Paleoproterozoic Synkinematic Magnesian High-K Magmatism from the Tamkoro-Bossangoa Massif, along the Bossangoa-Bossembele Shear Zone in North-Western Central African Republic

Abstract

The magnesian high-K calc-alkaline intrusive of the Tamkoro-Bossangoa Massif, North Western Central African Republic, were synkinematically emplaced in a sinistral strike-slip shear zone of Paleoproterozoic age. The rock sequences consist of orthogneisses with abundant coarse- to medium-grained quartz monzodiorite, quartz diorite and medium- to fine-grained biotite granite composition and cover a range of about 55 to 76 wt.-% SiO2. They display characteristics of shoshonitic and high-K calc-alkaline series. Quartz monzodiorite and quartz diorite are metaluminous, whereas granite is moderately peraluminous (1≤ A/CNK ≤ 1.1) and plot in the field of I-type granitoids. Major and trace element composition of the granitoids indicate that the source materials were derived from different crustal protoliths. Major and trace element composition are consistent with the magmatism which may have involved remelting of (1) a composite metagreywackes protolith in the upper crust and (2) amphibolitised high-K calc-alkaline basaltic andesites in the central domain of the NEFB (North Equatorial Fold Belt). SHRIMP zircon and titanite dating of granitic rocks gives a magmatic zircon and titanite age of 2069 ± 9.6 Ma and 2063 ± 28 Ma respectively, a metamorphic age of 500 Ma and 597 Ma. The plutonic rocks of Tamkoro-Bossangoa area resemble other Paleoproterozoic high-K calc-alkaline syntectonic plutons in western and central . They also display strong similarities with high-K calc-alkaline plutons of eastern and of the in NE Brazil.