COMPOSITIONAL COMPARISON OF BIOTITES FROM SYNCOLLISIONAL NEOARCHEAN BUNDELKHAND MIGMATITE GNEISS AND PALAEOPROTEROZOIC CHIPLAKOT GNEISS INDIA: IMPLICATION TO INFER THE PROTOLITH OF HOST MELT

The major oxide compositions of biotite from syn-collisional peraluminous Bundelkhand migmatite-gneiss and
Chiplakot gneiss were compared to determine the source rock of their host melt. Biotite from the Bundelkhand
migmatite-gneiss (BMB) had higher FeOt wt.% (Avg. - 25.73 wt.%, std. - 1.4) and FeOt/MgO (4.11, Std. - 0.61)
compared to Chiplakot gneiss biotite (CGB; FeOt wt.% -22.12, Std. - 0.99). This suggests that the host melt for
BMB was more leucocratic in nature. The high Al2O3 wt.% (Avg. -16.49 wt.%, std. - 0.51) and SiO2 wt.% (Avg.
- 35.07 wt.%, Std - 0.52) with a positive correlation between them in the CGB suggest that it was formed from a
peraluminous melt. This type of melt is generated from a pellitic source in a syn-collisional tectonic environment.
On the other hand, BMB shows low SiO2 wt.% (Avg. - 33.91 wt.%, Std. - 1.2) and Al2O3 wt.% (Avg. - 16.03, Std.
- 0.29) and has a negative correlation between SiO2 and Al2O3 wt.%. This suggests that the peraluminous host
melt in BMB was generated from an igneous source in a syn-collisional tectonic setting.