditions and provenance: Geology, v. 23, p. 921–924.
Harnois, L., 1988, The CIW index: A new chemical index of weathering: Sedimentary Geology, v. 55, p. 319–322
Herron, M.M., 1988, Geochemical classification of terrigenous sands and shales from core or log data: Journal of Sedimentary Research, v. 58, p. 820–829.
Lee, Y.I., 2002, Provenance derived from the geochemistry of late Paleozoic–early Mesozoic mudrocks of the Pyeongan Supergroup, Korea: Sedimentary Geology, v. 149, p. 219–235.
Meunier, A., Caner, L., Hubert, F., El Albani A., Preˆt, D. , 2013. The Weathering Intensity Scale (WIS): An alternative approach of the Chemical Index of Alteration (CIA). American Journal of Science, v. 313, p. 113–143.
Nesbitt, H.W., and Young, G.M., 1982, Early Proterozoic climates and plate motions inferred from major element chemistry of lutites: Nature, v. 299, p. 715–717. 
Nesbitt, H.W., and Young, G.M., 1984, Prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations: Geochimica Et Cosmochimica Acta, v. 48, p. 1523–1534.
Pettijohn, F.J., Potter, P.E., and Siever, R., 1987, Sand and Sandstone: New York, Springer-Verlag, 553 p.
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This Field photo shows the alternating layers of Fuchsite Quartz and Barite formed during Archean period, in Dharwar craton. Any suggestion about the interpretation?   
With Regards, Sagar
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Dear colleagues:
We need more hard facts. Tidal regimes, volcano-sedimentary sequences, the source of Cr and the host of Cr, as well as  exhalations are very difficult to be put together to give me a coherent picture. Or shall we cast aside the slogan "The present is the key to the past"  for these very old rocks ?  A chemical approach using the V/Cr ratio in the argillaceous layers (so-called fuchsite) may give an answer to the variation in the redox conditions. V increases with lowering of the Eh (more reducing) and Cr responds in the opposite direction (more oxidizing). If it gives a more coherent picture together with barite you get a bit closer to the large-scale environment. I would be very much reluctant to jump too fast into an interpretation of the depositional environment without proper knowledge of the mineralogy and chemistry. Nevertheless, a nice story, to think about.
Best regards
H.G.Dill
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In simple calcissilicated rocks, the granulitic facies would be attested by the presence of forsterite or grossular, up to fCOquantity.
Anyhow, the coexistence of Diopside and Enstatite in a quartz saturated rock, with minor retrometamophic poikiloblastic hornblende it's enough to testify a retrometamorphic path from granulite to amphibolite facies?
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Your question is in some what confused manner
are you asking or giving a statement?
As I understood you would like to know the mineral assemblage when the protolith is sedimentary either carbonate-greywacke
Granulite facies metamorphism occurs at temperatures of approximately 500 to 700 degrees celsius and pressures of 8-70 kbar.
Changes in mineralogy depends very much on protolith,
In case of pelites the mineral assemblage is - microcline +/- plagioclase +/- scapolite +/- garnet +/- cordierite (low-P) +/- andalusite (low-P) +/- kyanite (high-P) +/- sillimanite (moderate, low-P, high-T) +/- graphite +/- rutile +/- ilmenite +/- olivine +/- corundum +/- spinel +/- sapphirine (high T).
In case of quartz-feldspathic rocks the mineral assemblage is - microcline + plagioclase + garnet +/- pyroxene +/- hornblende.
whereas in case of calc-silicate rocks the mineral assemblage is- calcite, dolomite, quartz, diopside, scapolite, forsterite, wollastonite, graphite.
Small amounts of hornblende are often present, which is likely due to the water pressure being lower than lithostatic pressure during most granulite facies metamorphism.
Evidence for relatively low water pressures comes from fluid inclusion data indicating carbon dioxide-rich fluid compositions and from preservation of some bulk compositions that should have undergone nearly total melting at granulite temperatures if water pressure had been equal to lithostatic pressure.
Thus the presence of hornblende need not always indicate retrograde metamorphism, you observe it's textural association with pyroxene to ascertain the retrograde metamorphism.
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I got a sample of a nice looking blue rock (see photos attached), and I would like to know what rock is it.
This rock must be already known also commercially, because I recently saw a piece of this rock worked in the shape of a fruit (Pear, life size), decorated with a silver leaf.
It is not Lapis Lazuli (not the same colour, and it lacks the typical Pyrite granulation, even if a single small Pyrite crystal is visible). It is not Sodalite (not the same colour, and it lacks the typical white veining). It could be a Sulphur-poor variety of Hauynite of some sort, but which is it exactly? Where does it came from?
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Mineral / Rock ID from pictures is notoriously difficult, especially if more "exotic" materials are involved. Our department, the Department of Earth & Atmospheric Sciences Mineral Laboratory at the Metropolitan State University of Denver offers FREE non-destructive & certain destructive mineral identification services as part of our geoscientist training program and university community outreach. It is really free and by processing a sample of your rock you would aid in the training of our geoscience students. Takes usually one semester, but you would receive a fine, detailed report of various test results (XRF, XRD, physical & optical properties, etc.) and interpretations. Next batch of sample analysis starts beginning of February 2017. If you are interested, here is a link with details on the process and how to submit your sample: http://college.earthscienceeducation.net/MIN/MINID.pdf
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Sanukitoids are granitoids showing enrichment of both large-ion lithophile elements (K, Ba, Sr) and mafic elements (Mg, Cr and Ni) at the level of their SiO2 contents. It is generally thought that these granitoids, with high Mg#, were produced from a mantle source (supplying Mg, Cr and Ni) fluxed with a crust-derived fluid or melt carrying K, Ba, Sr, LREE and Th. A likely tectonic setting is a mantle wedge overlying a subducted oceanic slab undergoing dehydration or melting. Therefore, many authors consider presence of sanukitoids as a strong indicator of subduction, especially in the late Archaean. Can such rocks form in tectonic settings unrelated to subduction?   
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I believe you can find a detailed answer to your question is in chapter 3 of our book: Mints et al. "East European Craton: Early Precambrian History and 3D Models of Deep Crustal Structure" GSA Special Paper 510, 2015. You may copy Chapter 3 from ResearchGate.
In page 111 you can read:
Nature of sanukitoid magmas. As was shown above, the model Nd ages of sanukitoids definitely depend on the age of country TTG gneisses, which reflects either the age of the crust and the lithospheric mantle. Sanukitoids in the young Kuhmo–Segozero microcontinent have Nd isotopic parameters of the depleted mantle, whereas sanukitoids from the older Vodlozero and Kianta microcontinents are characterized by lowered initial εNd values. In the opinion of Kovalenko et al. [2005], the isotopic heterogeneity of sanukitoids is a result of different duration of a gap between enrichment of the mantle source and the moment of partial melting of that source, which produced sanukitoid magma. The two-stage model of the formation of sanukitoid magmas is a natural consequence of this statement. The first stage corresponds to the mantle metasomatism, i.e., enrichment of the mantle under effect of fluids or melts generated in the process of subduction or underplating of the crust by mantle-derived magmas. The second stage, which started 2.76–2.70 Ga ago, corresponds to the tectonothermal event (vigorous influx of extracrustal heat), which gave rise to the partial melting of the previously metasomatized mantle and generation of sanukitoid magma.
It should be noted, however, that a gap between formation of the crust (with or without participation of subduction) and formation of sanukitoids is cardinally different for three microcontinents making up the Karelian Craton. For the Kuhmo–Segozero microcontinent, this gap does not exceed 60 Ma. For the Kianta microcontinent, the gap is estimated at 60–100 Ma. Finally, for the ancient Vodlozero microcontinent, a gap could have been more than 150 Ma. These estimates convincingly show the absence of genetically predetermined succession of events: subduction → formation of continental crust of granite–greenstone domain → sanukitoid magmatism that completes formation of this domain. Following Kovalenko et al. [2005], Lobach–Zhuchenko et al. [2005b], and Bibikova et al. [2005b], we assume that the two-stage model is consistent with available geological and isotopic data, which reflect tectonic and geodynamic independence of the consecutive stages in the formation of sanukitoid magma. The crucial factor that initiated appearance of sanukitoids irrespective of prehistory of the crust is a thermal pulse dated at 2.76–2.70 Ga.
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Mafic mantle magmas underplating at the base of the continental arc crust and form the hot zone. These magmas could differentiated to the evolved melts by fractional crystalization and mixing with crustal partial melts (which produced by the heat and volatile transferring from the mafic mantle melts). It is likely that some parts of these magmas cooled and solidified, and form the basaltic sills in the base of arc crust.
Remobilization of the frozen andesitic melts (differentiated mantle magmas) by the newly injection of the hot mafic mantle derived magmas was reported from some of the continental arcs. I need to know whether intrusion of mafic mantle derived magmas could re-melting the cold mantle derived basaltic sills, too?
Thanks
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Dear Vahid,
So thanks. 
Best Regards,
Zahra
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for a pseudosection of granulites, generally we take XMg and XGrs data from epma of garnet. can we replace this by any other minerals.
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Can someone explain me how exactly a schist can be transformed to augen metagranitoid or migmatitic augen gneiss?
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Dear Dr. Santos:
The term schist is rather well established within the sequence of metamorphic rocks, originating from a  psammo-pelitic parent material with quartz, some feldspar and phyllosilicates. I will depict below the grain size, metamorphic stage and denomination of the rock arranged in the order of increasing p-T condition during metamorphism
1. Slate (< 0.1mm fine-grained) very-low grade stage
2. Phyllite (0.1 mm to 1.0 mm medium-grained) low grade stage
3. Schist (> 1.0 mm) may be homogeneous or spotted with porphyroblasts medium (to high grade). In some cases also of low-grade stage (see talc schist)
4.Gneiss (> 1.0 mm) layered, banded, flasered locally with "augen" or single porphyroblasts medium to high grade
There are transitions into calc-schists or calcsilicate-schists  in case of marls forming the protolith.
Maybe this is of help for your question.
H.G.Dill
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Samples from massive Ti-Fe ores associated to massif-type anorthosite exhibit zircon rimmed by baddeleyite + chlorite.
Although such texture has been reported in meteorite impacts, I wonder if there is any other type of occurrence for this texture with less extreme formation conditions? Thanks!
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Dear Alejandro,
Please have a look at these works.
Kind Regards,
Masoud Ovissi
Liu, Lin-Gin. "High-pressure phase transformations in baddeleyite and zircon, with geophysical implications." Earth and Planetary Science Letters 44.3 (1979): 390-396.
Scoates, James S., and Kevin R. Chamberlain. "Baddeleyite (ZrO2) and zircon (ZrSiO4) from anorthositic rocks of the Laramie anorthosite complex, Wyoming: petrologic consequences and U-Pb ages." American Mineralogist 80.11-12 (1995): 1317-1327.
Wall, C. J., et al. "Baddeleyite-Zircon Relationships in cumulates of the Archean Stillwater Complex: evidence from U-Pb geochronology and Hf isotope systematics." AGU Fall Meeting Abstracts. Vol. 1. 2010.
Kovalenko, N. I., and B. N. Ryzhenko. "Comparative study of the solubility of zircon and baddeleyite." Geochemistry International 47.4 (2009): 405-413.
Schärer, Urs, Jasper Berndt, and Alex Deutsch. "The genesis of deep-mantle xenocrystic zircon and baddeleyite megacrysts (Mbuji-Mayi kimberlite): trace-element patterns." European Journal of Mineralogy 23.2 (2011): 241-255.
Voznyak, Dmytro K., et al. "Baddeleyite segregations in zircon of the Azov zirconium-rare-earth deposit (Ukrainian Shield)." Mineralogia 44.3-4 (2013): 125-131.
Lewerentz, Alexander. "On the occurrence of baddeleyite in zircon in silica-saturated rocks." Dissertations in Geology at Lund University (2010).
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Rocks metamorphosed deep in the earth later appear on the surface due to weathering-erosion and or upliftment. Is there any way to estimate the stored stress in the rock when they reached the earth surface? Or are such data available?
Thank you
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Hi Tharanga,
Before answering the question of residual stress, one will have to answer the questions whether stress accumulates? and if so how? and what is the evidence to suggest that stress once accumulated and then later released? Also, if stress accumulates is there the necessity to release all that stress after the metamorphic rocks reached the surface? One can argue that stress was accommodated by re-crystallization to a new mineral assemblage and ductile deformation (strain) and therefore did not accumulate. What happens if the system of stress changes? There will be new deformation and re-crystallization. Does one want to argue that stress accumulates during successive stages of deformation? or whether all that was accommodated by re-crystallization and deformation? These are questions you have to look into closely before answering your main question.
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What is a useful method to quantify graphite contents in powdered rock samples? XRD does not work well due to the platy crystals and very strong preferred orientation, so I'm looking for an alternative method. Either by another analytical instrument, or by physical separation, or...
Thanks, Simon
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I'm an analytical chemist with experience in graphite exploration, and field sample analysis. The method we use is: precisely weigh a powdered sample (0.1 to 1 gram aliquot); leach with dilute HCl to remove carbonate carbon; roast in Leco furnace at 425 C until weight is stable (removes organic carbon); ash the residue and detect graphitic carbon-derived CO2 by IR.
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The O18 isotopic equilibrium temperature (between biotite-muscovite) in a metapelitic mylonite is 300 deg C. However, the stable paragenesis of these metapelites includes garnet, staurolite. The Ar-Ar age of recrystallized muscovite is 11-13 Ma. Can we say that ductile deformation related to mylonitization occurred 11-13 Ma?..Or is it the just the cooling age of the pelites which have undergone garnet and staurolite stable metamorphism earlier? What are the constraints??
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Dear Nirmalya,
deformation conditions seem to be thus well constrained. Consequently, I think grain size could be a possible explanation to understand the obtained ages. One interesting point that you could evaluate is whether the so called "closure temperatures" are valid, specially for mylonitic rocks (e.g., have a look on Igor Villa´s papers). I´ve been working on this topic for the last year and I think it´s not as easy as it´s thought due to the complexity and interaction of different processes during mylonitization (deformation, metamorphism, magmatism, fluids).
In any case, I am still not pretty sure whether both micas are contemporaneous or not. For example, the biotites >400 microns, do they represent the grain-size reducted biotites or the remnants of "underformed" biotites? Based on what you mention, I would still think that biotite nucleated prior to muscovite, although both could be afterwards homogeneised in terms of 18O. In that case, this event shouldn´t have affected K-Ar isotopy. 
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Hello, everyone, I want to discuss with you to learn about if my following thoughts are suitable for deep research. 
I want to compare the content of water, especially the structural water (OH), in nominally anhydrous minerals of granulite (Khondalite: gt-sill gneiss; mafic granulite: gt-px or two px granulite), S-type granulite, plagio-granite and then to discuss the influence of structural water in NAMs on decompression melting process of Khondalite and plagio-granite. As my previous study show that the S-type granite is formed by melting of granulite facies metasedimentary rocks and pagiogranite is generated by melting of basic rocks (most possibly the basic granulite or similar kinds of rocks), and there is concensus that granulite facies metamorphism occurrs at a dry condition and the water of protolith is dehydrated before the amphibolite facies metamorphism. So, I want to know if it is a good plan to learn about  how the stuctural water content of minerals in khondalite  work on the  melting process to produce S-type granite, and similar to the plagiogranite which is produced by melting of basic rocks.
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Dear Haozheng,
I could not agree more with Esther. In fact there are a few papers out there which undertook this "exercise" and could help you about the applied methodology and expected concentration levels of "water" in different NAMs from granulites.
Németh, Bianka, et al. "Melting, fluid migration and fluid-rock interactions in the lower crust beneath the Bakony-Balaton Highland volcanic field: a silicate melt and fluid inclusion study." Mineralogy and Petrology 109.2 (2015): 217-234.
Zhang, Li, Junfeng Zhang, and Zhenmin Jin. "Metamorphic P–T–water conditions of the Yushugou granulites from the southeastern Tianshan orogen: Implications for Paleozoic accretionary orogeny." Gondwana Research (2015).
Yang, Xiao‐Zhi, et al. "Water contrast between Precambrian and Phanerozoic continental lower crust in eastern China." Journal of Geophysical Research: Solid Earth (1978–2012) 113.B8 (2008).
In spite of some unjustified criticism on the methodology I would still recommend you with confidence to use the unpolarized infrared methodology (see references below) (this would save you a lot of time and effort and would not worsen significantly the accuracy of your quantitative results), or in some cases it would make possible to have any quantitative data at all). There are only a few absorbance conditions which should be met for accurate results. Note, however, that this methodology is rather limited if you would like to constrain the crystallographic orientation of particular absorbers in minerals.
Kovács, István, et al. "Quantitative absorbance spectroscopy with unpolarized light: Part II. Experimental evaluation and development of a protocol for quantitative analysis of mineral IR spectra." American Mineralogist 93.5-6 (2008): 765-778.
Sambridge, Malcolm, et al. "Quantitative absorbance spectroscopy with unpolarized light: Part I. Physical and mathematical development." American Mineralogist 93.5-6 (2008): 751-764.
You can have access to the digital spectra of several NAMs from granulites in the PULI spectral database for free and you have the opportunity to share your own spectra with the wider community ( puli.mfgi. hu ).
I hope that this was a help and good luck with your research,
Cheers,
Istvan
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High pressure granulite is always regarded as the indicator of collision process, especially, some high pressure pelitic granulite is regarded as the subduction-collision process involving sediments. So, I want to know, is there other tectonic process to produce high pressure granulite ?
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Dear Peng,
In attached link you will find a paper, reporting an occurrence of high pressure granulite in relation to a fault zone. Maybe it is the one, you are searching for.
Best Wishes,
Masoud Ovissi
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Can anyone suggest a good overview article on what makes Alpine Type serpentinites different from others? I know that plots of Cr# vs Mg# have different fields, but what else is different and why? Mineralogy? Any estimates of P-T conditions, or are they variable?
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Thanks!
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I would like to know if garnets in migmatite rocks form as a result of dehydration reactions or any other process and also to know how to determine if garnets were transported by the melt or originally formed as a result of metamorphic reactions
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As Marlina says, although in many cases garnet may have also formed during the subsolidus evolution of a migmatite, it commonly forms as a peritectic phase (solid product) of the melting reaction in both metabasic and metapelitic rocks (which are you looking at?). It forms by the incongruent breakdown of hornblende or biotite (which contain the H2O needed by the melt but contain way too much Fe, Mg and other stuff to dissolve) with quartz and feldspars that form the main chemical constituents of the melt. In such cases the garnet is usually spatially associated with leucosome pockets or veins, and may be relatively deficient in inclsuions relative to eralier formed garnet. Garnet (peritectic and subsolidus) can be transported long distances with the melt, as the work of Gary and others have shown (see attached paper for a more recent example where we suspect this happened), particularly if the garnet is small. However, as garnet commonly forms large grains (several miliimetres to centimetres across) it generally remains trapped (along with other peritectic minerals like opx, cpx, cordierite), within the residual source rocks (granulites).
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I've been having difficulties in terms of identifying or being able to tell the difference between the paleosome and neosome visually. How do you tell if the paleosome exist in the migmatite rock by just looking at the hand specimen?
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Dear Mr. Xaba:
4 terms need to be distinguished: Paleosome, neosome, melanosome, and leucosome. As the prefix indicates paleo is old, neo new, leuco light, and melano dark. Whereas paleo and neo is timely, leuco and melano is the color. In practice this means that the neosome is the product of anatexis that can be formed by reactions that produce for example graitic melt + garnet during fluid absent melting. In this case the quartzofeldspatic part is the leucosome, together with garnet forming the neosome. If you don't have an additional melanocratic phase like garnet or cordierite during anatexis, leucosome and neosome is the same. On the other hand the melanosome is the restite that did not melt and is formed by dark minerals, whereas the paleosome is the original rock of which the melt was extracted. The latter two terms are very difficult to distinguish is field and often chemical analyses is necessary.
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Does ridge push can reactivate oceanic fracture zones? 
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The answer given by Volker Kaminske is quite good, the oceanic lithosphere takes some 12-15 Ma to become brittle. But some precision should be made in the question issued by Carlos Ganade de Araujo itself. There's NO "MORB" lithosphere, MORB is a term specific for mid ocean ridge basalts, which make up oceanic crust, not lithosphere. The lithosphere under the oceanic crust  call the LID or oceanic mantle lithosphere, which comprises usually more than 90% of the thickness of an oceanic lithospheric plate, is not made of basalt, but of ultramafic rocks,such as peridotite, dunite and  pyroxenite, often serpentinized and tectonized.  
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For example: Eclogites could represent a range of protoliths such as picritic basalts crystallized in magma chambers within the mantle, subducted ocean floor or delaminated lower crustal material. Any papers/articles?
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A good review of d18O of minerals and rocks in mafic eclogites is in the work of Miller, Buick and Cartwright et al.
Miller, J. A., Cartwright, I., Buick, I. & Barnicoat, A. (2001). An O-isotope profile through the HP-LT Corsican ophiolite, France and its implications for fluid flow during subduction. Chemical Geology 178, 43-69.
Miller, J. A. & Cartwright, I. (2000). Distinguishing between seafloor alteration and fluid flow during subduction using stable isotope geochemistry: examples from Tethyan ophiolites in the Western Alps. Journal of Metamorphic Geology 18, 467-482.
For d18O in garnet from eclogites nice works are below, not all of them are oceanic crust but you will see a variety of d18O due to oceanic alteration, interaction with serpentinite and sedimentary fluids during subduction.
Errico, J. C., Barnes, J. D., Strickland, A. & Valley, J. W. (2013). Oxygen isotope zoning in garnets from Franciscan eclogite blocks: Evidence for rock-buffered fluid interaction in the mantle wedge. Contributions to Mineralogy and Petrology 166, 1161-1176.
Page, F. Z., Essene, E. J., Mukasa, S. B. & Valley, J. W. (2014). A garnet-zircon oxygen isotope record of subduction and exhumation fluids from the Franciscan complex, California. Journal of Petrology 55, 103-131.
Russell, A. K., Kitajima, K., Strickland, A., Medaris Jr, L. G., Schulze, D. J. & Valley, J. W. (2013). Eclogite-facies fluid infiltration: Constraints from d18O zoning in garnet. Contributions to Mineralogy and Petrology 165, 103-116.
Rubatto, D. & Angiboust, S. (2015). Oxygen isotope record of oceanic and high-pressure metasomatism: a P-T-time-fluid path for the Monviso eclogites (Italy) Contributions to Mineralogy and Petrology in press.
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Hello, everyone. My eclogite rocks contain many epidote and zoisite. Epidote can be used to determine ages by U-Pb dating, but I don't know if there are any method for U-Pb dating of zoisite? 
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Dear Mr. Huang,
which element do you want to use for this dating to get realiable geological results ?
Zoisite is Ca2Al3Si3O12(OH) and epidote has the chemical composition Ca2 (Fe,Al)3(SiO4)3(OH). There is only one mineral in this group of minerals, allanite or orthite which is related to the above s.s.s. Ca(REE,Ca)Al2(Fe++,Fe+++)(SiO4)(Si2O7)O(OH). The latter has also elevated U and Th contents and as such it is amenable for radioactive dating. I would direct my thoughts to garnet which is besides omphacite the most important constituent in eclogites and can tell you something about the age of formation. Sm/ Nd and Lu/Hf may be an option.
Best regards
H.G.Dill
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Hello folks,
I am studying the petrogenetic evolution of a polymetamorphic highly fractionated I-type granite. Geochemical and petrographical studies revealed two different varieties of this orthogneiss, namely a metaluminous (ASI 0.9-1.0) mafic variety and a weakly peraluminous (ASI 1.0-1.1) leucocratic variety. Rayleigh fractionation modelling argue for a derivation of the leucocratic orthogneiss through fractional crystallization from the melanocratic orthogneiss. Peraluminous (ASI 1.1) aplites represent the highest evolved member of this series.
My problem is, how do I explain this trend? So far I havent observed hornblende in the melanocratic gneiss, which would shift the composition of the residual melt towards peraluminous composition if fractionated. Generally, biotite is the only mafic mineral in these metagranitoids. The model of Chappell et al. (2012) in which a metaluminous I-type granite is produced through higher degrees of partial melting of a Cpx-rich source (e.g. basalt, andesite) is not favoured by the negative epsilon Hf values of zircons in both orthogneisses indicating a crustal protolith. Assimilation of crustal material could be a further explanation, but yet I dont see any evidence for that in my geochemical data.
Is it possible to make a metaluminous residual solid (cumulates) through fractional crystallization of a peraluminous melt? Do you have any other ideas to explain the transition of metaluminous to peraluminous composition of an I-type granite?
tyvm
Michael
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What do your biotites look like? Are they igneous or metamorphic? Any traces of residual amphibole? Is it possible the amphibole in the orthogneiss has been completely replaced by biotite during metamorphism? If, as you state, magmatic phenocrysts are very rare, metamorphism must have been extensive.
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1. Chemographic projections of mineral assemblages.
2. Generating P-T-t paths from petrographic observations.
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Dear Sandun,
For your question 1:
What do you mean by chemographic projections of mineral assemblage? Do you mean the AFM type diagrams? If you specify what type of projection do you want? It will help others to give you correct answer or some clue.
You may have a look on the page below, you may find it useful
For question 2:
Again, if I understood your question correctly, it is hard to generate P-T-t path simply based on petrographic observations. You may infer though from the petrograhic evidence you have in your samples. However, for correct P-T-t paths you have to have chemical composition of mineral assemblages you are interested in, and their age (t). There are several programs which can be used for P-T (and t, provided you know the age). Two already suggested by Alexeev, and you may check the link above for GIBBS.
Also, you may check PERPLEX, might be easy to use.
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The MgO contents under study range from 8-16%. I guess one is high degree of partial melting of the mantle peridotites, and another is  olivine cumulates. Can anyone recommond some related references which argue for these two aspects. Or are there other reasons for the  high magnesian contents in basalts? Thank you. 
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Can you provide a photomicrograph of the rock (having  unusually high Mg content) and the list of minerals present?  Just academic curiosity. Thanks. KNRAO
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Absolute dating is necessary for knowing specific time e.g. by isotope K/Ar in mica, especially in the crystalline rock: igneous and metamorphic rock. On the other hand, the sedimentary rock (as I know) usually provide the time of formation by age range of fossil e.g. Upper Miocene - Piocene. Is there any method to make it more specific like the crystalline one?
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The best way to obtain a numerical age for a sedimentary rock – other than through comparison of fossil content or magnetopolarity reversals with the geological timescale – is through the direct dating of volcanic ash layers (U-Pb and Ar-Ar techniques on mineral separates). The main difficulties with this approach relate to the mixing of grains of different age and significance, and alteration of the dated minerals. An approach that works really well in marine deposits of Oligocene-Miocene age is to measure Sr isotope ratios in microfossils and macrofossils. The seawater ratio is well established for that interval, and more or less linear. Glauconite dating is mostly a mess. Poor resolution.
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My research project is based on garnet composition within leucosome, melanosome, palaesome in Migmatite rock and so I would appreciate any information which specifies about this in a certain location called Kliprand, South Africa. The information is limited in this area of interest and I would appreciate any input regarding this topic.
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Wouldn't it be an idea to start reading about (garnets in) migmatites in general and seeing whether you can apply these general ideas to your field area?
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We can infer the source features and evolution of a magma during its ascent from spider plots of trace and REE elements, by normalizing the elemental content of rocks with different reservoir elemental composition. In case of granitic rocks (I-type), which have upper continental crustal-like primitive mantle normalized pattern (see attached file)  we mostly assume that either the rocks are crustal derived or mantle derived, but contaminated by crustal rocks. Can fractional crystallization of the primitive mafic magma (or andesitic; mantle derived)  give such  pattern?
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Dear Mr. Aminov,
you expect too much from a single set of trace elements normalized to a standard and overstretch the possibilities of such analyses. You have to take a more diversified approach also including REE (see first response of Dr. Towe), isotopes and last but not least carefully examine the lithology of the volcanic rock to see which processes affected this magmatic rock. It is not only the source that counts. On the way up a magma can also be contaminated.
Best regards
H.G.Dill
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I have been observing a metamorphic rock that contain Almandine garnet using SEM-EDS. The presence of garnets is confirmed by the very rock's XRD patterns (both Pyrope and Almandine are present).
Element analysis (SEM-EDS) of various points on Almandine/pyrope shows the following general chemical composition in wt%
Na - 0 - 1%      K - 0 - 1 %  Al - 17-19%
Mg - 4 -7 %     Si - 25 - 30%
Ca - 4 -1 %     (Total)Fe - 30 - 35 %
Strangely, Sulphur is there ranging 0 to 2%
Is it natural to have Sulphur in garnet? and are Na, K, Mg and Ca inter exchanging with each other?
Additional Info (XRF analysis (FP method) shows S element about 1.6 wt%. but XRD does not show any peak for possible Sulphur bearing minerals such as  pyrite or gypsum. Still the rock samples have strong sulphur smell).
Thank you in advance
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Dear Mr. Udagedara,
Using SEM-EDS is not suitable for accurate chemical analyzes of garnet.
Exact quantitative chemical analysis of garnet are possible only with an electron beam microprobe.
In almandine garnet may be present, the trace elements:
Sodium, potassium, chromium, vanadium and in very minor quantities, scandium, yttrium, europium, ytterbium, hafnium, thorium, uranium.
In pyrope garnet may be present, the trace elements:
chromium, iron, sodium (in eclogite), potassium, phosphorus, vanadium, nickel, scandium, ytterbium, lutetium.
Sulphur does not fit in the garnet crystal lattice. Measured sulfur contents come from tiny solid inclusions of sulfides such as pyrite, pyrrhotite, chalcopyrite, which are often found in garnet crystals.
Mg and Ca Sodium are interchangeable. Na and K are trace elements.
Best regards,
G. Grundmann
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Is it possible to have Fe2O3 in Sillimanite?   I observed (under SEI) a sillimanite looking grain (in a metamorphic rock sample)  with characteristic cross fractures in my SEM-EDS studies. But several points along the very same grain show the following composition;
Alumina - 58 - 61 wt%
Silica - 35-38 wt%
FeO+Fe2O3 - 3 -5 wt%
Is this gain is sillimanite or something else. Is it possible Alumina to be replaced with Fe2O3?
Thanks in Advance!
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Secondary hematite micro powder is quite common in some rocks when even mild oxidation is takin place. You do not have to have high hematite content because red staining gives very very strong effect. Obviously Al can folllow Fe and vice versa. This may not be taking place in your sample but it is worthy to check measurinf Fe content. Fe Ka spectral line is very efficient and you can get detection limit around 0.01wt%.
Cheers, HK
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Published XRF data sheets that I've gone through has H2O in different format. Those are LOI (Loss on Ign), H2O+, H2O-, H2O or water. 
Does this water or H2O means the sum of H2O+ and H2O-?
Or is there any other explanation for this?
And what is the reason for having different form of water in xrf data?
Thank you
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Actually LOI means "loss on ignition", therefore the sample has reached a temperature in which all volatiles are eliminated, this includes moisture water plus bound water in micas, amphiboles, epidote, etc. [in the form of (OH)-], and in some rocks even CO2 produced by decomposition of carbonates. If no carbonate is present, then LOI is H2O+ plus H2O-. LOI heating I understand that reaches some 700°C.  
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I have some quartzites which are ductilely deformed and dynamically recrystallized. Though these quartzites contain mica (1-2%), these micas are very fine grained and difficult to be collected. Therefore, Ar-Ar method is not suitable as we think. Also no indirect method like cross-cutting leucogranites are not there in the locality to where these samples belong. In that case which method may be suitable can any body suggest?
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Dear Mr. Chatterjee,
Quartzites often contain apatite, monazite and / or zircon crystals. If you find in your quartzites grains that are at one tenth of a millimeter in diameter, and contain at least 10 ppm uranium, then you should try the fission track dating methods.
Please compare two of my publications dealing with the apatite fission track dating method.
Best regards,
Guenter Grundmann
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Boninite genesis is still highly debated. Although the basic conditions (harzburgitic mantle + slab derived fluids at onset of subduction) are widely accepted, there are  individual processes in different regions. I am looking for publications wich focus on the role of fractionated differentiation during petrogenesis of the papuan new guinea boninites.  
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But from this reference for a start, you can trace backward and forward more references that are relevent to the boninites in Papua New Guinea:
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Could anyone please let me know that max and min value of CaO/Al2O3 and Na2O/Al2O3 in plagioclase or in feldspar?
Thanks in advance
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Not need for further explanation, your question has been answered through the discussion thanks to the input of all the participants. By the way, that figure is from one of my papers (Fig 3f): Campos Alvarez and Roser 2007. Geochemistry of black shales from the Lower Cretaceous Paja Formation, Eastern Cordillera, Colombia: Source weathering, provenance, and tectonic setting, Journal of South American Earth Sciences 23, 271–289, and simply reflects the abundance of clay minerals is indicated by low K2O/Al2O3 ratios (<0.3), similar with the ranges of clays (Fig. 3f) but significantly different from the higher ratios (0.3–0.9) typical of feldspars.........just keep it simple
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The integrity of the datafile, datafile format, and the program have been verified. I am using winCMP and thermodynamic dataset v1.02, as bundled with winTWQ v2.34, on a laptop running 64-bit Windows 7.
Running winCMP in multiple compatibility modes did not solve the problem. It seems that winCMP crashes when any amphibole oxide data is fed to it, including previously published analyses used in TWQ calculations.
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you can visit Dima DD website to find updated program, Ufortunately, this is in Russian, but you can ask someone to translate.
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Spreadsheet/software calculating seismic velocities in peridotite as a function of mantle peridotite modal composition and chemistry of olivine/opx?  I look for spreadsheet/software enabling the calculation of seismic velocities on the basis of mantle peridotite modal composition AND composition of major minerals. Crucial is the possibility of translating the small variations of forsterite content (2-4 mole %) and corresponding orthopyroxene mg# to seismic properties. I wonder if it is possible...?
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I agree with the above. Moreover, the big trade-off will be with temperature (and pressure), too. Another significant uncertainty is anelasticity, which is a hard problem. A few % change in the mineral content will have a theoretical effect on the velocity, but whether you would be able to calculate a reliable value is a different issue. This type of thing has been done before, ignoring anelasticity (see below), but doing so ignores a significant effect on the velocities:
A composite geologic and seismic profile beneath the southern Rio Grande rift, New Mexico, based on xenolith mineralogy, temperature, and pressure
J.M. Hamblocka,b,!, C.L. Andronicosa, K.C. Millerb, C.G. Barnesc, M-H. Ren b , M.G. Averill b , E.Y. Anthony b
Tectonophysics 442 (2007) 14–48
doi:10.1016/j.tecto.2007.04.006
They provide extra calculation materials in a supplement and refer to a spreadsheet by Hacker and Abers (2004).
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Based on EPMA data, the Sr value reaches up to 676 ppm (0.08 %wt) within the garnets (with andradite-dominant end-member) from a Fe-LREE distal skarn deposit. Also, ICP-OES data shows a relatively higher amount of this element (up to 840 ppm) in the sample contains ore minerals include magnetite, pyrite, pyrrhotite, calc-silicate minerals such as andradite and epidote, and secondary minerals comprise actinolite, calcite, quartz, and chlorite. It is worth noting that, marmorized limestone also yielded 10,346 ppm of Sr.
Lithologically, the Upper Cretaceous submarine andesitic rocks and the flysch-type assemblage including alternating thin to medium bedded sandstone, shale, marl, and conglomerate together with the thick bedded to massive limestone are the most common units in the area. Also, Granodiorite and gabbro are the dominant composition of Oligocene aged intrusive bodies.
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Dear Mr. Baghban:
Bivalent Sr can substitute for bivalent Ca. It is not an abnormally high amount of Sr in your andradite-dominated garnet s.s.s. and I advise to be very cautious and do not over-interpret one trace element alone. You have to look at these values in context with other elements chemically affiliated to them and the overall composition of the garnet. Extremely high values may be expected, as alkaline magmatic activity is involved in the skarn formation. Are there LREE-bearing minerals such as monazite or bastnaesite among the minerals ? On the other hand, take also a closer look at the limestone that provides the parent material for the exoskarn. What is the background.
Sr/Sr isotopes have often been used for genetic interpretation of garnet emplacement. See one paper below.
Sousa et al. (2013) Strontium isotope zoning in garnet: implications for metamorphic matrix equilibration, geochronology and phase equilibrium modeling.
Best regards
Harald G. Dill
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Low pressure metamorphic belt surrounded by granitic gneiss.
The granitic gneiss compositions vary from calc-alkaline to alkaline. What are the possible ways to find out the tectonic setting of a low pressure metamorphic belt?
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The fact that you talk about a metamorphic belt may already exclude some tectonic settings. Apart from geochemistry and (metamorphic) petrology, structural information is crucial. 
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Recently, the utilization of magnesium isotopes in tracing the global carbon cycle has attracted more and more researchers. It is suggested that the δ26Mg values in normal eclogites (not carbonated) are generally comparable to those of their protoliths and also the average mantle. This means the preservation of the original Mg isotopic composition during low temperature-high pressure metamorphism. My question is that can the original magmatic Mg isotopic composition also be preserved in the amphibolites or granulites from Archean cratons.
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As long as metamorphism is isochemical, i.e. no evidence for metasomatism, then I do not see a problem with the isotopic signature being preserved.
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Why isn't a Mass Balance Equation study in migmatites usual these days?
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Hi There,
As Marlina pointed out your question is a little vague. My guess is that you are asking about reintegration of melt with residue to calculate the original composition of the rock that melted. 
Whilst this may be possible in some cases i think the likely scenario is that in many cases partial melting is open system. This means leucosomes represent residual cumulates that are left behind after the loss of some (in may cases unknown) volume of granitic melt that has now migrated to higher levels in the crust. 
As a result a mass balance approach will still not result in calculating the original bulk composition of the unmelted protolith. There is a JMG special issue on crustal melting that covers a large amount of current migmatite research (link below). As well as recent books/reviews e.g. Mike Brown, Ed Sawyer, there is also a lot of active research with modelling of open systems e.g. Chris Yakymchuk, Fawna Korhonen etc
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I would like to distinguish these two lithologies to show a geochemical contrast between them in a figure. The figure presents a cross section through an oceanic core complex. The cross section is perpendicular to the ridge axis. 
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Jakub,
It is rather difficult, at least for me, to reply to you answer, that appears to be too generic to be answered with a simple and clear statement on the state of art on you problem.
I give to you some informations that are based on my experience of the natural laboratory of the ophiolitic peridotites from the Alps and Apennines (N-W Italy), and, accordingly concern the rifting stages of opening of the fossil Jurassic slow-ultraslow Ligurian Tethys basin.
I can say that :
1) lherzolites (and particularly fertile spinel – to plagioclase lherzolites), most probably derived from the sub-continental mantle lithosphere during the rifting stages of the basin, are exhumed and eventually exposed at the sea-floor close to the Ocean-Continent Transition (OCT) Zones of the rifted margins;
2) harzburgites (and, particularly. depleted reactive spinel harzburgites) frequently associated to large volumes of impregnated plagioclase peridotites, progressively replace sub-continental lherzolites ocean-wards. They are interpreted as products of melt/peridotite reaction caused by porous flow infiltration and percolation of early asthenospheric melts during the pre-oceanic magmatic rifting stages of the future basin.
3) refractory harzburgites, formed by oceanic partial melting and parental to the subsequent oceanic MORB magmatism of the basin, are doubtly described at the sea-floor during the embryonic stages of oceanic spreading.
In our cases, evident chemical contrast exist between fertile lherzolites, reactively depleted harzburgites and refertilized plagioclase peridotites, depending on the processes of formation, both melting and melt/rock interaction.
I don’t know if more informations on these situations and geodynamic settings are useful to your problem.
In the case, write again and I’ll give you appropriated references.
Giovanni
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Could anyone please let me know the standard procedure of measuring LOI in a rock sample
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Even better: first dry the powdered sample at 110 degrees to get rid of any adsorbed water. And I would think that 550 degrees is a bit low (I typically go for 800-900 degrees), but if there is a possibility of alkali-loss, then you may want to keep the temperature lower than that
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The mafic microgranular enclaves consists of plagioclase laths and chlorite. The presence of skeletal augite within chlorite suggests that the latter were altered from augite. The quartz and albitic plagioclase phenocrysts occur in the enclaves, possibly transfered from the host felsic magma. Many quartz and some albite phenocrysts coexist with calcite. The calcite exhibit smooth, regular boundaries with quartz. It is unlikely that the calcite was a post-magmatic alteration products but, rather, was crystallized simultaneously or slightly later than the plagioclase laths. 
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My bet would be that the calcite is secondary, considering the evidence for alteration. The metamorphic grade does not need to be high to get calcite - as long as you have fluids around of the correct composition, you can get calcite. I have seen it in < 1Ma volcanics too...
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I'm working with granulites and I have a sample with Feldpars exsolving Apatite; The sample also shows myrmekitic textures. I think is related with metasomatism, but I'm still not sure. I just found an article talking about this in granites, is by Broska, et. al. (2004) The geochemistry of phosphorus in different granite suites of Western Carpathians Slovakia: the role of apatite and P-bearing feldspar. 
I hope you can help me. 
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Thanks,
If the overprinting fluid contained REE's could you go straight to monazite? I have attached an image for your interest. The relationship with biotite appears far more transgressive than the relationship with the feldspar which is more equivocal. We confirmed that the mineral was monazite through SEM. The FOV is approximately 3 mm. 
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