A granitic rock that I am working on, the mafic minerals are dominantly titanate and biotite in thinsection. The titanate is wide spread, with rims of opaque minerals possible ilmenite and magnetite; and overgrowth of allanite.
It would be an unusual name, but if the titanite is primary and present at % levels, I don't see why not. What is the whole-rock TiO2 concentration? A more conventional name might be high-Ti granite.
High-Ti granite may have say 2% of Titanite (see for example https://www.irsm.cas.cz/materialy/acta_content/2011_04/9_Rene.pdf).
Any common accessory mineral of granite exceeds 5% of modal volume you can name the rock accordingly as biotite granite/ hornblende granite etc.
Similarly any mineral of significance is present which is not that regular according to normal mineral assemblage of the granite, you can mention it in the rock nomenclature though it doesn't constitute ~5%,
for example garnet bearing granite, tourmaline granite, rebeckite granite ..etc.
If the sphene is primary magmatic origin you can definitely mention it in the rock nomenclature....like titanate bearing granite
I am waiting for the geochemical results. Yes the titanate is magmatic with corana of ilmenite and in some case corona of plagioclase or allanite.
Dear Saleh: such high proportions of titanite (before called sphene) are not really so common in real granites, but in nepheline syenites and foyaites, where that mineral can form large crystals. Anyway, only if titanite amounts to 5% in vol. can the name titanite granite be used, if the proportion is less, the correct name should be titanite bearing biotite granite. So, I think, and it is quite possible, that the original magma could have been an alkaline magma, rich in Ti, and perhaps also in Zr and REE, which suffered severe contamination from a silica-rich country rock. The silica contamination avoided the crystallization of nepheline, but not that of titanite and zircon. Are there any nepheline bearing rocks near or associated to this titanite bearing-biotite granite, can a transition from alkaline to granitic rock be seen in the contacts of the pluton? Also it is quite curious that the titanite shows coronas of ilmenite, when what it is usually seen, especially in "S" type granites, is a corona of titanite around ilmenite! With regards, Sebastian.
There is no nepheline bearing rocks, the surrounding rocks are migmatites and diorites/granodiorites. As you rightly said the titanite surrounds ilmenite.
Dear Saleh: so the contamination hypothesis can be disregarded. However, you should determine the actual weight percentage of TiO2 in the rock, and ascertain if it is really too large compared to thta in "S" type granites. In Venezuelan biotite and two-mica granites it is quite common to observe very well developed titanite coronas around ilmenite grains, so for us here it is a quite common texture. Another idea I can suggest: an abnormal amount if TiO2 in an anatectic granite could be caused by the melting of sediments rich in TiO2, such as ilmenite-rutile paleo placers in beach or fluvial sandstones (or quartzites) interbedded with the metasedimentary source rock which gave rise to the granitic magma. With regards. Sebastian.
Dear Saleh,
I think that the titanate is accessory mineral of granite exceeds 5% of modal volume you can name the rock accordingly as biotite granite.
Cordially.
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