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Hello,
I would like to use the Petrograph software to create spider diagrams of rare earth element distributions. Unfortunately, I am having trouble importing my data in Excel format (attached file). I am receiving the error message “I’m not able to open this file.” I believe I have formatted the data according to the example shown in the article “Petrograph: a New Software to Visualize, Model, and Present Geochemical Data in Igneous Petrology” by Maurizio Petrelli et al. (2005). The article references a more detailed manual, but the link appears to be broken. I would be very grateful for any guidance regarding what I might be missing in the file format, or for a detailed manual or tutorial!
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Or you can plot in GCDkit (gcdkit.org) that does not have so many restrictions regarding the input format...
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Dear colleagues
Good morning. Diamonds have been known from various locations around the world, some of which are unconventional (far away from cratons). The Roman writer Pliny the Elder mentioned that diamonds had been found in the gold mines of Ancient Philippi in Greece. Have any diamond-related rocks (kimberlites, lamproites etc.) ever been found Greece? What is your opinion about the Ancient Philippi diamond occurrence (see attached PDF)? If you have any additional information, please provide it.
Best regards
Ioannis
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DEAR SHAHAB
GOOD MORNING AND THANK YOU FOR YOUR DETAILED REPLY. PLEASE READ CAREFULLY THE WHOLE ARTICLE ATTACHED TO THIS QUESTION, IT WILL GIVE ANSWERS TO ALL OF THE POINTS THAT YOU RAISED. REGARDING RECENT DIAMOND FINDINGS IN GREECE, MPOSKOS & KOSTOPOULOS 2001 HAVE FOUND UHP MICRODIAMONDS IN THE GREEK RHODOPE MASSIF (SEE PHOTO ATTACHED). THE ARTICLE IS ONE OF THE MOST CITED DIAMOND-RELATED PETROLOGICAL ARTICLES (WITH 337 CITATIONS).
BEST REGARDS
IOANNIS
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Dear colleagues
Good morning. Diamonds have been found in several geotectonically unconventional occurrences from around the world like Borneo, the Urals, NSW, California, Burma, Thailand, Victoria, Tasmania, Northern Ireland, the Appalachians, Northern Algeria and Sumatra. These areas are located away from cratons and mobile belts around cratons. No kimberlites or olivine lamproites have been found near these deposits, defying therefore Clifford's rule (that all diamonds are found in cratonic kimberlites). What is the source of these diamonds? Could it be lamprophyres for example?
Best regards
Ioannis Kamvisis
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Solely from the outward appearrance of a diamond X it is difficult to take any decision where it came from. This is especially valid for diamonds in placer deposit o , in general terms, reworked into sediments far off their "kitchen".
The following classification scheme elaborated shows some so-called unconventional types of diamond deposits, particularly among metamorphic terrains:
1)Magmatic deposits
1)Diamond in komatiites, lamprophyres and other ultrabasicrocks
2)Diamond in peridotites of ophiolite sequences
3)Diamond deposits bound to kimberlites
4)Diamond deposits bound to lamproites
2)Sedimentary deposits
1)Placer deposits
1)Alluvial-fluvial and nearshore-marine modern diamond placer deposits
2)Palaeoplacer diamond deposits
3)Alluvial-fluvial carbonado placer
3)Metamorphic deposits
1) Microdiamonds in impact structures (NÖRDLINGEN IMPACT CRATER 14 Ma)
2) Microdiamonds in high-pressure zones
3) Microdiamonds in garnet gneiss
4) Diamond in graphite schist
Glückauf
HGD
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Dear colleagues
Good morning. The IUGS TGIR (Task Group on Igneous Rocks) is planning to publish a book (glossary) on the classification of igneous rocks in 2025. Should the IUGS TGIR adopt the Lamprophyre clan or facies concept or both regarding the classification of lamprophyres, lamproites and kimberlites? A new 2024 article entitled "Some notes on the IUGS classification of lamprophyric rocks" concludes that both concepts are correct but they represent different perspectives of the matter. See PDF in Researchgate:
The clan (as updated by Kamvisis & Phani 2022) focuses on the interrelations between these rocks while the facies concept focuses on their formation under volatile-rich conditions (as proposed by Mitchell 1994). The new article suggests that both concepts should be adopted by the IUGS TGIR. What do you think? Comments are welcome.
Best regards
Ioannis Kamvisis
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dear Ioannis
The classification of lamprophyres, lamproites, and kimberlites has been a topic of ongoing discussion within the International Union of Geological Sciences (IUGS). Here are some key points from recent proposals and discussions:
  1. Ultramafic Lamprophyres: There is a proposal to integrate ultramafic lamprophyres into the IUGS classification system. This involves adding a new step in the classification process to distinguish ultramafic lamprophyres from other igneous rocks, such as kimberlites and olivine lamproites1.
  2. Mineralogical and Geochemical Definitions: New definitions have been proposed for lamprophyres, lamproites, and kimberlites based on their mineralogical and geochemical characteristics. This aims to provide a more precise and useful classification system2.
  3. Hierarchical System: The IUGS has suggested a hierarchical system that first deals with ‘exotic’ or ‘special’ rocks, such as lamprophyres, lamproites, and kimberlites, before moving on to more common igneous rocks2.
These proposals aim to create a more accurate and comprehensive classification system that can be widely adopted by geologists.
Is there a specific aspect of this classification that interests you the most?
1: Integrating Ultramafic Lamprophyres into the IUGS Classification of Igneous Rocks 2: Classification of Lamprophyres, Lamproites, Kimberlites
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Dear RG members, IUGS is planning a new edition of the classical "Le Maitre" book devoted to the classification and nomenclature of igneous rocks. A group of 17 igneous petrologists (hereafter TGIR - Task Group on Igneous Rocks) is working for three years to update specific definitions or proposing entirely new sections.
As the Chair of the TGIR, I would like to start a discussion with all the interested people that want to give help concerning this task. I and the other members of the TGIR will start posting a series of arguments that will greatly benefit from your comments, so I hope to receive stimulating feedback.
The IUGS book on the classification and nomenclature of igneous rocks (Le Bas) 2002 does not report any indication on two terms often reportd in igneous petrology studies, i.e., tholeiitic rock series and calc-alkaline (or calcalkaline) rock series.
Le Maitre (2002) only reports little comments on "tholeiitic basalt", simply defined as "A common variety of basalt composed of labradorite, augite, hypersthene (= enstatite) or pigeonite, with olivine (often showing a reaction relationship) or quartz, and often with interstitial glass. The Subcommission recommends that this term should be used instead of tholeiite.". IUGS distinguises various types of basalts (e.g., alkali basalt, high-alumina basalt, island arc basalt, mid-ocean ridge basalt, olivine basalt, olivine tholeiite, subalkali basalt, tholeiite, tholeiitic basalt, transitional basalt), but unfortunately without providing any key to distinguish among them.
In the definition of "Quartz dolerite", Le Maitre (2002) reports: "The rock has tholeiitic affinities and its pyroxenes are usually subcalcic augite accompanied by pigeonite or orthopyroxene.", but it is a pity that there is no definition for "tholeiitic affinity".
The new version of the IUGS book has to fill this gap. Several scientific articles have dealt with this topic, and two excellent reviews are written by Sheth et al. (2002) and Arculus (2003). Both the articles underline that the articles published in the last 40-50 years completely changed the original meaning of the term "calc-alkaline".
1. Peacock (1931) coined this term using a simple plot reporting both CaO vs SiO2 (usually with negative correlation) and (Na2O+K2O) vs SiO2 (usually with positive correlation). Depending on the SiO2 value where the two trends intersect, the rock series were defined as alkalic (<51 wt% SiO2), alkali-calcic (51-56 wt% SiO2), calc-alkalic (56-61 wt% SiO2) and calcic (>61 wt% SiO2). You understand that the term "calc-alkaline", when defined, had nothing to do with the actual meaning. As the term indicated, it was referring to lime ("Calc") and alkali.
2. Then Kennedy (1933) proposed the existence of a primary magma series evolving towards SiO2-saturated to SiO2-oversaturated compositions, defined it as "tholeiitic".
3. Only twenty years later, other authors started to connect "tholeiitic" and "calc-alkaline" terms referring respectively to series with and without iron enrichment with increasing SiO2 (Nockolds and Allen, 1953).
4. Thirteen years later, Kuno (1966) proposed for the term "calc-alkaline" a meaning of a magma that evolved under oxidized conditions, distinguishing two fields for "tholeiitic" and "calc-alkaline" series in his triangular plot AFM (A = alkali = Na2O+K2O; F = FeO*; M = MgO).
5. Eight years later (Miyashiro, 1974) used a simple equation to distinguish tholeiitic from calc-alkaline series: SiO2 (wt%) = 6.4 × FeO*/MgO + 42.8 (with tholeiitic rocks plotting above this straight line, and calc-alkaline rocks plotting below the line). Note that FeO* is total iron as FeO.
6. One year later, Middlemost (1975) proposed a simple diagram reporting A.I. (Alkali Index = (Na2O+K2O)/[(SiO2-43)*0.17] vs. Al2O3, to distinguish tholeiitic basalts (Note: only basalts) from calc-alkaline (or High-Al) basalts.
7. One year after, Peccerillo and Taylor (1976) published their famous article on Eocene Kastamonu igneous rocks (Pontites, NE Anatolia), proposing the K2O vs. SiO2 diagram, where they distinguished four series, with increasing K2O content and K2O/SiO2: 1) arc tholeiitic series, 2) calc-alkaline series, 3) high-K calc-alkaline series and 4) shoshonite series. These authors summarized a series of articles and inferences raised just after the birth of plate tectonics. Since then the term "calc-alkaline" started to be used as a sort of synonym of "subduction-related".
8. Nearly 10 years later, Middlemost (1985) noted that the typical andesitic rocks emplaced above subduction systems plot in the "calcic" field of Peacock (1931), and Icelandic tholeiites plot in the "calc-alkalic" field, to underline that the original meaning of "calc-alkalic" was completely distorted.
The Kuno (1966) and Miyashiro (1974) diagrams are useful discriminators for tholeiitic and calc-alkaline rock series but, as underlined by Sheth et al. (2002) they do not deal with CaO (Calc), so they refer to a concept that uses different criteria. Another problem of AFM is that evolved tholeiitic and calc-alkaline terms greatly overlap and the three components make up less than 50% of the oxides in the rocks.
This problem was particularly relevant, according to Arculus (2003), who proposed to use Kuno (1966) discrimination diagram [i.e., (FeO*/MgO) vs. SiO2] but instead of using "tholeiitic" and "calc-alkaline" terms, he suggested using High-Fe, Medium-Fe and Low-Fe. While reasonably solid, this proposal got little agreement by the scientific community, who demonstrated a great inertia in changing the two-term definition with a three-term definition.
What should IUGS do? We believe that it is unreasonable to propose to delete the "tholeiitic" and "calc-alkaline" terms, so we feel it is necessary to leave them, however, giving them the petrological significance proposed by Kuno (1966), Miyashiro (1974) and Arculus (2003), i.e., associated to differences in oxygen fugacity conditions and absolute FeO/MgO ratios.
We have to propose that the Peccerillo and Taylor (1976) diagram cannot be used as a reference to distinguish between tholeiitic and calc-alkaline rocks.
What is important, is that the idea of the IUGS TGIR the terms "tholeiitic" and "calc-alkaline" should not have any tectonic significance, i.e. tholeiitic compositions are not necessarily emplaced away from active subduction settings, an calc-alkaline does not mean emplacement above active subduction settings. We have to state that the term "tholeiitic" leaves the original significance of Kennedy (1933), but the term "calc-alkaline" has a completely different significance compared to the original statement of Peacock (1931).
Proposed items to be added in the Glossary of terms:
THOLEIITIC SERIES
Subalkaline rock series characterised by total iron enrichment with differentiation, leading to SiO2-saturated to SiO2-oversaturated compositions. The term should not be used to infer a specific tectonic setting. Tholeiitic series rocks have to plot in the tholeiitic series field of the AFM diagram of Kuno (1966; where A = alkali = Na2O+K2O; F = FeO*; M = MgO) or in the tholeiitic series field diagram of Miyashiro [1974; (FeO*/MgO) vs. SiO2]. In both cases FeO* is total iron expressed in the reduced form. If two iron oxidation states are available, FeO* = FeO + 0.8998*Fe2O3. In case only ferric iron is available, FeO* = 0.8998*Fe2O3. See calc-alkaline series.
CALC-ALKALINE (or CALCALKALINE) SERIES
Subalkaline rock series characterised by total iron depletion with differentiation, leading to SiO2-saturated to SiO2-oversaturated compositions. The term should not be used to infer a specific tectonic setting. Calc-alkaline series rocks have to plot in the calc-alkaline series field of the AFM diagram of Kuno (1966; where A = alkali = Na2O+K2O; F = FeO*; M = MgO) or in the calc-alkaline series field diagram of Miyashiro [1974; (FeO*/MgO) vs. SiO2]. In both cases FeO* is total iron expressed in the reduced form. If two iron oxidation states are available, FeO* = FeO + 0.8998*Fe2O3. In case only ferric iron is available, FeO* = 0.8998*Fe2O3. See tholeiitic series.
This is a first draft, and comments are very welcome. Considering it is a hotly debated topic, I invite all the RG members to be short and directly to the point.
Thanks,
michele
Middlemost, 1985: Magmas and magmatic rocks: An introduction to igneous petrology: London, UK, Longman, 266 pp.
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I agree with your new definitions. Fe-enrichment at the early stages of evolution is now the accepted criterion and in my opinion addresses important petrogenitic processes. Sheth is correct in pointing out that using intermediate Fe enrichment to distinguish "calc-alkaline" leaves out "calc" and barely addresses "alkaline." Middlemost is also correct in suggesting using names that reflect the criteria (e.g., "high-Fe"). But, as you say, "inertia" has entrenched the terms tholeiitic and calc-alkaline and attempts to revise at this late date, however appropriate, seem to gain little traction. I believe we get into problems, however, when we attempt to ascribe a tholeiitic or calc-alkaline parent. Fe-enrichment depends more on conditions (e.g., H2O and fO2) than on parent.
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Hi dear friends!
My question is short. Can basalts only be formed in a fore-arc environment without boninites in the association?
Thanks!
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Yes, Basaltic rocks can be formed in fore arc settings without boninite. Specifically in the embryonic stage of arc development. In this case Peperites ( an erupted basaltic lava in to wet sediments ) can be formed also. For further information I recommend you to read this paper.
Regards
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Hi dear geologist, I'm looking for a lab for geochemical, mineralogical and petrographical analysis of my rock samples. Which affordable lab would you recommend?
I would be glad if you could add addresses and even price information. Thanks in advance 🙏👌.
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Maybe you can visit https://cig.museo.unlp.edu.ar/
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I am planning to study a crop grown in lava rocks. What kind of lava rocks is this? I am planning to buy Lava Rocks in online shopping platform.
Do you have any idea about the geological features of this lava rock? Is this a basaltic lava rock?
Thank you for sharing your expertise, and I appreciate it.
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Dear Jayson
Hi I think they can be intermediate or acidic volcanic and volcanosedimentary rocks such as Rhyolite, Dacite , Andesite and related tuffs to these rocks.
With best wishes
Dr Gholamreza Fotoohi Rad
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Dear colleagues
Good day to you all. One of the most famous debates in Igneous Petrology is the relation between the diamondiferous rocks (i.e. lamprophyres, lamproites, orangeites and kimberlites). In 1991, the late geologist Nick Rock considered them to have similar petrological and geochemical signatures and were included in one group named the "Lamprophyre Clan". Recent publications have shown that relations do exist (e.g. see The "Lamprophyre Clan" Revisited 2022 paper in ResearchGate). The Version of Record is available online at: https://doi.org/10.1007/s12594-022-2153-4. One can also read the Version of Record through the Springer SharedIt link https://rdcu.be/cVljF (note that you need to use Wi-Fi in order to open the Springer SharedIt link).
On the other hand igneous petrologist Roger Mitchell, who disagreed with the idea, proposed the "Lamprophyre facies" concept which includes rocks that formed under volatile-rich conditions. Which one is correct? GPT-4 was also asked. The answer was that both terms can be correct, but they represent different perspectives in the study of these rocks. What is your opinion? Please comment.
Best regards
Ioannis Kamvisis
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Yes they are.
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Dear all,
I have been working on petrogenetic modeling of fractionation and partial melting processes for a while, but it appears that none of the current modeling program/software is able to successfully predict the hydrous phases behavior (e.g., amphibole and mica). There is no doubt that amphibole plays an important role at the late stage of magma evolution (e.g., on Si and Fe), and field evidence and thin section show that magma does fractionate amphibole, sometimes even to a large portion (e.g., hornblendite dike/vein). However, modeling programs (mostly MELTS, and some others such as Petrolog, etc.) I used predict nearly no amphibole (and/or mica) at the latest stage of magma fractionation even under water-saturated conditions. Also amphibole is generally absent during modeling of melting even an amphibolite. Many people have realized this problem, but I am wondering could any one provide a "better" modeling program or alternative methods to model these hydrous minerals, instead of empirically "assigning" a value to these minerals based on estimation of mineral modal proportions in cumulate assemblages (e.g., gabbro and hornblendite)? The purpose is to predict both major and trace element variations of magmas/melts evolving from intermediate (~56 wt.% SiO2) to highly felsic (>75 wt.% SiO2) composition.
Thank you.
Weiyao
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Thermocalc can be used to do amphiboles (see the work of Chris Yakymchuk)
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Dear colleagues
Good morning. I have found a rock speciment (first photo) within a crater in the Pindus mountains of Greece. Is it a volcanic carbonatite? A photomicrograph of a known carbonatite is also attached for comparison (second photo).
Best regards
Ioannis Kamvisis
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DEAR SEBASTIAN
GOOD MORNING. THANK YOU FOR GIVING ME THE CHANCE TO DISCUSS A MUCH DEBATED MATTER. THERE ARE AT LEAST 48 EXTRUSIVE (VOLCANIC) CARBONATITES APART FROM OLDONYO LENGAI (WOOLLEY & CHURCH 2005). EXAMPLES ARE THE GROSS BRUKKAROS VOLCANO (KURSZLAUKIS & LORENZ 1997) IN NAMIBIA AND THE CATANDA VOLCANO IN ANGOLA (CAMPENY ET AL . 2015). NO LAVA FLOW IS NEADED FOR A CARBONATITE VOLCANO TO OCCUR (E.G. DIATREME VOLCANOES). THE PIERIAN MOUNTAINS META-CARBONATITE DIKE DOESN'T LOOK LIKE AN OPHICALCITE (SEE ATTACHED GREEK OPHICALCITE PHOTO FROM LARISA) AND IT ISN'T ONE SINCE THESE ROCKS HAVE A MAGMATIC (MANTLE NOT CRUSTAL) SIGNATURE IN THEIR CARBONATE (SCHENKER ET AL. 2018). EXTRUSIVE CARBONATITES GENERALLY APPEAR IN CONTINENTAL RIFTS LIKE THE RIFTING OF THE PELAGONIAN ZONE ON THE PIERIAN MOUNTAINS. PLEASE COMMENT.
BEST REGARDS
IOANNIS
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Dear colleagues
Good morning. I recently visited a crater and collected a couple of samples from the ring. Could these be geyserites or something else?
Best regards
Ioannis
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Dear Michael
Good morning. Thank you for your detailed reply. Regarding carbonatites in Greece Schenker et al 2018 have found a meta-carbonatite dike on the Pierian mountains (see photo attached).
Best regards
Ioannis
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Baddeleyite is crucial to date mafic-ultramafic rocks. However, it is difficult to separate by physical processes. In a unique study, Guo et al. (2022) (https://pubs.acs.org/doi/10.1021/acsomega.1c06264) showed that baddeleyite can be very efficiently separated by digestion of relatively small amount of rock (19 gram) using acids (HF + HCl + HNO3) in which baddeleyite grains did not go into solution. SIMS dating (op. cit.) suggested that the U-Pb age of the separated baddeleyite grains were not affected by the acid based processes.
My question is that do you expect any disturbance of the U-Pb isotope systematics of baddeleyite by the acids in general? Should we use commercial grade acids (as done by the above authors) or purified acids? The aim is to date the baddeleyite grains by spot analysis (Ion probe or LA-ICPMS). Should't the relatively greater amount of acids used in the separation (120 mL 22 M HF and 60 mL 8 M HNO3) create some handling problem? If you have any experience with acid-based separation of baddeleyite, please share.
Thanks in advance.
Sukanta
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For geochronology, I agree with H.G. Dill to avoid solution processes whenever possible. You already have a fine to coarse powder that you can use with heavy liquid separation, clean up with acetone and hand pick the crystals after that. The main problem with acids is that you are dealing with undiuted version that have many drawbacks such as vapors, spill-over droplets, very strong reactions with powdered rocks and the non-least one, a higher health risk to the operator. These acids will eat through clothes and skin rapidly and one can end up in hospital for treatment if a pure HF droplet or vapor gets under the skin; it attacks the nerves and is extremely painful.
As for the effects of this rock powder dissolution method on the geochronology results, the problems can be many folds. Cracks in baddaleyite crystals can fill up with dirty acid filled with U and Pb from the dissolved minerals and a very thin (1-2 microns) layer of the surface can have partial leaching and/or contamination. This leaching can be offset by abrading the grains as with zircons in case of chemical geochronological analysis. The problem with using commercial grade is that you have no control on the amount of 204Pb you 'add' to the system through cracks and surface porosity. One mistake is to start with the assumption that baddeleyites are 'impermeable', which is not really the case. They have the same problems as zircons have.
The important thing is with which machine type you are measuring the iotopes, a 'classical' mass spectrometer from chemical dissolution and separation analysis or an ICPMS directly on polished grains?
Overall, the problem of baddaleyite separation and analysis are the same as with zircon, in both case the U and Pb are not that strongly attached to the crystal lattice, only the mineral lattice itself is strong enough to trap quite efficiently U and Pb. The best advice is to take the same precautions that one would use for zircon extraction and it should go well.
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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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Both alkali metasomatism (fenitization) and assimilation of silicate material may be present along the contacts zones between carbonatites and host rocks, but how to discriminate between these two processes
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This is an excellent question and I don't think that there's a good answer yet. In this paper:
We have a relatively simple (or simplistic) definition where fenites form outside the carbonatite, whereas assimilation reactions (which we term antiskarns) are inside the carbonatite. This has limitations in that it's not always easy to identify that a rock is actually a carbonatite, especially if carbonates are not the dominant minerals in it, and it appears as various veins or other challenging-to-interpret textures.
It also has limitations in that some carbonatites gradually grade to silicate rocks around them (particularly the ijolite family and related rocks) and there isn't a clear contact from which one can infer "inside" or "outside".
What about cases where there is a clear contact, but it seems as if small brittle cracks protrude from the carbonatite into its surrounding rocks, then filled with carbonatite melt, which then assimilates material from the country rock? Is it an antiskarn or a fenite?
I reckon that the mineral assemblages and elemental compositions will differ, but I am not sure how yet. We are still in the early days of understanding these systems so my recommendation to you would be that if you see something interesting, write something about it, and put it out into the community.
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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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Imagine you have some volcanic rock samples from a given area and about 30 km southwest there is an acidic pluton which is the same age as your rocks. Let's say that both your rocks and samples from the intrusion show perfect fractional crystallization trend on the La vs. La/Sm diagram with only several samples deviating from the trend line. Their common La/Sm ratio is constant, in this case, and let's say it is around 7, while La contents vary from 20 to over 60 ppm with one sample reaching up to 90 ppm. In this case, it seems reasonable to argue that they evolved together from the same source, I guess.
My question is, if we assume a hypotethical situation where the La/Sm ratio of the volcanics is, say, 25, whereas that of the samples from the acidic pluton is 7, would that imply that they evolved from different source regions?
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I am old-fashioned (geology-mineralogy-chemistry-advanced-level geosciences, .e.g., isotopes).. Therefore, in this case where only a chemical ratio forms centerpiece of a discussion of such a far-reaching issue, I can only respond in a way like that:
"One swallow does not make summer"
HGD
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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 am studying the thermal effect of the large Igneous Province recently. Is there any way to do it?
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Dear Xin Liu, China University of Petroleum - Beijing.
I recommend using the magnetic anomalies to estimate the Curie boundary, which indicates, direct or by analogy, the distribution of the thermal anomalies, present-day heat-flow, providing a clear marker for the thermodynamic effect in the crust and mantle. Therefore, I recommend first the use of magnetic anomalies, for example, from the EMAG2 datasets, it is free, and it has the wavelength (deep mantle large-scale structure) that you need in your research.
The knowledge of the magnetic anomalies in LIP (large igneous provinces) regions is a geophysical way, due that the mafic and ultramafic intrusions linked to those LIPs and their contrast in magnetic properties, magnetic susceptibility, using modeling and inversion.
Also, high densities contrast mafic/ultramafic rock compatible with serpentinized, also could show you in gravity anomaly inspection of a LIP, particularly regarding Bouguer complete anomaly map / Residual isostatic anomaly map.
I attached Jennifer Blanchard´s Marter of Science thesis, "Geophysical identification and characterization of mafic-ultramafic intrusions in plume centre regions", 2015, Carleton University, Ottawa, Ontario, Canada. I recommend reading in focus the Modeling methodology, it has wonderful examples.
Best regards, Mario E. Sigismondi
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Does the fact that these granitoids are deformed affect the choice of these diagrams?
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Hi Donald,
I recommend what Prof. Sebastián Grande suggested. To start with and understand from basics you may follow the book by Rollinson,
In addition, you may find many commonly used diagrams for the granite discrimination in numerous papers however below I mention several specific papers that can be useful too to look for granite discrimination if you have geochemical data e.g.,
1. Eby, G.N., 1990. The A-type granitoids: a review of their occurrence and chemical characteristics and speculations on their petrogenesis. Lithos 26, 115–134.
2, Eby, G.N., 1992. Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology 20, 641–644.
3. Pearce, J.A., Harris, N.B., Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J. Petrol. 25, 956–983.
4. Whalen, J.B., Curry, K.L., Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contrib. Miner. Petrol. 95, 407–419.
5. Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J., and Frost, C.D., 2001, A geochemical classification for granitic rocks. J. Petrol 42, pp. 2033–2048.
6. Frost, B.R., and Frost, C.D., 2008, A geochemical classification for feldspathic igneous rocks. Journal of Petrology, v. 49, pp. 1955–1969.
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Paleomagnetic studies show that the South China block was moving northward continuously from 300 to 260 Ma and has experienced an overall ∼27° clockwise rotation since then (Huang et al., 2018) ,and assuming a stationary Emeishan mantle plume, so if I want to do a numerical simulation of the geodynamics of the Emeishan mantle plume based on the above conditions. How can I do it?
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Hello dear;
I didn't research on Paleomagnetic studies, but i know 2 methods in order to behavioral study between two things. K-means clustering and Artificial Neural Network (ANN). you can read this combination method in this paper :
good luck
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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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Microscopic examination of a sample of low cretaceous igneous rock (alkaline bazaltoid or monchiquite?) revealed this foaming in the older generation of apatite (see photo). The central parts of apatite crystals are highly crowded with gas-liquid inclusions, the surfaces of crystals, just as younger generations are without them. Do you happen to know what that indicates? My timid guess is that it could be the release and decay of a supercritical fluid during crystallization, perhaps. I can't find anything like that in the literature.
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I have not seen yet it but it is too interesting case
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Is it recommended for granitoids?
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Biotite as a petrogenetic discriminator: Chemical insights from igneous, meta-igneous and meta-sedimentary rocks in Iran
DOI: 10.1016/j.lithos.2021.106016
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Any discrimination diagram or calculations would be helpful.
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Monazite and zircon are often closely associated with each others in the source rock and in placer deposits, alike. In the study which is available on request for download from the RG server you will find typical X morphological habits and x-y plot for discrimination of their origin and their behaviour during transport:
DILL, H.G., WEBER, B. and  KLOSA, D.  (2012) Crystal morphology  and mineral chemistry  of  monazite–zircon mineral assemblages in continental placer deposits (SE Germany): Ore guide and provenance marker.- Journal of Geochemical Exploration, 112: 322-346.
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My mafic meta-volcanic rocks can be devided into two groups. Group 1 rocks are distinct from Group 2 as displayed by their markedly higher concentrations of Fe2O3T (18.5-18.6 wt.%), TiO2 (3.5 wt.%) and P2O5 (1-1.1 wt.%), lower MgO (5.1-5.2 wt.%) and lower silica contents (SiO2 = 43.6%-44.3 wt.%). And the higher concentrations of the incompatible elements (i.e., Zr, Y, Nd, Sm, Nb and P) and lower concentrations of compatible elements (i.e., Cr and Ni) in Group1 are also distinct from Group 2. These features are similar to the Fe-Ti basalts which are characterized by iron- and titanium enrichment (FeOT>12 wt.%, TiO2>2 wt.% and FeOT/MgO>1.75) but silica depletion (Sinton et al., 1983; Hunter and Sparks, 1987; Furnes et al., 1998; Jang et al., 2001; Harper, 2003; Qian et al., 2006). Because of the absence of Fe-Ti oxides phenocrysts, most researchers consider that the high concentrations of iron and titanium were not caused by the cumulus Fe-Ti oxides, and the Fe-Ti basalts are interpreted to be products of moderate to high degree of Fenner trend differentiation of basaltic magma at low oxygen fugacity (Jang et al., 2001; Xu et al., 2001; Qian et al., 2006). However, there are many Fe-Ti oxide phenocrysts in my samples, and no cumulate structures were observed in my samples. So it is hard to get the conclusion that they were formed from the cumulation process, I  want to konw which process can cause this geochemical features. 
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I recently published on high Fe-Ti amphibolites at Broken Hill, Australia.
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Two andesitic samples have significant Tb negative anomaly. The same ones also have Pr negative anomaly which I can explain by a late apatite crystallisation and many apatite inclusions in phenocrysts. I cannot find any information on Tb.
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Hi Aleksandra, there is an interesting paper by Raimbault et al. (1993) on REE contents of apatites and scheelite and they are also discussing low Tb concentrations. The details are: Raimbault et al. (1993) in American Mineralogist 78: 1275-1285. Cheers Daniel
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Does negative Nb-Ta and Ti anomaly with No Zr- Hf anomaly suggest subduction setting? For the mafic dyke samples
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The answer to your question is: not always. Post-collisional or intraplate magmatism sourced from a hybrid mantle (crust+DM) presents geochemical (incompatible elements) and isotopic characteristics of the crustal component. Couzinié et al. (2016) (Earth and Planet. Sci. Lett.; Vol. 546) have demonstrated that a small (~10-25%) crustal component, transported to great depths in subduction zones as sediment or mechanically eroded sialic crust, is able to metasomatize/hybridize depleted mantle so that a rock sourced (e.g. high-K basalts) from this hybrid mantellic domain could provide incompatible element signatures (including Nb-Ta troughs), as well as radiogenic isotopic values (i.e. Hf, Nd), that dominantly reflect the crustal component. Therefore, let's picture a hypothetical scenario. Subduction during the Paleoproterozoic would generate arc-related magmatism and metasomatize/hybridize large swaths of the suprasubduction mantle. Right after continental collision, orogenic extensional collapse would partially melt this hybrid mantle and generate basalts (and fractionates) with a crustal-like geochemical signature, and therefore Nb-Ta anomaly. Extensional processes could (and probably would) continue during much longer periods due to periodic extensional/rifting. Therefore, basalts with Nb-Ta anomalies and other geochemical fingerprints of subduction zones could be generate in post-collisional or intracontinental settings. Nevertheless, they need to be sourced from mantle that was previously enriched and metasomatized by a (minor) crustal component delivered by an active subduction zone. Hope this helps. Cheers.
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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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I am beginning my undergraduate research in a granite quarry and am attempting petrogenetic modeling. However I can't seem to find good sources with all of the partition coefficients I need for trace elements. I am using Nash, 1983, and Henderson, 1984, currently. Thank you in advance!
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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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Can you recommend some software or articles to study?
The rock is pantellerite with main phenocrysts as amphiboles (Na and Na-Ca subroup) and intergrowth albite and sanidine.
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You can use the Al content and Fe/(Fe+Mg) ratios of the recalculated amphibole analyses to estimate the P, T and fO2 conditions. The relevant literature you should consult is as follows:
Anderson J.L. and Smith D.R. (1995). The effects of temperature and O2 on the Al-in-hornblende barometer. American Mineralogist, 80, 549-559.
Hammarstrom J.M and Zen E. (1986). Aluminum in hornblende: An empirical igneous geobarometer. American Mineralogy, 71: 1297-1313.
Hollister L.S., Grissom G.C., Peters E.K., Stowell H.H. and Sisson V.B. (1987). Confirmation of the empirical correlation of Al in hornblende with pressure of solidification of calc-alkaline plutons. American Mineralogy, 72: 231-239.
Johnson M.C. and Rutherford M.J. (1988). Experimental calibration of an Aluminium-in-hornblende geobarometer applicable to calc-alkaline rocks. EOS, 69, 1511.
Schmidt M.W. (1992). Amphibole composition in tonalite as a function of pressure: An experimental calibration of the Al-in-hornblende barometer". Contrib Mineral Petrol, 110: 304-310.
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The study area, located in the circum-Pacific accretionary complex, mainly consists of intra-oceanic surface rocks including chert, shale, pyroclastic rocks and basaltic lava. The basaltic rocks are mostly OIB-type (Jurassic Paleo-Pacific seamount) according to previous research.
Photo 3 shows two basaltic pillows within a matrix of basaltic tuff. The handspeciman of the pillow is black in color and heavy in weight. It also has scattered vesicles, and looks much like typical fine-grained basalt. However, its thin section looks not...
I need help to identify the rock type. It will be perfect if you also have such kind of rock.
Thank you.
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In this tissue other than olivine and pyroxene we see a kind of fossil structure with high cooling rate
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What is the conceptual difference between Geological Map and Stratigraphic Map?
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The geological map shows the distribution of the formations and their contact ( different kinds of rocks and faults).
There are three major types of maps they use: topographic, cross-sectional, and structural.
A structural map shows the geologic features of an area. Its appearance is similar to that of a topographic map, but a topographic map displays elevations of the Earth's surface and a structure map displays the elevation of a particular rock layer, generally beneath the surface. a geologic map shows the distribution of geologic features, including different kinds of rocks and faults.Rock units or geologic strata are shown by color or symbols to indicate where they are exposed at the surface. Isopach maps detail the variations in thickness of stratigraphic units.
A cross-sectional map shows the cross-section from the side.
So you can't talk about stratigraphic maps, but rather structural maps at different stratigraphic levels,
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Uncertainty in the values of eNd(t) or eHf(t) (epsilon Nd or Hf) of a particular sample (rock or mineral) depends on several things including uncertainties in the present day isotopic ratios and uncertainty of the instrument. If I have only the error values (say 2s) of present day isotopic ratios of a sample (say Sm/Nd and Nd/Nd), is it possible to propagate the error from these uncertainties alone and calculate the uncertainty in eNd(t) or epsilon Nd (initial)? If yes, can someone kindly share the any worked out calculation for it?
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Ickert, 2013 would be good start.
"Algorithms for estimating uncertainties in initial radiogenic isotope ratios and
model ages" Chemical Geology, v340.
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Is there some difference in major elements or trace elements content?
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Mineral chemistry alone is not going to be able to tell you whether your amphibole is of primary magmatic or metamorphic in origin. Many amphiboles are stable over a wide range of temperature and pressure conditions, and a single species may have either a magmatic or metamorphic origin. You need to make some thin sections and examine your samples under a microscope. Examine the textures and relationships between the amphiboles and the other minerals in the sample. Look at the regional structural information from where your specimens came from. All this ground work needs to be done before you dive into putting your amphiboles under an electron beam!
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Clay samples are heated at 950 degree centigrade (LOI method) before XRF analysis. Due to which Fe percentage increases in the XRF results. It is due to the oxidation of samples during fusion. Is there any procedure to correct the Fe value within the results?
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Hi Jorge
I agree it's certainly possible. However, since XRF only detects the Fe content not the O content, the meaured Fe content will not change as a result of its oxidation state: this was the point I was aiming to make.
Kindest Regards
Paul.
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The rhyolite is a mixture of a less evolved rhyolite (or dacite) and a more evolved rhyolite. It has two kinds of Opx phenocrysts: none zoning Opx with a little bit higher Mg# and reverse zoning Opx. There are also some Ca-clinopyroxene phenocrysts. Both the Opx phenocrysts have low CaO contents (< 2 wt.%). However, the Px microlites in the rhyolites have much higher CaO (3 - 8 wt.%), which belong to pigeonite. Please see the attached picture. How are these Low Ca Cpx (Pigeonite) microlites formed? Ps: There is positive correlation between CaO and Al2O3 for those Px microlites but not for phenocrysts.
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Seeing you classify the pigeontie as ‘microlites’, I assume the rhyolite groundmass crystallized relatively rapidly? If you think this is the case, I would investigate the possibility that the pigeoite crystallized under metastable conditions. A search for ‘pyroxene composiions under rapid cooling conditions’ should pull up some relevant papers.
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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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Based on earthquake data, how we can define the type of rocks and minerals within the earth?
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Lots of earthquake stations today, therefore, lots of data to study using the velocity of the waves. Scientists know a lot more information than previously and there is more to study. The data displayed in the lecture suggested by Dr. @ Borko Bulajic are amazing!
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I found a (meta-) gabbroic sample contains some garnets, next, I want to know the genesis of these garnets (igneous or metamorphic origin). What should I do? Could I distinguish them just by their major composition? If you know that how to solve this problem, please recommend some references to me. Thank you very much.
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Dear Chutian Shy,
Have you seen any oriented fabric in meta-gabbro. I want to know. If it is containing an oriented fabric where garnets are seen. Further, what is seen within the garner, is there any planar fabric inside the garner?
Sincerely ,
T K Goswami
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Please upload information related to any upcoming seminar or conferences in India related to Igneous Petrology.....
Thank You
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There have been many researches and papers on the Degan Igneous Province in India, but the latest international conference does not currently exist. Only last year, an international academic conference was held in Chengdu, China, about the Emeishan igneous province. I have published the latest articles on the causes of the Degen Igneous Province, welcome to read and communicate.
Best wishes,
Liu Chenming
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I'm looking for outcrops of andesites in the Carpathian Mts. Especially, like in Pieniny Mts. in Poland, where andesites are near an outcrops of radiolarites.
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The newest paper:
Anczkiewicz, A.A., Anczkiewicz, A. 2016. U–Pb zircon geochronology and anomalous Sr–Nd–Hf isotope systematics of late orogenic andesites: Pieniny Klippen Belt,Western Carpathians, South Poland. Chemical Geology, 427, 1–16.
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Is it possible to clearly differentiate igneous to metamorphic titanite/monazite based on their REE?
e.g. Eu, CE anomaly or enrichment of HREE
can anyone suggest references?
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Dear all,
I forgot to mention that I'm dealing with detritus, unfortunately it is not always easy to get nice well shaped crystals as the 50-200 µm fraction is mostly broken after the jaw crusher and the mill (especially titanite and monazite). However thanks D Raju for the suggestion!
Dear Mastoi, I'm still separating the samples and I'll process them at the LAICPMS for REE once ready, for the time being Dr Henrichs suggested me to follow the review from Engi (2017) "Petrochronology Based on REE-Minerals: Monazite, Allanite, Xenotime, Apatite"(doi.org/10.2138/rmg.2017.83.12) which seems to be extremely useful for this topic.
regards
Cesco
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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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I want to conduct chemistry analysis on an anonymous ultrabasic bodies. I want to adapt Mullen(1982)'s MnOX10-TiO2-P2O5X10 tertiary discrimination diagram to find its geotectonic condition. The SiO2 w.% of this ultrabasic bodies are plotted between 42%~46%. Can I use this method for my analysis?
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The best is to see initial details of the construction of any discrimination diagram. Application of the diagram for drawing meaningful conclusions requires that you plot data of rocks of similar composition. I mean, if a discriminant diagram is designed through use of basaltic rocks, it should be used for rocks of basaltic composition. It may not be appropriate to draw conclusions by plotting rhyolite or peridotite analyses on it. I think that Mullen was dealing with basaltic rocks and applying the diagram to ultrabasic rocks is a choice you can decide yourself.
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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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For example is there any way to recognize minerals (augite, plagioclase) as more sodic or calcic?
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For plagioclase there are a few determination charts, based on the extinction angle in the zone normal to (010) - the albite twin plane, as well as the cleavage plane= which function pretty well. Try fpr example this address: eps.mcgill.ca/~courses/c312/Labs/Optlab9-13.doc @ the McGill University
For clinopyroxene it's a bit more complicated because the optical properties depend on several compositional changes, the general idea is that the optical properties and the mineral assemblage offer some clues for the composition of certain phases. Sorry for the quality of typing in this box, I notice it has become very difficult to get what you type..
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I need some references related to Pegmatite occurrences of Nuristan Province of Afghanistan. 
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You may find some  information of use in my recent article for The Mineralogical Record published very recently.
Lyckberg Peter, 2017 The Mineralogical Record, Vol. 48, No. 5
September - October 2017 Gem pegmatites of northeastern Afghanistan
pg 610-675.  This special Issue is named "Afghan Pegmatites" and can be ordered for 25 USD plus shipping from http://www.minrec.org/detail.asp
You are also welcome to keep in touch. Tashakor.
Warm regards Peter Lyckberg
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Granite powder is an Aluino-silicate material claimed by some researchers to work as geopolymer raw material.  The Al:Si ratio is in the vicinity of 1:4 and not the magic ratio of 1:2.  The alkaline liquid activator and the soluble sodium silicate required does not work for GP as used to work for Flay Ash.
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Good discussion. Thanks all. Probably, we can not use granite powder as a geopolymer source material since it is mostly crystalline. However, it can  be a filler or partially reactive material in geopolymer mixes if there are geopolymer source materials such as fly ash, etc
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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 want to do some modelling in order to see if different degrees of partial melting had (or not) some influence on the chemical variability of granite samples (in this case I-type granites, therefore, derived from partial melting of the lower crust). For this, I'm considering a batch melting process. However, I'm not sure which modal composition of the residual solid should be assumed in the calculation of bulk distribuition coefficients. 
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For partial melting, it depends on the source. An amphibolite source in the deep crust would have a garnet-bearing residuum that would be depleted in plagioclase feldspar, so you might expect, for example high La/Yb and Sr/Y in the melt (the so-called adakite signature). At lowqwer pressure (less than 8 kb or so) garnet won't be stable and you will lose the garnet signature. If you have a biotite gneiss for a source, garnet will also be stable (even mid-crustal pressure) and the melt will be strongly enriched in LILE elements. I would look for these types of signatures before you start any kind of melting model. I would also point out that most granitoids, even S-types,  are not going to be simple partial melts, but complex mixtures of material derived from both crust and mantle.
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We want to compare the forming pressures of two types of rhyolites but we only have whole-rock compositions of the rhyolites. Are their any chemical index (Major elements? Trace elements? element ratios?) that could qualitatively indicate forming pressures of rhyolites?
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Dear Roman,
Thanks for your answer!
Yuxiang
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I follow the Niggli's diagrams for the amphibloite rocks which I am working on.
Could you help me how the Niggli ratio should be calculated?
Please let me know in details as well as an example.
Thanks.
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     Not today,but the petrological literature (mostly from Europe) till the mid to late seventies have used Niggli values for both igneous and metamorphic rocks. It would not be surprising if they are still used today. Niggli primarily used the values to describe magmas and not rocks. The Niggli norm/Barth Niggli norm is better than the CIPW norm, as it applicable to both metamorphic and igneous rocks. Certain parameters, for example, 'mg' approximates the Mg#, 'k' - alkalinity ratio, and 'w' - to calculate the oxidation of iron, are still useful.
     Are they still good parameters of geochemical association of rocks? Yes, if you construct a Niggli variation diagram and apply the interpretation indices devised by Niggli (as detailed in Petrochemical Calculations by Conrad Burri). The Niggli variation plot has the same limits as a Harker variation diagram - mainly applicable to co-magmatic rocks and set of lavas from a single volcano.   
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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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Dear Ebrahim: your questions has been already answered by several colleagues, however I must point out two things. First, fossils can only give relative ages, I usually tell my students this funny analogy: Dinosaur bones don't have a tag attached saying "I was born 75 Ma ago!"... So to calibrate relative paleonthologigal ages, and also paleomagnetic time scales, one should have in the first case, a basin which, at the same time, is fossil-rich and has interestratified volcanic tuffs, lava flows or sills, and in the second case, a complete sequence of lavas showing several paleomagnetic inversions, such as MORB lavas or plateau basalts. These fossil+igneous basins could be rift basins, fore-arc or back-arc basins. The igneous tabular bodies present in them can be dated (usually in bentonites from weathered rhyolite tuffs, basalt flows, or diabase sills), and help to give upper and lower age limits to the fossil bearing strata linked to them. And second, that the so called absolute age of a rock has been substituted by a quite more realistic term as apparent age. This is because of what Asoori stated: rocks can be affected by many alteration processes, from metamorphism to hydrothermal alteration to weathering, that isotopic systems can be severely altered and give apparent ages which are not the real crystallisation or metamorphism ages. Systems with soluble cations, such Rb-Sr, and K, or with radiogenic gases, such as Ar, are easily modified by these secondary processes. Therefore the best methods used nowadays for primary crystallisation ages of igneous and metaigneous rocks are those effected in zircon crystals. Zircon, being a mineral resistant to secondary alterations, usually holds the true isotopic content reflecting the radioactive decay of U isotopes to Pb isotopes. It is a sort of miniature "time capsule", whose zoning can even record several successive orogenic or thermal events. Other methods of dating involving inmobile trace elements are: Sm-Nd, Lu-Hf, and Re-Os, applicable to specific rock types, and even to some Cu or Pt ores.
In Paleozoic granites of the Coastal Cordillera of Venezuela K-Ar method in biotite calculated 30 years ago gave quite "young" ages of 33 Ma; 20 years ago Rb-Sr isochrones gave quite "old" ages of about 404 Ma; but more recent U-Pb ages in zircon (LA-ICP-MS) gave even older ages, reaching to almost 500 Ma. It's a difference of almost 100 Ma, quite significant, indeed. The young Tertiary age has been interpreted as the orogenic uplift age, the oldest age, 495 Ma as the crystallisatin age of the plutons, so the 404 Ma Rb-Sr age was an apparent age, which really doesn't relate to either event! Therefore, hydrothermal and/or low metamorphic grade alterations have happened in these rocks disrupting somehow the Rb-Sr isotopic system. That's why absolute ages are no longer called such, they are apparent ages. With regards. Sebastian.
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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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The spider diagrams of REE in plagiogranites does not have any Eu anomaly. How can I remove the effect of plagioclase to get the Eu anamoly in plagiogranite? Can anyone help me?
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I suggest to do analysis of individual minerals that may host REE in rocks.
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Hi everyone,
Does anyone have an idea about how do we know the partitioning coeffecient of Ti in rutile equilibrated with felsic melts? This is important for trace element modeling of felsic magma if rutile is stable in the magma source. I saw that Bedard (2006GCA) used a value of 45, but I am not sure if this value is appropriate. How was this determined? Is it too low? Because Ti is the constituent of rutile, obviously we cannot simply use the ratio of Ti in melts and Ti in rutile (0.6) if I understand correctly.
Thanks for your help!
Rongfeng Ge 
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Perhaps that makes sense. If rutile is present, then the magma is saturated with TiO2 and the concentration of Ti in the magma is fixed (the excess gets precipitated as rutile and other phases such as ilmenite). If this fixed concentration is 45 times less than the Ti content in rutile (in terms of weight percent, approximately 60%, assuming 100% TiO2 and no other components such as iron or Nb/Ta oxides), then there must be 1.33% Ti (or 2.2% TiO2) in the melt.
Iskandar
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I want to determination pressure of gabbro formation by Nimis and Taylor (2000) method, who can help me for doing the calculations?
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Hi Majid. You can also check the work of Dr. K. Putirka. His spreadsheet for P-T calculations using Cpx composition considers the Nimis' geobarometer.
You can find interesting info on his website:
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Whether  the partial melting of mantle lithosphere can directly produce andesitic melts? Who can provide me available references with repect to this process? Thanks.
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Partial melting of mantle lithosphere can directly produce andesitic melts, which has been documented by geochemical studies of Mesozoic andesitic rocks in eastern China (Chen et al., 2014, 2016). In this case, peridotite cannot serve as the lithology of mantle sources for andesitic magmatism. Instead, the partially melted are mafic lithologies such as garnet pyroxenite and hornblendite rather than ultramafic ones such as pyroxenite and hornblendite.
Chen, L., Zhao, Z.-F. & Zheng, Y.-F. (2014). Origin of andesitic rocks: geochemical constraints from Mesozoic volcanics in the Luzong basin, South China. Lithos 190, 220–239.
Chen, L., Zhao, Z.-F. & Zheng, Y.-F. (2016). Geochemical constraints on the origin of Late Mesozoic andesitic volcanics from the Ningwu basin in the Middle-Lower Yangtze Valley, South China. Lithos 254–255, 94–117.
Because of the incongruent melting of source rocks, the majority of felsic to mafic melts produced by partial melting of crustal or mantle lithologies are generally not in equilibrium with their residues. Although the melts of andesitic composition can be produced by partial melting of subducting mafic oceanic crust (eclogite), the oceanic-type eclogite is generally characterized by depletion in both melt-mobile incompartible trace elements such as LILE and LREE and their pertinent radiogenic isotopes. In comparison, the adakites of andesitic composition commonly show arc-style trace element signatures, precluding their derivation from partial melting of the subducting oceanic slab itself.
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  I have some diabase samples (SiO2=47-53 wt. %, MgO=6-10 wt. % and TiO2=0.7-1.2 wt. %), which consist of mainly clinopyroxene and plagioclase. There is no olivine and orthopyroxene appeared in the thin section. How could I calculate the melting temperature and pressure of the diabase samples?
  Thanks for your help! 
  With best regards
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Dear feng
to have a temperature estimation (but always make attention to the results that you get) you can use these two geothermometers:
- Putirka, K., 2008. Thermometers and Barometers for Volcanic Systems. In: Putirka, K., Tepley, F. (eds.). Minerals, Inclusions and Volcanic Processes: Reviews in Mineralogy and Geochemistry. Mineralogical Society of America, 69, 61-120.
- Thy, P., Lesher, C.E., Tegner, C., 2013. Further work on experimental plagioclase equilibria and the Skaergaard liquidus temperature. American Mineralogist, 98, 1360-1367.
The first one is a book where you can find,  among the other, a geothermometer based on the cpx-liquid equilibrium. Prof. Putirka in his personal website provides the excel file with the algorithms (http://www.fresnostate.edu/csm/ees/faculty-staff/putirka.html).
The second geothermometer works using the equilibrium plagioclase-liquid 
as you can imagine from the title of the paper. 
Cheers, Fabio
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As we know niobium and tantalum considered as incompatible, high field strength elements and the overall abundances of them in the continental crust are relatively low ..
Is that related to their mobility and their geochemical behaviour into the aqueous fluids which generated by dehydration of the subducting oceanic crust ? and how does their high ionic potential value made them immobile or insoluble into magmatic fluids ?
Unfortunately, I can't understand their geochemical behavior into late stage magmatic melts .. so please, I need any researches or references about them ...
Best regards ...
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Hi Ahmed,
in addition to the very informatif comments above, I'd like to share with you some more informations. As HFSE Nb, Ta, Zr and Hf are very resistant to alteration and therofore they likely used to truck and understand to evolution of magmas as well as they are useful in tectonic discrimination diagrams. Nb-Ta and Zr-Hf are chemicaly very similar twins and hence, they are expected to not fractionate from each other during diffrentiation, however such fractionation is often observed in magmatic rocks leading for example to positive or negative correlations between Nb/Ta and Zr/Hf ratios with increasing differentiation. As mentioned by Prof. W.L. Pohl one of the reasons could be a result of the fractional crystallization of Ti bearing phases like rutile, titanite and ilmenite (John et al. 2011; Mallmann et al. 2014). Some authors (Hui et al., 2011; Niu, 2012) propose the process of “mass-dependent fractionation during magmatism” to explain Nb-Ta and Zr-Hf fractionation in magmatic systems. They suggest that the lighter elements 90-96Zr and 93Nb would behave more incompatible than the heavier elements 174-180Hf and 181Ta in magmatic processes. The presence of halogens like F and Cl could play an important role  to facilitate the transport of the HFSE in the magma and the hydrothermal fluids, forming e.g. HFSE-F complexes which could lead to high enrichment of some HFSE (Agangi et al., 2010; Demartis et al., 2014; Sheard et al., 2012; Timofeev et al., 2015). High concentration of complexing ligands allowed HFSE to be transported in solution and to behave more incompatible as expected.
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1.How feldspar deformation occurs?
2.What  chemistry is involved in the deformation process of feldspar?
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As concerns plagioclase, you may interpret the metamorphic reactions as the inverse of the crystallization from a liquid.
A plagioclase crystallizing from a melt has higher Ca/Na ratio than the melt (and this is known for about one century). With decreasing temperature plagioclase tends to become more sodic and with a Ca/Na in equilibrium with that of the host magma.
The metamorphic grade is usually related to changing temperature, because many (not all) the metamorphic reactions are rather good geothermometers and relatively poor geobarometers (of course there are many exceptions of this simple definition).
Assuming a basaltic protholith (e.g., with a labradoritic to bytownitic plagioclase) the first step of metamorphism requires the loss of Ca from the plagioclase structure. E.g., at relatively low T conditions (zeolite to prehnite-pumpellyite facies) and variable but generally low P, the anorthite component of the plagioclase goes to form new metamorphic minerals such as lawsonite, prehnite, laumontite, heulandite, all Ca-Al-Si hydrous minerals). If plagioclase remains in the low-grade metamorphic rock, it is rich to very rich in the albite component, with a nearly pure NaAlSi3O8 composition.
Increase of the metamorphic grade (read increase of temperature) plagioclase accepts more and more Ca in its structure. Ca may derive from other minerals not stable at higher grade conditions (e.g., epidotes or amphiboles). Under these circumstances, when the plagioclase reaches an oligoclase composition, low-medium grade conditions are reached (oligoclase amphibolite facies).
With further increase of temperature, the composition of the plagioclase reaches andesine (medium grade) to arrive to labradorite in the high grade metamorphic rocks (e.g., granulite facies).
In conclusion, the amount of Ca (or, better, the Ca/(Ca+Na) ratio) can be considered a rough estimate of the maximum temperature reached by a basaltic system that experienced the full metamorphic cycle (from Ca-rich basalt to Ca-poor low-grade metamorphic rocks, eventually again to Ca-rich granulite).
Cheers,
michele
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Hello,
I measured the nickel content in pentlandite in two rocks which are genetically linked (a sheared chromitite and a talc-carbonate-schist). There is a depletion of nickel in the pentlandites of the talc-carbonate-schist relative to the sheared chromitite. Is this a common phenomenon and is there literature about this topic and its p-T-conditions (alteration of pentlandite in ultramafic rocks)?
Thanks
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Christian,
Start with the basics. First of all, verify that the pentlandite analyses are good quality, and that apparent Ni-depletion is not due to electron beam overlap on a nearby or underlying pyrrhotite or similar grain (apologies if you already checked this).
Secondly, determine the high-temp mineral paragenesis that the pentlandite is/was in equilibrium with. The Ni and Fe content will vary systematically depending on whether it is in contact or in equilibrium with troilite, hexagonal pyrrhotite or monoclinic pyrrhotite, or pyrite as the main Fe-sulphide mineral (see ref. Harris and Nickel in previous answer). These are the main high-temperature minerals that pentlandite would be in equilibrium with as it cools and exsolves from the monosulphide solid solution. These equilibria are controlled rather by fO2 and FS2 variations than P and T.
Thirdly, look to see whether this high-temperature assemblage has been modified or obliterated by low-temperature alteration (as seems likely in your case) - evidence of alteration of pyrrhotite to pyrite or Fe-oxides, presence of millerite or heazlewoodite, bravoite, awaruite etc. If the Ni depletion of pentlandite relates to particular assemblages, then you can start to develop a hypothesis of your own.
Another reference dealing with progressive serpentinization and talc-carbonate alteration and its effect on sulfides is that by Donaldson (1981) Economic Geology Vol. 76, p 1698. Redistribution of ore elements during serpentinization and talc-carbonate alteration of some Archean dunites, Western Australia.
Good luck.
Dave
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I am looking to expand from petrological perspective and learn a bit about the chemistry and physics with possible links and applications to geology/geoscience.
Advanced undergrad/postgrad level would be best.
So far I am familiar with the works of Nesse and Deer, Howie & Zussmann that I used for mineral identification in igneous petrology.
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 I suggest the textbook "Manual of Mineralogy by Klein and Hurlbut, 21/22 edition" this is the best introductory book for undergraduate of Mineralogy/Geology 
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I'm doing a petrography study of granitoids and I suspect, based on optical properties, the presence of these two minerals in my thin sections. However, I don't have any certainty and I don't know how to distinguish between them since they have very similar optical properties. I would appreciate any tips.
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Dear Mr. Quelhas,
The following optical data are very diagnostic:
Xenotime (one crystallographic axis/ straight extinction) vs. monazite (two crystallographic axis/ oblique extinction)
birefringence (X : 0.095-0.100) vs. (Mo: 0.049-0.050)
In a heavy mineral mount, X often looks like a carbonate mineral displaying some kind of a "pseudo-pleochroism".
X often morphologically shows up as "squares", whereas Mo is "rhomb-shaped".
Best regards
H.G.Dill
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In a geochemical book that mentions that sodic alkali basalts are relatively high TiO2 and in contrast potassic alkali basalts are characterized by low TiO2 content. I wonder which factors govern the content of TiO2 in basalts?
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I think that one of the factors is restite association in the mantle source at its melting.
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I found this texture, I have the impression that this ignimbrite was in contact with water. Is there any publication on vitreous ignimbrites ?.
thanks
picture description
the outcrop appears as a continuous mantle.
black is obsidian, and appears in spherical forms.
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Hi Juan--
If you observed this outcrop at the base of your ignimbrite, this is the basal vitrophyre of the ignimbrite deposit. A vitrophyre forms when a hot volcanic deposit (e.g. ash-flow tuff, rhyolite flow) comes into contact with the relatively cold surface of Earth. This sharp temperature gradient results in rapid cooling or quenching of the lowest part of the volcanic deposit, forming a glassy basal vitrophyre. I have observed vitrophyres up to 1-2 m-thick for ash-flow tuffs that were 100's of m thick. I have observed more chaotic and thicker vitrophyres (5-10 m-thick) in rhyolite flows, which can sometime cannibalize their own basal material during viscous flow.
The spherical feature you show in your photograph is called 'spherulitic texture'. This is common to the lower portions of ash-flow tuffs (ignimbrites). I have observed spherulitic texture in the black basal vitrophyre, but have also observed it higher up in an ignimbrite deposit, above the basal vitrophyre.
I suggest looking at this book for detailed discussion of both 'vitrophyres' and 'spherulitic texture':
Cas, R. A. F. and J. V. Wright (1987). Volcanic successions, modern and ancient.
Here are 2 papers I have authored about an extensive Miocene ignimbrite in the Gulf of California, which commonly displays a beautiful vitrophyre:
Bennett, S. E. K., et al. (2013). "Transtensional rifting in the proto-Gulf of California, near Bahía Kino, Sonora, México." Geological Society of America Bulletin 125(11/12): 1752-1782.
Bennett, S. E. K. and M. E. Oskin (2014). "Oblique rifting ruptures continents: Example from the Gulf of California shear zone." Geology 42(3): 215-218.
I also attach 2 photographs. The first photo shows a typical vitrophyre as the base of the Tuff of San Felipe. The second photo shows a close up of small spherulites in the vitrophyre of this tuff. Other locations of this tuff displayed spherulites up to ~5 cm in diameter.
I hope this information is useful for your interpretation of your ignimbrite!
Cheers,
Scott Bennett
U.S. Geological Survey
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Hello,
The Zr melt concentrations in the Laacher See Magma Reservoir have been estimated by Hans Schmincke and coworkers to be in the range of hundreds of ppm (ULST), O(1000ppm) (MLST) and around 3000 ppm (LST) for the lower H20-undersaturated, middle, and upper H20-saturated compositionally zoned magma chamber respectively.
I wonder how this may relate to Zircon saturation curves. Such curves have occasionnally been constrained experimentally for certain magma compositions (work by Mark Harrison, Bruce Watson and coworkers) but I am finding it difficult to translate how this may relate to the case of the Laacher See magmas.
Zircon solubility appears to be related to Zr concentration, Temperature and magma composition including SiO2 and TiO2 concentrations and the alkali/alumina index (eg. Harrison et al 2007) and one may also expect that it  also depends on the amount of dissolved volatiles (eg. water) in the melt.
I cannot find relevant papers which would enable to assess for what conditions Zircon saturation may be reached for the 3 end-member compositions of the zoned Laacher See magma chamber (or in a presumed basanite parent magma at LSE).
What intrigues me is that Zr contents seem to me to be very high at Laacher, yet Zircon occurrence seems to be "rare" and restricted to mostly very small zircon crystals in LST pumices and to some rare occurrences of sometimes  larger crystals (typically mm-sized xtals) in some cumulate nodules from LLST and MLST (eg. Schmitt 2006).
Is it that a large melt  H20 content suppresses Zircon crystallisation ?
Or that Zircon crystallization rates are too low in general in the LSE magma conditions  ?
I would be grateful for any insights into Zircon saturation and Zircon crystallization rates and what may control them at Laacher See (P: 115-200 MPa; H20: 2.5-5.7 vol% or so), or in basanite-tephrite magmas under crustal conditions.
I am also interested in any insights for Thorite crystallization in LSE magma conditions or in basanite-tephrite magmas under crustal conditions.
Thank you in advance for any suggestions or insights.
Happy New Year and Best Wishes,
Gerald
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Dear Gerhard,  Thanks a lot for all these info. Regarding the large Laacher See zircons, I fully agree with your pegmatite hypothesis and I have scanned a photo of a zircon that supports this - indeed you have already suggested similar observations you have made yourself. On the other hand for the large zircons in the older tephrite lavas I am less convinced that the same process could work (no obvious resorbption features). I'll attach the two scans to illustrate the contrast asap, in the coming days most probably.
Thanks again for the discussion and for the ref.
Beste Grüsse,
Gerald
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Hello everyone,
The Laacher See complex plinian explosive volcanic eruption (12.9 ky BP, East Eifel Volcanic Field, Germany) appears to be unique in having erupted both representative portions of the zoned chamber magmatic liquids as well as representative cumulates from chamber roof, sides and floor in what seems to be very large amounts.
In most plinian eruptions, it is inferred that less than 1% of the magma chamber volume is erupted in the end.
However at Laacher See this proportion is inferred to be at least an order of magnitude larger; and indeed much larger estimâtes are even quoted in the literature on LSE.
The Laacher See Eruption has been extensively studied for over 40 years and such case studies seem to fulfill the dream of volcanologists to understand eruptions as well as that of igneous petrologists to constrain the relation between cumulate pile developpement (crystal mush) and the magmatic liquid line of descent. 
I wonder if anyone has systematically ploughed the literature to assess how "unique" Laacher See complex plinian explosive eruptions may actually be ?
I would be grateful for any pointers or insights into this.
Happy holidays to everyone, and very best wishes for the New Year,
Gerald
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Hi everybody,
to me (and not only because I started science there), the Laacher See Tephra remains unique. Unlike the Alban Maar, that has had several eruptions separated by thousands of years and covering a large compositional range, the Laacher See Tephra is continuously zoned with much tighter compositional trends. At the final stages, the Laacher See erupted mafic phonolite together with basanite, that had just very recently mixing into the base of the magma chamber, and abundant cumulate and cognate syenite rocks, the latter suite contains hybrid syenite-carbonatite compositions, all have residual phonolitc interstitial glass.  Together with Axel Schmitt and a student of mine, we have dated zircons in these rocks, verifying earlier indications by U-series dating, that the crystal-rich mush / carapace had existed at least 20 ka before the eruption. (
Wetzel F, Schmitt AK, Kronz A, Wörner G (2010) In situ U-Th disequilibrium dating of pyrochlore at sub-millennial precision. Am Min 95: 1353-1356
Schmitt AK, Wetzel F, Cooper KM, Zou HB, Wörner G (2010) Magmatic longevity of Laacher See Volcano (Eifel, Germany) indicated by intrusive carbonatites. J Pet 50: 1053-1085
I envisage  that the eruption was fed from the remaining liquid core of an alkaline intrusive complex that was cooling outside in and was surrounded by crystal mush, syenites, carbonatite etc. 
The final stage of the eruption was strongly phreatomagmatic and "excavated" right into the alkaline intrusive complex that was still just above its solidus. The abundance of cumulate and syenite lithics stems from the fact that the phreatomagmatic explosions probably occurred at the base of a diatreme right inside the  shallow mush complex (but still at > 5 km depth).
Such a scenario is required by the observations and I am not aware of a similar case described in the literature.
Regards
Gerhard Wörner
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One has to consider plate tectonics, the age of  the of the volcanic ash or indurated phase (e.g. tonsteins) and that of distant plutons,using a refined technique such as single-crystal zircon U-Pb dating, the microchemistry of glass inclusions in volcanic quartz, paleowinds, , and  erosion of the the ultrasilicic volcanic ash, just to name several.
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Dear Paul, I think as already suggested by Martin Menzies, that the best should be to try to correlate as much as possible proximal and distal tephra. This can allow you at least to make a more confident attribution and dating of the possible source avoiding just one single data set and /or number date. Of coarse there are many possible sources but recently many papers on tephrostratigraphy have been published, especially in quaternary journals (eg.doi:10.1016/j.quascirev.2011.07.012; http://dx.doi.org/10.1016/j.quascirev.2012.09.009; http://dx.doi.org/10.1016/j.quascirev.2015.03.006; http://dx.doi.org/10.1016/j.quascirev.2014.04.002 and others) that could help to direct your effort. Data and literature related to very old volcanism are much less because often the proximal part is poorly known or unknown.  Have a good job.
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They have conspicuous concentration of vesicles in the center, irrespective of the orientation/inclination of the dyke.
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Dear Raghav
There are several feasible explanations to the examples you have shown. As you are aware, degassing in a magma can be triggered by pressure drop, reaching the saturation concentration for each volatile component at different pressures and that is the explanation you suggest (upper parts of the dykes, at lower pressure). Other possibility is volatile exolution as the magma solidifies; the concentration of volatiles in the melt increases as a consequence of volume reduction of the melt phase, reaching saturation and exolving. In confined dyke systems, this second option seems more probable and assuming a contact-inwards cooling, the vesicles are going to be concentrated in the center of the dyke, irrespective of the orientation of the dyke and even at higher pressures.  
Best regards 
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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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teaching earth & life sciences in a secondary school, I would like to find data about and to know how we explain size differences in colonnades diameter from basaltic (or rhyolitic) organs of distinct localizations?
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Dear Herve Levesque,
The answer should be complex but some of the factors influencing the size of the columns (diameter and height) probably are cooling rate, cooling surfaces, homogeneity and density of the magma, homogeneity of the thermal diffusivity.
Best regards
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Why such a long gap in the ages of same rock sample? Can anyone please suggest any good paper I can look into? 
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Thank You very much Marwan Wartes
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Hello!
I'm looking for published data in order to determine some kind of average value for the "crust residence time" of MOR igneous products and compare them with intra-oceanic supra subduction zone igneous products (specially data obtained using Lu-Hf isotopic system). 
Thanks
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Paulo-
A recent JGR paper by Rioux et al. on the Samail ophiolite came to mind.  I'm not sure if their work strictly satisfies your request (i.e. I don't think they used Lu-Hf).  However, it might be a starting point . . .
Good luck!
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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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Zircon Lu-Hf isotopic values are widely used to contribute to understanding of igneous petrogenesis. Epsilon Hf values of a suite of igneous rocks are often compared with those of different areas with different ages. Could anyone suggest a reference or references on zircon Lu-Hf values of Qiangtang terrane basement rocks?
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Dear Jovid,
I have attached some useful links. Please let me know if you need any additional information.
Best Regards,
Masoud Ovissi
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We have sampled an area (about 1000 Km2), which is part of a volcanic arc and regionally have geochemical characteristics of arc-type settings and I-type magma. 
35 samples were analysed and samples plot into the calc-alkaline to high-K-calc-alkaline fields. A/CNK index of the samples is almost high (in 1.2 to 1.7 range) and show perauminous characteristics.
What is the possible explanation about tectonic setting of these rocks?
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Perhaps you should specify what samples you analysed; basalts, granites, volaniclastics, sediments? Also, the term 'calc-alkaline' has quite a few different meanings - are you referring to the K-content of the samples?
If you are dealing with unaltered granitoids, then the tectonic setting COULD be collisional, or you could be dealing with heavily crustally contaminated continental arc magmas. Your interpretation will have to be based on the geological context more than the very restricted geochemical information you provide here. Remember that alteration may also increase the peraluminosity of your samples.
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I want to know the mechanism of the back arc basin.
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Sarmad - The basic answer to your question is that failure and infinite extension of the over-riding plate in the subduction zone will lead to backarc spreading. Sebastian has outlined some of the mechanisms. But the spreading direction can be orthogonal or oblique to the plate margin, depending on the convergence direction, the strength of the overriding plate and any other strain that might be imposed upon that plate.
You would probably be interested in the following papers: 
Lallemand et al (2005) G-cubed, v. 6, Q09006
Lallemand et al (2008) Tectonic, v. 27, TC301
Hope this helps.
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I know of no example where an igneous intrusion has been a positive factor for the hydrocarbon generation.  Intrusions destroy the stratigraphic potential for forming hydrocarbons and hydrocarbon reservoirs..  The only positive effect might be  elevated heat flow  at a 'province" scale (10,000's of sq miles).   Oil companies do not look for hydrocarbons in igneous provinces.
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I am asking in general.
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Dear colleagues,
another answer from the point of view of an economic geologist:
1. Lamproite-group rocks are dark-colored magmatic rocks enriched in K and Mg and hypabyssal or effusive in origin. Lamproites are peralkaline ultrapotassic Mg-enriched magmatic rocks with all hallmarks of ultrabasic rocks such as elevated Cr and Ni contents ( Mitchell 1991). They may contain leucite, phlogopite, and glass (fizroyite), plogopite, diopside, leucite (wyomingite) or phenocrysts of diopside and phlogopite in a fine-grained glassy matrix which chemically can be approximated to the composition of leucite (madupite). They may also contain amphibole, olivine, sanidine, spinel, apatite and nepheline together with some wadeite and priderite.
2. Kimberlite-group rocks are close to porphyritic alkaline peridotites. They contain phenocrysts of olivine which frequently serpentinized, phlogopite converted into chlorite, geikelite (= "Mg ilmenite"), and. chromian pyrope-enriched garnet. They float in a fine-grained matrix of calcite, olivine, and phlogopite (2 nd gen.). Accessory minerals are ilmenite, magnetite, spinel, monticellite, apatite and perovskite. Chrome diopside mineralization in kimberlites is an important guide to diamond deposits. Kimberlite is by definition a K-enriched ultramafic rock which derived from a depth of more than 150 km below surface (Clement and Skinner 1985, Kirkley et al. 1991). Moving upwards, the hypabyssal intrusions grade into diatreme breccias and pyroclastic rocks
3. Lamprophyre-group magmatic rocks are dark-colored like the afore-mentioned subcrustal rocks abundant in biotite, hornblende, pyroxene, present as phenocrysts in a fine-grained matrix of K and Na/Ca feldspar and/ or feldspathoids. According to the abundance of these minerals mentioned above they are subdivided into minette, kersantite, spessartite, camptonite, monchiquite, fourchite and alnoite.
No 1 - rocks are host of diamonds predominantly in Western Australia.
No-2- rocks are host of diamonds predominantly in Tanzania, Botswana, Angola, DR Congo, South Africa, Russia, Lesotho, Canada, Zimbabwe, Greenland, Gabon (metakimberlites)
No -3 - rocks gave besides diamonds (Michipicoten and Abitibi greenstone belts) also host to sapphire in Yogo Gulch, Montana, USA. It takes an outstanding position as it is bound to lamprophyre dykes classified as ouachitite ,a biotite monchiquite devoid of olivine with a glassy or analcime-bearing groundmass.
Best regards
Harald G.Dill
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I cant obtain the amount of Fe2O3, the procedure says that i need first obtain the excess of FeO , then the excess of iron being calculated to form FeO Fe2O3        ( this part i dont understand), from this the amount of Fe2O3 can be calculated. Please if someone have worked with that method it would be of great help some orientation about the procedure. Anyway here is the paper ( pp.39)
Regards
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Dear Eduardo,
Maybe you can find some information in:  Droop, GTR (1987): A general equation for estimating Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe analyses, using stoichiometric criteria. Mineralogical Magazine (51): 431-435. The paper is widely referenced. 
Though Droop is for probe analysis-results, it actually does refer to the paper by Carmichael (1967, not 1966) that you mention.
Just a suggestion, kind regards,
Maarten Broekmans
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Recently I've met an intreseting petrological phenomenon of a thin section cut from plagioclase granite, the profile can avaliable in the attachments.
The first graphy is a photomerge panaroma of an plagioclase, with a nearly vertical and sharply boundary in the middle of it(marked with red arrow), looks like two different crystal,  I really want to know the meaning of this phenomenon. Is this related to the syn-tectonic granite? There exist a micro-crack on the right side of this Plagioclase filled of quartze(marked with yellow arrow), which depict when the plagioclase crystalising while presence of a residual melt, which is a index of syn-tectonic granite. 
The second graphy is a relic of Plagiolase surrounded by Quartze, I can't read this phenomoneon either.
There exist some Biotite inside the Plagioclase that nearly parrall with its growth rhythm zone, is this has some specific meaning?
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Dear colleagues,
I would like to refer to the beginning of the discussion. The mineral association is obviously typical of a tonalite. These basic granites did neither go through strong regional metamorphism nor a pervasive dynamo-metamorphic process. There preferred sites of emplacement are deep-seated lineamentary fault zones in parts also thrust zones. See e.g. the locus typicus of tonalite along the the Insubrian Line which is one of the major sutur zones in the Alpine Fold Belt. The tonalite of the Adamello Massif is a darker granite lacking alkaline feldsapr but cannot be classified as a flaser or augengneiss. What counts in this case is its special geodynamic position which renders this intrusive rock different from the common granites hosting alkaline feldspar. The structural disturbances have left their imprints by creating a widely spaced set of shear- and thrust planes but no narrowly spaced foliation exists. Therefore the outward appearance is still that of granitoid rather than an gneiss.
H.G.Dill
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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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my rocks samples are amphibolite, however in the REE patterns, they show obviously Eu positive anomalies, they also show enrichment of Ba, Sr and Al, I have checked many references, none mafic magmas have   type chemical composition, I wonder anyone have some new opinions? Thank you.
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Extended REE spidergrams for amphibolites show the LREE-enriched nature of these samples with steep patterns (higher La/Yb). Zr, Ti, and Sr are also have to be included in these spidergrams to provide a comparison between the incompatible trace elements and the rare earth elements. The rare earth elements Zr, Y, and Ti generally are considered to be immobile during metamorphism with respect to major rock-forming minerals (Ludden and Thompson, 1979; Grauch, 1989). Because Sr may be mobile during metamorphism and weathering, Sr is used here only as a comparison with Eu contents as a ratio (Sr/Sr*) in order to examine the sample patterns. Rocks with plagioclase accumulations (i.e., gabbros) may exhibit positive Eu/Eu* and Sr/Sr* anomalies (like your samples), whereas rocks that have had plagioclase removed (i.e., basalts) may show negative Eu/Eu* and Sr/Sr* anomalies (Smith, 1994).
Also you can compare the Mg numbers for selected samples that show that the more evolved compositions (lower Mg numbers) have higher REE enrichments compared to the primitive compositions, indicating that the range in REE enrichments is probably the result of fractionating basaltic magmas within each group of samples rather than variable degrees of partial melting in the mantle source region.
If the samples have strongly positive Eu/Eu* and Sr/Sr* anomalies that are more typical of plutonic cumulate rocks with plagioclase. The Site 1067 amphibolites also display positive to negative Zr/Zr* values of 0.7-1.6, which can be directly related to the presence or absence of zircon in these samples.
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Dear all,
I am working on ophiolitic chromitites. My chromitites are disseminated, and I would like to separate the Mg-chromite from the silicate matrix. I will do the separation by Frantz magnetic separator. Would you help with the condition of the Frantz to make a successful separation of chromite? 
Thanks in advance,
Erdi
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Dear Mr. Avci,
your disseminated chromite ore should have a grain size > 0.1 mm to be applicable for an effective separation by means of the FRANTZ isodynamic separator, with the side tilt set at 15° and the forward tilt at 25°. Chromite normally shows the best recovery in a narrow interval of 0.3 to 0.37 Amps, but the full range is wider covering the current strength of 0.25 to 0.4. Interferences might come into existence as ilmenite, chlorite, hornblende s.s.s. and OPx are present. I mention only those minerals which you might encounter in ophiolitic sequences of the plutonic part. I do not know what is meant, when you speak of Mg chromite. Could it also be Cr-picotite or beresowskite?
Good luck!
H.G.Dill
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For instance, it could be recycled metasomatized oceanic lithosphere by long term storage in deep mantle. And, this is one of the major sources of mantle plumes which could metasomatize the sub-continental lithosphere by upwelling from deep mantle.
Also, can it be found in a metasomatized (enriched) lithospheric mantle by short term storage (in more shallow mantle) of subducting slab in a subduction zone or post-collisional environment (after slab break-off or delamination of a thermal boundary layer)?
In other words, can we use isotopic signatures of the EM2 mantle source in order to distinguish the possible agents of the mantle metasomatism (subduction or plume related)?
If no, How can we identify the correct metasomatism process (subduction or plume related) by using petrological methods?
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In my opinion, we have to re-think about the location where the EMII and other mantle sources of basalts are residing. In a convecting mantle it is hard to expect that the positions of these are fixed in space and time. If we are to assume that the basaltic volcanism we see today is a result of mixing and/or melting in these reservoirs, then there is the need that  those should reside in relatively fixed positions for relatively large geological periods of time, for those processes to take place in the manner we envisage them. This is likely to happen only in a layered sub-continental lithosphere.
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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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Archaean Sodic trachyandesites are rare but very typical rock type closely associated with calc-alkaline volcanic rocks. However, literature regarding origin of such mildly alkaline rocks with elevated incompatible trace elemental contents is rare. We have a late Archaean trachyandesite (SiO2 58%) with elevated Al2O3 (19%), Na2O (7%), HFSE (Zr, Nb, Hf, Th and U), REE and Ga contents. Enriched LREE, negative Eu anomaly and flat HREE pattern and negative eNd (-3.6) is not consistent with moderate SiO2 and undepleted V, Cr and Ni contents (183, 130 and 70 ppm respectively). Very low K2O (0.1%) and Rb (2 ppm) are notable. Can anybody discuss the origin of this rock.   
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Dear Dr. Dey,
I can only support what Dr. Grundmann has voiced and reiterate my slogan "geology-petrography-chemistry-isotope physics". The other way round is like doing  heart surgery first and a blood test in the aftermaths as we realize that something is going to get wrong.
Best regards
H.G.Dill
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On behalf of my lab-mate Soumi Chatterjee:
We are working on an alkali basalt sample, where we have documented some of this flower like aggregates of tiny euhedral to subhedral clinopyroxenes with minor amount of spinel occurring within fine grained basaltic matrix. EPMA indicates that they are Ti-rich Diopside. It would be extremely helpful if anybody can give some clue on their origin, textural significance etc. Moreover, any literature references would be highly appreciated. Attaching the corresponding photomicrograph as a Pdf file (see the attachment)
Fig Caption: Photomicrograph of the texture A) under Plane polarised light; B) under cross polars; C) Reflected light photograph; D) BSE image
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According to my experience, it is not a sieve cpx. It is probably Q xenocryst that reacted with alkaline undersaturated melt, and that is the reason for this relatively fast crystallization of cpx. If you find some examples of this reaction that is not complete (e.g. Q surrounded by such cpx), will be definite evidence for this reaction. Please look also my paper JOP 2004, fig2c: http://petrology.oxfordjournals.org/content/45/4/759/F2.expansion.html
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I would really appreciate if someone could provide references to publications about the Late Cretaceous (~77 Ma) magmatism (ecpecially mafic) in the CAOB or in the adjacent areas (North China Craton). Thank you in advance.
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Dear Dr. Malkovets,
my colleagues and me  studied Sb-W deposits in SE Asia. They are related to a Jurassic to Cretaceous arc-related magmatism. Perhaps this information may be of help to you and you will find more referenced papers of assistance to your work.
Best regards
H.G.Dill
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Hi everyone, I'm developing a research of mineral chemistry in phyllosilicates of alteration zones of porphyry deposits, like a complement, I want to know the theory about how is the variation of the chemical elements during the hydrothermal stages?.
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Please see attached manuscript. Also this reference: 
Geochemistry of Hydrothermal Ore Deposits, Volume 1, 1997
By Hubert Lloyd Barnes
Chapter 9 & 10.
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I am trying to find out more information about the formation of a stone from India that is used for building and is known in the stone trade as Kashmir White.  I have attached a couple of typical photos of the stone.  Normally I would hope to obtain a sample and petrographically examine it myself, but unfortunately do not have the time available to do so.
The stone appears to be a partially metamorphosed granite, apparently peraluminous with garnet formation.  I am interested in how the structures within the stone may have formed and its geological history.  
Any assistance would be most appreciated, thanks.  Barry Hunt
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Hi Barry,
I confirm Martin's view that Kashmir White (as far as I know most samples come in fact from Andar Pradesh state) is a typical garnet granulite, possibly former acid volcanics metamorphosed under granulite facies conditions. Orthopyroxene, diagnostic for granulite facies metamorphism is not present bed cause of the too high Al content of the rock. Interedsting is the fact that, in many samples, garnets are not evenly distributed in the groundmass, but concentrated along microshear zones (see top of attached photo), possibly the pathways by which granulite fluids (high-density CO2 and concentrated saline brines) have escaped during retrogradation. Jacques Touret
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I have the following thin section of alkali feldspar granite. Are blue minerals arfvedsonite?
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Dear Mr. Athari,
unlike many  other Na--bearing amphiboles arvedsonite has a negative optical character along the major elongation. It shows an oblique extinction between 10° and 25° which is different from that of glaucophane, crossite and riebeckite. So I suggest you do some further routine optical tests and disclose it to the audience. Thereby you can narrow down the field of speculation and in context with the associated minerals you may get a sound result. Have you got also aegirite in your rocks ? Arvedsonite is confined to agpaitic magmatic rocks with alk>al. Is this the case ?
If I had no further information and taken a closer look at the texture and the epidote,  I would have also tended to a low-T-high-P enclave as it was already mentioned by Dr. Keiter.
Best regards
H.G.Dill
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I have always read about synthsizing zeolithes from clay or chemical starting materials in hydrothermal conditions. But I have never met a paper talking about zeolithes synthesis in "normal" conditions, below 100°C. Have you?
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Thanks David. But it is again by "hydrothermal activation"....