Questions related to Metamorphic Petrology
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 🙏👌.
While doing research, I came across this thin section from a drill core. While looking at this with my mentor, he stated that it could be non-fibrolitic sillimanite. I do agree with this, but I wonder: Would just hydrothermal alteration cause the muscovite and sillimanite to have the same orientation, or could something else be at play? Any comments would be appreciated!
Garnet is a common mineral that appears in metamorphic rocks. It is also considered an accessory in igneous rocks and a detrital mineral in sedimentary rocks.
What are the key characteristics and approaches to differentiate between detrital, igneous, and metamorphic garnets in metasediments and igneous rocks?
I am working on a petrographic analysis, and I have a thin-section database, referred to partially metamorphic rocks such as meta-basalt, meta-andesite, meta-gabbro and so on.
In the thin-section results, I have got the percentage of several main minerals such as Quartz, Epidote, Feldspar, Chlorite and some other minerals which are significantly varying among samples from one to another. For example, Quartz is fluctuating between 0 and 59 percent in various samples.
In my research, I need to categorize the mineral percentages in three ranges: Low range, Middle range and High range. For example, when we say that there is a high quantity of Quartz in a metamorphosed rock, what exact percent we are dealing with?
I would appreciate if you could share your ideas about this question.
I'm working on an update to our previous global geochemical database. At the moment, it contains a little over one million geochemical analyses. It contains some basic geochronology data, crystallization dates for igneous rocks and depositional dates for sedimentary rocks. The database differs from GEOROC and EarthChem, in that it includes some interpretive metadata and estimates of geophysical properties derived from the bulk chemistry. I'd like to expand these capabilities going forward.
What would you like to see added or improved?
Here's a link to the previous version:
Sanukitoids are granitoids showing enrichment of both large-ion lithophile elements (K, Ba, Sr) and mafic elements (Mg, Cr and Ni) at the level of their SiO2 contents. It is generally thought that these granitoids, with high Mg#, were produced from a mantle source (supplying Mg, Cr and Ni) fluxed with a crust-derived fluid or melt carrying K, Ba, Sr, LREE and Th. A likely tectonic setting is a mantle wedge overlying a subducted oceanic slab undergoing dehydration or melting. Therefore, many authors consider presence of sanukitoids as a strong indicator of subduction, especially in the late Archaean. Can such rocks form in tectonic settings unrelated to subduction?
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
I've used several thermometers and the results seem to contradict one another quite allot. Maybe someone can suggest a method, that's most reliable?
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?
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 found quite huge idiomorphic apatite crystals (up to 0,5 mm) in the Anisian shallow water limestones and they look pretty much like porphyroblasts with pressure shadows. Limestones are highly recrystallized with mylonitic texture.
Whether an increase in temperature can cause the growth of apatites from phosphorus rich limestones?
What is the origin of phosphorus?
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.
I have Raman spectra of carbonaceous materials from metasedimentary rocks and working on the estimation of their peak metamorphic temperatures. How can I deconvolute the spectra using the voigt function in Peakfit software for obtaining Raman peak values i.e. the G, D1, D2, D3 bands values as well as FWHM values; and other related parameters i.e. R1, R2? Suggestions and guidelines would be highly appreciated. Thank you.
Hello Professors and colleagues
I am trying to draw a detailed Tectonic schematic cross section for a subducting slab focusing mainly on the transformation of shales and carbonates into greenschist facies schist and Thermal skarn overlying this slab .. ... i know that less is known about the 3D imagination of subduction zones and specially what happens to the sediments !
But what is the best schematic model i can follow from your opinion ?
Suggest references or attach your own images would enrich our discussion :)
Thanks in advance
There are numerous databases for geochemical analyses for rocks like georoc and the National Geochemical Database of the USGS or purely mineralogical databases like mineralienatlas, mindat or webmineral. But is there a database for quantification of minerals in rocks?
I am struggling to model a rock which contains the assemblage K-white mica + Na-white mica + chlorite + quartz + graphite + rutile. I have followed step by step the tutorial available on Perplex's website.
which suggests to model graphite-bearing rocks as an open system with respect to a binary H2O-CO2 fluid with buffered f(O2).
Following the tutorial, I have set a H2O-CO2 fluid in excess, modeled with equation 10 by Connolly & Cesare, 1993), buffered with X(O). Set SiO2 and O2 as excess components, then specified a sectioning value for X(O) of 0.33333333333333334 (1/3).
What I get from vertex is always the same error:
**error ver015* missing composant for O2.
I have tried everything. Changed equation, sectioning value, removed fluid/components in excess but it doesn't work.
Therefore, I was wondering if there is a better way to model a graphite-bearing rock.
Attached, you may find the DAT file for Perplex
Thank you very much.
I've put a photo of mineral that I do not know.
This mineral generally occurred near the contacts of chromite lenses on the surface of serpentine foliation like sheet Silicates. The color shows copper or bronze and metallic luster but it is a very strange formation such a mineral in a sheeted form especially in serpentinized dunite!
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.
Charnockite is an opx (usually hypersthene), quartz and feldspar bearing meta-igneous rock, mostly acidic in composition, and metamorphosed under granulite facies conditions. It is commonly found in Gondwana fragments such as in Sri Lanka and India. One of the key characteristic features of chranockite is that minerals of feldspar and quartz in the rock have a greenish appearance. Is there any scientific explanation for the cause of this colour?
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
Hello Professors and colleagues
I am studying Neoproterozoic meta-sediments can i apply the indices of alteration on it or it has to be on sedimentary rocks only ?
Thanks in advance
Hello, everyone. I'm calculating the fO2 and fS2 for my chlorite whose temperature is around 300~350 ℃. Anyone can provide a software or spreedsheet to calculate those numbers by using solution model of Walshe (1986). Or, you can also recommend other easier calculating method! Thanks a lot!
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?
We have gabbro, pyroxenite, and serpentinized peridotite in a small area (5*5 km), adjacent to a greenschist-facies subduction melange (5 km far to the west). We also have "metamorphic sole" rocks including Pl-Amp migmatite within the pyroxenite.
All of those ultramafic-mafic rocks are depleted in HFSE and enriched in Pb and Sr.
The serpentinized peridotite is slightly depleted in LREE with no Eu anomalies. It is also depleted in Th, U, P, and HFSE.
The pyroxenite is significantly depleted in Th, U, P, HFSE, and LREE. However, the uralited pyroxenite is nearly flat in REE diagram and enriched in Th, U and P.
The gabbros are enriched in LREE and LILE with positive Eu anomalies.
The migmatite of the metamorphic sole has similar pattern with the pyroxenite.
In V vs. Ti diagram most of them plot in/near the IAT (& slab-proximal BABB and FAB) area.
They were possibly the SZ(subduction zone)-proximal ophiolite (SSZ type), however, they were also possibly the lower crust and mantle of an island arc.
So the question is: when we lost the upper crust, how to name those ultramafic-mafic rock complex, island arc or ophiolite? (answered)
A new question is:
How to interpret the LREE depletion of the ultramafic rocks, which "seems to be contradict with SSZ origin"?
I am working with high grade metamorphosed manganese-rich pelitic rocks and i would like know if is possible to assess potencial primary or low grade mineralogy of these rocks using thermodynamic modelling (using pseudosection in THERMOCALC, for instance).
Cooperation in igneous and metamorphic petrology and help in U/Pb dating.
Hello Profs and collages
i am asking if i can apply the relation
CIA = Al2O3/Al2O3+CaO+Na2O+K2O for meta pelitic rocks such as schists and phylites to indicate that chemical weathering affected the precursor of those metamorphic rocks ?
or metamorphism and subsequent hydrothermal alteration will result in a valueless results ?
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.
Points are two-combinations of n phase names. Lines are three-combinations of phase names. Point and line are incident upon one another if the two phase names comprising the point are part of the name of the line (e.g., point AB and line ABE are incident upon one another). In attached figures, lines of perspective are red, perspective triangles are green, and points of perspective of pairs of green triangles are connected with orange lines. Brute force counting of adjacencies is doable for Desargues configuration (n=5) , but impractical as system number of phases increases.
I am in look out for literatures pertaining to allanite breakdown mehanisms in hybridized I-type meta-aluminous granite. The mafic differentiated source diorite (K2O-4-5%) and potash-rich (K2O 5-7%) granite are variably hybridized. A residual leucocratic micro-granite bearing (2-5%) modal allanite is emplaced along brittle-fractures during late stages of granite crystallization.
I have analyzed 2-5% modal allanite in a late to post-kinematic leucogranite, showing alteration to britholite-(Ce) and parisite-(Ce). The EPMA data shows the transformation is partial; somewhere between allanite - parisite-(Ce) solid solution join. Few Calkinsite-(Ce) is also suspected. The breakdown product of allanite are thorite and clay.
Thanks in advance.
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 have some grabbro samples, however, when I made EPMS analysis on the minerals in the rock slice, there are much more amphiboles than clinopyroxenes. Then I think the most clinopyroxenes should have altered to amphiboles. How could I distinguish between the two kinds of amphiboles?
My rocks are amphibolite وamphibolized gabbro, gneiss (overprinted by amphibolite facies retrograde metamorphism) and schist. I dont know how can I determinethe source of protolith. As I know Pb and Rb/Sr ratio change during this grade of metamorphism. Can Sm/Nd be usefull? Separated mineral or whole rock or both of them? Thank you so much in advance.
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
In simple calcissilicated rocks, the granulitic facies would be attested by the presence of forsterite or grossular, up to fCO2 quantity.
Anyhow, the coexistence of Diopside and Enstatite in a quartz saturated rock, with minor retrometamophic poikiloblastic hornblende it's enough to testify a retrometamorphic path from granulite to amphibolite facies?
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?
Mafic mantle magmas underplating at the base of the continental arc crust and form the hot zone. These magmas could differentiated to the evolved melts by fractional crystalization and mixing with crustal partial melts (which produced by the heat and volatile transferring from the mafic mantle melts). It is likely that some parts of these magmas cooled and solidified, and form the basaltic sills in the base of arc crust.
Remobilization of the frozen andesitic melts (differentiated mantle magmas) by the newly injection of the hot mafic mantle derived magmas was reported from some of the continental arcs. I need to know whether intrusion of mafic mantle derived magmas could re-melting the cold mantle derived basaltic sills, too?
Samples from massive Ti-Fe ores associated to massif-type anorthosite exhibit zircon rimmed by baddeleyite + chlorite.
Although such texture has been reported in meteorite impacts, I wonder if there is any other type of occurrence for this texture with less extreme formation conditions? Thanks!
What is a useful method to quantify graphite contents in powdered rock samples? XRD does not work well due to the platy crystals and very strong preferred orientation, so I'm looking for an alternative method. Either by another analytical instrument, or by physical separation, or...
The O18 isotopic equilibrium temperature (between biotite-muscovite) in a metapelitic mylonite is 300 deg C. However, the stable paragenesis of these metapelites includes garnet, staurolite. The Ar-Ar age of recrystallized muscovite is 11-13 Ma. Can we say that ductile deformation related to mylonitization occurred 11-13 Ma?..Or is it the just the cooling age of the pelites which have undergone garnet and staurolite stable metamorphism earlier? What are the constraints??
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.
High pressure granulite is always regarded as the indicator of collision process, especially, some high pressure pelitic granulite is regarded as the subduction-collision process involving sediments. So, I want to know, is there other tectonic process to produce high pressure granulite ?
Can anyone suggest a good overview article on what makes Alpine Type serpentinites different from others? I know that plots of Cr# vs Mg# have different fields, but what else is different and why? Mineralogy? Any estimates of P-T conditions, or are they variable?
I would like to know if garnets in migmatite rocks form as a result of dehydration reactions or any other process and also to know how to determine if garnets were transported by the melt or originally formed as a result of metamorphic reactions
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?
For example: Eclogites could represent a range of protoliths such as picritic basalts crystallized in magma chambers within the mantle, subducted ocean floor or delaminated lower crustal material. Any papers/articles?
Hello, everyone. My eclogite rocks contain many epidote and zoisite. Epidote can be used to determine ages by U-Pb dating, but I don't know if there are any method for U-Pb dating of zoisite?
I am studying the petrogenetic evolution of a polymetamorphic highly fractionated I-type granite. Geochemical and petrographical studies revealed two different varieties of this orthogneiss, namely a metaluminous (ASI 0.9-1.0) mafic variety and a weakly peraluminous (ASI 1.0-1.1) leucocratic variety. Rayleigh fractionation modelling argue for a derivation of the leucocratic orthogneiss through fractional crystallization from the melanocratic orthogneiss. Peraluminous (ASI 1.1) aplites represent the highest evolved member of this series.
My problem is, how do I explain this trend? So far I havent observed hornblende in the melanocratic gneiss, which would shift the composition of the residual melt towards peraluminous composition if fractionated. Generally, biotite is the only mafic mineral in these metagranitoids. The model of Chappell et al. (2012) in which a metaluminous I-type granite is produced through higher degrees of partial melting of a Cpx-rich source (e.g. basalt, andesite) is not favoured by the negative epsilon Hf values of zircons in both orthogneisses indicating a crustal protolith. Assimilation of crustal material could be a further explanation, but yet I dont see any evidence for that in my geochemical data.
Is it possible to make a metaluminous residual solid (cumulates) through fractional crystallization of a peraluminous melt? Do you have any other ideas to explain the transition of metaluminous to peraluminous composition of an I-type granite?
The MgO contents under study range from 8-16%. I guess one is high degree of partial melting of the mantle peridotites, and another is olivine cumulates. Can anyone recommond some related references which argue for these two aspects. Or are there other reasons for the high magnesian contents in basalts? Thank you.
Absolute dating is necessary for knowing specific time e.g. by isotope K/Ar in mica, especially in the crystalline rock: igneous and metamorphic rock. On the other hand, the sedimentary rock (as I know) usually provide the time of formation by age range of fossil e.g. Upper Miocene - Piocene. Is there any method to make it more specific like the crystalline one?
My research project is based on garnet composition within leucosome, melanosome, palaesome in Migmatite rock and so I would appreciate any information which specifies about this in a certain location called Kliprand, South Africa. The information is limited in this area of interest and I would appreciate any input regarding this topic.
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?
I have been observing a metamorphic rock that contain Almandine garnet using SEM-EDS. The presence of garnets is confirmed by the very rock's XRD patterns (both Pyrope and Almandine are present).
Element analysis (SEM-EDS) of various points on Almandine/pyrope shows the following general chemical composition in wt%
Na - 0 - 1% K - 0 - 1 % Al - 17-19%
Mg - 4 -7 % Si - 25 - 30%
Ca - 4 -1 % (Total)Fe - 30 - 35 %
Strangely, Sulphur is there ranging 0 to 2%
Is it natural to have Sulphur in garnet? and are Na, K, Mg and Ca inter exchanging with each other?
Additional Info (XRF analysis (FP method) shows S element about 1.6 wt%. but XRD does not show any peak for possible Sulphur bearing minerals such as pyrite or gypsum. Still the rock samples have strong sulphur smell).
Thank you in advance
Is it possible to have Fe2O3 in Sillimanite? I observed (under SEI) a sillimanite looking grain (in a metamorphic rock sample) with characteristic cross fractures in my SEM-EDS studies. But several points along the very same grain show the following composition;
Alumina - 58 - 61 wt%
Silica - 35-38 wt%
FeO+Fe2O3 - 3 -5 wt%
Is this gain is sillimanite or something else. Is it possible Alumina to be replaced with Fe2O3?
Thanks in Advance!
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?
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.
The integrity of the datafile, datafile format, and the program have been verified. I am using winCMP and thermodynamic dataset v1.02, as bundled with winTWQ v2.34, on a laptop running 64-bit Windows 7.
Running winCMP in multiple compatibility modes did not solve the problem. It seems that winCMP crashes when any amphibole oxide data is fed to it, including previously published analyses used in TWQ calculations.
Spreadsheet/software calculating seismic velocities in peridotite as a function of mantle peridotite modal composition and chemistry of olivine/opx? I look for spreadsheet/software enabling the calculation of seismic velocities on the basis of mantle peridotite modal composition AND composition of major minerals. Crucial is the possibility of translating the small variations of forsterite content (2-4 mole %) and corresponding orthopyroxene mg# to seismic properties. I wonder if it is possible...?
Based on EPMA data, the Sr value reaches up to 676 ppm (0.08 %wt) within the garnets (with andradite-dominant end-member) from a Fe-LREE distal skarn deposit. Also, ICP-OES data shows a relatively higher amount of this element (up to 840 ppm) in the sample contains ore minerals include magnetite, pyrite, pyrrhotite, calc-silicate minerals such as andradite and epidote, and secondary minerals comprise actinolite, calcite, quartz, and chlorite. It is worth noting that, marmorized limestone also yielded 10,346 ppm of Sr.
Lithologically, the Upper Cretaceous submarine andesitic rocks and the flysch-type assemblage including alternating thin to medium bedded sandstone, shale, marl, and conglomerate together with the thick bedded to massive limestone are the most common units in the area. Also, Granodiorite and gabbro are the dominant composition of Oligocene aged intrusive bodies.
Low pressure metamorphic belt surrounded by granitic gneiss.
The granitic gneiss compositions vary from calc-alkaline to alkaline. What are the possible ways to find out the tectonic setting of a low pressure metamorphic belt?
Recently, the utilization of magnesium isotopes in tracing the global carbon cycle has attracted more and more researchers. It is suggested that the δ26Mg values in normal eclogites (not carbonated) are generally comparable to those of their protoliths and also the average mantle. This means the preservation of the original Mg isotopic composition during low temperature-high pressure metamorphism. My question is that can the original magmatic Mg isotopic composition also be preserved in the amphibolites or granulites from Archean cratons.
I would like to distinguish these two lithologies to show a geochemical contrast between them in a figure. The figure presents a cross section through an oceanic core complex. The cross section is perpendicular to the ridge axis.