Trace element geochemistry and tectonic characterization of the granulite facies rocks from Southwest Obudu Plateau,southeastern Nigeria

The trace elements characteristics of the migmatitic gneisses (biotite-garnet- and hornblende-biotite), granulite facies rocks (charnockitic gneisses) and meta-peridotite in the area of Southwest Obudu Plateau indicate that the area exhibits a high degree of geochemical variability. Compatible trace elements (Ni and Cr) are comparatively high in the granulite facies rocks and meta-peridotite. Ni ranges from 28×10⁻⁶ to 266×10⁻⁶ whilst Cr ranges from 62×10⁻⁶ to 481×10⁻⁶ for the granulite facies rocks (charnockitic gneisses), and for the meta-peridotite Ni varies between 2045×10⁻⁶ and 2060×10⁻⁶. Incompatible trace elements show a higher variability in these rocks. The rocks in the area of Southwest Obudu Plateau generally are characterized by the high concentrations of Ba, Ce, Sr, Rb, Ga, Ni, Cr, Co, Zr, Pr and moderate concentrations of Cu, Sm and Th. The available data show that the charnockitic gneisses are of lower crustal origin. The enrichment of the meta-peridotite in compatible trace elements suggests the primitive mantle would be the source region, with slight contamination during ascent. These diverse origins collaborate the tectonic setting of the area as shown by discrimination diagrams. The diverse tectonic settings range from arc to collisional. Alkaline to sub-alkaline magmatism in the area was probably contemporaneous with the tectonic events that occurred in the area during the Proterozoic.