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Igneous Petrology - Science topic
Explore the latest questions and answers in Igneous Petrology, and find Igneous Petrology experts.
Questions related to Igneous Petrology
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!
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
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
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
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, 1975: https://www.sciencedirect.com/science/article/pii/0012825275900392
Middlemost, 1985: Magmas and magmatic rocks: An introduction to igneous petrology: London, UK, Longman, 266 pp.
Miyashiro, 1974: https://cir.nii.ac.jp/crid/1574231873970603392
Nockolds and Allen, 1953: https://www.sciencedirect.com/science/article/pii/0016703753900556
Peacock, 1931: https://www.journals.uchicago.edu/doi/abs/10.1086/623788
Peccerillo and Taylor, 1976: https://link.springer.com/article/10.1007/bf00384745
Sheth et al., 2002: https://www.tandfonline.com/doi/epdf/10.2747/0020-6814.44.8.686?needAccess=true
Hi dear friends!
My question is short. Can basalts only be formed in a fore-arc environment without boninites in the association?
Thanks!
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 🙏👌.
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.


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
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
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


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



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
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
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
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?
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?
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?
I am studying the thermal effect of the large Igneous Province recently. Is there any way to do it?
Does the fact that these granitoids are deformed affect the choice of these diagrams?
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?
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.
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.

Is it recommended for granitoids?
Any discrimination diagram or calculations would be helpful.
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.


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.
Does negative Nb-Ta and Ti anomaly with No Zr- Hf anomaly suggest subduction setting? For the mafic dyke samples

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.
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!
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
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.
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.





What is the conceptual difference between Geological Map and Stratigraphic Map?
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?
Is there some difference in major elements or trace elements content?
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?
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.


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?

Based on earthquake data, how we can define the type of rocks and minerals within the earth?
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.
Please upload information related to any upcoming seminar or conferences in India related to Igneous Petrology.....
Thank You
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.
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?
Cooperation in igneous and metamorphic petrology and help in U/Pb dating.
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?
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
For example is there any way to recognize minerals (augite, plagioclase) as more sodic or calcic?
I need some references related to Pegmatite occurrences of Nuristan Province of Afghanistan.
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.
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 ?
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.
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?
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.
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
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?



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?
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
I want to determination pressure of gabbro formation by Nimis and Taylor (2000) method, who can help me for doing the calculations?
Whether the partial melting of mantle lithosphere can directly produce andesitic melts? Who can provide me available references with repect to this process? Thanks.
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
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 ...
1.How feldspar deformation occurs?
2.What chemistry is involved in the deformation process of feldspar?
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
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.
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.
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?
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.
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
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
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.
They have conspicuous concentration of vesicles in the center, irrespective of the orientation/inclination of the dyke.
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.
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?
Why such a long gap in the ages of same rock sample? Can anyone please suggest any good paper I can look into?
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
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?
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?
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?
I want to know the mechanism of the back arc basin.
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
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?
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?

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.


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
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?
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
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?
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.
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
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.
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
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.
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?.
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
I have the following thin section of alkali feldspar granite. Are blue minerals arfvedsonite?

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?