| Popis: |
The High-K calc-alkaline granitoids in southern part of Hawal massif is an integral part of the well-exposed syn-to post collisional plutons in eastern Nigeria. The evolution of the rocks can be linked to the thermo-tectonic period of faulting, uplift, cooling, fractionation and high-level magmatism, which led to the intrusion of the granites and related rocks during the Palaeoproterozoic, about 580± 10 Ma. A total of nine granitic rocks, constituting seven biotite granites of varying grain sizes and two porphyritic granites were sampled in Mubi area to shed new light regarding their petrochemistry. Detailed field and laboratory investigations show that the area is characterized majorly by Pan African granitoids. The massif has S-type strongly peraluminous geochemical signature, high-K calc-alkaline, magnesian, granodiorite, exemplified by high ASI (averagely 0.81 to 1.59), low Na2O (average 2.09 wt. %), and CaO (average 2.37 wt. %). Moreso, they exhibit low FeOt/(FeOt + MgO) ratios (0.64 0.80 wt%), low to moderate Na2O+K2O-CaO ratio (2.41 5.41 wt%), high Na2O+K2O (average 6.42 wt%) and K2O/Na2O ratios (average 2.11 wt%), as well as high Mg# (30.49 50.22), low molar CaO/(MgO + FeOt) (0.19 0.63 wt%) and molar Al2O3/(MgO +FeOt) ratio (2.10 4.31 wt%). Discrimination diagram shows that the granitoids are products of sedimentary protolith (metagreywacke) formed within a syn-collision and supra-crustal setting. The constituent mineral assemblages in the granitoids (quartz, plagioclase, alkali feldspar, biotite, hornblende, titanite, iron oxides) from the northern Hawal massif are obviously related to the condition of evolution and compositions of the protolith. |
