I-types have relatively high sodium, Na2O greater than 3.2% , in felsic varieties, decreasing to more than 2.2% in mafic types.

S-types have relatively low sodium, Na2O normally less than 3.2% in rocks with approximately 5%K2O, decreasing to less than 2.2% in rocks with approximately 2% K2O.

S-types have been determined to have a Mol Al2O3/(Na2O+K2O+CaO) ratio of greater than 1.1 and I-types less than 1.1.

normative corundum in S-type granites, being greater than 1% CIPW corundum.

In I-type granites, less than 1% CIPW diopside is present.

presence of carbon or sulphur in the sedimentary source rocks results in S-types being much more reduced than I-types.

S-type granites are restricted in composition to high SiO2 types,

while I-type granites have a wide composition from felsic to mafic.

granitoids containing less than 655% SiO2 can generally be assumed to be I-type.

Another important geochemical feature of S- and I-type granites is the various isotope compositions. The initial Sr87/Sr86 ratios being higher in S-types because have been through an earlier sedimentary cycle.. A critical boundary of 0.7060 is suggested.  I-type granites have initial Sr87/Sr86 ratios between 0.704 and 0.706 (Chappell and White, 1974).

Mineralogically, Amphibole and pyroxene are more common in I-type granitoids, while S-type granitoids may have garnet, cordierite, and sillimanite.

Both types of granitoids may also contain biotite and muscovite.

 Respected mam thank you very much for adding such a informative answer. Can you please tell me about element behavior in spider diagram for such granite type.

S.type granite never exhibits enhanced magnetic susceptibility and does not contain accessory magnetite. I-type granite are predominantly magnetic, but not always.You must   calculate the peraluminosity index. 

In addition to the valuable information added by Asoori Latha, the metallic elements also can be used to differentiate between S-type and I-type granitoids. The earlier one is mostly enriched in the Sn, W, while the latter is mostly enriched in Cu and Mo metals. 

S-Type Granites

• Occur in regional metamorphic terranes

• Partial melting of metasediments

• High Al but contain no hornblende

• Biotite, muscovite, cordierite and garnet

• High Rb in source rocks

• Initial Sr ratios > 0.710

I-Type Granites

• Subduction zone continental margin

• High Ca and Na – Contain  hornblende and sphene

• Hornblende-rich inclusions

• Melting of deep crustal igneous rocks

• Source region poor in Rb

• Initial Sr isotope ratios

Thank you very much for informative  discussion by  Dr. František Hrouda,  Dr. Ahmed Hassan Ahmed and  Dr. Sudip Bhattacharyya.

S-type granites crystallizes from the viscous, relatively water-saturated magma at great depths. They can form autochthonous bodies and may be surrounded by gneisses and crystalline schists, very similar in composition. I-type granites are formed from the drier and more mobile magma melted deeper, but crystallize at higher levels. Their contacts are well defined, and high grade metamorphic rocks are usually not observed in the frame. Such plutons of S- and I-type granites I mapped in the Polar Urals.

Table 1

Original table of S- and I-type granite characteristics, as published by Chappell and White (1974)

I-types 

Relatively high sodium,

Na2O normally >3.2%

in felsic varieties, decreasing to

>2.2% in more mafic types Mol. Al2O3/(Na2O+K2O+ CaO)>1.1

CIPW normative diopside or < 1%

normative corundum

>1% CIPW normative corundum

Broad spectrum of compositions

from felsic to mafic. Regular inter-element variations within plutons;

linear or nonlinear variation diagrams

Tipo S

Relatively low sodium,

Na2O normally < 3.2% in rocks

with approximately 5% K2O,

decreasing to < 2.2% in rocks

with approximately 2% K2O

Mol. Al2O3/(Na2O+K2O+ CaO) < 1.1

Relatively restricted in composition to

high SiO2 types. 

Variation diagrams more irregular

This list remains essentially valid, although nearly 30 years of progress in understanding and characterizing these rocks has considerably

extended and refined it.

For the petrolographic observation:

S-type granites have Al-rich minerals such as garnet, cordierite, muscovite and Al-rich biotite, while I-type granites have hornblend and biotite.  

Information on the paper, Chappell and White (1992), would be useful for you for their geochemical characteristics.

Dear Abdul Shakoor: I've studied lots of "S" type granitoids, which are abundant in the Venezuelan cordilleras, most of them range from Devonian to Triassic. The most striking feature I've seen in them, besides all what was answered and explained before by various other colleagues, is the presence of muscovite, biotite, andalusite and garnet, sometimes even corundum, since they are strongly peraluminous. Another feature in them is the presence of ilmenite, since the reducing conditions -due to the presence of graphite of organic origin in metasediments undergoing partial fusion- prevent the oxydation of iron to Fe3+ to form magnetite. These ilmenite crystals quite often show spectacular coronas or reaction borders of red-brown titanite, especially when included in biotite.

Being more strict, epsilon-Sr and epsilon-Nd isotopic evidence shows that there are no pure "S" or "I" granitoids, each type comes from the partial fusion of either mostly sedimentary or mostly igneous parent rock. Look for a detailed and most revealing study about this problem made in the Southern Californian and Sierra Nevada batholiths in Faure, G. (1986) "Principles of Isotopic Geology", 2nd. Ed. John Wiley and Sons, in Chapter 13, part. 6a, pp. 231-233, and especially look at Figure 13.10 (epsilonCHUR-Nd vs. epsilonUR-Sr), where even a clear isotopic overlap occurs between both types of granitoids. It easy to understand that when the deep continental root of an orogen starts to melt it is impossible to separate both types of rocks, since they are usually intermingled, as outcrops show all over the world. So some igneous material contributes to the genesis of "S" type granitoids, and some sedimentary material does the same to the genesis of "I" type granitoids. With kind Regards. Sebastian.

Dear Professor Sebastián Grande, really it was good answer from you and i got alot of help from your answer and conclude better then before, once again thanks for sparing time and sharing of good knowledge.

and thanks to Dear Anna Soboleva ,Gabriel Rodríguez García ,Zongying Huang, for replying me.

Very informative answers, However, one should notice that the alphabatical soup of Chappell and White  has an inherent assumption for granitic melt to be produced from a single source. And this is hardly true for granites. that is why transition from I  to S or otherwise can not be explained by this classification scheme.

Dear Shakoor,

You now have some very good suggestions from a number of experts. Here are listed  some publications that deal with geochemical distinctions of granitoids and list many references that might be of interest to you:

Chappel 2004. In Ishihara symp. Granites and Associated metallogenesis-Geoscience Australia.   See also, Collins 2004. Ibid.

Clemens et al 1986. Am Miner 71, 317-24.

Dostal & Shellnutt 2015.Int Geol Rev http.//dx.doi.org/10.1080/00206814.2015.1052995

Eby GN 1990. Lithhos 26, 115-34.

Eby WA 1992. Geology 210, 641-4.

Frost et al 2001. J Petrol 42, 2033-48.

Hajialoghly et al 2010. Geol Mag 148, 250-68.

Song et al 2016. Tectonophys   DOI:10.1016/j.tecto.2016.03.023

Yang et al 2015.GSA Bull 1831-54.

Yang et al 2015. Lithos    doi:10.1016/j.lithos.2015.10.005

Yin  et al 2015. Gond Res   http:dx.doi.org//0.1016/j.gr.2015.06.016

Cheers, Qasim

Shakoor,

You asked somewhere if there are I-type granitoids in Rajasthan.

The Malani Igneous Suite (MIS) in western Rajasthan is a Large Ignous Province, one of the largest according to Kochhar. Hundreds of papers have been written on its within-plate, I-type character by SK Bhusan, N Kochhar, AK Sharma, KK Sharma, AK Singh and many others. A relatively new paper is by Kumar & Vallinayagam (2014, Geotectonics 48, 239-253). But two recent papers cast doubt on the within-plate origin of the MIS and argue for subduction-related origin (Dharma Rao et al 2012, Gondwana Res 22, 36-53; and Ashwal et al, 2013, Precamb Res 236, 265-81). By the way, Sisodia (2011, Current Sc 101, 946-51) considered MIS as related to meteorite impact!

The extension of the MIS in Nagar Parkar (SE Sindh, PK) has also been considered as within-plate, I-type and described well by Khan et al, 2012. JAES    http://dx.doi.org/10.1016/j.jseaes.2012.05.028

All best, Qasim Jan

I-type and S-type granites may be called as ortho- and para-granites respectively? 

Shakoor,

I apologize; I misread your question. The Malani Igneous suite (and the Nagar Parkar) have been classified mostly as A-type. But A-type in itself is complicated and incorporates granites of varied locales.

Ijaz: As Munazzam Mahar said, there are already more terms than necessary, and let us not add new terms, not at least until we understand the granitoids better.

Answer to Ijaz Ahmad: the terns "ortho" and "para" cannot be used in granites, they are specific for the PROTOLITHS of metamorphic rocks: "ortho" indicates an igneous protolith, and "para", a sedimentary one. Then, an orthogneiss could be a metagranitoid, but a paragneiss could be a metaconglomerate or meta-arkose. There are no "orthogranites" or "paragranites". With regards. Sebastian. 

Dear Dr.Qasim jan, thank you very much for sharing such papers above you mentioned from them all i have but two are new for me which i dont have  in my catalouge, as Ku ar 2104 and Dharma Rao 2012, and i got alot of help from Dr.Naresh Kochhar who worked alot on MIS suite, and once again Dr.Jan for you nice informative reply.

Naresh Kochhar is a wonderful person and an excellent scientist.

I shall send you the paper of Dharma Rao et al, perhaps via Hassan Agheem. Can you give me a complete authorship and journal for Ku ar 2014?

Best, Qasim

Dear, Dr.Sebastian Grande, thanks for reply and Thanks to Dear Munazzam and Dear ijaz.

Shakoor,

I sent this morning the two papers you requested via e-mail to Prof  Hasan Agheem. Hope you got them.

Best regards, Qasim Jan

I do not know well if I am remembering well!… In the petro genetic course was taught that existed two type of granite (one of them it has rich metal-genetic importance and connected to lot of magmatic rocks variety, magmatic influence zone to the neighbour area is bigger, (that is I-type granite) and another granite type which has more less magmatic rocks variety and metal-genetic importance (S-granite)…

Please correct me if mine remembering was wrong!

Best Regards.

LAH

Dear Laszlo: You remember well what was tought in that petrogenetic course! Indeed I-type granites are known to bear the huge Cu-Mo-porphyry deposits, associated with base metal veins, like in northern Chile and Utah-Arizona, while the S-type granites, such as the Cornwall Batholith in G.B., and the post-collisional granites of Malaysia, are more enriched in Sn, Nb and W, usually in skars and greisen of lesser extents than the Cu-Mo-porphyries. Regards, Sebastian.

Dear Sebstian thank you for response and clearing my knowledge in the field of Intrusive rock... In time of study the Volcanology and geotectonics was the most interested field by me... (in mu teaching period these two type of granites had not be mentioned)... that is why have the next question... What suggest the two prefix (*I* and *S*) of granites? Has anyone meet with common genesis of I-granite S-graanite?... Has anyone knowledge about such a meteorites (*asteroids, rocky planets Moon and Mars)  which has mineralogical property of S-type granite and I type granite?....

Best Regards,

LAH

Dear Laszlo: "I" granites are supposed to be products of partial fusion of metaigneous rocks, hence the "I", and of course "S" granites are supposed to be products of partial fusion of metasedimnetary rocks. This makes "I" granites usually meta-aluminous, less rich in quartz and alkali feldspar, having hornblende-biotite-titanite; and "S" granites are mostly peraluminous, due to great amount of alumino-silicates of the source rock, so they have muscovite-biotite and sometimes garnet, cordierite, aluminosilicates (andalusite-sillimanite) and even corundum (all of them alumina-rich phases). But really no granite is "pure", it is difficult to envisage a region in the root of a continental orogenic belt undergoing partial fusion or anatexis being formed exclusively of one type of rock, so "I" granites probably come from sources mostly made of metaigneous material, and S granites probably from sources mostly made of metasedimnetary material.

About asteroids and meteorites, Moon, Mercury and Mars, really there's little to say: they don't have any granitic rocks, only mafic-ultramafic rocks. Chondrites are all ultramafic, and achondrites range from mafic to ultramafic, being volcanic and plutonic rocks, some even cumulative. The Moon in particular has two types of terranes: the Highlands, which look lighter, because they are rich in plagioclase, being coarse grained plutonic, perhaps cumulative rocks too, such as gabbro, anorthosite, norite, troctolite; and the Maria or "seas", which are extensive and dark basaltic plains. In Mars all rocks found and anaylized so far are mafic, mostly basaltic, including Martian meteorites of the shergottite-naklite-chassigny suite. But a latest finding by the Curiosity probe, some months ago, were 10-20 cm diameter boulders of a possible TTG-suite, that is tonalite-trondhjemite-granodiorite (...), in a conglomerate at the base of Mt. Sharp (see attached file, in Spanish though... and the reference cited). This is the only mention of a "granitoid" rock out of the Earth, richer in silica than basalt, but still is a quite primitive "continental-like" material, resembling the granitoids typical of Archean terranes in terrestrial Precambrian shields, and probably of that same old age, which in Mars I think is called Noachian or Amazonian Era. Earth's large granitic batholiths, either I or S, are thus a unique, and very evolved product of the process of plate tectonics, aided by an abundance in water in our planet, a very happy combination so far only found on our good-old Earth, thanks to which we can enjoy large and dry continental land masses, where higher species. like us, can live and evolve! With regards. Sebastian. 

Dear Sebastian,

Thank you for this again made excellent answer and the attachment (with google translator I have read it)!

With it The “I” Granite and “S” granite become more explained and understandable for not specialised highly in magmagatic-vulcanic rocks…

I think these type of rocks (mainly “I” type and other type genetically connected to it) has bigger economically importance… and in Mars expedition too)… These morning I have found another information about Martian’s “granites” (these found against somewhat to actual tectonical model of Earth)

http://www.news.gatech.edu/2013/11/18/evidence-found-granite-mars

Best Regards,

P.S.

My prediction that exist asteroids (meteorites from) inner asteroids belt with granitoid structure,  

Dear Laszlo: Thanks for the article you sent. Surely it is outstanding finding a "feldspar-rich" rock in a Martian volcano. The problem arises when the word "feldspar" is used in such a generic sense. It is not the same to talk about alkali feldspar (K-Na rich) or plagioclase feldspar (Na-Ca rich). Therefore there's no reliable way to ascertain the presence of a rhyolitic flow there. Surely, the flow lacks mafic minerals, but it could be anorthositic in nature, and not rhyolitic. To make rhyolite alkali-felspar is needed, together with quartz, so until a detailed chemical analysis of this lava flow is provided there's no certainty that it is rhyolite, or that granitic bodies could have formed deep under this volcanic area. Anorthositic lavas are rare on Earth, but they do exist, and could explain very well this Martian finding. Also, the TTG boulders in the conglomerate are of a family of granitoids poor in alkali-feldspar, such as tonalite-trondhjemite. K is a troublesome element, it is very incompatible with mantle minerals and is not abundant at all in normal tholeiitic basalts. Its large ionic radius, a lot larger than Na and Ca, makes it difficult to be accepted either in plagioclase or in mafic minerals. So it usually gets to form his own minerals, such as sanidine (volcanic), anorthoclase (both volcanic or plutonic), or orthoclase and microcline (plutonic), also K-micas (muscovite-biotite) if water is present. Any way, it is a good start, and proves that Martian igneous petrology is more complex than what it seemed...

Also, I doubt much that any asteroid or meteorite coming from them, could develop a mineralogy rich in K-rich feldspar, plagioclase is known in meterorites, usually as an impact glass called maskelynite, but no mention of K-rich feldspar has ever been made in them. The feldspar-rich Lunar meteorites are anorthositic breccias, as also are a some of the lunar samples brought the Apollo missions. You need a planet for making rhyolite or granite, one with a long evolutionary geologic history, and probably with plate tectonics too! Regards and thanks again. Sebastian.

Dear Sebastian,

Again I get strong and nice post of you!…

The first 2/3 part of post it is teachable, the finish 1/3 part too… But an outsider of mainstream science will stop only at your 1/3 finish part of post:  

You have written (and you have written correct!)

“Also, I doubt much that any asteroid or meteorite coming from them, could develop a mineralogy rich in K-rich feldspar, plagioclase is known in meteorites, usually as an impact glass called maskelynite, but no mention of K-rich feldspar has ever been made in them. The feldspar-rich Lunar meteorites are anorthositic breccias, as also are a some of the lunar samples brought the Apollo missions. You need a planet for making rhyolite or granite, one with a long evolutionary geologic history, and probably with plate tectonics too! “ The main problem is that all asteroids of inner asteroid belt need a planet for making!... This conclusions come before one month intuitionally… Today answering to you have come intuitionally: The Ceres most oldest rock is younger like the most oldest rock of Earth! (prediction)

I do not know if you red translation made by me of “Bolygóerrozió” 2007 SZOKIMONDÓ):

http://planeterosion.blogspot.hu/ (this paper was started by an believer of PT and finished by an acceptor of Expanding Earth theory P.S. 1.)…

 As you observe Planet erosion theory which was refused by Hungarian Academics (their refusing explanation was mainly: I do not have astrological knowledge! But you can read it and it is made on mostly geological knowledge, interesting questionable point is “gravity”… Without their mention, Really I knew that was ! I have resolved in 2009, spring….:

 https://www.researchgate.net/publication/277364319_Tenyekkel_igazolhato_a_gravitacio_valos_oka (:( only Hungarian)

In The next year its translation perhaps will be ready with some remarks and influence of tectonics’ correction…

That pushed me to have intuitional resolution perhaps of a new genesis interpretation of “I” granite (I am not ready with verification such hypothesis, needs more study and information, but hard can find them)      

So Sebastian! I have formulated the next question: Why was abandoned totally such a theory like Geosynclinals theory?… In physics exist a science criteria that a new concept have to has main part the pre-existed concept…In case of PT that does not valabile!...

Thank you again for post… You have an excellent lithological knowledge! (Perhaps PT theory closing your eyes a bit as did with me). Perhaps with “dynamic” geosinclinal theory you better succeed in the your interpretations)...

Sunday evening  I have read a paper about volcanism of South Argentina, theoretical explanation used PT… Only in few minutes was able to find questionable parts: only basalts, lack of rhyolites in Subduction zone  (in your last post exist arguments), impossible geomorphology of area

Best Regards, Laszlo

PS. Expanding Earth theory has also its limits, but with an “mobile geosyncline theory” it can concur with PT…  

Article Tényekkel igazolható a gravitáció valós oka

Dear Laszlo: Evidence favouring plate tectonics is overwhelming nowadays, no modern geologist can work without appealing to some plate tectonic process, not even paleonthologists and paleoclimatologists, much less tectonists and petrologists! Probably some proccesses similar to the one stated in the "old geosynclinal theory" were at work in the very early Earth, when the lithosphere was probably thinner and hotter, so these foundering, mostly vertical movements could be have been quite possible, and perhaps even were able to generate some magmas, including Archaean TTG's. But a time came when the lithosphere got cooler and thicker, due to the exponential decay of radiogenic heat, inhibiting that old-style kind of tectonics, and initiating mostly horizontal movements of lithospheric fragments, which is what we now call plate tectonics. The time for this transition is most sought by geologists worldwide, and it probably occurred some 3.5 Ga ago. Many articles appear almost daily in the blog "Geology Page" where new advances are presented regarding this interesting and crucial topic of geology. However, once plate tectonics begun, it has never stopped again, and the Earth was changed for ever! Surely, there are some obscure points in some volcanic arcs and in other tectonic settings, the Trans-Mexican rfit is one of them, and the Southern Patagonian-Argentinian basalt is another, and there are dozens more of these local problems, but the theory works well even in Neoarchean and Paleoproterozoic belts, and up to today's belts and ranges. Plate tectonics is not a panacea, it was never supposed to be so! It is a very complex process, which has not simplfied geology at all, but instead it has added complications never ever imagined or expected, since it involves too many variables, many of which are not clearly understood, by the way... In the first class every semester I tell this lesson of "human humbleness" to my students of Petrology: "Nobody has ever seen or will ever see a "subduction zone", nor has been in a place inside the Earth where magma is being generated. All we have as evidence to be able to state that "something" very wide, long, thick and dense bents, slides and founders into the mantle is an array of seismic foci in the form of an inclined plane some 20 km thick, that this plane begins near an oceanic trench and dips at an angle inside the mantle: a Wadati-Benioff zone of intermediate to deep focus earthquakes, and that vertically above it, some 70-100 km behind the trench, a "magmatic arc" is formed somehow! So, we don´t have a dogma about subduction, this is not religious faith, it's science: all we have is a model which has been capable to explain a good number of situations in various tectonic settings around the world and in the geological past, but never will explain all of them!"

Nontheless, advances are made day after day to explain the possible "exceptions" to the general global tectonic scheme, new techniques of mantle seismic tomography are revealing things unimaginable some years ago, and geochemical evidence is everyday more and more complete and complex too. I believe that the main workings of PT are correct, but nobody can deny that there are indeed some strange "exceptions" to the global processes, which hopefully could be explained and understood in some near future. With regards, Sebastian.

Dear Sebastian,

You are well able to protect “your concept”  of plate tectonic …We know well the time of begging of PT. Interesting feature  that has same process like Theory of Relativity in physics… To strong support made by scientist writer in media… (not far, after formulation of quantum mechanics)…. My own concept beginning was when I wrote my philosophical book “Az Eszme” (The  IDEA) (edited in 1995) where  the plate tectonics accepted form was used for sustaining my non-conventional metaphysical system basics (only (this part needs rewrite!)… There was gotten a conclusion: That was impossible the Moon’s gravity was producing Earth tides when it was slow gravity field and distance was too far (the processes observed in satellites)… after these part was an explanation of Earth life apparitions based  CaCO3 behaviour water condition (actually exist some works which can be connected to this explanation and to ancient Chinese medicine of  acupuncture – such of way exist scientifically explanation of this medicine)… The next part was the human intelligence formation explanation main role  glacial periods)… Now come back to the tides! without knew the Galileo explanation ( of tides (http://galileo.rice.edu/sci/observations/tides.html ) was not teached in our school I got my own explanation (changing of outer core concentration connected to Earth rotation and orbiting).

We know well that Newton had given plausible explain of tides of Earth, but we know about the contradiction)…

Such a condition know the limits of (Geosinclinal theory- exact the strong part of PT: dynamism , Expanding Earth theory- seems the best, but has problem with the beginning expansion and the matter, an Plate Tectonics-, counting with to big plates, process subduction…    I would like to make a study of Plumes Theory and Strench tectonics but I do not have available works…

Best Regards Laszlo

I recommend this paper H-type (hybrid) granitoids: a proposed revision

of the granite-type classification and nomenclature of Castro Dorado 1991.

Trace chemistry of accessory minerals (as apatite: Sha and Chappel 1999) might be useful.

Dear David Llano,

Can you please provide me full reference of Castro Dorado (1991) paper?

Thanks,

Qasim

Sure, Please give me your e-mail.

[email protected]

I recommend Sudip's answer

Best Regards

I agree with Dr. Latha's observation. There are other parameters which can effectively differentiate between I and S type granite.

You can study the mineralogy, if garnet is present, then it is sure that the parent material was sedimentary and thus, S type.

The initial 87Sr/86Sr isotope ratio as low as 0.703, indicates I type granite. A higher ratio is indicative of S-type granite.

Presence of garnet or any other aluminosilicate mineral and the kind of plagioclase along with high Al2O3 should be a good support .

Mohd AZHARULHaq

yes indeed its good and informaive answer thanks.

Dear Abdul: most granites are not 100% "I" or "S" type, the roots of continental crust in active margins and collisional orogens are themselves the products of former orogenic clycles, so they roots are lithologically quite complex. Therefore it is almos impossible to envision that when anatexis occurs at those depths the source rock is going to be purely metaigneous or purely metasedimentary, one type opfm rock might predominate over the other, but mixed sources are probably the rule! One petrographic characteristic which I've found studying S-type anatectic granitoids in the Venezuelan cordilleras, is the ubiquitous presence of primary muscovite (and sometimes accesory andalusite) together with biotite, and the lack of hornblende or pyroxenes. Also, being influenced the partial fusion by the presence of graphite and sulfur, as one of the previous comments stated, the typical form of iron oxides present in S-type granitoids is ilmenite, and not magnetite. This ilmenite contains reduced iron (Fe2+) and often, if not always, shows a typical reaction corona of titanite, especially when included or closely related with biotite. Also, (Sr/Sr)0 systematics can help to discriminate between these two types of granitoids, with could occur closely spatially related, and even as parts of the same batholitic mass, as is it probably your study case.

Regards, Sebastián.

I am studying about volcanic rocks (basaltic andesite, andesite, dacite and rhyolite). I have found both our intermediate and felsic volcanic rocks plotted in the field of I- & S-type (Whalen, 1987). Na2O & Al2O3 content in felsic ranges 2.23-6.47 wt.% and 10.47-16.43 wt.%, whereas intermediate ranges 3.39-4.12 wt.% and 12.96-16.30 wt.% in our investigated samples. As per our study, the tectonic setting is continental marginal arc and influenced by fluid metasomatism along with little incorporation of sediments. Can anyone suggest what kind of conclusion can we make from this I and S-type signatures? please help!!

Dear Nongmaithem: as far as I know the alphabetic classification of anatectic granitoids is just for platónico rocks, and you are working in orogenic volcanics!!

Regards, Sebastián

Thank you Prof. Sebastian Grande yes i am working on the magmatic rocks of the Mighty Himalayan in its north western part. Another small query is that can we use the diagram of Whalen et al 1987 to plot intermediate volcanic rock suites if one wants to know which type (I, S, or A type)?

Dear Nongmaithem: I don't think so, those diagrams were designed for plutonic rocks, not for volcanics. Anyway, the solution to this riddle is to consult the original references of the work of Whalen et al. (1987), just to make sure. Regards, Sebastián.

Yes

A key is to look at if a granitoid contains at least one diagnostic indicator mineral, such as sillimanite, cordierite, muscovite, garnet, and

tourmaline, but lacks of magnetite. If yes, it may be of S-type. Then, take a look at its geochemical composition; S-type granites are commonly peraluminous (ANKC >1.1), calcalkaline, with K2O/Na2O ratio >1.0. If both the mineral assemblage and chemical composition satisfy the criteria, then the granitoid is mostly likely S-type.

Dear Prof.Xue-Ming Yang thanks for informative and nice answer.

Regards

Dr. Mastoi

Dear Prof. Mastoi:

A paper of mine may be found via the link below may be helpful in dealing with the topic you have raised here.

Article S-type granites in the western Superior Province: a marker o...

Best regards,

Xue-Ming Yang

Granites are classified as I & S type based on the source prolith that is subjected to partial melting (Ref. Chappell and White, 1974).

Granites are classified as Orogenic or Anorogenic based on the tectonic setting in which they are emplaced (eg. Pearce et al. 1984; Batchelor and Bowden, 1985; Maniar and Piccolli, 1989).

A-type granites are termed as anorogenic (eg. Collins et al. 1982; Whalen et al. 1987; Eby, 1992), can be anhydrous and or alkaline and are emplaced in extensional settings. These are usually within plate granite (WPG) in trace element tectonic discrimination diagrams (Ref. Pearce et al. 1984).

M-type granite is mantle derived plagiogranite that are associated with the gabbro and or sheeted dykes in ophiolites. These are confined to present or past oceanic crust.

I - type granites derived due to partial melting of an igneous source are mineralogically hornblende bearing (with or without biotite) and by virtue of alumina saturation I type granites are metaluminous. Na is usually more than K with relatively higher Na2O / K2O ratio. Some times sodic amphibole can also be present.

In contrast S - type granites derived due to partial melting of a sedimentary source is mineralogically biotite bearing with or without hornblende and peraluminous. Na is usually less than K with relatively lower Na2O / K2O ratio. S-type granites are corundum normative.

Both S and I type granites can be emplaced in orogenic or anorogenic tectonic settings

Thanks for informative answer dear v.v sesha sai

I have a new question.

-According to the Harker diagrams, which trace elements (Ba,Rb,Sr,Y,Z,Nb,Th) form a trend towards SiO2 or do not, or in what direction?

Dear all:

S-type granites don´t have hornblende, they can have biotite alone or biotite and muscovite, being the last micaceous mineral the most disctinctive. Also, when they are very peraluminous they contain almandine garnet, andalucite or cordierite. In the Venezuela Andes we have Paleozoic and Triassic "S" granites which have biotite, muscovite and andalucite, associated with garnet-muscovite pegmatites. That's why they are corundum normative! Another characteristic is they might have conspicuous titanite aureoles around ilmenite grains, especially if the ilmenite is included in biotite. Regards, Sebastian.