Geochemistry and Petrogenetic Evolution of Rocks around Bishewa-Ologomo area, part of Lafiagi Sheet 203, Northcentral Nigeria.

Abstract

Geochemical analysis of rock samples from Bishewa-Ologomo area was carried out for oxides of major and trace elements including rare earth using the XRF analytical method. The granitic rocks of the area are interpreted as being formed by partial melting due to its high LREE / HREE ratios and the presence of slight negative Eu anomalies. The result shows that the granites of this area are primarily of igneous source, but with possible sedimentary input during emplacement. The Rb versus Y+Nb, Nb versus Y and Rb versus SiO2 discrimination plots suggest that the evolution of the granitic rocks of the study area ranges from syn-collisional to volcanic arc origin. The high P2O5 values varying between 0.2%-0.57% for granodiorite, medium-grained biotite granite, quartz-mica schist and medium-coarse grained biotite-hornblende granite of the area are well above apatite saturation level of 0.14% [12] which can be correlated with progressive enrichment of the lighter REE (La – Sm) in the fractionating magma. All the metasediments of the area plot within the sedimentary field. The TiO2-K2O-P2O5 molecular discrimination diagram shows the mafic rocks of the study area are of the tholeiitic oceanic basalt origin.