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Hi François, Thanks. Unfortunately, I can't think of papers that certainly state the criteria. That doesn't mean they don't exist though. Maybe stuff published in the eighties to early noughties by Chappell and White?? You could look at: Chappell, B. W. (1984) Source rocks of I- and S-type granites in the Lachlan Fold Belt, southeastern Australia. Philosophical Transactions of the Royal Society of London A310, 693-707. Chappell, B. W. & White, A. J. R. (1992) I- and S-type granites in the Lachlan Fold Belt. Transactions of the Royal Society of Edinburgh Earth Sciences 83, 1–26. Chappell, B. W. & White, A. J. R. (2001) Two contrasting granite types: 25 years later. Australian Journal of Earth Sciences 48, 489-499. Hine, R., Williams, I. S., Chappell, B. W. & White, A. J. R. (1978) Contrasts between I- and S-type granitoids of the Kosciusko batholith. Journal of the Geological Society of Australia 25, 219–234. Maybe in these. The original 1974 paper probably stated some of this as well. It's copied in the 2001 paper, I believe. Anyway, have a look. Best wishes, JC John D. Clemens Professor in Geology & Exec. Head Dept of Earth Sciences, University of Stellenbosch, Private Bag X1, 7602 Matieland, South Africa tel: +27 (0)21 808 3159 fax: +27 (0)21 808 3129 e-mail: [log in to unmask] web page: http://www.sun.ac.za/geo/people/clemens_e.htm ________________________________________ From: Metamorphic Studies Group [[log in to unmask]] On Behalf Of Francois Guillot [[log in to unmask]] Sent: 21 September 2011 18:23 To: [log in to unmask] Subject: Re: distinguishing I- and S-type granites Hello John, I heard you at the last Hutton with great pleasure. Happy to read, especially from you as a great specialist of the question, simple and clearcut criteria regarding the mineral assemblage that characterizes I-types. Because only written data remain, could you suggest papers one could make citations of, that contain, that state such simple criteria? Thanking you in advance >Hi, > >Mike Brown suggested that what people need are some guidelines for recognising S- and I-types. Here are some simple quite reliable mineralogical criteria. > >If your rock has red-brown biotite with high Al and Ti contents or cordierite or monazite or pyrrhotite as the Fe sulphide then it's almost certainly an S-type. > >If your rock has hornblende or clinopyroxene, or titanite or magmatic epidote or the biotite is dull brown to greenish brown or the rock contains magnetite or alanite, you've got an I-type. > >Muscovite, andalusite and garnet can occur in both sorts, especially is you have fractionated highly felsic magmas involved. My impression is that muscovite is more common in fractionated I-types than it is in S-types. > >Isotope characteristics should be used with circumspection. There are high delta 18O I-types and I-types with very ancient sources can aslo have high initial Sr isotope ratios and low epsilon Nd. > >Likewise there are chemical indicators - Na2O/K2O is generally higher in I-types, as is CaO at a given SiO2 content. ASI (= A/CNK) is a tricky one. A lot of granites are peraluminous, but very few I-types have ASI > 1.1. There is commonly a rather telling variation in ASI with maficity (Fe + Mg). In S-types these are commonly positively correlated, due to the fact that mafic minerals responsible for the variation in maficity are peraluminous. In I-types, the trend is opposite, with the more mafic rocks having lower ASI. Accumulation of Hbl or Cpx does this. > >So, as I wrote earlier, it is the totality of evidence that points to the character of the source rock. Arriving at the point of knowing something pretty specific about the source is rather superior to knowing that you have an alkali-calcic granite (which could be either S- or I-type, actually). In short, beware of magic discriminant diagrams. They can work rather poorly and totally mislead you. Part of the reason for this, especially with tectonic discriminant diagrams, is incorrect assignment of the character of the rocks that were used to construct the field boundaries in the first place and incorrect assumptions regarding the sources of felsic magmas. > >I have spoken. > >JC > > >John D. Clemens >Professor in Geology & Exec. Head >Dept of Earth Sciences, University of Stellenbosch, >Private Bag X1, 7602 Matieland, South Africa >tel: +27 (0)21 808 3159 fax: +27 (0)21 808 3129 >e-mail: [log in to unmask] >web page: http://www.sun.ac.za/geo/people/clemens_e.htm -- Francois GUILLOT UNIVERSITE LILLE Nord de France - Lille 1 - Laboratoire CNRS FRE 3298, GEOSYSTEMES / batiment SN5, Sciences de la Terre / F-59655 VILLENEUVE D'ASCQ CEDEX (France) ( 33(0)--320 43 6731 (office) /-320 54 41 06 (home) /-320 43 49 10 (fax) - Skype pseudo: fjlguillot Alpes 1987: http://tel.archives-ouvertes.fr/tel-00011367/fr/ Alpes 2002: http://www.springerlink.com/content/2e91a1bml4bmpe0q/ Alpes 2005 (extraits): https://iris.univ-lille1.fr/dspace/bitstream/1908/998/1/50376-2005-Guillot.pdf Frasnien/Famennien 2006: http://geolfrance.brgm.fr/sommaire.asp?revue=1&annee=2006 Ardennes 2009: http://sp.lyellcollection.org/cgi/content/abstract/324/1/167 Chine 2010: http://springerlink.metapress.com/content/586n64736440121r/ ou bien : http://www.scichina.com:8080/sciDe/EN/abstract/abstract500940.shtml Alpes 2010: http://www.sciencedirect.com/science?_ob=GatewayURL&_method=citationSearch&_uoikey=B6X1D-50JPS58-1&_origin=SDEMFRHTML&_version=1&md5=d08d7bb772102dcc18cc40a0075d536e