Jurassic granitoids are widespread in the interior of South China. However, the genetic types of some plutons are still controversial. In this paper, we show an example (Fogang batholith) of how to distinguish I-, S- and A-type granitoids. Fogang batholith is the largest Jurassic granitic pluton, located in the Guangdong Province. With increasing differentiation, the contents of Nb and Ta progressively increase, whereas those of Zr and Hf show gradual decrease. Both Nb/Ta and Zr/Hf ratios show decrease with the fractionation of granitoids (15.3 - 3.6 and 38.9 - 17.3 respectively). Fractionation of zircons result in lower Zr/Hf ratio with strongly decreasing Zr concentration. Fractionation of amphibole and biotite produce decreased Nb/Ta ratio with the differentiation of granitoids. The Nb/Ta ratios of the Fogang granites correlate positively with Y/Ho ratios, indicating that the fluid also played a key role in the variation of the contents of Nb and Ta and Nb/Ta ratios in Fogang granitoids. The absence of Al-rich minerals and the negative correlation between Zr and P2O5 preclude the Fogang batholith to be S-type granite. Ga/Al and FeOT/MgO ratios correlate positively with the Ta and Nb contents, and Y/Ho and Nb/Ta ratios, implying that the high Ga/Al and FeOT/MgO ratios of Fogang granites result from fractionation and fluid-magma interaction. Therefore, the Fogang batholith is deduced to be metaluminous to slightly peraluminous I-type granitoids rather than A-type granites. This work highlights that the fluid-melt/rock interaction makes it difficult to directly define the genetic types of some granitic plutons.
|Translated title of the contribution||Petrogenesis of the Fogang highly fractionated I-type granitoids: Constraints from Nb, Ta, Zr and Hf|
|Number of pages||9|
|Journal||Yanshi Xuebao/Acta Petrologica Sinica|
|Publication status||Published - 2015|
- genetic classification
- South China
- Zr/Hf and Nb/Ta