TiO2 contents can definitely help. Velues > 4 wt.% are hard to reconcile with igneous and much more in agreement with a xenocrystic, residual biotite from the source rocks.

Thank you dear Martin. That is helpful for me in petrographic observations.

Thank you dear Bernardo. This is an interesting point I am looking for. But may you please let me know the reference text for it?Thank you.

for metamorphic/xenocrystic biotite please go to my web page and find references to my 2003 and 2008 papers where moslt literature is reviewed. for igneous biotite I don't have a reference at hand, but a simple google search or Deer et al's tables could help.

One should not that there are also meta-igneous biotites. These occur for example in some carbonatites in the Grenville Province. Geological context therefore is also important.

On the Rock Forming Minerals Volume dedicated to Phyllosilicates (Deer Howie and Zussman), at the chapter of Biotite you can read many references about this problem.

One of the most usefull rough discriminatory system is based on TiO2-FeO-MgO content.

Enrichment of TiO2 is typical of Orthomagmatic Biotites (Phlogopite-Annite series)

Progressive enrichment of FeO* in respect of TiO2 is typical of Biotites from late-stage crystallization from melt.

Progressive depletion of TiO2 and FeO and strong enrichment of MgO is typical of hydrothermal and metamorphic biotites.

In real it is not so easy and sharp, because, you know, metamorphic processes can evolve in many different P-T settings and can modify the relationship between FeO and MgO.

However, back to your questions, texture of biotite (absolute and relative to other phases) and TiO2 content are a good discriminatory method to define a magmatic or a metamorphic origin of your Biotite.

Following up - one needs to be careful as to the textural distictions you are looking for. There are lots of cases where biotite was incorporated into igneous sysstems in the form of disaggregated schlieren - e.g. the biotite - which may have completely re-equilibrated with the magma - may have not crystallized from the magma. One textural characteristic of such biotites is inclusions of trace phases not present in the host magma (e.g. zircons).

A possible method might lies on their F and Cl contents, if they have been measured by EPMA already. Usually but not always, activities of F and Cl in metamorphic fluids are much higher than those in silicate melt.

As Lucci Federico indicates important information is given by Deer, Howie and Zussman in Volume 3 of the "Rock Forming Minerals" where indicate geological environments which presents the biotite. The metamorphic biotite related to regional metamorphism and igneous biotite usually related to igneous intrusive rocks (granite, pegmatite granite, granodiorite, ...).

Thank you for your all valuable discussion.

Dear Bernardo Cesare, I think TiO2 is not a good parameter for my samples. Since I gained TiO2 of metamorphic Bt

I would advise to combine your EPMA data with detailed petrographic observations on textures and structures (e.g. reaction rims, corrosions, inclusions etc) of your biotites.

Yes, petrographic observations- key for this. Contains TiO2 (see above) non good indicator. In my rock - amfibolites TiO2 varied 1-6% (high grade condition above 750C). Often in granites biotite - late(post) magmatic mineral and resorbed amfibole.

May be public few images thin sections?

Hello, the chemical composition and texture of biotites is key for that, however you need to have a control and characterize the biotite of the different lithological units that you have in the study area. For example, in granite, metamorphic host rocks, xenoliths or enclaves, among others.

A recent study of this can be seen in: Alasino et al., 2014. Lithos 190–191, pag. 162.

Cheers,

Pablo

Distinguishing metamorphic from igneous trioctahedral micas (I guess you don't mean biotite s.s.) from routinely aquired microprobe data is almost impossible unless the mica doesn't contain elevated or depleted concentrations of elements normally acting as minor or trace components, i.e., Mn, Ba, Sr, Li, Rb, Co, Ni, Sc etc (see Tischendorf et al. 2001, Minor- and trace-element composition of trioctahedral micas: a review, Min.Mag., vol. 64, pp. 249-276. More perspective is the study of mineral and rock textures.

Thank you M.Cemal Göncüoglu, Alexey Berezin and H.-J. Förster.

I will read these papers.

The igneous carbonatites in the area just north of Ottawa, Canada that I have worked on in fact contain titanite rutile as fine elongate needles growing along the mica crystal planes giving a very visible effect, These are also phogopites in calcium-rich environment.

Are'nt they exolutions we observe frequently in high Ti-dark micas?

Absolutely but it is an idication of the high TiO2 in the solution.

First. I prefer to pay more attention to the field relations and then textural evidences and finally, on EPMA. As you will find in literatures, its more difficult to propose unique criteria, applicable to the all biotites around the world. Because just paying attention to chemical composition, means that chemistry is only variable in biotite formation. So, in summary, it is useful to pay more attention to the host rocks and their biotites (textural and composition), try to classification biotites of granites based on textural evidences and compare them with each other, with host rocks biotites and finally, with those on the literatures. May be it will help.

See Nachit et al. 2005 - Discrimination between primary magmatic biotites, reequilibrated biotites and neoformed biotites. C.R. Geoscience 337 (2005) 1415-1420.

Professor Fourestier, have you read about sagenitic biotites? It is a texture of rutile exsolution on biotite.

It is possible that the biotite s that contain the gaps is evidence of the formation of volcanic igneous rocks

Nargess Shirdashtzadeh